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This guide has been written for electrical Engineers who have todesign, realize, inspect or maintain electrical installations in compliancewith international Standards of the International ElectrotechnicalCommission (IEC).“Which technical solution will guarantee that all relevant safety rules aremet?” This question has been a permanent guideline for the elaboration ofthis document.An international Standard such as the IEC 60364 “Electrical Installationin Buldings” specifies extensively the rules to comply with to ensuresafety and predicted operational characteristics for all types of electricalinstallations. As the Standard must be extensive, and has to be applicableto all types of products and the technical solutions in use worldwide, thetext of the IEC rules is complex, and not presented in a ready-to-use order.The Standard cannot therefore be considered as a working handbook, butonly as a reference document.The aim of the present guide is to provide a clear, practical and stepby-stepexplanation for the complete study of an electrical installation,according to IEC 60364 and other relevant IEC Standards. Therefore, thefirst chapter (B) presents the methodology to be used, and each chapterdeals with one out of the eight steps of the study. The two last chapter aredevoted to particular supply sources, loads and locations, and appendixprovides additional information. Special attention must be paid to theEMC appendix, which is based on the broad and practical experience onelectromagnetic compatibility problems.We all hope that you, the user, will find this handbook genuinely helpful.Schneider Electric S.A.This technical guide is the result ofa collective effort.Technical advisor:Serge Volut - Jacques SchonekIllustrations and production:AXESS - Valence -FrancePrinting:Les Deux-Ponts - FranceEditionDecember 2008Price: 90 ISBN: 978.2.9531643.0.5N° dépôt légal: 1er semestre 2008© Schneider ElectricAll rights reserved in all countriesThe Electrical Installation Guide is a single document covering thetechniques, regulations and standards related to electrical installations.It is intended for electrical professionals in companies, design offices,inspection organisations, etc.This Technical Guide is aimed at professional users and is only intendedto provide them guidelines for the definition of an industrial, tertiary ordomestic electrical installation. Information and guidelines contained in thisGuide are provided AS IS. Schneider Electric makes no warranty of anykind, whether express or implied, such as but not limited to the warrantiesof merchantability and fitness for a particular purpose, nor assumes anylegal liability or responsibility for the accuracy, completeness, or usefulnessof any information, apparatus, product, or process disclosed in this Guide,nor represents that its use would not infringe privately owned rights.The purpose of this guide is to facilitate the implementation of Internationalinstallation standards for designers & contractors, but in all cases theoriginal text of International or local standards in force shall prevail.This new edition has been published to take into account changes intechniques, standards and regulations, in particular electrical installationstandard IEC 60364.We thank all the readers of the previous edition of this guide for theircomments that have helped improve the current edition.We also thank the many people and organisations, to numerous to namehere, who have contributed in one way or another to the preparation of thisguide.

AcknowlegementsThis guide has been realized by a team ofexperienced international experts, on the baseof IEC 60364 standard, and include the latestdevelopments in electrical standardization.We shall mention particularly the followingexperts and their area of expertise:ChapterChristian Collombet DBernard Jover QCharley Gros L, MDidier Fulchiron BDidier Mignardot JEmmanuel Genevray E, PEric Breuillé FFranck Mégret GGeoffroy De-Labrouhe KJacques Schonek A, C, D, G, NJean Marc Lupin L, MJean Paul Baudet NJean Paul Lionet EJérome Lecomte HMatei Iurascu F, HMichel Sacotte BYou can ask questions to these experts bysending a mail at the following address:FR-Tech-Com@schneider-electric.com

This guide has been written for electrical Engineers who have todesign, realize, inspect or maintain electrical installations in compliancewith international Standards of the International ElectrotechnicalCommission (IEC).“Which technical solution will guarantee that all relevant safety rules aremet?” This question has been a permanent guideline for the elaboration ofthis document.An international Standard such as the IEC 60364 “Electrical Installationin Buldings” specifies extensively the rules to comply with to ensuresafety and predicted operational characteristics for all types of electricalinstallations. As the Standard must be extensive, and has to be applicableto all types of products and the technical solutions in use worldwide, thetext of the IEC rules is complex, and not presented in a ready-to-use order.The Standard cannot therefore be considered as a working handbook, butonly as a reference document.The aim of the present guide is to provide a clear, practical and stepby-stepexplanation for the complete study of an electrical installation,according to IEC 60364 and other relevant IEC Standards. Therefore, thefirst chapter (B) presents the methodology to be used, and each chapterdeals with one out of the eight steps of the study. The two last chapter aredevoted to particular supply sources, loads and locations, and appendixprovides additional information. Special attention must be paid to theEMC appendix, which is based on the broad and practical experience onelectromagnetic compatibility problems.We all hope that you, the user, will find this handbook genuinely helpful.Schneider Electric S.A.This technical guide is the result ofa collective effort.Technical advisor:Serge Volut - Jacques SchonekIllustrations and production:AXESS - Valence -FrancePrinting:Les Deux-Ponts - FranceEditionDecember 2008Price: 90 ISBN: 978.2.9531643.0.5N° dépôt légal: 1er semestre 2008© Schneider ElectricAll rights reserved in all countriesThe Electrical Installation Guide is a single document covering thetechniques, regulations and standards related to electrical installations.It is intended for electrical professionals in companies, design offices,inspection organisations, etc.This Technical Guide is aimed at professional users and is only intendedto provide them guidelines for the definition of an industrial, tertiary ordomestic electrical installation. Information and guidelines contained in thisGuide are provided AS IS. Schneider Electric makes no warranty of anykind, whether express or implied, such as but not limited to the warrantiesof merchantability and fitness for a particular purpose, nor assumes anylegal liability or responsibility for the accuracy, completeness, or usefulnessof any information, apparatus, product, or process disclosed in this Guide,nor represents that its use would not infringe privately owned rights.The purpose of this guide is to facilitate the implementation of Internationalinstallation standards for designers & contractors, but in all cases theoriginal text of International or local standards in force shall prevail.This new edition has been published to take into account changes intechniques, standards and regulations, in particular electrical installationstandard IEC 60364.We thank all the readers of the previous edition of this guide for theircomments that have helped improve the current edition.We also thank the many people and organisations, to numerous to namehere, who have contributed in one way or another to the preparation of thisguide.

General rules of electricalinstallation designConnection to the MV utilitydistribution networkConnection to the LV utilitydistribution networkMV & LV architecture selectionguideLV DistributionProtection against electricshocksSizing and protection ofconductorsLV switchgear: functions &selectionProtection against voltagesurges in LVEnergy Efficiency in electricaldistributionPower factor correction andharmonic filteringHarmonic managementCharacteristics of particularsources and loadsResidential and other speciallocationsEMC guidelinesABCDEFGHJKLMNPQ

Guiding tools for more efficiency in electricaldistribution designTechnical knowledgePre-design help for budgetapproachDesign support Specification help Help in installation, use &maintenance10-30mn eLearning modules forindividual trainingArticles giving base skills aboutgeneral subjects: “CahiersTechniques”Selection criterias & methodto follow in order to pre-defineproject specification:b Architecture guideb ID-Spec softwarePractical data & methodsthrough major design guides:b Electrical Installation Guideb Protection guideb Industrial electrical networkdesign guideb ...Technical specification onproducts & solutions for tenderrequestProduct installation dataProduct how to use dataProduct maintenance dataProduct presentation of technicalcharacteristics in all SchneiderElectric product CataloguesSolutions and examples withrecommended architectures inSolution guides:b airportb automativeb foodb retailb officeb industrial buildingsb healthcareb ...Design Software:b My EcodialEcodial software provides acomplete design package forLV installations, in accordancewith IEC standards andrecommendations.Main features:v Create diagramsv Optimise circuit breakers curvesv Determine source powerv Follow step by step calculationv Print the project design fileb SISPRO buildingb ...Drawing source files forconnection, dimension, diagram,mounting & safety: CAD librarySchneider Electric - Electrical installation guide 2009 Schneider Electric - Electrical installation guide 2009

General contentsABCDEFGHGeneral rules of electrical installation design1 Methodology A22 Rules and statutory regulations A43 Installed power loads - Characteristics A104 Power loading of an installation A15Connection to the MV utility distribution network1 Supply of power at medium voltage B22 Procedure for the establishment of a new substation B143 Protection aspect B164 The consumer substation with LV metering B225 The consumer substation with MV metering B306 Constitution of MV/LV distribution substations B35Connection to the LV utility distribution network1 Low voltage utility distribution networks C22 Tariffs and metering C16MV & LV architecture selection guide1 Stakes for the user D32 Simplified architecture design process D43 Electrical installation characteristics D74 Technological characteristics D115 Architecture assessment criteria D136 Choice of architecture fundamentals D157 Choice of architecture details D198 Choice of equiment D249 Recommendations for architecture optimization D2610 Glossary D2911 ID-Spec software D3012 Example: electrical installation in a printworks D31LV Distribution1 Earthing schemes E22 The installation system E153 External influences (IEC 60364-5-51) E25Protection against electric shocks1 General F22 Protection against direct contact F43 Protection against indirect contact F64 Protection of goods due to insulation fault F175 Implementation of the TT system F196 Implementation of the TN system F237 Implementation of the IT system F298 Residual current differential devices RCDs F36Sizing and protection of conductors1 General G22 Practical method for determining the smallest allowable G7cross-sectional area of circuit conductors3 Determination of voltage drop G204 Short-circuit current G245 Particular cases of short-circuit current G306 Protective earthing conductor G377 The neutral conductor G428 Worked example of cable calculation G46LV switchgear: functions & selection1 The basic functions of LV switchgear H22 The switchgear H53 Choice of switchgear H104 Circuit breaker H11Schneider Electric - Electrical installation guide 2009

General contentsJKLMNPQProtection against voltage surges in LV1 General J22 Overvoltage protection devices J63 Protection against voltage surges in LV J114 Choosing a protection device J14Energy Efficiency in electrical distribution1 Introduction K22 Energy efficiency and electricity K33 Diagnosis through electrical measurement K74 Energy saving solutions K135 How to value energy savings K316 From returns on investment to sustained performance K34Power factor correction and harmonic filtering1 Reactive energy and power factor L22 Why to improve the power factor? L53 How to improve the power factor? L74 Where to install power correction capacitors? L105 How to decide the optimum level of compensation? L126 Compensation at the terminals of a transformer L157 Power factor correction of induction motors L188 Example of an installation before and after power factor correction L209 The effects of harmonics L2110 Implementation of capacitor banks L24Harmonic management1 The problem: M2Why is it necessary to detect and eliminate harmonics?2 Standards M33 General M44 Main effects of harmonics in installations M65 Essential indicators of harmonic distortion and M11measurement principles6 Measuring the indicators M147 Detection devices M168 Solutions to attenuate harmonics M17Characteristics of particular sources and loads1 Protection of a LV generator set and the downstream circuits N22 Uninterruptible Power Supply Units (UPS) N113 Protection of LV/LV transformers N244 Lighting circuits N275 Asynchronous motors N45Residential and other special locations1 Residential and similar premises P22 Bathrooms and showers P83 Recommendations applicable to special installations and locations P12EMC guidelines1 Electrical distribution Q22 Earthing principles and structures Q33 Implementation Q54 Coupling mechanism and counter-measures Q165 Wiring recommendations Q22Schneider Electric - Electrical installation guide 2009

Chapter AGeneral rules of electricalinstallation designA1234ContentsMethodologyRules and statutory regulations2.1 Definition of voltage ranges A42.2 Regulations A52.3 Standards A52.4 Quality and safety of an electrical installation A62.5 Initial testing of an installation A62.6 Periodic check-testing of an installation A72.7 Conformity (with standards and specifications) of equipmentused in the installationA72.8 Environment A8Installed power loads - CharacteristicsA103.1 Induction motors A103.2 Resistive-type heating appliances and incandescent lamps(conventional or halogen)A12Power loading of an installationA154.1 Installed power (kW) A154.2 Installed apparent power (kVA) A154.3 Estimation of actual maximum kVA demand A164.4 Example of application of factors ku and ks A174.5 Diversity factor A184.6 Choice of transformer rating A194.7 Choice of power-supply sources A20A2A4© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

A - General rules of electrical installation design1 MethodologyAFor the best results in electrical installation design it is recommended to read all thechapters of this guide in the order in which they are presented.A - General rules of electrical installation designB – Connection to the MV utility distributionnetworkC - Connection to the LV utility distributionnetworkD - MV & LV architecture selection guideE - LV DistributionF - Protection against electric shocksListing of power demandsThe study of a proposed electrical installation requires an adequate understanding ofall governing rules and regulations.The total power demand can be calculated from the data relative to the location andpower of each load, together with the knowledge of the operating modes (steadystate demand, starting conditions, non simultaneous operation, etc.)From these data, the power required from the supply source and (where appropriate)the number of sources necessary for an adequate supply to the installation arereadily obtained.Local information regarding tariff structures is also required to allow the best choiceof connection arrangement to the power-supply network, e.g. at medium voltage orlow voltage level.Service connectionThis connection can be made at:b Medium Voltage levelA consumer-type substation will then have to be studied, built and equipped. Thissubstation may be an outdoor or indoor installation conforming to relevant standardsand regulations (the low-voltage section may be studied separately if necessary).Metering at medium-voltage or low-voltage is possible in this case.b Low Voltage levelThe installation will be connected to the local power network and will (necessarily) bemetered according to LV tariffs.Electrical Distribution architectureThe whole installation distribution network is studied as a complete system.A selection guide is proposed for determination of the most suitable architecture.MV/LV main distribution and LV power distribution levels are covered.Neutral earthing arrangements are chosen according to local regulations, constraintsrelated to the power-supply, and to the type of loads.The distribution equipment (panelboards, switchgears, circuit connections, ...) aredetermined from building plans and from the location and grouping of loads.The type of premises and allocation can influence their immunity to externaldisturbances.Protection against electric shocksThe earthing system (TT, IT or TN) having been previously determined, then theappropriate protective devices must be implemented in order to achieve protectionagainst hazards of direct or indirect contact.© Schneider Electric - all rights reservedG - Sizing and protection of conductorsH - LV switchgear: functions & selectionCircuits and switchgearEach circuit is then studied in detail. From the rated currents of the loads, the levelof short-circuit current, and the type of protective device, the cross-sectional areaof circuit conductors can be determined, taking into account the nature of thecableways and their influence on the current rating of conductors.Before adopting the conductor size indicated above, the following requirements mustbe satisfied:b The voltage drop complies with the relevant standardb Motor starting is satisfactoryb Protection against electric shock is assuredThe short-circuit current Isc is then determined, and the thermal and electrodynamicwithstand capability of the circuit is checked.These calculations may indicate that it is necessary to use a conductor size largerthan the size originally chosen.The performance required by the switchgear will determine its type andcharacteristics.The use of cascading techniques and the discriminative operation of fuses andtripping of circuit breakers are examined.Schneider Electric - Electrical installation guide 2009

A - General rules of electrical installation design1 MethodologyAJ – Protection against voltage surges in LVK – Energy efficiency in electrical distributionL - Power factor correction and harmonic filteringM - Harmonic managementN - Characteristics of particular sources andloadsP - Residential and other special locationsQ - EMC guidelineProtection against overvoltagesDirect or indirect lightning strokes can damage electrical equipment at a distanceof several kilometers. Operating voltage surges, transient and industrial frequencyover-voltage can also produce the same consequences.The effects are examinedand solutions are proposed.Energy efficiency in electrial distributionImplementation of measuring devices with an adequate communication systemwithin the electrical installation can produce high benefits for the user or owner:reduced power consumption, reduced cost of energy, better use of electricalequipment.Reactive energyThe power factor correction within electrical installations is carried out locally,globally or as a combination of both methods.HarmonicsHarmonics in the network affect the quality of energy and are at the origin of manydisturbances as overloads, vibrations, ageing of equipment, trouble of sensitiveequipment, of local area networks, telephone networks. This chapter deals with theorigins and the effects of harmonics and explain how to measure them and presentthe solutions.Particular supply sources and loadsParticular items or equipment are studied:b Specific sources such as alternators or invertersb Specific loads with special characteristics, such as induction motors, lightingcircuits or LV/LV transformersb Specific systems, such as direct-current networksGeneric applicationsCertain premises and locations are subject to particularly strict regulations: the mostcommon example being residential dwellings.EMC GuidelinesSome basic rules must be followed in order to ensure Electromagnetic Compatibility.Non observance of these rules may have serious consequences in the operation ofthe electrical installation: disturbance of communication systems, nuisance trippingof protection devices, and even destruction of sensitive devices.Ecodial softwareEcodial software (1) provides a complete design package for LV installations, inaccordance with IEC standards and recommendations.The following features are included:b Construction of one-line diagramsb Calculation of short-circuit currentsb Calculation of voltage dropsb Optimization of cable sizesb Required ratings of switchgear and fusegearb Discrimination of protective devicesb Recommendations for cascading schemesb Verification of the protection of peopleb Comprehensive print-out of the foregoing calculated design data(1) Ecodial is a Merlin Gerin product and is available in Frenchand English versions.Schneider Electric - Electrical installation guide 2009© Schneider Electric - all rights reserved

A - General rules of electrical installation design2 Rules and statutory regulationsALow-voltage installations are governed by a number of regulatory and advisory texts,which may be classified as follows:b Statutory regulations (decrees, factory acts,etc.)b Codes of practice, regulations issued by professional institutions, job specificationsb National and international standards for installationsb National and international standards for products2.1 Definition of voltage rangesIEC voltage standards and recommendationsThree-phase four-wire or three-wire systems Single-phase three-wire systemsNominal voltage (V)Nominal voltage (V)50 Hz 60 Hz 60 Hz– 120/208 120/240– 240 –230/400 (1) 277/480 –400/690 (1) 480 –– 347/600 –1000 600 –(1) The nominal voltage of existing 220/380 V and 240/415 V systems shall evolvetoward the recommended value of 230/400 V. The transition period should be as shortas possible and should not exceed the year 2003. During this period, as a first step, theelectricity supply authorities of countries having 220/380 V systems should bring thevoltage within the range 230/400 V +6 %, -10 % and those of countries having240/415 V systems should bring the voltage within the range 230/400 V +10 %,-6 %. At the end of this transition period, the tolerance of 230/400 V ± 10 % shouldhave been achieved; after this the reduction of this range will be considered. All theabove considerations apply also to the present 380/660 V value with respect to therecommended value 400/690 V.Fig. A1 : Standard voltages between 100 V and 1000 V (IEC 60038 Edition 6.2 2002-07)© Schneider Electric - all rights reservedSeries ISeries IIHighest voltage Nominal system Highest voltage Nominal systemfor equipment (kV) voltage (kV) for equipment (kV) voltage (kV)3.6 (1) 3.3 (1) 3 (1) 4.40 (1) 4.16 (1)7.2 (1) 6.6 (1) 6 (1) – –12 11 10 – –– – – 13.2 (2) 12.47 (2)– – – 13.97 (2) 13.2 (2)– – – 14.52 (1) 13.8 (1)(17.5) – (15) – –24 22 20 – –– – – 26.4 (2) 24.94 (2)36 (3) 33 (3) – – –– – – 36.5 34.540.5 (3) – 35 (3) – –These systems are generally three-wire systems unless otherwise indicated.The values indicated are voltages between phases.The values indicated in parentheses should be considered as non-preferred values. It isrecommended that these values should not be used for new systems to be constructedin future.Note 1: It is recommended that in any one country the ratio between two adjacentnominal voltages should be not less than two.Note 2: In a normal system of Series I, the highest voltage and the lowest voltage donot differ by more than approximately ±10 % from the nominal voltage of the system.In a normal system of Series II, the highest voltage does not differ by more then +5 %and the lowest voltage by more than -10 % from the nominal voltage of the system.(1) These values should not be used for public distribution systems.(2) These systems are generally four-wire systems.(3) The unification of these values is under consideration.Fig. A2 : Standard voltages above 1 kV and not exceeding 35 kV(IEC 60038 Edition 6.2 2002-07)Schneider Electric - Electrical installation guide 2009

A - General rules of electrical installation design2 Rules and statutory regulationsA2.2 RegulationsIn most countries, electrical installations shall comply with more than one set ofregulations, issued by National Authorities or by recognized private bodies. It isessential to take into account these local constraints before starting the design.2.3 StandardsThis Guide is based on relevant IEC standards, in particular IEC 60364. IEC 60364has been established by medical and engineering experts of all countries in theworld comparing their experience at an international level. Currently, the safetyprinciples of IEC 60364 and 60479-1 are the fundamentals of most electricalstandards in the world (see table below and next page).IEC 60038 Standard voltagesIEC 60076-2 Power transformers - Temperature riseIEC 60076-3 Power transformers - Insulation levels, dielectric tests and external clearances in airIEC 60076-5 Power transformers - Ability to withstand short-circuitIEC 60076-10 Power transformers - Determination of sound levelsIEC 60146 Semiconductor convertors - General requirements and line commutated convertorsIEC 60255 Electrical relaysIEC 60265-1 High-voltage switches - High-voltage switches for rated voltages above 1 kV and less than 52 kVIEC 60269-1 Low-voltage fuses - General requirementsIEC 60269-2 Low-voltage fuses - Supplementary requirements for fuses for use by unskilled persons (fuses mainly for household and similar applications)IEC 60282-1 High-voltage fuses - Current-limiting fusesIEC 60287-1-1 Electric cables - Calculation of the current rating - Current rating equations (100% load factor) and calculation of losses - GeneralIEC 60364 Electrical installations of buildingsIEC 60364-1 Electrical installations of buildings - Fundamental principlesIEC 60364-4-41 Electrical installations of buildings - Protection for safety - Protection against electric shockIEC 60364-4-42 Electrical installations of buildings - Protection for safety - Protection against thermal effectsIEC 60364-4-43 Electrical installations of buildings - Protection for safety - Protection against overcurrentIEC 60364-4-44 Electrical installations of buildings - Protection for safety - Protection against electromagnetic and voltage disrurbanceIEC 60364-5-51 Electrical installations of buildings - Selection and erection of electrical equipment - Common rulesIEC 60364-5-52 Electrical installations of buildings - Selection and erection of electrical equipment - Wiring systemsIEC 60364-5-53 Electrical installations of buildings - Selection and erection of electrical equipment - Isolation, switching and controlIEC 60364-5-54 Electrical installations of buildings - Selection and erection of electrical equipment - Earthing arrangementsIEC 60364-5-55 Electrical installations of buildings - Selection and erection of electrical equipment - Other equipmentsIEC 60364-6-61 Electrical installations of buildings - Verification and testing - Initial verificationIEC 60364-7-701 Electrical installations of buildings - Requirements for special installations or locations - Locations containing a bath tub or shower basinIEC 60364-7-702 Electrical installations of buildings - Requirements for special installations or locations - Swimming pools and other basinsIEC 60364-7-703 Electrical installations of buildings - Requirements for special installations or locations - Locations containing sauna heatersIEC 60364-7-704 Electrical installations of buildings - Requirements for special installations or locations - Construction and demolition site installationsIEC 60364-7-705 Electrical installations of buildings - Requirements for special installations or locations - Electrical installations of agricultural and horticulturalpremisesIEC 60364-7-706 Electrical installations of buildings - Requirements for special installations or locations - Restrictive conducting locationsIEC 60364-7-707 Electrical installations of buildings - Requirements for special installations or locations - Earthing requirements for the installation of dataprocessing equipmentIEC 60364-7-708 Electrical installations of buildings - Requirements for special installations or locations - Electrical installations in caravan parks and caravansIEC 60364-7-709 Electrical installations of buildings - Requirements for special installations or locations - Marinas and pleasure craftIEC 60364-7-710 Electrical installations of buildings - Requirements for special installations or locations - Medical locationsIEC 60364-7-711 Electrical installations of buildings - Requirements for special installations or locations - Exhibitions, shows and standsIEC 60364-7-712 Electrical installations of buildings - Requirements for special installations or locations - Solar photovoltaic (PV) power supply systemsIEC 60364-7-713 Electrical installations of buildings - Requirements for special installations or locations - FurnitureIEC 60364-7-714 Electrical installations of buildings - Requirements for special installations or locations - External lighting installationsIEC 60364-7-715 Electrical installations of buildings - Requirements for special installations or locations - Extra-low-voltage lighting installationsIEC 60364-7-717 Electrical installations of buildings - Requirements for special installations or locations - Mobile or transportable unitsIEC 60364-7-740 Electrical installations of buildings - Requirements for special installations or locations - Temporary electrical installations for structures,amusement devices and booths at fairgrounds, amusement parks and circusesIEC 60427 High-voltage alternating current circuit-breakersIEC 60439-1 Low-voltage switchgear and controlgear assemblies - Type-tested and partially type-tested assembliesIEC 60439-2 Low-voltage switchgear and controlgear assemblies - Particular requirements for busbar trunking systems (busways)IEC 60439-3 Low-voltage switchgear and controlgear assemblies - Particular requirements for low-voltage switchgear and controlgear assemblies intended tobe installed in places where unskilled persons have access for their use - Distribution boardsIEC 60439-4 Low-voltage switchgear and controlgear assemblies - Particular requirements for assemblies for construction sites (ACS)IEC 60446 Basic and safety principles for man-machine interface, marking and identification - Identification of conductors by colours or numeralsIEC 60439-5 Low-voltage switchgear and controlgear assemblies - Particular requirements for assemblies intended to be installed outdoors in public places- Cable distribution cabinets (CDCs)IEC 60479-1 Effects of current on human beings and livestock - General aspectsIEC 60479-2 Effects of current on human beings and livestock - Special aspectsIEC 60479-3 Effects of current on human beings and livestock - Effects of currents passing through the body of livestock(Continued on next page)© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

A - General rules of electrical installation design2 Rules and statutory regulationsAIEC 60529IEC 60644IEC 60664IEC 60715IEC 60724IEC 60755IEC 60787IEC 60831IEC 60947-1IEC 60947-2IEC 60947-3IEC 60947-4-1IEC 60947-6-1IEC 61000IEC 61140IEC 61557-1IEC 61557-8IEC 61557-9IEC 61557-12IEC 61558-2-6IEC 62271-1IEC 62271-100IEC 62271-102IEC 62271-105IEC 62271-200IEC 62271-202Degrees of protection provided by enclosures (IP code)Spécification for high-voltage fuse-links for motor circuit applicationsInsulation coordination for equipment within low-voltage systemsDimensions of low-voltage switchgear and controlgear. Standardized mounting on rails for mechanical support of electrical devices in switchgearand controlgear installations.Short-circuit temperature limits of electric cables with rated voltages of 1 kV (Um = 1.2 kV) and 3 kV (Um = 3.6 kV)General requirements for residual current operated protective devicesApplication guide for the selection of fuse-links of high-voltage fuses for transformer circuit applicationShunt power capacitors of the self-healing type for AC systems having a rated voltage up to and including 1000 V - General - Performance, testingand rating - Safety requirements - Guide for installation and operationLow-voltage switchgear and controlgear - General rulesLow-voltage switchgear and controlgear - Circuit-breakersLow-voltage switchgear and controlgear - Switches, disconnectors, switch-disconnectors and fuse-combination unitsLow-voltage switchgear and controlgear - Contactors and motor-starters - Electromechanical contactors and motor-startersLow-voltage switchgear and controlgear - Multiple function equipment - Automatic transfer switching equipmentElectromagnetic compatibility (EMC)Protection against electric shocks - common aspects for installation and equipmentElectrical safety in low-voltage distribution systems up to 1000 V AC and 1500 V DC - Equipment for testing, measuring or monitoring of protectivemeasures - General requirementsElectrical safety in low-voltage distribution systems up to 1000 V AC and 1500 V DC - Equipment for testing, measuring or monitoring of protectivemeasuresElectrical safety in low-voltage distribution systems up to 1000 V AC and 1500 V DC - Equipment for insulation fault location in IT systemsElectrical safety in low-voltage distribution systems up to 1000 V AC and 1500 V DC - Equipment for testing, measuring or monitoring of protectivemeasures. Performance measuring and monitoring devices (PMD)Safety of power transformers, power supply units and similar - Particular requirements for safety isolating transformers for general useCommon specifications for high-voltage switchgear and controlgear standardsHigh-voltage switchgear and controlgear - High-voltage alternating-current circuit-breakersHigh-voltage switchgear and controlgear - Alternating current disconnectors and earthing switchesHigh-voltage switchgear and controlgear - Alternating current switch-fuse combinationsHigh-voltage switchgear and controlgear - Alternating current metal-enclosed switchgear and controlgear for rated voltages above 1 kV and up toand including 52 kVHigh-voltage/low voltage prefabricated substations(Concluded)2.4 Quality and safety of an electrical installationIn so far as control procedures are respected, quality and safety will be assuredonly if:b The initial checking of conformity of the electrical installation with the standard andregulation has been achievedb The electrical equipment comply with standardsb The periodic checking of the installation recommended by the equipmentmanufacturer is respected.2.5 Initial testing of an installation© Schneider Electric - all rights reservedBefore a utility will connect an installation to its supply network, strict precommissioningelectrical tests and visual inspections by the authority, or by itsappointed agent, must be satisfied.These tests are made according to local (governmental and/or institutional)regulations, which may differ slightly from one country to another. The principles ofall such regulations however, are common, and are based on the observance ofrigorous safety rules in the design and realization of the installation.IEC 60364-6-61 and related standards included in this guide are based on aninternational consensus for such tests, intended to cover all the safety measures andapproved installation practices normally required for residential, commercial and (themajority of) industrial buildings. Many industries however have additional regulationsrelated to a particular product (petroleum, coal, natural gas, etc.). Such additionalrequirements are beyond the scope of this guide.The pre-commissioning electrical tests and visual-inspection checks for installationsin buildings include, typically, all of the following:b Insulation tests of all cable and wiring conductors of the fixed installation, betweenphases and between phases and earthb Continuity and conductivity tests of protective, equipotential and earth-bondingconductorsb Resistance tests of earthing electrodes with respect to remote earthb Verification of the proper operation of the interlocks, if anyb Check of allowable number of socket-outlets per circuitSchneider Electric - Electrical installation guide 2009

A - General rules of electrical installation design2 Rules and statutory regulationsAb Cross-sectional-area check of all conductors for adequacy at the short-circuitlevels prevailing, taking account of the associated protective devices, materials andinstallation conditions (in air, conduit, etc.)b Verification that all exposed- and extraneous metallic parts are properly earthed(where appropriate)b Check of clearance distances in bathrooms, etc.These tests and checks are basic (but not exhaustive) to the majority of installations,while numerous other tests and rules are included in the regulations to coverparticular cases, for example: TN-, TT- or IT-earthed installations, installations basedon class 2 insulation, SELV circuits, and special locations, etc.The aim of this guide is to draw attention to the particular features of different typesof installation, and to indicate the essential rules to be observed in order to achievea satisfactory level of quality, which will ensure safe and trouble-free performance.The methods recommended in this guide, modified if necessary to comply with anypossible variation imposed by a utility, are intended to satisfy all precommissioningtest and inspection requirements.2.6 Periodic check-testing of an installationIn many countries, all industrial and commercial-building installations, together withinstallations in buildings used for public gatherings, must be re-tested periodically byauthorized agents.Figure A3 shows the frequency of testing commonly prescribed according to thekind of installation concerned.Type of installationTestingfrequencyInstallations which b Locations at which a risk of degradation, Annuallyrequire the protection fire or explosion existsof employeesb Temporary installations at worksitesb Locations at which MV installations existb Restrictive conducting locationswhere mobile equipment is usedOther casesEvery 3 yearsInstallations in buildings According to the type of establishment From one toused for public gatherings, and its capacity for receiving the public three yearswhere protection againstthe risks of fire and panicare requiredResidentialAccording to local regulationsFig A3 : Frequency of check-tests commonly recommended for an electrical installationConformity of equipment with the relevantstandards can be attested in several ways2.7 Conformity (with standards and specifications)of equipment used in the installationAttestation of conformityThe conformity of equipment with the relevant standards can be attested:b By an official mark of conformity granted by the certification body concerned, orb By a certificate of conformity issued by a certification body, orb By a declaration of conformity from the manufacturerThe first two solutions are generally not available for high voltage equipment.Declaration of conformityWhere the equipment is to be used by skilled or instructed persons, themanufacturer’s declaration of conformity (included in the technical documentation),is generally recognized as a valid attestation. Where the competence of themanufacturer is in doubt, a certificate of conformity can reinforce the manufacturer’sdeclaration.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

A - General rules of electrical installation design2 Rules and statutory regulationsANote: CE markingIn Europe, the European directives require the manufacturer or his authorizedrepresentative to affix the CE marking on his own responsibility. It means that:b The product meets the legal requirementsb It is presumed to be marketable in EuropeThe CE marking is neither a mark of origin nor a mark of conformity.Mark of conformityMarks of conformity are affixed on appliances and equipment generally used byordinary non instructed people (e.g in the field of domestic appliances). A mark ofconformity is delivered by certification body if the equipment meet the requirementsfrom an applicable standard and after verification of the manufacturer’s qualitymanagement system.Certification of QualityThe standards define several methods of quality assurance which correspond todifferent situations rather than to different levels of quality.AssuranceA laboratory for testing samples cannot certify the conformity of an entire productionrun: these tests are called type tests. In some tests for conformity to standards,the samples are destroyed (tests on fuses, for example).Only the manufacturer can certify that the fabricated products have, in fact,the characteristics stated.Quality assurance certification is intended to complete the initial declaration orcertification of conformity.As proof that all the necessary measures have been taken for assuring the quality ofproduction, the manufacturer obtains certification of the quality control system whichmonitors the fabrication of the product concerned. These certificates are issuedby organizations specializing in quality control, and are based on the internationalstandard ISO 9001: 2000.These standards define three model systems of quality assurance controlcorresponding to different situations rather than to different levels of quality:b Model 3 defines assurance of quality by inspection and checking of final products.b Model 2 includes, in addition to checking of the final product, verification of themanufacturing process. For example, this method is applied, to the manufacturer offuses where performance characteristics cannot be checked without destroying thefuse.b Model 1 corresponds to model 2, but with the additional requirement that thequality of the design process must be rigorously scrutinized; for example, where it isnot intended to fabricate and test a prototype (case of a custom-built product made tospecification).2.8 Environment© Schneider Electric - all rights reservedEnvironmental management systems can be certified by an independent body if theymeet requirements given in ISO 14001. This type of certification mainly concernsindustrial settings but can also be granted to places where products are designed.A product environmental design sometimes called “eco-design” is an approach ofsustainable development with the objective of designing products/services bestmeeting the customers’ requirements while reducing their environmental impactover their whole life cycle. The methodologies used for this purpose lead to chooseequipment’s architecture together with components and materials taking into accountthe influence of a product on the environment along its life cycle (from extraction ofraw materials to scrap) i.e. production, transport, distribution, end of life etc.In Europe two Directives have been published, they are called:b RoHS Directive (Restriction of Hazardous Substances) coming into force onJuly 2006 (the coming into force was on February 13 th , 2003, and the applicationdate is July 1 st , 2006) aims to eliminate from products six hazardous substances:lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls (PBB) orpolybrominated diphenyl ethers (PBDE).Schneider Electric - Electrical installation guide 2009

A - General rules of electrical installation design2 Rules and statutory regulationsAb WEEE Directive (Waste of Electrical and Electronic Equipment) coming intoforce in August 2005 (the coming into force was on February 13 th , 2003, andthe application date is August 13 th , 2005) in order to master the end of life andtreatments for household and non household equipment.In other parts of the world some new legislation will follow the same objectives.In addition to manufacturers action in favour of products eco-design, the contributionof the whole electrical installation to sustainable development can be significantlyimproved through the design of the installation. Actually, it has been shown that anoptimised design of the installation, taking into account operation conditions, MV/LVsubstations location and distribution structure (switchboards, busways, cables),can reduce substantially environmental impacts (raw material depletion, energydepletion, end of life)See chapter D about location of the substation and the main LV switchboard.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

A10A - General rules of electrical installation design3 Installed power loads -CharacteristicsAn examination of the actual apparentpowerdemands of different loads: anecessary preliminary step in the design of aLV installationThe examination of actual values of apparent-power required by each load enablesthe establishment of:b A declared power demand which determines the contract for the supply of energyb The rating of the MV/LV transformer, where applicable (allowing for expectedincreased load)b Levels of load current at each distribution boardThe nominal power in kW (Pn) of a motorindicates its rated equivalent mechanical poweroutput.The apparent power in kVA (Pa) supplied tothe motor is a function of the output, the motorefficiency and the power factor.Pa =Pnηcosϕ3.1 Induction motorsCurrent demandThe full-load current Ia supplied to the motor is given by the following formulae:b 3-phase motor: Ia = Pn x 1,000 / (√3 x U x η x cos ϕ)b 1-phase motor: Ia = Pn x 1,000 / (U x η x cos ϕ)whereIa: current demand (in amps)Pn: nominal power (in kW)U: voltage between phases for 3-phase motors and voltage between the terminalsfor single-phase motors (in volts). A single-phase motor may be connected phase-toneutralor phase-to-phase.η: per-unit efficiency, i.e. output kW / input kWcos ϕ: power factor, i.e. kW input / kVA inputSubtransient current and protection settingb Subtransient current peak value can be very high ; typical value is about 12to 15 times the rms rated value Inm. Sometimes this value can reach 25 times Inm.b Merlin Gerin circuit-breakers, Telemecanique contactors and thermal relays aredesigned to withstand motor starts with very high subtransient current (subtransientpeak value can be up to 19 times the rms rated value Inm).b If unexpected tripping of the overcurrent protection occurs during starting, thismeans the starting current exceeds the normal limits. As a result, some maximumswitchgear withstands can be reached, life time can be reduced and even somedevices can be destroyed. In order to avoid such a situation, oversizing of theswitchgear must be considered.b Merlin Gerin and Telemecanique switchgears are designed to ensure theprotection of motor starters against short-circuits. According to the risk, tables showthe combination of circuit-breaker, contactor and thermal relay to obtain type 1 ortype 2 coordination (see chapter N).Motor starting currentAlthough high efficiency motors can be found on the market, in practice their startingcurrents are roughly the same as some of standard motors.The use of start-delta starter, static soft start unit or variable speed drive allows toreduce the value of the starting current (Example : 4 Ia instead of 7.5 Ia).© Schneider Electric - all rights reservedCompensation of reactive-power (kvar) supplied to induction motorsIt is generally advantageous for technical and financial reasons to reduce the currentsupplied to induction motors. This can be achieved by using capacitors withoutaffecting the power output of the motors.The application of this principle to the operation of induction motors is generallyreferred to as “power-factor improvement” or “power-factor correction”.As discussed in chapter L, the apparent power (kVA) supplied to an induction motorcan be significantly reduced by the use of shunt-connected capacitors. Reductionof input kVA means a corresponding reduction of input current (since the voltageremains constant).Compensation of reactive-power is particularly advised for motors that operate forlong periods at reduced power.kW inputAs noted above cos = so so that a kVA input reduction in will kVA increase input willkVA inputincrease (i.e. improve) (i.e. improve) the value the of cos value ϕ. of cosSchneider Electric - Electrical installation guide 2009

A - General rules of electrical installation design3 Installed power loads -CharacteristicsA11The current supplied to the motor, after power-factor correction, is given by:cos I=Iacos 'where cos ϕ is the power factor before compensation and cos ϕ’ is the power factorafter compensation, Ia being the original current.Figure A4 below shows, in function of motor rated power, standard motor currentvalues for several voltage supplies.kW hp 230 V 380 - 400 V 440 - 500 V 690 V415 V 480 VA A A A A A0.18 - 1.0 - 0.6 - 0.48 0.350.25 - 1.5 - 0.85 - 0.68 0.490.37 - 1.9 - 1.1 - 0.88 0.64- 1/2 - 1.3 - 1.1 - -0.55 - 2.6 - 1.5 - 1.2 0.87- 3/4 - 1.8 - 1.6 - -- 1 - 2.3 - 2.1 - -0.75 - 3.3 - 1.9 - 1.5 1.11.1 - 4.7 - 2.7 - 2.2 1.6- 1-1/2 - 3.3 - 3.0 - -- 2 - 4.3 - 3.4 - -1.5 - 6.3 - 3.6 - 2.9 2.12.2 - 8.5 - 4.9 - 3.9 2.8- 3 - 6.1 - 4.8 - -3.0 - 11.3 - 6.5 - 5.2 3.83.7 - - - - - - -4 - 15 9.7 8.5 7.6 6.8 4.95.5 - 20 - 11.5 - 9.2 6.7- 7-1/2 - 14.0 - 11.0 - -- 10 - 18.0 - 14.0 - -7.5 - 27 - 15.5 - 12.4 8.911 - 38.0 - 22.0 - 17.6 12.8- 15 - 27.0 - 21.0 - -- 20 - 34.0 - 27.0 - -15 - 51 - 29 - 23 1718.5 - 61 - 35 - 28 21- 25 - 44 - 34 -22 - 72 - 41 - 33 24- 30 - 51 - 40 - -- 40 - 66 - 52 - -30 - 96 - 55 - 44 3237 - 115 - 66 - 53 39- 50 - 83 - 65 - -- 60 - 103 - 77 - -45 - 140 - 80 - 64 4755 - 169 - 97 - 78 57- 75 - 128 - 96 - -- 100 - 165 - 124 - -75 - 230 - 132 - 106 7790 - 278 - 160 - 128 93- 125 - 208 - 156 - -110 - 340 - 195 156 113- 150 - 240 - 180 - -132 - 400 - 230 - 184 134- 200 - 320 - 240 - -150 - - - - - - -160 - 487 - 280 - 224 162185 - - - - - - -- 250 - 403 - 302 - -200 - 609 - 350 - 280 203220 - - - - - - -- 300 - 482 - 361 - -250 - 748 - 430 - 344 250280 - - - - - - -- 350 - 560 - 414 - -- 400 - 636 - 474 - -300 - - - - - - -Fig. A4 : Rated operational power and currents (continued on next page)© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

A12A - General rules of electrical installation design3 Installed power loads -CharacteristicskW hp 230 V 380 - 400 V 440 - 500 V 690 V415 V 480 VA A A A A A315 - 940 - 540 - 432 313- 540 - - - 515 - -335 - - - - - - -355 - 1061 - 610 - 488 354- 500 - 786 - 590 - -375 - - - - - - -400 - 1200 - 690 - 552 400425 - - - - - - -450 - - - - - - -475 - - - - - - -500 - 1478 - 850 - 680 493530 - - - - - - -560 - 1652 - 950 - 760 551600 - - - - - - -630 - 1844 - 1060 - 848 615670 - - - - - - -710 - 2070 - 1190 - 952 690750 - - - - - - -800 - 2340 - 1346 - 1076 780850 - - - - - - -900 - 2640 - 1518 - 1214 880950 - - - - - - -1000 - 2910 - 1673 - 1339 970Fig. A4 : Rated operational power and currents (concluded)3.2 Resistive-type heating appliances andincandescent lamps (conventional or halogen)The current demand of a heating appliance or an incandescent lamp is easilyobtained from the nominal power Pn quoted by the manufacturer (i.e. cos ϕ = 1)(see Fig. A5).Nominal Current demand (A)power 1-phase 1-phase 3-phase 3-phase(kW) 127 V 230 V 230 V 400 V0.1 0.79 0.43 0.25 0.140.2 1.58 0.87 0.50 0.290.5 3.94 2.17 1.26 0.721 7.9 4.35 2.51 1.441.5 11.8 6.52 3.77 2.172 15.8 8.70 5.02 2.892.5 19.7 10.9 6.28 3.613 23.6 13 7.53 4.333.5 27.6 15.2 8.72 5.054 31.5 17.4 10 5.774.5 35.4 19.6 11.3 6.55 39.4 21.7 12.6 7.226 47.2 26.1 15.1 8.667 55.1 30.4 17.6 10.18 63 34.8 20.1 11.59 71 39.1 22.6 1310 79 43.5 25.1 14.4© Schneider Electric - all rights reservedFig. A5 : Current demands of resistive heating and incandescent lighting (conventional orhalogen) appliancesSchneider Electric - Electrical installation guide 2009

A - General rules of electrical installation design3 Installed power loads -CharacteristicsA13The currents are given by:b 3-phase case: I a =Pn U 3(1)(1)b 1-phase case: I a = PnUwhere is the voltage between the terminals of the equipment.where U is the voltage between the terminals of the equipment.For an incandescent lamp, the use of halogen gas allows a more concentrated lightsource. The light output is increased and the lifetime of the lamp is doubled.Note: At the instant of switching on, the cold filament gives rise to a very brief butintense peak of current.Fluorescent lamps and related equipmentThe power Pn (watts) indicated on the tube of a fluorescent lamp does not includethe power dissipated in the ballast.The current is is given by: by:P +I a = ballast PnU cos If no power-loss value is indicated for the ballast, a figure of 25% of Pn may be used.Where U = the voltage applied to the lamp, complete with its related equipment.If no power-loss value is indicated for the ballast, a figure of 25% of Pn may be used.Standard tubular fluorescent lampsWith (unless otherwise indicated):b cos ϕ = 0.6 with no power factor (PF) correction (2) capacitorb cos ϕ = 0.86 with PF correction (2) (single or twin tubes)b cos ϕ = 0.96 for electronic ballast.If no power-loss value is indicated for the ballast, a figure of 25% of Pn may be used.Figure A6 gives these values for different arrangements of ballast.Arrangement Tube power Current (A) at 230 V Tubeof lamps, starters (W) (3) Magnetic ballast Electronic lengthand ballasts ballast (cm)Without PF With PFcorrection correctioncapacitor capacitorSingle tube 18 0.20 0.14 0.10 6036 0.33 0.23 0.18 12058 0.50 0.36 0.28 150Twin tubes 2 x 18 0.28 0.18 602 x 36 0.46 0.35 1202 x 58 0.72 0.52 150(3) Power in watts marked on tubeFig. A6 : Current demands and power consumption of commonly-dimensioned fluorescentlighting tubes (at 230 V-50 Hz)Compact fluorescent lampsCompact fluorescent lamps have the same characteristics of economy and long lifeas classical tubes. They are commonly used in public places which are permanentlyilluminated (for example: corridors, hallways, bars, etc.) and can be mounted insituations otherwise illuminated by incandescent lamps (see Fig. A7 next page).(1) Ia in amps; U in volts. Pn is in watts. If Pn is in kW, thenmultiply the equation by 1,000(2) “Power-factor correction” is often referred to as“compensation” in discharge-lighting-tube terminology.Cos ϕ is approximately 0.95 (the zero values of V and Iare almost in phase) but the power factor is 0.5 due to theimpulsive form of the current, the peak of which occurs “late”in each half cycle© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

A14A - General rules of electrical installation design3 Installed power loads -CharacteristicsType of lamp Lamp power Current at 230 V(W)(A)Separated 10 0.080ballast lamp 18 0.11026 0.150Integrated 8 0.075ballast lamp 11 0.09516 0.12521 0.170Fig. A7 : Current demands and power consumption of compact fluorescent lamps (at 230 V - 50 Hz)The power in watts indicated on the tube ofa discharge lamp does not include the powerdissipated in the ballast.Discharge lampsFigure A8 gives the current taken by a complete unit, including all associatedancillary equipment.These lamps depend on the luminous electrical discharge through a gas or vapourof a metallic compound, which is contained in a hermetically-sealed transparentenvelope at a pre-determined pressure. These lamps have a long start-up time,during which the current Ia is greater than the nominal current In. Power and currentdemands are given for different types of lamp (typical average values which maydiffer slightly from one manufacturer to another).© Schneider Electric - all rights reservedType of Power Current In(A) Starting Luminous Average Utilizationlamp (W) demand PF not PF Ia/In Period efficiency timelife of(W) at corrected corrected (mins) (lumens lamp (h)230 V 400 V 230 V 400 V 230 V 400 V per watt)High-pressure sodium vapour lamps50 60 0.76 0.3 1.4 to 1.6 4 to 6 80 to 120 9000 b Lighting of70 80 1 0.45 large halls100 115 1.2 0.65 b Outdoor spaces150 168 1.8 0.85 b Public lighting250 274 3 1.4400 431 4.4 2.21000 1055 10.45 4.9Low-pressure sodium vapour lamps26 34.5 0.45 0.17 1.1 to 1.3 7 to 15 100 to 200 8000 b Lighting of36 46.5 0.22 to 12000 autoroutes66 80.5 0.39 b Security lighting,91 105.5 0.49 station131 154 0.69 b Platform, storageareasMercury vapour + metal halide (also called metal-iodide)70 80.5 1 0.40 1.7 3 to 5 70 to 90 6000 b Lighting of very150 172 1.80 0.88 6000 large areas by250 276 2.10 1.35 6000 projectors (for400 425 3.40 2.15 6000 example: sports1000 1046 8.25 5.30 6000 stadiums, etc.)2000 2092 2052 16.50 8.60 10.50 6 2000Mercury vapour + fluorescent substance (fluorescent bulb)50 57 0.6 0.30 1.7 to 2 3 to 6 40 to 60 8000 b Workshops80 90 0.8 0.45 to 12000 with very high125 141 1.15 0.70 ceilings (halls,250 268 2.15 1.35 hangars)400 421 3.25 2.15 b Outdoor lighting700 731 5.4 3.85 b Low light output (1)1000 1046 8.25 5.302000 2140 2080 15 11 6.1(1) Replaced by sodium vapour lamps.Note: these lamps are sensitive to voltage dips. They extinguish if the voltage falls to less than 50% of their nominal voltage, and willnot re-ignite before cooling for approximately 4 minutes.Note: Sodium vapour low-pressure lamps have a light-output efficiency which is superior to that of all other sources. However, use ofthese lamps is restricted by the fact that the yellow-orange colour emitted makes colour recognition practically impossible.Fig. A8 : Current demands of discharge lampsSchneider Electric - Electrical installation guide 2009

A - General rules of electrical installation design4 Power loading of an installationA16Fluorescent lighting (corrected to cos ϕ = 0.86)Type of application Estimated (VA/m 2 ) Average lightingfluorescent tube level (lux = lm/m 2 )with industrial reflector (1)Roads and highways 7 150storage areas, intermittent workHeavy-duty works: fabrication and 14 300assembly of very large work piecesDay-to-day work: office work 24 500Fine work: drawing offices 41 800high-precision assembly workshopsPower circuitsType of application Estimated (VA/m 2 )Pumping station compressed air 3 to 6Ventilation of premises 23Electrical convection heaters:private houses 115 to 146flats and apartments 90Offices 25Dispatching workshop 50Assembly workshop 70Machine shop 300Painting workshop 350Heat-treatment plant 700(1) example: 65 W tube (ballast not included), flux 5,100 lumens (Im),luminous efficiency of the tube = 78.5 Im / W.Fig. A9 : Estimation of installed apparent power4.3 Estimation of actual maximum kVA demandAll individual loads are not necessarily operating at full rated nominal power nornecessarily at the same time. Factors ku and ks allow the determination of themaximum power and apparent-power demands actually required to dimension theinstallation.Factor of maximum utilization (ku)In normal operating conditions the power consumption of a load is sometimes lessthan that indicated as its nominal power rating, a fairly common occurrence thatjustifies the application of an utilization factor (ku) in the estimation of realistic values.This factor must be applied to each individual load, with particular attention toelectric motors, which are very rarely operated at full load.In an industrial installation this factor may be estimated on an average at 0.75 formotors.For incandescent-lighting loads, the factor always equals 1.For socket-outlet circuits, the factors depend entirely on the type of appliances beingsupplied from the sockets concerned.© Schneider Electric - all rights reservedFactor of simultaneity (ks)It is a matter of common experience that the simultaneous operation of all installedloads of a given installation never occurs in practice, i.e. there is always some degreeof diversity and this fact is taken into account for estimating purposes by the use of asimultaneity factor (ks).The factor ks is applied to each group of loads (e.g. being supplied from a distributionor sub-distribution board). The determination of these factors is the responsibilityof the designer, since it requires a detailed knowledge of the installation and theconditions in which the individual circuits are to be exploited. For this reason, it is notpossible to give precise values for general application.Factor of simultaneity for an apartment blockSome typical values for this case are given in Figure A10 opposite page, and areapplicable to domestic consumers supplied at 230/400 V (3-phase 4-wires). In thecase of consumers using electrical heat-storage units for space heating, a factor of0.8 is recommended, regardless of the number of consumers.Schneider Electric - Electrical installation guide 2009

A - General rules of electrical installation design4 Power loading of an installationA17Number of downstream Factor ofconsumerssimultaneity (ks)2 to 4 15 to 9 0.7810 to 14 0.6315 to 19 0.5320 to 24 0.4925 to 29 0.4630 to 34 0.4435 to 39 0.4240 to 49 0.4150 and more 0.40Fig. A10 : Simultaneity factors in an apartment blockExample (see Fig. A11):5 storeys apartment building with 25 consumers, each having 6 kVA of installed load.The total installed load for the building is: 36 + 24 + 30 + 36 + 24 = 150 kVAThe apparent-power supply required for the building is: 150 x 0.46 = 69 kVAFrom Figure A10, it is possible to determine the magnitude of currents in differentsections of the common main feeder supplying all floors. For vertical rising mainsfed at ground level, the cross-sectional area of the conductors can evidently beprogressively reduced from the lower floors towards the upper floors.These changes of conductor size are conventionally spaced by at least 3-floorintervals.In the example, the current entering the rising main at ground level is:3150 x 0.46 x 10= 100 A400 3the current entering the third floor is:3(36 + 24) x 0.63 x 10= 55 A400 34thfloor6 consumers36 kVA0.783 rdfloor4 consumers24 kVA0.632ndfloor5 consumers30 kVA0.531 stfloor6 consumers36 kVA0.49groundfloor4 consumers24 kVA0.46Fig. A11 : Application of the factor of simultaneity (ks) to an apartment block of 5 storeys© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

A - General rules of electrical installation design4 Power loading of an installationA18Factor of simultaneity for distribution boardsFigure A12 shows hypothetical values of ks for a distribution board supplying anumber of circuits for which there is no indication of the manner in which the totalload divides between them.If the circuits are mainly for lighting loads, it is prudent to adopt ks values close tounity.Number ofFactor ofcircuitssimultaneity (ks)Assemblies entirely tested 0.92 and 34 and 5 0.86 to 9 0.710 and more 0.6Assemblies partially tested 1.0in every case chooseFig. A12 : Factor of simultaneity for distribution boards (IEC 60439)Factor of simultaneity according to circuit functionks factors which may be used for circuits supplying commonly-occurring loads, areshown in Figure A13.Circuit functionFactor of simultaneity (ks)Lighting 1Heating and air conditioning 1Socket-outlets 0.1 to 0.2 (1)Lifts and catering hoist (2) b For the most powerfulmotor 1b For the second mostpowerful motor 0.75b For all motors 0.60(1) In certain cases, notably in industrial installations, this factor can be higher.(2) The current to take into consideration is equal to the nominal current of the motor,increased by a third of its starting current.Fig. A13 : Factor of simultaneity according to circuit function4.4 Example of application of factors ku and ks© Schneider Electric - all rights reservedAn example in the estimation of actual maximum kVA demands at all levels of aninstallation, from each load position to the point of supply is given Fig. A14 (oppositepage).In this example, the total installed apparent power is 126.6 kVA, which correspondsto an actual (estimated) maximum value at the LV terminals of the MV/LV transformerof 65 kVA only.Note: in order to select cable sizes for the distribution circuits of an installation, thecurrent I (in amps) through a circuit is determined from the equation:I = kVA x 10 3U 3where kVA is the actual maximum 3-phase apparent-power value shown on thediagram for the circuit concerned, and U is the phase to- phase voltage (in volts).4.5 Diversity factorThe term diversity factor, as defined in IEC standards, is identical to the factor ofsimultaneity (ks) used in this guide, as described in 4.3. In some English-speakingcountries however (at the time of writing) diversity factor is the inverse of ks i.e. it isalways u 1.Schneider Electric - Electrical installation guide 2009

A - General rules of electrical installation design4 Power loading of an installationA19Level 1 Level 2 Level 3UtilizationApparent Utilization Apparent Simultaneity Apparent Simultaneity Apparent Simultaneity Apparentpower factor power factor power factor power factor power(Pa) max. demand demand demand demandkVA max. kVA kVA kVA kVAWorkshop A Lathe no. 1 5 0.8no. 2no. 3no. 4no. 1no. 25 socketoutlets10/16 A30 fluorescentlamps55522180.80.80.80.80.81Distributionbox3 1 3144441.61.6180.750.214.43.63PowercircuitPedestaldrillSocketouletsLightingcircuitWorkshop Adistributionbox0.918.9MaingeneraldistributionboardMGDBWorkshop B Compressor3 socketoutlets10/16 A10 fluorescentlampsWorkshop C Ventilation no. 1Ovenno. 2no. 1no. 25 socketoutlets10/16 A20 fluorescentlamps1510.612.52.515151820.8111111111210.612.52.5151518210.41Distributionbox10.28113552LightingcircuitPowvercircuitPowercircuit12 Workshop BSocketouletsdistribution4.3 boxSocketouletsLightingcircuit0.9Workshop Cdistributionbox0.915.637.80.965LV / MVFig A14 : An example in estimating the maximum predicted loading of an installation (the factor values used are for demonstration purposes only)4.6 Choice of transformer ratingWhen an installation is to be supplied directly from a MV/LV transformer andthe maximum apparent-power loading of the installation has been determined, asuitable rating for the transformer can be decided, taking into account the followingconsiderations (see Fig. A15):b The possibility of improving the power factor of the installation (see chapter L)b Anticipated extensions to the installationb Installation constraints (e.g. temperature)b Standard transformer ratingsApparent power In (A)kVA 237 V 410 V100 244 141160 390 225250 609 352315 767 444400 974 563500 1218 704630 1535 887800 1949 11271000 2436 14081250 3045 17601600 3898 22532000 4872 28162500 6090 35203150 7673 4436Fig. A15 : Standard apparent powers for MV/LV transformers and related nominal output currents© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

A - General rules of electrical installation design4 Power loading of an installationA20The nominal full-load current In on the LV side of a 3-phase transformer is given by:a x 10 3In = P U 3whereb Pa = kVA rating of the transformerb U = phase-to-phase voltage at no-load in volts (237 V or 410 V)b In is in amperes.For a single-phase transformer:a x 10 3In = P Vwherewhereb V = voltage between LV terminals at no-load (in volts)Simplified equation for 400 V (3-phase load)b In = kVA x 1.4The IEC standard for power transformers is IEC 60076.4.7 Choice of power-supply sourcesThe importance of maintaining a continuous supply raises the question of the use ofstandby-power plant. The choice and characteristics of these alternative sources arepart of the architecture selection, as described in chapter D.For the main source of supply the choice is generally between a connection to theMV or the LV network of the power-supply utility.In practice, connection to a MV source may be necessary where the load exceeds(or is planned eventually to exceed) a certain level - generally of the order of250 kVA, or if the quality of service required is greater than that normally availablefrom a LV network.Moreover, if the installation is likely to cause disturbance to neighbouring consumers,when connected to a LV network, the supply authorities may propose a MV service.Supplies at MV can have certain advantages: in fact, a MV consumer:b Is not disturbed by other consumers, which could be the case at LVb Is free to choose any type of LV earthing systemb Has a wider choice of economic tariffsb Can accept very large increases in loadIt should be noted, however, that:b The consumer is the owner of the MV/LV substation and, in some countries,he must build and equip it at his own expense. The power utility can, in certaincircumstances, participate in the investment, at the level of the MV line for exampleb A part of the connection costs can, for instance, often be recovered if a secondconsumer is connected to the MV line within a certain time following the originalconsumer’s own connectionb The consumer has access only to the LV part of the installation, access to theMV part being reserved to the utility personnel (meter reading, operations, etc.).However, in certain countries, the MV protective circuit-breaker (or fused load-breakswitch) can be operated by the consumerb The type and location of the substation are agreed between the consumer andthe utility© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Chapter BConnection to the MV utilitydistribution network123456ContentsSupply of power at medium voltage1.1 Power supply characteristics of medium voltage B2utility distribution network1.2 Different MV service connections B111.3 Some operational aspects of MV distribution networks B12Procedure for the establishment of a new substation B142.1 Preliminary informations B142.2 Project studies B152.3 Implementation B152.4 Commissioning B15Protection aspectB2B163.1 Protection against electric shocks B163.2 Protection of transformer and circuits B173.3 Interlocks and conditioned operations B19The consumer substation with LV meteringB224.1 General B224.2 Choice of MV switchgear B224.3 Choice of MV switchgear panel for a transformer circuit B254.4 Choice of MV/LV transformer B254.5 Instructions for use of MV equipment B29The consumer substation with MV meteringB325.1 General B325.2 Choice of panels B345.3 Parallel operation of transformers B35Constitution of MV/LV distribution substationsB376.1 Different types of substation B376.2 Indoor substation B376.3 Outdoor substation B39B© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network1 Supply of power at mediumvoltageBThe term "medium voltage" is commonly used for distribution systems with voltagesabove 1 kV and generally applied up to and including 52 kV (see IEC 601-01-28Standard).In this chapter, distribution networks which operate at voltages of 1,000 V or lessare referred to as Low-Voltage systems, while systems of power distribution whichrequire one stage of stepdown voltage transformation, in order to feed into low voltagenetworks, will be referred to as Medium- Voltage systems.For economic and technical reasons the nominal voltage of medium-voltagedistribution systems, as defined above, seldom exceeds 35 kV.The main features which characterize a powersupplysystem include:b The nominal voltage and related insulationlevelsb The short-circuit currentb The rated normal current of items of plantand equipmentb The earthing system1.1 Power supply characteristics of medium voltageutility distribution networkNominal voltage and related insulation levelsThe nominal voltage of a system or of an equipment is defined in IEC 60038 Standardas “the voltage by which a system or equipment is designated and to which certainoperating characteristics are referred”. Closely related to the nominal voltage is the“highest voltage for equipment” which concerns the level of insulation at normalworking frequency, and to which other characteristics may be referred in relevantequipment recommendations.The “highest voltage for equipment” is defined in IEC 60038 Standard as:“the maximum value of voltage for which equipment may be used, that occurs undernormal operating conditions at any time and at any point on the system. It excludesvoltage transients, such as those due to system switching, and temporary voltagevariations”.Notes:1- The highest voltage for equipment is indicated for nominal system voltageshigher than 1,000 V only. It is understood that, particularly for some categoriesof equipment, normal operation cannot be ensured up to this "highest voltage forequipment", having regard to voltage sensitive characteristics such as losses ofcapacitors, magnetizing current of transformers, etc. In such cases, IEC standardsspecify the limit to which the normal operation of this equipment can be ensured.2- It is understood that the equipment to be used in systems having nominal voltagenot exceeding 1,000 V should be specified with reference to the nominal systemvoltage only, both for operation and for insulation.3- The definition for “highest voltage for equipment” given in IEC 60038 Standardis identical to the definition given in IEC 62271-1 Standard for “rated voltage”.IEC 62271-1 Standard concerns switchgear for voltages exceeding 1,000 V.The following values of Figure B1, taken from IEC 60038 Standard, list themost-commonly used standard levels of medium-voltage distribution, and relatethe nominal voltages to corresponding standard values of “Highest Voltage forEquipment”.These systems are generally three-wire systems unless otherwise indicated. Thevalues shown are voltages between phases.The values indicated in parentheses should be considered as non-preferred values.It is recommended that these values should not be used for new systems to beconstructed in future.It is recommended that in any one country the ratio between two adjacent nominalvoltages should be not less than two.© Schneider Electric - all rights reservedSeries I (for 50 Hz and 60 Hz networks)Nominal system voltage Highest voltage for equipement(kV)(kV)3.3 (1) 3 (1) 3.6 (1)6.6 (1) 6 (1) 7.2 (1)11 10 12- 15 17.522 20 2433 (2) - 36 (2)- 35 (2) 40.5 (2)(1) These values should not be used for public distribution systems.(2) The unification of these values is under consideration.Fig. B1 : Relation between nominal system voltages and highest voltages for the equipmentSchneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network1 Supply of power at mediumvoltageIn order to ensure adequate protection of equipment against abnormally-mediumshort term power-frequency overvoltages, and transient overvoltages caused bylightning, switching, and system fault conditions, etc. all MV equipment must bespecified to have appropriate rated insulation levels.A "rated insulation level" is a set of specified dielectric withstand values coveringvarious operating conditions. For MV equipment, in addition to the "highest voltagefor equipment", it includes lightning impulse withstand and short-duration powerfrequency withstand.SwitchgearFigure B2 shown below, lists normal values of “withstand” voltage requirementsfrom IEC 62271-1 Standard. The choice between List 1 and List 2 values of tableB2 depends on the degree of exposure to lightning and switching overvoltages (1) ,the type of neutral earthing, and the type of overvoltage protection devices, etc. (forfurther guidance reference should be made to IEC 60071).BRated Rated lightning impulse withstand voltage Rated short-durationvoltage (peak value) power-frequencyU (r.m.s.withstand voltagevalue) List List 2 (r.m.s. value)To earth, Across the To earth, Across the To earth, Across thebetween isolating between isolating between isolatingpoles distance poles distance poles distanceand across and across and acrossopen open openswitching switching switchingdevice device device(kV) (kV) (kV) (kV) (kV) (kV) (kV)3.6 20 23 40 46 10 127.2 40 46 60 70 20 2312 60 70 75 85 28 3217.5 75 85 95 110 38 4524 95 110 125 145 50 6036 145 165 170 195 70 8052 - - 250 290 95 11072.5 - - 325 375 140 160Note: The withstand voltage values “across the isolating distance” are valid only forthe switching devices where the clearance between open contacts is designed to meetrequirements specified for disconnectors (isolators).Fig. B2 : Switchgear rated insulation levelsIt should be noted that, at the voltage levels in question, no switching overvoltageratings are mentioned. This is because overvoltages due to switching transients areless severe at these voltage levels than those due to lightning.TransformersFigure B3 shown below have been extracted from IEC 60076-3.The significance of list 1 and list 2 is the same as that for the switchgear table, i.e.the choice depends on the degree of exposure to lightning, etc.(1) This means basically that List 1 generally applies toswitchgear to be used on underground-cable systems whileList 2 is chosen for switchgear to be used on overhead-linesystems.Highest voltage Rated short duration Rated lightning impulsefor equipment power frequency withstand voltage(r.m.s.) withstand voltage (peak)(r.m.s.) List 1 List 2(kV) (kV) (kV) (kV)y 1.1 3 - -3.6 10 20 407.2 20 40 6012 28 60 7517.5 38 75 9524 50 95 12536 70 145 17052 95 25072.5 140 325Fig. B3 : Transformers rated insulation levelsSchneider Electric - Electrical installation guide 2009© Schneider Electric - all rights reserved

B - Connection to the MV publicdistribution network1 Supply of power at mediumvoltageBThe national standards of any particular countryare normally rationalized to include one or twolevels only of voltage, current, and fault-levels,etc.A circuit-breaker (or fuse switch, over a limitedvoltage range) is the only form of switchgearcapable of safely breaking all kinds of faultcurrents occurring on a power system.Other componentsIt is evident that the insulation performance of other MV components associatedwith these major items, e.g. porcelain or glass insulators, MV cables, instrumenttransformers, etc. must be compatible with that of the switchgear andtransformers noted above. Test schedules for these items are given in appropriateIEC publications.The national standards of any particular country are normally rationalized to includeone or two levels only of voltage, current, and fault-levels, etc.General note:The IEC standards are intended for worldwide application and consequentlyembrace an extensive range of voltage and current levels.These reflect the diverse practices adopted in countries of different meteorologic,geographic and economic constraints.Short-circuit currentStandard values of circuit-breaker short-circuit current-breaking capability arenormally given in kilo-amps.These values refer to a 3-phase short-circuit condition, and are expressed as theaverage of the r.m.s. values of the AC component of current in each of the threephases.For circuit-breakers in the rated voltage ranges being considered in this chapter,Figure B4 gives standard short-circuit current-breaking ratings.kV 3.6 7.2 12 17.5 24 36 52kA 8 8 8 8 8 8 8(rms) 10 12.5 12.5 12.5 12.5 12.5 12.516 16 16 16 16 16 2025 25 25 25 25 2540 40 40 40 40 4050Fig. B4 : Standard short-circuit current-breaking ratings© Schneider Electric - all rights reservedI pCurrent (I)22I'' kt min22I bI DC22I kTime (t)Fig. B5 : Graphic representation of short-circuit quantities asper IEC 60909Short-circuit current calculationThe rules for calculating short-circuit currents in electrical installations are presentedin IEC standard 60909.The calculation of short-circuit currents at various points in a power system canquickly turn into an arduous task when the installation is complicated.The use of specialized software accelerates calculations.This general standard, applicable for all radial and meshed power systems, 50 or60 Hz and up to 550 kV, is extremely accurate and conservative.It may be used to handle the different types of solid short-circuit (symmetrical ordissymmetrical) that can occur in an electrical installation:b Three-phase short-circuit (all three phases), generally the type producing thehighest currentsb Two-phase short-circuit (between two phases), currents lower than three-phase faultsb Two-phase-to-earth short-circuit (between two phases and earth)b Phase-to-earth short-circuit (between a phase and earth), the most frequent type(80% of all cases).When a fault occurs, the transient short-circuit current is a function of time andcomprises two components (see Fig. B5).b An AC component, decreasing to its steady-state value, caused by the variousrotating machines and a function of the combination of their time constantsb A DC component, decreasing to zero, caused by the initiation of the current and afunction of the circuit impedancesPractically speaking, one must define the short-circuit values that are useful inselecting system equipment and the protection system:b I’’ k : rms value of the initial symmetrical currentb I b : rms value of the symmetrical current interrupted by the switching device whenthe first pole opens at tmin (minimum delay)b I k : rms value of the steady-state symmetrical currentb I p : maximum instantaneous value of the current at the first peakb I DC : DC value of the currentSchneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network1 Supply of power at mediumvoltageThese currents are identified by subscripts 3, 2, 2E, 1, depending on the type ofshort-circuit, respectively three-phase, two-phase clear of earth, two-phase-to-earth,phase-to-earth.The method, based on the Thevenin superposition theorem and decomposition intosymmetrical components, consists in applying to the short-circuit point an equivalentsource of voltage in view of determining the current. The calculation takes place inthree steps.b Define the equivalent source of voltage applied to the fault point. It represents thevoltage existing just before the fault and is the rated voltage multiplied by a factortaking into account source variations, transformer on-load tap changers and thesubtransient behavior of the machines.b Calculate the impedances, as seen from the fault point, of each branch arriving atthis point. For positive and negative-sequence systems, the calculation does not takeinto account line capacitances and the admittances of parallel, non-rotating loads.b Once the voltage and impedance values are defined, calculate the characteristicminimum and maximum values of the short-circuit currents.The various current values at the fault point are calculated using:b The equations providedb A summing law for the currents flowing in the branches connected to the node:v I’’ k (see Fig. B6 for I’’ k calculation, where voltage factor c is defined by thestandard; geometric or algebraic summing)v I p = κ x 2 x I’’ k , where κ is less than 2, depending on the R/X ratio of the positivesequence impedance for the given branch; peak summingv I b = μ x q x I’’ k , where μ and q are less than 1, depending on the generators andmotors, and the minimum current interruption delay; algebraic summingv I k = I’’ k , when the fault is far from the generatorv I k = λ x I r , for a generator, where Ir is the rated generator current and λ is a factordepending on its saturation inductance; algebraic summing.BType of short-circuit3-phase2-phase2-phase-to-earthPhase-to-earth + 0 + 1 0I’’ kGeneral situationc Un3 Z 1c UnZ1 + Z2c Un 3 Z 2Z1 Z2 + Z2 Z0 + Z1 Z0c Un 3Z1 +Z 2 +Z 0Distant faultsc Un3 Z 1c Un2Z 1c Un 3Z 1 + 2Z 0c Un 32 Z1 + Z0Fig. B6 : Short-circuit currents as per IEC 60909CharacterizationThere are 2 types of system equipment, based on whether or not they react when afault occurs.Passive equipmentThis category comprises all equipment which, due to its function, must havethe capacity to transport both normal current and short-circuit current.This equipment includes cables, lines, busbars, disconnecting switches, switches,transformers, series reactances and capacitors, instrument transformers.For this equipment, the capacity to withstand a short-circuit without damageis defined in terms of:b Electrodynamic withstand (“peak withstand current”; value of the peak currentexpressed in kA), characterizing mechanical resistance to electrodynamic stressb Thermal withstand (“short time withstand current”; rms value expressed in kAfor duration between 0,5 and 3 seconds, with a preferred value of 1 second),characterizing maximum permissible heat dissipation.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network1 Supply of power at mediumvoltageBActive equipmentThis category comprises the equipment designed to clear short-circuit currents, i.e.circuit-breakers and fuses. This property is expressed by the breaking capacity and,if required, the making capacity when a fault occurs.b Breaking capacity (see Fig. B7)This basic characteristic of a fault interrupting device is the maximum current (rmsvalue expressed in kA) it is capable of breaking under the specific conditions definedby the standards; in the IEC 62271-100 standard, it refers to the rms value of theAC component of the short-circuit current. In some other standards, the rms valueof the sum of the 2 components (AC and DC) is specified, in which case, it is the“asymmetrical current”.The breaking capacity depends on other factors such as:v Voltagev R/X ratio of the interrupted circuitv Power system natural frequencyv Number of breaking operations at maximum current, for example the cycle:O - C/O - C/O (O = opening, C = closing)The breaking capacity is a relatively complicated characteristic to define and ittherefore comes as no surprise that the same device can be assigned differentbreaking capacities depending on the standard by which it is defined.b Short-circuit making capacityIn general, this characteristic is implicitly defined by the breaking capacity because adevice should be able to close for a current that it can break.Sometimes, the making capacity needs to be higher, for example for circuit-breakersprotecting generators.The making capacity is defined in terms of peak value (expressed in kA) because thefirst asymmetric peak is the most demanding from an electrodynamic point of view.For example, according to standard IEC 62271-100, a circuit-breaker used in a 50 Hzpower system must be able to handle a peak making current equal to 2.5 times therms breaking current (2.6 times for 60 Hz systems).Making capacity is also required for switches, and sometimes for disconnectors, evenif these devices are not able to clear the fault.b Prospective short-circuit breaking currentSome devices have the capacity to limit the fault current to be interrupted.Their breaking capacity is defined as the maximum prospective breaking current thatwould develop during a solid short-circuit across the upstream terminals of the device.Specific device characteristicsThe functions provided by various interrupting devices and their main constraints arepresented in Figure B8.Current (I)I ACTime (t)Device Isolation of Current switching Main constrainstwo active conditionsnetworks Normal FaultDisconnector Yes No No Longitudinal input/output isolationSwitch No Yes No Making and breaking of normalload currentShort-circuit making capacityContactor No Yes No Rated making and breakingcapacitiesMaximum making and breakingcapacitiesDuty and endurancecharacteristicsCircuit-breaker No Yes Yes Short-circuit breaking capacityShort-circuit making capacity© Schneider Electric - all rights reservedI DCI AC : Peak of the periodic componentI DC : Aperiodic componentFig. B7 : Rated breaking current of a circuit-breaker subjectedto a short-circuit as per IEC 60056Fuse No No Yes Minimum short-circuit breakingcapacityMaximum short-circuit breakingcapacityFig. B8 : Functions provided by interrupting devicesSchneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network1 Supply of power at mediumvoltageThe most common normal current rating forgeneral-purpose MV distribution switchgear is400 A.Rated normal currentThe rated normal current is defined as “the r.m.s. value of the current which can becarried continuously at rated frequency with a temperature rise not exceeding thatspecified by the relevant product standard”.The rated normal current requirements for switchgear are decided at the substationdesign stage.The most common normal current rating for general-purpose MV distributionswitchgear is 400 A.In industrial areas and medium-load-density urban districts, circuits rated at 630 Aare sometimes required, while at bulk-supply substations which feed into MVnetworks,800 A; 1,250 A; 1,600 A; 2,500 A and 4,000 A circuit-breakers are listed as standardratings for incoming-transformer circuits, bus-section and bus-coupler CBs, etc.For MV/LV transformer with a normal primary current up to roughly 60 A,a MV switch-fuse combination can be used . For higher primary currents,switch-fuse combination usually does not have the required performances.There are no IEC-recommended rated current values for switch-fuse combinations.The actual rated current of a given combination, meaning a switchgear baseand defined fuses, is provided by the manufacturer of the combination as a table"fuse reference / rated current". These values of the rated current are defined byconsidering parameters of the combination as:b Normal thermal current of the fusesb Necessary derating of the fuses, due to their usage within the enclosure.When combinations are used for protecting transformers, then further parametersare to be considered, as presented in Appendix A of the IEC 62271-105 and in theIEC 60787. They are mainly:b The normal MV current of the transformerb The possible need for overloading the transformerb The inrush magnetizing currentb The MV short-circuit powerb The tapping switch adjustment range.Manufacturers usually provide an application table "service voltage / transformerpower / fuse reference" based on standard distribution network and transformerparameters, and such table should be used with care, if dealing with unusualinstallations.In such a scheme, the load-break switch should be suitably fitted with a trippingdevice e.g. with a relay to be able to trip at low fault-current levels which must cover(by an appropriate margin) the rated minimum breaking current of the MV fuses. Inthis way, medium values of fault current which are beyond the breaking capability ofthe load-break switch will be cleared by the fuses, while low fault-current values, thatcannot be correctly cleared by the fuses, will be cleared by the tripped load-breakswitch.Influence of the ambient temperature and altitude on the rated currentNormal-current ratings are assigned to all current-carrying electrical appliances,and upper limits are decided by the acceptable temperature rise caused by theI 2 R (watts) dissipated in the conductors, (where I = r.m.s. current in amperes andR = the resistance of the conductor in ohms), together with the heat producedby magnetic-hysteresis and eddy-current losses in motors, transformers, steelenclosures, etc. and dielectric losses in cables and capacitors, where appropriate.The temperature rise above the ambient temperature will depend mainly on therate at which the heat is removed. For example, large currents can be passedthrough electric motor windings without causing them to overheat, simply becausea cooling fan fixed to the shaft of the motor removes the heat at the same rate as itis produced, and so the temperature reaches a stable value below that which coulddamage the insulation and result in a burnt-out motor.The normal-current values recommended by IEC are based on ambientairtemperatures common to temperate climates at altitudes not exceeding1,000 metres, so that items which depend on natural cooling by radiation andair-convection will overheat if operated at rated normal current in a tropical climateand/ or at altitudes exceeding 1,000 metres. In such cases, the equipment has to bederated, i.e. be assigned a lower value of normal current rating.The case of transformer is addressed in IEC 60076-2.B© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network1 Supply of power at mediumvoltage© Schneider Electric - all rights reservedBEarth faults on medium-voltage systemscan produce dangerous voltage levels onLV installations. LV consumers (and substationoperating personnel) can be safeguardedagainst this danger by:b Restricting the magnitude of MV earth-faultcurrentsb Reducing the substation earthing resistanceto the lowest possible valueb Creating equipotential conditions at thesubstation and at the consumer’s installationFaultHVI fI fLVR sFig. B9 : Transferred potentialV= I f R sConsumer(1) The others being unearthed. A particular case of earth-faultcurrent limitation is by means of a Petersen coil.123NEarthing systemsEarthing and equipment-bonding earth connections require careful consideration,particularly regarding safety of the LV consumer during the occurrence of a shortcircuitto earth on the MV system.Earth electrodesIn general, it is preferable, where physically possible, to separate the electrodeprovided for earthing exposed conductive parts of MV equipment from the electrodeintended for earthing the LV neutral conductor. This is commonly practised in ruralsystems where the LV neutral-conductor earth electrode is installed at one or twospans of LV distribution line away from the substation.In most cases, the limited space available in urban substations precludes thispractice, i.e. there is no possibility of separating a MV electrode sufficiently froma LV electrode to avoid the transference of (possibly dangerous) voltages to theLV system.Earth-fault currentEarth-fault current levels at medium voltage are generally (unless deliberatelyrestricted) comparable to those of a 3-phase short-circuit.Such currents passing through an earth electrode will raise its voltage to a mediumvalue with respect to “remote earth” (the earth surrounding the electrode will beraised to a medium potential; “remote earth” is at zero potential).For example, 10,000 A of earth-fault current passing through an electrode with an(unusually low) resistance of 0.5 ohms will raise its voltage to 5,000 V.Providing that all exposed metal in the substation is “bonded” (connected together)and then connected to the earth electrode, and the electrode is in the form of (or isconnected to) a grid of conductors under the floor of the substation, then there is nodanger to personnel, since this arrangement forms an equipotential “cage” in whichall conductive material, including personnel, is raised to the same potential.Transferred potentialA danger exists however from the problem known as Transferred Potential. It will beseen in Figure B9 that the neutral point of the LV winding of the MV/LV transformeris also connected to the common substation earth electrode, so that the neutralconductor, the LV phase windings and all phase conductors are also raised to theelectrode potential.Low-voltage distribution cables leaving the substation will transfer this potential toconsumers installations. It may be noted that there will be no LV insulation failurebetween phases or from phase to neutral since they are all at the same potential. It isprobable, however, that the insulation between phase and earth of a cable or somepart of an installation would fail.SolutionsA first step in minimizing the obvious dangers of transferred potentials is to reducethe magnitude of MV earth-fault currents. This is commonly achieved by earthing theMV system through resistors or reactors at the star points of selected transformers (1) ,located at bulk-supply substations.A relatively medium transferred potential cannot be entirely avoided by this means,however, and so the following strategy has been adopted in some countries.The equipotential earthing installation at a consumer’s premises represents a remoteearth, i.e. at zero potential. However, if this earthing installation were to be connectedby a low-impedance conductor to the earth electrode at the substation, then theequipotential conditions existing in the substation would also exist at the consumer’sinstallation.Low-impedance interconnectionThis low-impedance interconnection is achieved simply by connecting the neutralconductor to the consumer’s equipotential installation, and the result is recognized asthe TN earthing system (IEC 60364) as shown in diagram A of Figure B10 next page.The TN system is generally associated with a Protective Multiple Earthing (PME)scheme, in which the neutral conductor is earthed at intervals along its length (every3 rd or 4 th pole on a LV overhead-line distributor) and at each consumer’s serviceposition. It can be seen that the network of neutral conductors radiating from asubstation, each of which is earthed at regular intervals, constitutes, together withthe substation earthing, a very effective low-resistance earth electrode.Schneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network1 Supply of power at mediumvoltageBDiagramRs valueA - TN-aMVLV12B - IT-aMVLV12Cases A and BNo particular resistance value for Rs is imposedin these cases33NNR SR SC - TT-aMVLV1D - IT-bMVLV1Cases C and DUw - UoRs yIm23N23NWhereUw = the rated normal-frequency withstandvoltage for low-voltage equipment atconsumer installationsUo = phase to neutral voltage at consumer'sinstallationsIm = maximum value of MV earth-fault currentR SR SE - TT-bMVR SLVR N123NF - IT-cIn cases E and F the LV protective conductors (bonding exposed conductive parts) in the substationare earthed via the substation earth electrode, and it is therefore the substation LV equipment (only)that could be subjected to overvoltage.MVR SLVR N123NCases E and FRs y Uws - UImWhereUws = the normal-frequency withstand voltagefor low-voltage equipments in thesubstation (since the exposed conductiveparts of these equipments are earthedvia Rs)U = phase to neutral voltage at the substationfor the TT(s) system, but the phase-tophasevoltage for the IT(s) systemIm = maximum value of MV earth-fault currentNotes:b For TN-a and IT-a, the MV and LV exposed conductive parts at the substation and those at the consumer’s installations, together with theLV neutral point of the transformer, are all earthed via the substation electrode system.b For TT-a and IT-b, the MV and LV exposed conductive parts at the substation, together with the LV neutral point of the transformer are earthed viathe substation electrode system.b For TT-b and IT-c, the LV neutral point of the transformer is separately earthed outside of the area of influence of the substation earth electrode.Uw and Uws are commonly given the (IEC 60364-4-44) value Uo + 1200 V, where Uo is the nominal phase-to-neutral voltage of the LV systemconcerned.Fig. B10 : Maximum earthing resistance Rs at a MV/LV substation to ensure safety during a short-circuit to earth fault on the medium-voltage equipment for differentearthing systemsThe combination of restricted earth-fault currents, equipotential installations andlow resistance substation earthing, results in greatly reduced levels of overvoltageand limited stressing of phase-to-earth insulation during the type of MV earth-faultsituation described above.Limitation of the MV earth-fault current and earth resistance of the substationAnother widely-used earthing system is shown in diagram C of Figure B10. It will beseen that in the TT system, the consumer’s earthing installation (being isolated fromthat of the substation) constitutes a remote earth.This means that, although the transferred potential will not stress the phase-to-phaseinsulation of the consumer’s equipment, the phase-to-earth insulation of all threephases will be subjected to overvoltage.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network1 Supply of power at mediumvoltageB10© Schneider Electric - all rights reservedThe strategy in this case, is to reduce the resistance of the substation earthelectrode, such that the standard value of 5-second withstand-voltage-to-earth forLV equipment and appliances will not be exceeded.Practical values adopted by one national electrical power-supply authority, on its20 kV distribution systems, are as follows:b Maximum earth-fault current in the neutral connection on overhead line distributionsystems, or mixed (O/H line and U/G cable) systems, is 300 Ab Maximum earth-fault current in the neutral connection on underground systems is1,000 AThe formula required to determine the maximum value of earthing resistance Rs atthethesubstation,substation,totoensureensurethatthatthetheLVLVwithstandwithstandvoltagevoltage willwillnotnotbebeexceeded,exceeded,is:is:Uw UoRs = in ohms (see cases C and D in Figure B10). C10).ImWhereWhereUw = the lowest standard value (in volts) of short-term (5 s) withstand voltage for theconsumer’s installation and appliances = Uo + 1200 V (IEC 60364-4-44)Uo = phase to neutral voltage (in volts) at the consumer’s LV service positionIm = maximum earth-fault current on the MV system (in amps). This maximum earthfault current Im is the vectorial sum of maximum earth-fault current in the neutralconnection and total unbalanced capacitive current of the network.A third form of system earthing referred to as the “IT” system in IEC 60364 iscommonly used where continuity of supply is essential, e.g. in hospitals, continuousprocessmanufacturing, etc. The principle depends on taking a supply from anunearthed source, usually a transformer, the secondary winding of which isunearthed, or earthed through a medium impedance (u1,000 ohms). In these cases,an insulation failure to earth in the low-voltage circuits supplied from the secondarywindings will result in zero or negligible fault-current flow, which can be allowed topersist until it is convenient to shut-down the affected circuit to carry out repair work.Diagrams B, D and F (Figure B10)They show IT systems in which resistors (of approximately 1,000 ohms) are includedin the neutral earthing lead.If however, these resistors were removed, so that the system is unearthed, thefollowing notes apply.Diagram B (Figure B10)All phase wires and the neutral conductor are “floating” with respect to earth, to whichthey are “connected” via the (normally very medium) insulation resistances and (verysmall) capacitances between the live conductors and earthed metal (conduits, etc.).Assuming perfect insulation, all LV phase and neutral conductors will be raised byelectrostatic induction to a potential approaching that of the equipotential conductors.In practice, it is more likely, because of the numerous earth-leakage paths of all liveconductors in a number of installations acting in parallel, that the system will behavesimilarly to the case where a neutral earthing resistor is present, i.e. all conductorswill be raised to the potential of the substation earth.In these cases, the overvoltage stresses on the LV insulation are small or nonexistent.Diagrams D and F (Figure B10)In these cases, the medium potential of the substation (S/S) earthing system acts onthe isolated LV phase and neutral conductors:b Through the capacitance between the LV windings of the transformer and thetransformer tankb Through capacitance between the equipotential conductors in the S/S and thecores of LV distribution cables leaving the S/Sb Through current leakage paths in the insulation, in each case.At positions outside the area of influence of the S/S earthing, system capacitancesexist between the conductors and earth at zero potential (capacitances betweencores are irrelevant - all cores being raised to the same potential).The result is essentially a capacitive voltage divider, where each “capacitor” isshunted by (leakage path) resistances.In general, LV cable and installation wiring capacitances to earth are muchlarger, and the insulation resistances to earth are much smaller than those of thecorresponding parameters at the S/S, so that most of the voltage stresses appear atthe substation between the transformer tank and the LV winding.The rise in potential at consumers’ installations is not likely therefore to be a problemwhere the MV earth-fault current level is restricted as previously mentioned.Schneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network1 Supply of power at mediumvoltageOverhead lineAll IT-earthed transformers, whether the neutral point is isolated or earthed througha medium impedance, are routinely provided with an overvoltage limiting devicewhich will automatically connect the neutral point directly to earth if an overvoltagecondition approaches the insulation-withstand level of the LV system.In addition to the possibilities mentioned above, several other ways in which theseovervoltages can occur are described in Clause 3.1.This kind of earth-fault is very rare, and when does occur is quickly detected andcleared by the automatic tripping of a circuit-breaker in a properly designed andconstructed installation.Safety in situations of elevated potentials depends entirely on the provision ofproperly arranged equipotential areas, the basis of which is generally in the form of awidemeshed grid of interconnected bare copper conductors connected to verticallydrivencopper-clad (1) steel rods.The equipotential criterion to be respected is that which is mentioned in Chapter Fdealing with protection against electric shock by indirect contact, namely: that thepotential between any two exposed metal parts which can be touched simultaneouslyby any parts the body must never, under any circumstances, exceed 50 V in dryconditions, or 25 V in wet conditions.Special care should be taken at the boundaries of equipotential areas to avoid steeppotential gradients on the surface of the ground which give rise to dangerous “steppotentials”.This question is closely related to the safe earthing of boundary fences and is furtherdiscussed in Sub-clause 3.1.B111.2 Different MV service connectionsAccording to the type of medium-voltage network, the following supply arrangementsare commonly adopted.Fig. B11 : Single-line serviceSingle-line serviceThe substation is supplied by a single circuit tee-off from a MV distributor (cable orline).In general, the MV service is connected into a panel containing a load-break/isolating switch-fuse combination and earthing switches, as shown in Figure B11.In some countries a pole-mounted transformer with no MV switchgear or fuses(at the pole) constitutes the “substation”. This type of MV service is very common inrural areas.Protection and switching devices are remote from the transformer, and generallycontrol a main overhead line, from which a number of these elementary service linesare tapped.Underground cablering mainFig. B12 : Ring-main service(1) Copper is cathodic to most other metals and thereforeresists corrosion.(2) A ring main is a continuous distributor in the form of aclosed loop, which originates and terminates on one set ofbusbars. Each end of the loop is controlled by its own circuitbreaker.In order to improve operational flexibility the busbarsare often divided into two sections by a normally closed bussectioncircuit-breaker, and each end of the ring is connectedto a different section.An interconnector is a continuous untapped feeder connectingthe busbars of two substations. Each end of the interconnectoris usually controlled by a circuit beaker.An interconnector-distributor is an interconnector whichsupplies one or more distribution substations along its length.Ring-main serviceRing-main units (RMU) are normally connected to form a MV ring main (2) orinterconnector-distributor (2) , such that the RMU busbars carry the full ring-main orinterconnector current (see Fig. B12).The RMU consists of three units, integrated to form a single assembly, viz:b 2 incoming units, each containing a load break/isolating switch and a circuitearthing switchb 1 outgoing and general protection unit, containing a load-break switch andMV fuses, or a combined load-break/fuse switch, or a circuit-breaker and isolatingswitch, together with a circuit-earthing switch in each case.All load-break switches and earthing switches are fully rated for short-circuit currentmakingduty.This arrangement provides the user with a two-source supply, thereby reducingconsiderably any interruption of service due to system faults or operations by thesupply authority, etc.The main application for RMUs is in utility supply MV underground-cable networks inurban areas.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network1 Supply of power at mediumvoltageB12Parallel feeders serviceWhere a MV supply connection to two lines or cables originating from the samebusbar of a substation is possible, a similar MV switchboard to that of a RMU iscommonly used (see Fig. B13).The main operational difference between this arrangement and that of a RMU is thatthe two incoming panels are mutually interlocked, such that one incoming switch onlycan be closed at a time, i.e. its closure prevents the closure of the other.On the loss of power supply, the closed incoming switch must be opened and the(formerly open) switch can then be closed.The sequence may be carried out manually or automatically.This type of switchboard is used particularly in networks of medium-load density andin rapidly-expanding urban areas supplied by MV underground cable systems.1.3 Some operational aspects of MV distributionnetworks© Schneider Electric - all rights reservedParalleled undergroundcable distributorsFig. B13 : Parallel feeders serviceOverhead linesMedium winds, ice formation, etc., can cause the conductors of overhead lines totouch each other, thereby causing a momentary (i.e. not permanent) short-circuitfault.Insulation failure due to broken ceramic or glass insulators, caused by air-bornedebris; careless use of shot-guns, etc., or again, heavily polluted insulator surfaces,can result in a short-circuit to earth.Many of these faults are self-clearing. For example, in dry conditions, brokeninsulators can very often remain in service undetected, but are likely to flashover toearth (e.g. to a metal supporting structure) during a rainstorm. Moreover, pollutedsurfaces generally cause a flashover to earth only in damp conditions.The passage of fault current almost invariably takes the form of an electric arc, theintense heat of which dries the current path, and to some extent, re-establishes itsinsulating properties. In the meantime, protective devices have usually operated toclear the fault, i.e. fuses have blown or a circuit-breaker has tripped.Experience has shown that in the large majority of cases, restoration of supply byreplacing fuses or by re-closing a circuit-breaker will be successful.For this reason it has been possible to considerably improve the continuity of serviceon MV overhead-line distribution networks by the application of automatic circuitbreakerreclosing schemes at the origin of the circuits concerned.These automatic schemes permit a number of reclosing operations if a first attemptfails, with adjustable time delays between successive attempts (to allow de-ionizationof the air at the fault) before a final lock-out of the circuit-breaker occurs, after all(generally three) attempts fail.Other improvements in service continuity are achieved by the use of remotelycontrolledsection switches and by automatic isolating switches which operate inconjunction with an auto-reclosing circuit-breaker.This last scheme is exemplified by the final sequence shown in Figure B14 nextpage.The principle is as follows: if, after two reclosing attempts, the circuit-breaker trips,the fault is assumed to be permanent, then there are two possibilities:b The fault is on the section downstream the Automatic Line Switch, and while thefeeder is dead the ALS opens to isolate this section of the network, before the third(and final) reclosing takes place,b The fault is on the section upstream the ALS and the circuit-breaker will make athird reclosing attempt and thus trip and lock out.While these measures have greatly improved the reliability of supplies fromMV overhead line systems, the consumers must, where considered necessary, maketheir own arrangements to counter the effects of momentary interruptions to supply(between reclosures), for example:b Uninterruptible standby emergency powerb Lighting that requires no cooling down before re-striking (“hot restrike”).Schneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network1 Supply of power at mediumvoltageB13O21- Cycle 1SRI O1 fI o15 to 30 sI nSRO3fault0.3 s 0.4 sPermanent fault2 - Cycle 2SRa - Fault on main feederI O1fO2SR1O3SR2O4I nI o0.3 s 0.4 s15 to 30s15 to 30 sfault0.4 sPermanent fault0.45 sb - Fault on section supplied through Automatic Line SwitchI fO1O2SR1 O3I n15 to 30 s15 to 30 sSR2I oFault0.3 s 0.4 s0.4 sOpening of ALSFig. B14 : Automatic reclosing cycles of a circuit-breaker controlling a radial MV feederUnderground cable networksFaults on underground cable networks are sometimes the result of carelessworkmanship by cable jointers or by cable laying contractors, etc., but are morecommonly due to damage from tools such as pick-axes, pneumatic drills and trenchexcavating machines, and so on, used by other utilities.Insulation failures sometimes occur in cable terminating boxes due to overvoltage,particularly at points in a MV system where an overhead line is connected to anunderground cable. The overvoltage in such a case is generally of atmosphericorigin, and electromagnetic-wave reflection effects at the joint box (where the naturalimpedance of the circuit changes abruptly) can result in overstressing of the cableboxinsulation to the point of failure. Overvoltage protection devices, such as lightningarresters, are frequently installed at these locations.Faults occurring in cable networks are less frequent than those on overhead (O/H)line systems, but are almost invariably permanent faults, which require more time forlocalization and repair than those on O/H lines.Where a cable fault occurs on a ring, supply can be quickly restored to all consumerswhen the faulty section of cable has been determined.If, however, the fault occurs on a radial feeder, the delay in locating the fault andcarrying out repair work can amount to several hours, and will affect all consumersdownstream of the fault position. In any case, if supply continuity is essential on all,or part of, an installation, a standby source must be provided.Centralized remote control, based on SCADA(Supervisory Control And Data Acquisition)systems and recent developments in IT(Information Technology) techniques, isbecoming more and more common in countriesin which the complexity of highly interconnectedsystems justifies the expenditure.Remote control of MV networksRemote control on MV feeders is useful to reduce outage durations in case of cablefault by providing an efficient and fast mean for loop configuration. This is achievedby motor operated switches implemented in some of the substations along the loopassociated with relevant remote telecontrol units. Remote controled substation willalways be reenergized through telecontroled operation when the other ones couldhave to wait for further manual operation.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network2 Procedure for the establishmentof a new substationB14Large consumers of electricity are invariably supplied at MV.On LV systems operating at 120/208 V (3-phase 4-wires), a load of 50 kVA might beconsidered to be “large”, while on a 240/415 V 3-phase system a “large” consumercould have a load in excess of 100 kVA. Both systems of LV distribution are commonin many parts of the world.As a matter of interest, the IEC recommends a “world” standard of 230/400 V for3-phase 4-wire systems. This is a compromise level and will allow existing systemswhich operate at 220/380 V and at 240/415 V, or close to these values, to complywith the proposed standard simply by adjusting the off-circuit tapping switches ofstandard distribution transformers.The distance over which the energy has to be transmitted is a further factor inconsidering an MV or LV service. Services to small but isolated rural consumers areobvious examples.The decision of a MV or LV supply will depend on local circumstances andconsiderations such as those mentioned above, and will generally be imposed by theutility for the district concerned.When a decision to supply power at MV has been made, there are two widelyfollowedmethods of proceeding:1 - The power-supplier constructs a standard substation close to the consumer’spremises, but the MV/LV transformer(s) is (are) located in transformer chamber(s)inside the premises, close to the load centre2 - The consumer constructs and equips his own substation on his own premises, towhich the power supplier makes the MV connectionIn method no. 1 the power supplier owns the substation, the cable(s) to thetransformer(s), the transformer(s) and the transformer chamber(s), to which he hasunrestricted access.The transformer chamber(s) is (are) constructed by the consumer (to plans andregulations provided by the supplier) and include plinths, oil drains, fire walls andceilings, ventilation, lighting, and earthing systems, all to be approved by the supplyauthority.The tariff structure will cover an agreed part of the expenditure required to providethe service.Whichever procedure is followed, the same principles apply in the conception andrealization of the project. The following notes refer to procedure no. 2.© Schneider Electric - all rights reservedThe consumer must provide certain data to theutility at the earliest stage of the project.2.1 Preliminary informationBefore any negotiations or discussions can be initiated with the supply authorities,the following basic elements must be established:Maximum anticipated power (kVA) demandDetermination of this parameter is described in Chapter A, and must take intoaccount the possibility of future additional load requirements. Factors to evaluate atthis stage are:b The utilization factor (ku)b The simultaneity factor (ks)Layout plans and elevations showing location of proposed substationPlans should indicate clearly the means of access to the proposed substation, withdimensions of possible restrictions, e.g. entrances corridors and ceiling height,together with possible load (weight) bearing limits, and so on, keeping in mind that:b The power-supply personnel must have free and unrestricted access to theMV equipment in the substation at all timesb Only qualified and authorized consumer’s personnel are allowed access to thesubstationb Some supply authorities or regulations require that the part of the installation operatedby the authority is located in a separated room from the part operated by the customer.Degree of supply continuity requiredThe consumer must estimate the consequences of a supply failure in terms of itsduration:b Loss of productionb Safety of personnel and equipmentSchneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network2 Procedure for the establishmentof a new substationThe utility must give specific information to theprospective consumer.2.2 Project studiesFrom the information provided by the consumer, the power-supplier must indicate:The type of power supply proposed, and define:b The kind of power-supply system: overheadline or underground-cable networkb Service connection details: single-line service, ring-main installation, or parallelfeeders, etc.b Power (kVA) limit and fault current levelThe nominal voltage and rated voltage (Highest voltage for equipment)Existing or future, depending on the development of the system.Metering details which define:b The cost of connection to the power networkb Tariff details (consumption and standing charges)B15The utility must give official approval of theequipment to be installed in the substation,and of proposed methods of installation.2.3 ImplementationBefore any installation work is started, the official agreement of the power-suppliermust be obtained. The request for approval must include the following information,largely based on the preliminary exchanges noted above:b Location of the proposed substationb Single-line diagram of power circuits and connections, together with earthingcircuitproposalsb Full details of electrical equipment to be installed, including performancecharacteristicsb Layout of equipment and provision for metering componentsb Arrangements for power-factor improvement if requiredb Arrangements provided for emergency standby power plant (MV or LV) if eventuallyrequiredAfter testing and checking of the installation byan independent test authority, a certificate isgranted which permits the substation to be putinto service.2.4 CommissioningWhen required by the authority, commissioning tests must be successfully completedbefore authority is given to energize the installation from the power supply system.Even if no test is required by the authority it is better to do the following verification tests:b Measurement of earth-electrode resistancesb Continuity of all equipotential earth-and safety bonding conductorsb Inspection and functional testing of all MV componentsb Insulation checks of MV equipmentb Dielectric strength test of transformer oil (and switchgear oil if appropriate), ifapplicableb Inspection and testing of the LV installation in the substationb Checks on all interlocks (mechanical key and electrical) and on all automaticsequencesb Checks on correct protective-relay operation and settingsIt is also imperative to check that all equipment is provided, such that any properlyexecuted operation can be carried out in complete safety. On receipt of the certificateof conformity (if required):b Personnel of the power-supply authority will energize the MV equipment and checkfor correct operation of the meteringb The installation contractor is responsible for testing and connection of theLV installationWhen finally the substation is operational:b The substation and all equipment belongs to the consumerb The power-supply authority has operational control over all MV switchgear in thesubstation, e.g. the two incoming load-break switches and the transformer MV switch(or CB) in the case of a RingMainUnit, together with all associated MV earthing switchesb The power-supply personnel has unrestricted access to the MV equipmentb The consumer has independent control of the MV switch (or CB) of the transformer(s)only, the consumer is responsible for the maintenance of all substation equipment,and must request the power-supply authority to isolate and earth the switchgear toallow maintenance work to proceed. The power supplier must issue a signed permitto-workto the consumers maintenance personnel, together with keys of locked-offisolators, etc. at which the isolation has been carried out.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network3 Protection aspectB16The subject of protection in the electrical power industry is vast: it covers all aspectsof safety for personnel, and protection against damage or destruction of property,plant, and equipment.These different aspects of protection can be broadly classified according to thefollowing objectives:b Protection of personnel and animals against the dangers of overvoltages andelectric shock, fire, explosions, and toxic gases, etc.b Protection of the plant, equipment and components of a power system againstthe stresses of short-circuit faults, atmospheric surges (lightning) and power-systeminstability (loss of synchronism) etc.b Protection of personnel and plant from the dangers of incorrect power-systemoperation, by the use of electrical and mechanical interlocking. All classes ofswitchgear (including, for example, tap-position selector switches on transformers,and so on...) have well-defined operating limits. This means that the order in whichthe different kinds of switching device can be safely closed or opened is vitallyimportant. Interlocking keys and analogous electrical control circuits are frequentlyused to ensure strict compliance with correct operating sequences.It is beyond the scope of a guide to describe in full technical detail the numerousschemes of protection available to power-systems engineers, but it is hoped that thefollowing sections will prove to be useful through a discussion of general principles.While some of the protective devices mentioned are of universal application,descriptions generally will be confined to those in common use on MV andLV systems only, as defined in Sub-clause 1.1 of this Chapter.Protection against electric shocks andovervoltages is closely related to theachievement of efficient (low resistance)earthing and effective application of theprinciples of equipotential environments.3.1 Protection against electric shocksProtective measures against electric shock are based on two common dangers:b Contact with an active conductor, i.e. which is live with respect to earth in normalcircumstances. This is referred to as a “direct contact” hazard.b Contact with a conductive part of an apparatus which is normally dead, but whichhas become live due to insulation failure in the apparatus. This is referred to as an“indirect contact” hazard.It may be noted that a third type of shock hazard can exist in the proximity of MV orLV (or mixed) earth electrodes which are passing earth-fault currents. This hazardis due to potential gradients on the surface of the ground and is referred to as a“step-voltage” hazard; shock current enters one foot and leaves by the other foot, andis particular dangerous for four-legged animals. A variation of this danger, known asa “touch voltage” hazard can occur, for instance, when an earthed metallic part issituated in an area in which potential gradients exist.Touching the part would cause current to pass through the hand and both feet.Animals with a relatively long front-to-hind legs span are particularly sensitive tostep-voltage hazards and cattle have been killed by the potential gradients caused bya low voltage (230/400 V) neutral earth electrode of insufficiently low resistance.Potential-gradient problems of the kind mentioned above are not normallyencountered in electrical installations of buildings, providing that equipotentialconductors properly bond all exposed metal parts of equipment and all extraneousmetal (i.e. not part of an electrical apparatus or the installation - for examplestructural steelwork, etc.) to the protective-earthing conductor.© Schneider Electric - all rights reservedDirect-contact protection or basic protectionThe main form of protection against direct contact hazards is to contain all live partsin housings of insulating material or in metallic earthed housings, by placing out ofreach (behind insulated barriers or at the top of poles) or by means of obstacles.Where insulated live parts are housed in a metal envelope, for example transformers,electric motors and many domestic appliances, the metal envelope is connected tothe installation protective earthing system.For MV switchgear, the IEC standard 62271-200 (Prefabricated Metal Enclosedswitchgear and controlgear for voltages up to 52 kV) specifies a minimum ProtectionIndex (IP coding) of IP2X which ensures the direct-contact protection. Furthermore,the metallic enclosure has to demonstrate an electrical continuity, then establishinga good segregation between inside and ouside of the enclosure. Proper grounding ofthe enclosure further participates to the electrical protection of the operators undernormal operating conditions.For LV appliances this is achieved through the third pin of a 3-pin plug and socket.Total or even partial failure of insulation to the metal, can raise the voltage of theenvelope to a dangerous level (depending on the ratio of the resistance of the leakagepath through the insulation, to the resistance from the metal envelope to earth).Schneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network3 Protection aspectIndirect-contact protection or fault protectionA person touching the metal envelope of an apparatus with a faulty insulation, asdescribed above, is said to be making an indirect contact.An indirect contact is characterized by the fact that a current path to earth exists(through the protective earthing (PE) conductor) in parallel with the shock currentthrough the person concerned.Case of fault on L.V. systemExtensive tests have shown that, providing the potential of the metal envelope is notgreater than 50 V with respect to earth, or to any conductive material within reachingdistance, no danger exists.Indirect-contact hazard in the case of a MV faultIf the insulation failure in an apparatus is between a MV conductor and the metalenvelope, it is not generally possible to limit the rise of voltage of the envelope to50 V or less, simply by reducing the earthing resistance to a low value. The solutionin this case is to create an equipotential situation, as described in Sub-clause 1.1“Earthing systems”.B173.2 Protection of transformer and circuitsGeneralThe electrical equipment and circuits in a substation must be protected in orderto avoid or to control damage due to abnormal currents and/or voltages. Allequipment normally used in power system installations have standardized short-timewithstand ratings for overcurrent and overvoltage. The role of protective scheme isto ensure that this withstand limits can never be exceeded. In general, this meansthat fault conditions must be cleared as fast as possible without missing to ensurecoordination between protective devices upstream and downstream the equipementto be protected. This means, when there is a fault in a network, generally severalprotective devices see the fault at the same time but only one must act.These devices may be:b Fuses which clear the faulty circuit directly or together with a mechanical trippingattachment, which opens an associated three-phase load-break switchb Relays which act indirectly on the circuit-breaker coilTransformer protectionStresses due to the supply networkSome voltage surges can occur on the network such as :b Atmospheric voltage surgesAtmospheric voltage surges are caused by a stroke of lightning falling on or near anoverhead line.b Operating voltage surgesA sudden change in the established operating conditions in an electrical networkcauses transient phenomena to occur. This is generally a high frequency or dampedoscillation voltage surge wave.For both voltage surges, the overvoltage protection device generally used is avaristor (Zinc Oxide).In most cases, voltage surges protection has no action on switchgear.Stresses due to the loadOverloading is frequently due to the coincidental demand of a number of smallloads, or to an increase in the apparent power (kVA) demand of the installation,due to expansion in a factory, with consequent building extensions, and so on. Loadincreases raise the temperature of the wirings and of the insulation material. Asa result, temperature increases involve a reduction of the equipment working life.Overload protection devices can be located on primary or secondary side of thetransformer.The protection against overloading of a transformer is now provided by a digital relaywhich acts to trip the circuit-breaker on the secondary side of the transformer. Suchrelay, generally called thermal overload relay, artificially simulates the temperature,taking into account the time constant of the transformer. Some of them are able totake into account the effect of harmonic currents due to non linear loads (rectifiers,computer equipment, variable speed drives…).This type of relay is also able topredict the time before overload tripping and the waiting time after tripping. So, thisinformation is very helpful to control load shedding operation.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network3 Protection aspectB18In addition, larger oil-immersed transformers frequently have thermostats with twosettings, one for alarm purposes and the other for tripping.Dry-type transformers use heat sensors embedded in the hottest part of the windingsinsulation for alarm and tripping.Internal faultsThe protection of transformers by transformer-mounted devices, against the effectsof internal faults, is provided on transformers which are fitted with airbreathingconservator tanks by the classical Buchholz mechanical relay (see Fig. B15). Theserelays can detect a slow accumulation of gases which results from the arcing ofincipient faults in the winding insulation or from the ingress of air due to an oil leak.This first level of detection generally gives an alarm, but if the condition deterioratesfurther, a second level of detection will trip the upstream circuit-breaker.An oil-surge detection feature of the Buchholz relay will trip the upstream circuitbreaker“instantaneously” if a surge of oil occurs in the pipe connecting the main tankwith the conservator tank.Such a surge can only occur due to the displacement of oil caused by a rapidlyformed bubble of gas, generated by an arc of short-circuit current in the oil.By specially designing the cooling-oil radiator elements to perform a concerting action,“totally filled” types of transformer as large as 10 MVA are now currently available.Fig. B15 : Transformer with conservator tankExpansion of the oil is accommodated without an excessive rise in pressure by the“bellows” effect of the radiator elements. A full description of these transformers isgiven in Sub-clause 4.4 (see Fig. B16).Evidently the Buchholz devices mentioned above cannot be applied to this design; amodern counterpart has been developed however, which measures:b The accumulation of gasb Overpressureb OvertemperatureThe first two conditions trip the upstream circuit-breaker, and the third condition tripsthe downstream circuit-breaker of the transformer.Internal phase-to-phase short-circuitInternal phase-to-phase short-circuit must be detected and cleared by:b 3 fuses on the primary side of the tranformer orb An overcurrent relay that trips a circuit-breaker upstream of the transformerInternal phase-to-earth short-circuitThis is the most common type of internal fault. It must be detected by an earth faultrelay. Earth fault current can be calculated with the sum of the 3 primary phasecurrents (if 3 current transformers are used) or by a specific core current transformer.If a great sensitivity is needed, specific core current transformer will be prefered. Insuch a case, a two current transformers set is sufficient (see Fig. B17).Fig. B16 : Totally filled transformerProtection of circuitsThe protection of the circuits downstream of the transformer must comply with theIEC 60364 requirements.HV LV123123Discrimination between the protective devices upstream anddownstream of the transformerThe consumer-type substation with LV metering requires discriminative operationbetween the MV fuses or MV circuit-breaker and the LV circuit-breaker or fuses.The rating of the MV fuses will be chosen according to the characteristics of thetransformer.© Schneider Electric - all rights reservedOvercurrent relay E/F relayFig. B17 : Protection against earth fault on the MV windingNThe tripping characteristics of the LV circuit-breaker must be such that, for anoverload or short-circuit condition downstream of its location, the breaker will tripsufficiently quickly to ensure that the MV fuses or the MV circuit-breaker will not beadversely affected by the passage of overcurrent through them.The tripping performance curves for MV fuses or MV circuit-breaker and LV circuitbreakersare given by graphs of time-to-operate against current passing throughthem. Both curves have the general inverse-time/current form (with an abruptdiscontinuity in the CB curve at the current value above which “instantaneous”tripping occurs).These curves are shown typically in Figure B18.Schneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network3 Protection aspectTimeDCABMinimum pre-arcingtime of MV fuseB/A u 1.35 at anymoment in timeD/C u 2 at anycurrent valueCircuit breakertrippingcharacteristicCurrentFig. B18 : Discrimination between MV fuse operation and LVcircuit-breaker tripping, for transformer protectionU 1 MV LV U 2Fig. B19 : MV fuse and LV circuit-breaker configurationb In order to achieve discrimination:All parts of the fuse or MV circuit-breaker curve must be above and to the right of theCB curve.b In order to leave the fuses unaffected (i.e. undamaged):All parts of the minimum pre-arcing fuse curve must be located to the right of the CBcurve by a factor of 1.35 or more (e.g. where, at time T, the CB curve passes througha point corresponding to 100 A, the fuse curve at the same time T must pass througha point corresponding to 135 A, or more, and so on...) and, all parts of the fuse curvemust be above the CB curve by a factor of 2 or more (e.g. where, at a current level Ithe CB curve passes through a point corresponding to 1.5 seconds, the fuse curveat the same current level I must pass through a point corresponding to 3 seconds, ormore, etc.).The factors 1.35 and 2 are based on standard maximum manufacturing tolerancesfor MV fuses and LV circuit-breakers.In order to compare the two curves, the MV currents must be converted to theequivalent LV currents, or vice-versa.Where a LV fuse-switch is used, similar separation of the characteristic curves of theMV and LV fuses must be respected.b In order to leave the MV circuit-breaker protection untripped:All parts of the minimum pre-arcing fuse curve must be located to the right of theCB curve by a factor of 1.35 or more (e.g. where, at time T, the LV CB curve passesthrough a point corresponding to 100 A, the MV CB curve at the same time T mustpass through a point corresponding to 135 A, or more, and so on...) and, all parts ofthe MV CB curve must be above the LV CB curve (time of LV CB curve must be lessor equal than MV CB curves minus 0.3 s)The factors 1.35 and 0.3 s are based on standard maximum manufacturingtolerances for MV current transformers, MV protection relay and LV circuit-breakers.In order to compare the two curves, the MV currents must be converted to theequivalent LV currents, or vice-versa.B19Choice of protective device on the primary side of thetransformerAs explained before, for low reference current, the protection may be by fuses or bycircuit-breaker.When the reference current is high, the protection will be achieved by circuit-breaker.Protection by circuit-breaker provides a more sensitive transformer protectioncompared with fuses. The implementation of additional protections (earth faultprotection, thermal overload protection) is easier with circuit-breakers.3.3 Interlocks and conditioned operationsMechanical and electrical interlocks are included on mechanisms and in the controlcircuits of apparatus installed in substations, as a measure of protection against anincorrect sequence of manœuvres by operating personnel.Mechanical protection between functions located on separate equipment(e.g. switchboard and transformer) is provided by key-transfer interlocking.An interlocking scheme is intended to prevent any abnormal operational manœuvre.Some of such operations would expose operating personnel to danger, some otherswould only lead to an electrical incident.Basic interlockingBasic interlocking functions can be introduced in one given functionnal unit; someof these functions are made mandatory by the IEC 62271‐200, for metal-enclosedMV switchgear, but some others are the result of a choice from the user.Considering access to a MV panel, it requires a certain number of operationswhich shall be carried out in a pre-determined order. It is necessary to carry outoperations in the reverse order to restore the system to its former condition. Eitherproper procedures, or dedicated interlocks, can ensure that the required operationsare performed in the right sequence. Then such accessible compartment will beclassified as “accessible and interlocked” or “accessible by procedure”. Even forusers with proper rigorous procedures, use of interlocks can provide a further helpfor safety of the operators.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network3 Protection aspectB20Key interlockingBeyond the interlocks available within a given functionnal unit (see also 4.2), themost widely-used form of locking/interlocking depends on the principle of key transfer.The principle is based on the possibility of freeing or trapping one or several keys,according to whether or not the required conditions are satisfied.These conditions can be combined in unique and obligatory sequences, therebyguaranteeing the safety of personnel and installation by the avoidance of an incorrectoperational procedure.Non-observance of the correct sequence of operations in either case may haveextremely serious consequences for the operating personnel, as well as for theequipment concerned.Note: It is important to provide for a scheme of interlocking in the basic design stageof planning a MV/LV substation. In this way, the apparatuses concerned will beequipped during manufacture in a coherent manner, with assured compatibility ofkeys and locking devices.Service continuityFor a given MV switchboard, the definition of the accessible compartments as wellas their access conditions provide the basis of the “Loss of Service Continuity”classification defined in the standard IEC 62271‐200. Use of interlocks or only properprocedure does not have any influence on the service continuity. Only the request foraccessing a given part of the switchboard, under normal operation conditions, resultsin limiting conditions which can be more or less severe regarding the continuity of theelectrical distribution process.Interlocks in substationsIn a MV/LV distribution substation which includes:b A single incoming MV panel or two incoming panels (from parallel feeders) or twoincoming/outgoing ring-main panelsb A transformer switchgear-and-protection panel, which can include a load-break/disconnecting switch with MV fuses and an earthing switch, or a circuit-breaker andline disconnecting switch together with an earthing switchb A transformer compartmentInterlocks allow manœuvres and access to different panels in the following conditions:Basic interlocks, embedded in single functionnal unitsb Operation of the load-break/isolating switchv If the panel door is closed and the associated earthing switch is openb Operation of the line-disconnecting switch of the transformer switchgear - andprotection panelv If the door of the panel is closed, andv If the circuit-breaker is open, and the earthing switch(es) is (are) openb Closure of an earthing switchv If the associated isolating switch(es) is (are) open (1)b Access to an accessible compartment of each panel, if interlocks have beenspecifiedv If the isolating switch for the compartment is open and the earthing switch(es) forthe compartment is (are) closedb Closure of the door of each accessible compartment, if interlocks have beenspecifiedv If the earthing switch(es) for the compartment is (are) closedFunctional interlocks involving several functional units or separate equipmentb Access to the terminals of a MV/LV transformerv If the tee-off functional unit has its switch open and its earthing switch closed.According to the possibility of back-feed from the LV side, a condition on the LV mainbreaker can be necessary.© Schneider Electric - all rights reserved(1) If the earthing switch is on an incoming circuit, theassociated isolating switches are those at both ends of thecircuit, and these should be suitably interlocked. In suchsituation, the interlocking function becomes a multi-units keyinterlock.Practical exampleIn a consumer-type substation with LV metering, the interlocking scheme mostcommonly used is MV/LV/TR (high voltage/ low voltage/transformer).The aim of the interlocking is:b To prevent access to the transformer compartment if the earthing switch has notbeen previously closedb To prevent the closure of the earthing switch in a transformer switchgear-andprotectionpanel, if the LV circuit-breaker of the transformer has not been previouslylocked “open” or “withdrawn”Schneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network3 Protection aspectSMV switch and LV CB closedOSMV fuses accessibleSFig. B20 : Example of MV/LV/TR interlockingOOTransformer MV terminals accessibleLegendKey absentKey freeKey trappedPanel or doorSSSOAccess to the MV or LV terminals of a transformer, (protected upstream by aMV switchgear-and-protection panel, containing a MV load-break / isolatingswitch, MV fuses, and a MV earthing switch) must comply with the strict proceduredescribed below, and is illustrated by the diagrams of Figure B20.Note: The transformer in this example is provided with plug-in type MV terminalconnectors which can only be removed by unlocking a retaining device common toall three phase connectors (1) .The MV load-break / disconnecting switch is mechanically linked with theMV earthing switch such that only one of the switches can be closed, i.e. closureof one switch automatically locks the closure of the other.Procedure for the isolation and earthing of the power transformer, and removalof the MV plug-type shrouded terminal connections (or protective cover)Initial conditionsb MV load-break/disconnection switch and LV circuit-breaker are closedb MV earthing switch locked in the open position by key “O”b Key “O” is trapped in the LV circuit-breaker as long as that circuit-breaker is closedStep 1b Open LV CB and lock it open with key “O”b Key “O” is then releasedStep 2b Open the MV switchb Check that the “voltage presence” indicators extinguish when the MV switch isopenedStep 3b Unlock the MV earthing switch with key “O” and close the earthing switchb Key “O” is now trappedStep 4The access panel to the MV fuses can now be removed (i.e. is released by closure ofthe MV earthing switch). Key “S” is located in this panel, and is trapped when the MVswitch is closedb Turn key “S” to lock the MV switch in the open positionb Key “S” is now releasedStep 5Key “S” allows removal of the common locking device of the plug-type MV terminalconnectors on the transformer or of the common protective cover over the terminals,as the case may be.In either case, exposure of one or more terminals will trap key “S” in the interlock.The result of the foregoing procedure is that:b The MV switch is locked in the open position by key “S”.Key “S” is trapped at the transformer terminals interlock as long as the terminals areexposed.b The MV earthing switch is in the closed position but not locked, i.e. may be openedor closed. When carrying out maintenance work, a padlock is generally used to lockthe earthing switch in the closed position, the key of the padlock being held by theengineer supervizing the work.b The LV CB is locked open by key “O”, which is trapped by the closed MV earthingswitch. The transformer is therefore safely isolated and earthed.It may be noted that the upstream terminal of the load-break disconnecting switchmay remain live in the procedure described as the terminals in question are locatedin a separate non accessible compartment in the particular switchgear underdiscussion. Any other technical solution with exposed terminals in the accessedcompartment would need further de-energisation and interlocks.B21(1) Or may be provided with a common protective cover overthe three terminals.Schneider Electric - Electrical installation guide 2009© Schneider Electric - all rights reserved

B - Connection to the MV publicdistribution network4 The consumer substationwith LV meteringB224.1 GeneralA consumer substation with LV metering is an electrical installation connected to autility supply system at a nominal voltage of 1 kV - 35 kV, and includes a singleMV/LV transformer generally not exceeding 1,250 kVA.FunctionsThe substationAll component parts of the substation are located in one room, either in an existingbuilding, or in the form of a prefabricated housing exterior to the building.Connection to the MV networkConnection at MV can be:b Either by a single service cable or overhead line, orb Via two mechanically interlocked load-break switches with two service cables fromduplicate supply feeders, orb Via two load-break switches of a ring-main unitThe transformerSince the use of PCB (1) -filled transformers is prohibited in most countries,the preferred available technologies are:b Oil-immersed transformers for substations located outside premisesb Dry-type, vacuum-cast-resin transformers for locations inside premises, e.g.multistoreyed buildings, buildings receiving the public, and so on...MeteringMetering at low voltage allows the use of small metering transformers at modest cost.Most tariff structures take account of MV/LV transformer losses.LV installation circuitsA low-voltage circuit-breaker, suitable for isolation duty and locking off facilities, to:b Supply a distribution boardb Protect the transformer against overloading and the downstream circuits againstshort-circuit faults.One-line diagramsThe diagrams on the following page (see Fig. B21) represent the different methodsof MV service connection, which may be one of four types:b Single-line serviceb Single-line service (equipped for extension to form a ring main)b Duplicate supply serviceb Ring main service© Schneider Electric - all rights reserved(1) Polychlorinated biphenyl4.2 Choice of MV switchgearStandards and specificationsThe switchgear and equipment described below are rated for 1 kV - 24 kV systemsand comply with the following international standards:IEC 62271-1, 62271-200, 60265-1, 62271-102, 62271-100, 62271-105Local regulations can also require compliance with national standards as:b France:UTEb United Kingdom: BSb Germany:VDEb United States of America: ANSIType of equipmentIn addition of Ring Main Units discussed in section 1.2, all kinds of switchgeararrangements are possible when using modular switchgear, and provisions for laterextensions are easily realized.Schneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network4 The consumer substationwith LV meteringB23Power supplysystemServiceconnectionMV protection andMV/LV transformationLV meteringand isolationLV distributionand protectionSupplier/consumerinterfaceTransformerLV terminalsDownstream terminalsof LV isolatorSingle-line serviceProtectionProtectionSingle-line service(equipped for extensionto form a ring main)Permitted if only onetransformer and rated powerlow enough to accomodatethe limitations of fuses andcombinationsProtectionDuplicatesupplyservicePermitted if only onetransformer and rated powerlow enough to accomodatethe limitations of fuses andcombinationsProtection+Auto-changeoverswitchRing mainserviceProtectionAutomaticLV standbysourceAlways permittedFig. B21 : Consumer substation with LV metering© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network4 The consumer substationwith LV meteringB24Operational safety of metal enclosed switchgearDescriptionThe following notes describe a “state-of-the art” load-break / disconnecting-switchpanel (see Fig. B22) incorporating the most modern developments for ensuring:b Operational safetyb Minimum space requirementsb Extendibility and flexibilityb Minimum maintenance requirementsEach panel includes 3 compartments:b Switchgear: the load-break disconnecting switch is incorporated in an hermeticallysealed (for life) molded epoxy-resin unitb Connections: by cable at terminals located on the molded switch unitb Busbars: modular, such that any number of panels may be assembled side-by-sideto form a continuous switchboard, and for control and indication a low voltage cabinetwhich can accommodate automatic control and relaying equipment. An additionalcabinet may be mounted above the existing one if further space is required.Cable connections are provided inside a cable-terminating compartment at thefront of the unit, to which access is gained by removal of the front panel of thecompartment.The units are connected electrically by means of prefabricated sections of busbars.Site erection is effected by following the assembly instructions.Operation of the switchgear is simplified by the grouping of all controls andindications on a control panel at the front of each unit.The technology of these switchgear units is essentially based on operational safety,ease of installation and low maintenance requirements.Switchgear internal safety measuresb The load-break/disconnecting switch fully satisfies the requirement of “reliableposition indicating device” as defined in IEC 62271-102 (disconnectors and earthingswitches)b The functionnal unit incorporates the basic interlocks specified by theIEC 62271‐200 (prefabricated metal enclosed switchgear and controlgear):v Closure of the switch is not possible unless the earth switch is openv Closure of the earthing switch is only possible if the load break/isolating switch isopenb Access to the cable compartment, which is the only user-accessible compartmentduring operation, is secured by further interlocks:v Opening of the access panel to the cable terminations compartment (1) is onlypossible if the earthing switch is closedv The load-break/disconnecting switch is locked in the open position when theabove-mentioned access panel is open. Opening of the earthing switch is thenpossible, for instance to allow a dielectric test on the cables.With such features, the switchboard can be operated with live busbars and cables,except for the unit where the access to cables is made. It complies then with theLoss of Service Continuity class LSB2A, as defined in the IEC 62271‐200.Apart from the interlocks noted above, each switchgear panel includes:b Built-in padlocking facilities on the operation leversb 5 predrilled sets of fixing holes for possible future interlocking locks© Schneider Electric - all rights reservedFig. B22 : Metal enclosed MV load break disconnecting switch(1) Where MV fuses are used they are located in thiscompartment.Operationsb Operating handles, levers, etc. required for switching operations are groupedtogether on a clearly illustrated panelb All closing-operation levers are identical on all units (except those containing acircuit-breaker)b Operation of a closing lever requires very little effortb Opening or closing of a load-break/disconnecting switch can be by lever or bypush-button for automatic switchesb Conditions of switches (Open, Closed, Spring-charged), are clearly indicatedSchneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network4 The consumer substationwith LV metering4.3 Choice of MV switchgear panel for a transformercircuitB25Three types of MV switchgear panel are generally available:b Load-break switch and separate MV fuses in the panelb Load-break switch/MV fuses combinationb Circuit-breakerSeven parameters influence the optimum choice:b The primary current of the transformerb The insulating medium of the transformerb The position of the substation with respect to the load centreb The kVA rating of the transformerb The distance from switchgear to the transformerb The use of separate protection relays (as opposed to direct-acting trip coils).Note: The fuses used in the load-break/switch fuses combination have striker-pinswhich ensure tripping of the 3-pole switch on the operation of one (or more) fuse(s).4.4 Choice of MV/LV transformerCharacteristic parameters of a transformerA transformer is characterized in part by its electrical parameters, but also by itstechnology and its conditions of use.Electrical characteristicsb Rated power (Pn): the conventional apparent-power in kVA on which other designparametervalues and the construction of the transformer are based. Manufacturingtests and guarantees are referred to this ratingb Frequency: for power distribution systems of the kind discussed in this guide, thefrequency will be 50 Hz or 60 Hzb Rated primary and secondary voltages: For a primary winding capable of operating atmore than one voltage level, a kVA rating corresponding to each level must be given.The secondary rated voltage is its open circuit valueb Rated insulation levels are given by overvoltage-withstand test values at powerfrequency, and by high voltage impulse tests values which simulate lightningdischarges. At the voltage levels discussed in this guide, overvoltages caused byMV switching operations are generally less severe than those due to lightning, sothat no separate tests for switching-surge withstand capability are madeb Off-circuit tap-selector switch generally allows a choice of up to ± 2.5% and ± 5%level about the rated voltage of the highest voltage winding. The transformer must bede-energized before this switch is operatedb Winding configurations are indicated in diagrammatic form by standard symbols forstar, delta and inter-connected-star windings; (and combinations of these for specialduty, e.g. six-or twelve-phase rectifier transformers, etc.) and in an IEC-recommendedalphanumeric code. This code is read from left-to-right, the first letter refers to thehighest voltage winding, the second letter to the next highest, and so on:v Capital letters refer to the highest voltage windingD = deltaY = starZ = interconnected-star (or zigzag)N = neutral connection brought out to a terminalv Lower-case letters are used for tertiary and secondary windingsd = deltay = starz = interconnected-star (or zigzag)n = neutral connection brought out to a terminalv A number from 0 to 11, corresponding to those, on a clock dial (“0” is used insteadof “12”) follows any pair of letters to indicate the phase change (if any) which occursduring the transformation.A very common winding configuration used for distribution transformers is thatof a Dyn 11 transformer, which has a delta MV winding with a star-connectedsecondary winding the neutral point of which is brought out to a terminal. The phasechange through the transformer is +30 degrees, i.e. phase 1 secondary voltage isat “11 o’clock” when phase 1 of the primary voltage is at “12 o’clock”, as shown inFigure B31 page B34. All combinations of delta, star and zigzag windings produce aphase change which (if not zero) is either 30 degrees or a multiple of 30 degrees.IEC 60076-4 describes the “clock code” in detail.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network4 The consumer substationwith LV meteringB26Characteristics related to the technology and utilization of the transformerThis list is not exhaustive:b Choice of technologyThe insulating medium is:v Liquid (mineral oil) orv Solid (epoxy resin and air)b For indoor or outdoor installationb Altitude (

B - Connection to the MV publicdistribution network4 The consumer substationwith LV meteringThere are two ways in which this pressure limitation is commonly achieved:b Hermetically-sealed totally-filled tank (up to 10 MVA at the present time)Developed by a leading French manufacturer in 1963, this method was adopted by thenational utility in 1972, and is now in world-wide service (see Fig. B24).Expansion of the liquid is compensated by the elastic deformation of the oil-coolingpassages attached to the tank.The “total-fill” technique has many important advantages over other methods:v Oxydation of the dielectric liquid (with atmospheric oxygen) is entirely precludedv No need for an air-drying device, and so no consequent maintenance (inspectionand changing of saturated dessicant)v No need for dielectric-strength test of the liquid for at least 10 yearsv Simplified protection against internal faults by means of a DGPT device is possiblev Simplicity of installation: lighter and lower profile (than tanks with a conservator)and access to the MV and LV terminals is unobstructedv Immediate detection of (even small) oil leaks; water cannot enter the tankb Air-breathing conservator-type tank at atmospheric pressureExpansion of the insulating liquid is taken up by a change in the level of liquid inan expansion (conservator) tank, mounted above the transformer main tank, asshown in Figure B25. The space above the liquid in the conservator may be filledwith air which is drawn in when the level of liquid falls, and is partially expelledwhen the level rises. When the air is drawn in from the surrounding atmosphere it isadmitted through an oil seal, before passing through a dessicating device (generallycontaining silica-gel crystals) before entering the conservator. In some designs oflarger transformers the space above the oil is occupied by an impermeable air bagso that the insulation liquid is never in contact with the atmosphere. The air entersand exits from the deformable bag through an oil seal and dessicator, as previouslydescribed. A conservator expansion tank is obligatory for transformers rated above10 MVA (which is presently the upper limit for “total-fill” type transformers).B27Fig. B24 : Hermetically-sealed totally-filled tankChoice of technologyAs discussed above, the choice of transformer is between liquid-filled or dry type.For ratings up to 10 MVA, totally-filled units are available as an alternative toconservator-type transformers.A choice depends on a number of considerations, including:b Safety of persons in proximity to the transformer. Local regulations and officialrecommendations may have to be respectedb Economic considerations, taking account of the relative advantages of each techniqueThe regulations affecting the choice are:b Dry-type transformer:v In some countries a dry-type transformer is obligatory in high apartment blocksv Dry-type transformers impose no constraints in other situationsb Transformers with liquid insulation:v This type of transformer is generally forbidden in high apartment blocksv For different kinds of insulation liquids, installation restrictions, or minimumprotection against fire risk, vary according to the class of insulation usedv Some countries in which the use of liquid dielectrics is highly developed, classifythe several categories of liquid according to their fire performance. This latter isassessed according to two criteria: the flash-point temperature, and the minimumcalorific power. The principal categories are shown in Figure B26 in which aclassification code is used for convenience.As an example, French standard defines the conditions for the installation of liquidfilledtransformers. No equivalent IEC standard has yet been established.The French standard is aimed at ensuring the safety of persons and property andrecommends, notably, the minimum measures to be taken against the risk of fire.Fig. B25 : Air-breathing conservator-type tank at atmospherepressureCode Dielectric fluid Flash-point Minimum calorific power(°C)(MJ/kg)O1 Mineral oil < 300 -K1 High-density hydrocarbons > 300 48K2 Esters > 300 34 - 37K3 Silicones > 300 27 - 28L3 Insulating halogen liquids - 12Fig. B26 : Categories of dielectric fluids© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network4 The consumer substationwith LV meteringB28The main precautions to observe are indicated in Figure B27.b For liquid dielectrics of class L3 there are no special measures to be takenb For dielectrics of classes O1 and K1 the measures indicated are applicable only ifthere are more than 25 litres of dielectric liquid in the transformerb For dielectrics of classes K2 and K3 the measures indicated are applicable only ifthere are more than 50 litres of dielectric liquid in the transformer.Class No. of Locationsof litres above Chamber or enclosed area reserved to qualified Reserved to trained personnel Other chambersdielectric which and authorized personnel, and separated from any and isolated from work areas or locations (2)fluid measures other building by a distance D by fire-proof walls (2 hours rating)must be D > 8 m 4 m < D < 8 m D < 4 m (1) in the direc- No openings With opening(s)takention of occupied areasO1 25 No special Interposition of Fire-proof wall Measures Measures Measuresmeasures a fire-proof (2 hour rating) (1 + 2) (1 + 2 + 5) (1A + 2 + 4) (3)K1 screen against adjoining or 3 or 3 or 3(1 hour rating) building or 4 or (4 + 5)K2 50 No special measures Interposition of a No special Measures 1A Measures 1K3 fire-proof screen measures or 3 or 3(1 hour rating) or 4 or 4L3No special measuresMeasure 1: Arrangements such that if the dielectric escapes from the transformer, it will be completely contained (in a sump, by sills around thetransformer, and by blocking of cable trenches, ducts and so on, during construction).Measure 1A: In addition to measure 1, arrange that, in the event of liquid ignition there is no possibility of the fire spreading (any combustiblematerial must be moved to a distance of at least 4 metres from the transformer, or at least 2 metres from it if a fire-proof screen [of 1 hour rating] isinterposed).Measure 2: Arrange that burning liquid will extinguish rapidly and naturally (by providing a pebble bed in the containment sump).Measure 3: An automatic device (gas, pressure & thermal relay, or Buchholz) for cutting off the primary power supply, and giving an alarm, if gasappears in the transformer tank.Measure 4: Automatic fire-detection devices in close proximity to the transformer, for cutting off primary power supply, and giving an alarm.Measure 5: Automatic closure by fire-proof panels (1/2 hour minimum rating) of all openings (ventilation louvres, etc.) in the walls and ceiling ofthe substation chamber.Notes:(1) A fire-proof door (rated at 2 hours) is not considered to be an opening.(2) Transformer chamber adjoining a workshop and separated from it by walls, the fire-proof characteristics of which are not rated for 2 hours.Areas situated in the middle of workshops the material being placed (or not) in a protective container.(3) It is indispensable that the equipment be enclosed in a chamber, the walls of which are solid, the only orifices being those necessary forventilation purposes.Fig. B27 : Safety measures recommended in electrical installations using dielectric liquids of classes 01, K1, K2 or K3The determination of optimal powerOversizing a transformerIt results in:b Excessive investment and unecessarily high no-load losses, butb Lower on-load lossesUndersizing a transformerIt causes:b A reduced efficiency when fully loaded, (the highest efficiency is attained in therange 50% - 70% full load) so that the optimum loading is not achievedb On long-term overload, serious consequences forv The transformer, owing to the premature ageing of the windings insulation, and inextreme cases, resulting in failure of insulation and loss of the transformerv The installation, if overheating of the transformer causes protective relays to tripthe controlling circuit-breaker.© Schneider Electric - all rights reservedDefinition of optimal powerIn order to select an optimal power (kVA) rating for a transformer, the followingfactors must be taken into account:b List the power of installed power-consuming equipment as described in Chapter Ab Decide the utilization (or demand) factor for each individual item of loadb Determine the load cycle of the installation, noting the duration of loads and overloadsb Arrange for power-factor correction, if justified, in order to:v Reduce cost penalties in tariffs based, in part, on maximum kVA demandv Reduce the value of declared load (P(kVA) = P (kW)/cos ϕ)b Select, among the range of standard transformer ratings available, taking intoaccount all possible future extensions to the installation.It is important to ensure that cooling arrangements for the transformer are adequate.Schneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network4 The consumer substationwith LV metering4.5 Instructions for use of MV equipmentB29The purpose of this chapter is to provide general guidelines on how to avoidor greatly reduce MV equipment degradation on sites exposed to humidity andpollution.Fig. B28 : SM6 metal enclosed indoor MV eqpuipmentNormal service conditions for indoor MV equipmentAll MV equipments comply with specific standards and with the IEC 62271-1standard “Common specifications for high-voltage switchgear and controlgear”,which defines the normal conditions for the installation and use of such equipment.For instance, regarding humidity, the standard mentions:The conditions of humidity are as follows:b The average value of the relative humidity, measured over a period of 24 h doesnot exceed 90%;b The average value of the water vapour pressure, over a period of 24 h does notexceed 2.2 kPa;b The average value of the relative humidity, over a period of one month does notexceed 90%;b The average value of water vapour pressure, over a period of one month does notexceed 1.8 kPa;Under these conditions, condensation may occasionally occur.NOTE 1: Condensation can be expected where sudden temperature changes occurin period of high humidity.NOTE 2: To withstand the effects of high humidity and condensation, such as abreakdown of insulation or corrosion of metallic parts, switchgear designed for suchconditions and tested accordingly shoul be used.NOTE 3: Condensation may be prevented by special design of the building orhousing, by suitable ventilation and heating of the station or by use of dehumifyingequipment.As indicated in the standard, condensation may occasionally occur even undernormal conditions. The standard goes on to indicate special measures concerningthe substation premises that can be implemented to prevent condensation.Use under severe conditionsUnder certain severe conditions concerning humidity and pollution, largely beyondthe normal conditions of use mentioned above, correctly designed electricalequipment can be subject to damage by rapid corrosion of metal parts and surfacedegradation of insulating parts.Remedial measures for condensation problemsb Carefully design or adapt substation ventilation.b Avoid temperature variations.b Eliminate sources of humidity in the substation environment.b Install an air conditioning system.b Make sure cabling is in accordance with applicable rules.Remedial measures for pollution problemsb Equip substation ventilation openings with chevron-type baffles to reduce entryof dust and pollution.b Keep substation ventilation to the minimum required for evacuation of transformerheat to reduce entry of pollution and dust.b Use MV cubicles with a sufficiently high degree of protection (IP).b Use air conditioning systems with filters to restrict entry of pollution and dust.b Regularly clean all traces of pollution from metal and insulating parts.VentilationSubstation ventilation is generally required to dissipate the heat produced bytransformers and to allow drying after particularly wet or humid periods.However, a number of studies have shown that excessive ventilation can drasticallyincrease condensation.Ventilation should therefore be kept to the minimum level required.Furthermore, ventilation should never generate sudden temperature variations thatcan cause the dew point to be reached.For this reason:Natural ventilation should be used whenever possible. If forced ventilation isnecessary, the fans should operate continuously to avoid temperature fluctuations.Guidelines for sizing the air entry and exit openings of substations are presentedhereafter.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network4 The consumer substationwith LV meteringB30Calculation methodsA number of calculation methods are available to estimate the required size ofsubstation ventilation openings, either for the design of new substations or theadaptation of existing substations for which condensation problems have occurred.The basic method is based on transformer dissipation.The required ventilation opening surface areas S and S’ can be estimated using thefollowing formulas:S 1.8 x 10-4 PHand S' 1.10 x S200 mmminiS'where:S = Lower (air entry) ventilation opening area [m²] (grid surface deducted)S’= Upper (air exit) ventilation opening area [m²] (grid surface deducted)P = Total dissipated power [W]P is the sum of the power dissipated by:b The transformer (dissipation at no load and due to load)b The LV switchgearb The MV switchgearH = Height between ventilation opening mid-points [m]See Fig. B29Note:This formula is valid for a yearly average temperature of 20 °C and a maximumaltitude of 1,000 m.Fig. B29 : Natural ventilationSHIt must be noted that these formulae are able to determine only one order ofmagnitude of the sections S and S', which are qualified as thermal section, i.e. fullyopen and just necessary to evacuate the thermal energy generated inside the MV/LVsubstation.The pratical sections are of course larger according ot the adopted technologicalsolution.Indeed, the real air flow is strongly dependant:b on the openings shape and solutions adopted to ensure the cubicle protectionindex (IP): metal grid, stamped holes, chevron louvers,...b on internal components size and their position compared to the openings:transformer and/or retention oil box position and dimensions, flow channel betweenthe components, ...b and on some physical and environmental parameters: outside ambienttemperature, altitude, magnitude of the resulting temperature rise.The understanding and the optimization of the attached physical phenomena aresubject to precise flow studies, based on the fluid dynamics laws, and realized withspecific analytic software.Example:Transformer dissipation = 7,970 WLV switchgear dissipation = 750 WMV switchgear dissipation = 300 WThe height between ventilation opening mid-points is 1.5 m.Calculation:Dissipated Power P = 7,970 + 750 + 300 = 9,020 WS 1.8 x 10-4 P1.5 1.32 m 2 and S' 1.1 x 1.32 1.46 m 2Fig. B30 : Ventilation opening locationsVentilation opening locationsTo favour evacuation of the heat produced by the transformer via natural convection,ventilation openings should be located at the top and bottom of the wall near thetransformer. The heat dissipated by the MV switchboard is negligible.To avoid condensation problems, the substation ventilation openings should belocated as far as possible from the switchboard (see Fig. B 30).© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network4 The consumer substationwith LV meteringType of ventilation openingsTo reduce the entry of dust, pollution, mist, etc., the substation ventilation openingsshould be equipped with chevron-blade baffles.Always make sure the baffles are oriented in the right direction (see Fig. B31).B31Fig. B31 : Chevron-blade bafflesTemperature variations inside cubiclesTo reduce temperature variations, always install anti-condensation heaters insideMV cubicles if the average relative humidity can remain high over a long period oftime. The heaters must operate continuously, 24 hours a day all year long.Never connect them to a temperature control or regulation system as this could leadto temperature variations and condensation as well as a shorter service life for theheating elements. Make sure the heaters offer an adequate service life (standardversions are generally sufficient).Temperature variations inside the substationThe following measures can be taken to reduce temperature variations inside thesubstation:b Improve the thermal insulation of the substation to reduce the effects of outdoortemperature variations on the temperature inside the substation.b Avoid substation heating if possible. If heating is required, make sure the regulationsystem and/or thermostat are sufficiently accurate and designed to avoid excessivetemperature swings (e.g. no greater than 1 °C).If a sufficiently accurate temperature regulation system is not available, leave theheating on continuously, 24 hours a day all year long.b Eliminate cold air drafts from cable trenches under cubicles or from openings in thesubstation (under doors, roof joints, etc.).Substation environment and humidityVarious factors outside the substation can affect the humidity inside.b PlantsAvoid excessive plant growth around the substation.b Substation waterproofingThe substation roof must not leak. Avoid flat roofs for whichwaterproofing is difficult to implement and maintain.b Humidity from cable trenchesMake sure cable trenches are dry under all conditions.A partial solution is to add sand to the bottom of the cable trench.Pollution protection and cleaningExcessive pollution favours leakage current, tracking and flashover on insulators.To prevent MV equipment degradation by pollution, it is possible to either protect theequipment against pollution or regularly clean the resulting contamination.ProtectionIndoor MV switchgear can be protected by enclosures providing a sufficiently highdegree of protection (IP).CleaningIf not fully protected, MV equipment must be cleaned regularly to preventdegradation by contamination from pollution.Cleaning is a critical process. The use of unsuitable products can irreversiblydamage the equipment.For cleaning procedures, please contact your Schneider Electric correspondent.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network5 The consumer substationwith MV meteringB32A consumer substation with MV meteringis an electrical installation connected to autility supply system at a nominal voltage of1 kV - 35 kV and generally includes a singleMV/LV transformer which exceeds 1,250 kVA,or several smaller transformers.The rated current of the MV switchgear doesnot normally exceed 400 A.5.1 GeneralFunctionsThe substationAccording to the complexity of the installation and the manner in which the load isdivided, the substation:b Might include one room containing the MV switchboard and metering panel(s),together with the transformer(s) and low-voltage main distribution board(s),b Or might supply one or more transformer rooms, which include local LV distributionboards, supplied at MV from switchgear in a main substation, similar to thatdescribed above.These substations may be installed, either:b Inside a building, orb Outdoors in prefabricated housings.Connection to the MV networkConnection at MV can be:b Either by a single service cable or overhead line, orb Via two mechanically interlocked load-break switches with two service cables fromduplicate supply feeders, orb Via two load-break switches of a ring-main unit.MeteringBefore the installation project begins, the agreement of the power-supply utilityregarding metering arrangements must be obtained.A metering panel will be incorporated in the MV switchboard. Voltage transformersand current transformers, having the necessary metering accuracy, may be includedin the main incoming circuit-breaker panel or (in the case of the voltage transformer)may be installed separately in the metering panel.Transformer roomsIf the installation includes a number of transformer rooms, MV supplies from the mainsubstation may be by simple radial feeders connected directly to the transformers, orby duplicate feeders to each room, or again, by a ring-main, according to the degreeof supply availability desired.In the two latter cases, 3-panel ring-main units will be required at each transformerroom.Local emergency generatorsEmergency standby generators are intended to maintain a power supply to essentialloads, in the event of failure of the power supply system.CapacitorsCapacitors will be installed, according to requirements:b In stepped MV banks at the main substation, orb At LV in transformer rooms.TransformersFor additional supply-security reasons, transformers may be arranged for automaticchangeover operation, or for parallel operation.© Schneider Electric - all rights reservedOne-line diagramsThe diagrams shown in Figure B32 next page represent:b The different methods of MV service connection, which may be one of four types:v Single-line servicev Single-line service (equipped for extension to form a ring main)v Duplicate supply servicev Ring main serviceb General protection at MV, and MV metering functionsb Protection of outgoing MV circuitsb Protection of LV distribution circuitsSchneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network5 The consumer substationwith MV meteringB33Power supplysystemService connectionSupplier/consumerinterfaceMV protectionand meteringMV distribution and protectionof outgoing circuitsDownstream terminals ofMV isolator for the installationLV distributionand protectionLV terminals oftransformerSingle-line serviceProtectionLVSingle-line service(equipped forextension to forma ring main)A single transformerDuplicatesupplyserviceAutomatic LV/MVstandby sourceProtection+ automaticchangeoverfeatureProtectionRing-mainserviceAutomatic LVstandby sourceFig. B32 : Consumer substation with MV metering© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network5 The consumer substationwith MV meteringB345.2 Choice of panelsA substation with MV metering includes, in addition to the panels described in 4.2,panels specifically designed for metering and, if required, for automatic or manualchangeover from one source to another.Metering and general protectionThese two functions are achieved by the association of two panels:b One panel containing the VTb The main MV circuit-breaker panel containing the CTs for measurement andprotectionThe general protection is usually against overcurrent (overload and short-circuit) andearth faults. Both schemes use protective relays which are sealed by the powersupplyutility.© Schneider Electric - all rights reservedMV distributionpanels forwhich standbysupply isrequiredAutomaticchangeoverpanelBusbartransitionpanelFrom standby generatorP y 20,000 kVATo remainderof the MVswitchboardFig. B33 : Section of MV switchboard including standby supplypanelSubstation including generatorsGenerator in stand alone operationIf the installation needs great power supply availability, a MV standby generator setcan be used. In such a case, the installation must include an automatic changeover.In order to avoid any posssibility of parallel operation of the generator with the powersupply network, a specific panel with automatic changeover is needed (see Fig. B33).b ProtectionSpecific protective devices are intended to protect the generator itself. It must benoted that, due to the very low short-circuit power of the generator comparing withthe power supply network, a great attention must be paid to protection discrimination.b ControlA voltage regulator controlling an alternator is generally arranged to respond to areduction of voltage at its terminals by automatically increasing the excitation currentof the alternator, until the voltage is restored to normal. When it is intended thatthe alternator should operate in parallel with others, the AVR (Automatic VoltageRegulator) is switched to “parallel operation” in which the AVR control circuit isslightly modified (compounded) to ensure satisfactory sharing of kvars with the otherparallel machines.When a number of alternators are operating in parallel under AVR control, anincrease in the excitation current of one of them (for example, carried out manuallyafter switching its AVR to Manual control) will have practically no effect on the voltagelevel. In fact, the alternator in question will simply operate at a lower power factor(more kVA, and therefore more current) than before.The power factor of all the other machines will automatically improve, such that theload power factor requirements are satisfied, as before.Generator operating in parallel with the utility supply networkTo connect a generator set on the network, the agreement of the power supply utilityis usually required. Generally the equipement (panels, protection relays) must beapproved by the utility.The following notes indicate some basic consideration to be taken into account forprotection and control.b ProtectionTo study the connection of generator set, the power supply utility needs some dataas follows :v Power injected on the networkv Connection modev Short-circuit current of the generator setv Voltage unbalance of the generatorv etc.Depending on the connection mode, dedicated uncoupling protection functions arerequired :v Under-voltage and over-voltage protectionv Under-frequency and over-frequency protectionv Zero sequence overvoltage protectionv Maximum time of coupling (for momentary coupling)v Reverse real powerFor safety reasons, the switchgear used for uncoupling must also be providedwith the characteristics of a disconnector (i.e total isolation of all active conductorsbetween the generator set and the power supply network).Schneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network5 The consumer substationwith MV meteringb ControlWhen generators at a consumer’s substation operate in parallel with all thegeneration of the utility power supply system, supposing the power system voltage isreduced for operational reasons (it is common to operate MV systems within a rangeof ± 5% of nominal voltage, or even more, where load-flow patterns require it), anAVR set to maintain the voltage within ± 3% (for example) will immediately attempt toraise the voltage by increasing the excitation current of the alternator.Instead of raising the voltage, the alternator will simply operate at a lower powerfactor than before, thereby increasing its current output, and will continue to do so,until it is eventually tripped out by its overcurrent protective relays. This is a wellknownproblem and is usually overcome by the provision of a “constant powerfactor”control switch on the AVR unit.By making this selection, the AVR will automatically adjust the excitation currentto match whatever voltage exists on the power system, while at the same timemaintaining the power factor of the alternator constant at the pre-set value (selectedon the AVR control unit).In the event that the alternator becomes decoupled from the power system, the AVRmust be automatically (rapidly) switched back to “constant-voltage” control.B355.3 Parallel operation of transformersThe need for operation of two or more transformers in parallel often arises due to:b Load growth, which exceeds the capactiy of an existing transformerb Lack of space (height) for one large transformerb A measure of security (the probability of two transformers failing at the same timeis very small)b The adoption of a standard size of transformer throughout an installationTotal power (kVA)The total power (kVA) available when two or more transformers of the samekVA rating are connected in parallel, is equal to the sum of the individual ratings,providing that the percentage impedances are all equal and the voltage ratios areidentical.Transformers of unequal kVA ratings will share a load practically (but not exactly)in proportion to their ratings, providing that the voltage ratios are identical and thepercentage impedances (at their own kVA rating) are identical, or very nearly so.In these cases, a total of more than 90% of the sum of the two ratings is normallyavailable.It is recommended that transformers, the kVA ratings of which differ by morethan 2:1, should not be operated permanently in parallel.Conditions necessary for parallel operationAll paralleled units must be supplied from the same network.The inevitable circulating currents exchanged between the secondary circuits ofparalleled transformers will be negligibly small providing that:b Secondary cabling from the transformers to the point of paralleling haveapproximately equal lengths and characteristicsb The transformer manufacturer is fully informed of the duty intended for thetransformers, so that:v The winding configurations (star, delta, zigzag star) of the several transformershave the same phase change between primary and secondary voltagesv The short-circuit impedances are equal, or differ by less than 10%v Voltage differences between corresponding phases must not exceed 0.4%v All possible information on the conditions of use, expected load cycles, etc. shouldbe given to the manufacturer with a view to optimizing load and no-load losses© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network5 The consumer substationwith MV meteringB36Common winding arrangementsAs described in 4.4 “Electrical characteristics-winding configurations” therelationships between primary, secondary, and tertiary windings depend on:b Type of windings (delta, star, zigzag)b Connection of the phase windingsDepending on which ends of the windings form the star point (for example), astar winding will produce voltages which are 180° displaced with respect to thoseproduced if the opposite ends had been joined to form the star point. Similar 180°changes occur in the two possible ways of connecting phase-to-phase coils to formdelta windings, while four different combinations of zigzag connections are possible.b The phase displacement of the secondary phase voltages with respect to thecorresponding primary phase voltages.As previously noted, this displacement (if not zero) will always be a multiple of30° and will depend on the two factors mentioned above, viz type of windings andconnection (i.e. polarity) of the phase windings.By far the most common type of distribution transformer winding configuration is theDyn 11 connection (see Fig. B34).Voltage vectors1V 121N232311N2Windingscorrespondence233V 12 on the primary winding produces V 1N in thesecondary winding and so on ...Fig. B34 : Phase change through a Dyn 11 transformer© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network6 Constitution ofMV/LV distribution substationsMV/LV substations are constructed according to the magnitude of the load and thekind of power system in question.Substations may be built in public places, such as parks, residential districts, etc. oron private premises, in which case the power supply authority must have unrestrictedaccess. This is normally assured by locating the substation, such that one of itswalls, which includes an access door, coincides with the boundary of the consumerspremises and the public way.B376.1 Different types of substationSubstations may be classified according to metering arrangements (MV or LV) andtype of supply (overhead line or underground cable).The substations may be installed:b Either indoors in room specially built for the purpose, within a building, orb An outdoor installation which could be :v Installed in a dedicated enclosure prefabricated or not, with indoor equipment(switchgear and transformer)v Ground mounted with outdoor equipment (switchgear and transformers)v Pole mounted with dedicated outdoor equipment (swithgear and transformers)Prefabricated substations provide a particularly simple, rapid and competitive choice.6.2 Indoor substationConceptionFigure B35 shows a typical equipment layout recommended for a LV meteringsubstation.Remark: the use of a cast-resin dry-type transformer does not need a fireprotectionoil sump. However, periodic cleaning is needed.MV connections to transformer(included in a panel or free-standing)LV connectionsfromtransformerLV switchgear2 incomingMV panelsMVswitchingandprotectionpanelCurrenttransformersprovided bypower-supplyauthorityConnection to the powersupplynetwork by single-coreor three-core cables,with or without a cable trenchTransformerFig. B35 : Typical arrangment of switchgear panels for LV meteringOil sumpLV cabletrench© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network6 Constitution ofMV/LV distribution substationsB38Service connections and equipment interconnectionsAt high voltageb Connections to the MV system are made by, and are the responsibility of the utilityb Connections between the MV switchgear and the transformers may be:v By short copper bars where the transformer is housed in a panel forming part ofthe MV switchboardv By single-core screened cables with synthetic insulation, with possible use of plugintype terminals at the transformerAt low voltageb Connections between the LV terminals of the transformer and the LV switchgearmay be:v Single-core cablesv Solid copper bars (circular or rectangular section) with heat-shrinkable insulationMetering (see Fig. B36)b Metering current transformers are generally installed in the protective cover of thepower transformer LV terminals, the cover being sealed by the supply utilityb Alternatively, the current transformers are installed in a sealed compartment withinthe main LV distribution cabinetb The meters are mounted on a panel which is completely free from vibrationsb Placed as close to the current transformers as possible, andb Are accessible only to the utility100MV supplyLV distributionCommon earth busbarfor the substationSafety accessories800 miniMetersFig. B36 : Plan view of typical substation with LV meteringEarthing circuitsThe substation must include:b An earth electrode for all exposed conductive parts of electrical equipment in thesubstation and exposed extraneous metal including:v Protective metal screensv Reinforcing rods in the concrete base of the substation© Schneider Electric - all rights reservedSubstation lightingSupply to the lighting circuits can be taken from a point upstream or downstreamof the main incoming LV circuit-breaker. In either case, appropriate overcurrentprotection must be provided. A separate automatic circuit (or circuits) is (are)recommended for emergency lighting purposes.Operating switches, pushbuttons, etc. are normally located immediately adjacent toentrances.Lighting fittings are arranged such that:b Switchgear operating handles and position indication markings are adequatelyilluminatedb All metering dials and instruction plaques and so on, can be easily readSchneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network6 Constitution ofMV/LV distribution substationsMaterials for operation and safetyAccording to local safety rules, generally, the substation is provided with:b Materials for assuring safe exploitation of the equipment including:v Insulating stool and/or an insulating mat (rubber or synthetic)v A pair of insulated gloves stored in an envelope provided for the purposev A voltage-detecting device for use on the MV equipmentv Earthing attachments (according to type of switchgear)b Fire-extinguishing devices of the powder or CO2 typeb Warning signs, notices and safety alarms:v On the external face of all access doors, a DANGER warning plaque andprohibition of entry notice, together with instructions for first-aid care for victims ofelectrical accidents.B396.3 Outdoor substationsOutdoor substation with prefabricated enclosuresA prefabricated MV/LV substation complying with IEC 62271-202 standard includes :b equipement in accordance with IEC standardsb a type tested enclosure, which means during its design, it has undergone a batteryof tests (see Fig. B37):v Degree of protectionv Functional testsv Temperature classv Non-flammable materialsv Mechanical resistance of the enclosurev Sound levelv Insulation levelv Internal arc withstandv Earthing circuit testv Oil retention,…Use of equipment conformto IEC standards:b Degree of protectionb Electromagneticcompatibilityb Functional testsb Temperature classb Non-flammablematerialsLVEarthing circuit testMVOil retentionMechanical resistanceof the enclosure:b Sound levelb Insulation levelb Internal arcingwithstandFig. B37 : Type tested substation according to IEC 62271-202 standardWalk-in Non walk-in Half burieda - b -UndergroundFig. B38 : The four designs according to IEC 62271-202standard and two pictures [a] walk-in type MV/LV substation;[b] half buried type MV/LV substationMain benefits are :b Safety:v For public and operators thanks to a high reproducible quality levelb Cost effective:v Manufactured, equipped and tested in the factoryb Delivery timev Delivered ready to be connected.IEC 62271-202 standard includes four main designs (see Fig. B38)b Walk-in type substation :v Operation protected from bad weather conditionsb Non walk-in substationv Ground space savings, and outdoors operationsb Half buried substationv Limited visual impactb Underground substationv Blends completely into the environment.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

B - Connection to the MV publicdistribution network6 Constitution ofMV/LV distribution substationsB40Outdoor substations without enclosures (see Fig. B39)These kinds of outdoor substation are common in some countries, based onweatherproof equipment exposed to the elements.These substations comprise a fenced area in which three or more concrete plinthsare installed for:b A ring-main unit, or one or more switch-fuse or circuit-breaker unit(s)b One or more transformer(s), andb One or more LV distribution panel(s).Pole mounted substationsField of applicationThese substations are mainly used to supply isolated rural consumers from MVoverhead line distribution systems.ConstitutionIn this type of substation, most often, the MV transformer protection is provided byfuses.Lightning arresters are provided, however, to protect the transformer and consumersas shown in Figure B40.General arrangement of equipmentAs previously noted the location of the substation must allow easy access, not onlyfor personnel but for equipment handling (raising the transformer, for example) andthe manœuvring of heavy vehicles.LightningarrestersLV circuit breaker D1Earthing conductor 25 mm 2 copperProtective conductor coverSafety earth mat© Schneider Electric - all rights reservedFig. B39 : Outdoor substations without enclosuresFig. B40 : Pole-mounted transformer substationSchneider Electric - Electrical installation guide 2009

Chapter CConnection to the LV utilitydistribution network12ContentsLow-voltage utility distribution networks1.1 Low-voltage consumers C21.2 Low-voltage distribution networks C101.3 The consumer service connection C111.4 Quality of supply voltage C15Tariffs and meteringC2C16C© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

C - Connecion to the LV publicdistribution network1 Low-voltage utility distributionnetworksCThe most-common LV supplies are within therange 120 V single phase to 240/415 V3-phase 4-wires.Loads up to 250 kVA can be supplied at LV, butpower-supply organizations generally proposea MV service at load levels for which theirLV networks are marginally adequate.An international voltage standard for 3-phase4-wire LV systems is recommended by theIEC 60038 to be 230/400 V1.1 Low-voltage consumersIn Europe, the transition period on the voltage tolerance to “230V/400V + 10% / - 10%”has been extended for another 5 years up to the year 2008.Low-voltage consumers are, by definition, those consumers whose loads can besatisfactorily supplied from the low-voltage system in their locality.The voltage of the local LV network may be 120/208 V or 240/415 V, i.e. the loweror upper extremes of the most common 3-phase levels in general use, or at someintermediate level, as shown in Figure C1.An international voltage standard for 3-phase 4-wire LV systems is recommendedby the IEC 60038 to be 230/400 V.Loads up to 250 kVA can be supplied at LV, but power-supply organizationsgenerally propose a MV service at load levels for which their LV networks aremarginally adequate.© Schneider Electric - all rights reservedCountry Frequency & tolerance Domestic (V) Commercial (V) Industrial (V)(Hz & %)Afghanistan 50 380/220 (a) 380/220 (a) 380/220 (a)220 (k)Algeria 50 ± 1.5 220/127 (e) 380/220 (a) 10,000220 (k) 220/127 (a) 5,5006,600380/220 (a)Angola 50 380/220 (a) 380/220 (a) 380/220 (a)220 (k)Antigua and Barbuda 60 240 (k) 400/230 (a) 400/230 (a)120 (k) 120/208 (a) 120/208 (a)Argentina 50 ± 2 380/220 (a) 380/220 (a)220 (k) 220 (k)Armenia 50 ± 5 380/220 (a) 380/220 (a) 380/220 (a)220 (k) 220 (k)Australia 50 ± 0.1 415/240 (a) 415/240 (a) 22,000240 (k) 440/250 (a) 11,000440 (m) 6,600415/240440/250Austria 50 ± 0.1 230 (k) 380/230 (a) (b) 5,000230 (k) 380/220 (a)Azerbaijan 50 ± 0.1 208/120 (a) 208/120 (a)240/120 (k) 240/120 (k)Bahrain 50 ± 0.1 415/240 (a) 415/240 (a) 11,000240 (k) 240 (k) 415/240 (a)240 (k)Bangladesh 50 ± 2 410/220 (a) 410/220 (a) 11,000220 (k) 410/220 (a)Barbados 50 ± 6 230/115 (j) 230/115 (j) 230/400 (g)115 (k) 200/115 (a) 230/155 (j)220/115 (a)Belarus 50 380/220 (a) 380/220 (a) 380/220 (a)220 (k) 220 (k)220/127 (a)127 (k)Belgium 50 ± 5 230 (k) 230 (k) 6,600230 (a) 230 (a) 10,0003N, 400 3N, 400 11,00015,000Bolivia 50 ± 0.5 230 (k) 400/230 (a) 400/230 (a)230 (k)Botswana 50 ± 3 220 (k) 380/220 (a) 380/220 (a)Brazil 60 220 (k) 220/380 (a) 13,800127 (k) 127/220 (a) 11,200220/380 (a)127/220 (a)Brunei 50 ± 2 230 230 11,00068,000Bulgaria 50 ± 0.1 220 220/240 1,000690380Fig. C1 : Voltage of local LV network and their associated circuit diagrams (continued on next page)Schneider Electric - Electrical installation guide 2009

C - Connecion to the LV publicdistribution network1 Low-voltage utility distributionnetworksCountry Frequency & tolerance Domestic (V) Commercial (V) Industrial (V)(Hz & %)Cambodia 50 ± 1 220 (k) 220/300 220/380Cameroon 50 ± 1 220/260 (k) 220/260 (k) 220/380 (a)Canada 60 ± 0.02 120/240 (j) 347/600 (a) 7,200/12,500480 (f) 347/600 (a)240 (f) 120/208120/240 (j) 600 (f)120/208 (a) 480 (f)240 (f)Cape Verde 220 220 380/400Chad 50 ± 1 220 (k) 220 (k) 380/220 (a)Chile 50 ± 1 220 (k) 380/220 (a) 380/220 (a)China 50 ± 0.5 220 (k) 380/220 (a) 380/220 (a)220 (k) 220 (k)Colombia 60 ± 1 120/240 (g) 120/240 (g) 13,200120 (k) 120 (k) 120/240 (g)Congo 50 220 (k) 240/120 (j) 380/220 (a)120 (k)Croatia 50 400/230 (a) 400/230 (a) 400/230 (a)230 (k) 230 (k)Cyprus 50 ± 0.1 240 (k) 415/240 11,000415/240Czech Republic 50 ± 1 230 500 400,000230/400 220,000110,00035,00022,00010,0006,0003,000Denmark 50 ± 1 400/230 (a) 400/230 (a) 400/230 (a)Djibouti 50 400/230 (a) 400/230 (a)Dominica 50 230 (k) 400/230 (a) 400/230 (a)Egypt 50 ± 0.5 380/220 (a) 380/220 (a) 66,000220 (k) 220 (k) 33,00020,00011,0006,600380/220 (a)Estonia 50 ± 1 380/220 (a) 380/220 (a) 380/220 (a)220 (k) 220 (k)Ethiopia 50 ± 2.5 220 (k) 380/231 (a) 15 000380/231 (a)Falkland Islands 50 ± 3 230 (k) 415/230 (a) 415/230 (a)Fidji Islands 50 ± 2 415/240 (a) 415/240 (a) 11,000240 (k) 240 (k) 415/240 (a)Finland 50 ± 0.1 230 (k) 400/230 (a) 690/400 (a)400/230 (a)France 50 ± 1 400/230 (a) 400/230 20,000230 (a) 690/400 10,000590/100 230/400Gambia 50 220 (k) 220/380 380Georgia 50 ± 0.5 380/220 (a) 380/220 (a) 380/220 (a)220 (k) 220 (k)Germany 50 ± 0.3 400/230 (a) 400/230 (a) 20,000230 (k) 230 (k) 10,0006,000690/400400/230Ghana 50 ± 5 220/240 220/240 415/240 (a)Gibraltar 50 ± 1 415/240 (a) 415/240 (a) 415/240 (a)Greece 50 220 (k) 6,000 22,000230 380/220 (a) 20,00015,0006,600Granada 50 230 (k) 400/230 (a) 400/230 (a)Hong Kong 50 ± 2 220 (k) 380/220 (a) 11,000220 (k) 386/220 (a)Hungary 50 ± 5 220 220 220/380Iceland 50 ± 0.1 230 230/400 230/400Fig. C1 : Voltage of local LV network and their associated circuit diagrams (continued on next page)C© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

C - Connecion to the LV publicdistribution network1 Low-voltage utility distributionnetworks© Schneider Electric - all rights reservedCCountry Frequency & tolerance Domestic (V) Commercial (V) Industrial (V)(Hz & %)India 50 ± 1.5 440/250 (a) 440/250 (a) 11,000230 (k) 230 (k) 400/230 (a)440/250 (a)Indonesia 50 ± 2 220 (k) 380/220 (a) 150,00020,000380/220 (a)Iran 50 ± 5 220 (k) 380/220 (a) 20,00011,000400/231 (a)380/220 (a)Iraq 50 220 (k) 380/220 (a) 11,0006,6003,000380/220 (a)Ireland 50 ± 2 230 (k) 400/230 (a) 20,00010,000400/230 (a)Israel 50 ± 0.2 400/230 (a) 400/230 (a) 22,000230 (k) 230 (k) 12,6006,300400/230 (a)Italy 50 ± 0.4 400/230 (a) 400/230 (a) 20,000230 (k) 15,00010,000400/230 (a)Jamaica 50 ± 1 220/110 (g) (j) 220/110 (g) (j) 4,0002,300220/110 (g)Japan (east) + 0.1 200/100 (h) 200/100 (h) 140,000- 0.3 (up to 50 kW) 60,00020,0006,000200/100 (h)Jordan 50 380/220 (a) 380/220 (a) 400 (a)400/230 (k)Kazakhstan 50 380/220 (a) 380/220 (a) 380/220 (a)220 (k) 220 (k)220/127 (a)127 (k)Kenya 50 240 (k) 415/240 (a) 415/240 (a)Kirghizia 50 380/220 (a) 380/220 (a) 380/220 (a)220 (k) 220 (k)220/127 (a)127 (k)Korea (North) 60 +0, -5 220 (k) 220/380 (a) 13,6006,800Korea (South) 60 100 (k) 100/200 (j)Kuwait 50 ± 3 240 (k) 415/240 (a) 415/240 (a)Laos 50 ± 8 380/220 (a) 380/220 (a) 380/220 (a)Lesotho 220 (k) 380/220 (a) 380/220 (a)Latvia 50 ± 0.4 380/220 (a) 380/220 (a) 380/220 (a)220 (k) 220 (k)Lebanon 50 220 (k) 380/220 (a) 380/220 (a)Libya 50 230 (k) 400/230 (a) 400/230 (a)127 (k) 220/127 (a) 220/127 (a)230 (k)127 (k)Lithuania 50 ± 0.5 380/220 (a) 380/220 (a) 380/220 (a)220 (k) 220 (k)Luxembourg 50 ± 0.5 380/220 (a) 380/220 (a) 20,00015,0005,000Macedonia 50 380/220 (a) 380/220 (a) 10,000220 (k) 220 (k) 6,600380/220 (a)Madagascar 50 220/110 (k) 380/220 (a) 35,0005,000380/220Fig. C1 : Voltage of local LV network and their associated circuit diagrams (continued on next page)Schneider Electric - Electrical installation guide 2009

C - Connecion to the LV publicdistribution network1 Low-voltage utility distributionnetworksCountry Frequency & tolerance Domestic (V) Commercial (V) Industrial (V)(Hz & %)Malaysia 50 ± 1 240 (k) 415/240 (a) 415/240 (a)415 (a)Malawi 50 ± 2.5 230 (k) 400 (a) 400 (a)230 (k)Mali 50 220 (k) 380/220 (a) 380/220 (a)127 (k) 220/127 (a) 220/127 (a)220 (k)127 (k)Malta 50 ± 2 240 (k) 415/240 (a) 415/240 (a)Martinique 50 127 (k) 220/127 (a) 220/127 (a)127 (k)Mauritania 50 ± 1 230 (k) 400/230 (a) 400/230 (a)Mexico 60 ± 0.2 127/220 (a) 127/220 (a) 13,800220 (k) 220 (k) 13,200120 (l) 120 (l) 277/480 (a)127/220 (b)Moldavia 50 380/220 (a) 380/220 (a) 380/220 (a)220 (k) 220 (k)220/127 (a)127 (k)Morocco 50 ± 5 380/220 (a) 380/220 (a) 225,000220/110 (a) 150,00060,00022,00020,000Mozambique 50 380/220 (a) 380/220 (a) 6,00010,000Nepal 50 ± 1 220 (k) 440/220 (a) 11,000220 (k) 440/220 (a)Netherlands 50 ± 0.4 230/400 (a) 230/400 (a) 25,000230 (k) 20,00012,00010,000230/400New Zealand 50 ± 1.5 400/230 (e) (a) 400/230 (e) (a) 11,000230 (k) 230 (k) 400/230 (a)460/230 (e)Niger 50 ± 1 230 (k) 380/220 (a) 15,000380/220 (a)Nigeria 50 ± 1 230 (k) 400/230 (a) 15,000220 (k) 380/220 (a) 11,000400/230 (a)380/220 (a)Norway 50 ± 2 230/400 230/400 230/400690Oman 50 240 (k) 415/240 (a) 415/240 (a)240 (k)Pakistan 50 230 (k) 400/230 (a) 400/230 (a)230 (k)Papua New Guinea 50 ± 2 240 (k) 415/240 (a) 22,000240 (k) 11,000415/240 (a)Paraguay 50 ± 0.5 220 (k) 380/220 (a) 22,000220 (k) 380/220 (a)Philippines (Rep of the) 60 ± 0.16 110/220 (j) 13,800 13,8004,160 4,1602,400 2,400110/220 (h) 440 (b)110/220 (h)Poland 50 ± 0.1 230 (k) 400/230 (a) 1,000690/400400/230 (a)Portugal 50 ± 1 380/220 (a) 15,000 15,000220 (k) 5,000 5,000380/220 (a) 380/220 (a)220 (k)Qatar 50 ± 0.1 415/240 (k) 415/240 (a) 11,000415/240 (a)Fig. C1 : Voltage of local LV network and their associated circuit diagrams (continued on next page)C© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

C - Connecion to the LV publicdistribution network1 Low-voltage utility distributionnetworks© Schneider Electric - all rights reservedCCountry Frequency & tolerance Domestic (V) Commercial (V) Industrial (V)(Hz & %)Romania 50 ± 0.5 220 (k) 220/380 (a) 20,000220/380 (a) 10,0006,000220/380 (a)Russia 50 ± 0.2 380/220 (a) 380/220 (a) 380/220 (a)220 (k) 220 (k)Rwanda 50 ± 1 220 (k) 380/220 (a) 15,0006,600380/220 (a)Saint Lucia 50 ± 3 240 (k) 415/240 (a) 11,000415/240 (a)Samoa 400/230San Marino 50 ± 1 230/220 380 15,000380Saudi Arabia 60 220/127 (a) 220/127 (a) 11,000380/220 (a) 7,200380/220 (a)The Solomon Islands 50 ± 2 240 415/240 415/240Senegal 50 ± 5 220 (a) 380/220 (a) 90,000127 (k) 220/127 (k) 30,0006,600Serbia and Montenegro 50 380/220 (a) 380/220 (a) 10,000220 (k) 220 (k) 6,600380/220 (a)Seychelles 50 ± 1 400/230 (a) 400/230 (a) 11,000400/230 (a)Sierra Leone 50 ± 5 230 (k) 400/230 (a) 11,000230 (k) 400Singapore 50 400/230 (a) 400/230 (a) 22,000230 (k) 6,600400/230 (a)Slovakia 50 ± 0.5 230 230 230/400Slovenia 50 ± 0.1 220 (k) 380/220 (a) 10,0006,600380/220 (a)Somalia 50 230 (k) 440/220 (j) 440/220 (g)220 (k) 220/110 (j) 220/110 (g)110 (k) 230 (k)South Africa 50 ± 2.5 433/250 (a) 11,000 11,000400/230 (a) 6,600 6,600380/220 (a) 3,300 3,300220 (k) 433/250 (a) 500 (b)400/230 (a) 380/220 (a)380/220 (a)Spain 50 ± 3 380/220 (a) (e) 380/220 (a) 15,000220 (k) 220/127 (a) (e) 11,000220/127 (a) 380/220 (a)127 (k)Sri Lanka 50 ± 2 230 (k) 400/230 (a) 11,000230 (k) 400/230 (a)Sudan 50 240 (k) 415/240 (a) 415/240 (a)240 (k)Swaziland 50 ± 2.5 230 (k) 400/230 (a) 11,000230 (k) 400/230 (a)Sweden 50 ± 0.5 400/230 (a) 400/230 (a) 6,000230 (k) 230 (k) 400/230 (a)Switzerland 50 ± 2 400/230 (a) 400/230 (a) 20,00010,0003,0001,000690/500Syria 50 220 (k) 380/220 (a) 380/220 (a)115 (k) 220 (k)200/115 (a)Tadzhikistan 50 380/220 (a) 380/220 (a) 380/220 (a)220 (k) 220 (k)220/127 (a)127 (k)Fig. C1 : Voltage of local LV network and their associated circuit diagrams (continued on next page)Schneider Electric - Electrical installation guide 2009

C - Connecion to the LV publicdistribution network1 Low-voltage utility distributionnetworksCountry Frequency & tolerance Domestic (V) Commercial (V) Industrial (V)(Hz & %)Tanzania 50 400/230 (a) 400/230 (a) 11,000400/230 (a)Thailand 50 220 (k) 380/220 (a) 380/220 (a)220 (k)Togo 50 220 (k) 380/220 (a) 20,0005,500380/220 (a)Tunisia 50 ± 2 380/220 (a) 380/220 (a) 30,000220 (k) 220 (k) 15,00010,000380/220 (a)Turkmenistan 50 380/220 (a) 380/220 (a) 380/220 (a)220 (k) 220 (k)220/127 (a)127 (k)Turkey 50 ± 1 380/220 (a) 380/220 (a) 15,0006,300380/220 (a)Uganda + 0.1 240 (k) 415/240 (a) 11,000415/240 (a)Ukraine + 0.2 / - 1.5 380/220 (a) 380/220 (a) 380/220 (a)220 (k) 220 (k) 220 (k)United Arab Emirates 50 ± 1 220 (k) 415/240 (a) 6,600380/220 (a) 415/210 (a)220 (k) 380/220 (a)United Kingdom 50 ± 1 230 (k) 400/230 (a) 22,000(except Northern 11,000Ireland) 6,6003,300400/230 (a)United Kingdom 50 ± 0.4 230 (k) 400/230 (a) 400/230 (a)(Including Northern 220 (k) 380/220 (a) 380/220 (a)Ireland)United States of 60 ± 0.06 120/240 (j) 265/460 (a) 14,400America 120/208 (a) 120/240 (j) 7,200Charlotte 120/208 (a) 2,400(North Carolina)575 (f)460 (f)240 (f)265/460 (a)120/240 (j)120/208 (a)United States of 60 ± 0.2 120/240 (j) 480 (f) 13,200America 120/208 (a) 120/240 (h) 4,800Detroit (Michigan) 120/208 (a) 4,160480 (f)120/240 (h)120/208 (a)United States of 60 ± 0.2 120/240 (j) 4,800 4,800America 120/240 (g) 120/240 (g)Los Angeles (California)United States of 60 ± 0.3 120/240 (j) 120/240 (j) 13,200America 120/208 (a) 120/240 (h) 2,400Miami (Florida) 120/208 (a) 480/277 (a)120/240 (h)United States of 60 120/240 (j) 120/240 (j) 12,470America New York 120/208 (a) 120/208 (a) 4,160(New York) 240 (f) 277/480 (a)480 (f)United States of 60 ± 0.03 120/240 (j) 265/460 (a) 13,200America 120/240 (j) 11,500Pittsburg 120/208 (a) 2,400(Pennsylvania) 460 (f) 265/460 (a)230 (f) 120/208 (a)460 (f)230 (f)Fig. C1 : Voltage of local LV network and their associated circuit diagrams (continued on next page)C© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

C - Connecion to the LV publicdistribution network1 Low-voltage utility distributionnetworksCCountry Frequency & tolerance Domestic (V) Commercial (V) Industrial (V)(Hz & %)United States of 60 120/240 (j) 227/480 (a) 19,900America 120/240 (j) 12,000Portland (Oregon) 120/208 (a) 7,200480 (f) 2,400240 (f) 277/480 (a)120/208 (a)480 (f)240 (f)United States of 60 ± 0.08 120/240 (j) 277/480 (a) 20,800America 120/240 (j) 12,000San Francisco 4,160(California)277/480 (a)120/240 (g)United States of 60 ± 0.08 120/240 (j) 277/480 (c) 12,470America 120/208 (a) 120/240(h) 7,200Toledo (Ohio) 120/208 (j) 4,8004,160480 (f)277/480 (a)120/208 (a)Uruguay 50 ± 1 220 (b) (k) 220 (b) (k) 15,0006,000220 (b)Vietnam 50 ± 0.1 220 (k) 380/220 (a) 35,00015,00010,0006,000Yemen 50 250 (k) 440/250 (a) 440/250 (a)Zambia 50 ± 2.5 220 (k) 380/220 (a) 380 (a)Zimbabwe 50 225 (k) 390/225 (a) 11,000390/225 (a)Circuit diagrams(a) Three-phase star;Four-wire:Earthed neutral(b) Three-phase star:Three-wire(c) Three-phase star;Three-wire:Earthed neutral(d) Three-phase star;Four-wire:Non-earthed neutral(e) Two-phase star;Three-wireEarthed neutral(f) Three-phase delta:Three-wire(g) Three-phase delta;Four-wire:Earthed mid point ofone phase(h) Three-phase open delta;Four-wire:Earthed mid point of onephase(i) Three-phaseopen delta:Earthed junctionof phasesVVk© Schneider Electric - all rights reserved(j) Single-phase;Three-wire:Earthed mid point(k) Single-phase;Two-wire:Earthed end of phase(l) Single-phase;Two-wireUnearthedFig. C1 : Voltage of local LV network and their associated circuit diagrams (concluded)(m) Single-wire:Earthed return (swer)(n) DC:Three-wire:UnearthedSchneider Electric - Electrical installation guide 2009

C - Connecion to the LV publicdistribution network1 Low-voltage utility distributionnetworksResidential and commercial consumersThe function of a LV “mains” distributor is to provide service connections(underground cable or overhead line) to a number of consumers along its route.The current-rating requirements of distributors are estimated from the number ofconsumers to be connected and an average demand per consumer.The two principal limiting parameters of a distributor are:b The maximum current which it is capable of carrying indefinitely, andb The maximum length of cable which, when carrying its maximum current, will notexceed the statutory voltage-drop limitThese constraints mean that the magnitude of loads which utilities are willing toconnect to their LV distribution mains, is necessarily restricted.For the range of LV systems mentioned in the second paragraph of this sub-clause(1.1) viz: 120 V single phase to 240/415 V 3-phase, typical maximum permitted loadsconnected to a LV distributor might (1) be (see Fig. C2):CSystem Assumed max. permitted current kVAper consumer service120 V 1-phase 2-wire 60 A 7.2120/240 V 1-phase 3-wire 60 A 14.4120/208 V 3-phase 4-wire 60 A 22220/380 V 3-phase 4-wire 120 A 80230/400 V 3-phase 4-wire 120 A 83240/415 V 3-phase 4-wire 120 A 86Fig. C2 : Typical maximum permitted loads connected to a LV distributorPractices vary considerably from one power supply organization to another, and no“standardized” values can be given.Factors to be considered include:b The size of an existing distribution network to which the new load is to be connectedb The total load already connected to the distribution networkb The location along the distribution network of the proposed new load, i.e. close tothe substation, or near the remote end of the distribution network, etcIn short, each case must be examined individually.The load levels listed above are adequate for all normal residential consumers, andwill be sufficient for the installations of many administrative, commercial and similarbuildings.(1) The Figure C2 values shown are indicative only, being(arbitrarily) based on 60 A maximum service currents for thefirst three systems, since smaller voltage drops are allowed atthese lower voltages, for a given percentage statutory limit.The second group of systems is (again, arbitrarily) based on amaximum permitted service current of 120 A.Medium-size and small industrial consumers (with dedicatedLV lines direct from a utility supply MV/LV substation)Medium and small industrial consumers can also be satisfactorily supplied at lowvoltage.For loads which exceed the maximum permitted limit for a service from a distributor,a dedicated cable can usually be provided from the LV distribution fuse- (or switch-)board, in the power utility substation.Generaly, the upper load limit which can be supplied by this means is restricted onlyby the available spare transformer capacity in the substation.In practice, however:b Large loads (e.g. > 300 kVA) require correspondingly large cables, so that,unless the load centre is close to the substation, this method can be economicallyunfavourableb Many utilities prefer to supply loads exceeding 200 kVA (this figure varies withdifferent suppliers) at medium voltageFor these reasons, dedicated supply lines at LV are generally applied (at 220/380 Vto 240/415 V) to a load range of 80 kVA to 250 kVA.Consumers normally supplied at low voltage include:b Residential dwellingsb Shops and commercial buildingsb Small factories, workshops and filling stationsb Restaurantsb Farms, etcSchneider Electric - Electrical installation guide 2009© Schneider Electric - all rights reserved

C - Connecion to the LV publicdistribution network1 Low-voltage utility distributionnetworksC10In cities and large towns, standardizedLV distribution cables form a network throughlink boxes. Some links are removed, so thateach (fused) distributor leaving a substationforms a branched open-ended radial system,as shown in Figure C31.2 LV distribution networksIn European countries the standard 3-phase 4-wire distribution voltage level is230/400 V. Many countries are currently converting their LV systems to the latest IECstandard of 230/400 V nominal (IEC 60038). Mediumto large-sized towns and cities have underground cable distribution systems.MV/LV distribution substations, mutually spaced at approximately 500-600 metres,are typically equipped with:b A 3-or 4-way MV switchboard, often made up of incoming and outgoing loadbreakswitches forming part of a ring main, and one or two MV circuit-breakers orcombined fuse/ load-break switches for the transformer circuitsb One or two 1,000 kVA MV/LV transformersb One or two (coupled) 6-or 8-way LV 3-phase 4-wire distribution fuse boards, ormoulded-case circuit-breaker boards, control and protect outgoing 4-core distributioncables, generally referred to as “distributors”The output from a transformer is connected to the LV busbars via a load-breakswitch, or simply through isolating links.In densely-loaded areas, a standard size of distributor is laid to form a network,with (generally) one cable along each pavement and 4-way link boxes located inmanholes at street corners, where two cables cross.Recent trends are towards weather-proof cabinets above ground level, either againsta wall, or where possible, flush-mounted in the wall.Links are inserted in such a way that distributors form radial circuits from thesubstation with open-ended branches (see Fig. C3). Where a link box unites adistributor from one substation with that from a neighbouring substation, the phaselinks are omitted or replaced by fuses, but the neutral link remains in place.4-waylink boxHV/LVsubstationServicecablePhase linksremoved© Schneider Electric - all rights reservedFig. C3 : Showing one of several ways in which a LV distribution network may be arranged forradial branched-distributor operation, by removing (phase) linksSchneider Electric - Electrical installation guide 2009

C - Connecion to the LV publicdistribution network1 Low-voltage utility distributionnetworksIn less-densely loaded urban areas a moreeconomicsystem of tapered radial distributionis commonly used, in which conductors ofreduced size are installed as the distance froma substation increasesImproved methods using insulated twistedconductors to form a pole mounted aerial cableare now standard practice in many countriesIn Europe, each utility-supply distributionsubstation is able to supply at LV an areacorresponding to a radius of approximately300 metres from the substation.North and Central American systems ofdistribution consist of a MV network from whichnumerous (small) MV/LV transformers eachsupply one or several consumers, by directservice cable (or line) from the transformerlocationThis arrangement provides a very flexible system in which a complete substation canbe taken out of service, while the area normally supplied from it is fed from link boxesof the surrounding substations.Moreover, short lengths of distributor (between two link boxes) can be isolated forfault-location and repair.Where the load density requires it, the substations are more closely spaced, andtransformers up to 1,500 kVA are sometimes necessary.Other forms of urban LV network, based on free-standing LV distribution pillars,placed above ground at strategic points in the network, are widely used in areas oflower load density. This scheme exploits the principle of tapered radial distributors inwhich the distribution cable conductor size is reduced as the number of consumersdownstream diminish with distance from the substation.In this scheme a number of large-sectioned LV radial feeders from the distributionboard in the substation supply the busbars of a distribution pillar, from which smallerdistributors supply consumers immediately surrounding the pillar.Distribution in market towns, villages and rural areas generally has, for many years,been based on bare copper conductors supported on wooden, concrete or steelpoles, and supplied from pole-mounted or ground-mounted transformers.In recent years, LV insulated conductors, twisted to form a two-core or 4-core selfsupporting cable for overhead use, have been developed, and are considered to besafer and visually more acceptable than bare copper lines.This is particularly so when the conductors are fixed to walls (e.g. under-eaveswiring) where they are hardly noticeable.As a matter of interest, similar principles have been applied at higher voltages, andself supporting “bundled” insulated conductors for MV overhead installations are nowavailable for operation at 24 kV.Where more than one substation supplies a village, arrangements are made at poleson which the LV lines from different substations meet, to interconnect correspondingphases.North and Central American practice differs fundamentally from that in Europe, inthat LV networks are practically nonexistent, and 3-phase supplies to premises inresidential areas are rare.The distribution is effectively carried out at medium voltage in a way, which againdiffers from standard European practices. The MV system is, in fact, a 3-phase4-wire system from which single-phase distribution networks (phase and neutralconductors) supply numerous single-phase transformers, the secondary windingsof which are centre-tapped to produce 120/240 V single-phase 3-wire supplies.The central conductors provide the LV neutrals, which, together with the MV neutralconductors, are solidly earthed at intervals along their lengths.Each MV/LV transformer normally supplies one or several premises directly from thetransformer position by radial service cable(s) or by overhead line(s).Many other systems exist in these countries, but the one described appears to bethe most common.Figure C4 (next page) shows the main features of the two systems.C11Service components and metering equipmentwere formerly installed inside a consumer’sbuilding. The modern tendency is to locatethese items outside in a weatherproof cabinet1.3 The consumer-service connectionIn the past, an underground cable service or the wall-mounted insulated conductorsfrom an overhead line service, invariably terminated inside the consumer’s premises,where the cable-end sealing box, the utility fuses (inaccessible to the consumer) andmeters were installed.A more recent trend is (as far as possible) to locate these service components in aweatherproof housing outside the building.The utility/consumer interface is often at the outgoing terminals of the meter(s) or,in some cases, at the outgoing terminals of the installation main circuit-breaker(depending on local practices) to which connection is made by utility staff, following asatisfactory test and inspection of the installation.A typical arrangement is shown in Figure C5 (next page).© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

C - Connecion to the LV publicdistribution network1 Low-voltage utility distributionnetworksC121 2 313.8 kV / 2.4-4.16 kVNEach MV/LV transformer shownrepresents many similar units2.4 kV / 120-240 V1 ph - 3 wiredistributiontransformer23NHV (1)For primary voltages > 72.5 kV(see note) primarywinding may be:- Delta- Earthed star- Earthed zigzagDepending on the country concernedTertiary delta normally(not always) used if theprimary winding is not delta1 ph MV / 230 Vservice transformerto isolated consumer(s)(rural supplies)}1N1NMV (2)Resistor replacedby a Petersencoil on O/H linesystems in somecountriesPhN2N2N3 phMV / 230/400 V4-wire distributiontransformerN1 2 3 NN 1 2 3Main 3 ph and neutralLV distribution networkMV distributor(1) 132 kV for example(2) 11 kV for exampleNote: At primary voltages greater than 72.5 kV in bulk-supply substations, it is common practice in some European countriesto use an earthed-star primary winding and a delta secondary winding. The neutral point on the secondary side is thenprovided by a zigzag earthing reactor, the star point of which is connected to earth through a resistor.Frequently, the earthing reactor has a secondary winding to provide LV 3-phase supplies for the substation. It is then referredto as an “earthing transformer”.Fig. C4 : Widely-used American and European-type systemsCB© Schneider Electric - all rights reservedM FAFig. C5 : Typical service arrangement for TT-earthed systemsSchneider Electric - Electrical installation guide 2009

C - Connecion to the LV publicdistribution network1 Low-voltage utility distributionnetworksLV consumers are normally supplied accordingto the TN or TT system, as described inchapters F and G. The installation main circuitbreakerfor a TT supply must include a residualcurrent earth-leakage protective device. For aTN service, overcurrent protection by circuitbreakeror switch-fuse is requiredA MCCB -moulded case circuit-breaker- which incorporates a sensitive residualcurrentearth-fault protective feature is mandatory at the origin of any LV installationforming part of a TT earthing system. The reason for this feature and relatedleakage-current tripping levels are discussed in Clause 3 of Chapter G.A further reason for this MCCB is that the consumer cannot exceed his (contractual)declared maximum load, since the overload trip setting, which is sealed by thesupply authority, will cut off supply above the declared value. Closing and tripping ofthe MCCB is freely available to the consumer, so that if the MCCB is inadvertentlytripped on overload, or due to an appliance fault, supplies can be quickly restoredfollowing correction of the anomaly.In view of the inconvenience to both the meter reader and consumer, the location ofmeters is nowadays generally outside the premises, either:b In a free-standing pillar-type housing as shown in Figures C6 and C7b In a space inside a building, but with cable termination and supply authority’s fuseslocated in a flush-mounted weatherproof cabinet accessible from the public way, asshown in Figure C8 next pageb For private residential consumers, the equipment shown in the cabinet inFigure C5 is installed in a weatherproof cabinet mounted vertically on a metalframe in the front garden, or flush-mounted in the boundary wall, and accessible toauthorized personnel from the pavement. Figure C9 (next page) shows the generalarrangement, in which removable fuse links provide the means of isolationC13MFCBAIn this kind of installation it is often necessary to place the main installation circuitbreakersome distance from the point of utilization, e.g. saw-mills, pumping stations,etc.Fig. C6 : Typical rural-type installationCBMFThe main installation CB is located in the consumer’s premises in cases where it isset to trip if the declared kVA load demand is exceeded.Fig. C7 : Semi-urban installations (shopping precincts, etc.)A© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

C - Connecion to the LV publicdistribution network1 Low-voltage utility distributionnetworksC14CBMFAThe service cable terminates in a flushmounted wall cabinet which contains theisolating fuse links, accessible from the public way. This method is preferred foresthetic reasons, when the consumer can provide a suitable metering and mainswitchlocation.Fig. C8 : Town centre installationsInterfaceService cableUtilityConsumerInstallationIsolation byfuse linksMeter cabinetMeterMaincircuitbreakerFig. C9 : Typical LV service arrangement for residential consumers© Schneider Electric - all rights reservedIn the field of electronic metering, techniques have developed which make theiruse attractive by utilities either for electricity metering and for billing purposes, theliberalisation of the electricity market having increased the needs for more datacollection to be returned from the meters. For example electronic metering can alsohelp utilities to understand their customers’ consumption profiles. In the same way,they will be useful for more and more power line communication and radio-frequencyapplications as well.In this area, prepayment systems are also more and more employed wheneconomically justified. They are based on the fact that for instance consumers havingmade their payment at vending stations, generate tokens to pass the informationconcerning this payment on to the meters. For these systems the key issues aresecurity and inter-operability which seem to have been addressed successfullynow. The attractiveness of these systems is due to the fact they not only replace themeters but also the billing systems, the reading of meters and the administration ofthe revenue collection.Schneider Electric - Electrical installation guide 2009

C - Connecion to the LV publicdistribution network1 Low-voltage utility distributionnetworksAn adequate level of voltage at the consumerssupply-service terminals is essential forsatisfactory operation of equipment andappliances. Practical values of current, andresulting voltage drops in a typical LV system,show the importance of maintaining a highPower Factor as a means of reducing voltagedrop.1.4 Quality of supply voltageThe quality of the LV network supply voltage in its widest sense implies:b Compliance with statutory limits of magnitude and frequencyb Freedom from continual fluctuation within those limitsb Uninterrupted power supply, except for scheduled maintenance shutdowns, or as aresult of system faults or other emergenciesb Preservation of a near-sinusoidal wave formIn this Sub-clause the maintenance of voltage magnitude only will be discussed.In most countries, power-supply authorities have a statutory obligation to maintainthe level of voltage at the service position of consumers within the limits of ± 5% (orin some cases ± 6% or more-see table C1) of the declared nominal value.Again, IEC and most national standards recommend that LV appliances be designedand tested to perform satisfactorily within the limits of ± 10% of nominal voltage. Thisleaves a margin, under the worst conditions (of minus 5% at the service position, forexample) of 5% allowable voltage drop in the installation wiring.The voltage drops in a typical distribution system occur as follows: the voltage atthe MV terminals of a MV/LV transformer is normally maintained within a ± 2% bandby the action of automatic onload tapchangers of the transformers at bulk-supplysubstations, which feed the MV network from a higher-voltage subtransmissionsystem.If the MV/LV transformer is in a location close to a bulk-supply substation, the ± 2%voltage band may be centered on a voltage level which is higher than the nominalMV value. For example, the voltage could be 20.5 kV ± 2% on a 20 kV system. In thiscase, the MV/LV distribution transformer should have its MV off-circuit tapping switchselected to the + 2.5% tap position.Conversely, at locations remote from bulk supply substations a value of 19.5 kV ±2% is possible, in which case the off-circuit tapping switch should be selected to the- 5% position.The different levels of voltage in a system are normal, and depend on the systempowerflow pattern. Moreover, these voltage differences are the reason for the term“nominal” when referring to the system voltage.C15Practical application(1) Transformers designed for the 230/400 V IEC standardwill have a no-load output of 420 V, i.e. 105% of the nominalvoltageWith the MV/LV transformer correctly selected at its off-circuit tapping switch, anunloaded transformer output voltage will be held within a band of ± 2% of its no-loadvoltage output.To ensure that the transformer can maintain the necessary voltage level when fullyloaded, the output voltage at no-load must be as high as possible without exceedingthe upper + 5% limit (adopted for this example). In present-day practice, the windingratios generally give an output voltage of about 104% at no-load (1) , when nominalvoltage is applied at MV, or is corrected by the tapping switch, as described above.This would result in a voltage band of 102% to 106% in the present case.A typical LV distribution transformer has a short-circuit reactance voltage of 5%. If itis assumed that its resistance voltage is one tenth of this value, then the voltage dropwithin the transformer when supplying full load at 0.8 power factor lagging, will be:V% drop = R% cos ϕ + X% sin ϕ= 0.5 x 0.8 + 5 x 0.6= 0.4 + 3 = 3.4%The voltage band at the output terminals of the fully-loaded transformer will thereforebe (102 - 3.4) = 98.6% to (106 - 3.4) = 102.6%.The maximum allowable voltage drop along a distributor is therefore 98.6 - 95 = 3.6%.This means, in practical terms, that a medium-sized 230/400 V 3-phase 4-wiredistribution cable of 240 mm 2 copper conductors would be able to supply a total loadof 292 kVA at 0.8 PF lagging, distributed evenly over 306 metres of the distributor.Alternatively, the same load at the premises of a single consumer could be suppliedat a distance of 153 metres from the transformer, for the same volt-drop, and so on...As a matter of interest, the maximum rating of the cable, based on calculationsderived from IEC 60287 (1982) is 290 kVA, and so the 3.6% voltage margin is notunduly restrictive, i.e. the cable can be fully loaded for distances normally required inLV distribution systems.Furthermore, 0.8 PF lagging is appropriate to industrial loads. In mixed semiindustrialareas 0.85 is a more common value, while 0.9 is generally used forcalculations concerning residential areas, so that the volt-drop noted above may beconsidered as a “worst case” example.Schneider Electric - Electrical installation guide 2009© Schneider Electric - all rights reserved

C - Connecion to the LV publicdistribution network2 Tariffs and meteringC16No attempt will be made in this guide to discuss particular tariffs, since there appearsto be as many different tariff structures around the world as there are utilities.Some tariffs are very complicated in detail but certain elements are basic to all ofthem and are aimed at encouraging consumers to manage their power consumptionin a way which reduces the cost of generation, transmission and distribution.The two predominant ways in which the cost of supplying power to consumers canbe reduced, are:b Reduction of power losses in the generation, transmission and distribution ofelectrical energy. In principle the lowest losses in a power system are attained whenall parts of the system operate at unity power factorb Reduction of the peak power demand, while increasing the demand at low-loadperiods, thereby exploiting the generating plant more fully, and minimizing plantredundancyReduction of lossesAlthough the ideal condition noted in the first possibility mentioned above cannotbe realized in practice, many tariff structures are based partly on kVA demand, aswell as on kWh consumed. Since, for a given kW loading, the minimum value of kVAoccurs at unity power factor, the consumer can minimize billing costs by taking stepsto improve the power factor of the load (as discussed in Chapter L). The kVA demandgenerally used for tariff purposes is the maximum average kVA demand occurringduring each billing period, and is based on average kVA demands, over fixed periods(generally 10, 30 or 60 minute periods) and selecting the highest of these values.The principle is described below in “principle of kVA maximum-demand metering”.Reduction of peak power demandThe second aim, i.e. that of reducing peak power demands, while increasing demandat low-load periods, has resulted in tariffs which offer substantial reduction in the costof energy at:b Certain hours during the 24-hour dayb Certain periods of the yearThe simplest example is that of a residential consumer with a storage-type waterheater (or storage-type space heater, etc.). The meter has two digital registers, oneof which operates during the day and the other (switched over by a timing device)operates during the night. A contactor, operated by the same timing device, closesthe circuit of the water heater, the consumption of which is then indicated on theregister to which the cheaper rate applies. The heater can be switched on and off atany time during the day if required, but will then be metered at the normal rate. Largeindustrial consumers may have 3 or 4 rates which apply at different periods duringa 24-hour interval, and a similar number for different periods of the year. In suchschemes the ratio of cost per kWh during a period of peak demand for the year, andthat for the lowest-load period of the year, may be as much as 10: 1.MetersIt will be appreciated that high-quality instruments and devices are necessary toimplement this kind of metering, when using classical electro-mechanical equipment.Recent developments in electronic metering and micro-processors, together withremote ripple-control (1) from an utility control centre (to change peak-period timingthroughout the year, etc.) are now operational, and facilitate considerably theapplication of the principles discussed.In most countries, some tariffs, as noted above, are partly based on kVA demand,in addition to the kWh consumption, during the billing periods (often 3-monthlyintervals). The maximum demand registered by the meter to be described, is, in fact,a maximum (i.e. the highest) average kVA demand registered for succeeding periodsduring the billing interval.© Schneider Electric - all rights reserved(1) Ripple control is a system of signalling in which a voicefrequency current (commonly at 175 Hz) is injected into theLV mains at appropriate substations. The signal is injectedas coded impulses, and relays which are tuned to the signalfrequency and which recognize the particular code will operateto initiate a required function. In this way, up to 960 discretecontrol signals are available.Schneider Electric - Electrical installation guide 2009

C - Connecion to the LV publicdistribution network2 Tariffs and meteringFigure C10 shows a typical kVA demand curve over a period of two hours dividedinto succeeding periods of 10 minutes. The meter measures the average value ofkVA during each of these 10 minute periods.C17kVAMaximum average valueduring the 2 hour intervalAverage valuesfor 10 minuteperiods0 1 2 hrstFig. C10 : Maximum average value of kVA over an interval of 2 hoursPrinciple of kVA maximum demand meteringA kVAh meter is similar in all essentials to a kWh meter but the current and voltagephase relationship has been modified so that it effectively measures kVAh (kilovolt-ampere-hours).Furthermore, instead of having a set of decade counter dials,as in the case of a conventional kWh meter, this instrument has a rotating pointer.When the pointer turns it is measuring kVAh and pushing a red indicator before it.At the end of 10 minutes the pointer will have moved part way round the dial (it isdesigned so that it can never complete one revolution in 10 minutes) and is thenelectrically reset to the zero position, to start another 10 minute period. The redindicator remains at the position reached by the measuring pointer, and that position,corresponds to the number of kVAh (kilo-volt-ampere-hours) taken by the load in10 minutes. Instead of the dial being marked in kVAh at that point however it can bemarked in units of average kVA. The following figures will clarify the matter.Supposing the point at which the red indicator reached corresponds to 5 kVAh.It is known that a varying amount of kVA of apparent power has been flowing for10 minutes, i.e. 1/6 hour.If now, the 5 kVAh is divided by the number of hours, then the average kVA for theperiod is obtained.In this case the average kVA for the period will be:5 x 1 = 5 x 6 = 30 kVA16Every point around the dial will be similarly marked i.e. the figure for average kVA willbe 6 times greater than the kVAh value at any given point. Similar reasoning can beapplied to any other reset-time interval.At the end of the billing period, the red indicator will be at the maximum of all theaverage values occurring in the billing period.The red indicator will be reset to zero at the beginning of each billing period. Electromechanicalmeters of the kind described are rapidly being replaced by electronicinstruments. The basic measuring principles on which these electronic metersdepend however, are the same as those described above.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Chapter DMV & LV architecture selectionguide12345678ContentsStakes for the userSimplified architecture design process2.1 The architecture design D42.2 The whole process D5Electrical installation characteristicsD73.1 Activity D73.2 Site topology D73.3 Layout latitude D73.4 Service reliability D83.5 Maintainability D83.6 Installation flexibility D83.7 Power demand D83.8 Load distribution D93.9 Power interruption sensitivity D93.10 Disturbance sensitivity D93.11 Disturbance capability of circuits D103.12 Other considerations or constraints D10Technological characteristicsD3D4D114.1 Environment, atmosphere D114.2 Service Index D114.3 Other considerations D12Architecture assessment criteriaD135.1 On-site work time D135.2 Environmental impact D135.3 Preventive maintenance level D135.4 Availability of electrical power supply D14Choice of architecture fundamentalsD156.1 Connection to the upstream network D156.2 MV circuit configuration D166.3 Number and distribution of MV/LV transformation substations D176.4 Number of MV/LV transformers D186.5 MV back-up generator D18Choice of architecture detailsD197.1 Layout D197.2 Centralized or distributed layout D207.3 Presence of an Uninterruptible Power Supply (UPS) D227.4 Configuration of LV circuits D22Choice of equimentD24D© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guideD9101112Recommendations for architecture optimizationD269.1 On-site work time D269.2 Environmental impact D269.3 Preventive maintenance volume D289.4 Electrical power availability D28GlossaryD29ID-Spec softwareExample: electrical installation in a printworksD30D3112.1 Brief description D3112.2 Installation characteristics D3112.3 Technological characteristics D3112.4 Architecture assessment criteria D3212.5 Choice of technogical solutions D34© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide1 Stakes for the userChoice of distribution architectureThe choice of distribution architecture has a decisive impact on installationperformance throughout its lifecycle:b right from the construction phase, choices can greatly influence the installationtime, possibilities of work rate, required competencies of installation teams, etc.b there will also be an impact on performance during the operation phase in termsof quality and continuity of power supply to sensitive loads, power losses in powersupply circuits,b and lastly, there will be an impact on the proportion of the installation that can berecycled in the end-of-life phase.The Electrical Distribution architecture of an installation involves the spatialconfiguration, the choice of power sources, the definition of different distributionlevels, the single-line diagram and the choice of equipment.The choice of the best architecture is often expressed in terms of seeking acompromise between the various performance criteria that interest the customer whowill use the installation at different phases in its lifecycle. The earlier we search forsolutions, the more optimization possibilities exist (see Fig. D1).DPotential foroptimizationEcodialPreliminarydesignID-SpecDetailleddesignInstallationExploitationFig. D1 : Optimization potentialA successful search for an optimal solution is also strongly linked to the ability forexchange between the various players involved in designing the various sections ofa project:b the architect who defines the organization of the building according to userrequirements,b the designers of different technical sections (lighting, heating, air conditioning,fluids, etc.),b the user’s representatives e.g. defining the process.The following paragraphs present the selection criteria as well as the architecturedesign process to meet the project performance criteria in the context of industrialand tertiary buildings (excluding large sites).© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide2 Simplified architecture designprocess2.1 The architecture designThe architecture design considered in this document is positioned at the DraftDesign stage. It generally covers the levels of MV/LV main distribution, LV powerdistribution, and exceptionally the terminal distribution level. (see Fig. D2).DMV/LV maindistributionLV powerdistributionLV terminaldistributionM M M MFig. D2 : Example of single-line diagramThe design of an electrical distribution architecture can be described by a 3-stageprocess, with iterative possibilities. This process is based on taking account of theinstallation characteristics and criteria to be satisfied.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide2 Simplified architecture designprocess2.2 The whole processThe whole process is described briefly in the following paragraphs and illustrated onFigure D3.The process described in this document is not intended as the only solution. Thisdocument is a guide intended for the use of electrical installation designers.DDataStepSee § 3InstallationcharacteristicsDeliverableSee § 6Step 1Choice offundamentalsSchematicdiagramSee § 7Step 2Choice ofarchitecturedetailsDetaileddiagramSee § 4TechnologicalcharacteristicsSee § 8Step 3Choice ofequipmentTechno.SolutionSee § 5AssessmentcriteriaASSESSMENTSee § 9OptimisationrecommendationsDefinitivesolutionFig. D3 : Flow diagram for choosing the electrical distribution architectureStep 1: Choice of distribution architecture fundamentalsThis involves defining the general features of the electrical installation. It is basedon taking account of macroscopic characteristics concerning the installation and itsusage.These characteristics have an impact on the connection to the upstream network,MV circuits, the number of transformer substations, etc.At the end of this step, we have several distribution schematic diagram solutions,which are used as a starting point for the single-line diagram. The definitive choice isconfirmed at the end of the step 2.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide2 Simplified architecture designprocessDStep 2: choice of architecture detailsThis involves defining the electrical installation in more detail. It is based on theresults of the previous step, as well as on satisfying criteria relative to implementationand operation of the installation.The process loops back into step1 if the criteria are not satisfied. An iterative processallows several assessment criteria combinations to be analyzed.At the end of this step, we have a detailed single-line diagram.Step 3: choice of equipmentThe choice of equipment to be implemented is carried out in this stage, and resultsfrom the choice of architecture. The choices are made from the manufacturercatalogues, in order to satisfy certain criteria.This stage is looped back into step 2 if the characteristics are not satisfied.AssessmentThis assessment step allows the Engineering Office to have figures as a basis fordiscussions with the customer and other players.According to the result of these discussions, it may be possible to loop back into step 1.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide3 Electrical installationcharacteristicsThese are the main installation characteristics enabling the defining of thefundamentals and details of the electrical distribution architecture. For each of thesecharacteristics, we supply a definition and the different categories or possible values.3.1 ActivityDefinition:Main economic activity carried out on the site.DIndicative list of sectors considered for industrial buildings:b Manufacturingb Food & Beverageb LogisticsIndicative list of sectors considered for tertiary buildings:b Offices buildingsb Hypermarketsb Shopping malls3.2 Site topologyDefinition:Architectural characteristic of the building(s), taking account of the number ofbuildings, number of floors, and of the surface area of each floor.Different categories:b Single storey building,b Multi-storey building,b Multi-building site,b High-rise building.3.3 Layout latitudeDefinition:Characteristic taking account of constraints in terms of the layout of the electricalequipment in the building:b aesthetics,b accessibility,b presence of dedicated locations,b use of technical corridors (per floor),b use of technical ducts (vertical).Different categories:b Low: the position of the electrical equipment is virtually imposedb Medium: the position of the electrical equipment is partially imposed, to thedetriment of the criteria to be satisfiedb High: no constraints. The position of the electrical equipment can be defined tobest satisfy the criteria.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide3 Electrical installationcharacteristics3.4 Service reliabilityDefinition:The ability of a power system to meet its supply function under stated conditions fora specified period of time.DDifferent categories:b Minimum: this level of service reliability implies risk of interruptions related toconstraints that are geographical (separate network, area distant from powerproduction centers), technical (overhead line, poorly meshed system), or economic(insufficient maintenance, under-dimensioned generation).b Standardb Enhanced: this level of service reliability can be obtained by special measurestaken to reduce the probability of interruption (underground network, strong meshing,etc.)3.5 MaintainabilityDefinition:Features input during design to limit the impact of maintenance actions on theoperation of the whole or part of the installation.Different categories:b Minimum: the installation must be stopped to carry out maintenance operations.b Standard: maintenance operations can be carried out during installationoperations, but with deteriorated performance. These operations must be preferablyscheduled during periods of low activity. Example: several transformers with partialredundancy and load shedding.b Enhanced: special measures are taken to allow maintenance operations withoutdisturbing the installation operations. Example: double-ended configuration.3.6 Installation flexibilityDefinition:Possibility of easily moving electricity delivery points within the installation, or toeasily increase the power supplied at certain points. Flexibility is a criterion whichalso appears due to the uncertainty of the building during the pre-project summarystage.Different categories:b No flexibility: the position of loads is fixed throughout the lifecycle, due to the highconstraints related to the building construction or the high weight of the suppliedprocess. E.g.: smelting works.b Flexibility of design: the number of delivery points, the power of loads or theirlocation are not precisely known.b Implementation flexibility: the loads can be installed after the installation iscommissioned.b Operating flexibility: the position of loads will fluctuate, according to process reorganization.Examples:v industrial building: extension, splitting and changing usagev office building: splitting© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide3 Electrical installationcharacteristics3.7 Power demandDefinition:The sum of the apparent load power (in kVA), to which is applied a usage coefficient.This represents the maximum power which can be consumed at a given time for theinstallation, with the possibility of limited overloads that are of short duration.Significant power ranges correspond to the transformer power limits most commonlyused:b < 630kVAb from 630 to 1250kVAb from 1250 to 2500kVAb > 2500kVAD3.8 Load distributionDefinition:A characteristic related to the uniformity of load distribution (in kVA / m²) over an areaor throughout the building.Different categories:b Uniform distribution: the loads are generally of an average or low unit power andspread throughout the surface area or over a large area of the building (uniformdensity).E.g.: lighting, individual workstationsb intermediate distribution: the loads are generally of medium power, placed ingroups over the whole building surface areaE.g.: machines for assembly, conveying, workstations, modular logistics “sites”b localized loads: the loads are generally high power and localized in several areasof the building (non-uniform density).E.g.: HVAC3.9 Power Interruption SensitivityDefinition:The aptitude of a circuit to accept a power interruption.* indicative value, supplied by standard EN50160:“Characteristics of the voltage supplied by public distributionnetworks”.Different categories:b “Sheddable” circuit: possible to shut down at any time for an indefinite durationb Long interruption acceptable: interruption time > 3 minutes *b Short interruption acceptable: interruption time < 3 minutes *b No interruption acceptable.We can distinguish various levels of severity of an electrical power interruption,according to the possible consequences:b No notable consequence,b Loss of production,b Deterioration of the production facilities or loss of sensitive data,b Causing mortal danger.This is expressed in terms of the criticality of supplying of loads or circuits.b Non-critical:The load or the circuit can be “shed” at any time. E.g.: sanitary water heating circuit.b Low criticality:A power interruption causes temporary discomfort for the occupants of a building,without any financial consequences. Prolonging of the interruption beyond the criticaltime can cause a loss of production or lower productivity. E.g.: heating, ventilationand air conditioning circuits (HVAC).b Medium criticalityA power interruption causes a short break in process or service. Prolonging ofthe interruption beyond a critical time can cause a deterioration of the productionfacilities or a cost of starting for starting back up.E.g.: refrigerated units, lifts.b High criticalityAny power interruption causes mortal danger or unacceptable financial losses.E.g.: operating theatre, IT department, security department.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide3 Electrical installationcharacteristics3.10 Disturbance sensitivityD10DefinitionThe ability of a circuit to work correctly in presence of an electrical powerdisturbance.A disturbance can lead to varying degrees of malfunctioning. E.g.: stopping working,incorrect working, accelerated ageing, increase of losses, etcTypes of disturbances with an impact on circuit operations:b brown-outs,b overvoltagesb voltage distortion,b voltage fluctuation,b voltage imbalance.Different categories:b low sensitivity: disturbances in supply voltages have very little effect on operations.E.g.: heating device.b medium sensitivity: voltage disturbances cause a notable deterioration inoperations.E.g.: motors, lighting.b high sensitivity: voltage disturbances can cause operation stoppages or even thedeterioration of the supplied equipment.E.g.: IT equipment.The sensitivity of circuits to disturbances determines the design of shared ordedicated power circuits. Indeed it is better to separate “sensitive” loads from“disturbing” loads. E.g.: separating lighting circuits from motor supply circuits.This choice also depends on operating features. E.g.: separate power supply oflighting circuits to enable measurement of power consumption.3.11 Disturbance capability of circuitsDefinitionThe ability of a circuit to disturb the operation of surrounding circuits due tophenomena such as: harmonics, in-rush current, imbalance, High Frequencycurrents, electromagnetic radiation, etc.Different categoriesb Non disturbing: no specific precaution to takeb moderate or occasional disturbance: separate power supply may be necessary inthe presence of medium or high sensitivity circuits. E.g.: lighting circuit generatingharmonic currents.b Very disturbing: a dedicated power circuit or ways of attenuating disturbances areessential for the correct functioning of the installation. E.g.: electrical motor with astrong start-up current, welding equipment with fluctuating current.3.12 Other considerations or constraints© Schneider Electric - all rights reservedb EnvironmentE.g.: lightning classification, sun exposureb Specific rulesE.g.: hospitals, high rise buildings, etc.b Rule of the Energy DistributorExample: limits of connection power for LV, access to MV substation, etcb Attachment loadsLoads attached to 2 independent circuits for reasons of redundancy.b Designer experienceConsistency with previous designs or partial usage of previous designs,standardization of sub-assemblies, existence of an installed equipment base.b Load power supply constraintsVoltage level (230V, 400V, 690V), voltage system (single-phase, three-phase with orwithout neutral, etc)Schneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide4 Technological characteristicsThe technological solutions considered concern the various types of MV and LVequipment, as well as Busbar Trunking Systems .The choice of technological solutions is made following the choice of single-linediagram and according to characteristics given below.4.1 Environment, atmosphereA notion taking account of all of the environmental constraints (average ambienttemperature, altitude, humidity, corrosion, dust, impact, etc.) and bringing togetherprotection indexes IP and IK.Different categories:b Standard: no particular environmental constraintsb Enhanced: severe environment, several environmental parameters generateimportant constraints for the installed equipmentb Specific: atypical environment, requiring special enhancementsD114.2 Service IndexThe service index (IS) is a value that allows us to characterize an LV switchboardaccording to user requirements in terms of operation, maintenance, and scalability.The different index values are indicated in the following table (Fig D4):Operation Maintenance UpgradeLevel 1IS = 1 • •Operation may lead to completestoppage of the switchboardIS = • 1 •Operation may lead to completestoppage of the switchboardIS = • • 1Operation may lead to completestoppage of the switchboardLevel 2IS = 2 • •Operation may lead to stoppage ofonly the functional unitIS = • 2 •Operation may lead to stoppage ofonly the functional unit, with work onconnectionsIS = • • 2Operation may lead to stoppageof only the functional unit, withfunctional units provided for back-upLevel 3IS = 3 • •Operation may lead to stoppage ofthe power of the functional unit onlyIS = • 3 •Operation may lead to stoppage ofonly the functional unit, without workon connectionsIS = • • 3Operation may lead to stoppage ofonly the functional unit, with totalfreedom in terms of upgradeFig. D4 : Different index valuesb Examples of an operation event: turning off a circuit-breaker, switching operation toenergize/de-energize a machineb Example of a maintenance operation: tightening connectionsb Example of an upgrade operation: connecting an additional feederThere are a limited number of relevant service indices (see Fig. D5)IS Operation Maintenance Upgrade1 1 1 Switching off the whole switchboard Working time > 1h, with total nonavailability2 1 12 2 3 Working time between 1/4h and 1h,with work on connectionsIndividually switching off the functional2 3 2 unit and re-commissioning < 1hExtension not plannedPossible adding of functional unitswithout stopping the switchboardPossible adding of functional units withstopping the switchboard2 3 3 Possible adding of functional unitsWorking time between 1/4h and 1h, without stopping the switchboardwithout work on connections3 3 2Possible adding of functional units withIndividually switching off the functionalstopping the switchboard3 3 3unit and re-commissioning < 1/4hPossible adding of functional unitswithout stopping the switchboardFig. D5 : Relevant service indices (IS)© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide4 Technological characteristicsD12The types of electrical connections of functional units can be denoted by a threelettercode:b The first letter denotes the type of electrical connection of the main incomingcircuit,b The second letter denotes the type of electrical connection of the main outgoingcircuit,b The third letter denotes the type of electrical connection of the auxiliary circuits.The following letters are used:b F for fixed connections,b D for disconnectable connections,b W for withdrawable connections.Service ratings are related to other mechanical parameters, such as the ProtectionIndex (IP), form of internal separations, the type of connection of functional units orswitchgear (Fig. D6):Service ratingProtection indexIPForm1 1 1 2 X X 1 F F F2 1 1 2 X B 1 F F F2 2 3 2 X B 3b W F D2 3 2 2 X B 3b W F W2 3 3 2 X B 3b W W W3 3 2 2 X B 3b W W W3 3 3 2 X B 3b W W WFunctional UnitWithdrawabilityFig. D6 : Correspondence between service index and other mechanical parametersTechnological examples are given in chapter E2.b Definition of the protection index: see IEC 60529: “Degree of protection given byenclosures (IP code)”,b Definitions of the form and withdrawability: see IEC 60439-1: “Low-voltageswitchgear and controlgear assemblies; part 1: type-tested and partially type-testedassemblies”.4.3 Other considerationsOther considerations have an impact on the choice of technological solutions:b Designer experience,b Consistency with past designs or the partial use of past designs,b Standardization of sub-assemblies,b The existence of an installed equipment base,b Utilities requirements,b Technical criteria: target power factor, backed-up load power, presence of harmonicgenerators…These considerations should be taken into account during the detailed electricaldefinition phase following the draft design stage.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide5 Architecture assessment criteriaCertain decisive criteria are assessed at the end of the 3 stages in definingarchitecture, in order to validate the architecture choice. These criteria are listedbelow with the different allocated levels of priority.5.1 On-site work timeTime for implementing the electrical equipment on the site.D13Different levels of priority:b Secondary: the on-site work time can be extended, if this gives a reduction inoverall installation costs,b Special: the on-site work time must be minimized, without generating anysignificant excess cost,b Critical: the on-site work time must be reduced as far as possible, imperatively,even if this generates a higher total installation cost,5.2 Environmental impactTaking into consideration environmental constraints in the installation design. Thistakes account of: consumption of natural resources, Joule losses (related to CO 2emission), “recyclability” potential, throughout the installation’s lifecycle.Different levels of priority:b Non significant: environmental constraints are not given any special consideration,b Minimal: the installation is designed with minimum regulatory requirements,b Proactive: the installation is designed with a specific concern for protectingthe environment. Excess cost is allowed in this situation. E.g.: using low-losstransformers.The environmental impact of an installation will be determined according to themethod carrying out an installation lifecycle analysis, in which we distinguishbetween the following 3 phases:b manufacture,b operation,b end of life (dismantling, recycling).In terms of environmental impact, 3 indicators (at least) can be taken into accountand influenced by the design of an electrical installation. Although each lifecyclephase contributes to the three indicators, each of these indicators is mainly related toone phase in particular:b consumption of natural resources mainly has an impact on the manufacturingphase,b consumption of energy has an impact on the operation phase,b “recycleability” potential has an impact on the end of life.The following table details the contributing factors to the 3 environmental indicators(Fig D7).IndicatorsNatural resources consumptionPower consumption«Recyclability» potentialContributorsMass and type of materials usedJoule losses at full load and no loadMass and type of material usedFig D7 : Contributing factors to the 3 environmental indicators© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide5 Architecture assessment criteria5.3 Preventive maintenance levelD14Definition:Number of hours and sophistication of maintenance carried out during operations inconformity with manufacturer recommendations to ensure dependable operation ofthe installation and the maintaining of performance levels (avoiding failure: tripping,down time, etc).Different categories:b Standard: according to manufacturer recommendations.b Enhanced: according to manufacturer recommendations, with a severeenvironment,b Specific: specific maintenance plan, meeting high requirements for continuity ofservice, and requiring a high level of maintenance staff competency.5.4 Availability of electrical power supplyDefinition:This is the probability that an electrical installation be capable of supplying qualitypower in conformity with the specifications of the equipment it is supplying. This isexpressed by an availability level:Availability (%) = (1 - MTTR/ MTBF) x 100MTTR (Mean Time To Repair): the average time to make the electrical system onceagain operational following a failure (this includes detection of the reason for failure,its repair and re-commissioning),MTBF (Mean Time Between Failure): measurement of the average time for whichthe electrical system is operational and therefore enables correct operation of theapplication.The different availability categories can only be defined for a given type ofinstallation. E.g.: hospitals, data centers.Example of classification used in data centers:Tier 1: the power supply and air conditioning are provided by one single channel,without redundancy, which allows availability of 99.671%,Tier 2: the power supply and air conditioning are provided by one single channel,with redundancy, which allows availability of 99.741%,Tier 3: the power supply and air conditioning are provided by several channels, withone single redundant channel, which allows availability of 99.982%,Tier 4: the power supply and air conditioning are provided by several channels, withredundancy, which allows availability of 99.995%.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide6 Choice of architecturefundamentalsThe single-line diagram can be broken down into different key parts, which aredetermined throughout a process in 2 successive stages. During the first stage wemake the following choices:b connection to the utilities network,b configuration of MV circuits,b number of power transformers,b number and distribution of transformation substations,b MV back-up generatorD156.1 Connection to the upstream networkThe main configurations for possible connection are as follows (see Fig. D8 for MVservice):b LV service,b MV single-line service,b MV ring-main service,b MV duplicate supply service,b MV duplicate supply service with double busbar.Metering, protection, disconnection devices, located in the delivery substations arenot represented on the following diagrams. They are often specific to each utilitiescompany and do not have an influence on the choice of installation architecture.For each connection, one single transformer is shown for simplification purposes, butin the practice, several transformers can be connected.(MLVS: Main Low Voltage Switchboard)a) Single-line: b) Ring-main:MVLVMVLVMLVSMLVSc) Duplicate supply: d) Double busbar with duplicate supply:MVMVMVLVMLVSFig. D8 : MV connection to the utilities networkLVMLVS1LVMLVS2© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide6 Choice of architecturefundamentalsFor the different possible configurations, the most probable and usual set ofcharacteristics is given in the following table:ConfigurationD16Characteristic toconsiderLVMVSimple-line Ring-main Duplicate supply Duplicate supplywith doublebusbarsActivity Any Any Any Hi-tech, sensitiveoffice, health-careSite topology Single building Single building Single building Single building Several buildingsService reliability Minimal Minimal Standard Enhanced EnhancedPower demand < 630kVA ≤ 1250kVA ≤ 2500kVA > 2500kVA > 2500kVAOther connectionconstraintsAny Isolated site Low density urbanareaHigh densityurban areaAnyUrban area withutility constraint6.2 MV circuit configurationThe main possible connection configurations are as follows (Fig. D9):b single feeder, one or several transformersb open ring, one MV incomerb open ring, 2 MV incomersThe basic configuration is a radial single-feeder architecture, with one singletransformer.In the case of using several transformers, no ring is realised unless all of thetransformers are located in a same substation.Closed-ring configuration is not taken into account.a) Single feeder: b) Open ring, 1 MV substation:c) Open ring, 2 MV substations:MV MV MV MV MVMVMVMVLVLVLVLVLVLVLVLVMLVS 1MLVS nMLVS 1MLVS 2MLVS nMLVS 1MLVS 2MLVS nFig. D9 : MV circuit configuration© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide6 Choice of architecturefundamentalsFor the different possible configurations, the most probable and usual set ofcharacteristics is given in the table on Fig D10.MV circuit configurationCharacteristic toconsiderSite topologySingle feederAny< 25000m²Open ring1 MV substationBuilding with onelevel or severalbuildings≤ 25000m²Open ring2 MV substationsSeveral buildings≥ 25000m²Maintainability Minimal or standard Enhanced EnhancedPower demand Any > 1250kVA > 2500kVADisturbance sensitivityLong interruptionacceptableFig. D10 : Typical values of the installation characteristicsShort interruptionacceptableShort interruptionacceptableD17Another exceptional configuration: power supply by 2 MV substations and connectionof the transformers to each of these 2 substations (MV “double ended” connection).6.3 Number and distribution of MV/LVtransformation substationsMain characteristics to consider to determine the transformation substations:b Surface area of building or siteb Power demand, (to be compared with standardized transformer power),b Load distributionThe preferred basic configuration comprises one single substation. Certain factorscontribute to increasing the number of substations (> 1):b A large surface area (> 25000m²),b The site configuration: several buildings,b Total power > 2500kVA,b Sensitivity to interruption: need for redundancy in the case of a fire.Characteristic toconsiderConfiguration1 substation withN transformersN substationsN transformers(identical substations)Building configuration < 25000m² ≥ 25000m²1 building with severalfloorsN substationsM transformers(different powers)≥ 25000m²several buildingsPower demand < 2500kVA ≥ 2500kVA ≥ 2500kVALoad distribution Localized loads Uniform distribution Medium densityFig. D11 : Typical characteristics of the different configurations© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide6 Choice of architecturefundamentals6.4 Number of MV/LV transformersD18Main characteristics to consider to determine the number of transformers:b Surface of building or siteb Total power of the installed loadsb Sensitivity of circuits to power interruptionsb Sensitivity of circuits to disturbancesb Installation scalabilityThe basic preferred configuration comprises a single transformer supplying the totalpower of the installed loads. Certain factors contribute to increasing the number oftransformers (> 1), preferably of equal power:b A high total installed power (> 1250kVA): practical limit of unit power(standardization, ease of replacement, space requirement, etc),b A large surface area (> 5000m²): the setting up of several transformers as close aspossible to the distributed loads allows the length of LV trunking to be reducedb A need for partial redundancy (down-graded operation possible in the case of atransformer failure) or total redundancy (normal operation ensured in the case atransformer failure)b Separating of sensitive and disturbing loads (e.g.: IT, motors)6.5 MV back-up generatorMain characteristics to consider for the implementation of an MV back-up generator:b Site activityb Total power of the installed loadsb Sensitivity of circuits to power interruptionsb Availability of the public distribution networkThe preferred basic configuration does not include an MV generator. Certain factorscontribute to installing an MV generator:b Site activity: process with co-generation, optimizing the energy bill,b Low availability of the public distribution network.Installation of a back-up generator can also be carried out at LV level.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide7 Choice of architecture detailsThis is the second stage in designing of the electrical installation. During this stagewe carry out the following choices are carried out:b Layout,b Centralized or decentralized distribution,b Presence of back-up generators,b Presence of uninterruptible power supplies,b Configuration of LV circuits,b Architecture combinations.D197.1 LayoutPosition of the main MV and LV equipment on the site or in the building.This layout choice is applied to the results of stage 1.Selection guide:b Place power sources as close as possible to the barycenter of power consumers,b Reduce atmospheric constraints: building dedicated premises if the layout in theworkshop is too restrictive (temperature, vibrations, dust, etc.),b Placing heavy equipment (transformers, generators, etc) close to walls or mainexists for ease of maintenance,A layout example is given in the following diagram (Fig. D12):FinishingGlobal currentconsumerBarycenterPanelshopOfficePaintingFig. D12 : The position of the global current consumer barycenter guides the positioning of power sources© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide7 Choice of architecture details7.2 Centralized or distributed layoutIn centralized layout, current consumers are connected to the power sourcesby a star-connection. Cables are suitable for centralized layout, with point to pointlinks between the MLVS and current consumers or sub-distribution boards (radialdistribution, star- distribution) (Fig. D13):D20Fig. D13: Example of centralized layout with point to point linksIn decentralized layout, current consumers are connected to sources via a busway.Busbar trunking systems are well suited to decentralized layout, to supply manyloads that are spread out, making it easy to change, move or add connections(Fig D14):Fig. D14 : Example of decentralized layout, with busbar trunking links© Schneider Electric - all rights reservedFactors in favour of centralized layout (see summary table in Fig. D15):b Installation flexibility: no,b Load distribution: localized loads (high unit power loads).Factors in favor of decentralized layout:b Installation flexibility: "Implementation" flexibility (moving of workstations, etc…),b Load distribution: uniform distribution of low unit power loadsSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide7 Choice of architecture detailsLoad distributionFlexibility Localized loads IntermediatedistributionUniform distributedNo flexibilityDesign flexibilityCentralizedImplementationflexibility Centralized DecentralizedOperation flexibilityDecentralizedD21Fig. D15 : Recommendations for centralized or decentralized layoutPower supply by cables gives greater independence of circuits (lighting, powersockets, HVAC, motors, auxiliaries, security, etc), reducing the consequences of afault from the point of view of power availability.The use of busbar trunking systems allows load power circuits to be combined andsaves on conductors by taking advantage of a clustering coefficient. The choicebetween cable and busbar trunking, according to the clustering coefficient, allows usto find an economic optimum between investment costs, implementation costs andoperating costs.These two distribution modes are often combined.Presence of back-up generators (Fig. D16)Here we only consider LV back-up generators.The electrical power supply supplied by a back-up generator is produced by analternator, driven by a thermal engine.No power can be produced until the generator has reached its rated speed. This typeof device is therefore not suitable for an uninterrupted power supply.According to the generator’s capacity to supply power to all or only part of theinstallation, there is either total or partial redundancy.A back-up generator functions generally disconnected from the network. A sourceswitching system is therefore necessary.The generator can function permanently or intermittently. Its back-up time dependson the quantity of available fuel.GLV switchboardFig. D16 : Connection of a back-up generatorThe main characteristics to consider for implementing LV back-up generator:b Sensitivity of loads to power interruption,b Availability of the public distribution network,b Other constraints (e.g.: generators compulsory in hospitals or high-vise buildings)The presence of generators can be decided to reduce the energy bill or due to theopportunity for co-generation. These two aspects are not taken into account in thisguide.The presence of a back-up generator is essential if the loads cannot be shed foran indefinite duration (long interruption only acceptable) or if the utility networkavailability is low.Determining the number of back-up generator units is in line with the same criteriaas determining the number of transformers, as well as taking account of economicand availability considerations (redundancy, start-up reliability, maintenance facility).© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide7 Choice of architecture details7.3 Presence of an Uninterruptible Power Supply (UPS)D22The electrical power from a UPS is supplied from a storage unit: batteries or inertiawheel. This system allows us to avoid any power failure. The back-up time of thesystem is limited: from several minutes to several hours.The simultaneous presence of a back-up generator and a UPS unit is used forpermanently supply loads for which no failure is acceptable (Fig. D17). The back-uptime of the battery or the inertia wheel must be compatible with the maximum timefor the generator to start up and be brought on-line.A UPS unit is also used for supply power to loads that are sensitive to disturbances(generating a “clean” voltage that is independent of the network).Main characteristics to be considered for implementing a UPS:b Sensitivity of loads to power interruptions,b Sensitivity of loads to disturbances.The presence of a UPS unit is essential if and only if no failure is acceptable.GLV SwitchboardNormalBy-passNon-criticalcircuitMLVSASIFig. D18 : Radial single feeder configurationCriticalcircuitFig. D17 : Example of connection for a UPS7.4 Configuration of LV circuits© Schneider Electric - all rights reservedMLVSFig. D19 : Two-pole configurationMLVSNOFig. D20 : Two-pole configuration with two ½ MLVS and NO linkMain possible configurations (see figures D18 to D25):b Radial single feeder configuration: This is the reference configuration andthe most simple. A load is connected to only one single source. This configurationprovides a minimum level of availability, since there is no redundancy in case ofpower source failure.b Two-pole configuration: The power supply is provided by 2 transformers,connected to the same MV line. When the transformers are close, they are generallyconnected in parallel to the same MLVS.b Variant: two-pole with two ½ MLVS: In order to increase the availability in caseof failure of the busbars or authorize maintenance on one of the transformers,it is possible to split the MLVS into 2 parts, with a normally open link (NO). Thisconfiguration generally requires an Automatic Transfer Switch, (ATS).b Shedable switchboard (simple disconnectable attachment): A series ofshedable circuits can be connected to a dedicated switchboard. The connection tothe MLVS is interrupted when needed (overload, generator operation, etc)b Interconnected switchboards: If transformers are physically distant from oneanother, they may be connected by a busbar trunking. A critical load can be suppliedby one or other of the transformers. The availability of power is therefore improved,since the load can always be supplied in the case of failure of one of the sources.The redundancy can be:v Total: each transformer being capable of supplying all of the installation,v Partial: each transformer only being able to supply part of the installation. In thiscase, part of the loads must be disconnected (load-shedding) in the case of one ofthe transformers failing.Schneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide7 Choice of architecture detailsLV swichboardFig. D21 : Shedable switchboardMLVSMLVSMLVSb Ring configuration: This configuration can be considered as an extension of theconfiguration with interconnection between switchboards. Typically, 4 transformersconnected to the same MV line, supply a ring using busbar trunking. A given loadis then supplied power by several clustered transformers. This configuration is wellsuited to extended installations, with a high load density (in kVA/m²). If all of the loadscan be supplied by 3 transformers, there is total redundancy in the case of failureof one of the transformers. In fact, each busbar can be fed power by one or otherof its ends. Otherwise, downgraded operation must be considered (with partial loadshedding). This configuration requires special design of the protection plan in orderto ensure discrimination in all of the fault circumstances.b Double-ended power supply: This configuration is implemented in cases wheremaximum availability is required. The principle involves having 2 independent powersources, e.g.:v 2 transformers supplied by different MV lines,v 1 transformer and 1 generator,v 1 transformer and 1 UPS.An automatic transfer switch (ATS) is used to avoid the sources being parallelconnected. This configuration allows preventive and curative maintenance to becarried out on all of the electrical distribution system upstream without interruptingthe power supply.b Configuration combinations: An installation can be made up of several subasssemblieswith different configurations, according to requirements for theavailability of the different types of load. E.g.: generator unit and UPS, choice bysectors (some sectors supplied by cables and others by busbar trunking).D23BusbarorGorUPSFig. D22 : Interconnected switchboardsMLVSBusbarMLVSFig. D24 : Double-ended configuration with automatic transfer switch12 3BusbarBusbarGBusbarMLVSMLVSMLVSMLVSBusbarFig. D23 : Ring configurationFig. D25 : Example of a configuration combination1: Single feeder, 2: Switchboard interconnection, 3: Double-ended© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide7 Choice of architecture detailsFor the different possible configurations, the most probable and usual set ofcharacteristics is given in the following table:D24Characteristic to beconsideredConfigurationRadial Two-pole Sheddable load InterconnectedswitchboardsSite topology Any Any Any 1 level5 to 25000m²Ring1 level5 to 25000m²Location latitude Any Any Any Medium of high Medium or high AnyDouble-endedMaintainability Minimal Standard Minimal Standard Standard EnhancedAnyPower demand < 2500kVA Any Any ≥ 1250kVA > 2500kVA AnyLoad distribution Localized loads Localized loads Localized load Intermediate oruniforme distributionUniform distributionLocalized loadsInterruptions sensitivityLonginterruptionacceptableLonginterruptionacceptableSheddableLonginterruptionacceptableLonginterruptionacceptableShort or nointerruptionDisturbances sensitivity Low sensitivity High sensitivity Low sensitivity High sensitivity High sensitivity High sensitivityOther constraints / / / / / Double-endedloads© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide8 Choice of equipmentThe choice of equipment is step 3 in the design of an electrical installation. The aimof this step is to select equipment from the manufacturers’ catalogues. The choice oftechnological solutions results from the choice of architecture.List of equipment to consider:b MV/LV substation,b MV switchboards,b Transformers,b LV switchboards,b Busbar trunking,b UPS units,b Power factor correction and filtering equipment.D25Criteria to consider:b Atmosphere, environment,b Service index,b Offer availability per country,b Utilities requirements,b Previous architecture choices.The choice of equipment is basically linked to the offer availability in the country. Thiscriterion takes into account the availability of certain ranges of equipment or localtechnical support.The detailed selection of equipment is out of the scope of this document.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide9 Recommendations forarchitecture optimizationThese recommendations are intended to guide the designer towards architectureupgrades which allow him to improve assessment criteria.9.1 On-site workD26To be compatible with the “special” or “critical” work-site time, it is recommended tolimit uncertainties by applying the following recommendations:b Use of proven solutions and equipment that has been validated and tested bymanufacturers (“functional” switchboard or “manufacturer” switchboard according tothe application criticality),b Prefer the implementation of equipment for which there is a reliable distributionnetwork and for which it is possible to have local support (supplier well established),b Prefer the use of factory-built equipment (MV/LV substation, busbar trunking),allowing the volume of operations on site to be limited,b Limit the variety of equipment implemented (e.g. the power of transformers),b Avoid mixing equipment from different manufacturers.9.2 Environmental impactThe optimization of the environmental assessment of an installation will involvereducing:b Power losses at full load and no load during installation operation,b Overall, the mass of materials used to produce the installation.Taken separately and when looking at only one piece of equipment, these 2objectives may seem contradictory. However, when applied to whole installation, itis possible to design the architecture to contribute to both objectives. The optimalinstallation will therefore not be the sum of the optimal equipment taken separately,but the result of an optimization of the overall installation.Figure D26 gives an example of the contribution per equipment category to theweight and energy dissipation for a 3500 kVA installation spread over 10000m².LV switchboardand switchgearLV switchboardand switchgear5 %LV cablesand trunking10 %LV cablesand trunking75 %Transformers46 %Transformers20 %44 %Total loss for equipment considered: 414 MWh Total mass of equipment considered: 18,900 kgFig. D26 : Example of the spread of losses and the weight of material for each equipment category© Schneider Electric - all rights reservedGenerally speaking, LV cables and trunking as well as the MV/LV transformers arethe main contributors to operating losses and the weight of equipment used.Environmental optimization of the installation by the architecture will thereforeinvolve:b reducing the length of LV circuits in the installation,b clustering LV circuits wherever possible to take advantage of the factor ofsimultaneity ks (see chapter A: General rules of electrical installation design, Chapter– Power loading of an installation, 4.3 “Estimation of actual maximum kVA demand”)Schneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide9 Recommendations forarchitecture optimizationObjectivesReducing the length of LVcircuitsResourcesPlacing MV/LV substations as close as possible to the barycenterof all of the LV loads to be suppliedClustering LV circuitsWhen the simultaneity factor of a group of loads to be suppliedis less than 0.7, the clustering of circuits allows us to limit thevolume of conductors supplying power to these loads.In real terms this involves:b setting up sub-distribution switchboards as close as possible tothe barycenter of the groups of loads if they are localized,b setting up busbar trunking systems as close as possible to thebarycenter of the groups of loads if they are distributed.The search for an optimal solution may lead to consider severalclustering scenarios.In all cases, reducing the distance between the barycenter ofa group of loads and the equipment that supplies them powerallows to reduce environmental impact.D27Fig. D27 : Environmental optimization : Objectives and Ressources.As an example figure D28 shows the impact of clustering circuits on reducingthe distance between the barycenter of the loads of an installation and that of thesources considered (MLVS whose position is imposed). This example concerns amineral water bottling plant for which:b the position of electrical equipment (MLVS) is imposed in the premises outside ofthe process area for reasons of accessibility and atmosphere constraints,b the installed power is around 4 MVA.In solution No.1, the circuits are distributed for each workshop.In solution No. 2, the circuits are distributed by process functions (production lines).SolutionBarycenter positionWorkshop 1 Workshop 2 Workshop 3 StorageN°1MLVS areaWorkshop 1BarycenterWorkshop 2BarycenterWorkshop 3BarycenterN°2 Workshop 1 Workshop 2 Workshop 3 StorageMLVS areaFig. D28 : Example of barycenter positioningBarycenterline 1Barycenterline 2Barycenterline 3Barycenterline 3© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide9 Recommendations forarchitecture optimizationD28Without changing the layout of electrical equipment, the second solution allows usto achieve gains of around 15% on the weight of LV cables to be installed (gain onlengths) and a better uniformity of transformer power.To supplement the optimizations carried out in terms of architecture, the followingpoints also contribute to the optimization:b the setting up of LV power factor correction to limit losses in the transformers andLV circuits if this compensation is distributed,b the use of low loss transformers,b the use of aluminum LV busbar trunking when possible, since natural resources ofthis metal are greater.9.3 Preventive maintenance volumeRecommendations for reducing the volume of preventive maintenance:b Use the same recommendations as for reducing the work site time,b Focus maintenance work on critical circuits,b Standardize the choice of equipment,b Use equipment designed for severe atmospheres (requires less maintenance).9.4 Electrical power availabilityRecommendations for improving the electrical power availability:b Reduce the number of feeders per switchboard, in order to limit the effects of apossible failure of a switchboard,b Distributing circuits according to availability requirements,b Using equipment that is in line with requirements (see Service Index, 4.2),b Follow the selection guides proposed for steps 1 & 2 (see Fig. D3 page D5).Recommendations to increase the level of availability:b Change from a radial single feeder configuration to a two-pole configuration,b Change from a two-pole configuration to a double-ended configuration,b Change from a double-ended configuration to a uninterruptible configuration with aUPS unit and a Static Transfer Switchb Increase the level of maintenance (reducing the MTTR, increasing the MTBF)© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide10 GlossaryArchitecture: choice of a single-line diagram and technological solutions, fromconnection to the utility network through to load power supply circuits.Main MV/LV distribution: Level upstream of the architecture, from connectionto the network utility through to LV distribution equipment on the site (MLVS – orequivalent).MLVS – Main Low Voltage Switchboard: Main switchboard downstream of theMV/LV transformer, starting point of power distribution circuits in the installationLV power distribution: intermediate level in the architecture, downstream of themain level through to the sub-distribution switchboards (spatial and functionaldistribution of electrical power in the circuits).LV terminal distribution: Downstream level of the architecture, downstream of thesub-distribution switchboards through to the loads. This level of distribution is notdealt with in this guide.Single-line diagram: general electrical schematic diagram to represent the mainelectrical equipment and their interconnection.MV substation, transformation substation: Enclosures grouping together MVequipment and/or MV/LV transformers. These enclosures can be shared or separate,according to the site layout, or the equipment technology. In certain countries, theMV substation is assimilated with the delivery substation.Technological solution: Resulting from the choice of technology for an installationsub-assembly, from among the different products and equipment proposed by themanufacturer.Characteristics: Technical or environmental data relative to the installation, enablingthe best-suited architecture to be selected.Criteria: Parameters for assessing the installation, enabling selection of thearchitecture that is the best-suited to the needs of the customer.D29© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide11 ID-Spec softwareID-Spec is a new software which aims at helping the designer to be more productivein draft design phase and argue easily his design decisions.It supports the designer in selecting the relevant single line diagram patterns for maindistribution and sub distribution and in adapting these patterns to his project. It alsosupports the designer in equipment technology and rating selection. Its generatesautomatically the corresponding design specification documentation including singleline diagram and its argument, list and specification of the corresponding equipment.D30© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide12 Example: electrical installationin a printworks12.1 Brief descriptionPrinting of personalized mailshots intended for mail order sales.12.2 Installation characteristicsCharacteristicActivitySite topologyLayout latitudeService reliabilityCategoryMechanicalsingle storey building,10000m² (8000m² dedicated to the process, 2000m² forancillary areas)HighStandardD31MaintainabilityInstallation flexibilityPower demandLoad distributionPower interruptions sensitivityDisturbance sensitivityDisturbance capabilityOther constraintsStandardb No flexibility planned:v HVACv Process utilitiesv Office power supplyb Possible flexibility:v finishing, putting in envelopesv special machines, installed at a later datev rotary machines (uncertainty at the draft design stage)3500kVAIntermediate distributionb Sheddable circuits:v offices (apart from PC power sockets)v air conditioning, office heatingv social premisesv maintenance premisesb long interruptions acceptable:v printing machinesv workshop HVAC (hygrometric control)v Finishing, envelope fillingv Process utilities (compressor, recycling of cooled water)b No interruptions acceptable:v servers, office PCsb Average sensitivity:v motors, lightingb High sensitivity:v ITNo special precaution to be taken due to the connection tothe EdF network (low level of disturbance)Non disturbingb Building with lightning classification: lightning surgearresters installedb Power supply by overhead single feeder line12.3 Technological characteristicsCriteriaAtmosphere, environmentService index 211Offer availability by countryOther criteriaCategoryb IP: standard (no dust, no water protection)b IK: standard (use of technical pits, dedicated premises)b °C: standard (temperature regulation)No problem (project carried out in France)Nothing particular© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide12 Example: electrical installationin a printworks12.4 Architecture assessment criteriaD32CriteriaOn-site work timeEnvironmental impactPreventive maintenance costsPower supply availabilityCategorySecondaryMinimal: compliance with European standard regulationsStandardLevel IStep 1: Architecture fundamentalsChoice Main criteria SolutionConnection to upstreamnetworkIsolated sitesingle branch circuitMV Circuits Layout + criticality single feederNumber of transformers Power > 2500kVA 2 x 2000kVANumber and distribution ofsubstationsSurface area and powerdistributionMV Generator Site activity No2 possible solutions: 1substation or 2 substationsb if 1 substations: NO linkbetween MLVSb if 2 substations:interconnected switchboardsMVMVMVMVLVLVLVLVMLVS 1 MLVS 2 MLVS 1 MLVS 2TrunkingFig. D29 : Two possible single-line diagrams© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide12 Example: electrical installationin a printworksStep 2: Architecture details“1 substation” solutionChoice Main criteria SolutionLayout Atmospheric constraint Dedicated premisesCentralized or decentralizedlayoutPresence of back-upgeneratorUniform loads, distributedpower, scalability possibilitiesNon-uniform loads, direct linkfrom MLVSCriticality ≤ lowNetwork availability: standardb Decentralized with busbartrunking:v finishing sector, envelopefillingb Centralized with cables:v special machines,rotary machines, HVAC,process utilities, offices(2 switchboards), office airconditioning, social premises,maintenanceNo back-up generatorPresence of UPS Criticality UPS unit for servers and officePCsLV circuit configuration2 transformers, possiblepartial redundancyb Two-pole, variant 2 ½ MLVS+ NO link (reduction of the Iscby MLVS, no redundancyb process (≤ weak)b sheddable circuit for noncriticalloadsD33MVLVMVLVMLVS 1 MLVS 2ASIHVACTrunkingSheddableOfficesMachinesFig. D30 : Detailed single-line diagram (1 substation)© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

D - MV & LV architecture selection guide12 Example: electrical installationin a printworks12.5 Choice of technological solutions:Choice Main criteria SolutionMV/LV substation Atmosphere, environment indoor (dedicated premises)D34MV switchboard Offer availability by country SM6 (installation produced inFrance)Transformers Atmosphere, environment cast resin transfo (avoidsconstraints related to oil)LV switchboard Atmosphere, IS MLVS: Prisma + PSub-distribution: Prisma +Busbar trunking Installed power to besuppliedUPS unitsPower factor correctionInstalled power to besupplied, back-up timeInstalled power, presence ofharmonicsCanalis KSGalaxy PWLV, standard, automatic(Average Q, ease ofinstallation)“2 substation” solutionDitto apart from:LV circuit: 2 remote MLVS connected via busbar trunkingMVLVMVLVMLVS 1 MLVS 2TrunkingTrunkingSheddableASIHVACMachinesOfficesFig. D31 : Detailed single-line diagram (2 substations)© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Chapter ELV Distribution123ContentsEarthing schemes1.1 Earthing connections E21.2 Definition of standardised earthing schemes E31.3 Characteristics of TT, TN and IT systems E61.4 Selection criteria for the TT, TN and IT systems E81.5 Choice of earthing method - implementation E101.6 Installation and measurements of earth electrodes E11The installation systemE2E152.1 Distribution boards E152.2 Cables and busways E18External influences (IEC 60364-5-51)E253.1 Definition and reference standards E253.2 Classification E253.3 List of external influences E253.4 Protection provided for enclosed equipment: codes IP and IK E28E© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations1 Earthing schemesEIn a building, the connection of all metal partsof the building and all exposed conductive partsof electrical equipment to an earth electrodeprevents the appearance of dangerously highvoltages between any two simultaneouslyaccessible metal parts4Extraneousconductiveparts4HeatingWaterBranchedprotectiveconductorsto individualconsumersGas 5155Fig. E1 : An example of a block of flats in which the mainearthing terminal (6) provides the main equipotential connection;the removable link (7) allows an earth-electrode-resistancecheck273336Mainprotectiveconductor1.1 Earthing connectionsDefinitionsNational and international standards (IEC 60364) clearly define the various elementsof earthing connections. The following terms are commonly used in industry and inthe literature. Bracketed numbers refer to Figure E1 :b Earth electrode (1): A conductor or group of conductors in intimate contact with,and providing an electrical connection with Earth (cf details in section 1.6 of Chapter E.)b Earth: The conductive mass of the Earth, whose electric potential at any point isconventionally taken as zerob Electrically independent earth electrodes: Earth electrodes located at such adistance from one another that the maximum current likely to flow through one ofthem does not significantly affect the potential of the other(s)b Earth electrode resistance: The contact resistance of an earth electrode with theEarthb Earthing conductor (2): A protective conductor connecting the main earthingterminal (6) of an installation to an earth electrode (1) or to other means of earthing(e.g. TN systems);b Exposed-conductive-part: A conductive part of equipment which can be touchedand which is not a live part, but which may become live under fault conditionsb Protective conductor (3): A conductor used for some measures of protection againstelectric shock and intended for connecting together any of the following parts:v Exposed-conductive-partsv Extraneous-conductive-partsv The main earthing terminalv Earth electrode(s)v The earthed point of the source or an artificial neutralb Extraneous-conductive-part: A conductive part liable to introduce a potential,generally earth potential, and not forming part of the electrical installation (4).For example:v Non-insulated floors or walls, metal framework of buildingsv Metal conduits and pipework (not part of the electrical installation) for water, gas,heating, compressed-air, etc. and metal materials associated with themb Bonding conductor (5): A protective conductor providing equipotential bondingb Main earthing terminal (6): The terminal or bar provided for the connection ofprotective conductors, including equipotential bonding conductors, and conductorsfor functional earthing, if any, to the means of earthing.ConnectionsThe main equipotential bonding systemThe bonding is carried out by protective conductors and the aim is to ensure that,in the event of an incoming extraneous conductor (such as a gas pipe, etc.) beingraised to some potential due to a fault external to the building, no difference ofpotential can occur between extraneous-conductive-parts within the installation.The bonding must be effected as close as possible to the point(s) of entry into thebuilding, and be connected to the main earthing terminal (6).However, connections to earth of metallic sheaths of communications cables requirethe authorisation of the owners of the cables.Supplementary equipotential connectionsThese connections are intended to connect all exposed-conductive-parts and allextraneous-conductive-parts simultaneously accessible, when correct conditionsfor protection have not been met, i.e. the original bonding conductors present anunacceptably high resistance.Connection of exposed-conductive-parts to the earth electrode(s)The connection is made by protective conductors with the object of providing a lowresistancepath for fault currents flowing to earth.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations1 Earthing schemesComponents (see Fig. E2)Effective connection of all accessible metal fixtures and all exposed-conductive-partsof electrical appliances and equipment, is essential for effective protection againstelectric shocks.Component parts to consider:as exposed-conductive-partsCablewaysb Conduitsb Impregnated-paper-insulated lead-coveredcable, armoured or unarmouredb Mineral insulated metal-sheathed cable(pyrotenax, etc.)Switchgearb cradle of withdrawable switchgearAppliancesb Exposed metal parts of class 1 insulatedappliancesNon-electrical elementsb metallic fittings associated with cableways(cable trays, cable ladders, etc.)b Metal objects:v Close to aerial conductors or to busbarsv In contact with electrical equipment.as extraneous-conductive-partsElements used in building constructionb Metal or reinforced concrete (RC):v Steel-framed structurev Reinforcement rodsv Prefabricated RC panelsb Surface finishes:v Floors and walls in reinforced concretewithout further surface treatmentvTiled surfacebMetallic covering:vMetallic wall coveringBuilding services elements other than electricalb Metal pipes, conduits, trunking, etc. for gas,water and heating systems, etc.b Related metal components (furnaces, tanks,reservoirs, radiators)b Metallic fittings in wash rooms, bathrooms,toilets, etc.b Metallised papersEComponent parts not to be considered:as exposed-conductive-partsDiverse service channels, ducts, etc.b Conduits made of insulating materialb Mouldings in wood or other insulatingmaterialb Conductors and cables without metallic sheathsSwitchgearb Enclosures made of insulating materialAppliancesb All appliances having class II insulationregardless of the type of exterior envelopeas extraneous-conductive-partsb Wooden-block floorsb Rubber-covered or linoleum-covered floorsb Dry plaster-block partitionb Brick wallsb Carpets and wall-to-wall carpetingFig. E2 : List of exposed-conductive-parts and extraneous-conductive-partsThe different earthing schemes (often referredto as the type of power system or systemearthing arrangements) described characterisethe method of earthing the installationdownstream of the secondary winding of aMV/LV transformer and the means used forearthing the exposed conductive-parts of theLV installation supplied from it1.2 Definition of standardised earthing schemesThe choice of these methods governs the measures necessary for protection againstindirect-contact hazards.The earthing system qualifies three originally independent choices made by thedesigner of an electrical distribution system or installation:b The type of connection of the electrical system (that is generally of the neutralconductor) and of the exposed parts to earth electrode(s)b A separate protective conductor or protective conductor and neutral conductorbeing a single conductorb The use of earth fault protection of overcurrent protective switchgear which clearonly relatively high fault currents or the use of additional relays able to detect andclear small insulation fault currents to earthIn practice, these choices have been grouped and standardised as explained below.Each of these choices provides standardised earthing systems with threeadvantages and drawbacks:b Connection of the exposed conductive parts of the equipment and of the neutralconductor to the PE conductor results in equipotentiality and lower overvoltages butincreases earth fault currentsb A separate protective conductor is costly even if it has a small cross-sectional areabut it is much more unlikely to be polluted by voltage drops and harmonics, etc. than aneutral conductor is. Leakage currents are also avoided in extraneous conductive partsb Installation of residual current protective relays or insulation monitoring devices aremuch more sensitive and permits in many circumstances to clear faults before heavydamage occurs (motors, fires, electrocution). The protection offered is in additionindependent with respect to changes in an existing installation© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations1 Earthing schemesNeutralEarthExposed conductive partsEarthL1L2L3NPETT system (earthed neutral) (see Fig. E3)One point at the supply source is connected directly to earth. All exposedandextraneous-conductive-parts are connected to a separate earth electrode at theinstallation. This electrode may or may not be electrically independent of the sourceelectrode. The two zones of influence may overlap without affecting the operation ofprotective devices.TN systems (exposed conductive parts connected to theneutral)ERnFig. E3 : TT SystemNeutralEarthRnFig. E4 : TN-C systemExposed conductive partsNeutralL1L2L3PENL1L2L3NPEThe source is earthed as for the TT system (above). In the installation, all exposedandextraneous-conductive-parts are connected to the neutral conductor. The severalversions of TN systems are shown below.TN-C system (see Fig. E4)The neutral conductor is also used as a protective conductor and is referred to asa PEN (Protective Earth and Neutral) conductor. This system is not permitted forconductors of less than 10 mm 2 or for portable equipment.The TN-C system requires an effective equipotential environment within theinstallation with dispersed earth electrodes spaced as regularly as possible sincethe PEN conductor is both the neutral conductor and at the same time carries phaseunbalance currents as well as 3 rd order harmonic currents (and their multiples).The PEN conductor must therefore be connected to a number of earth electrodes inthe installation.Caution: In the TN-C system, the “protective conductor” function has priority overthe “neutral function”. In particular, a PEN conductor must always be connected tothe earthing terminal of a load and a jumper is used to connect this terminal to theneutral terminal.TN-S system (see Fig. E5)The TN-S system (5 wires) is obligatory for circuits with cross-sectional areas lessthan 10 mm 2 for portable equipment.The protective conductor and the neutral conductor are separate. On undergroundcable systems where lead-sheathed cables exist, the protective conductor isgenerally the lead sheath. The use of separate PE and N conductors (5 wires)is obligatory for circuits with cross-sectional areas less than 10 mm 2 for portableequipment.TN-C-S system (see Fig. E6 below and Fig. E7 next page)RnFig. E5 : TN-S systemThe TN-C and TN-S systems can be used in the same installation. In the TN-C-Ssystem, the TN-C (4 wires) system must never be used downstream of the TN-S(5 wires) system, since any accidental interruption in the neutral on the upstreampart would lead to an interruption in the protective conductor in the downstream partand therefore a danger.PENPE5 x 50 mm 2L1L2L3NPE16 mm2 6 mm2 16 mm2 16 mm2PENBadBadTN-C scheme not permitteddownstream of TN-S scheme© Schneider Electric - all rights reservedFig. E6 : TN-C-S systemSchneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations1 Earthing schemes4 x 95 mm 2L1L2L3PENN16 mm 2 10 mm 2 6 mm 2 6 mm 2PENPENCorrect Incorrect Correct IncorrectPEN connected to the neutralterminal is prohibitedS < 10 mm 2TNC prohibitedENeutralExposed conductive partsFig. E7 : Connection of the PEN conductor in the TN-C systemIsolated orimpedance-earthedFig. E8 : IT system (isolated neutral)MV/LVEarthL1L2L3NPEIT system (isolated or impedance-earthed neutral)IT system (isolated neutral)No intentional connection is made between the neutral point of the supply sourceand earth (see Fig. E8).Exposed- and extraneous-conductive-parts of the installation are connected to anearth electrode.In practice all circuits have a leakage impedance to earth, since no insulationis perfect. In parallel with this (distributed) resistive leakage path, there is thedistributed capacitive current path, the two paths together constituting the normalleakage impedance to earth (see Fig. E9).Example (see Fig. E10)In a LV 3-phase 3-wire system, 1 km of cable will have a leakage impedance due toC1, C2, C3 and R1, R2 and R3 equivalent to a neutral earth impedance Zct of 3,000to 4,000 Ω, without counting the filtering capacitances of electronic devices.C1C2C3R1R2R3IT system (impedance-earthed neutral)An impedance Zs (in the order of 1,000 to 2,000 Ω) is connected permanentlybetween the neutral point of the transformer LV winding and earth (see Fig. E11).All exposed- and extraneous-conductive-parts are connected to an earth electrode.The reasons for this form of power-source earthing are to fix the potential of a smallnetwork with respect to earth (Zs is small compared to the leakage impedance) and toreduce the level of overvoltages, such as transmitted surges from the MV windings,static charges, etc. with respect to earth. It has, however, the effect of slightlyincreasing the first-fault current level.Fig. E9 : IT system (isolated neutral)MV/LVMV/LVZctZsFig. E10 : Impedance equivalent to leakage impedances in anIT systemFig. E11 : IT system (impedance-earthed neutral)© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations1 Earthing schemes1.3 Characteristics of TT, TN and IT systemsThe TT system:b Technique for the protection of persons: theexposed conductive parts are earthed andresidual current devices (RCDs) are usedb Operating technique: interruption for the firstinsulation faultTT system (see Fig. E12)EFig. E12 : TT systemNote: If the exposed conductive parts are earthed at a number of points, an RCDmust be installed for each set of circuits connected to a given earth electrode.The TN system:b Technique for the protection of persons:v Interconnection and earthing of exposedconductive parts and the neutral are mandatoryv Interruption for the first fault using overcurrentprotection (circuit-breakers or fuses)b Operating technique: interruption for the firstinsulation faultMain characteristicsb Simplest solution to design and install. Used in installations supplied directly by thepublic LV distribution network.b Does not require continuous monitoring during operation (a periodic check on theRCDs may be necessary).b Protection is ensured by special devices, the residual current devices (RCD), whichalso prevent the risk of fire when they are set to y 500 mA.b Each insulation fault results in an interruption in the supply of power, however theoutage is limited to the faulty circuit by installing the RCDs in series (selective RCDs)or in parallel (circuit selection).b Loads or parts of the installation which, during normal operation, cause high leakagecurrents, require special measures to avoid nuisance tripping, i.e. supply the loadswith a separation transformer or use specific RCDs (see section 5.1 in chapter F).TN system (see Fig. E13 and Fig. E14 )PENFig. E13 : TN-C system© Schneider Electric - all rights reservedFig. E14 : TN-S systemNPESchneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations1 Earthing schemesMain characteristicsb Generally speaking, the TN system:v requires the installation of earth electrodes at regular intervals throughout theinstallationv Requires that the initial check on effective tripping for the first insulation faultbe carried out by calculations during the design stage, followed by mandatorymeasurements to confirm tripping during commissioningv Requires that any modification or extension be designed and carried out by aqualified electricianv May result, in the case of insulation faults, in greater damage to the windings ofrotating machinesv May, on premises with a risk of fire, represent a greater danger due to the higherfault currentsb In addition, the TN-C system:v At first glance, would appear to be less expensive (elimination of a device pole andof a conductor)v Requires the use of fixed and rigid conductorsv Is forbidden in certain cases:- Premises with a risk of fire- For computer equipment (presence of harmonic currents in the neutral)b In addition, the TN-S system:v May be used even with flexible conductors and small conduitsv Due to the separation of the neutral and the protection conductor, provides a cleanPE (computer systems and premises with special risks)EIT system:b Protection technique:v Interconnection and earthing of exposedconductive partsv Indication of the first fault by an insulationmonitoring device (IMD)v Interruption for the second fault usingovercurrent protection (circuit-breakers or fuses)b Operating technique:v Monitoring of the first insulation faultv Mandatory location and clearing of the faultv Interruption for two simultaneous insulationfaultsIT system (see Fig. E15)CardewIMDFig. E15 : IT systemMain characteristicsb Solution offering the best continuity of service during operationb Indication of the first insulation fault, followed by mandatory location and clearing,ensures systematic prevention of supply outagesb Generally used in installations supplied by a private MV/LV or LV/LV transformerb Requires maintenance personnel for monitoring and operationb Requires a high level of insulation in the network (implies breaking up the networkif it is very large and the use of circuit-separation transformers to supply loads withhigh leakage currents)b The check on effective tripping for two simultaneous faults must be carried out bycalculations during the design stage, followed by mandatory measurements duringcommissioning on each group of interconnected exposed conductive partsb Protection of the neutral conductor must be ensured as indicated in section 7.2 ofChapter G© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations1 Earthing schemesESelection does not depend on safety criteria.The three systems are equivalent in termsof protection of persons if all installation andoperating rules are correctly followed.The selection criteria for the best system(s)depend on the regulatory requirements,the required continuity of service, operatingconditions and the types of network and loads.1.4 Selection criteria for the TT, TN and IT systemsIn terms of the protection of persons, the three system earthing arrangements(SEA) are equivalent if all installation and operating rules are correctly followed.Consequently, selection does not depend on safety criteria.It is by combining all requirements in terms of regulations, continuity of service,operating conditions and the types of network and loads that it is possible todetermine the best system(s) (see Fig. E16).Selection is determined by the following factors:b Above all, the applicable regulations which in some cases impose certain types ofSEAb Secondly, the decision of the owner if supply is via a private MV/LV transformer(MV subscription) or the owner has a private energy source (or a separate-windingtransformer)If the owner effectively has a choice, the decision on the SEA is taken followingdiscussions with the network designer (design office, contractor)The discussions must cover:b First of all, the operating requirements (the required level of continuity of service)and the operating conditions (maintenance ensured by electrical personnel or not,in-house personnel or outsourced, etc.)b Secondly, the particular characteristics of the network and the loads(see Fig. E17 next page)© Schneider Electric - all rights reservedTT TN-S TN-C IT1 IT2 CommentsElectrical characteristicsFault current - - - - - + - - Only the IT system offers virtually negligible first-fault currentsFault voltage - - - + - In the IT system, the touch voltage is very low for the first fault,but is considerable for the secondTouch voltage +/- - - - + - In the TT system, the touch voltage is very low if system isequipotential, otherwise it is highProtectionProtection of persons against indirect contact + + + + + All SEAs (system earthing arrangement) are equivalent,if the rules are followedProtection of persons with emergency + - - + - Systems where protection is ensured by RCDs are not sensitivegenerating setsto a change in the internal impedance of the sourceProtection against fire (with an RCD) + + Not + + All SEAs in which RCDs can be used are equivalent.allowedThe TN-C system is forbidden on premises where there is a risk of fireOvervoltagesContinuous overvoltage + + + - + A phase-to-earth overvoltage is continuous in the IT systemif there is a first insulation faultTransient overvoltage + - - + - Systems with high fault currents may cause transient overvoltagesOvervoltage if transformer breakdown - + + + + In the TT system, there is a voltage imbalance between(primary/secondary)the different earth electrodes. The other systems are interconnectedto a single earth electrodeElectromagnetic compatibilityImmunity to nearby lightning strikes - + + + + In the TT system, there may be voltage imbalances betweenthe earth electrodes. In the TT system, there is a significant currentloop between the two separate earth electrodesImmunity to lightning strikes on MV lines - - - - - All SEAs are equivalent when a MV line takes a direct lightning strikeContinuous emission of an + + - + + Connection of the PEN to the metal structures of the building iselectromagnetic fieldconducive to the continuous generation of electromagnetic fieldsTransient non-equipotentiality of the PE + - - + - The PE is no longer equipotential if there is a high fault currentContinuity of serviceInterruption for first fault - - - + + Only the IT system avoids tripping for the first insulation faultVoltage dip during insulation fault + - - + - The TN-S, TNC and IT (2 nd fault) systems generate high faultcurrents which may cause phase voltage dipsInstallationSpecial devices - + + - - The TT system requires the use of RCDs. The IT system requiresthe use of IMDsNumber of earth electrodes - + + -/+ -/+ The TT system requires two distinct earth electrodes. The IT systemoffers a choice between one or two earth electrodesNumber of cables - - + - - Only the TN-C system offers, in certain cases, a reduction inthe number of cablesMaintenanceCost of repairs - - - - - - - - The cost of repairs depends on the damage caused bythe amplitude of the fault currentsInstallation damage + - - ++ - Systems causing high fault currents require a check onthe installation after clearing the faultFig. E16 : Comparison of system earthing arrangementsSchneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations1 Earthing schemesType of network Advised Possible Not advisedVery large network with high-quality earth electrodes TT, TN, IT (1)for exposed conductive parts (10 Ω max.)or mixedVery large network with low-quality earth electrodes TN TN-S IT (1)for exposed conductive parts (> 30 Ω)TN-CDisturbed area (storms) TN TT IT (2)(e.g. television or radio transmitter)Network with high leakage currents (> 500 mA) TN (4) IT (4)TT(3) (4)Network with outdoor overhead lines TT (5) TN (5) (6) IT (6)Emergency standby generator set IT TT TN (7)Type of loadsLoads sensitive to high fault currents (motors, etc.) IT TT TN (8)ELoads with a low insulation level (electric furnaces, TN (9) TT (9) ITwelding machines, heating elements, immersion heaters,equipment in large kitchens)Numerous phase-neutral single-phase loads TT (10) IT (10)(mobile, semi-fixed, portable) TN-S TN-C (10)Loads with sizeable risks (hoists, conveyers, etc.) TN (11) TT (11) IT (11)Numerous auxiliaries (machine tools) TN-S TN-C TT (12)IT(12 bis)MiscellaneousSupply via star-star connected power transformer (13) TT IT IT (13)without neutral with neutralPremises with risk of fire IT (15) TN-S (15) TN-C (14)Increase in power level of LV utility subscription, TT (16)LVrequiring a private substationMV/LVInstallation with frequent modifications TT (17) TN (18)IT (18)Installation where the continuity of earth circuits is uncertain TT (19) TN-S TN-C(work sites, old installations) IT (19)Electronic equipment (computers, PLCs) TN-S TT TN-CMachine control-monitoring network, PLC sensors and actuators IT (20) TN-S, TTTT (15)(1) When the SEA is not imposed by regulations, it is selected according to the level of operating characteristics (continuity of service that ismandatory for safety reasons or desired to enhance productivity, etc.)Whatever the SEA, the probability of an insulation failure increases with the length of the network. It may be a good idea to break up thenetwork, which facilitates fault location and makes it possible to implement the system advised above for each type of application.(2) The risk of flashover on the surge limiter turns the isolated neutral into an earthed neutral. These risks are high for regions with frequentthunder storms or installations supplied by overhead lines. If the IT system is selected to ensure a higher level of continuity of service, thesystem designer must precisely calculate the tripping conditions for a second fault.(3) Risk of RCD nuisance tripping.(4) Whatever the SEA, the ideal solution is to isolate the disturbing section if it can be easily identified.(5) Risks of phase-to-earth faults affecting equipotentiality.(6) Insulation is uncertain due to humidity and conducting dust.(7) The TN system is not advised due to the risk of damage to the generator in the case of an internal fault. What is more, when generator setssupply safety equipment, the system must not trip for the first fault.(8) The phase-to-earth current may be several times higher than In, with the risk of damaging or accelerating the ageing of motor windings, or ofdestroying magnetic circuits.(9) To combine continuity of service and safety, it is necessary and highly advised, whatever the SEA, to separate these loads from the rest ofthe installation (transformers with local neutral connection).(10) When load equipment quality is not a design priority, there is a risk that the insulation resistance will fall rapidly. The TT system with RCDsis the best means to avoid problems.(11) The mobility of this type of load causes frequent faults (sliding contact for bonding of exposed conductive parts) that must be countered.Whatever the SEA, it is advised to supply these circuits using transformers with a local neutral connection.(12) Requires the use of transformers with a local TN system to avoid operating risks and nuisance tripping at the first fault (TT) or a double fault (IT).(12 bis) With a double break in the control circuit.(13) Excessive limitation of the phase-to-neutral current due to the high value of the zero-phase impedance (at least 4 to 5 times the directimpedance). This system must be replaced by a star-delta arrangement.(14) The high fault currents make the TN system dangerous. The TN-C system is forbidden.(15) Whatever the system, the RCD must be set to Δn y 500 mA.(16) An installation supplied with LV energy must use the TT system. Maintaining this SEA means the least amount of modifications on theexisting network (no cables to be run, no protection devices to be modified).(17) Possible without highly competent maintenance personnel.(18) This type of installation requires particular attention in maintaining safety. The absence of preventive measures in the TN system meanshighly qualified personnel are required to ensure safety over time.(19) The risks of breaks in conductors (supply, protection) may cause the loss of equipotentiality for exposed conductive parts. A TT system or aTN-S system with 30 mA RCDs is advised and is often mandatory. The IT system may be used in very specific cases.(20) This solution avoids nuisance tripping for unexpected earth leakage.Fig. E17 : Influence of networks and loads on the selection of system earthing arrangements© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations1 Earthing schemes1.5 Choice of earthing method - implementationAfter consulting applicable regulations, Figures E16 and E17 can be used as an aidin deciding on divisions and possible galvanic isolation of appropriate sections of aproposed installation.E10Division of sourceThis technique concerns the use of several transformers instead of employing onehigh-rated unit. In this way, a load that is a source of network disturbances (largemotors, furnaces, etc.) can be supplied by its own transformer.The quality and continuity of supply to the whole installation are thereby improved.The cost of switchgear is reduced (short-circuit current level is lower).The cost-effectiveness of separate transformers must be determined on a case bycase basis.Network islandsThe creation of galvanically-separated “islands” by means of LV/LV transformersmakes it possible to optimise the choice of earthing methods to meet specificrequirements (see Fig. E18 and Fig. E19 ).MV/LVIT systemIMDLV/LVTN-S systemFig. E18 : TN-S island within an IT systemMV/LVTN-STN-S systemLV/LVITIMDLV/LVITIMDHospitalOperating roomFig. E19 : IT islands within a TN-S system© Schneider Electric - all rights reservedConclusionThe optimisation of the performance of the whole installation governs the choice ofearthing system.Including:b Initial investments, andb Future operational expenditures, hard to assess, that can arise from insufficientreliability, quality of equipment, safety, continuity of service, etc.An ideal structure would comprise normal power supply sources, local reservepower supply sources (see section 1.4 of Chapter E) and the appropriate earthingarrangements.Schneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations1 Earthing schemesA very effective method of obtaining a lowresistanceearth connection is to bury aconductor in the form of a closed loop in thesoil at the bottom of the excavation for buildingfoundations.The resistance R of such an electrode (inhomogeneous soil) is given (approximately) inohms by: R = 2 whereLL L = length of the buried conductor in metres in metresρ = soil resistivity in ohm-metresFor n rods: R = 1 n Lwhere1.6 Installation and measurements of earthelectrodesThe quality of an earth electrode (resistance as low as possible) depends essentiallyon two factors:b Installation methodb Type of soilInstallation methodsThree common types of installation will be discussed:Buried ring (see Fig. E20)This solution is strongly recommended, particularly in the case of a new building.The electrode should be buried around the perimeter of the excavation made forthe foundations. It is important that the bare conductor be in intimate contact withthe soil (and not placed in the gravel or aggregate hard-core, often forming a basefor concrete). At least four (widely-spaced) vertically arranged conductors from theelectrode should be provided for the installation connections and, where possible,any reinforcing rods in concrete work should be connected to the electrode.The conductor forming the earth electrode, particularly when it is laid in anexcavation for foundations, must be in the earth, at least 50 cm below the hard-coreor aggregate base for the concrete foundation. Neither the electrode nor the verticalrising conductors to the ground floor, should ever be in contact with the foundationconcrete.For existing buildings, the electrode conductor should be buried around the outsidewall of the premises to a depth of at least 1 metre. As a general rule, all verticalconnections from an electrode to above-ground level should be insulated for thenominal LV voltage (600-1,000 V).The conductors may be:b Copper: Bare cable (u 25 mm 2 ) or multiple-strip (u 25 mm 2 and u 2 mm thick)b Aluminium with lead jacket: Cable (u 35 mm 2 )b Galvanised-steel cable: Bare cable (u 95 mm 2 ) or multiple-strip (u 100 mm 2and u 3 mm thick)The approximate resistance R of the electrode in ohms:R = 2 whereLL = length where of the buried conductor in metresL = length of conductor in metresρ = resistivity of the soil in ohm-metres (see “Influence of the type of soil” next page)Earthing rods (see Fig. E21)Vertically driven earthing rods are often used for existing buildings, and for improving(i.e. reducing the resistance of) existing earth electrodes.The rods may be:b Copper or (more commonly) copper-clad steel. The latter are generally 1 or2 metres long and provided with screwed ends and sockets in order to reachconsiderable depths, if necessary (for instance, the water-table level in areas of highsoil resistivity)b Galvanised (see note (1) next page) steel pipe u 25 mm diameter orrod u 15 mm diameter, u 2 metres long in each case.E11L u 3 mFig. E20 : Conductor buried below the level of the foundations,i.e. not in the concreteFig. E21 : Earthing rodsRods connected in parallel© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations1 Earthing schemesE12For a vertical plate electrode: R = 0.8 LMeasurements on earth electrodes in similarsoils are useful to determine the resistivityvalue to be applied for the design of an earthelectrodesystemIt is often necessary to use more than one rod, in which case the spacing betweenthem should exceed the depth to which they are driven, by a factor of 2 to 3.The total resistance (in homogeneous soil) is then equal to the resistance of one rod,divided by the number of rods in question. The approximate resistance R obtained is:R = 1 if the distance separating the rods > 4Ln LwherewhereL = the length of the rod in metresρ = resistivity of the soil in ohm-metres (see “Influence of the type of soil” below)n = the number of rodsVertical plates (see Fig. E22)Rectangular plates, each side of which must be u 0.5 metres, are commonly used asearth electrodes, being buried in a vertical plane such that the centre of the plate isat least 1 metre below the surface of the soil.The plates may be:b Copper of 2 mm thicknessb Galvanised (1) steel of 3 mm thicknessThe resistance R in ohms is given (approximately), by:R = 0.8 LL = the perimeter of the plate in metresρ = resistivity of the soil in ohm-metres (see “Influence of the type of soil” below)Influence of the type of soilType of soilMean value of resistivityin ΩmSwampy soil, bogs 1 - 30Silt alluvium 20 - 100Humus, leaf mould 10 - 150Peat, turf 5 - 100Soft clay 50Marl and compacted clay 100 - 200Jurassic marl 30 - 40Clayey sand 50 - 500Siliceous sand 200 - 300Stoney ground 1,500 - 3,000Grass-covered-stoney sub-soil 300 - 500Chalky soil 100 - 300Limestone 1,000 - 5,000Fissured limestone 500 - 1,000Schist, shale 50 - 300Mica schist 800Granite and sandstone 1,500 - 10,000Modified granite and sandstone 100 - 600Fig. E23 : Resistivity (Ωm) for different types of soil2 mm thickness (Cu)Type of soilAverage value of resistivityin ΩmFertile soil, compacted damp fill 50Arid soil, gravel, uncompacted non-uniform fill 500Stoney soil, bare, dry sand, fissured rocks 3,000© Schneider Electric - all rights reservedFig. E22 : Vertical plate(1) Where galvanised conducting materials are used for earthelectrodes, sacrificial cathodic protection anodes may benecessary to avoid rapid corrosion of the electrodes wherethe soil is aggressive. Specially prepared magnesium anodes(in a porous sack filled with a suitable “soil”) are available fordirect connection to the electrodes. In such circumstances, aspecialist should be consultedFig. E24 : Average resistivity (Ωm) values for approximate earth-electSchneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations1 Earthing schemesMeasurement and constancy of the resistance between anearth electrode and the earthThe resistance of the electrode/earth interface rarely remains constantAmong the principal factors affecting this resistance are the following:b Humidity of the soilThe seasonal changes in the moisture content of the soil can be significant at depthsof up to 2 meters.At a depth of 1 metre the resistivity and therefore the resistance can vary by a ratioof 1 to 3 between a wet winter and a dry summer in temperate regionsb FrostFrozen earth can increase the resistivity of the soil by several orders of magnitude.This is one reason for recommending the installation of deep electrodes, in particularin cold climatesb AgeingThe materials used for electrodes will generally deteriorate to some extent forvarious reasons, for example:v Chemical reactions (in acidic or alkaline soils)v Galvanic: due to stray DC currents in the earth, for example from electric railways,etc. or due to dissimilar metals forming primary cells. Different soils acting onsections of the same conductor can also form cathodic and anodic areas withconsequent loss of surface metal from the latter areas. Unfortunately, the mostfavourable conditions for low earth-electrode resistance (i.e. low soil resistivity) arealso those in which galvanic currents can most easily flow.b OxidationBrazed and welded joints and connections are the points most sensitive to oxidation.Thorough cleaning of a newly made joint or connection and wrapping with a suitablegreased-tape binding is a commonly used preventive measure.Measurement of the earth-electrode resistanceThere must always be one or more removable links to isolate an earth electrode sothat it can be tested.There must always be removable links which allow the earth electrode to be isolatedfrom the installation, so that periodic tests of the earthing resistance can be carriedout. To make such tests, two auxiliary electrodes are required, each consisting of avertically driven rod.b Ammeter method (see Fig. E25)E13AUt1Tt2Fig. E25 : Measurement of the resistance to earth of the earth electrode of an installation bymeans of an ammeterUA = RT+ Rt= Tt11i1UB = Rt+ R t tt = 1 21 2i2UC = Rt+ R t TT = 22i3When the source voltage U is constant (adjusted to be the same value for each test)then:URT = 1i + 1 i 12 i1 3 2 © Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations1 Earthing schemesE14In order to avoid errors due to stray earth currents (galvanic -DC- or leakage currentsfrom power and communication networks and so on) the test current should beAC, but at a different frequency to that of the power system or any of its harmonics.Instruments using hand-driven generators to make these measurements usuallyproduce an AC voltage at a frequency of between 85 Hz and 135 Hz.The distances between the electrodes are not critical and may be in differentdirections from the electrode being tested, according to site conditions. A number oftests at different spacings and directions are generally made to cross-check the testresults.b Use of a direct-reading earthing-resistance ohmmeterThese instruments use a hand-driven or electronic-type AC generator, togetherwith two auxiliary electrodes, the spacing of which must be such that the zone ofinfluence of the electrode being tested should not overlap that of the test electrode (C).The test electrode (C) furthest from the electrode (X) under test, passes a currentthrough the earth and the electrode under test, while the second test electrode (P)picks up a voltage. This voltage, measured between (X) and (P), is due to the testcurrent and is a measure of the contact resistance (of the electrode under test) withearth. It is clear that the distance (X) to (P) must be carefully chosen to give accurateresults. If the distance (X) to (C) is increased, however, the zones of resistance ofelectrodes (X) and (C) become more remote, one from the other, and the curve ofpotential (voltage) becomes more nearly horizontal about the point (O).In practical tests, therefore, the distance (X) to (C) is increased until readings takenwith electrode (P) at three different points, i.e. at (P) and at approximately 5 metreson either side of (P), give similar values. The distance (X) to (P) is generally about0.68 of the distance (X) to (C).VGXVGPICvoltage-drop dueto the resistanceof electrode (X)OVGvoltage-drop dueto the resistanceof electrode (C)a) the principle of measurement is based on assumed homogeneous soil conditions. Where thezones of influence of electrodes C and X overlap, the location of test electrode P is difficult todetermine for satisfactory results.XPCO© Schneider Electric - all rights reservedb) showing the effect on the potential gradient when (X) and (C) are widely spaced. The locationof test electrode P is not critical and can be easily determined.Fig. E26 : Measurement of the resistance to the mass of earth of electrode (X) using an earthelectrode-testingohmmeter.Schneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations2 The installation systemDistribution switchboards, including the mainLV switchboard (MLVS), are critical to thedependability of an electrical installation.They must comply with well-defined standardsgoverning the design and construction ofLV switchgear assembliesThe load requirements dictate the type ofdistribution switchboard to be installed2.1 Distribution switchboardsA distribution switchboard is the point at which an incoming-power supply dividesinto separate circuits, each of which is controlled and protected by the fuses orswitchgear of the switchboard. A distribution switchboard is divided into a numberof functional units, each comprising all the electrical and mechanical elementsthat contribute to the fulfilment of a given function. It represents a key link in thedependability chain.Consequently, the type of distribution switchboard must be perfectly adapted to itsapplication. Its design and construction must comply with applicable standards andworking practises.The distribution switchboard enclosure provides dual protection:b Protection of switchgear, indicating instruments, relays, fusegear, etc. againstmechanical impacts, vibrations and other external influences likely to interfere withoperational integrity (EMI, dust, moisture, vermin, etc.)b The protection of human life against the possibility of direct and indirect electricshock (see degree of protection IP and the IK index in section 3.3 of Chapter E).Types of distribution switchboardsDistribution switchboards may differ according to the kind of application and thedesign principle adopted (notably in the arrangement of the busbars).Distribution switchboards according to specific applicationsThe principal types of distribution switchboards are:b The main LV switchboard - MLVS - (see Fig. E27a)b Motor control centres - MCC - (see Fig. E27b)b Sub-distribution switchboards (see Fig. E28)b Final distribution switchboards (see Fig. E29)Distribution switchboards for specific applications (e.g. heating, lifts, industrialprocesses) can be located:b Adjacent to the main LV switchboard, orb Near the application concernedSub-distribution and final distribution switchboards are generally distributedthroughout the site.E15abFig. E27 : [a] A main LV switchboard - MLVS - (Prisma Plus P) with incoming circuits in the formof busways - [b] A LV motor control centre - MCC - (Okken)a b cFig. E28 : A sub-distribution switchboard (Prisma Plus G)Fig. E29 : Final distribution switchboards [a] Prisma Plus G Pack; [b] Kaedra; [c] mini-Pragma© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations2 The installation systemE16A distinction is made between:b Traditional distribution switchboards in whichswitchgear and fusegear, etc. are fixed to achassis at the rear of an enclosureb Functional distribution switchboards forspecific applications, based on modular andstandardised design.Fig. E30 : Assembly of a final distribution switchboard withfixed functional units (Prisma Plus G)Fig. E31 : Distribution switchboard with disconnectablefunctional unitsTwo technologies of distribution switchboardsTraditional distribution switchboardsSwitchgear and fusegear, etc. are normally located on a chassis at the rear of theenclosure. Indications and control devices (meters, lamps, pushbuttons, etc.) aremounted on the front face of the switchboard.The placement of the components within the enclosure requires very careful study,taking into account the dimensions of each item, the connections to be made to it,and the clearances necessary to ensure safe and trouble-free operation. .Functional distribution switchboardsGenerally dedicated to specific applications, these distribution switchboards aremade up of functional modules that include switchgear devices together withstandardised accessories for mounting and connections, ensuring a high level ofreliability and a great capacity for last-minute and future changes.b Many advantagesThe use of functional distribution switchboards has spread to all levels of LVelectrical distribution, from the main LV switchboard (MLVS) to final distributionswitchboards, due to their many advantages:v System modularity that makes it possible to integrate numerous functions in asingle distribution switchboard, including protection, control, technical managementand monitoring of electrical installations. Modular design also enhances distributionswitchboard maintenance, operation and upgradesv Distribution switchboard design is fast because it simply involves adding functionalmodulesv Prefabricated components can be mounted fasterv Finally, these distribution switchboards are subjected to type tests that ensure ahigh degree of dependability.The new Prisma Plus G and P ranges of functional distribution switchboards fromSchneider Electric cover needs up to 3200 A and offer:v Flexibility and ease in building distribution switchboardsv Certification of a distribution switchboard complying with standard IEC 60439 andthe assurance of servicing under safe conditionsv Time savings at all stages, from design to installation, operation and modificationsor upgradesv Easy adaptation, for example to meet the specific work habits and standards indifferent countriesFigures E27a, E28 and E29 show examples of functional distribution switchboardsranging for all power ratings and figure E27b shows a high-power industrial functionaldistribution switchboard.b Main types of functional unitsThree basic technologies are used in functional distribution switchboards.v Fixed functional units (see Fig. E30)These units cannot be isolated from the supply so that any intervention formaintenance, modifications and so on, requires the shutdown of the entiredistribution switchboard. Plug-in or withdrawable devices can however be used tominimise shutdown times and improve the availability of the rest of the installation.v Disconnectable functional units (see Fig. E31)Each functional unit is mounted on a removable mounting plate and provided with ameans of isolation on the upstream side (busbars) and disconnecting facilities on thedownstream (outgoing circuit) side. The complete unit can therefore be removed forservicing, without requiring a general shutdown.v Drawer-type withdrawable functional units (see Fig. E32)The switchgear and associated accessories for a complete function are mounted ona drawer-type horizontally withdrawable chassis. The function is generally complexand often concerns motor control.Isolation is possible on both the upstream and downstream sides by the completewithdrawal of the drawer, allowing fast replacement of a faulty unit without deenergisingthe rest of the distribution switchboard.© Schneider Electric - all rights reservedFig. E32 : Distribution switchboard with withdrawable functionalunits in drawersSchneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations2 The installation systemCompliance with applicable standards isessential in order to ensure an adequatedegree of dependabilityThree elements of standard IEC 60439-1contribute significantly to dependability:b Clear definition of functional unitsb Forms of separation between adjacentfunctional units in accordance with userrequirementsb Clearly defined routine tests and type testsStandardsDifferent standardsCertain types of distribution switchboards (in particular, functional distributionswitchboards) must comply with specific standards according to the application orenvironment involved.The reference international standard is IEC 60439-1 type-tested and partially typetestedassembliesStandard IEC 60439-1b Categories of assembliesStandard IEC 60439-1 distinguishes between two categories of assemblies:v Type-tested LV switchgear and controlgear assemblies (TTA), which do not divergesignificantly from an established type or system for which conformity is ensured bythe type tests provided in the standardv Partially type-tested LV switchgear and controlgear assemblies (PTTA), which maycontain non-type-tested arrangements provided that the latter are derived from typetestedarrangementsWhen implemented in compliance with professional work standards andmanufacturer instructions by qualified personnel, they offer the same level of safetyand quality.b Functional unitsThe same standard defines functional units:v Part of an assembly comprising all the electrical and mechanical elements thatcontribute to the fulfilment of the same functionv The distribution switchboard includes an incoming functional unit and one or morefunctional units for outgoing circuits, depending on the operating requirements of theinstallationWhat is more, distribution switchboard technologies use functional units that may befixed, disconnectable or withdrawable (see section 3.1 of Chapter E).b Forms (see Fig. E33)Separation of functional units within the assembly is provided by forms that arespecified for different types of operation.The various forms are numbered from 1 to 4 with variations labelled “a” or “b”. Eachstep up (from 1 to 4) is cumulative, i.e. a form with a higher number includes thecharacteristics of forms with lower numbers. The standard distinguishes:v Form 1: No separationv Form 2: Separation of busbars from the functional unitsv Form 3: Separation of busbars from the functional units and separation of allfunctional units, one from another, except at their output terminalsv Form 4: As for Form 3, but including separation of the outgoing terminals of allfunctional units, one from anotherThe decision on which form to implement results from an agreement between themanufacturer and the user.The Prima Plus functional range offers solutions for forms 1, 2b, 3b, 4a, 4b.E17Form 1 Form 2a Form 2b Form 3aForm 3b Form 4a Form 4bFig. E33 : Representation of different forms of LV functional distribution switchboardsBusbarSeparation© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations2 The installation systemE18Total accessibility of electrical information andintelligent distribution switchboards are now arealityb Type tests and routine testsThey ensure compliance of each distribution switchboard with the standard. Theavailability of test documents certified by independent organisations is a guaranteefor users.Remote monitoring and control of the electrical installationRemote monitoring and control are no longer limited to large installations.These functions are increasingly used and provide considerable cost savings.The main potential advantages are:b Reductions in energy billsb Reductions in structural costs to maintain the installation in running orderb Better use of the investment, notably concerning optimisation of the installation lifecycleb Greater satisfaction for energy users (in a building or in process industries) due toimproved power availability and/or qualityThe above possibilities are all the more an option given the current deregulation ofthe electrical-energy sector.Modbus is increasingly used as the open standard for communication within thedistribution switchboard and between the distribution switchboard and customerpower monitoring and control applications. Modbus exists in two forms, twisted pair(RS 485) and Ethernet-TCP/IP (IEEE 802.3).The www.modbus.org site presents all bus specifications and constantly updates thelist of products and companies using the open industrial standard.The use of web technologies has largely contributed to wider use by drasticallyreducing the cost of accessing these functions through the use of an interface that isnow universal (web pages) and a degree of openness and upgradeability that simplydid not exist just a few years ago.Two types of distribution are possible:b By insulated wires and cablesb By busbar trunking (busways)2.2 Cables and busway trunkingDistribution by insulated conductors and cablesDefinitionsb ConductorA conductor comprises a single metallic core with or without an insulating envelope.b CableA cable is made up of a number of conductors, electrically separated, but joinedmechanically, generally enclosed in a protective flexible sheath.b CablewayThe term cableway refers to conductors and/or cables together with the means ofsupport and protection, etc. for example : cable trays, ladders, ducts, trenches, andso on… are all “cableways”.© Schneider Electric - all rights reservedConductor markingConductor identification must always respect the following three rules:b Rule 1The double colour green and yellow is strictly reserved for the PE and PENprotection conductors.b Rule 2v When a circuit comprises a neutral conductor, it must be light blue or marked “1” forcables with more than five conductorsv When a circuit does not have a neutral conductor, the light blue conductor may beused as a phase conductor if it is part of a cable with more than one conductorb Rule 3Phase conductors may be any colour except:v Green and yellowv Greenv Yellowv Light blue (see rule 2)Schneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations2 The installation systemConductors in a cable are identified either by their colour or by numbers (see Fig. E34).Number of Circuit Fixed cablewaysconductors Insulated conductors Rigid and flexible multiincircuitconductor cablesPh Ph Pn N PE Ph Ph Ph N PE1 Protection or earth G/Y2 Single-phase between phases b b BL LBSingle-phase between phase and neutral b LB BL LBSingle-phase between phase and neutral b G/Y BL G/Y+ protection conductor3 Three-phase without neutral b b b BL B LB2 phases + neutral b b LB BL B LB2 phases + protection conductor b b G/Y BL LB G/YSingle-phase between phase and neutral b LB G/Y BL LB G/Y+ protection conductor4 Three-phase with neutral b b b LB BL B BL LBThree-phase with neutral + protection conductor b b b G/Y BL B LB G/Y2 phases + neutral + protection conductor b b LB G/Y BL B LB G/YThree-phase with PEN conductor b b b G/Y BL B LB G/Y5 Three-phase + neutral + protection conductor b b b LB G/Y BL B BL LB G/Y> 5 Protection conductor: G/Y - Other conductors: BL: with numberingThe number “1” is reserved for the neutral conductor if it existsG/Y: Green and yellow BL: Black b : As indicated in rule 3 LB: Light blue B: BrownE19Fig. E34 : Conductor identification according to the type of circuitNote: If the circuit includes a protection conductor and if the available cable does nothave a green and yellow conductor, the protection conductor may be:b A separate green and yellow conductorb The blue conductor if the circuit does not have a neutral conductorb A black conductor if the circuit has a neutral conductorIn the last two cases, the conductor used must be marked by green and yellowbands or markings at the ends and on all visible lengths of the conductor.Equipment power cords are marked similar to multi-conductor cables (see Fig. E35).Distribution and installation methods (see Fig. E36)Distribution takes place via cableways that carry single insulated conductors orcables and include a fixing system and mechanical protection.Floor subdistributionswichboardFinaldistributionswichboardNBlack conductorLight blue conductorFig. E35 : Conductor identification on a circuit-breaker with aphase and a neutralMain LV switchboard(MLVS)Fig. E36 : Radial distribution using cables in a hotelHeating, etc.Building utilities sub-distribution swichboard© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations2 The installation systemE20Busways, also referred to as busbar trunkingsystems, stand out for their ease of installation,flexibility and number of possible connectionpointsBusbar trunking (busways)Busbar trunking is intended to distribute power (from 20 A to 5000 A) and lighting(in this application, the busbar trunking may play a dual role of supplying electricalpower and physically holding the lights).Busbar trunking system componentsA busbar trunking system comprises a set of conductors protected by an enclosure(see Fig. E37). Used for the transmission and distribution of electrical power, busbartrunking systems have all the necessary features for fitting: connectors, straights,angles, fixings, etc. The tap-off points placed at regular intervals make poweravailable at every point in the installation.Straight trunkingTap-off points todistribute currentFixing system for ceilings, walls orraised floor, etc.End piecePower UnitRange of clip-on tap-off units toconnect a load (e.g.: a machine) tothe busbar trunkingAngleFig. E37 : Busbar trunking system design for distribution of currents from 25 to 4000 A.The various types of busbar trunking:Busbar trunking systems are present at every level in electrical distribution: fromthe link between the transformer and the low voltage switch switchboard (MLVS)to the distribution of power sockets and lighting to offices, or power distribution toworkshops.© Schneider Electric - all rights reservedFig. E38 : Radial distribution using buswaysWe talk about a distributed network architecture.Schneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations2 The installation systemThere are essentially three categories of busways.b Transformer to MLVS busbar trunkingInstallation of the busway may be considered as permanent and will most likely neverbe modified. There are no tap-off points.Frequently used for short runs, it is almost always used for ratings above 1,600 /2,000 A, i.e. when the use of parallel cables makes installation impossible. Buswaysare also used between the MLVS and downstream distribution switchboards.The characteristics of main-distribution busways authorize operational currents from1,000 to 5,000 A and short-circuit withstands up to 150 kA.b Sub-distribution busbar trunking with low or high tap-off densitiesDownstream of main-distribution busbar trunking , two types of applications must besupplied:v Mid-sized premises (industrial workshops with injection presses and metalworkmachines or large supermarkets with heavy loads). The short-circuit and currentlevels can be fairly high (respectively 20 to 70 kA and 100 to 1,000 A)v Small sites (workshops with machine-tools, textile factories with small machines,supermarkets with small loads). The short-circuit and current levels are lower(respectively 10 to 40 kA and 40 to 400 A)Sub-distribution using busbar trunking meets user needs in terms of:v Modifications and upgrades given the high number of tap-off pointsv Dependability and continuity of service because tap-off units can be connectedunder energized conditions in complete safetyThe sub-distribution concept is also valid for vertical distribution in the form of 100 to5,000 A risers in tall buildings.b Lighting distribution busbar trunkingLighting circuits can be distributed using two types of busbar trunking according towhether the lighting fixtures are suspended from the busbar trunking or not.v busbar trunking designed for the suspension of lighting fixturesThese busways supply and support light fixtures (industrial reflectors, dischargelamps, etc.). They are used in industrial buildings, supermarkets, department storesand warehouses. The busbar trunkings are very rigid and are designed for one ortwo 25 A or 40 A circuits. They have tap-off outlets every 0.5 to 1 m.v busbar trunking not designed for the suspension of lighting fixturesSimilar to prefabricated cable systems, these busways are used to supply all typesof lighting fixtures secured to the building structure. They are used in commercialbuildings (offices, shops, restaurants, hotels, etc.), especially in false ceilings. Thebusbar trunking is flexible and designed for one 20 A circuit. It has tap-off outletsevery 1.2 m to 3 m.Busbar trunking systems are suited to the requirements of a large number ofbuildings.b Industrial buildings: garages, workshops, farm buildings, logistic centers, etc.b Commercial areas: stores, shopping malls, supermarkets, hotels, etc.b Tertiary buildings: offices, schools, hospitals, sports rooms, cruise liners, etc.StandardsBusbar trunking systems must meet all rules stated in IEC 439-2.This defines the manufacturing arrangements to be complied with in the designof busbar trunking systems (e.g.: temperature rise characteristics, short-circuitwithstand, mechanical strength, etc.) as well as test methods to check them.Standard IEC 439-2 defines 13 compulsory type-tests on configurations or systemcomponents..By assembling the system components on the site according to the assemblyinstructions, the contractor benefits from conformity with the standard.The advantages of busbar trunking systemsE21Flexibilityb Easy to change configuration (on-site modification to change production lineconfiguration or extend production areas).b Reusing components (components are kept intact): when an installation is subjectto major modifications, the busbar trunking is easy to dismantle and reuse.b Power availability throughout the installation (possibility of having a tap-off pointevery meter).b Wide choice of tap-off units.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations2 The installation systemE22Simplicityb Design can be carried out independently from the distribution and layout of currentconsumers.b Performances are independent of implementation: the use of cables requires a lotof derating coefficients.b Clear distribution layoutb Reduction of fitting time: the trunking system allows fitting times to be reduced byup to 50% compared with a traditional cable installation.b Manufacturer’s guarantee.b Controlled execution times: the trunking system concept guarantees that there areno unexpected surprises when fitting. The fitting time is clearly known in advanceand a quick solution can be provided to any problems on site with this adaptable andscalable equipment.b Easy to implement: modular components that are easy to handle, simple and quickto connect.Dependabilityb Reliability guaranteed by being factory-builtb Fool-proof unitsb Sequential assembly of straight components and tap-off units making it impossibleto make any mistakesContinuity of serviceb The large number of tap-off points makes it easy to supply power to any newcurrent consumer. Connecting and disconnecting is quick and can be carried out incomplete safety even when energized. These two operations (adding or modifying)take place without having to stop operations.b Quick and easy fault location since current consumers are near to the lineb Maintenance is non existent or greatly reducedMajor contribution to sustainable developmentb Busbar trunking systems allow circuits to be combined. Compared with atraditional cable distribution system, consumption of copper raw materials andinsulators is divided by 3 due to the busbar trunking distributed network concept(see Fig. E39).Distribution typeBranchedExample:30 m of Canalis KS 250A equipped with 10 25 A, four-pole feedersConductorsInsulators ConsumptionΣI x k sI 1I 2I 3I 4I 5I 6I 7R R R R R R Rks: clustering coefficient= 0.6CentralizedAlu: 128 mm²Copper equivalent: 86 mm²4 kg1 000 JoulesΣI x k sI 1I 2I 3I 4I 5I 6I 7 Copper: 250 mm²R R R R R R Rks: clustering coefficient= 0.6Fig. E39 : Example: 30 m of Canalis KS 250A equipped with 10 25 A, four-pole feeders12 kg1 600 Joulesb Reusable device and all of its components are fully recyclable.b Does not contain PVC and does not generate toxic gases or waste.b Reduction of risks due to exposure to electromagnetic fields.© Schneider Electric - all rights reservedNew functional features for CanalisBusbar trunking systems are getting even better. Among the new features we canmention:b Increased performance with a IP55 protection index and new ratings of 160 Athrough to 1000 A (Ks).b New lighting offers with pre-cabled lights and new light ducts.b New fixing accessories. Quick fixing system, cable ducts, shared support with“VDI” (voice, data, images) circuits.Schneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations2 The installation systemBusbar trunking systems are perfectly integrated with the environment:b white color to enhance the working environment, naturally integrated in a range ofelectrical distribution products.b conformity with European regulations on reducing hazardous materials (RoHS).Examples of Canalis busbar trunking systemsE23Fig. E40 : Flexible busbar trunking not capable of supporting light fittings : Canalis KDP (20 A)Fig. E41 : Rigid busbar trunking able to support light fittings : Canalis KBA or KBB (25 and 40 A)Fig. E42 : Lighting duct : Canalis KBX (25 A)Fig. E43 : A busway for medium power distribution : Canalis KN (40 up to 160 A)© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations2 The installation systemE24Fig. E44 : A busway for medium power distribution : Canalis KS (100 up to 1000 A)Fig. E45 : A busway for high power distribution : Canalis KT (800 up to 1000 A)© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations3 External influences(IEC 60364-5-51)External influences shall be taken into accountwhen choosing:b The appropriate measures to ensure thesafety of persons (in particular in speciallocations or electrical installations)b The characteristics of electrical equipment,such as degree of protection (IP), mechanicalwithstand (IK), etc.3.1 Definition and reference standardsEvery electrical installation occupies an environment that presents a variable degreeof risk:b For peopleb For the equipment constituting the installationConsequently, environmental conditions influence the definition and choice ofappropriate installation equipment and the choice of protective measures for thesafety of persons.The environmental conditions are referred to collectively as “external influences”.Many national standards concerned with external influences include a classificationscheme which is based on, or which closely resembles, that of international standardIEC 60364-5-51.E25If several external influences appear at thesame time, they can have independent ormutual effects and the degree of protection mustbe chosen accordingly3.2 ClassificationEach condition of external influence is designated by a code comprising a group oftwo capital letters and a number as follows:First letter (A, B or C)The first letter relates to the general category of external influence :b A = environmentb B = utilisationb C = construction of buildingsSecond letterThe second letter relates to the nature of the external influence.NumberThe number relates to the class within each external influence.Additional letter (optional)Used only if the effective protection of persons is greater than that indicated by thefirst IP digit.When only the protection of persons is to be specified, the two digits of the IP codeare replaced by the X’s.Example: IP XXB.ExampleFor example the code AC2 signifies:A = environmentAC = environment-altitudeAC2 = environment-altitude > 2,000 m3.3 List of external influencesFigure E46 below is from IEC 60364-5-51, which should be referred to if furtherdetails are required.Code External influences Characteristics required for equipmentA - EnvironmentAA Ambient temperature (°C)Low High Specially designed equipment or appropriate arrangementsAA1 - 60 °C + 5 °CAA2 - 40 °C + 5 °CAA3 - 25 °C + 5 °CAA4 - 5° C + 40 °C Normal (special precautions in certain cases)AA5 + 5 °C + 40 °C NormalAA6 + 5 °C + 60 °C Specially designed equipment or appropriate arrangementsAA7 - 25 °C + 55 °CAA8 - 50 °C + 40 °CFig. E46 : List of external influences (taken from Appendix A of IEC 60364-5-51) (continued on next page)© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations3 External influences(IEC 60364-5-51)E26© Schneider Electric - all rights reservedCode External influences Characteristics required for equipmentA - EnvironmentAB Atmospheric humidityAir temperature °C Relative humidity % Absolute humidity g/m 3Low High Low High Low HighAB1 - 60 °C + 5 °C 3 100 0.003 7 Appropriate arrangements shall be madeAB2 - 40 °C + 5 °C 10 100 0.1 7AB3 - 25 °C + 5 °C 10 100 0.5 7AB4 - 5° C + 40 °C 5 95 1 29 NormalAB5 + 5 °C + 40 °C 5 85 1 25 NormalAB6 + 5 °C + 60 °C 10 100 1 35 Appropriate arrangements shall be madeAB7 - 25 °C + 55 °C 10 100 0.5 29AB8 - 50 °C + 40 °C 15 100 0.04 36AC AltitudeAC1 y 2000 m NormalAC2 > 2000 m May necessitate precaution (derating factors)AD Presence of waterAD1 Negligible Outdoor or non-weather protected locations IPX0AD2 Free-falling drops IPX1 or IPX2AD3 Sprays IPX3AD4 Splashes IPX4AD5 Jets Locations where hose water is used regularly IPX5AD6 Waves Seashore locations (piers, beaches, quays…) IPX6AD7 Immersion Water 150 mm above the highest point and IPX7equipment not more than 1m below the surfaceAD8 Submersion Equipment is permanently and totally covered IPX8AE Presence of foreign solid bodiesSmallest dimension ExampleAE1 Negligible IP0XAE2 Small objects 2.5 mm Tools IP3XAE3 Very small objects 1 mm Wire IP4XAE4 Light dust IP5X if dust penetration is not harmful to functioningAE5 Moderate dust IP6X if dust should not penetrateAE6 Heavy dust IP6XAF Presence of corrosive or polluting substancesAF1 Negligible NormalAF2 Atmospheric According to the nature of the substanceAF3 Intermittent, accidental Protection against corrosionAF4 Continuous Equipment specially designedAG Mechanical stress impactAG1 Low severity NormalAG2 Medium severity Standard where applicable or reinforced materialAG3 High severity Reinforced protectionAH VibrationsAH1 Low severity Household or similar NormalAH2 Medium severity Usual industrial conditions Specially designed equipment or special arrangementsAH3 High severity Severe industrial conditionsAJ Other mechanical stressesAK Presence of flora and/or mould growthAH1 No hazard NormalAH2 HazardAL Presence of faunaAH1 No hazard NormalAH2 HazardAM Electromagnetic, electrostatic or ionising influences / Low frequency electromagnetic phenomena / HarmonicsAM1 Harmonics, interharmonics Refer to applicable IEC standardsAM2 Signalling voltageAM3 Voltage amplitude variationsAM4 Voltage unbalanceAM5 Power frequency variationsAM6 Induced low-frequency voltagesAM7 Direct current in a.c. networksAM8 Radiated magnetic fieldsAM9 Electric fieldAM21 Induced oscillatory voltages or currentsFig. E46 : List of external influences (taken from Appendix A of IEC 60364-5-51) (continued on next page)Schneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations3 External influences(IEC 60364-5-51)Code External influences Characteristics required for equipmentA - EnvironmentAM22 Conducted unidirectional transients of the nanosecond time scale Refer to applicable IEC standardsAM23 Conducted unidirectional transients of the microsecond to the millisecondtime scaleAM24 Conducted oscillatory transientsAM25 Radiated high frequency phenomenaAM31 Electrostatic dischargesAM41 IonisationAN Solar radiationAN1 Low NormalAN2 MediumAN3 HighAP Seismic effectAP1 Negligible NormalAP2 Low severityAP3 Medium severityAP4 High severityAQ LightningAQ1 Negligible NormalAQ2 Indirect exposureAQ3 Direct exposureAR Movement of airAQ1 Low NormalAQ2 MediumAQ3 HighAS WindAQ1 Low NormalAQ2 MediumAQ3 HighB - UtilizationBA Capability of personsBA1 Ordinary NormalBA2 ChildrenBA3 HandicappedBA4 InstructedBA5 SkilledBB Electrical resistance of human bodyBC Contact of persons with earth potentialBC1 None Class of equipment according to IEC61140BC2 LowBC3 FrequentBC4 ContinuousBD Condition of evacuation in case of emergencyBD1 Low density / easy exit NormalBD2 Low density / difficult exitBD3 High density / easy exitBD4 High density / difficult exitBE Nature of processed or stored materialsBE1 No significant risks NormalBE2 Fire risksBE3 Explosion risksBE4 Contamination risksC - Construction of buildingCA Construction materialsCA1 Non combustible NormalCA2 CombustibleCB Building designCB1 Negligible risks NormalCB2 Propagation of fireCB3 MovementCB4 lexible or unstableFig. E46 : List of external influences (taken from Appendix A of IEC 60364-5-51) (concluded)E27© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations3 External influences(IEC 60364-5-51)3.4 Protection provided for enclosed equipment:codes IP and IKE28IP code definition (see Fig. E47)The degree of protection provided by an enclosure is indicated in the IP code,recommended in IEC 60529.Protection is afforded against the following external influences:b Penetration by solid bodiesb Protection of persons against access to live partsb Protection against the ingress of dustb Protection against the ingress of liquidsNote: the IP code applies to electrical equipment for voltages up to and including72.5 kV.Elements of the IP Code and their meaningsA brief description of the IP Code elements is given in the following chart(see Fig. E48).ElementNumeralsor lettersMeaning for the protectionof equipmentMeaning for theprotection of personsCode lettersIPFirstcharacteristicnumeral0123456Against ingress of solid foreignobjects(non-protected)u 50 mm diameteru 12.5 mm diameteru 2.5 mm diameteru 1.0 mm diameterDust-protectedDust-tightAgainst access tohazardous parts with(non-protected)Back of handFingerToolWireWireWireCode letters(International Protection)IP 2 3 C HSecondcharacteristicnumeral012345678Against ingress of water withharmful effects(non-protected)Vertically drippingDripping (15° tilted)SprayingSplashingJettingPowerful jettingTemporary immersionContinuous immersionFirst characteristic numeral(numerals 0 to 6, or letter X)Second characteristic numeral(numerals 0 to 6, or letter X)Additional letter (optional)(letters A, B, C, D)Additionalletter(optional)ABCDAgainst access tohazardous parts withback of handFingerToolWire© Schneider Electric - all rights reservedSupplementary letter (optional)(letters H, M, S, W)Where a characteristic numeral is not required to be specified,it shall be replaced by the letter "X" ("XX" if both numeralsare omitted). Additional letters and/or supplementary lettersmay be omitted without replacement.Fig. E47 : IP Code arrangementSupplementaryletter(optional)HMSWFig. E48 : Elements of the IP CodeSupplementary information specific to:High-voltage apparatusMotion during water testStationary during water testWeather conditionsSchneider Electric - Electrical installation guide 2009

E - Distribution in low-voltage installations3 External influences(IEC 60364-5-51)IK Code definitionStandard IEC 62262 defines an IK code that characterises the aptitude of equipmentto resist mechanical impacts on all sides (see Fig. E49).IK code Impact energy AG code(in Joules)00 001 y 0.1402 y 0.20 AG103 y 0.3504 y 0.5005 y 0.7006 y 107 y 2 AG208 y 5 AG309 y 1010 y 20 AG4E29Fig. E49 : Elements of the IK CodeIP and IK code specifications for distribution switchboardsThe degrees of protection IP and IK of an enclosure must be specified as a functionof the different external influences defined by standard IEC 60364-5-51, in particular:b Presence of solid bodies (code AE)b Presence of water (code AD)b Mechanical stresses (no code)b Capability of persons (code BA)b …Prisma Plus switchboards are designed for indoor installation.Unless the rules, standards and regulations of a specific country stipulate otherwise,Schneider Electric recommends the following IP and IK values (see Fig. E50 andFig. E51 )IP recommendationsIP codes according to conditionsNormal without risk of vertically falling water Technical rooms 30Normal with risk of vertically falling water Hallways 31Very severe with risk of splashing water Workshops 54/55from all directionsFig. E50 : IP recommendationsIK recommendationsIK codes according to conditionsNo risk of major impact Technical rooms 07Significant risk of major impact that could Hallways 08 (enclosuredamage deviceswith door)Maximum risk of impact that could damage Workshops 10the enclosureFig. E51 : IK recommendations© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Chapter FProtection against electric shocks12345678ContentsGeneral1.1 Electric shock F21.2 Protection against electric shock F31.3 Direct and indirect contact F3Protection against direct contact2.1 Measures of protection against direct contact F42.2 Additional measure of protection against direct contact F6Protection against indirect contact3.1 Measures of protection: two levels F63.2 Automatic disconnection for TT system F73.3 Automatic disconnection for TN systems F83.4 Automatic disconnection on a second fault in an IT system F103.5 Measures of protection against direct or indirect contactwithout automatic disconnection of supplyProtection of goods in case of insulation faultF2F4F6F13F174.1 Measures of protection against fire risk with RCDs F174.2 Ground Fault Protection (GFP) F17Implementation of the TT systemF195.1 Protective measures F195.2 Coordination of residual current protective devices F20Implementation of the TN systemF236.1 Preliminary conditions F236.2 Protection against indirect contact F236.3 High-sensitivity RCDs F276.4 Protection in high fire-risk locations F286.5 When the fault current-loop impedance is particularly high F28Implementation of the IT systemF297.1 Preliminary conditions F297.2 Protection against indirect contact F307.3 High-sensitivity RCDs F347.4 Protection in high fire-risk locations F357.5 When the fault current-loop impedance is particularly high F35Residual current differential devices (RCDs)F368.1 Types of RCDs F368.2 Description F368.3 Sensitivity of RDCs to disturbances F39F© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

F - Protection against electric shock1 GeneralFWhen a current exceeding 30 mA passesthrough a part of a human body, the personconcerned is in serious danger if the current isnot interrupted in a very short time.The protection of persons against electricshock in LV installations must be provided inconformity with appropriate national standardsstatutory regulations, codes of practice, officialguides and circulars etc.Relevant IEC standards include: IEC 60364,IEC 60479 series, IEC 61008, IEC 61009 andIEC 60947-2.1.1 Electric shockAn electric shock is the pathophysiological effect of an electric current through thehuman body.Its passage affects essentially the muscular, circulatory and respiratory functions andsometimes results in serious burns. The degree of danger for the victim is a functionof the magnitude of the current, the parts of the body through which the currentpasses, and the duration of current flow.IEC publication 60479-1 updated in 2005 defines four zones of current-magnitude/time-duration, in each of which the pathophysiological effects are described (see FigF1). Any person coming into contact with live metal risks an electric shock.Curve C1 shows that when a current greater than 30 mA passes through a humanbeing from one hand to feet, the person concerned is likely to be killed, unless thecurrent is interrupted in a relatively short time.The point 500 ms/100 mA close to the curve C1 corresponds to a probability of heartfibrillation of the order of 0.14%.The protection of persons against electric shock in LV installations must be providedin conformity with appropriate national standards and statutory regulations, codes ofpractice, official guides and circulars, etc. Relevant IEC standards include: IEC 60364series, IEC 60479 series, IEC 60755, IEC 61008 series, IEC 61009 series and IEC60947-2.Duration of currentflow I (ms)10,000ABC 1 C 2 C 35,0002,0001,000500AC-4.1AC-4.2AC-4.320010050AC-1AC-2 AC-3 AC-420100.1 0.2 0.5 1 2 5 10 20 50 100 200 500 2,000 10,0001,000 5,000Body currentI s (mA)AC-1 zone: ImperceptibleAC-2 zone: PerceptibleAC-3 zone : Reversible effects: muscular contractionAC-4 zone: Possibility of irreversible effectsAC-4-1 zone: Up to 5%probability of heart fibrillationAC-4-2 zone: Up to 50% probability of heart fibrillationAC-4-3 zone: More than 50% probability of heart fibrillationA curve: Threshold of perception of currentB curve: Threshold of muscular reactionsC 1 curve: Threshold of 0% probability of ventricularfibrillationC 2 curve: Threshold of 5% probability of ventricularfibrillationC 3 curve: Threshold of 50% probability of ventricularfibrillationFig. F1 : Zones time/current of effects of AC current on human body when passing from left hand to feet© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

F - Protection against electric shock1 General1.2 Protection against electric shockThe fundamental rule of protection against electric shock is provided by thedocument IEC 61140 which covers both electrical installations and electricalequipment.Hazardous-live-parts shall not be accessible and accessible conductive parts shallnot be hazardous.This requirement needs to apply under:b Normal conditions, andb Under a single fault conditionVarious measures are adopted to protect against this hazard, and include:b Automatic disconnection of the power supply to the connected electrical equipmentb Special arrangements such as:v The use of class II insulation materials, or an equivalent level of insulationv Non-conducting location, out of arm’s reach or interposition of barriersv Equipotential bondingv Electrical separation by means of isolating transformersF1.3 Direct and indirect contactTwo measures of protection against directcontact hazards are often required, since, inpractice, the first measure may not be infallibleStandards and regulations distinguish two kindsof dangerous contact,b Direct contactb Indirect contactand corresponding protective measuresDirect contactA direct contact refers to a person coming into contact with a conductor which is livein normal circumstances (see Fig. F2).IEC 61140 standard has renamed “protection against direct contact” with the term“basic protection”. The former name is at least kept for information.Indirect contactAn indirect contact refers to a person coming into contact with an exposedconductive-partwhich is not normally alive, but has become alive accidentally (dueto insulation failure or some other cause).The fault current raise the exposed-conductive-part to a voltage liable to behazardous which could be at the origin of a touch current through a person cominginto contact with this exposed-conductive-part (see Fig. F3).IEC 61140 standard has renamed “protection against indirect contact” with the term“fault protection”. The former name is at least kept for information.1 2 3 PE1 2 3 NIdBusbarsInsulationfailureIsIsIs: Touch currentId: Insulation fault currentFig. F2 : Direct contactFig F3 : Indirect contact© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

F - Protection against electric shock2 Protection against direct contactTwo complementary measures are commonly used as protection against thedangers of direct contact:b The physical prevention of contact with live parts by barriers, insulation,inaccessibility, etc.b Additional protection in the event that a direct contact occurs, despite or due tofailure of the above measures. This protection is based on residual-current operatingdevice with a high sensitivity (IΔn y 30 mA) and a low operating time. These devicesare highly effective in the majority of case of direct contact.FIEC and national standards frequentlydistinguish two protections:b Complete (insulation, enclosures)b Partial or particular2.1 Measures of protection against direct contactProtection by the insulation of live partsThis protection consists of an insulation which complies with the relevant standards(see Fig. F4). Paints, lacquers and varnishes do not provide an adequate protection.Fig. F4 : Inherent protection against direct contact by insulation of a 3-phase cable with outersheathFig. F5 : Example of isolation by envelopeProtection by means of barriers or enclosuresThis measure is in widespread use, since many components and materials areinstalled in cabinets, assemblies, control panels and distribution boards (see Fig. F5).To be considered as providing effective protection against direct contact hazards,these equipment must possess a degree of protection equal to at least IP 2X orIP XXB (see chapter E sub-clause 3.4).Moreover, an opening in an enclosure (door, front panel, drawer, etc.) must only beremovable, open or withdrawn:b By means of a key or tool provided for this purpose, orb After complete isolation of the live parts in the enclosure, orb With the automatic interposition of another screen removable only with a key ora tool. The metal enclosure and all metal removable screen must be bonded to theprotective earthing conductor of the installation.Partial measures of protectionb Protection by means of obstacles, or by placing out of arm’s reachThis protection is reserved only to locations to which skilled or instructedpersons only have access. The erection of this protective measure is detailed inIEC 60364-4-41.Particular measures of protectionb Protection by use of extra-low voltage SELV (Safety Extra-Low Voltage) or bylimitation of the energy of discharge.These measures are used only in low-power circuits, and in particular circumstances,as described in section 3.5.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

F - Protection against electric shock2 Protection against direct contactAn additional measure of protection againstthe hazards of direct contact is provided by theuse of residual current operating device, whichoperate at 30 mA or less, and are referred to asRCDs of high sensitivityFig. F6 : High sensitivity RCD2.2 Additional measure of protection against directcontactAll the preceding protective measures are preventive, but experience has shownthat for various reasons they cannot be regarded as being infallible. Among thesereasons may be cited:b Lack of proper maintenanceb Imprudence, carelessnessb Normal (or abnormal) wear and tear of insulation; for instance flexure and abrasionof connecting leadsb Accidental contactb Immersion in water, etc. A situation in which insulation is no longer effectiveIn order to protect users in such circumstances, highly sensitive fast trippingdevices, based on the detection of residual currents to earth (which may or maynot be through a human being or animal) are used to disconnect the powersupply automatically, and with sufficient rapidity to prevent injury to, or death byelectrocution, of a normally healthy human being (see Fig. F6).These devices operate on the principle of differential current measurement, in whichany difference between the current entering a circuit and that leaving it (on a systemsupplied from an earthed source) be flowing to earth, either through faulty insulationor through contact of an earthed part, such as a person, with a live conductor.Standardised residual-current devices, referred to as RCDs, sufficiently sensitive forprotection against direct contact are rated at 30 mA of differential current.According to IEC 60364-4-41, additional protection by means of high sensitivityRCDs (I∆n y 30 mA) must be provided for circuits supplying socket-outlets with arated current y 20 A in all locations, and for circuits supplying mobile equipment witha rated current y 32 A for use outdoors.This additional protection is required in certain countries for circuits supplying socketoutletsrated up to 32 A, and even higher if the location is wet and/or temporary(such as work sites for instance).It is also recommended to limit the number of socket-outlets protected by a RCD(e.g. 10 socket-outlets for one RCD).Chapter P section 3 itemises various common locations in which RCDs ofhigh sensitivity are obligatory (in some countries), but in any case, are highlyrecommended as an effective protection against both direct and indirect contacthazards.F© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

F - Protection against electric shock3 Protection against indirectcontactExposed-conductive-parts used in the manufacturing process of an electricalequipment is separated from the live parts of the equipment by the “basic insulation”.Failure of the basic insulation will result in the exposed-conductive-parts being alive.Touching a normally dead part of an electrical equipment which has become live dueto the failure of its insulation, is referred to as an indirect contact.FProtection against indirect contact hazardscan be achieved by automatic disconnection ofthe supply if the exposed-conductive-parts ofequipment are properly earthed3.1 Measures of protection: two levelsTwo levels of protective measures exist:b 1 st level: The earthing of all exposed-conductive-parts of electrical equipment in theinstallation and the constitution of an equipotential bonding network (see chapter Gsection 6).b 2 sd level: Automatic disconnection of the supply of the section of the installationconcerned, in such a way that the touch-voltage/time safety requirements arerespected for any level of touch voltage Uc (1) (see Fig. F7).EarthconnectionUcFig. F7 : Illustration of the dangerous touch voltage UcThe greater the value of Uc, the greater the rapidity of supply disconnection requiredto provide protection (see Fig. F8). The highest value of Uc that can be toleratedindefinitely without danger to human beings is 50 V a.c.Reminder of the theoretical disconnecting-time limitsUo (V) 50 < Uo y 120 120 < Uo y 230 230 < Uo y 400 Uo > 400System TN or IT 0.8 0.4 0.2 0.1TT 0.3 0.2 0.07 0.04Fig. F8 : Maximum safe duration of the assumed values of AC touch voltage (in seconds)© Schneider Electric - all rights reserved(1) Touch voltage Uc is the voltage existing (as the result ofinsulation failure) between an exposed-conductive-part andany conductive element within reach which is at a different(generally earth) potential.Schneider Electric - Electrical installation guide 2009

F - Protection against electric shock3 Protection against indirectcontactAutomatic disconnection for TT system isachieved by RCD having a sensitivity ofI i 50 n where R RA is the resistance of theAinstallation earth electrode3.2 Automatic disconnection for TT systemPrincipleIn this system all exposed-conductive-parts and extraneous-conductive-parts ofthe installation must be connected to a common earth electrode. The neutral pointof the supply system is normally earthed at a pint outside the influence area of theinstallation earth electrode, but need not be so. The impedance of the earth-fault looptherefore consists mainly in the two earth electrodes (i.e. the source and installationelectrodes) in series, so that the magnitude of the earth fault current is generallytoo small to operate overcurrent relay or fuses, and the use of a residual currentoperated device is essential.This principle of protection is also valid if one common earth electrode only is used,notably in the case of a consumer-type substation within the installation area, wherespace limitation may impose the adoption of a TN system earthing, but where allother conditions required by the TN system cannot be fulfilled.Protection by automatic disconnection of the supply used in TT system is by RCD ofwhere Rsensitivity: I i 50 nRAwhereinstallation earth electrodeR A is the resistance of the earth electrode for the installationI Δn is the rated residual operating current of the RCDFor temporary supplies (to work sites, …) and agricultural and horticultural premises,the value of 50 V is replaced by 25 V.Example (see Fig. F9)b The resistance of the earth electrode of substation neutral R n is 10 Ω.b The resistance of the earth electrode of the installation R A is 20 Ω.b The earth-fault loop current I d = 7.7 A.b The fault voltage U f = I d x R A = 154 V and therefore dangerous, butI Δn = 50/20 = 2.5 A so that a standard 300 mA RCD will operate in about 30 mswithout intentional time delay and will clear the fault where a fault voltage exceedingappears on an exposed-conductive-part.FUo (1) (V)T (s)50 < Uo y 120 0.3120 < Uo y 230 0.2230 < Uo y 400 0.07Uo > 400 0.04(1) Uo is the nominal phase to earth voltageFig. F10 : Maximum disconnecting time for AC final circuits not exceeding 32 AR n = 10 ΩSubstationearthelectrodeR A = 20 ΩInstallationearthelectrodeU f123NPEFig. F9 : Automatic disconnection of supply for TT systemSpecified maximum disconnection timeThe tripping times of RCDs are generally lower than those required in the majorityof national standards; this feature facilitates their use and allows the adoption of aneffective discriminative protection.The IEC 60364-4-41 specifies the maximum operating time of protective devicesused in TT system for the protection against indirect contact:b For all final circuits with a rated current not exceeding 32 A, the maximumdisconnecting time will not exceed the values indicated in Figure F10b For all other circuits, the maximum disconnecting time is fixed to 1s. This limitenables discrimination between RCDs when installed on distribution circuits.RCD is a general term for all devices operating on the residual-current principle.RCCB (Residual Current Circuit-Breaker) as defined in IEC 61008 series is a specificclass of RCD.Type G (general) and type S (Selective) of IEC 61008 have a tripping time/currentcharacteristics as shown in Figure F11 next page. These characteristics allow a certaindegree of selective tripping between the several combination of ratings and types, asshown later in sub-clause 4.3. Industrial type RCD according to IEC 60947-2 providemore possibilities of discrimination due to their flexibility of time-delaying.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

F - Protection against electric shock3 Protection against indirectcontactx I Δn 2 5 > 5Domestic Instantaneous 0.3 0.15 0.04 0.04Type S 0.5 0.2 0.15 0.15Industrial Instantaneous 0.3 0.15 0.04 0.04Time-delay (0.06) 0.5 0.2 0.15 0.15Time-delay (other) According to manufacturer© Schneider Electric - all rights reservedF230Id== (64.3 x10 -3 3,576 A (≈ 22 In based on a NSX160 circuit-breaker).50 m35 mm 2 The “instantaneous” magnetic trip unit adjustment of the circuit-breaker is many timeDCless than this short-circuit value, so that positive operation in the shortest possibleFig. F11 : Maximum operating time of RCD’s (in seconds)3.3 Automatic disconnection for TN systemsThe automatic disconnection for TN system isachieved by overcurrent protective devices orRCD’sPrincipleIn this system all exposed and extraneous-conductive-parts of the installation areconnected directly to the earthed point of the power supply by protective conductors.ABAs noted in Chapter E Sub-clause 1.2, the way in which this direct connection iscarried out depends on whether the TN-C, TN-S, or TN-C-S method of implementingthe TN principle is used. In figure F12 the method TN-C is shown, in which theneutral conductor acts as both the Protective-Earth and Neutral (PEN) conductor. Inall TN systems, any insulation fault to earth results in a phase to neutral short-circuit.High fault current levels allow to use overcurrent protection but can give rise to touchvoltages exceeding 50% of the phase to neutral voltage at the fault position duringthe short disconnection time.In practice for utility distribution network, earth electrodes are normally installed atregular intervals along the protective conductor (PE or PEN) of the network, whilethe consumer is often required to install an earth electrode at the service entrance.On large installations additional earth electrodes dispersed around the premises areoften provided, in order to reduce the touch voltage as much as possible. In high-riseapartment blocks, all extraneous conductive parts are connected to the protectiveconductor at each level. In order to ensure adequate protection, the earth-faultcurrentId = Uo or 0.8 Uo u must I be higher or equal to Ia, where:Zs Zcb Uo = nominal phase to neutral voltageb Id = the fault currentb Ia = current equal to the value required to operate the protective device in the timespecifiedb Zs = earth-fault current loop impedance, equal to the sum of the impedances of thesource, the live phase conductors to the fault position, the protective conductors fromthe fault position back to the sourceb Zc = the faulty-circuit loop impedance (see “conventional method” Sub-clause 6.2)Note: The path through earth electrodes back to the source will have (generally)much higher impedance values than those listed above, and need not be considered.Example (see Fig. F12)230The fault voltage Uf = = 115 V and and is is hazardous;122The fault loop impedance Zs=Zab + Zbc + Zde + Zen + Zna.N3FIf Zbc and Zde are predominant, then:PENENSX160L“conventional Zs = 2= 64method” . 3 m , , so and so that in this example will give an estimated fault current of35 mm 2 Stime is assured.Fig. F12 : Automatic disconnection in TN systemU fNote: Some authorities base such calculations on the assumption that a voltagedrop of 20% occurs in the part of the impedance loop BANE.This method, which is recommended, is explained in chapter F sub-clause 6.2“conventional“conventionalmethod”method”andandininthisthisexampleexamplewillwillgivegiveananestimatedestimatedfaultfaultcurrentcurrentofof3230 x 0.8 x 10= 2,816 A ((≈ 18 In).64.3Schneider Electric - Electrical installation guide 2009

F - Protection against electric shock3 Protection against indirectcontactSpecified maximum disconnection timeThe IEC 60364-4-41 specifies the maximum operating time of protective devicesused in TN system for the protection against indirect contact:b For all final circuits with a rated current not exceeding 32 A, the maximumdisconnecting time will not exceed the values indicated in Figure F13b For all other circuits, the maximum disconnecting time is fixed to 5s. This limitenables discrimination between protective devices installed on distribution circuitsNote: The use of RCDs may be necessary on TN-earthed systems. Use of RCDs onTN-C-S systems means that the protective conductor and the neutral conductor must(evidently) be separated upstream of the RCD. This separation is commonly made atthe service entrance.Uo (1) (V)T (s)50 < Uo y 120 0.8120 < Uo y 230 0.4230 < Uo y 400 0.2Uo > 400 0.1(1) Uo is the nominal phase to earth voltageFFig. F13 : Maximum disconnecting time for AC final circuits not exceeding 32 AIf the protection is to be provided by a circuitbreaker,it is sufficient to verify that the faultcurrent will always exceed the current-settinglevel of the instantaneous or short-time delaytripping unit (Im)Protection by means of circuit-breaker (see Fig. F14)The instantaneous trip unit of a circuit-breaker will eliminate a short-circuit to earth inless than 0.1 second.In consequence, automatic disconnection within the maximum allowable time willalways be assured, since all types of trip unit, magnetic or electronic, instantaneousor slightly retarded, are suitable: Ia = Im. The maximum tolerance authorisedby the relevant standard, however, must always be taken into consideration. It issufficient therefore that the fault current Uo Uoor 0.8 determined by by calculation (or estimatedZs Zc(or estimated on site) on site) be greater be greater than than the instantaneous the instantaneous trip-setting trip-setting current, current, or than or than the very short-the very short-time tripping threshold level, to be sure of tripping within the permittedtime limit.Ia can be determined from the fuseProtection by means of fuses (see Fig. F15)performance curve. In any case, protection The value of current which assures the correct operation of a fuse can becannot be achieved if the loop impedance Zs ascertained from a current/time performance graph for the fuse concerned.or Zc exceeds a certain valuetherefore that The the fault current Uo Uoor 0.8 as determined by calculation above, must (or largely estimated exceed thatZs Zcon site) be greater necessary than the to ensure instantaneous positive operation trip-setting of current, the fuse. or The than condition the very short-to observetherefore is that Ia < Uo Uoor 0.8 as as indicated Figure in Figure F15. F15.Zs Zct1: Short-time delayed trip2: Instantaneous tript12Im Uo/ZsFig. F14 : Disconnection by circuit-breaker for a TN systemItc = 0.4 sFig. F15 : Disconnection by fuses for a TN systemIaUo/ZsI© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

F - Protection against electric shock3 Protection against indirectcontactExample: The nominal phase to neutral voltage of the network is 230 V andthe maximum disconnection time given by the graph in Figure F15 is 0.4 s.The corresponding value of Ia can be read from the graph. Using the voltage (230 V)and the current Ia,Ia,thethecompletecompletelooploopimpedanceimpedanceororthethecircuitcircuitlooploopimpedanceimpedancecancan230be calculated from Zs = or Zc = 0.8 230 . This impedance value must never beIaIaexceeded and should preferably be substantially less to ensure satisfactory fuseoperation.F10Protection by means of Residual Current Devices forTN-S circuitsResidual Current Devices must be used where:b The loop impedance cannot be determined precisely (lengths difficult to estimate,presence of metallic material close to the wiring)b The fault current is so low that the disconnecting time cannot be met by usingovercurrent protective devicesThe rated tripping current of RCDs being in the order of a few amps, it is well belowthe fault current level. RCDs are consequently well adapted to this situation.In practice, they are often installed in the LV sub distribution and in many countries,the automatic disconnection of final circuits shall be achieved by Residual CurrentDevices.3.4 Automatic disconnection on a second fault in anIT systemIn this type of system:b The installation is isolated from earth, or the neutral point of its power-supplysource is connected to earth through a high impedanceb All exposed and extraneous-conductive-parts are earthed via an installation earthelectrode.© Schneider Electric - all rights reservedIn IT system the first fault to earth should notcause any disconnectionFig. F16 : Phases to earth insulation monitoring deviceobligatory in IT system(1) Resistive leakage current to earth through the insulation isassumed to be negligibly small in the example.First fault situationOn the occurrence of a true fault to earth, referred to as a “first fault”, the fault currentis very low, such that the rule Id x R A y 50 V (see F3.2) is fulfilled and no dangerousfault voltages can occur.In practice the current Id is low, a condition that is neither dangerous to personnel,nor harmful to the installation.However, in this system:b A permanent monitoring of the insulation to earth must be provided, coupled withan alarm signal (audio and/or flashing lights, etc.) operating in the event of a firstearth fault (see Fig. F16)b The rapid location and repair of a first fault is imperative if the full benefits of theIT system are to be realised. Continuity of service is the great advantage afforded bythe system.For a network formed from 1 km of new conductors, the leakage (capacitive)impedance to earth Zf is of the order of 3,500 Ω per phase. In normal operation, thecapacitive current (1) to earth is therefore:UoZf = 2303,500 = 66 mA per phase.During a phase to earth fault, as indicated in Figure F17 opposite page, the currentpassing through the electrode resistance RnA is the vector sum of the capacitivecurrents in the two healthy phases. The voltages of the healthy phases have(because of the fault) increased to 3 the normal phase voltage, so that the capacitivecurrents increase by the same amount. These currents are displaced, one from theother by 60°, so that when added vectorially, this amounts to 3 x 66 mA = 198 mA, inthe present example.The fault voltage Uf is therefore equal to 198 x 5 x 10 -3 = 0.99 V, which is obviouslyharmless.The current through the short-circuit to earth is given by the vector sum of theneutral-resistor current Id1 (=153 mA) and the capacitive current Id2 (198 mA).Since the exposed-conductive-parts of the installation are connected directly toearth, the neutral impedance Zct plays practically no part in the production of touchvoltages to earth.Schneider Electric - Electrical installation guide 2009

F - Protection against electric shock3 Protection against indirectcontactId1BId1 + Id2123NPEZ ct = 1,500 ΩΩZfR nA = 5 ΩId2U fF11Fig. F17 : Fault current path for a first fault in IT systemThe simultaneous existence of two earth faults(if not both on the same phase) is dangerous,and rapid clearance by fuses or automaticcircuit-breaker tripping depends on the type ofearth-bonding scheme, and whether separateearthing electrodes are used or not, in theinstallation concernedSecond fault situationOn the appearance of a second fault, on a different phase, or on a neutral conductor,a rapid disconnection becomes imperative. Fault clearance is carried out differently ineach of the following cases:1 st caseIt concerns an installation in which all exposed conductive parts are bonded to acommon PE conductor, as shown in Figure F18.In this case no earth electrodes are included in the fault current path, so that a highlevel of fault current is assured, and conventional overcurrent protective devices areused, i.e. circuit-breakers and fuses.The first fault could occur at the end of a circuit in a remote part of the installation,while the second fault could feasibly be located at the opposite end of the installation.For this reason, it is conventional to double the loop impedance of a circuit, whencalculating the anticipated fault setting level for its overcurrent protective device(s).Where the system includes a neutral conductor in addition to the 3 phaseconductors, the lowest short-circuit fault currents will occur if one of the (two) faults isfrom the neutral conductor to earth (all four conductors are insulated from earth in anIT scheme). In four-wire IT installations, therefore, the phase-to-neutral voltage mustbe used to calculate short-circuit protective levels i.e. 0.8 Uo u I a(1)where2 ZcUo = phase to neutral voltageZc = impedance of the circuit fault-current loop (see F3.3)Ia = current level for trip setting(1) Based on the “conventional method” noted in the firstexample of Sub-clause 3.3.If no neutral conductor is distributed, then the voltage to use for the fault-currentcalculation is the phase-to-phase value, i.e. 0.83 Uo(1)u I a2 Zcb Maximum tripping timesDisconnecting times for IT system depends on how the different installation andsubstation earth electrodes are interconnected.For final circuits supplying electrical equipment with a rated current not exceeding32 A and having their exposed-conductive-parts bonded with the substation earthelectrode, the maximum tripping time is given in table F8. For the other circuitswithin the same group of interconnected exposed-conductive-parts, the maximumdisconnecting time is 5 s. This is due to the fact that any double fault situation withinthis group will result in a short-circuit current as in TN system.For final circuits supplying electrical equipment with a rated current not exceeding32 A and having their exposed-conductive-parts connected to an independent earthelectrode electrically separated from the substation earth electrode, the maximumtripping time is given in Figure F13. For the other circuits within the same group ofnon interconnected exposed-conductive-parts, the maximum disconnecting time is1s. This is due to the fact that any double fault situation resulting from one insulationfault within this group and another insulation fault from another group will generate afault current limited by the different earth electrode resistances as in TT system.Schneider Electric - Electrical installation guide 2009© Schneider Electric - all rights reserved

F - Protection against electric shock3 Protection against indirectcontactKAIdFJ123NPENSX160160 A50 m50 m35 mm 2 35 mm 2G HD CEBR AF12Fig. F18 : Circuit-breaker tripping on double fault situation when exposed-conductive-parts areconnected to a common protective conductorb Protection by circuit-breakerIn the case shown in Figure F18, the adjustments of instantaneous and short-timedelay overcurrent trip unit must be decided. The times recommended here above canbe readily complied with. The short-circuit protection provided by the NSX160 circuitbreakeris suitable to clear a phase to phase short-circuit occurring at the load endsof the circuits concerned.Reminder: In an IT system, the two circuits involved in a phase to phase short-circuitare assumed to be of equal length, with the same cross sectional area conductors,the PE conductors being the same cross sectional area as the phase conductors. Insuch a case, the impedance of the circuit loop when using the “conventional method”(sub clause 6.2) will be twice that calculated for one of the circuits in the TN case,shown in Chapter F sub clause 3.3.LSo that The the resistance of of circuit 1 loop FGHJ = 22RJH= 2 in m where:aρ = resistance of copper rod 1 meter long of cross sectional area 1 mm 2 , in mΩL = length of the circuit in metersa = cross sectional area of the conductor in mm 2FGHJ = 2 x 22.5 x 50/35 = 64.3 mΩand the loop resistance B, C, D, E, F, G, H, J will be 2 x 64.3 = 129 mΩ.The fault current will therefore be 0.8 x 3 x 230 x 10 3 /129 = 2,470 A.b Protection by fusesThe current I a for which fuse operation must be assured in a time specified accordingto here above can be found from fuse operating curves, as described in figure F15.The current indicated should be significantly lower than the fault currents calculatedfor the circuit concerned.b Protection by Residual current circuit-breakers (RCCBs)For low values of short-circuit current, RCCBs are necessary. Protection againstindirect contact hazards can be achieved then by using one RCCB for each circuit.2 nd caseb It concerns exposed conductive parts which are earthed either individually (each parthaving its own earth electrode) or in separate groups (one electrode for each group).If all exposed conductive parts are not bonded to a common electrode system, thenit is possible for the second earth fault to occur in a different group or in a separatelyearthed individual apparatus. Additional protection to that described above forcase 1, is required, and consists of a RCD placed at the circuit-breaker controllingeach group and each individually-earthed apparatus.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

F - Protection against electric shock3 Protection against indirectcontactThe reason for this requirement is that the separate-group electrodes are “bonded”through the earth so that the phase to phase short-circuit current will generally belimited when passing through the earth bond by the electrode contact resistanceswith the earth, thereby making protection by overcurrent devices unreliable. Themore sensitive RCDs are therefore necessary, but the operating current of the RCDsmust evidently exceed that which occurs for a first fault (see Fig. F19).Leakage capacitance First fault current(µF)(A)1 0.075 0.3630 2.17Note: 1 µF is the 1 km typical leakage capacitance for4-conductor cable.Fig. F19 : Correspondence between the earth leakage capacitance and the first fault currentF13For a second fault occurring within a group having a common earth-electrodesystem, the overcurrent protection operates, as described above for case 1.Note 1: See also Chapter G Sub-clause 7.2, protection of the neutral conductor.Note 2: In 3-phase 4-wire installations, protection against overcurrent in the neutralconductor is sometimes more conveniently achieved by using a ring-type currenttransformer over the single-core neutral conductor (see Fig. F20).Case 1Case 2NRCDRCDNRCDRCDRnΩPIMRAGroupearthRnΩPIMGroupearth 1RA1RA2Groupearth 2Fig. F20 : Application of RCDs when exposed-conductive-parts are earthed individually or by group on IT systemExtra-low voltage is used where the risksare great: swimming pools, wandering-leadhand lamps, and other portable appliances foroutdoor use, etc.3.5 Measures of protection against direct or indirectcontact without automatic disconnection of supplyThe use of SELV (Safety Extra-Low Voltage)Safety by extra low voltage SELV is used in situations where the operation of electricalequipment presents a serious hazard (swimming pools, amusement parks, etc.).This measure depends on supplying power at extra-low voltage from the secondarywindings of isolating transformers especially designed according to national or tointernational (IEC 60742) standard. The impulse withstand level of insulation betweenthe primary and secondary windings is very high, and/or an earthed metal screenis sometimes incorporated between the windings. The secondary voltage neverexceeds 50 V rms.Three conditions of exploitation must be respected in order to provide satisfactoryprotection against indirect contact:b No live conductor at SELV must be connected to earthb Exposed-conductive-parts of SELV supplied equipment must not be connected toearth, to other exposed conductive parts, or to extraneous-conductive-partsb All live parts of SELV circuits and of other circuits of higher voltage must beseparated by a distance at least equal to that between the primary and secondarywindings of a safety isolating transformer.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

F - Protection against electric shock3 Protection against indirectcontactThese measures require that:b SELV circuits must use conduits exclusively provided for them, unless cables whichare insulated for the highest voltage of the other circuits are used for the SELV circuitsb Socket outlets for the SELV system must not have an earth-pin contact. TheSELV circuit plugs and sockets must be special, so that inadvertent connection to adifferent voltage level is not possible.Note: In normal conditions, when the SELV voltage is less than 25 V, there is noneed to provide protection against direct contact hazards. Particular requirementsare indicated in Chapter P, Clause 3: “special locations”.F14The use of PELV (Protection by Extra Low Voltage) (see Fig. F21)This system is for general use where low voltage is required, or preferred for safetyreasons, other than in the high-risk locations noted above. The conception is similarto that of the SELV system, but the secondary circuit is earthed at one point.IEC 60364-4-41 defines precisely the significance of the reference PELV. Protectionagainst direct contact hazards is generally necessary, except when the equipmentis in the zone of equipotential bonding, and the nominal voltage does not exceed25 V rms, and the equipment is used in normally dry locations only, and large-areacontact with the human body is not expected. In all other cases, 6 V rms is themaximum permitted voltage, where no direct contact protection is provided.230 V / 24 VFig. F21 : Low-voltage supplies from a safety isolating transformerFELV system (Functional Extra-Low Voltage)Where, for functional reasons, a voltage of 50 V or less is used, but not all of therequirements relating to SELV or PELV are fulfilled, appropriate measures describedin IEC 60364-4-41 must be taken to ensure protection against both direct andindirect contact hazards, according to the location and use of these circuits.Note: Such conditions may, for example, be encountered when the circuit containsequipment (such as transformers, relays, remote-control switches, contactors)insufficiently insulated with respect to circuits at higher voltages.© Schneider Electric - all rights reservedThe electrical separation of circuits is suitablefor relatively short cable lengths and high levelsof insulation resistance. It is preferably used foran individual appliance230 V/230 VFig. F22 : Safety supply from a class II separation transformerThe electrical separation of circuits (see Fig. F22)The principle of the electrical separation of circuits (generally single-phase circuits)for safety purposes is based on the following rationale.The two conductors from the unearthed single-phase secondary winding of aseparation transformer are insulated from earth.If a direct contact is made with one conductor, a very small current only will flow intothe person making contact, through the earth and back to the other conductor, viathe inherent capacitance of that conductor with respect to earth. Since the conductorcapacitance to earth is very small, the current is generally below the level of perception.As the length of circuit cable increases, the direct contact current will progressivelyincrease to a point where a dangerous electric shock will be experienced.Even if a short length of cable precludes any danger from capacitive current, a lowvalue of insulation resistance with respect to earth can result in danger, since thecurrent path is then via the person making contact, through the earth and back to theother conductor through the low conductor-to-earth insulation resistance.For these reasons, relatively short lengths of well insulated cables are essential inseparation systems.Transformers are specially designed for this duty, with a high degree of insulationbetween primary and secondary windings, or with equivalent protection, such as anearthed metal screen between the windings. Construction of the transformer is toclass II insulation standards.Schneider Electric - Electrical installation guide 2009

F - Protection against electric shock3 Protection against indirectcontactAs indicated before, successful exploitation of the principle requires that:b No conductor or exposed conductive part of the secondary circuit must beconnected to earth,b The length of secondary cabling must be limited to avoid large capacitance values (1) ,b A high insulation-resistance value must be maintained for the cabling and appliances.These conditions generally limit the application of this safety measure to anindividual appliance.In the case where several appliances are supplied from a separation transformer, it isnecessary to observe the following requirements:b The exposed conductive parts of all appliances must be connected together by aninsulated protective conductor, but not connected to earth,b The socket outlets must be provided with an earth-pin connection. The earth-pinconnection is used in this case only to ensure the interconnection (bonding) of allexposed conductive parts.In the case of a second fault, overcurrent protection must provide automaticdisconnection in the same conditions as those required for an IT system of powersystem earthing.F15Class II equipment symbol:Class II equipmentThese appliances are also referred to as having “double insulation” since in classII appliances a supplementary insulation is added to the basic insulation (seeFig. F23).No conductive parts of a class II appliance must be connected to a protective conductor:b Most portable or semi-fixed equipment, certain lamps, and some types oftransformer are designed to have double insulation. It is important to take particularcare in the exploitation of class II equipment and to verify regularly and often that theclass II standard is maintained (no broken outer envelope, etc.). Electronic devices,radio and television sets have safety levels equivalent to class II, but are not formallyclass II appliancesb Supplementary insulation in an electrical installation: IEC 60364-4-41(Sub-clause413-2) and some national standards such as NF C 15-100 (France) describe inmore detail the necessary measures to achieve the supplementary insulation duringinstallation work.Active partBasic insulationSupplementary insulationFig. F23 : Principle of class II insulation levelA simple example is that of drawing a cable into a PVC conduit. Methods are alsodescribed for distribution switchboards.b For distribution switchboards and similar equipment, IEC 60439-1 describes a setof requirements, for what is referred to as “total insulation”, equivalent to class IIb Some cables are recognised as being equivalent to class II by many national standardsIn principle, safety by placing simultaneouslyaccessibleconductive parts out-of-reach, or byinterposing obstacles, requires also a nonconductingfloor, and so is not an easily appliedprinciple(1) It is recommended in IEC 364-4-41 that the product of thenominal voltage of the circuit in volts and length in metres ofthe wiring system should not exceed 100,000, and that thelength of the wiring system should not exceed 500 m.Out-of-arm’s reach or interposition of obstaclesBy these means, the probability of touching a live exposed-conductive-part, while atthe same time touching an extraneous-conductive-part at earth potential, is extremelylow (see Fig. F24 next page). In practice, this measure can only be applied in a drylocation, and is implemented according to the following conditions:b The floor and the wall of the chamber must be non-conducting, i.e. the resistanceto earth at any point must be:v > 50 kΩ (installation voltage y 500 V)v > 100 kΩ (500 V < installation voltage y 1000 V)Resistance is measured by means of “MEGGER” type instruments (hand-operatedgenerator or battery-operated electronic model) between an electrode placed on thefloor or against the wall, and earth (i.e. the nearest protective earth conductor). Theelectrode contact area pressure must be evidently be the same for all tests.Different instruments suppliers provide electrodes specific to their own product, sothat care should be taken to ensure that the electrodes used are those supplied withthe instrument.Schneider Electric - Electrical installation guide 2009© Schneider Electric - all rights reserved

F - Protection against electric shock3 Protection against indirectcontactb The placing of equipment and obstacles must be such that simultaneous contactwith two exposed-conductive-parts or with an exposed conductive-part and anextraneous-conductive-part by an individual person is not possible.b No exposed protective conductor must be introduced into the chamber concerned.b Entrances to the chamber must be arranged so that persons entering are not atrisk, e.g. a person standing on a conducting floor outside the chamber must not beable to reach through the doorway to touch an exposed-conductive-part, such as alighting switch mounted in an industrial-type cast-iron conduit box, for example.InsulatedwallsF16Insulatedobstacles2.5 mElectricalapparatusInsulated floorElectricalapparatusElectricalapparatus> 2 m< 2 mFig. F24 : Protection by out-of arm’s reach arrangements and the interposition of non-conducting obstaclesEarth-free equipotential chambers areassociated with particular installations(laboratories, etc.) and give rise to a number ofpractical installation difficultiesEarth-free equipotential chambersIn this scheme, all exposed-conductive-parts, including the floor (1) are bonded bysuitably large conductors, such that no significant difference of potential can existbetween any two points. A failure of insulation between a live conductor and themetal envelope of an appliance will result in the whole “cage” being raised to phaseto-earthvoltage, but no fault current will flow. In such conditions, a person enteringthe chamber would be at risk (since he/she would be stepping on to a live floor).Suitable precautions must be taken to protect personnel from this danger (e.g. nonconductingfloor at entrances, etc.). Special protective devices are also necessary todetect insulation failure, in the absence of significant fault current.MConductivefloor© Schneider Electric - all rights reserved(1) Extraneous conductive parts entering (or leaving) theequipotential space (such as water pipes, etc.) must beencased in suitable insulating material and excluded from theequipotential network, since such parts are likely to be bondedto protective (earthed) conductors elsewhere in the installation.Fig. F25 : Equipotential bonding of all exposed-conductive-parts simultaneously accessibleSchneider Electric - Electrical installation guide 2009Insulating material

F - Protection against electric shock4 Protection of goodsin case of insulation faultThe standards consider the damage (mainly fire) of goods due to insulation faultsto be high. Therefore, for location with high risk of fire, 300 mA Residual CurrentDevices must be used. For the other locations, some standards relies on techniquecalled « Ground Fault Protection » (GFP).RCDs are very effective devices to provideprotection against fire risk due to insulationfault because they can detect leakage current(ex : 300 mA) wich are too low for the otherprotections, but sufficient to cause a fire4.1 Measures of protection against fire risk withRCDsRCDs are very effective devices to provide protection against fire risk due toinsulation fault. This type of fault current is actually too low to be detected by theother protection (overcurrent, reverse time).For TT, IT TN-S systems in which leakage current can appear, the use of 300 mAsensitivity RCDs provides a good protection against fire risk due to this type of fault.An investigation has shown that the cost of the fires in industrial and tertiarybuildings can be very great.The analysis of the phenomena shows that fire risk due to electicity is linked tooverheating due to a bad coordination between the maximum rated current of thecable (or isolated conductor) and the overcurrent protection setting.Overheating can also be due to the modification of the initial method of installation(addition of cables on the same support).This overheating can be the origin of electrical arc in humid environment. Theseelectrical arcs evolve when the fault current-loop impedance is greater than 0.6 Ωand exist only when an insulation fault occurs. Some tests have shown that a300 mA fault current can induce a real risk of fire (see Fig. F26).F17Beginning of fireFig. F26 : Origin of fires in buildingsId

F - Protection against electric shock4 Protection of goodsin case of insulation faultPositioning GFP devices in the installationType / installation level Main-distribution Sub-distribution CommentsSource Ground Return v Used(SGR)Residual Sensing (RS) v b Often used(SGR)Zero Sequence v b Rarely used(SGR)v Possibleb Recommended or requiredF18© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

F - Protection against electric shock5 Implementation of the TT system5.1 Protective measuresProtection against indirect contactGeneral caseProtection against indirect contact is assured by RCDs, the sensitivity IΔn of which50 Vcomplies with the condition I n i(1) (1)RAThe choice of sensitivity of the residual current device is a function of the resistanceR A of the earth electrode for the installation, and is given in Figure F28.IΔnMaximum resistance of the earth electrode(50 V) (25 V)3 A 16 Ω 8 Ω1 A 50 Ω 25 Ω500 mA 100 Ω 50 Ω300 mA 166 Ω 83 Ω30 mA 1666 Ω 833 ΩF19Fig. F28 : The upper limit of resistance for an installation earthing electrode which must not beexceeded, for given sensitivity levels of RCDs at U L voltage limits of 50 V and 25 VCase of distribution circuits (see Fig. F29)IEC 60364-4-41 and a number of national standards recognize a maximum trippingtime of 1 second in installation distribution circuits (as opposed to final circuits). Thisallows a degree of selective discrimination to be achieved:b At level A: RCD time-delayed, e.g. “S” typeb At level B: RCD instantaneousARCDCase where the exposed conductive parts of an appliance, or group ofappliances, are connected to a separate earth electrode (see Fig. F30)Protection against indirect contact by a RCD at the circuit-breaker level protectingeach group or separately-earthed individual appliance.In each case, the sensitivity must be compatible with the resistance of the earthelectrode concerned.RCDFig. F29 : Distribution circuitsBRCDHigh-sensitivity RCDs (see Fig. F31)According to IEC 60364-4-41, high sensitivity RCDs (y 30 mA) must be used forprotection of socket outlets with rated current y 20 A in all locations. The use of suchRCDs is also recommended in the following cases:b Socket-outlet circuits in wet locations at all current ratingsb Socket-outlet circuits in temporary installationsb Circuits supplying laundry rooms and swimming poolsb Supply circuits to work-sites, caravans, pleasure boats, and travelling fairsSee 2.2 and chapter P, section 3RA1RA2Distant locationFig. F30 : Separate earth electrodeFig. F31 : Circuit supplying socket-outlets(1) 25 V for work-site installations, agricultural establishments, etc.Schneider Electric - Electrical installation guide 2009© Schneider Electric - all rights reserved

F - Protection against electric shock5 Implementation of the TT systemIn high fire risk locations (see Fig. F32)RCD protection at the circuit-breaker controlling all supplies to the area at risk isnecessary in some locations, and mandatory in many countries.The sensitivity of the RCD must be y 500 mA, but a 300 mA sensitivity isrecommended.Protection when exposed conductive parts are not connectedto earth (see Fig. F33)(In the case of an existing installation where the location is dry and provision ofan earthing connection is not possible, or in the event that a protective earth wirebecomes broken).RCDs of high sensitivity (y 30 mA) will afford both protection against indirect-contacthazards, and the additional protection against the dangers of direct-contact.F20Fire-risklocationFig. F32 : Fire-risk locationFig. F33 : Unearthed exposed conductive parts (A)5.2 Coordination of residual current protectivedevicesDiscriminative-tripping coordination is achieved either by time-delay or by subdivisionof circuits, which are then protected individually or by groups, or by a combination ofboth methods.Such discrimination avoids the tripping of any RCD, other than that immediatelyupstream of a fault position:b With equipment currently available, discrimination is possible at three or fourdifferent levels of distribution :v At the main general distribution boardv At local general distribution boardsv At sub-distribution boardsv At socket outlets for individual appliance protectionb In general, at distribution boards (and sub-distribution boards, if existing) and onindividual-appliance protection, devices for automatic disconnection in the event ofan indirect-contact hazard occurring are installed together with additional protectionagainst direct-contact hazards.© Schneider Electric - all rights reservedDiscrimination between RCDsThe general specification for achieving total discrimination between two RCDs is asfollow:b The ratio between the rated residual operating currents must be > 2b Time delaying the upstream RCDDiscrimination is achieved by exploiting the several levels of standardized sensitivity:30 mA, 100 mA, 300 mA and 1 A and the corresponding tripping times, as shownopposite page in Figure F34.Schneider Electric - Electrical installation guide 2009

F - Protection against electric shock5 Implementation of the TT systemt (ms)10,0001,0005003002502001501301006040IIIselective RCDsdomestic Sand industrial(settings I and II)RCD 30 mAgeneral domesticand industrial setting 0F211015 30 60Current(mA)1001503005006001,0001 1.5 10 100 500 1,000 (A)Fig. F34 : Total discrimination at 2 levelsFig. F35 : Total discrimination at 2 levelsAARCD 300 mAtype SRelay with separatetoroidal CT 3 Adelay time 500 msRCD30 mAFig. F36 : Total discrimination at 3 or 4 levelsBRCCB 1 Adelay time 250 msCBRCCB 300 Adelay time 50 msor type SDRCCB30 mADiscrimination at 2 levels (see Fig. F35)Protectionb Level A: RCD time-delayed setting I (for industrial device) or type S (for domesticdevice) for protection against indirect contactsb Level B: RCD instantaneous, with high sensitivity on circuits supplying socketoutletsor appliances at high risk (washing machines, etc.) See also Chapter PClause 3Schneider Electric solutionsb Level A: Compact or Multi 9 circuit-breaker with adaptable RCD module(Vigi NSX160 or Vigi NC100), setting I or S typeb Level B: Circuit-breaker with integrated RCD module (DPN Vigi) or adaptableRCD module (e.g. Vigi C60 or Vigi NC100) or VigicompactNote: The setting of upstream RCCB must comply with selectivity rules and take intoaccount all the downstream earth leakage currents.Discrimination at 3 or 4 levels (see Fig. F36)Protectionb Level A: RCD time-delayed (setting III)b Level B: RCD time-delayed (setting II)b Level C: RCD time-delayed (setting I) or type Sb Level D: RCD instantaneousSchneider Electric solutionsb Level A: Circuit-breaker associated with RCD and separate toroidal transformer(Vigirex RH328AP)b Level B: Vigicompact or Vigirexb Level C: Vigirex, Vigicompact or Vigi NC100 or Vigi C60b Level D:v Vigicompact orv Vigirex orv Multi 9 with integrated or adaptable RCD module : Vigi C60 or DPN VigiNote: The setting of upstream RCCB must comply with selectivity rules and take intoaccount all the downstream earth leakage currents© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

F - Protection against electric shock5 Implementation of the TT systemDiscriminative protection at three levels (see Fig. F37)Withdrawable Masterpactor VisucompactMV/LVF22NSX400NSX100 MADiscont.VigicompactNSX100Setting 1300 mANC100L MAinstantaneous300 mANC100diff.300 mAselectiveSLeakage currentof the filter: 20 mATerminalboard© Schneider Electric - all rights reservedLeakage current equal to 3.5 mA persocket outlet (Information technologyequipement): max 4 sockets outlets.Fig. F37 : Typical 3-level installation, showing the protection of distribution circuits in a TT-earthed system. One motor is provided with specific protectionSchneider Electric - Electrical installation guide 2009

F - Protection against electric shock6 Implementation of the TN system6.1 Preliminary conditionsAt the design stage, the maximum permitted lengths of cable downstream of aprotective circuit-breaker (or set of fuses) must be calculated, while during theinstallation work certain rules must be fully respected.Certain conditions must be observed, as listed below and illustrated in Figure F38.1. PE conductor must be regularly connected to earth as much as possible.2. The PE conductor must not pass through ferro-magnetic conduit, ducts, etc. orbe mounted on steel work, since inductive and/or proximity effects can increase theeffective impedance of the conductor.3. In the case of a PEN conductor (a neutral conductor which is also used as aprotective conductor), connection must be made directly to the earth terminal of anappliance (see 3 in Figure F38) before being looped to the neutral terminal of thesame appliance.4. Where the conductor y 6 mm 2 for copper or 10 mm 2 for aluminium, or where acable is movable, the neutral and protective conductors should be separated (i.e. aTN-S system should be adopted within the installation).5. Earth faults may be cleared by overcurrent-protection devices, i.e. by fuses andcircuit-breakers.The foregoing list indicates the conditions to be respected in the implementation of aTN scheme for the protection against indirect contacts.F23152 25PEN3PE N45TN-C systemTN-C-S systemRpnANotes:b The TN scheme requires that the LV neutral of the MV/LV transformer, the exposedconductive parts of the substation and of the installation, and the extraneous conductiveparts in the substation and installation, all be earthed to a common earthing system.b For a substation in which the metering is at low-voltage, a means of isolation is required atthe origin of the LV installation, and the isolation must be clearly visible.b A PEN conductor must never be interrupted under any circumstances. Control andprotective switchgear for the several TN arrangements will be:v 3-pole when the circuit includes a PEN conductor,v Preferably 4-pole (3 phases + neutral) when the circuit includes a neutral with a separatePE conductor.Fig. F38 : Implementation of the TN system of earthingThree methods of calculation are commonlyused:b The method of impedances, based on thetrigonometric addition of the system resistancesand inductive reactancesb The method of compositionb The conventional method, based on anassumed voltage drop and the use of preparedtables6.2 Protection against indirect contactMethods of determining levels of short-circuit currentIn TN-earthed systems, a short-circuit to earth will, in principle, always providesufficient current to operate an overcurrent device.The source and supply mains impedances are much lower than those of theinstallation circuits, so that any restriction in the magnitude of earth-fault currentswill be mainly caused by the installation conductors (long flexible leads to appliancesgreatly increase the “fault-loop” impedance, with a corresponding reduction of shortcircuitcurrent).The most recent IEC recommendations for indirect-contact protection on TN earthingsystems only relates maximum allowable tripping times to the nominal systemvoltage (see Figure F12 in Sub-clause 3.3).© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

F - Protection against electric shock6 Implementation of the TN systemF24For calculations, modern practice is to usesoftware agreed by National Authorities, andbased on the method of impedances, such asEcodial 3. National Authorities generally alsopublish Guides, which include typical values,conductor lengths, etc.The reasoning behind these recommendations is that, for TN systems, the currentwhich must flow in order to raise the potential of an exposed conductive part to 50 Vor more is so high that one of two possibilities will occur:b Either the fault path will blow itself clear, practically instantaneously, orb The conductor will weld itself into a solid fault and provide adequate current tooperate overcurrent devicesTo ensure correct operation of overcurrent devices in the latter case, a reasonablyaccurate assessment of short-circuit earth-fault current levels must be determined atthe design stage of a project.A rigorous analysis requires the use of phase-sequence-component techniquesapplied to every circuit in turn. The principle is straightforward, but the amount ofcomputation is not considered justifiable, especially since the zero-phase-sequenceimpedances are extremely difficult to determine with any reasonable degree ofaccuracy in an average LV installation.Other simpler methods of adequate accuracy are preferred. Three practical methodsare:b The “method of impedances”, based on the summation of all the impedances(positive-phase-sequence only) around the fault loop, for each circuitb The “method of composition”, which is an estimation of short-circuit current atthe remote end of a loop, when the short-circuit current level at the near end of theloop is knownb The “conventional method” of calculating the minimum levels of earth-faultcurrents, together with the use of tables of values for obtaining rapid resultsThese methods are only reliable for the case in which the cables that make up theearth-fault-current loop are in close proximity (to each other) and not separated byferro-magnetic materials.Method of impedancesThis method summates the positive-sequence impedances of each item (cable, PEconductor, transformer, etc.) included in the earth-fault loop circuit from which theshort-circuit earth-fault current is calculated, using the formula:UI =( R) + ( X)2 2where(ΣR) 2 = (the sum of all resistances in the loop) 2 at the design stage of a project.and (ΣX) 2 = (the sum of all inductive reactances in the loop) 2and U = nominal system phase-to-neutral voltage.The application of the method is not always easy, because it supposes a knowledgeof all parameter values and characteristics of the elements in the loop. In manycases, a national guide can supply typical values for estimation purposes.Method of compositionThis method permits the determination of the short-circuit current at the end ofa loop from the known value of short-circuit at the sending end, by means of theapproximate formula:UI = IscU+ Zs.IscwhereIsc where = upstream short-circuit currentI = end-of-loop short-circuit currentU = nominal system phase voltageZs = impedance of loopNote: in this method the individual impedances are added arithmetically (1) asopposed to the previous “method of impedances” procedure.© Schneider Electric - all rights reserved(1) This results in a calculated current value which is less thanthat it would actually flow. If the overcurrent settings are basedon this calculated value, then operation of the relay, or fuse, isassured.Conventional methodThis method is generally considered to be sufficiently accurate to fix the upper limitof cable lengths.PrincipleThe principle bases the short-circuit current calculation on the assumption that thevoltage at the origin of the circuit concerned (i.e. at the point at which the circuitprotective device is located) remains at 80% or more of the nominal phase to neutralvoltage. The 80% value is used, together with the circuit loop impedance, to computethe short-circuit current.Schneider Electric - Electrical installation guide 2009

F - Protection against electric shock6 Implementation of the TN systemThe maximum length of any circuit of aTN-earthed installation is: 0.8 Uo Sphmax = 1+m Ia( )This coefficient takes account of all voltage drops upstream of the point considered.In LV cables, when all conductors of a 3-phase 4-wire circuit are in close proximity(which is the normal case), the inductive reactance internal to and betweenconductors is negligibly small compared to the cable resistance.This approximation is considered to be valid for cable sizes up to 120 mm 2 .Above that size, the resistance value R is increased as follows:Core size (mm 2 )S = 150 mm 2S = 185 mm 2S = 240 mm 2Value of resistanceR+15%R+20%R+25%The maximum length of a circuit in a TN-earthed installation is given by the formula:0.8 Uo SphLmax= 1+m Ia( )where:Lmax = maximum length in metresUo = phase volts = 230 V for a 230/400 V systemρ = resistivity at normal working temperature in ohm-mm 2 /metre(= 22.5 10 -3 for copper; = 36 10 -3 for aluminium)Ia = trip current setting for the instantaneous operation of a circuit-breaker, orIa = the current which assures operation of the protective fuse concerned, in thespecified time.m =SphSPEF25The following tables give the length of circuitwhich must not be exceeded, in order thatpersons be protected against indirect contacthazards by protective devicesIdABImagnLPESph = cross-sectional area of the phase conductors of the circuit concerned in mm 2SPE = cross-sectional area of the protective conductor concerned in mm 2 .(see Fig. F39)TablesThe following tables, applicable to TN systems, have been established according tothe “conventional method” described above.The tables give maximum circuit lengths, beyond which the ohmic resistance of theconductors will limit the magnitude of the short-circuit current to a level below thatrequired to trip the circuit-breaker (or to blow the fuse) protecting the circuit, withsufficient rapidity to ensure safety against indirect contact.Correction factor mFigure F40 indicates the correction factor to apply to the values given in Figures F41to F44 next pages, according to the ratio Sph/SPE, the type of circuit, and theconductor materials.The tables take into account:b The type of protection: circuit-breakers or fusesb Operating-current settingsb Cross-sectional area of phase conductors and protective conductorsb Type of system earthing (see Fig. F45 page F27)b Type of circuit-breaker (i.e. B, C or D) (1)The tables may be used for 230/400 V systems.Equivalent tables for protection by Compact and Multi 9 circuit-breakers (MerlinGerin) are included in the relevant catalogues.SPESphCFig. F39 : Calculation of L max. for a TN-earthed system, usingthe conventional method(1) For the definition of type B, C, D circuit-breakers, refer tochapter H, clause 4.2Circuit Conductor m = Sph/SPE (or PEN)material m = 1 m = 2 m = 3 m = 43P + N or P + N Copper 1 0.67 0.50 0.40Aluminium 0.62 0.42 0.31 0.25Fig. F40 : Correction factor to apply to the lengths given in tables F40 to F43 forTN systemsSchneider Electric - Electrical installation guide 2009© Schneider Electric - all rights reserved

F - Protection against electric shock6 Implementation of the TN systemCircuits protected by general purpose circuit-breakers (Fig. F41)F26Nominal Instantaneous or short-time-delayed tripping current Im (amperes)crosssectionalareaofconductorsmm 2 50 63 80 100 125 160 200 250 320 400 500 560 630 700 800 875 1000 1120 1250 1600 2000 2500 3200 4000 5000 6300 8000 10000 125001.5 100 79 63 50 40 31 25 20 16 13 10 9 8 7 6 6 5 4 42.5 167 133 104 83 67 52 42 33 26 21 17 15 13 12 10 10 8 7 7 5 44 267 212 167 133 107 83 67 53 42 33 27 24 21 19 17 15 13 12 11 8 7 5 46 400 317 250 200 160 125 100 80 63 50 40 36 32 29 25 23 20 18 16 13 10 8 6 5 410 417 333 267 208 167 133 104 83 67 60 53 48 42 38 33 30 27 21 17 13 10 8 7 5 416 427 333 267 213 167 133 107 95 85 76 67 61 53 48 43 33 27 21 17 13 11 8 7 5 425 417 333 260 208 167 149 132 119 104 95 83 74 67 52 42 33 26 21 17 13 10 8 735 467 365 292 233 208 185 167 146 133 117 104 93 73 58 47 36 29 23 19 15 12 950 495 396 317 283 251 226 198 181 158 141 127 99 79 63 49 40 32 25 20 16 1370 417 370 333 292 267 233 208 187 146 117 93 73 58 47 37 29 23 1995 452 396 362 317 283 263 198 158 127 99 79 63 50 40 32 25120 457 400 357 320 250 200 160 125 100 80 63 50 40 32150 435 388 348 272 217 174 136 109 87 69 54 43 35185 459 411 321 257 206 161 128 103 82 64 51 41240 400 320 256 200 160 128 102 80 64 51Fig. F41 : Maximum circuit lengths (in metres) for different sizes of copper conductor and instantaneous-tripping-current settings for general-purpose circuit-breakersin 230/240 V TN system with m = 1Circuits protected by Compact or Multi 9 circuit-breakers for industrial ordomestic use (Fig. F42 to Fig. F44)Sph Rated current (A)mm 2 1 2 3 4 6 10 16 20 25 32 40 50 63 80 100 1251.5 1200 600 400 300 200 120 75 60 48 37 30 24 19 15 12 102.5 1000 666 500 333 200 125 100 80 62 50 40 32 25 20 164 1066 800 533 320 200 160 128 100 80 64 51 40 32 266 1200 800 480 300 240 192 150 120 96 76 60 48 3810 800 500 400 320 250 200 160 127 100 80 6416 800 640 512 400 320 256 203 160 128 10225 800 625 500 400 317 250 200 16035 875 700 560 444 350 280 22450 760 603 475 380 304Fig. F42 : Maximum circuit lengths (in meters) for different sizes of copper conductor and rated currents for type B (1) circuit-breakers in a 230/240 V single-phase orthree-phase TN system with m = 1© Schneider Electric - all rights reservedSph Rated current (A)mm 2 1 2 3 4 6 10 16 20 25 32 40 50 63 80 100 1251.5 600 300 200 150 100 60 37 30 24 18 15 12 9 7 6 52.5 500 333 250 167 100 62 50 40 31 25 20 16 12 10 84 533 400 267 160 100 80 64 50 40 32 25 20 16 136 600 400 240 150 120 96 75 60 48 38 30 24 1910 667 400 250 200 160 125 100 80 63 50 40 3216 640 400 320 256 200 160 128 101 80 64 5125 625 500 400 312 250 200 159 125 100 8035 875 700 560 437 350 280 222 175 140 11250 760 594 475 380 301 237 190 152Fig. F43 : Maximum circuit lengths (in metres) for different sizes of copper conductor and rated currents for type C (1) circuit-breakers in a 230/240 V single-phase orthree-phase TN system with m = 1(1) For the definition of type B and C circuit-breakers refer tochapter H clause 4.2.Schneider Electric - Electrical installation guide 2009

F - Protection against electric shock6 Implementation of the TN systemSph Rated current (A)mm 2 1 2 3 4 6 10 16 20 25 32 40 50 63 80 100 1251.5 429 214 143 107 71 43 27 21 17 13 11 9 7 5 4 32.5 714 357 238 179 119 71 45 36 29 22 18 14 11 9 7 64 571 381 286 190 114 71 80 46 36 29 23 18 14 11 96 857 571 429 286 171 107 120 69 54 43 34 27 21 17 1410 952 714 476 286 179 200 114 89 71 57 45 36 29 2316 762 457 286 320 183 143 114 91 73 57 46 3725 714 446 500 286 223 179 143 113 89 71 5735 625 700 400 313 250 200 159 125 80 10050 848 543 424 339 271 215 170 136 109Fig. F44 : Maximum circuit lengths (in metres) for different sizes of copper conductor and rated currents for type D (1) circuit-breakers in a 230/240 V single-phase orthree-phase TN system with m = 1RA1Fig. F45 : Separate earth electrodeRA2Distant locationExampleA 3-phase 4-wire (230/400 V) installation is TN-C earthed. A circuit is protected by atype B circuit-breaker rated at 63 A, and consists of an aluminium cored cable with50 mm 2 phase conductors and a neutral conductor (PEN) of 25 mm 2 .What is the maximum length of circuit, below which protection of persons againstindirect-contact hazards is assured by the instantaneous magnetic tripping relay ofthe circuit-breaker?Figure F42 gives, for 50 mm 2 and a 63 A type B circuit-breaker, 603 metres, to whichmust be applied a factor of 0.42 (Figure F40 for m = Sph = 2)..SPEThe maximum length of circuit is therefore:603 x 0.42 = 253 metres.Particular case where one or more exposed conductive part(s)is (are) earthed to a separate earth electrodeProtection must be provided against indirect contact by a RCD at the origin of anycircuit supplying an appliance or group of appliances, the exposed conductive partsof which are connected to an independent earth electrode.The sensitivity of the RCD must be adapted to the earth electrode resistance (RA2 inFigure F45). See specifications applicable to TT system.F276.3 High-sensitivity RCDs (see Fig. F31)Fig. F46 : Circuit supplying socket-outletsAccording to IEC 60364-4-41, high sensitivity RCDs (y 30 mA) must be used forprotection of socket outlets with rated current y 20 A in all locations. The use of suchRCDs is also recommended in the following cases:b Socket-outlet circuits in wet locations at all current ratingsb Socket-outlet circuits in temporary installationsb Circuits supplying laundry rooms and swimming poolsb Supply circuits to work-sites, caravans, pleasure boats, and travelling fairsSee 2.2 and chapter P, al section 3.(1) For the definition of type D circuit-breaker refer to chapter HSub-clause 4.2.Schneider Electric - Electrical installation guide 2009© Schneider Electric - all rights reserved

F - Protection against electric shock6 Implementation of the TN system6.4 Protection in high fire-risk locationAccording to IEC 60364-422-3.10, circuits in high fire-risk locations must beprotected by RCDs of sensitivity y 500 mA. This excludes the TN-C arrangement andTN-S must be adopted.A preferred sensitivity of 300 mA is mandatory in some countries (see Fig. F47).6.5 When the fault current-loop impedance isparticularly highWhen the earth-fault current is limited due to an inevitably high fault-loop impedance,so that the overcurrent protection cannot be relied upon to trip the circuit within theprescribed time, the following possibilities should be considered:F28Fig. F47 : Fire-risk location2 y Irm y 4InGreat length of cableFire-risklocationPE or PENFig. F48 : Circuit-breaker with low-set instantaneous magnetictrippingSuggestion 1 (see Fig. F48)b Install a circuit-breaker which has a lower instantaneous magnetic tripping level, forexample:2In y Irm y 4InThis affords protection for persons on circuits which are abnormally long. It mustbe checked, however, that high transient currents such as the starting currents ofmotors will not cause nuisance trip-outs.b Schneider Electric solutionsv Type G Compact (2Im y Irm y 4Im)v Type B Multi 9 circuit-breakerSuggestion 2 (see Fig. F49)b Install a RCD on the circuit. The device does not need to be highly-sensitive(HS) (several amps to a few tens of amps). Where socket-outlets are involved, theparticular circuits must, in any case, be protected by HS (y 30 mA) RCDs; generallyone RCD for a number of socket outlets on a common circuit.b Schneider Electric solutionsv RCD Multi 9 NG125 : IΔn = 1 or 3 Av Vigicompact REH or REM: IΔn = 3 to 30 Av Type B Multi 9 circuit-breakerSuggestion 3Increase the size of the PE or PEN conductors and/or the phase conductors, toreduce the loop impedance.Suggestion 4Add supplementary equipotential conductors. This will have a similar effect to thatof suggestion 3, i.e. a reduction in the earth-fault-loop resistance, while at the sametime improving the existing touch-voltage protection measures. The effectivenessof this improvement may be checked by a resistance test between each exposedconductive part and the local main protective conductor.For TN-C installations, bonding as shown in Figure F50 is not allowed, andsuggestion 3 should be adopted.PhasesNeutralPE© Schneider Electric - all rights reservedFig. F49 : RCD protection on TN systems with high earth-faultloopimpedanceFig. F50 : Improved equipotential bondingSchneider Electric - Electrical installation guide 2009

F - Protection against electric shock7 Implementation of the IT systemThe basic feature of the IT earthing system is that, in the event of a short-circuit toearth fault, the system can continue to operate without interruption. Such a fault isreferred to as a “first fault”.In this system, all exposed conductive parts of an installation are connected viaPE conductors to an earth electrode at the installation, while the neutral point of thesupply transformer is:b Either isolated from earthb Or connected to earth through a high resistance (commonly 1,000 ohms or more)This means that the current through an earth fault will be measured in milli-amps,which will not cause serious damage at the fault position, or give rise to dangeroustouch voltages, or present a fire hazard. The system may therefore be allowed tooperate normally until it is convenient to isolate the faulty section for repair work. Thisenhances continuity of service.In practice, the system earthing requires certain specific measures for its satisfactoryexploitation:b Permanent monitoring of the insulation with respect to earth, which must signal(audibly or visually) the occurrence of the first faultb A device for limiting the voltage which the neutral point of the supply transformercan reach with respect to earthb A “first-fault” location routine by an efficient maintenance staff. Fault location isgreatly facilitated by automatic devices which are currently availableb Automatic high-speed tripping of appropriate circuit-breakers must take place inthe event of a “second fault” occurring before the first fault is repaired. The secondfault (by definition) is an earth fault affecting a different live conductor than that of thefirst fault (can be a phase or neutral conductor) (1) .The second fault results in a short-circuit through the earth and/or throughPE bonding conductors.F297.1 Preliminary conditions (see Fig. F51 and Fig. F52)Minimum functions required Components and devices ExamplesProtection against overvoltages (1) Voltage limiter Cardew Cat power frequencyNeutral earthing resistor (2) Resistor Impedance Zx(for impedance earthing variation)Overall earth-fault monitor (3) Permanent insulation Vigilohm TR22Awith alarm for first fault condition monitor PIM with alarm feature or XM 200Automatic fault clearance (4) Four-pole circuit-breakers Compact circuit-breakeron second fault and (if the neutral is distributed) or RCD-MSprotection of the neutralall 4 poles tripconductor against overcurrentLocation of first fault (5) With device for fault-location Vigilohm systemon live system, or by successiveopening of circuitsFig. F51 : Essential functions in IT schemes and examples with Merlin Gerin productsHV/LV4L1L2L3N44(1) On systems where the neutral is distributed, as shown inFigure F56.2 1 3Fig. F52 : Positions of essential functions in 3-phase 3-wire IT-earthed systemSchneider Electric - Electrical installation guide 20095© Schneider Electric - all rights reserved

F - Protection against electric shock7 Implementation of the IT systemF30Modern monitoring systems greatly facilitatefirst-fault location and repairFault-location systems comply withIEC 61157-9 standard7.2 Protection against indirect contactFirst-fault conditionThe earth-fault current which flows under a first-fault condition is measured in milliamps.The fault voltage with respect to earth is the product of this current and theresistance of the installation earth electrode and PE conductor (from the faultedcomponent to the electrode). This value of voltage is clearly harmless and couldamount to several volts only in the worst case (1,000 Ω earthing resistor will pass230 mA (1) and a poor installation earth-electrode of 50 ohms, would give 11.5 V, forexample).An alarm is given by the permanent insulation monitoring device.Principle of earth-fault monitoringA generator of very low frequency a.c. current, or of d.c. current, (to reduce theeffects of cable capacitance to negligible levels) applies a voltage between theneutral point of the supply transformer and earth. This voltage causes a small currentto flow according to the insulation resistance to earth of the whole installation, plusthat of any connected appliance.Low-frequency instruments can be used on a.c. systems which generate transientd.c. components under fault conditions. Certain versions can distinguish betweenresistive and capacitive components of the leakage current.Modern equipment allow the measurement of leakage-current evolution, so thatprevention of a first fault can be achieved.Examples of equipmentb Manual fault-location (see Fig. F53)The generator may be fixed (example: XM100) or portable (example: GR10Xpermitting the checking of dead circuits) and the receiver, together with the magneticclamp-type pick-up sensor, are portable.MERLIN GERINXM100XM100ON/OFFP12 P50P100GR10XRM10NFig. F53 : Non-automatic (manual) fault location© Schneider Electric - all rights reserved(1) On a 230/400 V 3-phase system.b Fixed automatic fault location (see Fig. F54 next page)The monitoring relay XM100, together with the fixed detectors XD1 or XD12 (eachconnected to a toroidal CT embracing the conductors of the circuit concerned)provide a system of automatic fault location on a live installation.Moreover, the level of insulation is indicated for each monitored circuit, and twolevels are checked: the first level warns of unusually low insulation resistance so thatpreventive measures may be taken, while the second level indicates a fault conditionand gives an alarm.Schneider Electric - Electrical installation guide 2009

F - Protection against electric shock7 Implementation of the IT systemMERLIN GERINXM100Toroidal CTsXM1001 to 12 circuitsXD1F31XD1 XD1 XD12Fig. F54 : Fixed automatic fault locationb Automatic monitoring, logging, and fault location (see Fig. F55)The Vigilohm System also allows access to a printer and/or a PC which providesa global review of the insulation level of an entire installation, and records thechronological evolution of the insulation level of each circuit.The central monitor XM100, together with the localization detectors XD08 and XD16,associated with toroidal CTs from several circuits, as shown below in Figure F55,provide the means for this automatic exploitation.MERLIN GERINXM100XM100MERLIN GERINXL08MERLIN GERINXL16897678XD08XD16Fig. F55 : Automatic fault location and insulation-resistance data logging© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

F - Protection against electric shock7 Implementation of the IT systemF32Implementation of permanent insulation-monitoring (PIM) devicesb ConnectionThe PIM device is normally connected between the neutral (or articificial neutral)point of the power-supply transformer and its earth electrode.b SupplyPower supply to the PIM device should be taken from a highly reliable source. Inpractice, this is generally directly from the installation being monitored, throughovercurrent protective devices of suitable short-circuit current rating.b Level settingsCertain national standards recommend a first setting at 20% below the insulationlevel of the new installation. This value allows the detection of a reduction of theinsulation quality, necessitating preventive maintenance measures in a situation ofincipient failure.The detection level for earth-fault alarm will be set at a much lower level.By way of an example, the two levels might be:v New installation insulation level: 100 kΩv Leakage current without danger: 500 mA (fire risk at > 500 mA)v Indication levels set by the consumer:- Threshold for preventive maintenance: 0.8 x 100 = 80 kΩ- Threshold for short-circuit alarm: 500 ΩNotes:v Following a long period of shutdown, during which the whole, or part of the installationremains de-energized, humidity can reduce the general level of insulation resistance.This situation, which is mainly due to leakage current over the damp surface ofhealthy insulation, does not constitute a fault condition, and will improve rapidly as thenormal temperature rise of current-carrying conductors reduces the surface humidity.v The PIM device (XM) can measure separately the resistive and the capacitivecurrent components of the leakage current to earth, thereby deriving the trueinsulation resistance from the total permanent leakage current.© Schneider Electric - all rights reservedThree methods of calculation are commonlyused:b The method of impedances, based on thetrigonometric addition of the system resistancesand inductive reactancesb The method of compositionb The conventional method, based on anassumed voltage drop and the use of preparedtablesThe case of a second faultA second earth fault on an IT system (unless occurring on the same conductoras the first fault) constitutes a phase-phase or phase-to-neutral fault, and whetheroccurring on the same circuit as the first fault, or on a different circuit, overcurrentprotective devices (fuses or circuit-breakers) would normally operate an automaticfault clearance.The settings of overcurrent tripping relays and the ratings of fuses are the basicparameters that decide the maximum practical length of circuit that can besatisfactorily protected, as discussed in Sub-clause 6.2.Note: In normal circumstances, the fault current path is through commonPE conductors, bonding all exposed conductive parts of an installation, and so thefault loop impedance is sufficiently low to ensure an adequate level of fault current.Where circuit lengths are unavoidably long, and especially if the appliances of acircuit are earthed separately (so that the fault current passes through two earthelectrodes), reliable tripping on overcurrent may not be possible.In this case, an RCD is recommended on each circuit of the installation.Where an IT system is resistance earthed, however, care must be taken to ensurethat the RCD is not too sensitive, or a first fault may cause an unwanted trip-out.Tripping of residual current devices which satisfy IEC standards may occur at valuesof 0.5 ΙΔn to ΙΔn, where ΙΔn is the nominal residual-current setting level.Methods of determining levels of short-circuit currentA reasonably accurate assessment of short-circuit current levels must be carried outat the design stage of a project.A rigorous analysis is not necessary, since current magnitudes only are important forthe protective devices concerned (i.e. phase angles need not be determined) so thatsimplified conservatively approximate methods are normally used. Three practicalmethods are:b The method of impedances, based on the vectorial summation of all the (positivephase-sequence)impedances around a fault-current loopb The method of composition, which is an approximate estimation of short-circuitcurrent at the remote end of a loop, when the level of short-circuit current at the nearend of the loop is known. Complex impedances are combined arithmetically in thismethodb The conventional method, in which the minimum value of voltage at the origin ofa faulty circuit is assumed to be 80% of the nominal circuit voltage, and tables areused based on this assumption, to give direct readings of circuit lengths.Schneider Electric - Electrical installation guide 2009

F - Protection against electric shock7 Implementation of the IT systemThe software Ecodial is based on the “methodof impedance”The maximum length of an IT earthed circuit is:b For a 3-phase 3-wire scheme0.8 Uo 3 SphLmax=2 Ia1+m( )b For a 3-phase 4-wire scheme0.8 Uo S1Lmax=2 Ia1+m( )These methods are reliable only for the cases in which wiring and cables whichmake up the fault-current loop are in close proximity (to each other) and are notseparated by ferro-magnetic materials.Methods of impedancesThis method as described in Sub-clause 6.2, is identical for both the IT andTN systems of earthing.Methods of compositionThis method as described in Sub-clause 6.2, is identical for both the IT andTN systems of earthing.Conventional method (see Fig. F56)The principle is the same for an IT system as that described in Sub-clause 6.2 for aTN system : the calculation of maximum circuit lengths which should not be exceededdownstream of a circuit-breaker or fuses, to ensure protection by overcurrent devices.It is clearly impossible to check circuit lengths for every feasible combination of twoconcurrent faults.All cases are covered, however, if the overcurrent trip setting is based on theassumption that a first fault occurs at the remote end of the circuit concerned,while the second fault occurs at the remote end of an identical circuit, as alreadymentioned in Sub-clause 3.4. This may result, in general, in one trip-out onlyoccurring (on the circuit with the lower trip-setting level), thereby leaving the systemin a first-fault situation, but with one faulty circuit switched out of service.b For the case of a 3-phase 3-wire installation the second fault can only cause aphase/phase short-circuit, so that the voltage to use in the formula for maximumcircuit length is 3 Uo.The maximum circuit length is given by:F330.8 Uo 3 SphLmax=metres2 Ia1+m( )b For the case of a 3-phase 4-wire installation the lowest value of fault current willoccur if one of the faults is on a neutral conductor. In this case, Uo is the value to usefor computing the maximum cable length, and0.8 Uo S1Lmax=2 Ia1+m( )metresi.e. 50% only of the length permitted for a TN scheme (1)NNPECDABPEIdIdIdIdNon distributed neutralFig. F56 : Calculation of Lmax. for an IT-earthed system, showing fault-current path for a double-fault condition(1) Reminder: There is no length limit for earth-fault protectionon a TT scheme, since protection is provided by RCDs of highsensitivity.Schneider Electric - Electrical installation guide 2009Distributed neutral© Schneider Electric - all rights reserved

F - Protection against electric shock7 Implementation of the IT systemF34The following tables (1) give the length of circuitwhich must not be exceeded, in order thatpersons be protected against indirect contacthazards by protective devicesIn the preceding formulae:Lmax = longest circuit in metresUo = phase-to-neutral voltage (230 V on a 230/400 V system)ρ = resistivity at normal operating temperature (22.5 x 10 -3 ohms-mm 2 /m for copper,36 x 10 -3 ohms-mm 2 /m for aluminium)Ia = overcurrent trip-setting level in amps, or Ia = current in amps required to clearthe fuse in the specified timem =SphSPESPE = cross-sectional area of PE conductor in mm 2S1 = S neutral if the circuit includes a neutral conductorS1 = Sph if the circuit does not include a neutral conductorTablesThe following tables have been established according to the “conventional method”described above.The tables give maximum circuit lengths, beyond which the ohmic resistance ofthe conductors will limit the magnitude of the short-circuit current to a level belowthat required to trip the circuit-breaker (or to blow the fuse) protecting the circuit,with sufficient rapidity to ensure safety against indirect contact. The tables take intoaccount:b The type of protection: circuit-breakers or fuses, operating-current settingsb Cross-sectional area of phase conductors and protective conductorsb Type of earthing schemeb Correction factor: Figure F57 indicates the correction factor to apply to the lengthsgiven in tables F40 to F43, when considering an IT systemCircuit Conductor m = Sph/SPE (or PEN)material m = 1 m = 2 m = 3 m = 43 phases Copper 0.86 0.57 0.43 0.34Aluminium 0.54 0.36 0.27 0.213ph + N or 1ph + N Copper 0.50 0.33 0.25 0.20Aluminium 0.31 0.21 0.16 0.12Fig. F57 : Correction factor to apply to the lengths given in tables F41 to F44 for TN systemsExampleA 3-phase 3-wire 230/400 V installation is IT-earthed.One of its circuits is protected by a circuit-breaker rated at 63 A, and consists of analuminium-cored cable with 50 mm 2 phase conductors. The 25 mm 2 PE conductoris also aluminum. What is the maximum length of circuit, below which protection ofpersons against indirect-contact hazards is assured by the instantaneous magnetictripping relay of the circuit-breaker?Figure F42 indicates 603 metres, to which must be applied a correction factor of 0.36(m = 2 for aluminium cable).The maximum length is therefore 217 metres.7.3 High-sensitivity RCDs© Schneider Electric - all rights reservedFig. F62 : Circuit supplying socket-outlets(1) The tables are those shown in Sub-clause 6.2 (FiguresF41 to F44). However, the table of correction factors (FigureF57) which takes into account the ratio Sph/SPE, and of thetype of circuit (3-ph 3-wire; 3-ph 4-wire; 1-ph 2-wire) as wellas conductor material, is specific to the IT system, and differsfrom that for TN.According to IEC 60364-4-41, high sensitivity RCDs (y 30 mA) must be used forprotection of socket outlets with rated current y 20 A in all locations. The use of suchRCDs is also recommended in the following cases:b Socket-outlet circuits in wet locations at all current ratingsb Socket-outlet circuits in temporary installationsb Circuits supplying laundry rooms and swimming poolsb Supply circuits to work-sites, caravans, pleasure boats, and travelling fairsSee 2.2 and chapter P, al section 3Schneider Electric - Electrical installation guide 2009

F - Protection against electric shock7 Implementation of the IT system7.4 Protection in high fire-risk locationsProtection by a RCD of sensitivity y 500 mA at the origin of the circuit supplying thefire-risk locations is mandatory in some countries (see Fig. F59).A preferred sensitivity of 300 mA may be adopted.7.5 When the fault current-loop impedance isparticularly highWhen the earth-fault current is restricted due to an inevitably high fault-loopimpedance, so that the overcurrent protection cannot be relied upon to trip the circuitwithin the prescribed time, the following possibilities should be considered:Fig. F59 : Fire-risk location2 y I rm y 4I nGreat length of cablePEFig. F60 : A circuit-breaker with low-set instantaneousmagnetic tripFire-risklocationSuggestion 1 (see Fig. F60)b Install a circuit-breaker which has an instantaneous magnetic tripping element withan operation level which is lower than the usual setting, for example:2In y Irm y 4InThis affords protection for persons on circuits which are abnormally long. It mustbe checked, however, that high transient currents such as the starting currents ofmotors will not cause nuisance trip-outs.b Schneider Electric solutionsv Compact NSX with G trip unit or Micrologic trip unit (2Im y Irm y 4Im)v Type B Multi 9 circuit-breakerSuggestion 2 (see Fig. F61)Install a RCD on the circuit. The device does not need to be highly-sensitive (HS)(several amps to a few tens of amps). Where socket-outlets are involved, theparticular circuits must, in any case, be protected by HS (y 30 mA) RCDs; generallyone RCD for a number of socket outlets on a common circuit.b Schneider Electric solutionsv RCD Multi 9 NG125 : ΙΔn = 1 or 3 Av Vigicompact MH or ME: ΙΔn = 3 to 30 ASuggestion 3Increase the size of the PE conductors and/or the phase conductors, to reduce theloop impedance.Suggestion 4 (see Fig. F62)Add supplementary equipotential conductors. This will have a similar effect to thatof suggestion 3, i.e. a reduction in the earth-fault-loop resistance, while at the sametime improving the existing touch-voltage protection measures. The effectivenessof this improvement may be checked by a resistance test between each exposedconductive part and the local main protective conductor.F35PhasesNeutralPEFig. F61 : RCD protectionFig. F62 : Improved equipotential bonding© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

F - Protection against electric shock8 Residual current devices (RCDs)F36Industrial circuit-breakers with an integratedRCD are covered in IEC 60947-2 and itsappendix B8.1 Types of RCDsResidual current devices (RCD) are commonly incorporated in or associated with thefollowing components:b Industrial-type moulded-case circuit-breakers (MCCB) and air circuit-breakers(ACB) conforming to IEC 60947-2 and its appendix B and Mb Industrial type miniature circuit-breakers (MCB) conforming to IEC 60947-2 and itsappendix B and Mb Household and similar miniature circuit-breakers (MCB) complying with IEC 60898,IEC 61008, IEC 61009b Residual load switch conforming to particular national standardsb Relays with separate toroidal (ring-type) current transformers, conforming toIEC 60947-2 Appendix MRCDs are mandatorily used at the origin of TT-earthed installations, where theirability to discriminate with other RCDs allows selective tripping, thereby ensuring thelevel of service continuity required.Industrial type circuit-breakers with integrated or adaptableRCD module (see Fig. F63)Industrial type circuit-breakerVigi CompactFig. F63 : Industrial-type CB with RCD moduleMulti 9 DIN-rail industrialCircuit-breaker with adaptable Vigi RCD moduleHousehold or domestic circuit-breakers withan integrated RCD are covered in IEC 60898,IEC 61008 and IEC 61009Adaptable residual current circuit-breakers, including DIN-rail mounted units (e.g.Compact or Multi 9), are available, to which may be associated an auxiliary RCDmodule (e.g. Vigi).The ensemble provides a comprehensive range of protective functions (isolation,protection against short-circuit, overload, and earth-fault.Household and similar miniature circuit-breakers with RCD(see Fig. F64)© Schneider Electric - all rights reservedThe incoming-supply circuitbreakercan also have timedelayedcharacteristics andintegrate a RCD (type S).“Monobloc” Déclic Vigi residual current circuit-breakersintended for protection of terminal socket-outlet circuitsin domestic and tertiary sector applications.Fig. F64 : Domestic residual current circuit-breakers (RCCBs) for earth leakage protectionSchneider Electric - Electrical installation guide 2009

F - Protection against electric shock8 Residual current devices (RCDs)Residual current load break switches arecovered by particular national standards.RCDs with separate toroidal currenttransformers are standardized in IEC 60947-2appendix MResidual current circuit-breakers and RCDs with separatetoroidal current transformer (see Fig. F65)RCDs with separate toroidal CTs can be used in association with circuit-breakers orcontactors.F37Fig. F65 : RCDs with separate toroidal current transformers (Vigirex)I1I2Fig. F66 : The principle of RCD operationI38.2 DescriptionPrincipleThe essential features are shown schematically in Figure F66 below.A magnetic core encompasses all the current-carrying conductors of an electriccircuit and the magnetic flux generated in the core will depend at every instant onthe arithmetical sum of the currents; the currents passing in one direction beingconsidered as positive (Ι1), while those passing in the opposite direction will benegative (Ι2).In a normally healthy circuit Ι1 + Ι2 = 0 and there will be no flux in the magnetic core,and zero e.m.f. in its coil.An earth-fault current Ιd will pass through the core to the fault, but will return to thesource via the earth, or via protective conductors in a TN-earthed system.The current balance in the conductors passing through the magnetic core thereforeno longer exists, and the difference gives rise to a magnetic flux in the core.The difference current is known as the “residual” current and the principle is referredto as the “residual current” principle.The resultant alternating flux in the core induces an e.m.f. in its coil, so that a currentI3 flows in the tripping-device operating coil. If the residual current exceeds the valuerequired to operate the tripping device either directly or via an electronic relay, thenthe associated circuit-breaker will trip.8.3 Sensitivity of RDCs to disturbancesIn certain cases, aspects of the environment can disturb the correct operation ofRCDs:b “nuisance” tripping: Break in power supply without the situation being reallyhazardous. This type of tripping is often repetitive, causing major inconvenience anddetrimental to the quality of the user's electrical power supply.b non-tripping, in the event of a hazard. Less perceptible than nuisance tripping,these malfunctions must still be examined carefully since they undermine user safety.This is why international standards define 3 categories of RCDs according to theirimmunity to this type of disturbance (see below).© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

F - Protection against electric shock8 Residual current devices (RCDs)F38I100%90%10 s (f = 100 kHz)10%tca.0.5 s60%Fig. F67 : Standardized 0.5 µs/100 kHz current transient waveUUmax0.5Ut1.2 s 50 sFig. F68 : Standardized 1.2/50 µs voltage transient waveI10.9Main disturbance typesPermanent earth leakage currentsEvery LV installation has a permanent leakage current to earth, which is either dueto:b Unbalance of the intrinsic capacitance between live conductors and earth for threephasecircuits orb Capacitance between live conductors and earth for single-phase circuitsThe larger the installation the greater its capacitance with consequently increasedleakage current.The capacitive current to earth is sometimes increased significantly by filteringcapacitors associated with electronic equipment (automation, IT and computerbasedsystems, etc.).In the absence of more precise data, permanent leakage current in a giveninstallation can be estimated from the following values, measured at 230 V 50 Hz:Single-phase or three-phase line: 1.5 mA /100mb Heating floor: 1mA / kWb Fax terminal, printer: 1 mAb Microcomputer, workstation: 2 mAb Copy machine: 1.5 mASince RCDs complying with IEC and many national standards may operate under,the limitation of permanent leakage current to 0.25 IΔn, by sub-division of circuitswill, in practice, eliminate any unwanted tripping.For very particular cases, such as the extension, or partial renovation of extendedIT-earthed installations, the manufacturers must be consulted.High frequency components (harmonics, transients, etc.), are generated bycomputer equipment power supplies, converters, motors with speed regulators,fluorescent lighting systems and in the vicinity of high power switching devices andreactive energy compensation banks.Part of these high frequency currents may flow to earth through parasiticcapacitances. Although not hazardous for the user, these currents can still cause thetripping of differential devices.EnergizationThe initial energization of the capacitances mentioned above gives rise to highfrequency transient currents of very short duration, similar to that shown inFigure F67.The sudden occurrence of a first-fault on an IT-earthed system also causes transientearth-leakage currents at high frequency, due to the sudden rise of the two healthyphases to phase/phase voltage above earth.Common mode overvoltagesElectrical networks are subjected to overvoltages due to lightning strikes or to abruptchanges of system operating conditions (faults, fuse operation, switching, etc.).These sudden changes often cause large transient voltages and currents in inductiveand capacitive circuits. Records have established that, on LV systems, overvoltagesremain generally below 6 kV, and that they can be adequately represented by theconventional 1.2/50 μs impulse wave (see Fig. F68).0.5These overvoltages give rise to transient currents represented by a current impulsewave of the conventional 8/20 μs form, having a peak value of several tens ofamperes (see Fig. F69).The transient currents flow to earth via the capacitances of the installation.Non-sinusoidal fault currents© Schneider Electric - all rights reserved0.1Fig. F69 : Standardized current-impulse wave 8/20 µstType AC, A, BStandard IEC 60755 (General requirements for residual current operated protectivedevices) defines three types of RCD depending on the characteristics of the faultcurrent:b Type ACRCD for which tripping is ensured for residual sinusoidal alternating currents.b Type ARCD for which tripping is ensured:v for residual sinusoidal alternating currents,v for residual pulsating direct currents,Schneider Electric - Electrical installation guide 2009

F - Protection against electric shock8 Residual current devices (RCDs)b Type BRCD for which tripping is ensured:v as for type A,v for pure direct residual currents which may result from three-phase rectifyingcircuits.Cold: in the cases of temperatures under - 5 °C, very high sensitivityelectromechanical relays in the RCD may be “welded” by the condensation – freezingaction.Type “Si” devices can operate under temperatures down to - 25 °C.Atmospheres with high concentrations of chemicals or dust: the special alloysused to make the RCDs can be notably damaged by corrosion. Dust can also blockthe movement of mechanical parts.See the measures to be taken according to the levels of severity defined bystandards in Fig. F70.Regulations define the choice of earth leakage protection and its implementation.The main reference texts are as follows:b Standard IEC 60364-3:v This gives a classification (AFx) for external influences in the presence of corrosiveor polluting substances.v It defines the choice of materials to be used according to extreme influences.F39DisturbednetworkInfluence ofthe electricalnetworkClean networkSuperimmunizedresidual currentprotectionsType A if: kStandardimmunizedresidual currentprotectionsType ACSiE kresidual currentprotectionsSiE kresidual currentprotections+Appropriateadditionalprotection(sealed cabinetor unit)AF1 AF2 AF3 AF4SiE kresidual currentprotections+Appropriateadditionalprotection(sealed cabinetor unit +overpressure)b Externalinfluences:negligible,b Externalinfluences:presenceof corrosiveor pollutingatmosphericagents,b Externalinfluences:intermittentor accidentalaction ofcertaincommonchemicals,b Externalinfluences:permanentaction ofcorrosiveor pollutingchemicalsb Equipmentcharacteristics:normal.b Equipmentcharacteristics:e.g. conformitywith salt mistor atmosphericpollution tests.b Equipmentcharacteristics:corrosionprotection.b Equipmentcharacteristics:specificallystudiedaccording tothe type ofproducts.Examples of exposed sitesIron and steel works.Marinas, trading ports, boats, sea edges, navalshipyards.Swimming pools, hospitals, food & beverage.Petrochemicals.Breeding facilities, tips.External influencesPresence of sulfur, sulfur vapor, hydrogensulfide.Salt atmospheres, humid outside, lowtemperatures.Chlorinated compounds.Hydrogen, combustion gases, nitrogenoxides.Hydrogen sulfide.Fig. F70 : External influence classification according to IEC 60364-3 standard© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

F - Protection against electric shock8 Residual current devices (RCDs)Immunity level for Merlin Gerin residual current devicesThe Merlin Gerin range comprises various types of RCDs allowing earth leakageprotection to be adapted to each application. The table below indicates the choices tobe made according to the type of probable disturbances at the point of installation.Device typeNuisancetrippingsNon-trippingsHighfrequencyleakagecurrentFault currentRectifiedalternatingPure directLowtemperatures(down to- 25 °C)CorrosionDustACbF40A b b bSI b b b b bSiE b b b b b bB b b b b b bFig. F71 : Immunity level of Merlin Gerin RCDsImmunity to nuisance trippingType Si/SiE RCDs have been designed to avoid nuisance tripping or non-tripping incase of polluted network , lightning effect, high frequency currents, RF waves, etc.Figure F72 below indicates the levels of tests undergone by this type of RCDs.Disturbance type Rated test wave ImmunityContinuous disturbancesMulti9 :ID-RCCB, DPN Vigi, Vigi C60, VigiC120, Vigi NG125SI / SiE typeHarmonics 1 kHz Earth leakage current = 8 x I∆nTransient disturbances© Schneider Electric - all rights reservedLightning induced overvoltageLightning induced currentSwitching transient, indirectlightning currentsDownstream surge arresteroperation, capacitance loadingElectromagnetic compatibilityInductive load switchingsfluorescent lights, motors, etc.)Fluorescent lights, thyristorcontrolled circuits, etc.RF waves (TV&radio, broadcact,telecommunications,etc.)1.2 / 50 µs pulse(IEC/EN 61000-4-5)8 / 20 µs pulse(IEC/EN 61008)0.5 µs / 100 kHz“ ring wave ”(IEC/EN 61008)4.5 kV between conductors 5.5 kV /earth5 kA peak400 A peak10 ms pulse 500 ARepeated bursts(IEC 61000-4-4)RF conductedwaves(IEC 61000-4-6)RF radiated waves80 MHz to 1 GHz(IEC 61000-4-3)4 kV / 400 kHz66 mA (15 kHz to 150 kHz)30 V (150 kHz to 230 MHz)30 V / mFig. F72 : Immunity to nuisance tripping tests undergone by Merlin Gerin RCDsSchneider Electric - Electrical installation guide 2009

F - Protection against electric shock8 Residual current devices (RCDs)Recommendations concerning the installation of RCDs withseparate toroidal current transformersThe detector of residual current is a closed magnetic circuit (usually circular) ofvery high magnetic permeability, on which is wound a coil of wire, the ensembleconstituting a toroidal (or ring-type) current transformer.Because of its high permeability, any small deviation from perfect symmetry ofthe conductors encompassed by the core, and the proximity of ferrous material(steel enclosure, chassis members, etc.) can affect the balance of magnetic forcessufficiently, at times of large load currents (motor-starting current, transformerenergizing current surge, etc.) to cause unwanted tripping of the RCD.Unless particular measures are taken, the ratio of operating current IΔn to maximumphase current Iph (max.) is generally less than 1/1,000.This limit can be increased substantially (i.e. the response can be desensitized) byadopting the measures shown in Figure F73, and summarized in Figure F74.F41LL = twice the diameter ofthe magnetic ring coreFig. F73 : Three measures to reduce the ratio IΔn/Iph (max.)Measures Diameter Sensitivity(mm)diminution factorCareful centralizing of cables through the ring core 3Oversizing of the ring core ø 50 → ø 100 2ø 80 → ø 200 2ø 120 → ø 300 6Use of a steel or soft-iron shielding sleeve ø 50 4b Of wall thickness 0.5 mm ø 80 3b Of length 2 x inside diameter of ring core ø 120 3b Completely surrounding the conductors and ø 200 2overlapping the circular core equally at both endsThese measures can be combined. By carefully centralizing the cables in a ring coreof 200 mm diameter, where a 50 mm core would be large enough, and using a sleeve,the ratio 1/1,000 could become 1/30,000.Fig. F74 : Means of reducing the ratio IΔn/Iph (max.)© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

F - Protection against electric shock8 Residual current devices (RCDs)F42abIn1InInIn1 In2 In3 In4Fig. F75 : Residual current circuit-breakers (RCCBs)Choice of characteristics of a residual-current circuit-breaker(RCCB - IEC 61008)Rated currentThe rated current of a RCCB is chosen according to the maximum sustained loadcurrent it will carry.b If the RCCB is connected in series with, and downstream of a circuit-breaker, therated current of both items will be the same, i.e. In u In1 (see Fig. F75a)b If the RCCB is located upstream of a group of circuits, protected by circuitbreakers,as shown in Figure F75b, then the RCCB rated current will be given by:In u ku x ks (In1 + In2 + In3 + In4)Electrodynamic withstand requirementsProtection against short-circuits must be provided by an upstream SCPD (Short-Circuit Protective Device) but it is considered that where the RCCB is located in thesame distribution box (complying with the appropriate standards) as the downstreamcircuit-breakers (or fuses), the short-circuit protection afforded by these (outgoingcircuit)SCPDs is an adequate alternative. Coordination between the RCCB and theSCPDs is necessary, and manufacturers generally provide tables associating RCCBsand circuit-breakers or fuses (see Fig. F76).Circuit-breaker and RCCB association – maxi Isc (r.m.s) value in kAUpstream circuit-breaker DT40 DT40N C60N C60H C60L C120N C120H NG125N NG125HDownstream 2P I 20A 6.5 6.5 6.5 6.5 6.5 3 4.5 4.5 4.5RCCB 230V IN-A 40A 6 10 20 30 30 10 10 15 15IN-A 63A 6 10 20 30 30 10 10 15 15I 100A 15 15 15 154P I 20A 4.5 4.5 4.5 4.5 4.5 2 3 3 3400V IN-A 40A 6 10 10 15 15 7 7 15 15IN-A 63A 6 10 10 15 15 7 7 15 15NG 125NA 10 16 25 50Fuses and RCCB association – maxi Isc (r.m.s) value in kAgG upstream fuse 20A 63A 100A 125ADownstream 2P I 20A 8RCCB 230V IN-A 40A 30 20IN-A 63A 30 20I 100A 64P I 20A 8400V IN-A 40A 30 20IN-A 63A 30 20NG 125NA 50Fig. F76 : Typical manufacturers coordination table for RCCBs, circuit-breakers, and fuses (Merlin Gerin products)© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Chapter GSizing and protection of conductors12345678ContentsGeneral1.1 Methodology and definition G21.2 Overcurrent protection principles G41.3 Practical values for a protective scheme G41.4 Location of protective devices G61.5 Conductors in parallel G6Practical method for determining the smallest allowable G7cross-sectional area of circuit conductors2.1 General G72.2 General method for cables G72.3 Recommended simplified approach for cables G162.4 Busbar trunking systems G18Determination of voltage dropG203.1 Maximum voltage drop limit G203.2 Calculation of voltage drop in steady load conditions G21Short-circuit currentG244.1 Short-circuit current at the secondary terminals of G24a MV/LV distribution transformer4.2 3-phase short-circuit current (Isc) at any point within G25a LV installation4.3 Isc at the receiving end of a feeder in terms of the Isc G28at its sending end4.4 Short-circuit current supplied by an alternator or an inverter G29Particular cases of short-circuit currentG305.1 Calculation of minimum levels of short-circuit current G305.2 Verification of the withstand capabilities of cables under G35short-circuit conditionsProtective earthing conductorG376.1 Connection and choice G376.2 Conductor sizing G386.3 Protective conductor between MV/LV transformer and G40the main general distribution board (MGDB)6.4 Equipotential conductor G41The neutral conductorG427.1 Sizing the neutral conductor G427.2 Protection of the neutral conductor G427.3 Breaking of the neutral conductor G447.4 Isolation of the neutral conductor G44Worked example of cable calculationG2G46G© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors1 GeneralGComponent parts of an electric circuit and itsprotection are determined such that all normaland abnormal operating conditions are satisfied1.1 Methodology and definitionMethodology (see Fig. G1 )Following a preliminary analysis of the power requirements of the installation, asdescribed in Chapter B Clause 4, a study of cabling (1) and its electrical protection isundertaken, starting at the origin of the installation, through the intermediate stagesto the final circuits.The cabling and its protection at each level must satisfy several conditions at thesame time, in order to ensure a safe and reliable installation, e.g. it must:b Carry the permanent full load current, and normal short-time overcurrentsb Not cause voltage drops likely to result in an inferior performance of certain loads,for example: an excessively long acceleration period when starting a motor, etc.Moreover, the protective devices (circuit-breakers or fuses) must:b Protect the cabling and busbars for all levels of overcurrent, up to and includingshort-circuit currentsb Ensure protection of persons against indirect contact hazards, particularly inTN- and IT- earthed systems, where the length of circuits may limit the magnitudeof short-circuit currents, thereby delaying automatic disconnection (it may beremembered that TT- earthed installations are necessarily protected at the origin bya RCD, generally rated at 300 mA).The cross-sectional areas of conductors are determined by the general methoddescribed in Sub-clause 2 of this Chapter. Apart from this method some nationalstandards may prescribe a minimum cross-sectional area to be observed for reasonsof mechanical endurance. Particular loads (as noted in Chapter N) require that thecable supplying them be oversized, and that the protection of the circuit be likewisemodified.Power demand:- kVA to be supplied- Maximum load current I BConductor sizing:- Selection of conductor type and insulation- Selection of method of installation- Taking account of correction factors fordifferent environment conditions- Determination of cross-sectional areas usingtables giving the current carrying capabilityVerification of the maximum voltage drop:- Steady state conditions- Motor starting conditionsCalculation of short-circuit currents:- Upstream short-circuit power- Maximum values- Minimum values at conductor end© Schneider Electric - all rights reserved(1) The term “cabling” in this chapter, covers all insulatedconductors, including multi-core and single-core cables andinsulated wires drawn into conduits, etc.Fig. G1 : Flow-chart for the selection of cable size and protective device rating for a given circuitSchneider Electric - Electrical installation guide 2009Selection of protective devices:- Rated current- Breaking capability- Implementation of cascading- Check of discrimination

G - Sizing and protection of conductors1 GeneralDefinitionsMaximum load current: IBb At the final circuits level, this current corresponds to the rated kVA of the load.In the case of motor-starting, or other loads which take a high in-rush current,particularly where frequent starting is concerned (e.g. lift motors, resistance-typespot welding, and so on) the cumulative thermal effects of the overcurrents must betaken into account. Both cables and thermal type relays are affected.b At all upstream circuit levels this current corresponds to the kVA to be supplied,which takes account of the factors of simultaneity (diversity) and utilization, ks and kurespectively, as shown in Figure G2.Main distributionboardCombined factors of simultaneity(or diversity) and utilization:ks x ku = 0.69IB = (80+60+100+50) x 0.69 = 200 AGSub-distributionboard80 A 60 A 100 A50 AMNormal loadmotor current50 AFig. G2 : Calculation of maximum load current IBMaximum permissible current: IzThis is the maximum value of current that the cabling for the circuit can carryindefinitely, without reducing its normal life expectancy.The current depends, for a given cross sectional area of conductors, on severalparameters:b Constitution of the cable and cable-way (Cu or Alu conductors; PVC or EPR etc.insulation; number of active conductors)b Ambient temperatureb Method of installationb Influence of neighbouring circuitsOvercurrentsAn overcurrent occurs each time the value of current exceeds the maximum loadcurrent IB for the load concerned.This current must be cut off with a rapidity that depends upon its magnitude, ifpermanent damage to the cabling (and appliance if the overcurrent is due to adefective load component) is to be avoided.Overcurrents of relatively short duration can however, occur in normal operation; twotypes of overcurrent are distinguished:b OverloadsThese overcurrents can occur in healthy electric circuits, for example, due to anumber of small short-duration loads which occasionally occur co-incidentally: motorstarting loads, and so on. If either of these conditions persists however beyond agiven period (depending on protective-relay settings or fuse ratings) the circuit will beautomatically cut off.b Short-circuit currentsThese currents result from the failure of insulation between live conductors or/andbetween live conductors and earth (on systems having low-impedance-earthedneutrals) in any combination, viz:v 3 phases short-circuited (and to neutral and/or earth, or not)v 2 phases short-circuited (and to neutral and/or earth, or not)v 1 phase short-circuited to neutral (and/or to earth)© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors1 General1.2 Overcurrent protection principlesA protective device is provided at the origin of the circuit concerned (see Fig. G3 andFig. G4).b Acting to cut-off the current in a time shorter than that given by the I 2 tcharacteristic of the circuit cablingb But allowing the maximum load current IB to flow indefinitelyThe characteristics of insulated conductors when carrying short-circuit currentscan, for periods up to 5 seconds following short-circuit initiation, be determinedapproximately by the formula:I 2 t = k 2 S 2 which shows that the allowable heat generated is proportional to thesquared cross-sectional-area of the condutor.GtMaximumloadcurrentI 2 t cablecharacteristicwheret: Duration of short-circuit current (seconds)S: Cross sectional area of insulated conductor (mm 2 )I: Short-circuit current (A r.m.s.)k: Insulated conductor constant (values of k 2 are given in Figure G52 )For a given insulated conductor, the maximum permissible current varies accordingto the environment. For instance, for a high ambient temperature (θa1 > θa2), Iz1 isless than Iz2 (see Fig. G5). θ means “temperature”.Note:v ISC: 3-phase short-circuit currentv ISCB: rated 3-ph. short-circuit breaking current of the circuit-breakerv Ir (or Irth) (1) : regulated “nominal” current level; e.g. a 50 A nominal circuit-breakercan be regulated to have a protective range, i.e. a conventional overcurrent trippinglevel (see Fig. G6 opposite page) similar to that of a 30 A circuit-breaker.IB IrIzISCB ICUFig. G3 : Circuit protection by circuit-breakertTemporaryoverloadCircuit-breakertripping curveI1.3 Practical values for a protective schemeThe following methods are based on rules laid down in the IEC standards, and arerepresentative of the practices in many countries.General rulesA protective device (circuit-breaker or fuse) functions correctly if:b Its nominal current or its setting current In is greater than the maximum loadcurrent IB but less than the maximum permissible current Iz for the circuit, i.e.IB y In y Iz corresponding to zone “a” in Figure G6b Its tripping current I2 “conventional” setting is less than 1.45 Iz which correspondsto zone “b” in Figure G6The “conventional” setting tripping time may be 1 hour or 2 hours according to localstandards and the actual value selected for I2. For fuses, I2 is the current (denotedIf) which will operate the fuse in the conventional time.I 2 t cablecharacteristict1 2Fuse curveθa1 > θa2© Schneider Electric - all rights reservedTemporaryoverloadIBIr cIz IzFig. G4 : Circuit protection by fuses(1) Both designations are commonly used in differentstandards.5 sII 2 t = k 2 S 2IIz1 < Iz2Fig. G5 : I 2 t characteristic of an insulated conductor at two different ambient temperaturesSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors1 GeneralLoadsCircuit cablingMaximum load current IBMaximum load current Iz1.45 Iz0IBNominal current In orits regulated current IrI n I 2zone aIzzone bConventional overcurrenttrip current I2Protective device1.45 Iz IscISCBzone c3-ph short-circuitfault-current breaking ratingIB y In y Iz zone aI2 y 1.45 Iz zone bISCB u ISC zone cGFig. G6 : Current levels for determining circuir breaker or fuse characteristicsb Its 3-phase short-circuit fault-current breaking rating is greater than the 3-phaseshort-circuit current existing at its point of installation. This corresponds to zone “c” inFigure G6.Criteria for circuit-breakers:IB y In y Iz and ISCB u ISC.Criteria for fuses:IB y In y Iz/k3 and ISCF u ISC.Applicationsb Protection by circuit-breakerBy virtue of its high level of precision the current I2 is always less than 1.45 In (or1.45 Ir) so that the condition I2 y 1.45 Iz (as noted in the “general rules” above) willalways be respected.v Particular caseIf the circuit-breaker itself does not protect against overloads, it is necessary toensure that, at a time of lowest value of short-circuit current, the overcurrent deviceprotecting the circuit will operate correctly. This particular case is examined in Subclause5.1.b Protection by fusesThe condition I2 y 1.45 Iz must be taken into account, where I2 is the fusing (meltinglevel) current, equal to k2 x In (k2 ranges from 1.6 to 1.9) depending on the particularfuse concerned.A further factor k3 has been introduced ( k = k 23 ) such that I2 y 1.45 Iz1.45will be valid if In y Iz/k3.For fuses type gG:In < 16 A → k3 = 1.31In u 16 A → k3 = 1.10Moreover, the short-circuit current breaking capacity of the fuse ISCF must exceedthe level of 3-phase short-circuit current at the point of installation of the fuse(s).b Association of different protective devicesThe use of protective devices which have fault-current ratings lower than the faultlevel existing at their point of installation are permitted by IEC and many nationalstandards in the following conditions:v There exists upstream, another protective device which has the necessary shortcircuitrating, andv The amount of energy allowed to pass through the upstream device is less thanthat which can be withstood without damage by the downstream device and allassociated cabling and appliances.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors1 GeneralIn pratice this arrangement is generally exploited in:v The association of circuit-breakers/fusesv The technique known as “cascading” or “series rating” in which the strongcurrent-limiting performance of certain circuit-breakers effectively reduces theseverity of downstream short-circuitsPossible combinations which have been tested in laboratories are indicated in certainmanufacturers catalogues.1.4 Location of protective devicesGA protective device is, in general, required at theorigin of each circuitabBPP 2 P 3 P 450 mm 2 10 mm 2 25 mm 2< 3 mAP 1P 2 BP 3scBsShort-circuitprotectivedeviceOverloadprotectivedeviceGeneral rule (see Fig. G7a)A protective device is necessary at the origin of each circuit where a reduction ofpermissible maximum current level occurs.Possible alternative locations in certain circumstances(see Fig. G7b)The protective device may be placed part way along the circuit:b If AB is not in proximity to combustible material, andb If no socket-outlets or branch connections are taken from ABThree cases may be useful in practice:b Consider case (1) in the diagramv AB y 3 metres, andv AB has been installed to reduce to a practical minimum the risk of a short-circuit(wires in heavy steel conduit for example)b Consider case (2)v The upstream device P1 protects the length AB against short-circuits inaccordance with Sub-clause 5.1b Consider case (3)v The overload device (S) is located adjacent to the load. This arrangement isconvenient for motor circuits. The device (S) constitutes the control (start/stop) andoverload protection of the motor while (SC) is: either a circuit-breaker (designed formotor protection) or fuses type aMv The short-circuit protection (SC) located at the origin of the circuit conforms withthe principles of Sub-clause 5.1Circuits with no protection (see Fig. G7c)Eitherb The protective device P1 is calibrated to protect the cable S2 against overloadsand short-circuitsOrb Where the breaking of a circuit constitutes a risk, e.g.v Excitation circuits of rotating machinesv circuits of large lifting electromagnetsv the secondary circuits of current transformersNo circuit interruption can be tolerated, and the protection of the cabling is ofsecondary importance.Case (1) Case (2)Case (3)1.5 Conductors in parallel© Schneider Electric - all rights reservedcP 1 : C60 rated 15 A2.5 mm 2Fig. G7 : Location of protective devicesS 2 :1.5 mm2Conductors of the same cross-sectional-area, the same length, and of the samematerial, can be connected in parallel.The maximum permissible current is the sum of the individual-core maximumcurrents, taking into account the mutual heating effects, method of installation, etc.Protection against overload and short-circuits is identical to that for a single-cablecircuit.The following precautions should be taken to avoid the risk of short-circuits on theparalleled cables:b Additional protection against mechanical damage and against humidity, by theintroduction of supplementary protectionb The cable route should be chosen so as to avoid close proximity to combustiblematerialsSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors2 Practical method for determiningthe smallest allowable crosssectionalarea of circuit conductors2.1 GeneralThe reference international standard for the study of cabling is IEC 60364-5-52:“Electrical installation of buildings - Part 5-52: Selection and erection of electricalequipment - Wiring system”.A summary of this standard is presented here, with examples of the most commonlyused methods of installation. The current-carrying capacities of conductors in alldifferent situations are given in annex A of the standard. A simplified method for useof the tables of annex A is proposed in informative annex B of the standard.2.2 General method for cablesPossible methods of installation for different types ofconductors or cablesThe different admissible methods of installation are listed in Figure G8, inconjonction with the different types of conductors and cables.GConductors and cables Method of installationWithout Clipped Conduit Cable trunking Cable Cable ladder On Supportfixings direct (including ducting Cable tray insulators wireskirting trunking,Cable bracketsflush floor trunking)Bare conductors – – – – – – + –Insulated conductors – – + + + – + –Sheathed Multi-core + + + + + + 0 +cables(includingarmoured Single-core 0 + + + + + 0 +andmineralinsulated)+ Permitted.– Not permitted.0 Not applicable, or not normally used in practice.Fig. G8 : Selection of wiring systems (table 52-1 of IEC 60364-5-52)© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors2 Practical method for determiningthe smallest allowable crosssectionalarea of circuit conductorsPossible methods of installation for different situations:Different methods of installation can be implemented in different situations. Thepossible combinations are presented in Figure G9.The number given in this table refer to the different wiring systems considered.(see also Fig. G10)GSituationsMethod of installationWithout With Conduit Cable trunking Cable Cable ladder On Supportfixings fixings (including ducting cable tray, insulators wireskirting trunking,cable bracketsflush floor trunking)Building voids 40, 46, 0 15, 16, – 43 30, 31, 32, – –15, 16 41, 42 33, 34Cable channel 56 56 54, 55 0 44, 45 30, 31, 32, – –33, 34Buried in ground 72, 73 0 70, 71 – 70, 71 0 –Embedded in structure 57, 58 3 1, 2, 50, 51, 52, 53 44, 45 0 – –59, 60Surface mounted – 20, 21 4, 5 6, 7, 8, 9, 12, 13, 14 6, 7, 30, 31, 32, 36 –22, 23 8, 9 33, 34Overhead – – 0 10, 11 – 30, 31, 32 36 3533, 34Immersed 80 80 0 – 0 0 – –– Not permitted.0 Not applicable, or not normally used in practice.Fig. G9 : Erection of wiring systems (table 52-2 of IEC 60364-5-52)© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors2 Practical method for determiningthe smallest allowable crosssectionalarea of circuit conductorsExamples of wiring systems and reference methods ofinstallationsAn illustration of some of the many different wiring systems and methods ofinstallation is provided in Figure G10.Several reference methods are defined (with code letters A to G), groupinginstallation methods having the same characteristics relative to the current-carryingcapacities of the wiring systems.Item No. Methods of installation Description Reference method ofinstallation to be used toobtain current-carryingcapacity1 Insulated conductors or single-core A1cables in conduit in a thermallyinsulated wallRoomG2 Multi-core cables in conduit in a A2thermally insulated wallRoom4 Insulated conductors or single-core B1cables in conduit on a wooden, ormasonry wall or spaced less than0,3 x conduit diameter from it5 Multi-core cable in conduit on a B2wooden, or mansonry wall or spacedless than 0,3 x conduit diameterfrom it20 Single-core or multi-core cables: C- fixed on, or sapced less than 0.3 x cablediameter from a wooden wall30 On unperforated tray C0.3 D e0.3 D eFig. G10 : Examples of methods of installation (part of table 52-3 of IEC 60364-5-52) (continued on next page)© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors2 Practical method for determiningthe smallest allowable crosssectionalarea of circuit conductorsItem No. Methods of installation Description Reference method ofinstallation to be used toobtain current-carryingcapacity31 0.3 DOn perforated tray E or Fe0.3 D eMaximum operating temperature:G1036 Bare or insulated conductors on Ginsulators70 Multi-core cables in conduit or in cable Dducting in the ground71 Single-core cable in conduit or in cable Dducting in the groundFig. G10 : Examples of methods of installation (part of table 52-3 of IEC 60364-5-52)The current-carrying capacities given in the subsequent tables have beendetermined so that the maximum insulation temperature is not exceeded forsustained periods of time.For different type of insulation material, the maximum admissible temperature isgiven in Figure G11.Type of insulation Temperature limit °CPolyvinyl-chloride (PVC)70 at the conductorCross-linked polyethylene (XLPE) and ethylene 90 at the conductorpropylene rubber (EPR)Mineral (PVC covered or bare exposed to touch) 70 at the sheathMineral (bare not exposed to touch and not in105 at the seathcontact with combustible material)Fig. G11 : Maximum operating temperatures for types of insulation (table 52-4 of IEC 60364-5-52)© Schneider Electric - all rights reservedCorrection factors:In order to take environnement or special conditions of installation into account,correction factors have been introduced.The cross sectional area of cables is determined using the rated load current I Bdivided by different correction factors, k 1 , k 2 , ...:II' = BBk1⋅k2 ...I’ B is the corrected load current, to be compared to the current-carrying capacity ofthe considered cable.Schneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors2 Practical method for determiningthe smallest allowable crosssectionalarea of circuit conductorsb Ambient temperatureThe current-carrying capacities of cables in the air are based on an average airtemperature equal to 30 °C. For other temperatures, the correction factor is given inFigure G12 for PVC, EPR and XLPE insulation material.The related correction factor is here noted k 1 .Ambient temperature °C InsulationPVCXLPE and EPR10 1.22 1.1515 1.17 1.1220 1.12 1.0825 1.06 1.0435 0.94 0.9640 0.87 0.9145 0.79 0.8750 0.71 0.8255 0.61 0.7660 0.50 0.7165 - 0.6570 - 0.5875 - 0.5080 - 0.41G11Fig. G12 : Correction factors for ambient air temperatures other than 30 °C to be applied to thecurrent-carrying capacities for cables in the air (from table A.52-14 of IEC 60364-5-52)The current-carrying capacities of cables in the ground are based on an averageground temperature equal to 20 °C. For other temperatures, the correction factor isgiven in Figure G13 for PVC, EPR and XLPE insulation material.The related correction factor is here noted k 2 .Ground temperature °C InsulationPVCXLPE and EPR10 1.10 1.0715 1.05 1.0425 0.95 0.9630 0.89 0.9335 0.84 0.8940 0.77 0.8545 0.71 0.8050 0.63 0.7655 0.55 0.7160 0.45 0.6565 - 0.6070 - 0.5375 - 0.4680 - 0.38Fig. G13 : Correction factors for ambient ground temperatures other than 20 °C to be applied tothe current-carrying capacities for cables in ducts in the ground (from table A.52-15 ofIEC 60364-5-52)© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors2 Practical method for determiningthe smallest allowable crosssectionalarea of circuit conductorsb Soil thermal resistivityThe current-carrying capacities of cables in the ground are based on a groundresistivity equal to 2.5 K.m/W. For other values, the correction factor is given inFigure G14.The related correction factor is here noted k3.Thermal resistivity, K.m/W 1 1.5 2 2.5 3Correction factor 1.18 1.1 1.05 1 0.96Fig. G14 : Correction factors for cables in buried ducts for soil thermal resistivities other than 2.5K.m/W to be applied to the current-carrying capacities for reference method D (table A52.16 ofIEC 60364-5-52)G12Based on experience, a relationship exist between the soil nature and resistivity.Then, empiric values of correction factors k3 are proposed in Figure G15, dependingon the nature of soil.Nature of soilk3Very wet soil (saturated) 1.21Wet soil 1.13Damp soil 1.05Dry soil 1.00Very dry soil (sunbaked) 0.86Fig. G15 : Correction factor k3 depending on the nature of soilb Grouping of conductors or cablesThe current-carrying capacities given in the subsequent tables relate to singlecircuits consisting of the following numbers of loaded conductors:v Two insulated conductors or two single-core cables, or one twin-core cable(applicable to single-phase circuits);v Three insulated conductors or three single-core cables, or one three-core cable(applicable to three-phase circuits).Where more insulated conductors or cables are installed in the same group, a groupreduction factor (here noted k4) shall be applied.Examples are given in Figures G16 to G18 for different configurations (installationmethods, in free air or in the ground).Figure G16 gives the values of correction factor k4 for different configurations ofunburied cables or conductors, grouping of more than one circuit or multi-corecables.© Schneider Electric - all rights reservedArrangement Number of circuits or multi-core cables Reference methods(cables touching) 1 2 3 4 5 6 7 8 9 12 16 20Bunched in air, on a 1.00 0.80 0.70 0.65 0.60 0.57 0.54 0.52 0.50 0.45 0.41 0.38 Methods A to Fsurface, embedded orenclosedSingle layer on wall, floor 1.00 0.85 0.79 0.75 0.73 0.72 0.72 0.71 0.70 No further reduction Method Cor unperforated trayfactor for more thanSingle layer fixed directly 0.95 0.81 0.72 0.68 0.66 0.64 0.63 0.62 0.61 nine circuits orunder a wooden ceilingmulti-core cablesSingle layer on a 1.00 0.88 0.82 0.77 0.75 0.73 0.73 0.72 0.72 Methods E and Fperforated horizontal orvertical traySingle layer on ladder 1.00 0.87 0.82 0.80 0.80 0.79 0.79 0.78 0.78support or cleats etc.Fig. G16 : Reduction factors for groups of more than one circuit or of more than one multi-core cable (table A.52-17 of IEC 60364-5-52)Schneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors2 Practical method for determiningthe smallest allowable crosssectionalarea of circuit conductorsFigure G17 gives the values of correction factor k 4 for different configurations ofunburied cables or conductors, for groups of more than one circuit of single-corecables in free air.Method of installation Number Number of three-phase Use as aof tray circuits multiplier torating for 2 3Perforated 31 Touching 1 0.98 0.91 0.87 Three cables intrayshorizontal2 0.96 0.87 0.81 formation20 mm3 0.95 0.85 0.78Vertical 31 Touching 1 0.96 0.86 Three cables inperforatedverticaltrays 2 0.95 0.84 formation225 mmG13Ladder 32 1 1.00 0.97 0.96 Three cables insupports,Touchinghorizontalcleats, etc... 33 2 0.98 0.93 0.89 formation34 3 0.97 0.90 0.8620 mmDePerforated 31 1 1.00 0.98 0.96 Three cables in2Detraystrefoil formation2 0.97 0.93 0.8920 mm3 0.96 0.92 0.86Vertical 31 De Spaced 1 1.00 0.91 0.89perforatedtrays225 mm2 1.00 0.90 0.862DeLadder 32 2DeDe1 1.00 1.00 1.00supports,cleats, etc... 33 2 0.97 0.95 0.9334 20 mm 3 0.96 0.94 0.90Fig. G17 : Reduction factors for groups of more than one circuit of single-core cables to be applied to reference rating for one circuit of single-core cables in free air- Method of installation F. (table A.52.21 of IEC 60364-5-52)© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors2 Practical method for determiningthe smallest allowable crosssectionalarea of circuit conductorsFigure G18 gives the values of correction factor k4 for different configurations ofcables or conductors laid directly in the ground.Number Cable to cable clearance (a) aof circuits Nil (cables One cable 0.125 m 0.25 m 0.5 mtouching) diameter2 0.75 0.80 0.85 0.90 0.903 0.65 0.70 0.75 0.80 0.854 0.60 0.60 0.70 0.75 0.805 0.55 0.55 0.65 0.70 0.806 0.50 0.55 0.60 0.70 0.80aMulti-core cablesaaG14aSingle-core cablesaaFig. G18 : Reduction factors for more than one circuit, single-core or multi-core cables laiddirectly in the ground. Installation method D. (table 52-18 of IEC 60364-5-52)b Harmonic currentThe current-carrying capacity of three-phase, 4-core or 5-core cables is based onthe assumption that only 3 conductors are fully loaded.However, when harmonic currents are circulating, the neutral current can besignificant, and even higher than the phase currents. This is due to the fact that the3 rd harmonic currents of the three phases do not cancel each other, and sum up inthe neutral conductor.This of course affects the current-carrying capacity of the cable, and a correctionfactor noted here k5 shall be applied.In addition, if the 3 rd harmonic percentage h 3 is greater than 33%, the neutral currentis greater than the phase current and the cable size selection is based on the neutralcurrent. The heating effect of harmonic currents in the phase conductors has also tobe taken into account.The values of k5 depending on the 3 rd harmonic content are given in Figure G19.Third harmonic content Correction factorof phase current % Size selection is based Size selection is basedon phase currenton neutral current0 - 15 1.015 - 33 0.8633 - 45 0.86> 45 1.0© Schneider Electric - all rights reservedFig. G19 : Correction factors for harmonic currents in four-core and five-core cables (table D.52.1of IEC 60364-5-52)Admissible current as a function of nominal cross-sectionalarea of conductorsIEC standard 60364-5-52 proposes extensive information in the form of tablesgiving the admissible currents as a function of cross-sectional area of cables. Manyparameters are taken into account, such as the method of installation, type ofinsulation material, type of conductor material, number of loaded conductors.Schneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors2 Practical method for determiningthe smallest allowable crosssectionalarea of circuit conductorsAs an example, Figure G20 gives the current-carrying capacities for differentmethods of installation of PVC insulation, three loaded copper or aluminiumconductors, free air or in ground.NominalInstallation methodscross-sectional A1 A2 B1 B2 C Darea of conductors(mm 2 )1 2 3 4 5 6 7Copper1.5 13.5 13 15.5 15 17.5 182.5 18 17.5 21 20 24 244 24 23 28 27 32 316 31 29 36 34 41 3910 42 39 50 46 57 5216 56 52 68 62 76 6725 73 68 89 80 96 8635 89 83 110 99 119 10350 108 99 134 118 144 12270 136 125 171 149 184 15195 164 150 207 179 223 179120 188 172 239 206 259 203150 216 196 - - 299 230185 245 223 - - 341 258240 286 261 - - 403 297300 328 298 - - 464 336Aluminium2.5 14 13.5 16.5 15.5 18.5 18.54 18.5 17.5 22 21 25 246 24 23 28 27 32 3010 32 31 39 36 44 4016 43 41 53 48 59 5225 57 53 70 62 73 6635 70 65 86 77 90 8050 84 78 104 92 110 9470 107 98 133 116 140 11795 129 118 161 139 170 138120 149 135 186 160 197 157150 170 155 - - 227 178185 194 176 - - 259 200240 227 207 - - 305 230300 261 237 - - 351 260G15Fig. G20 : Current-carrying capacities in amperes for different methods of installation, PVC insulation, three loaded conductors, copper or aluminium, conductortemperature: 70 °C, ambient temperature: 30 °C in air, 20 °C in ground (table A.52.4 of IEC 60364-5-52)© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors2 Practical method for determiningthe smallest allowable crosssectionalarea of circuit conductors2.3 Recommended simplified approach for cablesIn order to facilitate the selection of cables, 2 simplified tables are proposed, forunburied and buried cables.These tables summarize the most commonly used configurations and give easieraccess to the information.b Unburied cables:G16Reference Number of loaded conductors and type of insulationmethodsA1 2 PVC 3 PVC 3 XLPE 2 XLPEA2 3 PVC 2 PVC 3 XLPE 2 XLPEB1 3 PVC 2 PVC 3 XLPE 2 XLPEB2 3 PVC 2 PVC 3 XLPE 2 XLPEC 3 PVC 2 PVC 3 XLPE 2 XLPEE 3 PVC 2 PVC 3 XLPE 2 XLPEF 3 PVC 2 PVC 3 XLPE 2 XLPE1 2 3 4 5 6 7 8 9 10 11 12 13Size (mm 2 )Copper1.5 13 13 . 5 14.5 15.5 17 18.5 19.5 22 23 24 26 -2.5 17.5 18 19.5 21 23 25 27 30 31 33 36 -4 23 24 26 28 31 34 36 40 42 45 49 -6 29 31 34 36 40 43 46 51 54 58 63 -10 39 42 46 50 54 60 63 70 75 80 86 -16 52 56 61 68 73 80 85 94 100 107 115 -25 68 73 80 89 95 101 110 119 127 135 149 16135 - - - 110 117 126 137 147 158 169 185 20050 - - - 134 141 153 167 179 192 207 225 24270 - - - 171 179 196 213 229 246 268 289 31095 - - - 207 216 238 258 278 298 328 352 377120 - - - 239 249 276 299 322 346 382 410 437150 - - - - 285 318 344 371 395 441 473 504185 - - - - 324 362 392 424 450 506 542 575240 - - - - 380 424 461 500 538 599 641 679Aluminium2.5 13.5 14 15 16.5 18.5 19.5 21 23 24 26 28 -4 17.5 18.5 20 22 25 26 28 31 32 35 38 -6 23 24 26 28 32 33 36 39 42 45 49 -10 31 32 36 39 44 46 49 54 58 62 67 -16 41 43 48 53 58 61 66 73 77 84 91 -25 53 57 63 70 73 78 83 90 97 101 108 12135 - - - 86 90 96 103 112 120 126 135 15050 - - - 104 110 117 125 136 146 154 164 18470 - - - 133 140 150 160 174 187 198 211 23795 - - - 161 170 183 195 211 227 241 257 289120 - - - 186 197 212 226 245 263 280 300 337150 - - - - 226 245 261 283 304 324 346 389185 - - - - 256 280 298 323 347 371 397 447240 - - - - 300 330 352 382 409 439 470 530Fig. G21a : Current-carrying capacity in amperes (table B.52-1 of IEC 60364-5-52)© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors2 Practical method for determiningthe smallest allowable crosssectionalarea of circuit conductorsCorrection factors are given in Figure G21b for groups of several circuits or multicorecables:ArrangementNumber of circuits or multi-core cables 2 3 4 6 9 12 16 20Embedded or enclosed 1.00 0.80 0.70 0.70 0.55 0.50 0.45 0.40 0.40Single layer on walls, floors 1.00 0.85 0.80 0.75 0.70 0.70 - - -or on unperforatedtraysSingle layer fixed directly 0.95 0.80 0.70 0.70 0.65 0.60 - - -under a ceilingSingle layer on perforated 1.00 0.90 0.80 0.75 0.75 0.70 - - -horizontal trays or on vertical traysSingle layer on cable 1.00 0.85 0.80 0.80 0.80 0.80 - - -ladder supports or cleats, etc...Fig. G21b : Reduction factors for groups of several circuits or of several multi-core cables(table B.52-3 of IEC 60364-5-52)G17b Buried cables:Installation Size Number of loaded conductors and type of insulationmethod mm 2 Two PVC Three PVC Two XLPE Three XLPEDCopper1.5 22 18 26 222.5 29 24 34 294 38 31 44 376 47 39 56 4610 63 52 73 6116 81 67 95 7925 104 86 121 10135 125 103 146 12250 148 122 173 14470 183 151 213 17895 216 179 252 211120 246 203 287 240150 278 230 324 271185 312 258 363 304240 361 297 419 351300 408 336 474 396DAluminium2.5 22 18.5 26 224 29 24 34 296 36 30 42 3610 48 40 56 4716 62 52 73 6125 80 66 93 7835 96 80 112 9450 113 94 132 11270 140 117 163 13895 166 138 193 164120 189 157 220 186150 213 178 249 210185 240 200 279 236240 277 230 322 272300 313 260 364 308Fig. G22 : Current-carrying capacity in amperes (table B.52-1 of IEC 60364-5-52)© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors2 Practical method for determiningthe smallest allowable crosssectionalarea of circuit conductors2.4 Busbar trunking systemsThe selection of busbar trunking systems is very straightforward, using the dataprovided by the manufacturer. Methods of installation, insulation materials, correctionfactors for grouping are not relevant parameters for this technology.The cross section area of any given model has been determined by the manufacturerbased on:b The rated current,b An ambient air temperature equal to 35 °C,b 3 loaded conductors.Rated currentThe rated current can be calculated taking account of:b The layout,b The current absorbed by the different loads connected along the trunking system.G18Ambient temperatureA correction factor has to be applied for temperature higher than 35 °C. Thecorrection factor applicable to medium and high power range (up to 4,000 A) is givenin Figure G23a.°C 35 40 45 50 55Correction factor 1 0.97 0.93 0.90 0.86Fig. G23a : Correction factor for air temperature higher than 35 °CNeutral currentWhere 3 rd harmonic currents are circulating, the neutral conductor may be carrying asignificant current and the corresponding additional power losses must be taken intoaccount.Figure G23b represents the maximum admissible phase and neutral currents (perunit) in a high power busbar trunking system as functions of 3 rd harmonic level.1.4Maximum admissible current (p.u)1.210.80.60.40.2Neutral conductorPhase conductor00 10 20 30 4050 60 703 rd harmonic current level (%)80 90© Schneider Electric - all rights reservedFig. G23b : Maximum admissible currents (p.u.) in a busbar trunking system as functions of the3 rd harmonic level.Schneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors2 Practical method for determiningthe smallest allowable crosssectionalarea of circuit conductorsThe layout of the trunking system depends on the position of the current consumers,the location of the power source and the possibilities for fixing the system.v One single distribution line serves a 4 to 6 meter areav Protection devices for current consumers are placed in tap-off units, connecteddirectly to usage points.v One single feeder supplies all current consumers of different powers.Once the trunking system layout is established, it is possible to calculate theabsorbed current I n on the distribution line.I n is equal to the sum of absorbed currents by the current I n consumers: I n = Σ I B .The current consumers do not all work at the same time and are not permanently onfull load, so we have to use a clustering coefficient k S : I n = Σ (I B . k S ).Application Number of current consumers Ks CoefficientLighting, Heating 1Distribution (engineeringworkshop)2...34...56...910...4040 and over0.90.80.70.60.5Note : for industrial installations, remember to take account of upgrading of the machineequipment base. As for a switchboard, a 20 % margin is recommended:I n ≤ I B x k s x 1.2.Fig G24 : Clustering coefficient according to the number of current consumersG19© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors3 Determination of voltage dropThe impedance of circuit conductors is low but not negligible: when carryingload current there is a voltage drop between the origin of the circuit and the loadterminals. The correct operation of a load (a motor, lighting circuit, etc.) dependson the voltage at its terminals being maintained at a value close to its rated value.It is necessary therefore to determine the circuit conductors such that at full-loadcurrent, the load terminal voltage is maintained within the limits required for correctperformance.This section deals with methods of determining voltage drops, in order to check that:b They comply with the particular standards and regulations in forceb They can be tolerated by the loadb They satisfy the essential operational requirements3.1 Maximum voltage dropMaximum allowable voltage-drop vary from one country to another. Typical values forLV installations are given below in Figure G25.G20Type of installations Lighting Other usescircuits (heating and power)A low-voltage service connection from 3% 5%a LV public power distribution networkConsumers MV/LV substation supplied 6% 8%from a public distribution MV systemFig. G25 : Maximum voltage-drop between the service-connection point and the point of utilizationThese voltage-drop limits refer to normal steady-state operating conditions and donot apply at times of motor starting, simultaneous switching (by chance) of severalloads, etc. as mentioned in Chapter A Sub-clause 4.3 (factor of simultaneity, etc.).When voltage drops exceed the values shown in Figure G25, larger cables (wires)must be used to correct the condition.The value of 8%, while permitted, can lead to problems for motor loads; for example:b In general, satisfactory motor performance requires a voltage within ± 5% of itsrated nominal value in steady-state operation,b Starting current of a motor can be 5 to 7 times its full-load value (or even higher).If an 8% voltage drop occurs at full-load current, then a drop of 40% or more willoccur during start-up. In such conditions the motor will either:v Stall (i.e. remain stationary due to insufficient torque to overcome the load torque)with consequent over-heating and eventual trip-outv Or accelerate very slowly, so that the heavy current loading (with possiblyundesirable low-voltage effects on other equipment) will continue beyond the normalstart-up periodb Finally an 8% voltage drop represents a continuous power loss, which, for continuousloads will be a significant waste of (metered) energy. For these reasons it isrecommended that the maximum value of 8% in steady operating conditions should notbe reached on circuits which are sensitive to under-voltage problems (see Fig. G26).MV consumer© Schneider Electric - all rights reservedLV consumer8% (1)5% (1)Load(1) Between the LV supply point and the loadFig. G26 : Maximum voltage dropSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors3 Determination of voltage drop3.2 Calculation of voltage drop in steady loadconditionsUse of formulaeFigure G27 below gives formulae commonly used to calculate voltage drop in agiven circuit per kilometre of length.If:b IB: The full load current in ampsb L: Length of the cable in kilometresb R: Resistance of the cable conductor in Ω/km222.5 Ω mm / kmR =for copper2S c.s.a. in mm( )236 Ω mm / kmR =2S c.s.a. in mm( )for aluminiumNote: R is negligible above a c.s.a. of 500 mm 2b X: inductive reactance of a conductor in Ω/kmNote: X is negligible for conductors of c.s.a. less than 50 mm 2 . In the absence of anyother information, take X as being equal to 0.08 Ω/km.b ϕ: phase angle between voltage and current in the circuit considered, generally:v Incandescent lighting: cos ϕ = 1v Motor power:- At start-up: cos ϕ = 0.35- In normal service: cos ϕ = 0.8b Un: phase-to-phase voltageb Vn: phase-to-neutral voltageFor prefabricated pre-wired ducts and bustrunking, resistance and inductivereactance values are given by the manufacturer.G21CircuitVoltage drop (ΔU)in volts in %( )Single phase: phase/phase ∆U = 2I B R cos ϕ + X sin ϕ L100 ∆UUnSingle phase: phase/neutral ∆U = 2I B( R cos ϕ + X sin ϕ)L100 ∆ UVnBalanced 3-phase: 3 phases ∆U = 3 I B( R cos ϕ + X sin ϕ)L 100 ∆ U(with or without neutral)UnFig. G27 : Voltage-drop formulaeSimplified tableCalculations may be avoided by using Figure G28 next page, which gives, withan adequate approximation, the phase-to-phase voltage drop per km of cable perampere, in terms of:b Kinds of circuit use: motor circuits with cos ϕ close to 0.8, or lighting with a cos ϕclose to 1.b Type of cable; single-phase or 3-phaseVoltage drop in a cable is then given by:K x IB x LK is given by the table,IB is the full-load current in amps,L is the length of cable in km.The column motor power “cos ϕ = 0.35” of Figure G28 may be used to compute thevoltage drop occurring during the start-up period of a motor (see example no. 1 afterthe Figure G28).© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors3 Determination of voltage dropG22c.s.a. in mm 2 Single-phase circuit Balanced three-phase circuitMotor power Lighting Motor power LightingNormal service Start-upNormal service Start-upCu Al cos ϕ = 0.8 cos ϕ = 0.35 cos ϕ = 1 cos ϕ = 0.8 cos ϕ = 0.35 cos ϕ = 11.5 24 10.6 30 20 9.4 252.5 14.4 6.4 18 12 5.7 154 9.1 4.1 11.2 8 3.6 9.56 10 6.1 2.9 7.5 5.3 2.5 6.210 16 3.7 1.7 4.5 3.2 1.5 3.616 25 2.36 1.15 2.8 2.05 1 2.425 35 1.5 0.75 1.8 1.3 0.65 1.535 50 1.15 0.6 1.29 1 0.52 1.150 70 0.86 0.47 0.95 0.75 0.41 0.7770 120 0.64 0.37 0.64 0.56 0.32 0.5595 150 0.48 0.30 0.47 0.42 0.26 0.4120 185 0.39 0.26 0.37 0.34 0.23 0.31150 240 0.33 0.24 0.30 0.29 0.21 0.27185 300 0.29 0.22 0.24 0.25 0.19 0.2240 400 0.24 0.2 0.19 0.21 0.17 0.16300 500 0.21 0.19 0.15 0.18 0.16 0.13Fig. G28 : Phase-to-phase voltage drop ΔU for a circuit, in volts per ampere per km© Schneider Electric - all rights reserved1,000 A400 VFig. G29 : Example 150 m / 35 mm 2 CuIB = 100 A(500 A during start-up)ExamplesExample 1 (see Fig. G29)A three-phase 35 mm 2 copper cable 50 metres long supplies a 400 V motor taking:b 100 A at a cos ϕ = 0.8 on normal permanent loadb 500 A (5 In) at a cos ϕ = 0.35 during start-upThe voltage drop at the origin of the motor cable in normal circumstances (i.e. withthe distribution board of Figure G29 distributing a total of 1,000 A) is 10 V phase-tophase.What is the voltage drop at the motor terminals:b In normal service?b During start-up?Solution:b Voltage drop in normal service conditions:∆∆U% = 100 UUnTable G28 shows 1 V/A/km so that:ΔU for the cable = 1 x 100 x 0.05 = 5 VΔU total = 10 + 5 = 15 V = i.e.15400 x 100 = 3.75%This value is less than that authorized (8%) and is satisfactory.b Voltage drop during motor start-up:ΔUcable = 0.52 x 500 x 0.05 = 13 VOwing to the additional current taken by the motor when starting, the voltage drop atthe distribution board will exceed 10 Volts.Supposing that the infeed to the distribution board during motor starting is900 + 500 = 1,400 A then the voltage drop at the distribution board will increaseapproximately pro rata, i.e.10 x 1,400= 14 V1,000ΔU distribution board = 14 VΔU for the motor cable = 13 VΔU total = 13 + 14 = 27 V i.e.27400 x 100 = 6.75%a value which is satisfactory during motor starting.Schneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors3 Determination of voltage dropExample 2 (see Fig. G30)A 3-phase 4-wire copper line of 70 mm 2 c.s.a. and a length of 50 m passes a currentof 150 A. The line supplies, among other loads, 3 single-phase lighting circuits, eachof 2.5 mm 2 c.s.a. copper 20 m long, and each passing 20 A.It is assumed that the currents in the 70 mm 2 line are balanced and that the threelighting circuits are all connected to it at the same point.What is the voltage drop at the end of the lighting circuits?Solution:b Voltage drop in the 4-wire line:∆∆U% = 100 UUnFigure G28 shows 0.55 V/A/kmΔU line = 0.55 x 150 x 0.05 = 4.125 V phase-to-phasewhich gives: 4 . 125 = 2.38 Vphase to neutral.3b Voltage drop in any one of the lighting single-phase circuits:ΔU for a single-phase circuit = 18 x 20 x 0.02 = 7.2 VThe total voltage drop is therefore7.2 + 2.38 = 9.6 V9.6 Vx 100 = 4.2%230 VThis value is satisfactory, being less than the maximum permitted voltage drop of 6%.G2350 m / 70 mm2 CuIB = 150 A20 m / 2.5 mm2 CuIB = 20 AFig. G30 : Example 2© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors4 Short-circuit currentKnowing the levels of 3-phase symmetricalshort-circuit currents (Isc) at different pointsin an installation is an essential feature of itsdesignA knowledge of 3-phase symmetrical short-circuit current values (Isc) at strategicpoints of an installation is necessary in order to determine switchgear (fault currentrating), cables (thermal withstand rating), protective devices (discriminative tripsettings) and so on...In the following notes a 3-phase short-circuit of zero impedance (the so-called boltedshort-circuit) fed through a typical MV/LV distribution transformer will be examined.Except in very unusual circumstances, this type of fault is the most severe, and iscertainly the simplest to calculate.Short-circuit currents occurring in a network supplied from a generator and also inDC systems are dealt with in Chapter N.The simplified calculations and practical rules which follow give conservative resultsof sufficient accuracy, in the large majority of cases, for installation design purposes.G244.1 Short-circuit current at the secondary terminalsof a MV/LV distribution transformerThe case of one transformerb In a simplified approach, the impedance of the MV system is assumed to beInnegligibly small, so that: IscInP 3x 100 x 10= where = and:UscU20 3P = kVA rating of the transformerU 20 = phase-to-phase secondary volts on open circuitIn = nominal current in ampsIsc = short-circuit fault current in ampsUsc = short-circuit impedance voltage of the transformer in %.Typical values of Usc for distribution transformers are given in Figure G31.Transformer rating Usc in %(kVA) Oil-immersed Cast-resindry type50 to 750 4 6800 to 3,200 6 6Fig. G31 : Typical values of Usc for different kVA ratings of transformers with MV windings y 20 kVb Example400 kVA transformer, 420 V at no loadUsc = 4%3400 x 10550x 100In= = 550 A I sc = = 13.7 kA420 x 34© Schneider Electric - all rights reservedIsc 1 Isc 2 Isc 3Isc 1 + Isc 2 + Isc 3Fig. G32 : Case of several transformers in parallelThe case of several transformers in parallel feeding a busbarThe value of fault current on an outgoing circuit immediately downstream ofthe busbars (see Fig. G32) can be estimated as the sum of the Isc from eachtransformer calculated separately.It is assumed that all transformers are supplied from the same MV network, in whichcase the values obtained from Figure G31 when added together will give a slightlyhigher fault-level value than would actually occur.Other factors which have not been taken into account are the impedance of thebusbars and of the circuit-breakers.The conservative fault-current value obtained however, is sufficiently accurate forbasic installation design purposes. The choice of circuit-breakers and incorporatedprotective devices against short-circuit fault currents is described in Chapter H Subclause4.4.Schneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors4 Short-circuit current4.2 3-phase short-circuit current (Isc) at any pointwithin a LV installationIn a 3-phase installation Isc at any point is given by:UIsc = 20 where3 ZTU 20 = phase-to-phase voltage of the open circuited secondary windings of the powersupply transformer(s).Z T = total impedance per phase of the installation upstream of the fault location (in Ω)Method of calculating Z TEach component of an installation (MV network, transformer, cable, circuit-breaker,busbar, and so on...) is characterized by its impedance Z, comprising an elementof resistance (R) and an inductive reactance (X). It may be noted that capacitivereactances are not important in short-circuit current calculations.ZXThe parameters R, X and Z are expressed in ohms, and are related by the sides of aright angled triangle, as shown in the impedance diagram of Figure G33.The method consists in dividing the network into convenient sections, and tocalculate the R and X values for each.Where sections are connected in series in the network, all the resistive elements inthe section are added arithmetically; likewise for the reactances, to give R T and X T .The impedance (Z T ) for the combined sections concerned is then calculated fromG25Fig. G33 : Impedance diagramR2Z = R + X 2T T TAny two sections of the network which are connected in parallel, can, ifpredominantly both resistive (or both inductive) be combined to give a singleequivalent resistance (or reactance) as follows:Let R1 and R2 be the two resistances connected in parallel, then the equivalentresistance R3 will be given by:R1x R2X1x X2R3= or for reactances X3=R 1 + R2X 1 + X2It should be noted that the calculation of X3 concerns only separated circuit withoutmutual inductance. If the circuits in parallel are close togother the value of X3 will benotably higher.Determination of the impedance of each componentb Network upstream of the MV/LV transformer (see Fig. G34)The 3-phase short-circuit fault level P SC , in kA or in MVA (1) is given by the powersupply authority concerned, from which an equivalent impedance can be deduced.Psc Uo (V) Ra (mΩ) Xa (mΩ)250 MVA 420 0.07 0.7500 MVA 420 0.035 0.351Fig. G34 : The impedance of the MV network referred to the LV side of the MV/LV transformer(1) Short-circuit MVA: 3 E L Isc where:b E L = phase-to-phase nominal system voltage expressed inkV (r.m.s.)b Isc = 3-phase short-circuit current expressed in kA (r.m.s.)(2) up to 36 kVA formula which makes this deduction and at the same time converts the impedanceto an equivalent value at LV is given, as follows:UZs = 02PscwhereZs = impedance of the MV voltage network, expessed in milli-ohmsUo = phase-to-phase no-load LV voltage, expressed in voltsPsc = MV 3-phase short-circuit fault level, expressed in kVAThe upstream (MV) resistance Ra is generally found to be negligible compared withthe corresponding Xa, the latter then being taken as the ohmic value for Za. If moreaccurate calculations are necessary, Xa may be taken to be equal to 0.995 Za andRa equal to 0.1 Xa.Figure G36 gives values for Ra and Xa corresponding to the most common MV (2)short-circuit levels in utility power-supply networks, namely, 250 MVA and 500 MVA.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors4 Short-circuit currentb Transformers (see Fig. G35)The impedance Ztr of a transformer, viewed from the LV terminals, is given by theformula:Ztr =UPn 202 x Usc100G26where:U 20 = open-circuit secondary phase-to-phase voltage expressed in voltsPn = rating of the transformer (in kVA)Usc = the short-circuit impedance voltage of the transformer expressed in %The transformer windings resistance Rtr can be derived from the total losses asfollows:2Pcu x 10Pcu = 3I3n x Rtr so that Rtr =23Inin milli-ohmswherePcu = total losses in wattsIn = nominal full-load current in ampsRtr = resistance of one phase of the transformer in milli-ohms (the LV andcorresponding MV winding for one LV phase are included in this resistance value).2 2Xtr = Ztr −RtrFor an approximate calculation Rtr may be ignored since X ≈ Z in standarddistribution type transformers.Rated Oil-immersed Cast-resinPower Usc (%) Rtr (mΩ) Xtr (mΩ) Ztr (mΩ) Usc (%) Rtr (mΩ) Xtr (mΩ) Ztr (mΩ)(kVA)100 4 37.9 59.5 70.6 6 37.0 99.1 105.8160 4 16.2 41.0 44.1 6 18.6 63.5 66.2200 4 11.9 33.2 35.3 6 14.1 51.0 52.9250 4 9.2 26.7 28.2 6 10.7 41.0 42.3315 4 6.2 21.5 22.4 6 8.0 32.6 33.6400 4 5.1 16.9 17.6 6 6.1 25.8 26.5500 4 3.8 13.6 14.1 6 4.6 20.7 21.2630 4 2.9 10.8 11.2 6 3.5 16.4 16.8800 6 2.9 12.9 13.2 6 2.6 13.0 13.21,000 6 2.3 10.3 10.6 6 1.9 10.4 10.61,250 6 1.8 8.3 8.5 6 1.5 8.3 8.51,600 6 1.4 6.5 6.6 6 1.1 6.5 6.62,000 6 1.1 5.2 5.3 6 0.9 5.2 5.3Fig. G35 : Resistance, reactance and impedance values for typical distribution 400 V transformers with MV windings y 20 kV© Schneider Electric - all rights reserved(1) For 50 Hz systems, but 0.18 mΩ/m length at 60 Hzb Circuit-breakersIn LV circuits, the impedance of circuit-breakers upstream of the fault location mustbe taken into account. The reactance value conventionally assumed is 0.15 mΩ perCB, while the resistance is neglected.b BusbarsThe resistance of busbars is generally negligible, so that the impedance is practicallyall reactive, and amounts to approximately 0.15 mΩ/metre (1) length for LV busbars(doubling the spacing between the bars increases the reactance by about 10% only).b Circuit conductorsLThe resistance of a conductor is given by the formula: Rc = ρwhereSρ = the resistivity constant of the conductor material at the normal operatingtemperature being:v 22.5 mΩ.mm 2 /m for copperv 36 mΩ.mm 2 /m for aluminiumL = length of the conductor in mS = c.s.a. of conductor in mm 2Schneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors4 Short-circuit currentCable reactance values can be obtained from the manufacturers. For c.s.a. of lessthan 50 mm 2 reactance may be ignored. In the absence of other information, a valueof 0.08 mΩ/metre may be used (for 50 Hz systems) or 0.096 mΩ/metre (for 60 Hzsystems). For prefabricated bus-trunking and similar pre-wired ducting systems, themanufacturer should be consulted.b MotorsAt the instant of short-circuit, a running motor will act (for a brief period) as agenerator, and feed current into the fault.In general, this fault-current contribution may be ignored. However, if the totalpower of motors running simultaneously is higher than 25% of the total powerof transformers, the influence of motors must be taken into account. Their totalcontribution can be estimated from the formula:Iscm = 3.5 In from each motor i.e. 3.5mIn for m similar motors operating concurrently.The motors concerned will be the 3-phase motors only; single-phase-motorcontribution being insignificant.b Fault-arc resistanceShort-circuit faults generally form an arc which has the properties of a resistance.The resistance is not stable and its average value is low, but at low voltage thisresistance is sufficient to reduce the fault-current to some extent. Experience hasshown that a reduction of the order of 20% may be expected. This phenomenon willeffectively ease the current-breaking duty of a CB, but affords no relief for its faultcurrentmaking duty.b Recapitulation table (see Fig. G36)G27Parts of power-supply system R (mΩ) X (mΩ)Supply networkRaFigure G34Xa = 0.1TransformerPcu x 10 3Figure G35Rtr =3In2Xa = 0 995 Za Za =U 20 2. ;Psc2 2Ztr −RtrRtr is often negligible compared to Xtr with Ztr =for transformers > 100 kVAUPn x Usc100Circuit-breaker Negligible XD = 0.15 mΩ/poleMBusbars Negligible for S > 200 mm 2 in the formula: XB = 0.15 mΩ/mL (1)R = ρSCircuit conductors (2) L (1) Cables: Xc = 0.08 mΩ/mR = ρSMotorsSee Sub-clause 4.2 Motors(often negligible at LV)Three-phase shortUcircuit current in kA Isc = 202 23 RT+ XTU 20 : Phase-to-phase no-load secondary voltage of MV/LV transformer (in volts).Psc: 3-phase short-circuit power at MV terminals of the MV/LV transformers (in kVA).Pcu: 3-phase total losses of the MV/LV transformer (in watts).Pn: Rating of the MV/LV transformer (in kVA).Usc: Short-circuit impedance voltage of the MV/LV transfomer (in %).R T : Total resistance. X T : Total reactance(1) ρ = resistivity at normal temperature of conductors in serviceb ρ = 22.5 mΩ x mm 2 /m for copperb ρ = 36 mΩ x mm 2 /m for aluminium(2) If there are several conductors in parallel per phase, then divide the resistance of one conductor by the number ofconductors. The reactance remains practically unchanged.Fig. G36 : Recapitulation table of impedances for different parts of a power-supply system© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors4 Short-circuit currentb Example of short-circuit calculations (see Fig. G37)G28LV installation R (mΩ) X (mΩ) RT (mΩ) XT (mΩ)MV network 0.035 0.351Psc = 500 MVATransformer 2.24 8.1020 kV/420 VPn = 1000 kVAUsc = 5%Pcu = 13.3 x 10 3 wattsSingle-core cables22.5 55 m copper Rc = x = 0.124 x 240 mm 2 /phase4 240Xc = 0.08 x 5 = 0.40 2.41 8.85 Isc1 = 26 kAMain RD = 0 XD = 0.15circuit-breakerBusbars RB = 0 XB = 1.5 2.41 10.5 Isc2 = 22 kA10 mThree-core cable100 m100Rc = 22.5 x = 23.6895 mm 2 copper95Xc = 100 x 0.08 = 8 26.1 18.5 Isc3 = 7.4 kAThree-core cable20 m Rc = 22.5 x= 45 Xc = 20 x 0.08 = 1.6 71.1 20.1 Isc4 = 3.2 kA10 mm 2 copper10final circuitsIsc =4202 23 RT+ XTFig. G37 : Example of short-circuit current calculations for a LV installation supplied at 400 V (nominal) from a 1,000 kVA MV/LV transformer4.3 Isc at the receiving end of a feeder as a functionof the Isc at its sending end© Schneider Electric - all rights reserved400 VIB = 55 A47,5 mm 2 , Cu20 mIB = 160 AIsc = 28 kAIsc = ?Fig. G38 : Determination of downstream short-circuit currentlevel Isc using Figure G39The network shown in Figure G38 typifies a case for the application of Figure G39next page, derived by the «method of composition» (mentioned in Chapter F Subclause6.2). These tables give a rapid and sufficiently accurate value of short-circuitcurrent at a point in a network, knowing:b The value of short-circuit current upstream of the point consideredb The length and composition of the circuit between the point at which the shortcircuitcurrent level is known, and the point at which the level is to be determinedIt is then sufficient to select a circuit-breaker with an appropriate short-circuit faultrating immediately above that indicated in the tables.If more precise values are required, it is possible to make a detailled calculation(see Sub-Clause 4.2) or to use a software package, such as Ecodial. In such a case,moreover, the possibility of using the cascading technique should be considered,in which the use of a current limiting circuit-breaker at the upstream position wouldallow all circuit-breakers downstream of the limiter to have a short-circuit currentrating much lower than would otherwise be necessary (See chapter H Sub-Clause 4.5).MethodSelect the c.s.a. of the conductor in the column for copper conductors (in thisexample the c.s.a. is 47.5 mm 2 ).Search along the row corresponding to 47.5 mm 2 for the length of conductor equalto that of the circuit concerned (or the nearest possible on the low side). Descendvertically the column in which the length is located, and stop at a row in the middlesection (of the 3 sections of the Figure) corresponding to the known fault-currentlevel (or the nearest to it on the high side).In this case 30 kA is the nearest to 28 kA on the high side. The value of short-circuitcurrent at the downstream end of the 20 metre circuit is given at the intersection ofthe vertical column in which the length is located, and the horizontal row correspondingto the upstream Isc (or nearest to it on the high side).This value in the example is seen to be 14.7 kA.The procedure for aluminium conductors is similar, but the vertical column must beascended into the middle section of the table.In consequence, a DIN-rail-mounted circuit-breaker rated at 63 A and Isc of 25 kA(such as a NG 125N unit) can be used for the 55 A circuit in Figure G38.A Compact rated at 160 A with an Isc capacity of 25 kA (such as a NS160 unit) canbe used to protect the 160 A circuit.Schneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors4 Short-circuit currentCopper 230 V / 400 Vc.s.a. of phase Length of circuit (in metres)conductors (mm 2 )1.5 1.3 1.8 2.6 3.6 5.2 7.3 10.3 14.6 212.5 1.1 1.5 2.1 3.0 4.3 6.1 8.6 12.1 17.2 24 344 1.2 1.7 2.4 3.4 4.9 6.9 9.7 13.7 19.4 27 39 556 1.8 2.6 3.6 5.2 7.3 10.3 14.6 21 29 41 58 8210 2.2 3.0 4.3 6.1 8.6 12.2 17.2 24 34 49 69 97 13716 1.7 2.4 3.4 4.9 6.9 9.7 13.8 19.4 27 39 55 78 110 155 22025 1.3 1.9 2.7 3.8 5.4 7.6 10.8 15.2 21 30 43 61 86 121 172 243 34335 1.9 2.7 3.8 5.3 7.5 10.6 15.1 21 30 43 60 85 120 170 240 340 48047.5 1.8 2.6 3.6 5.1 7.2 10.2 14.4 20 29 41 58 82 115 163 231 326 46170 2.7 3.8 5.3 7.5 10.7 15.1 21 30 43 60 85 120 170 240 34095 2.6 3.6 5.1 7.2 10.2 14.5 20 29 41 58 82 115 163 231 326 461120 1.6 2.3 3.2 4.6 6.5 9.1 12.9 18.3 26 37 52 73 103 146 206 291 412150 1.2 1.8 2.5 3.5 5.0 7.0 9.9 14.0 19.8 28 40 56 79 112 159 224 317 448185 1.5 2.1 2.9 4.2 5.9 8.3 11.7 16.6 23 33 47 66 94 133 187 265 374 529240 1.8 2.6 3.7 5.2 7.3 10.3 14.6 21 29 41 58 83 117 165 233 330 466 659300 2.2 3.1 4.4 6.2 8.8 12.4 17.6 25 35 50 70 99 140 198 280 396 5612x120 2.3 3.2 4.6 6.5 9.1 12.9 18.3 26 37 52 73 103 146 206 292 412 5832x150 2.5 3.5 5.0 7.0 9.9 14.0 20 28 40 56 79 112 159 224 317 448 6342x185 2.9 4.2 5.9 8.3 11.7 16.6 23 33 47 66 94 133 187 265 375 530 749553x120 3.4 4.9 6.9 9.7 13.7 19.4 27 39 55 77 110 155 219 309 438 6193x150 3.7 5.3 7.5 10.5 14.9 21 30 42 60 84 119 168 238 336 476 6723x185 4.4 6.2 8.8 12.5 17.6 25 35 50 70 100 141 199 281 398 562Isc upstream Isc downstream(in kA)(in kA)100 93 90 87 82 77 70 62 54 45 37 29 22 17.0 12.6 9.3 6.7 4.9 3.5 2.5 1.8 1.3 0.990 84 82 79 75 71 65 58 51 43 35 28 22 16.7 12.5 9.2 6.7 4.8 3.5 2.5 1.8 1.3 0.980 75 74 71 68 64 59 54 47 40 34 27 21 16.3 12.2 9.1 6.6 4.8 3.5 2.5 1.8 1.3 0.970 66 65 63 61 58 54 49 44 38 32 26 20 15.8 12.0 8.9 6.6 4.8 3.4 2.5 1.8 1.3 0.960 57 56 55 53 51 48 44 39 35 29 24 20 15.2 11.6 8.7 6.5 4.7 3.4 2.5 1.8 1.3 0.950 48 47 46 45 43 41 38 35 31 27 22 18.3 14.5 11.2 8.5 6.3 4.6 3.4 2.4 1.7 1.2 0.940 39 38 38 37 36 34 32 30 27 24 20 16.8 13.5 10.6 8.1 6.1 4.5 3.3 2.4 1.7 1.2 0.935 34 34 33 33 32 30 29 27 24 22 18.8 15.8 12.9 10.2 7.9 6.0 4.5 3.3 2.4 1.7 1.2 0.930 29 29 29 28 27 27 25 24 22 20 17.3 14.7 12.2 9.8 7.6 5.8 4.4 3.2 2.4 1.7 1.2 0.925 25 24 24 24 23 23 22 21 19.1 17.4 15.5 13.4 11.2 9.2 7.3 5.6 4.2 3.2 2.3 1.7 1.2 0.920 20 20 19.4 19.2 18.8 18.4 17.8 17.0 16.1 14.9 13.4 11.8 10.1 8.4 6.8 5.3 4.1 3.1 2.3 1.7 1.2 0.915 14.8 14.8 14.7 14.5 14.3 14.1 13.7 13.3 12.7 11.9 11.0 9.9 8.7 7.4 6.1 4.9 3.8 2.9 2.2 1.6 1.2 0.910 9.9 9.9 9.8 9.8 9.7 9.6 9.4 9.2 8.9 8.5 8.0 7.4 6.7 5.9 5.1 4.2 3.4 2.7 2.0 1.5 1.1 0.87 7.0 6.9 6.9 6.9 6.9 6.8 6.7 6.6 6.4 6.2 6.0 5.6 5.2 4.7 4.2 3.6 3.0 2.4 1.9 1.4 1.1 0.85 5.0 5.0 5.0 4.9 4.9 4.9 4.9 4.8 4.7 4.6 4.5 4.3 4.0 3.7 3.4 3.0 2.5 2.1 1.7 1.3 1.0 0.84 4.0 4.0 4.0 4.0 4.0 3.9 3.9 3.9 3.8 3.7 3.6 3.5 3.3 3.1 2.9 2.6 2.2 1.9 1.6 1.2 1.0 0.73 3.0 3.0 3.0 3.0 3.0 3.0 2.9 2.9 2.9 2.9 2.8 2.7 2.6 2.5 2.3 2.1 1.9 1.6 1.4 1.1 0.9 0.72 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 1.9 1.9 1.9 1.8 1.8 1.7 1.6 1.4 1.3 1.1 1.0 0.8 0.61 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 0.9 0.9 0.9 0.8 0.8 0.7 0.6 0.6 0.5Aluminium 230 V / 400 Vc.s.a. of phase Length of circuit (in metres)conductors (mm 2 )2.5 1.4 1.9 2.7 3.8 5.4 7.6 10.8 15.3 224 1.1 1.5 2.2 3.1 4.3 6.1 8.6 12.2 17.3 24 356 1.6 2.3 3.2 4.6 6.5 9.2 13.0 18.3 26 37 5210 1.9 2.7 3.8 5.4 7.7 10.8 15.3 22 31 43 61 8616 2.2 3.1 4.3 6.1 8.7 12.2 17.3 24 35 49 69 98 13825 1.7 2.4 3.4 4.8 6.8 9.6 13.5 19.1 27 38 54 76 108 153 21635 1.7 2.4 3.4 4.7 6.7 9.5 13.4 18.9 27 38 54 76 107 151 214 30247.5 1.6 2.3 3.2 4.6 6.4 9.1 12.9 18.2 26 36 51 73 103 145 205 290 41070 2.4 3.4 4.7 6.7 9.5 13.4 19.0 27 38 54 76 107 151 214 303 42895 2.3 3.2 4.6 6.4 9.1 12.9 18.2 26 36 51 73 103 145 205 290 411120 2.9 4.1 5.8 8.1 11.5 16.3 23 32 46 65 92 130 184 259 367150 3.1 4.4 6.3 8.8 12.5 17.7 25 35 50 71 100 141 199 282 399185 2.6 3.7 5.2 7.4 10.4 14.8 21 30 42 59 83 118 167 236 333 471240 1.2 1.6 2.3 3.3 4.6 6.5 9.2 13.0 18.4 26 37 52 73 104 147 208 294 415300 1.4 2.0 2.8 3.9 5.5 7.8 11.1 15.6 22 31 44 62 88 125 177 250 353 4992x120 1.4 2.0 2.9 4.1 5.8 8.1 11.5 16.3 23 33 46 65 92 130 184 260 367 5192x150 1.6 2.2 3.1 4.4 6.3 8.8 12.5 17.7 25 35 50 71 100 141 200 282 3992x185 1.9 2.6 3.7 5.2 7.4 10.5 14.8 21 30 42 59 83 118 167 236 334 4722x240 2.3 3.3 4.6 6.5 9.2 13.0 18.4 26 37 52 74 104 147 208 294 415 5873x120 2.2 3.1 4.3 6.1 8.6 12.2 17.3 24 34 49 69 97 138 195 275 389 5513x150 2.3 3.3 4.7 6.6 9.4 13.3 18.8 27 37 53 75 106 150 212 299 423 5983x185 2.8 3.9 5.5 7.8 11.1 15.7 22 31 44 63 89 125 177 250 354 500 7073x240 3.5 4.9 6.9 9.8 13.8 19.5 28 39 55 78 110 156 220 312 441 623Note: for a 3-phase system having 230 V between phases, divide the above lengths by 3Fig. G39 : Isc at a point downstream, as a function of a known upstream fault-current value and the length and c.s.a. of the intervening conductors,in a 230/400 V 3-phase system4.4 Short-circuit current supplied by a generator oran inverter: Please refer to Chapter NG29© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors5 Particular cases of short-circuitcurrent5.1 Calculation of minimum levels of short-circuitcurrentIf a protective device in a circuit is intendedonly to protect against short-circuit faults, it isessential that it will operate with certainty at thelowest possible level of short-circuit current thatcan occur on the circuitIn general, on LV circuits, a single protective device protects against all levels ofcurrent, from the overload threshold through the maximum rated short-circuit currentbreakingcapability of the device.In certain cases, however, overload protective devices and separate short-circuitprotective devices are used.Examples of such arrangementsFigures G40 to G42 show some common arrangements where overload andshort-circuit protections are achieved by separate devices.G30aM fuses(no protectionagainst overload)Load breaking contactorwith thermal overload relayCircuit breaker withinstantaneous magneticshort-circuit protective relay onlyFig. G40 : Circuit protected by aM fusesLoad breaking contactorwith thermal overload relayFig. G41 : Circuit protected by circuit-breaker without thermaloverload relayAs shown in Figures G40 and G41, the most common circuits using separatedevices control and protect motors.Figure G42a constitutes a derogation in the basic protection rules, and is generallyused on circuits of prefabricated bustrunking, lighting rails, etc.Variable speed driveFigure G42b shows the functions provided by the variable speed drive, and ifnecessary some additional functions provided by devices such as circuit-breaker,thermal relay, RCD.© Schneider Electric - all rights reservedS1Load withincorporatedoverloadprotectionCircuit breaker DS2 < S1Fig. G42a : Circuit-breaker D provides protection against shortcircuitfaults as far as and including the loadProtection to be provided Protection generally provided Additional protectionby the variable speed driveCable overload Yes = (1) Not necessary if (1)Motor overload Yes = (2) Not necessary if (2)Downstream short-circuit YesVariable speed drive overload YesOvervoltageYesUndervoltageYesLoss of phaseYesUpstream short-circuitCircuit-breaker(short-circuit tripping)Internal faultCircuit-breaker(short-circuit andoverload tripping)Downstream earth fault (self protection) RCD u 300 mA(indirect contact)Direct contact faultRCD y 30 mAFigure G42b : Protection to be provided for variable speeed drive applicationsSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors5 Particular cases of short-circuitcurrentThe protective device must fulfill:b instantaneous trip setting Im < Isc min for acircuit-breakerb fusion current Ia < Isc min for a fuseConditions to be fulfilledThe protective device must therefore satisfy the two following conditions:b Its fault-current breaking rating must be greater than Isc, the 3-phase short-circuitcurrent at its point of installationb Elimination of the minimum short-circuit current possible in the circuit, in a time tccompatible with the thermal constraints of the circuit conductors, where:2 2K S (valid for tc < 5 seconds)tc iI2sc minComparison of the tripping or fusing performance curve of protective devices, withthe limit curves of thermal constraint for a conductor shows that this condition issatisfied if:b Isc (min) > Im (instantaneous or short timedelay circuit-breaker trip setting currentlevel), (see Fig. G45)b Isc (min) > Ia for protection by fuses. The value of the current Ia corresponds tothe crossing point of the fuse curve and the cable thermal withstand curve(see Fig. G44 and G45)tG31t = k2 S 2I 2ImIFig. G45 : Protection by circuit-breakertt = k2 S 2I 2IaIFig. G46 : Protection by aM-type fusestFig. G47 : Protection by gl-type fusesIat = k2 S 2I 2I© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors5 Particular cases of short-circuitcurrentIn practice this means that the length of circuitdownstream of the protective device must notexceed a calculated maximum length:0.8 U SphLmax =2ρImPractical method of calculating LmaxThe limiting effect of the impedance of long circuit conductors on the value ofshort-circuit currents must be checked and the length of a circuit must be restrictedaccordingly.The method of calculating the maximum permitted length has already beendemonstrated in TN- and IT- earthed schemes for single and double earth faults,respectively (see Chapter F Sub-clauses 6.2 and 7.2). Two cases are consideredbelow:1 - Calculation of L max for a 3-phase 3-wire circuitThe minimum short-circuit current will occur when two phase wires are shortcircuitedat the remote end of the circuit (see Fig. G46).P0.8 U LLoadG32Fig G46 : Definition of L for a 3-phase 3-wire circuitUsing the “conventional method”, the voltage at the point of protection P is assumedto be 80% of the nominal voltage during a short-circuit fault, so that 0.8 U = Isc Zd,where:Zd = impedance of the fault loopIsc = short-circuit current (ph/ph)U = phase-to-phase nominal voltageFor cables y 120 mm 2 , reactance may be neglected, so that2LZd = ρ (1)Sphwhere:ρ = resistivity of conductor material at the average temperature during a short-circuit,Sph = c.s.a. of a phase conductor in mm 2L = length in metresThe condition for the cable protection is Im y Isc with Im = magnetic trip currentsetting of the CB.This leads to Im y 0.8 U which gives L y 0.8 U SphZdLmax =2ρImwith U = 400 Vρ = 1.25 x 0.018 = 0.023 Ω.mm 2 /m (2) (Cu)Lmax = maximum circuit length in metresk SphLmax = Im© Schneider Electric - all rights reserved(1) For larger c.s.a.’s, the resistance calculated for theconductors must be increased to account for the non-uniformcurrent density in the conductor (due to “skin” and “proximity”effects)Suitable values are as follows:150 mm 2 : R + 15%185 mm 2 : R + 20%240 mm 2 : R + 25%300 mm 2 : R + 30%(2) The high value for resistivity is due to the elevatedtemperature of the conductor when passing short-circuitcurrent2 - Calculation of Lmax for a 3-phase 4-wire 230/400 V circuitThe minimum Isc will occur when the short-circuit is between a phase conductor andthe neutral.A calculation similar to that of example 1 above is required, but using the followingformulae (for cable y 120 mm 2 (1) ).b Where Sn for the neutral conductor = Sph for the phase conductor3,333 SphLmax =Imb If Sn for the neutral conductor < Sph, thenL 6,666 Sph 1max =where m =SphIm1+mSnFor larger c.s.a.’s than those listed, reactance values must be combined with those ofresistance to give an impedance. Reactance may be taken as 0.08 mΩ/m for cables(at 50 Hz). At 60 Hz the value is 0.096 mΩ/m.Schneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors5 Particular cases of short-circuitcurrentTabulated values for LmaxFigure G47 below gives maximum circuit lengths (Lmax) in metres, for:b 3-phase 4-wire 400 V circuits (i.e. with neutral) andb 1-phase 2-wire 230 V circuitsprotected by general-purpose circuit-breakers.In other cases, apply correction factors (given in Figure G53) to the lengths obtained.The calculations are based on the above methods, and a short-circuit trip level within± 20% of the adjusted value Im.For the 50 mm 2 c.s.a., calculation are based on a 47.5 mm 2 real c.s.a.Operating current c.s.a. (nominal cross-sectional-area) of conductors (in mm 2 )level Im of theinstantaneousmagnetic trippingelement (in A) 1.5 2.5 4 6 10 16 25 35 50 70 95 120 150 185 24050 100 167 267 40063 79 133 212 31780 63 104 167 250 417100 50 83 133 200 333125 40 67 107 160 267 427160 31 52 83 125 208 333200 25 42 67 100 167 267 417250 20 33 53 80 133 213 333 467320 16 26 42 63 104 167 260 365 495400 13 21 33 50 83 133 208 292 396500 10 17 27 40 67 107 167 233 317560 9 15 24 36 60 95 149 208 283 417630 8 13 21 32 63 85 132 185 251 370700 7 12 19 29 48 76 119 167 226 333 452800 6 10 17 25 42 67 104 146 198 292 396875 6 10 15 23 38 61 95 133 181 267 362 4571000 5 8 13 20 33 53 83 117 158 233 317 400 4351120 4 7 12 18 30 48 74 104 141 208 283 357 388 4591250 4 7 11 16 27 43 67 93 127 187 253 320 348 4111600 5 8 13 21 33 52 73 99 146 198 250 272 321 4002000 4 7 10 17 27 42 58 79 117 158 200 217 257 3202500 5 8 13 21 33 47 63 93 127 160 174 206 2563200 4 6 10 17 26 36 49 73 99 125 136 161 2004000 5 8 13 21 29 40 58 79 100 109 128 1605000 4 7 11 17 23 32 47 63 80 87 103 1286300 5 8 13 19 25 37 50 63 69 82 1028000 4 7 10 15 20 29 40 50 54 64 8010000 5 8 12 16 23 32 40 43 51 6412500 4 7 9 13 19 25 32 35 41 51G33Fig. G47 : Maximum circuit lengths in metres for copper conductors (for aluminium, the lengths must be multiplied by 0.62)Figures G48 to G50 next page give maximum circuit length (Lmax) in metres for:b 3-phase 4-wire 400 V circuits (i.e. with neutral) andb 1-phase 2-wire 230 V circuitsprotected in both cases by domestic-type circuit-breakers or with circuit-breakershaving similar tripping/current characteristics.In other cases, apply correction factors to the lengths indicated. These factors aregiven in Figure G51 next page.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors5 Particular cases of short-circuitcurrentRated current of c.s.a. (nominal cross-sectional-area) of conductors (in mm 2 )circuit-breakers (in A) 1.5 2.5 4 6 10 16 25 35 506 200 333 533 80010 120 200 320 480 80016 75 125 200 300 500 80020 60 100 160 240 400 64025 48 80 128 192 320 512 80032 37 62 100 150 250 400 625 87540 30 50 80 120 200 320 500 70050 24 40 64 96 160 256 400 560 76063 19 32 51 76 127 203 317 444 60380 15 25 40 60 100 160 250 350 475100 12 20 32 48 80 128 200 280 380125 10 16 26 38 64 102 160 224 304Fig. G48 : Maximum length of copper-conductor circuits in metres protected by B-type circuit-breakersG34Rated current of c.s.a. (nominal cross-sectional-area) of conductors (in mm2)circuit-breakers (in A) 1.5 2.5 4 6 10 16 25 35 506 100 167 267 400 66710 60 100 160 240 400 64016 37 62 100 150 250 400 625 87520 30 50 80 120 200 320 500 70025 24 40 64 96 160 256 400 560 76032 18.0 31 50 75 125 200 313 438 59440 15.0 25 40 60 100 160 250 350 47550 12.0 20 32 48 80 128 200 280 38063 9.5 16.0 26 38 64 102 159 222 30280 7.5 12.5 20 30 50 80 125 175 238100 6.0 10.0 16.0 24 40 64 100 140 190125 5.0 8.0 13.0 19.0 32 51 80 112 152Fig. G49 : Maximum length of copper-conductor circuits in metres protected by C-type circuit-breakersRated current of c.s.a. (nominal cross-sectional-area) of conductors (in mm2)circuit-breakers (in A) 1.5 2.5 4 6 10 16 25 35 501 429 7142 214 357 571 8573 143 238 381 571 9524 107 179 286 429 7146 71 119 190 286 476 76210 43 71 114 171 286 457 71416 27 45 71 107 179 286 446 625 84820 21 36 57 86 143 229 357 500 67925 17.0 29 46 69 114 183 286 400 54332 13.0 22 36 54 89 143 223 313 42440 11.0 18.0 29 43 71 114 179 250 33950 9.0 14.0 23 34 57 91 143 200 27163 7.0 11.0 18.0 27 45 73 113 159 21580 5.0 9.0 14.0 21 36 57 89 125 170100 4.0 7.0 11.0 17.0 29 46 71 100 136125 3.0 6.0 9.0 14.0 23 37 57 80 109Fig. G50 : Maximum length of copper-conductor circuits in metres protected by D-type circuit-breakers© Schneider Electric - all rights reservedCircuit detail3-phase 3-wire 400 V circuit or 1-phase 2-wire 400 V circuit (no neutral) 1.731-phase 2-wire (phase and neutral) 230 V circuit 13-phase 4-wire 230/400 V circuit or 2-phase 3-wire 230/400 V circuit Sph / S neutral = 1 1(i.e with neutral) Sph / S neutral = 2 0.67Fig. G51 : Correction factor to apply to lengths obtained from Figures G47 to G50Note: IEC 60898 accepts an upper short-circuit-current tripping range of 10-50 In fortype D circuit-breakers. European standards, and Figure G50 however, are based ona range of 10-20 In, a range which covers the vast majority of domestic and similarinstallations.Schneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors5 Particular cases of short-circuitcurrentExamplesExample 1In a 1-phase 2-wire installation the protection is provided by a 50 A circuit-breakertype NSX80HMA, the instantaneous short-circuit current trip, is set at 500 A(accuracy of ± 20%), i.e. in the worst case would require 500 x 1,2 = 600 A to trip.The cable c.s.a. = 10 mm 2 and the conductor material is copper.In Figure G47, the row Im = 500 A crosses the column c.s.a. = 10 mm 2 at the valuefor Lmax of 67 m. The circuit-breaker protects the cable against short-circuit faults,therefore, provided that its length does not exceed 67 metres.Example 2In a 3-phase 3-wire 400 V circuit (without neutral), the protection is provided by a220 A circuit-breaker type NSX250N with an instantaneous short-circuit current tripunit type MA set at 2,000 A (± 20%), i.e. a worst case of 2,400 A to be certain oftripping. The cable c.s.a. = 120 mm 2 and the conductor material is copper.In Figure G47 the row Im = 2,000 A crosses the column c.s.a. = 120 mm 2 at thevalue for Lmax of 200 m. Being a 3-phase 3-wire 400 V circuit (without neutral), acorrection factor from Figure G51 must be applied. This factor is seen to be 1.73.The circuit-breaker will therefore protect the cable against short-circuit current,provided that its length does not exceed 200 x 1.73= 346 metres.G355.2 Verification of the withstand capabilities ofcables under short-circuit conditionsIn general, verification of the thermal-withstandcapability of a cable is not necessary, except incases where cables of small c.s.a. are installedclose to, or feeding directly from, the maingeneral distribution boardThermal constraintsWhen the duration of short-circuit current is brief (several tenths of a secondup to five seconds maximum) all of the heat produced is assumed to remain inthe conductor, causing its temperature to rise. The heating process is said to beadiabatic, an assumption that simplifies the calculation and gives a pessimistic result,i.e. a higher conductor temperature than that which would actually occur, since inpractice, some heat would leave the conductor and pass into the insulation.For a period of 5 seconds or less, the relationship I 2 t = k 2 S 2 characterizes thetime in seconds during which a conductor of c.s.a. S (in mm 2 ) can be allowed tocarry a current I, before its temperature reaches a level which would damage thesurrounding insulation.The factor k 2 is given in Figure G52 below.Insulation Conductor copper (Cu) Conductor aluminium (Al)PVC 13,225 5,776XLPE 20,449 8,836Fig. G52 : Value of the constant k 2The method of verification consists in checking that the thermal energy I 2 t perohm of conductor material, allowed to pass by the protecting circuit-breaker (frommanufacturers catalogues) is less than that permitted for the particular conductor (asgiven in Figure G53 below).S (mm 2 ) PVC XLPECopper Aluminium Copper Aluminium1.5 0.0297 0.0130 0.0460 0.01992.5 0.0826 0.0361 0.1278 0.05524 0.2116 0.0924 0.3272 0.14146 0.4761 0.2079 0.7362 0.318110 1.3225 0.5776 2.0450 0.883616 3.3856 1.4786 5.2350 2.262025 8.2656 3.6100 12.7806 5.522535 16.2006 7.0756 25.0500 10.824150 29.839 13.032 46.133 19.936Fig. G53 : Maximum allowable thermal stress for cables I 2 t (expressed in ampere 2 x second x 10 6 )© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors5 Particular cases of short-circuitcurrentExampleIs a copper-cored XLPE cable of 4 mm 2 c.s.a. adequately protected by aC60N circuit-breaker?Figure G53 shows that the I 2 t value for the cable is 0.3272 x 10 6 , while the maximum“let-through” value by the circuit-breaker, as given in the manufacturer’s catalogue, isconsiderably less (< 0.1.10 6 A 2 s).The cable is therefore adequately protected by the circuit-breaker up to its full ratedbreaking capability.G36Electrodynamic constraintsFor all type of circuit (conductors or bus-trunking), it is necessary to takeelectrodynamic effects into account.To withstand the electrodynamic constraints, the conductors must be solidly fixedand the connection must be strongly tightened.For bus-trunking, rails, etc. it is also necessary to verify that the electrodynamicwithstand performance is satisfactory when carrying short-circuit currents. The peakvalue of current, limited by the circuit-breaker or fuse, must be less than the busbarsystem rating. Tables of coordination ensuring adequate protection of their productsare generally published by the manufacturers and provide a major advantage of suchsystems.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors6 Protective earthing conductor(PE)PEPECorrectIncorrectFig. G54 : A poor connection in a series arrangement will leaveall downstream appliances unprotectedPEN6.1 Connection and choiceProtective (PE) conductors provide the bonding connection between all exposedand extraneous conductive parts of an installation, to create the main equipotentialbonding system. These conductors conduct fault current due to insulation failure(between a phase conductor and an exposed conductive part) to the earthed neutralof the source. PE conductors are connected to the main earthing terminal of theinstallation.The main earthing terminal is connected to the earthing electrode (see Chapter E)by the earthing conductor (grounding electrode conductor in the USA).PE conductors must be:b Insulated and coloured yellow and green (stripes)b Protected against mechanical and chemical damageIn IT and TN-earthed schemes it is strongly recommended that PE conductorsshould be installed in close proximity (i.e. in the same conduits, on the same cabletray, etc.) as the live cables of the related circuit. This arrangement ensures theminimum possible inductive reactance in the earth-fault current carrying circuits.It should be noted that this arrangement is originally provided by bus-trunking.ConnectionPE conductors must:b Not include any means of breaking the continuity of the circuit (such as a switch,removable links, etc.)b Connect exposed conductive parts individually to the main PE conductor, i.e. inparallel, not in series, as shown in Figure G54b Have an individual terminal on common earthing bars in distribution boards.TT schemeThe PE conductor need not necessarily be installed in close proximity to the liveconductors of the corresponding circuit, since high values of earth-fault current arenot needed to operate the RCD-type of protection used in TT installations.IT and TN schemesThe PE or PEN conductor, as previously noted, must be installed as close aspossible to the corresponding live conductors of the circuit and no ferro-magneticmaterial must be interposed between them. A PEN conductor must always beconnected directly to the earth terminal of an appliance, with a looped connectionfrom the earth terminal to the neutral terminal of the appliance (see Fig. G55).b TN-C scheme (the neutral and PE conductor are one and the same, referred to asa PEN conductor)The protective function of a PEN conductor has priority, so that all rules governingPE conductors apply strictly to PEN conductorsb TN-C to TN-S transitionThe PE conductor for the installation is connected to the PEN terminal or bar (seeFig. G56) generally at the origin of the installation. Downstream of the point ofseparation, no PE conductor can be connected to the neutral conductor.G37PENPENFig. G55 : Direct connection of the PEN conductor to the earthterminal of an applianceFig. G56 : The TN-C-S scheme© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors6 Protective earthing conductor(PE)Types of materialsMaterials of the kinds mentioned below in Figure G57 can be used for PE conductors,provided that the conditions mentioned in the last column are satisfied.G38Type of protective earthing conductor (PE) IT scheme TN scheme TT scheme Conditions to be respectedSupplementary In the same cable Strongly Strongly recommended Correct The PE conductor mustconductor as the phases, or in recommended be insulated to the samethe same cable runlevel as the phasesIndependent of the Possible (1) Possible (1) (2) Correct b The PE conductor mayphase conductors be bare or insulated (2)Metallic housing of bus-trunking or of other Possible (3) PE possible (3) Correct b The electrical continuityprefabricated prewired ducting (5) PEN possible (8) must be assured by protectionExternal sheath of extruded, mineral- insulated Possible (3) PE possible (3) Possible against deterioration byconductors (e.g. «pyrotenax» type systems) PEN not recommended(2)(3) mechanical, chemical andCertain extraneous conductive elements (6) Possible (4) PE possible (4) Possibleelectrochemical hazardssuch as: PEN forbidden b Their conductanceb Steel building structuresmust be adequateb Machine framesb Water pipes (7)Metallic cable ways, such as, conduits (9) , Possible (4) PE possible (4) Possibleducts, trunking, trays, ladders, and so on… PEN not recommended (2)(4)Forbidden for use as PE conductors, are: metal conduits (9) , gas pipes, hot-water pipes, cable-armouring tapes (9) or wires (9)(1) In TN and IT schemes, fault clearance is generally achieved by overcurrent devices (fuses or circuit-breakers) so that the impedanceof the fault-current loop must be sufficiently low to assure positive protective device operation. The surest means of achieving a low loopimpedance is to use a supplementary core in the same cable as the circuit conductors (or taking the same route as the circuit conductors).This solution minimizes the inductive reactance and therefore the impedance of the loop.(2) The PEN conductor is a neutral conductor that is also used as a protective earth conductor. This means that a current may be flowingthrough it at any time (in the absence of an earth fault). For this reason an insulated conductor is recommended for PEN operation.(3) The manufacturer provides the necessary values of R and X components of the impedances (phase/PE, phase/PEN) to include in thecalculation of the earth-fault loop impedance.(4) Possible, but not recomended, since the impedance of the earth-fault loop cannot be known at the design stage. Measurements on thecompleted installation are the only practical means of assuring adequate protection for persons.(5) It must allow the connection of other PE conductors. Note: these elements must carry an indivual green/yellow striped visual indication,15 to 100 mm long (or the letters PE at less than 15 cm from each extremity).(6) These elements must be demountable only if other means have been provided to ensure uninterrupted continuity of protection.(7) With the agreement of the appropriate water authorities.(8) In the prefabricated pre-wired trunking and similar elements, the metallic housing may be used as a PEN conductor, in parallel with thecorresponding bar, or other PE conductor in the housing.(9) Forbidden in some countries only. Universally allowed to be used for supplementary equipotential conductors.Fig. G57 : Choice of protective conductors (PE)6.2 Conductor sizingFigure G58 below is based on IEC 60364-5-54. This table provides two methods ofdetermining the appropriate c.s.a. for both PE or PEN conductors.© Schneider Electric - all rights reservedc.s.a. of phase Minimum c.s.a. of Minimum c.s.a. ofconductors Sph (mm 2 ) PE conductor (mm 2 ) PEN conductor (mm 2 )Cu AlSimplified S ph y 16 S(2) ph S(3) ph S(3) phmethod (1) 16 < S ph y 25 16 1625 < S ph y 35 2535 < S ph y 50 S ph /2 S ph /2S ph > 50 S S ph /2Adiabatic methodAny size(1) Data valid if the prospective conductor is of the same material as the line conductor. Otherwise, a correction factor must be applied.(2) When the PE conductor is separated from the circuit phase conductors, the following minimum values must be respected:b 2.5 mm 2 if the PE is mechanically protectedb 4 mm 2 if the PE is not mechanically protected(3) For mechanical reasons, a PEN conductor, shall have a cross-sectional area not less than 10 mm 2 in copper or 16 mm 2 in aluminium.(4) Refer to table G53 for the application of this formula.Fig. G58 : Minimum cross section area of protective conductorsSPE/PEN =(3) (3)(4)(4)I 2⋅tkSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors6 Protective earthing conductor(PE)The two methods are:b Adiabatic (which corresponds with that described in IEC 60724)This method, while being economical and assuring protection of the conductoragainst overheating, leads to small c.s.a.’s compared to those of the correspondingcircuit phase conductors. The result is sometimes incompatible with the necessityin IT and TN schemes to minimize the impedance of the circuit earth-fault loop, toensure positive operation by instantaneous overcurrent tripping devices. This methodis used in practice, therefore, for TT installations, and for dimensioning an earthingconductor (1) .b SimplifiedThis method is based on PE conductor sizes being related to those of thecorresponding circuit phase conductors, assuming that the same conductor materialis used in each case.Thus, in Figure G58 for:Sph y 16 mm 2 SPE = Sph16 < Sph y 35 mm 2 SPE = 16 mm 2Sph > 35 mm Sph2 SPE = 2: when, in TT scheme, the installation earth electrode is beyond the zone ofNote: when, in a TT scheme, the installation earth electrode is beyond the zone ofinfluence of the source earthing electrode, the c.s.a. of the PE conductor can belimited to 25 mm 2 (for copper) or 35 mm 2 (for aluminium).The neutral cannot be used as a PEN conductor unless its c.s.a. is equal to or largerthan 10 mm 2 (copper) or 16 mm 2 (aluminium).Moreover, a PEN conductor is not allowed in a flexible cable. Since a PEN conductorfunctions also as a neutral conductor, its c.s.a. cannot, in any case, be less than thatnecessary for the neutral, as discussed in Subclause 7.1 of this Chapter.This c.s.a. cannot be less than that of the phase conductors unless:b The kVA rating of single-phase loads is less than 10% of the total kVA load, andb Imax likely to pass through the neutral in normal circumstances, is less than thecurrent permitted for the selected cable size.Furthermore, protection of the neutral conductor must be assured by the protectivedevices provided for phase-conductor protection (described in Sub-clause 7.2 of thisChapter).Values of factor k to be used in the formulaeThese values are identical in several national standards, and the temperature riseranges, together with factor k values and the upper temperature limits for the differentclasses of insulation, correspond with those published in IEC 60724 (1984).The data presented in Figure G59 are those most commonly needed for LV installationdesign.G39k valuesNature of insulationPolyvinylchloride (PVC)Final temperature (°C) 160 250Initial temperature (°C) 30 30Insulated conductors Copper 143 176not incoporated in Aluminium 95 116cables or bareconductors in contactSteel 52 64with cable jacketsConductors of a Copper 115 143multi-core-cable Aluminium 76 94Cross-linked-polyethylene(XLPE)Ethylene-propylene-rubber(EPR)(1) Grounding electrode conductorFig. G59 : k factor values for LV PE conductors, commonly used in national standards andcomplying with IEC 60724Schneider Electric - Electrical installation guide 2009© Schneider Electric - all rights reserved

G - Sizing and protection of conductors6 Protective earthing conductor(PE)6.3 Protective conductor between MV/LV transformerand the main general distribution board (MGDB)These conductors must be sized according tonational practicesAll phase and neutral conductors upstream of the main incoming circuit-breakercontrolling and protecting the MGDB are protected by devices at the MV side of thetransformer. The conductors in question, together with the PE conductor, must bedimensioned accordingly. Dimensioning of the phase and neutral conductors fromthe transformer is exemplified in Sub-clause 7.5 of this chapter (for circuit C1 of thesystem illustrated in Fig. G65).Recommended conductor sizes for bare and insulated PE conductors from thetransformer neutral point, shown in Figure G60, are indicated below in Figure G61.The kVA rating to consider is the sum of all (if more than one) transformersconnected to the MGDB.G40PEMain earth barfor the LV installationMGDBFig. G60 : PE conductor to the main earth bar in the MGDBThe table indicates the c.s.a. of the conductors in mm 2 according to:b The nominal rating of the MV/LV transformer(s) in kVAb The fault-current clearance time by the MV protective devices, in secondsb The kinds of insulation and conductor materialsIf the MV protection is by fuses, then use the 0.2 seconds columns.In IT schemes, if an overvoltage protection device is installed (between thetransformer neutral point and earth) the conductors for connection of the deviceshould also be dimensioned in the same way as that described above forPE conductors.Transformer Conductor Bare PVC-insulated XLPE-insulatedrating in kVA material conductors conductors conductors(230/400 V Copper t(s) 0.2 0.5 - 0.2 0.5 - 0.2 0.5 -output) Aluminium t(s) - 0.2 0.5 - 0.2 0.5 - 0.2 0.5y100 c.s.a. of PE 25 25 25 25 25 25 25 25 25160 conductors 25 25 35 25 25 50 25 25 35200 SPE (mm 2 ) 25 35 50 25 35 50 25 25 50250 25 35 70 35 50 70 25 35 50315 35 50 70 35 50 95 35 50 70400 50 70 95 50 70 95 35 50 95500 50 70 120 70 95 120 50 70 95630 70 95 150 70 95 150 70 95 120800 70 120 150 95 120 185 70 95 1501,000 95 120 185 95 120 185 70 120 1501,250 95 150 185 120 150 240 95 120 185© Schneider Electric - all rights reservedFig. G61 : Recommended c.s.a. of PE conductor between the MV/LV transformer and the MGDB,as a function of transformer ratings and fault-clearance times.Schneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors6 Protective earthing conductor(PE)6.4 Equipotential conductorThe main equipotential conductorThis conductor must, in general, have a c.s.a. at least equal to half of that of thelargest PE conductor, but in no case need exceed 25 mm 2 (copper) or 35 mm 2(aluminium) while its minimum c.s.a. is 6 mm 2 (copper) or 10 mm 2 (aluminium).Supplementary equipotential conductorThis conductor allows an exposed conductive part which is remote from the nearestmain equipotential conductor (PE conductor) to be connected to a local protectiveconductor. Its c.s.a. must be at least half of that of the protective conductor to whichit is connected.If it connects two exposed conductive parts (M1 and M2 in Figure G62) its c.s.a.must be at least equal to that of the smaller of the two PE conductors (for M1 andM2). Equipotential conductors which are not incorporated in a cable, should beprotected mechanically by conduits, ducting, etc. wherever possible.Other important uses for supplementary equipotential conductors concern thereduction of the earth-fault loop impedance, particulary for indirect-contact protectionschemes in TN- or IT-earthed installations, and in special locations with increasedelectrical risk (refer to IEC 60364-4-41).G41Between two exposed conductive partsif SPE1 y SPE2then SLS = SPE1SPE1SPE2Between an exposed conductive partand a metallic structureSLS =SPE2SPE1SLSSLSMetal structures(conduits, girders…)M 1 M 2M 1Fig. G62 : Supplementary equipotential conductors© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors7 The neutral conductorThe c.s.a. and the protection of the neutral conductor, apart from its current-carryingrequirement, depend on several factors, namely:b The type of earthing system, TT, TN, etc.b The harmonic currentsb The method of protection against indirect contact hazards according to themethods described belowThe color of the neutral conductor is statutorily blue. PEN conductor, when insulated,shall be marked by one of the following methods :b Green-and-yellow throughout its length with, in addition, light blue markings at theterminations, orb Light blue throughout its length with, in addition, green-and-yellow markings at theterminationsG427.1 Sizing the neutral conductorInfluence of the type of earthing systemTT and TN-S schemesb Single-phase circuits or those of c.s.a. y 16 mm 2 (copper) 25 mm 2 (aluminium): thec.s.a. of the neutral conductor must be equal to that of the phasesb Three-phase circuits of c.s.a. > 16 mm 2 copper or 25 mm 2 aluminium: the c.s.a. ofthe neutral may be chosen to be:v Equal to that of the phase conductors, orv Smaller, on condition that:- The current likely to flow through the neutral in normal conditions is less than thepermitted value Iz. The influence of triplen (1) harmonics must be given particularconsideration or- The neutral conductor is protected against short-circuit, in accordance with thefollowing Sub-clause G-7.2- The size of the neutral conductor is at least equal to 16 mm 2 in copper or 25 mm 2 inaluminiumTN-C schemeThe same conditions apply in theory as those mentioned above, but in practice,the neutral conductor must not be open-circuited under any circumstances sinceit constitutes a PE as well as a neutral conductor (see Figure G58 “c.s.a. of PENconductor” column).IT schemeIn general, it is not recommended to distribute the neutral conductor, i.e. a 3-phase3-wire scheme is preferred. When a 3-phase 4-wire installation is necessary,however, the conditions described above for TT and TN-S schemes are applicable.(1) Harmonics of order 3 and multiple of 3Influence of harmonic currentsEffects of triplen harmonicsHarmonics are generated by the non-linear loads of the installation (computers,fluorescent lighting, rectifiers, power electronic choppers) and can produce highcurrents in the Neutral. In particular triplen harmonics of the three Phases have atendency to cumulate in the Neutral as:b Fundamental currents are out-of-phase by 2π/3 so that their sum is zerob On the other hand, triplen harmonics of the three Phases are always positioned inthe same manner with respect to their own fundamental, and are in phase with eachother (see Fig. G63a).I 1 H1+I 1 H3© Schneider Electric - all rights reservedI 2 H1 + I 2 H3I 3 H1+ I 3 H333I N = I k H1 + I k H3110 + 3 I H3Fig. G63a : Triplen harmonics are in phase and cumulate in the NeutralSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors7 The neutral conductorFigure G63b shows the load factor of the neutral conductor as a function of thepercentage of 3 rd harmonic.In practice, this maximum load factor cannot exceed 3.I NeutralPhase2.01.81.61.41.21.00.80.60.40.20Ii 3 (%)0 20 40 60 80 100G43Fig. G63b : Load factor of the neutral conductor vs the percentage of 3 rd harmonicCompact NSX100 circuit breakerReduction factors for harmonic currents in four-core and five-core cables withfour cores carrying currentThe basic calculation of a cable concerns only cables with three loaded conductorsi.e there is no current in the neutral conductor. Because of the third harmonic current,there is a current in the neutral. As a result, this neutral current creates an hotenvironment for the 3 phase conductors and for this reason, a reduction factor forphase conductors is necessary (see Fig. G63).Reduction factors, applied to the current-carrying capacity of a cable with threeloaded conductors, give the current-carrying capacity of a cable with four loadedconductors, where the current in the fourth conductor is due to harmonics. Thereduction factors also take the heating effect of the harmonic current in the phaseconductors into account.b Where the neutral current is expected to be higher than the phase current, then thecable size should be selected on the basis of the neutral currentb Where the cable size selection is based on a neutral current which is notsignificantly higher than the phase current, it is necessary to reduce the tabulatedcurrent carrying capacity for three loaded conductorsb If the neutral current is more than 135% of the phase current and the cable size isselected on the basis of the neutral current then the three phase conductors will notbe fully loaded. The reduction in heat generated by the phase conductors offsets theheat generated by the neutral conductor to the extent that it is not necessary to applyany reduction factor to the current carrying capacity for three loaded conductors.b In order to protect cables, the fuse or circuit-breaker has to be sized taking intoaccount the greatest of the values of the line currents (phase or neutral). However,there are special devices (for example the Compact NSX circuit breaker equippedwith the OSN tripping unit), that allow the use of a c.s.a. of the phase conductorssmaller than the c.s.a. of the neutral conductor. A big economic gain can thus bemade.Third harmonic content Reduction factorof phase current Size selection is based on Size selection is based on(%) phase current neutral current0 - 15 1.0 -15 - 33 0.86 -33 - 45 - 0.86> 45 - 1.0Fig. G63 : Reduction factors for harmonic currents in four-core and five-core cables(according to IEC 60364-5-52)© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors7 The neutral conductorG44ExamplesConsider a three-phase circuit with a design load of 37 A to be installed using fourcorePVC insulated cable clipped to a wall, installation method C. From Figure G24,a 6 mm 2 cable with copper conductors has a current-carrying capacity of 40 A andhence is suitable if harmonics are not present in the circuit.b If 20 % third harmonic is present, then a reduction factor of 0,86 is applied and thedesign load becomes: 37/0.86 = 43 A.For this load a 10 mm 2 cable is necessary.In this case, the use of a special protective device (Compact NSX equipped with theOSN trip unit for instance) would allow the use of a 6 mm 2 cable for the phases andof 10 mm 2 for the neutral.b If 40 % third harmonic is present, the cable size selection is based on the neutralcurrent which is: 37 x 0,4 x 3 = 44,4 A and a reduction factor of 0,86 is applied,leading to a design load of: 44.4/0.86 = 51.6 A.For this load a 10 mm 2 cable is suitable.b If 50 % third harmonic is present, the cable size is again selected on the basis ofthe neutral current, which is: 37 x 0,5 x 3 = 55,5 A .In this case the rating factor is1 and a 16 mm 2 cable is required.In this case, the use of a special protective device (Compact NSX equipped with theOSN trip for instance) would allow the use of a 6 mm 2 cable for the phases and of10 mm 2 for the neutral.7.2 Protection of the neutral conductor(see Fig. G64 next page)Protection against overloadIf the neutral conductor is correctly sized (including harmonics), no specificprotection of the neutral conductor is required because it is protected by the phaseprotection.However, in practice, if the c.s.a. of the neutral conductor is lower than the phasec.s.a, a neutral overload protection must be installed.Protection against short-circuitIf the c.s.a. of the neutral conductor is lower than the c.s.a. of the phase conductor,the neutral conductor must be protected against short-circuit.If the c.s.a. of the neutral conductor is equal or greater than the c.s.a. of the phaseconductor, no specific protection of the neutral conductor is required because it isprotected by the phase protection.7.3 Breaking of the neutral conductor(see Fig. G64 next page)© Schneider Electric - all rights reservedThe need to break or not the neutral conductor is related to the protection againstindirect contact.In TN-C schemeThe neutral conductor must not be open-circuited under any circumstances since itconstitutes a PE as well as a neutral conductor.In TT, TN-S and IT schemesIn the event of a fault, the circuit-breaker will open all poles, including the neutralpole, i.e. the circuit-breaker is omnipolar.The action can only be achieved with fuses in an indirect way, in which the operationof one or more fuses triggers a mechanical trip-out of all poles of an associatedseries-connected load-break switch.7.4 Isolation of the neutral conductor(see Fig. G64 next page)It is considered to be the good practice that every circuit be provided with the meansfor its isolation.Schneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors7 The neutral conductorSingle-phase(Phase-Neutral)TT TN-C TN-S ITN N N Noror(B)NNSingle-phase(Phase-Phase)or(A)or(A)Three-phasefour wiresSn u SphG45NNNorN(B)NThree-phasefour wiresSn < SphN N Nor(B)N(A) Authorized for TT or TN-S systems if a RCD is installed at the origin of the circuit or upstream of it, and if no artificialneutral is distributed downstream of its location(B) The neutral overcurrent protection is not necessary:b If the neutral conductor is protected against short-circuits by a device placed upstream, or,b If the circuit is protected by a RCD which sensitivity is less than 15% of the neutral admissible current.Fig. G64 : The various situations in which the neutral conductor may appear© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors8 Worked example of cablecalculationWorked example of cable calculation (see Fig. G65)The installation is supplied through a 1,000 kVA transformer. The process requiresa high degree of supply continuity and this is provided by the installation of a 500 kVA400 V standby generator and the adoption of a 3-phase 3-wire IT system at the maingeneral distribution board. The remainder of the installation is isolated by a 400 kVA400/400 V transformer. The downstream network is a TT-earthed 3-phase 4-wiresystem. Following the single-line diagram shown in Figure G65 below, a reproductionof the results of a computer study for the circuit C1, the circuit-breaker Q1, the circuitC6 and the circuit-breaker Q6. These studies were carried out with ECODIAL 3.3software (a Merlin Gerin product).This is followed by the same calculations carried out by the method described in thisguide.T11000 kVA 400 V 50 HzG46C1Circuit 1G5GP = 500 kVAU = 400 VQ1Q6B2Q3Switchboard 2Ks = 1.00ib = 826.8 AC5Q5Circuit 5C6Circuit 6B4Q12Switchboard 4Ks = 1.00ib = 250.0 AT6P = 400 kVAU = 400 VC12Circuit 12Q7C7Circuit 7L12x1ku = 1.0ib = 250.00 AP = 147.22 kWQ9B8Q10Q11Switchboard 8Ks = 1.00ib = 490.0 AC9Circuit 9C10Circuit 10C11Circuit 11© Schneider Electric - all rights reservedL9x1Fig. G65 : Example of single-line diagramku = 1.0ib = 250.00 AP = 147.22 kWL10x1ku = 1.0ib = 160.00 AP = 94.22 kWL11x1ku = 1.0ib = 80.00 AP = 47.11 kWSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors8 Worked example of cablecalculationCalculation using software Ecodial 3.3General network characteristicsEarthing systemITNeutral distributedNoVoltage (V) 400Frequency (Hz) 50Transformer T1Number of transformers 1Upstream fault level (MVA) 500Rating (kVA) 1,000Short-circuit impedance voltage (%) 6Resistance of MV network (mΩ) 0.0351Reactance of MV network (mΩ) 0.351Transformer resistance RT (mΩ) 2.293Transformer reactance XT (mΩ) 10.3333-phase short-circuit current Ik3 (kA) 23.3Cable C1Maximum load current (A) 1,374Type of insulationPVCConductor materialCopperAmbient temperature (°C) 30Single-core or multi-core cableSingleInstallation methodFNumber of circuits in close proximity (table G21b) 1Other coefficient 1Selected cross-sectional area (mm 2 ) 6 x 95Protective conductor 1 x 120Length (m) 5Voltage drop ΔU (%) .122Voltage drop ΔU total (%) .1223-phase short-circuit current Ik3 (kA) 231-phase-to-earth fault current Id (kA) 17Circuit-breaker Q13-ph short-circuit current Ik3 upstreamof the circuit-breaker (kA) 23Maximum load current (A) 1,374Number of poles and protected poles3P3DCircuit-breaker NT 16TypeH 1 – 42 kATripping unit typeMicrologic 5 ARated current (A) 1,600Busbars B2Maximum load current (A) 1,374TypeStandard onedgeAmbient temperature (°C) 30Dimensions (m and mm)1 m2x5 mm x 63 mmMaterialCopper3-ph short-circuit current Ik3 (kA) 233-ph peak value of short-circuit current Ik (kA) 48Resistance of busbar R (mΩ) 2.52Reactance of busbar X (mΩ) 10.8Circuit-breaker Q63-ph short-circuit current upstreamof the circuit-breaker Ik3 (kA) 23Maximum load current (A) 560Number of poles and protected poles3P3DCircuit-breakerNS800TypeN – 50 kATripping unit type Micrologic 2.0Rated current (A) 800Limit of discrimination (kA)TotalCable C6Maximum load current (A) 560Type of insulationPVCConductor materialCopperAmbient temperature (°C) 30Single-core or multi-core cableSingleInstallation methodFNumber of circuits in close proximity (table G20) 1Other coefficient 1Selected cross-sectional area (mm 2 ) 1 x 300Protective conductor 1 x 150Length (m) 15Voltage drop ΔU (%) .38Voltage drop ΔU total (%) .543-phase short-circuit current Ik3 (kA) 201-phase-to-earth fault current Id (kA) 13.7Specific sizing constraintOverloadsG47Fig. G66 : Partial results of calculation carried out with Ecodial software (Merlin Gerin)The same calculation using the simplified methodrecommended in this guideDimensioning circuit C1The MV/LV 1,000 kVA transformer has a rated no-load voltage of 420 V. Circuit C1must be suitable for a current of31,000 x 10IB = = 1,374 A per phase3 x 420Six single-core PVC-insulated copper cables in parallel will be used for each phase.These cables will be laid on cable trays according to method F. The “k” correctionfactors are as follows:k 1 = 1 (see table G12, temperature = 30 °C)k 4 = 0.87 (see table G17, touching cables, 1 tray, u 3 circuits)Other correction factors are not relevant in this example.The corrected load current is:IB1,374I' B = = = 1,579 Ak1⋅k4 0.87Each conductor will therefore carry 263 A. Figure G21a G23 indicates that the the c.s.a. is is95 mm 2 .© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors8 Worked example of cablecalculationG48The resistances and the inductive reactances for the six conductors in parallel are,for a length of 5 metres:for a length of 5 metres:22.5 x 5R = =95 x 60.20 mΩ (cable resistance: 22.5 22.5 m mΩ.mm 2 /m)ΩX = 0.08 x 5 = 0.40 mΩ (cable reactance: 0.08 mΩ/m)Dimensioning circuit C6Circuit C6 supplies a 400 kVA 3-phase 400/400 V isolating transformer3400.10Primary current = = 550 A420. 3A single-core cable laid laid on on a a cable cable tray tray (without (without any any other other cable) cable) in an in ambient an ambient air airtemperature of 30 °C is proposed. The circuit-breaker is set at 560 AThe method of installation is characterized by the reference letter F, and the “k”correcting factors are all equal to 1.A c.s.a. of 240 mm 2 is appropriate.The resistance and inductive reactance are respectively:22.5 x 15R = = 1.4 mΩ240X = 0.08 x 15 = 1.2 mΩCalculation of short-circuit currents for the selection of circuit-breakersQ 1 and Q 6 (see Fig. G67)Circuits components R (mΩ) X (mΩ) Z (mΩ) Ikmax (kA)parts500 MVA at 0.04 0.36the MV source network1 MVA transformer 2.2 9.8 10.0 23Cable C1 0.20 0.4Sub-total for Q1 2.44 10.6 10.9 23Busbar B2 3.6 7.2Cable C6 1.4 1.2Sub-total for Q6 4.0 8.4 9.3 20Fig. G67 : Example of short-circuit current evaluationThe protective conductorThermal requirements: Figures G58 and G59 show that, when using the adiabaticmethod the c.s.a. for for the the protective earth earth (PE) (PE) conductor conductor for circuit for C1 circuit will be: C1 will be:34,800 x 0.21432= 108 mmA single 120 mm 2 conductor dimensioned for other reasons mentioned later istherefore largely sufficient, provided that it also satisfies the requirements for indirectcontactprotection (i.e. that its impedance is sufficiently low).For the circuit C6, the c.s.a. of its PE conductor should be:29,300 x 0.22= 92 mm143In this case a 95 mm 2 conductor may be adequate if the indirect-contact protectionconditions are also satisfied.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

G - Sizing and protection of conductors8 Worked example of cablecalculationProtection against indirect-contact hazardsFor circuit C6 of Figure G65, Figures F45 and F61, or the formula given page F27may be used for a 3-phase 3-wire circuit.The maximum permitted length of the circuit is given by :0.8 x 240 x 230 3 x 1,000Lmax =2 x 22.5 1+ 240= 70 m⎛ ⎞x 630 x 11⎝ 95 ⎠(The value in the denominator 630 x 11 I= Im i.e. the current level at which theinstantaneous short-circuit magnetic trip of the 630 A circuit-breaker operates).The length of 15 metres is therefore fully protected by “instantaneous” overcurrentdevices.Voltage dropFrom Figure G28 it can be seen that:b For the cable C1 (6 x 95mm 2 per phase)-1 -1∆U = 0.42 (V A km ) x 1,374 (A) x 0.008 = 1.54 V3∆U% = 100 1.54 = 0.38%400 xb For the circuit C6∆U 0.21 (V A -1 km -1= ) x 433 (A) x 0.015 = 1.36 V3∆U% = 100 1.36 = 0.34%400 xAt the circuit terminals of the LV/LV transformer the percentage volt-dropΔU% = 0.72%G49© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Chapter HLV switchgear: functions &selection1234ContentsThe basic functions of LV switchgear1.1 Electrical protection H21.2 Isolation H31.3 Switchgear control H4The switchgear2.1 Elementary switching devices H52.2 Combined switchgear elements H9Choice of switchgearH2H5H103.1 Tabulated functional capabilities H103.2 Switchgear selection H10Circuit-breakerH114.1 Standards and description H114.2 Fundamental characteristics of a circuit-breaker H134.3 Other characteristics of a circuit-breaker H154.4 Selection of a circuit-breaker H184.5 Coordination between circuit-breakers H224.6 Discrimination MV/LV in a consumer’s substation H28H© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

H - LV switchgear: functions & selection1 The basic functions ofLV switchgearThe role of switchgear is:b Electrical protectionb Safe isolation from live partsb Local or remote switchingNational and international standards define the manner in which electric circuits ofLV installations must be realized, and the capabilities and limitations of the variousswitching devices which are collectively referred to as switchgear.The main functions of switchgear are:b Electrical protectionb Electrical isolation of sections of an installationb Local or remote switchingThese functions are summarized below in Figure H1.Electrical protection at low voltage is (apart from fuses) normally incorporated incircuit-breakers, in the form of thermal-magnetic devices and/or residual-currentoperatedtripping devices (less-commonly, residual voltage- operated devices- acceptable to, but not recommended by IEC).In addition to those functions shown in Figure H1, other functions, namely:b Over-voltage protectionb Under-voltage protectionare provided by specific devices (lightning and various other types of voltage-surgearrester, relays associated with contactors, remotely controlled circuit-breakers, andwith combined circuit-breaker/isolators… and so on)HElectrical protection Isolation Controlagainstb Overload currents b Isolation clearly indicated b Functional switchingb Short-circuit currents by an authorized fail-proof b Emergency switchingb Insulation failure mechanical indicator b Emergency stoppingb A gap or interposed insulating b Switching off forbarrier between the open mechanical maintenancecontacts, clearly visibleFig. H1 : Basic functions of LV switchgear© Schneider Electric - all rights reservedElectrical protection assures:b Protection of circuit elements against thethermal and mechanical stresses of short-circuitcurrentsb Protection of persons in the event ofinsulation failureb Protection of appliances and apparatus beingsupplied (e.g. motors, etc.)1.1 Electrical protectionThe aim is to avoid or to limit the destructive or dangerous consequences ofexcessive (short-circuit) currents, or those due to overloading and insulation failure,and to separate the defective circuit from the rest of the installation.A distinction is made between the protection of:b The elements of the installation (cables, wires, switchgear…)b Persons and animalsb Equipment and appliances supplied from the installationThe protection of circuitsv Against overload; a condition of excessive current being drawn from a healthy(unfaulted) installationv Against short-circuit currents due to complete failure of insulation betweenconductors of different phases or (in TN systems) between a phase and neutral (orPE) conductorProtection in these cases is provided either by fuses or circuit-breaker, in thedistribution board at the origin of the final circuit (i.e. the circuit to which the loadis connected). Certain derogations to this rule are authorized in some nationalstandards, as noted in chapter H1 sub-clause 1.4.The protection of personsv Against insulation failures. According to the system of earthing for the installation(TN, TT or IT) the protection will be provided by fuses or circuit-breakers, residualcurrent devices, and/or permanent monitoring of the insulation resistance of theinstallation to earthThe protection of electric motorsv Against overheating, due, for example, to long term overloading, stalled rotor,single-phasing, etc. Thermal relays, specially designed to match the particularcharacteristics of motors are used.Such relays may, if required, also protect the motor-circuit cable against overload.Short-circuit protection is provided either by type aM fuses or by a circuit-breakerfrom which the thermal (overload) protective element has been removed, orotherwise made inoperative.Schneider Electric - Electrical installation guide 2009

H - LV switchgear: functions & selection1 The basic functions ofLV switchgearA state of isolation clearly indicated by anapproved “fail-proof” indicator, or the visibleseparation of contacts, are both deemed tosatisfy the national standards of many countries1.2 IsolationThe aim of isolation is to separate a circuit or apparatus (such as a motor, etc.) fromthe remainder of a system which is energized, in order that personnel may carry outwork on the isolated part in perfect safety.In principle, all circuits of an LV installation shall have means to be isolated.In practice, in order to maintain an optimum continuity of service, it is preferred toprovide a means of isolation at the origin of each circuit.An isolating device must fulfil the following requirements:b All poles of a circuit, including the neutral (except where the neutral is a PENconductor) must open (1)b It must be provided with a locking system in open position with a key (e.g. bymeans of a padlock) in order to avoid an unauthorized reclosure by inadvertenceb It must comply with a recognized national or international standard(e.g. IEC 60947-3) concerning clearance between contacts, creepage distances,overvoltage withstand capability, etc.:Other requirements apply:v Verification that the contacts of the isolating device are, in fact, open.The verification may be:- Either visual, where the device is suitably designed to allow the contacts to be seen(some national standards impose this condition for an isolating device located at theorigin of a LV installation supplied directly from a MV/LV transformer)- Or mechanical, by means of an indicator solidly welded to the operating shaftof the device. In this case the construction of the device must be such that, in theeventuality that the contacts become welded together in the closed position, theindicator cannot possibly indicate that it is in the open positionv Leakage currents. With the isolating device open, leakage currents between theopen contacts of each phase must not exceed:- 0.5 mA for a new device- 6.0 mA at the end of its useful lifev Voltage-surge withstand capability, across open contacts. The isolating device,when open must withstand a 1.2/50 μs impulse, having a peak value of 6, 8 or 12 kVaccording to its service voltage, as shown in Figure H2. The device must satisfythese conditions for altitudes up to 2,000 metres. Correction factors are given inIEC 60664-1 for altitudes greater than 2,000 metres.Consequently, if tests are carried out at sea level, the test values must be increasedby 23% to take into account the effect of altitude. See standard IEC 60947.HService (nominalvoltage(V)Impulse withstandpeak voltage category(for 2,000 metres)(kV)IIIIV230/400 4 6400/690 6 8690/1,000 8 12Fig. H2 : Peak value of impulse voltage according to normal service voltage of test specimen.The degrees III and IV are degrees of pollution defined in IEC 60664-1(1) the concurrent opening of all live conductors, while notalways obligatory, is however, strongly recommended (forreasons of greater safety and facility of operation). The neutralcontact opens after the phase contacts, and closes beforethem (IEC 60947-1).© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

H - LV switchgear: functions & selection1 The basic functions ofLV switchgearHSwitchgear-control functions allow systemoperating personnel to modify a loaded systemat any moment, according to requirements,and include:b Functional control (routine switching, etc.)b Emergency switchingb Maintenance operations on the power system1.3 Switchgear controlIn broad terms “control” signifies any facility for safely modifying a load-carryingpower system at all levels of an installation. The operation of switchgear is animportant part of power-system control.Functional controlThis control relates to all switching operations in normal service conditions forenergizing or de-energizing a part of a system or installation, or an individual pieceof equipment, item of plant, etc.Switchgear intended for such duty must be installed at least:b At the origin of any installationb At the final load circuit or circuits (one switch may control several loads)Marking (of the circuits being controlled) must be clear and unambiguous.In order to provide the maximum flexibility and continuity of operation, particularlywhere the switching device also constitutes the protection (e.g. a circuit-breaker orswitch-fuse) it is preferable to include a switch at each level of distribution, i.e. oneach outgoing way of all distribution and subdistribution boards.The manœuvre may be:b Either manual (by means of an operating lever on the switch) orb Electric, by push-button on the switch or at a remote location (load-shedding andreconnection, for example)These switches operate instantaneously (i.e. with no deliberate delay), and thosethat provide protection are invariably omni-polar (1) .The main circuit-breaker for the entire installation, as well as any circuit-breakersused for change-over (from one source to another) must be omni-polar units.Emergency switching - emergency stopAn emergency switching is intended to de-energize a live circuit which is, or couldbecome, dangerous (electric shock or fire).An emergency stop is intended to halt a movement which has become dangerous.In the two cases:b The emergency control device or its means of operation (local or at remotelocation(s)) such as a large red mushroom-headed emergency-stop pushbutton mustbe recognizable and readily accessible, in proximity to any position at which dangercould arise or be seenb A single action must result in a complete switching-off of all live conductors(2) (3)b A “break glass” emergency switching initiation device is authorized, but inunmanned installations the re-energizing of the circuit can only be achieved bymeans of a key held by an authorized personIt should be noted that in certain cases, an emergency system of braking, mayrequire that the auxiliary supply to the braking-system circuits be maintained untilfinal stoppage of the machinery.Switching-off for mechanical maintenance workThis operation assures the stopping of a machine and its impossibility to beinadvertently restarted while mechanical maintenance work is being carried outon the driven machinery. The shutdown is generally carried out at the functionalswitching device, with the use of a suitable safety lock and warning notice at theswitch mechanism.© Schneider Electric - all rights reserved(1) One break in each phase and (where appropriate) onebreak in the neutral.(2) Taking into account stalled motors.(3) In a TN schema the PEN conductor must never beopened, since it functions as a protective earthing wire as wellas the system neutral conductor.Schneider Electric - Electrical installation guide 2009

H - LV switchgear: functions & selection2 The switchgearFig. H5 : Symbol for a disconnector (or isolator)Fig. H6 : Symbol for a load-break switch2.1 Elementary switching devicesDisconnector (or isolator) (see Fig. H5)This switch is a manually-operated, lockable, two-position device (open/closed)which provides safe isolation of a circuit when locked in the open position. Itscharacteristics are defined in IEC 60947-3. A disconnector is not designed to makeor to break current (1) and no rated values for these functions are given in standards.It must, however, be capable of withstanding the passage of short-circuit currentsand is assigned a rated short-time withstand capability, generally for 1 second,unless otherwise agreed between user and manufacturer. This capability is normallymore than adequate for longer periods of (lower-valued) operational overcurrents,such as those of motor-starting. Standardized mechanical-endurance, overvoltage,and leakage-current tests, must also be satisfied.Load-breaking switch (see Fig. H6)This control switch is generally operated manually (but is sometimes provided withelectrical tripping for operator convenience) and is a non-automatic two-positiondevice (open/closed).It is used to close and open loaded circuits under normal unfaulted circuit conditions.It does not consequently, provide any protection for the circuit it controls.IEC standard 60947-3 defines:b The frequency of switch operation (600 close/open cycles per hour maximum)b Mechanical and electrical endurance (generally less than that of a contactor)b Current making and breaking ratings for normal and infrequent situationsWhen closing a switch to energize a circuit there is always the possibility thatan unsuspected short-circuit exists on the circuit. For this reason, load-breakswitches are assigned a fault-current making rating, i.e. successful closure againstthe electrodynamic forces of short-circuit current is assured. Such switches arecommonly referred to as “fault-make load-break” switches. Upstream protectivedevices are relied upon to clear the short-circuit faultCategory AC-23 includes occasional switching of individual motors. The switchingof capacitors or of tungsten filament lamps shall be subject to agreement betweenmanufacturer and user.The utilization categories referred to in Figure H7 do not apply to an equipmentnormally used to start, accelerate and/or stop individual motors.ExampleA 100 A load-break switch of category AC-23 (inductive load) must be able:b To make a current of 10 In (= 1,000 A) at a power factor of 0.35 laggingb To break a current of 8 In (= 800 A) at a power factor of 0.45 laggingb To withstand short duration short-circuit currents when closedHUtilization category Typical applications Cos ϕ Making BreakingFrequent Infrequent current x In current x Inoperations operationsAC-20A AC-20B Connecting and disconnecting - - -under no-load conditionsAC-21A AC-21B Switching of resistive loads 0.95 1.5 1.5including moderate overloadsAC-22A AC-22B Switching of mixed resistive 0.65 3 3and inductive loads, includingmoderate overloadsAC-23A AC-23B Switching of motor loads or 0.45 for I y 100 A 10 8other highly inductive loads 0.35 for I > 100 AFig. H7 : Utilization categories of LV AC switches according to IEC 60947-3(1) i.e. a LV disconnector is essentially a dead systemswitching device to be operated with no voltage on either sideof it, particularly when closing, because of the possibility of anunsuspected short-circuit on the downstream side. Interlockingwith an upstream switch or circuit-breaker is frequently used.Schneider Electric - Electrical installation guide 2009© Schneider Electric - all rights reserved

H - LV switchgear: functions & selection2 The switchgearHFig. H8 : Symbol for a bistable remote control switchControlcircuitFig. H9 : Symbol for a contactorPowercircuitRemote control switch (see Fig. H8)This device is extensively used in the control of lighting circuits where the depressionof a pushbutton (at a remote control position) will open an already-closed switch orclose an opened switch in a bistable sequence.Typical applications are:b Two-way switching on stairways of large buildingsb Stage-lighting schemesb Factory illumination, etc.Auxiliary devices are available to provide:b Remote indication of its state at any instantb Time-delay functionsb Maintained-contact featuresContactor (see Fig. H9)The contactor is a solenoid-operated switching device which is generally heldclosed by (a reduced) current through the closing solenoid (although variousmechanically-latched types exist for specific duties). Contactors are designed tocarry out numerous close/open cycles and are commonly controlled remotely byon-off pushbuttons. The large number of repetitive operating cycles is standardized intable VIII of IEC 60947-4-1 by:b The operating duration: 8 hours; uninterrupted; intermittent; temporary of 3, 10, 30,60 and 90 minutesb Utilization category: for example, a contactor of category AC3 can be used for thestarting and stopping of a cage motorb The start-stop cycles (1 to 1,200 cyles per hour)b Mechanical endurance (number of off-load manœuvres)b Electrical endurance (number of on-load manœuvres)b A rated current making and breaking performance according to the category ofutilization concernedExample:A 150 A contactor of category AC3 must have a minimum current-breaking capabilityof 8 In (= 1,200 A) and a minimum current-making rating of 10 In (= 1,500 A) at apower factor (lagging) of 0.35.Discontactor (1)A contactor equipped with a thermal-type relay for protection against overloadingdefines a “discontactor”. Discontactors are used extensively for remote push-buttoncontrol of lighting circuits, etc., and may also be considered as an essential elementin a motor controller, as noted in sub-clause 2.2. “combined switchgear elements”.The discontactor is not the equivalent of a circuit-breaker, since its short-circuitcurrent breaking capability is limited to 8 or 10 In. For short-circuit protectiontherefore, it is necessary to include either fuses or a circuit-breaker in series with,and upstream of, the discontactor contacts.© Schneider Electric - all rights reservedTwo classes of LV cartridge fuse are verywidely used:b For domestic and similar installations type gGb For industrial installations type gG, gM or aMFig. H10 : Symbol for fuses(1) This term is not defined in IEC publications but is commonlyused in some countries.Fuses (see Fig. H10)The first letter indicates the breaking range:b “g” fuse-links (full-range breaking-capacity fuse-link)b “a” fuse-links (partial-range breaking-capacity fuse-link)The second letter indicates the utilization category; this letter defines with accuracythe time-current characteristics, conventional times and currents, gates.For exampleb “gG” indicates fuse-links with a full-range breaking capacity for general applicationb “gM” indicates fuse-links with a full-range breaking capacity for the protection ofmotor circuitsb “aM” indicates fuse-links with a partial range breaking capacity for the protection ofmotor circuitsFuses exist with and without “fuse-blown” mechanical indicators. Fuses break acircuit by controlled melting of the fuse element when a current exceeds a givenvalue for a corresponding period of time; the current/time relationship beingpresented in the form of a performance curve for each type of fuse. Standards definetwo classes of fuse:b Those intended for domestic installations, manufactured in the form of a cartridgefor rated currents up to 100 A and designated type gG in IEC 60269-1 and 3b Those for industrial use, with cartridge types designated gG (general use); and gMand aM (for motor-circuits) in IEC 60269-1 and 2Schneider Electric - Electrical installation guide 2009

H - LV switchgear: functions & selection2 The switchgeargM fuses require a separate overload relay, asdescribed in the note at the end of sub-clause 2.1.The main differences between domestic and industrial fuses are the nominalvoltage and current levels (which require much larger physical dimensions) andtheir fault-current breaking capabilities. Type gG fuse-links are often used for theprotection of motor circuits, which is possible when their characteristics are capableof withstanding the motor-starting current without deterioration.A more recent development has been the adoption by the IEC of a fuse-type gM formotor protection, designed to cover starting, and short-circuit conditions. This type offuse is more popular in some countries than in others, but at the present time theaM fuse in combination with a thermal overload relay is more-widely used.A gM fuse-link, which has a dual rating is characterized by two current values. Thefirst value In denotes both the rated current of the fuse-link and the rated current ofthe fuseholder; the second value Ich denotes the time-current characteristic of thefuse-link as defined by the gates in Tables II, III and VI of IEC 60269-1.These two ratings are separated by a letter which defines the applications.For example: In M Ich denotes a fuse intended to be used for protection ofmotor circuits and having the characteristic G. The first value In corresponds tothe maximum continuous current for the whole fuse and the second value Ichcorresponds to the G characteristic of the fuse link. For further details see note at theend of sub-clause 2.1.An aM fuse-link is characterized by one current value In and time-currentcharacteristic as shown in Figure H14 next page.Important: Some national standards use a gI (industrial) type fuse, similar in all mainessentails to type gG fuses.Type gI fuses should never be used, however, in domestic and similar installations.Fusing zones - conventional currentsThe conditions of fusing (melting) of a fuse are defined by standards, according totheir class.Class gG fusesThese fuses provide protection against overloads and short-circuits.Conventional non-fusing and fusing currents are standardized, as shown inFigure H12 and in Figure H13.b The conventional non-fusing current Inf is the value of current that the fusibleelement can carry for a specified time without melting.Example: A 32 A fuse carrying a current of 1.25 In (i.e. 40 A) must not melt in lessthan one hour (table H13)b The conventional fusing current If (= I2 in Fig. H12) is the value of current whichwill cause melting of the fusible element before the expiration of the specified time.Example: A 32 A fuse carrying a current of 1.6 In (i.e. 52.1 A) must melt in one houror lessIEC 60269-1 standardized tests require that a fuse-operating characteristic liesbetween the two limiting curves (shown in Figure H12) for the particular fuse undertest. This means that two fuses which satisfy the test can have significantly differentoperating times at low levels of overloading.Ht1 hourInf I2Minimumpre-arcingtime curveFuse-blowcurveIRated current (1) Conventional non- Conventional ConventionalIn (A) fusing current fusing current time (h)InfI2In y 4 A 1.5 In 2.1 In 14 < In < 16 A 1.5 In 1.9 In 116 < In y 63 A 1.25 In 1.6 In 163 < In y 160 A 1.25 In 1.6 In 2160 < In y 400 A 1.25 In 1.6 In 3400 < In 1.25 In 1.6 In 4Fig. H12 : Zones of fusing and non-fusing for gG and gM fuses(1) Ich for gM fusesFig. H13 : Zones of fusing and non-fusing for LV types gG and gM class fuses (IEC 60269-1and 60269-2-1)© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

H - LV switchgear: functions & selection2 The switchgearClass aM fuses protect against short-circuitcurrents only, and must always be associatedwith another device which protects againstoverloadb The two examples given above for a 32 A fuse, together with the foregoing noteson standard test requirements, explain why these fuses have a poor performance inthe low overload rangeb It is therefore necessary to install a cable larger in ampacity than that normallyrequired for a circuit, in order to avoid the consequences of possible long termoverloading (60% overload for up to one hour in the worst case)By way of comparison, a circuit-breaker of similar current rating:b Which passes 1.05 In must not trip in less than one hour; andb When passing 1.25 In it must trip in one hour, or less (25% overload for up to onehour in the worst case)Class aM (motor) fusesThese fuses afford protection against short-circuit currents only and must necessarilybe associated with other switchgear (such as discontactors or circuit-breakers) inorder to ensure overload protection < 4 In. They are not therefore autonomous. SinceaM fuses are not intended to protect against low values of overload current, no levelsof conventional non-fusing and fusing currents are fixed. The characteristic curves fortesting these fuses are given for values of fault current exceeding approximately 4 In(see Fig. H14), and fuses tested to IEC 60269 must give operating curves which fallwithin the shaded area.Note: the small “arrowheads” in the diagram indicate the current/time “gate” valuesfor the different fuses to be tested (IEC 60269).© Schneider Electric - all rights reservedH4 I nx I nFig. H14 : Standardized zones of fusing for type aM fuses (allcurrent ratings)ItTf TaTtc0.005 s0.02 s0.01 sTf: Fuse pre-arc fusing timeTa: Arcing timeTtc: Total fault-clearance timeFig. H15 : Current limitation by a fuseMini m umpre-arcingtime cu r v eFuse- b l o wncu r v eProspectivefault-current peakrms value of the ACcomponent of theprospective fault curentCurrent peaklimited by the fuse(1) For currents exceeding a certain level, depending on thefuse nominal current rating, as shown below in Figure H16.tRated short-circuit breaking currentsA characteristic of modern cartridge fuses is that, owing to the rapidity of fusionin the case of high short-circuit current levels (1) , a current cut-off begins beforethe occurrence of the first major peak, so that the fault current never reaches itsprospective peak value (see Fig. H15).This limitation of current reduces significantly the thermal and dynamic stresseswhich would otherwise occur, thereby minimizing danger and damage at the faultposition. The rated short-circuit breaking current of the fuse is therefore based on therms value of the AC component of the prospective fault current.No short-circuit current-making rating is assigned to fuses.ReminderShort-circuit currents initially contain DC components, the magnitude and duration ofwhich depend on the XL/R ratio of the fault current loop.Close to the source (MV/LV transformer) the relationship Ipeak / Irms (ofAC component) immediately following the instant of fault, can be as high as 2.5(standardized by IEC, and shown in Figure H16 next page).At lower levels of distribution in an installation, as previously noted, XL is smallcompared with R and so for final circuits Ipeak / Irms ~ 1.41, a condition whichcorresponds with Figure H15.The peak-current-limitation effect occurs only when the prospective rmsAC component of fault current attains a certain level. For example, in the Figure H16graph, the 100 A fuse will begin to cut off the peak at a prospective fault current(rms) of 2 kA (a). The same fuse for a condition of 20 kA rms prospective currentwill limit the peak current to 10 kA (b). Without a current-limiting fuse the peakcurrent could attain 50 kA (c) in this particular case. As already mentioned, at lowerdistribution levels in an installation, R greatly predominates XL, and fault levels aregenerally low. This means that the level of fault current may not attain values highenough to cause peak current limitation. On the other hand, the DC transients (in thiscase) have an insignificant effect on the magnitude of the current peak, as previouslymentioned.Note: On gM fuse ratingsA gM type fuse is essentially a gG fuse, the fusible element of which corresponds tothe current value Ich (ch = characteristic) which may be, for example, 63 A. This isthe IEC testing value, so that its time/ current characteristic is identical to that of a63 A gG fuse.This value (63 A) is selected to withstand the high starting currents of a motor, thesteady state operating current (In) of which may be in the 10-20 A range.This means that a physically smaller fuse barrel and metallic parts can be used,since the heat dissipation required in normal service is related to the lower figures(10-20 A). A standard gM fuse, suitable for this situation would be designated 32M63(i.e. In M Ich).The first current rating In concerns the steady-load thermal performance of thefuselink, while the second current rating (Ich) relates to its (short-time) startingcurrentperformance. It is evident that, although suitable for short-circuit protection,Schneider Electric - Electrical installation guide 2009

H - LV switchgear: functions & selection2 The switchgearProspective faultcurrent (kA) peak10050201052(a)Maximum possible currentpeak characteristici.e. 2.5 Irms (IEC)(c)(b)160A100A50A11 2 5 10 20 50 100AC component of prospectivefault current (kA) rmsNominalfuseratingsPeak currentcut-offcharacteristiccurvesFig. H16 : Limited peak current versus prospective rms valuesof the AC component of fault current for LV fusesoverload protection for the motor is not provided by the fuse, and so a separatethermal-type relay is always necessary when using gM fuses. The only advantageoffered by gM fuses, therefore, when compared with aM fuses, are reduced physicaldimensions and slightly lower cost.2.2 Combined switchgear elementsSingle units of switchgear do not, in general, fulfil all the requirements of the threebasic functions, viz: Protection, control and isolation.Where the installation of a circuit-breaker is not appropriate (notably where theswitching rate is high, over extended periods) combinations of units specificallydesigned for such a performance are employed. The most commonly-usedcombinations are described below.Switch and fuse combinationsTwo cases are distinguished:b The type in which the operation of one (or more) fuse(s) causes the switch to open.This is achieved by the use of fuses fitted with striker pins, and a system of switchtripping springs and toggle mechanisms (see Fig. H17)b The type in which a non-automatic switch is associated with a set of fuses in acommon enclosure.In some countries, and in IEC 60947-3, the terms “switch-fuse” and “fuse-switch”have specific meanings, viz:v A switch-fuse comprises a switch (generally 2 breaks per pole) on the upstreamside of three fixed fuse-bases, into which the fuse carriers are inserted (see Fig. H18)v A fuse-switch consists of three switch blades each constituting a double-break perphase.These blades are not continuous throughout their length, but each has a gap in thecentre which is bridged by the fuse cartridge. Some designs have only a single breakper phase, as shown in Figure H19.HFig. H17 : Symbol for an automatic tripping switch-fuseFig. H18 : Symbol for a non-automatic fuse-switchFig. H19 : Symbol for a non-automatic switch-fuseFig. H20 : Symbol for a fuse disconnector + discontactorFig. H21 : Symbol for a fuse-switch disconnector + discontactorThe current range for these devices is limited to 100 A maximum at 400 V 3-phase,while their principal use is in domestic and similar installations. To avoid confusionbetween the first group (i.e. automatic tripping) and the second group, the term“switch-fuse” should be qualified by the adjectives “automatic” or “non-automatic”.Fuse – disconnector + discontactorFuse - switch-disconnector + discontactorAs previously mentioned, a discontactor does not provide protection against shortcircuitfaults. It is necessary, therefore, to add fuses (generally of type aM) to performthis function. The combination is used mainly for motor control circuits, where thedisconnector or switch-disconnector allows safe operations such as:b The changing of fuse links (with the circuit isolated)b Work on the circuit downstream of the discontactor (risk of remote closure of thediscontactor)The fuse-disconnector must be interlocked with the discontactor such that no openingor closing manœuvre of the fuse disconnector is possible unless the discontactor isopen ( Figure H20), since the fuse disconnector has no load-switching capability.A fuse-switch-disconnector (evidently) requires no interlocking (Figure H21).The switch must be of class AC22 or AC23 if the circuit supplies a motor.Circuit-breaker + contactorCircuit-breaker + discontactorThese combinations are used in remotely controlled distribution systems in which therate of switching is high, or for control and protection of a circuit supplying motors.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

H - LV switchgear: functions & selection3 Choice of switchgear3.1 Tabulated functional capabilitiesAfter having studied the basic functions of LV switchgear (clause 1, Figure H1) andthe different components of switchgear (clause 2), Figure H22 summarizes thecapabilities of the various components to perform the basic functions.H10Isolation Control Electrical protectionSwitchgear Functional Emergency Emergency Switching for Overload Short-circuit Electricitem switching stop mechanical shock(mechanical) maintenanceIsolator (or bdisconnector) (4)Switch (5) b b b (1) b (1) (2) bResidual b b b (1) b (1) (2) b bdevice(RCCB) (5)Switch- b b b (1) b (1) (2) bdisconnectorContactor b b (1) b (1) (2) b b (3)Remote control b b (1) bswitchFuse b b bCircuit b b (1) b (1) (2) b b bbreakerCircuit-breaker b b b (1) b (1) (2) b b bdisconnector (5)Residual b b b (1) b (1) (2) b b b band overcurrentcircuit-breaker(RCBO) (5)Point of Origin of each All points where, In general at the At the supply At the supply Origin of each Origin of each Origin of circuitsinstallation circuit for operational incoming circuit point to each point to each circuit circuit where the(general reasons it may to every machine machine earthing systemprinciple) be necessary distribution and/or on the is appropriateto stop the board machine TN-S, IT, TTprocessconcerned(1) Where cut-off of all active conductors is provided(2) It may be necessary to maintain supply to a braking system(3) If it is associated with a thermal relay (the combination is commonly referred to as a “discontactor”)(4) In certain countries a disconnector with visible contacts is mandatory at the origin of a LV installation supplied directly from a MV/LV transformer(5) Certain items of switchgear are suitable for isolation duties (e.g. RCCBs according to IEC 61008) without being explicitly marked as suchFig. H22 : Functions fulfilled by different items of switchgear3.2 Switchgear selection© Schneider Electric - all rights reservedSoftware is being used more and more in the field of optimal selection of switchgear.Each circuit is considered one at a time, and a list is drawn up of the requiredprotection functions and exploitation of the installation, among those mentioned inFigure H22 and summarized in Figure H1.A number of switchgear combinations are studied and compared with each otheragainst relevant criteria, with the aim of achieving:b Satisfactory performanceb Compatibility among the individual items; from the rated current In to the fault-levelrating Icub Compatibility with upstream switchgear or taking into account its contributionb Conformity with all regulations and specifications concerning safe and reliablecircuit performanceIn order to determine the number of poles for an item of switchgear, reference ismade to chapter G, clause 7 Fig. G64. Multifunction switchgear, initially more costly,reduces installation costs and problems of installation or exploitation. It is often foundthat such switchgear provides the best solution.Schneider Electric - Electrical installation guide 2009

H - LV switchgear: functions & selection4 Circuit-breakerThe circuit-breaker/disconnector fulfills all of thebasic switchgear functions, while, by means ofaccessories, numerous other possibilities existAs shown in Figure H23 the circuit-breaker/ disconnector is the only item ofswitchgear capable of simultaneously satisfying all the basic functions necessary inan electrical installation.Moreover, it can, by means of auxiliary units, provide a wide range of other functions,for example: indication (on-off - tripped on fault); undervoltage tripping; remotecontrol… etc. These features make a circuit-breaker/ disconnector the basic unit ofswitchgear for any electrical installation.FunctionsPossible conditionsIsolationbControl Functional bEmergency switching b (With the possibility of a trippingcoil for remote control)Switching-off for mechanical bmaintenanceProtection Overload bShort-circuitbInsulation faultb (With differential-current relay)Undervoltageb (With undervoltage-trip coil)Remote controlb Added or incorporatedIndication and measurementb (Generally optional with anelectronic tripping device)Fig. H23 : Functions performed by a circuit-breaker/disconnectorH11Industrial circuit-breakers must comply withIEC 60947-1 and 60947-2 or other equivalentstandards.Domestic-type circuit-breakers must comply withIEC standard 60898, or an equivalent nationalstandardPower circuit terminals4.1 Standards and descriptionStandardsFor industrial LV installations the relevant IEC standards are, or are due to be:b 60947-1: general rulesb 60947-2: part 2: circuit-breakersb 60947-3: part 3: switches, disconnectors, switch-disconnectors and fusecombination unitsb 60947-4: part 4: contactors and motor startersb 60947-5: part 5: control-circuit devices and switching elementsb 60947-6: part 6: multiple function switching devicesb 60947-7: part 7: ancillary equipmentFor domestic and similar LV installations, the appropriate standard is IEC 60898, oran equivalent national standard.Fig. H24 : Main parts of a circuit-breakerContacts and arc-divingchamberFool-proof mechanicalindicatorLatching mechanismTrip mechanism andprotective devicesDescriptionFigure H24 shows schematically the main parts of a LV circuit-breaker and its fouressential functions:b The circuit-breaking components, comprising the fixed and moving contacts andthe arc-dividing chamberb The latching mechanism which becomes unlatched by the tripping device ondetection of abnormal current conditionsThis mechanism is also linked to the operation handle of the breaker.b A trip-mechanism actuating device:v Either: a thermal-magnetic device, in which a thermally-operated bi-metal stripdetects an overload condition, while an electromagnetic striker pin operates atcurrent levels reached in short-circuit conditions, orv An electronic relay operated from current transformers, one of which is installed oneach phaseb A space allocated to the several types of terminal currently used for the mainpower circuit conductorsDomestic circuit-breakers (see Fig. H25 next page) complying with IEC 60898 andsimilar national standards perform the basic functions of:b Isolationb Protection against overcurrent© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

H - LV switchgear: functions & selection4 Circuit-breakerSome models can be adapted to provide sensitive detection (30 mA) of earthleakagecurrent with CB tripping, by the addition of a modular block, while othermodels (RCBOs, complying with IEC 61009 and CBRs complying with IEC 60947-2Annex B) have this residual current feature incorporated as shown in Figure H26.Apart from the above-mentioned functions further features can be associated withthe basic circuit-breaker by means of additional modules, as shown in Figure H27;notably remote control and indication (on-off-fault).15432Fig. H25 : Domestic-type circuit-breaker providing overcurrentprotection and circuit isolation featuresO-OFFO-OFF O-OFFH12Fig. H27 : “Multi 9” system of LV modular switchgear componentsFig. H26 : Domestic-type circuit-breaker as above (Fig. H25)with incorparated protection against electric shocksMoulded-case circuit-breakers complying with IEC 60947-2 are available from 100to 630 A and provide a similar range of auxiliary functions to those described above(see Figure H28).Air circuit-breakers of large current ratings, complying with IEC 60947-2, aregenerally used in the main switch board and provide protector for currents from630 A to 6300 A, typically.(see Figure H29).In addition to the protection functions, the Micrologic unit provides optimizedfunctions such as measurement (including power quality functions), diagnosis,communication, control and monitoring.© Schneider Electric - all rights reservedFig. H28 : Example of a Compact NSX industrial type of circuitbreakercapable of numerous auxiliary functionsFig. H29 : Example of air circuit-breakers. Masterpact provides many control features in its“Micrologic” tripping unitSchneider Electric - Electrical installation guide 2009

H - LV switchgear: functions & selection4 Circuit-breaker4.2 Fundamental characteristics of a circuit-breakerThe fundamental characteristics of a circuit-breaker are:b Its rated voltage Ueb Its rated current Inb Its tripping-current-level adjustment ranges for overload protection (Ir (1) or Irth (1) )and for short-circuit protection (Im) (1)b Its short-circuit current breaking rating (Icu for industrial CBs; Icn for domestictypeCBs).Rated operational voltage (Ue)This is the voltage at which the circuit-breaker has been designed to operate, innormal (undisturbed) conditions.Other values of voltage are also assigned to the circuit-breaker, corresponding todisturbed conditions, as noted in sub-clause 4.3.Rated current (In)This is the maximum value of current that a circuit-breaker, fitted with a specifiedovercurrent tripping relay, can carry indefinitely at an ambient temperature stated bythe manufacturer, without exceeding the specified temperature limits of the currentcarrying parts.ExampleA circuit-breaker rated at In = 125 A for an ambient temperature of 40 °C will beequipped with a suitably calibrated overcurrent tripping relay (set at 125 A). Thesame circuit-breaker can be used at higher values of ambient temperature however,if suitably “derated”. Thus, the circuit-breaker in an ambient temperature of 50 °Ccould carry only 117 A indefinitely, or again, only 109 A at 60 °C, while complyingwith the specified temperature limit.Derating a circuit-breaker is achieved therefore, by reducing the trip-current settingof its overload relay, and marking the CB accordingly. The use of an electronic-typeof tripping unit, designed to withstand high temperatures, allows circuit-breakers(derated as described) to operate at 60 °C (or even at 70 °C) ambient.Note: In for circuit-breakers (in IEC 60947-2) is equal to Iu for switchgear generally,Iu being the rated uninterrupted current.H13Frame-size ratingA circuit-breaker which can be fitted with overcurrent tripping units of different currentlevel-setting ranges, is assigned a rating which corresponds to the highest currentlevel-settingtripping unit that can be fitted.ExampleA Compact NSX630N circuit-breaker can be equipped with 11 electronic trip unitsfrom 150 A to 630 A. The size of the circuit-breaker is 630 A.0.4 InRated current ofthe tripping unitInAdjustmentrangeOverload tripcurrent settingIrCircuit breakerframe-size rating160 A 360 A 400 A 630 AFig. H30 : Example of a NSX630N circuit-breaker equipped witha Micrologic 6.3E trip unit adjusted to 0.9, to give Ir = 360 A(1) Current-level setting values which refer to the currentoperatedthermal and “instantaneous” magnetic trippingdevices for over-load and short-circuit protection.Overload relay trip-current setting (Irth or Ir)Apart from small circuit-breakers which are very easily replaced, industrial circuitbreakersare equipped with removable, i.e. exchangeable, overcurrent-trip relays.Moreover, in order to adapt a circuit-breaker to the requirements of the circuitit controls, and to avoid the need to install over-sized cables, the trip relays aregenerally adjustable. The trip-current setting Ir or Irth (both designations arein common use) is the current above which the circuit-breaker will trip. It alsorepresents the maximum current that the circuit-breaker can carry without tripping.That value must be greater than the maximum load current IB, but less than themaximum current permitted in the circuit Iz (see chapter G, sub-clause 1.3).The thermal-trip relays are generally adjustable from 0.7 to 1.0 times In, but whenelectronic devices are used for this duty, the adjustment range is greater; typically 0.4to 1 times In.Example (see Fig. H30)A NSX630N circuit-breaker equipped with a 400 A Micrologic 6.3E overcurrent triprelay, set at 0.9, will have a trip-current setting:Ir = 400 x 0.9 = 360 ANote: For circuit-breakers equipped with non-adjustable overcurrent-trip relays,Ir = In. Example: for C60N 20 A circuit-breaker, Ir = In = 20 A.Schneider Electric - Electrical installation guide 2009© Schneider Electric - all rights reserved

H - LV switchgear: functions & selection4 Circuit-breakerShort-circuit relay trip-current setting (Im)Short-circuit tripping relays (instantaneous or slightly time-delayed) are intended totrip the circuit-breaker rapidly on the occurrence of high values of fault current. Theirtripping threshold Im is:b Either fixed by standards for domestic type CBs, e.g. IEC 60898, or,b Indicated by the manufacturer for industrial type CBs according to relatedstandards, notably IEC 60947-2.For the latter circuit-breakers there exists a wide variety of tripping devices whichallow a user to adapt the protective performance of the circuit-breaker to theparticular requirements of a load (see Fig. H31, Fig. H32 and Fig. H33).H14Type of Overload Short-circuit protectionprotective protectionrelayDomestic Thermal- Ir = In Low setting Standard setting High setting circuitbreakers magnetic type B type C type DIEC 60898 3 In y Im y 5 In 5 In y Im y 10 In 10 In y Im y 20 In (1)Modular Thermal- Ir = In Low setting Standard setting High settingindustrial (2) magnetic fixed type B or Z type C type D or Kcircuit-breakers 3.2 In y fixed y 4.8 In 7 In y fixed y 10 In 10 In y fixed y 14 InIndustrial (2) Thermal- Ir = In fixed Fixed: Im = 7 to 10 Incircuit-breakers magnetic Adjustable: Adjustable:IEC 60947-2 0.7 In y Ir y In - Low setting : 2 to 5 In- Standard setting: 5 to 10 InElectronic Long delay Short-delay, adjustable0.4 In y Ir y In 1.5 Ir y Im y 10 IrInstantaneous (I) fixedI = 12 to 15 In(1) 50 In in IEC 60898, which is considered to be unrealistically high by most European manufacturers (Merlin Gerin = 10 to 14 In).(2) For industrial use, IEC standards do not specify values. The above values are given only as being those in common use.Fig. H31 : Tripping-current ranges of overload and short-circuit protective devices for LV circuit-breakerst (s )t (s )IrImIiIcuI(A© Schneider Electric - all rights reservedIrImIcuI(AFig. H32 : Performance curve of a circuit-breaker thermalmagneticprotective schemeIr: Overload (thermal or long-delay) relay trip-currentsettingIm: Short-circuit (magnetic or short-delay) relay tripcurrentsettingIi: Short-circuit instantaneous relay trip-current setting.Icu: Breaking capacityFig. H33 : Performance curve of a circuit-breaker electronic protective schemeSchneider Electric - Electrical installation guide 2009

H - LV switchgear: functions & selection4 Circuit-breakerThe short-circuit current-breaking performanceof a LV circuit-breaker is related (approximately)to the cos ϕ of the fault-current loop. Standardvalues for this relationship have beenestablished in some standardsIsolating featureA circuit-breaker is suitable for isolating a circuit if it fulfills all the conditionsprescribed for a disconnector (at its rated voltage) in the relevant standard (seesub-clause 1.2). In such a case it is referred to as a circuit-breaker-disconnector andmarked on its front face with the symbolAll Multi 9, Compact NSX and Masterpact LV switchgear of Schneider Electricranges are in this category.Rated short-circuit breaking capacity (Icu or Icn)The short-circuit current-breaking rating of a CB is the highest (prospective) valueof current that the CB is capable of breaking without being damaged. The valueof current quoted in the standards is the rms value of the AC component of thefault current, i.e. the DC transient component (which is always present in the worstpossible case of short-circuit) is assumed to be zero for calculating the standardizedvalue. This rated value (Icu) for industrial CBs and (Icn) for domestic-type CBs isnormally given in kA rms.Icu (rated ultimate s.c. breaking capacity) and Ics (rated service s.c. breakingcapacity) are defined in IEC 60947-2 together with a table relating Ics with Icu fordifferent categories of utilization A (instantaneous tripping) and B (time-delayedtripping) as discussed in subclause 4.3.Tests for proving the rated s.c. breaking capacities of CBs are governed bystandards, and include:b Operating sequences, comprising a succession of operations, i.e. closing andopening on short-circuitb Current and voltage phase displacement. When the current is in phase with thesupply voltage (cos ϕ for the circuit = 1), interruption of the current is easier thanthat at any other power factor. Breaking a current at low lagging values of cos ϕ isconsiderably more difficult to achieve; a zero power-factor circuit being (theoretically)the most onerous case.In practice, all power-system short-circuit fault currents are (more or less) at laggingpower factors, and standards are based on values commonly considered to berepresentative of the majority of power systems. In general, the greater the level offault current (at a given voltage), the lower the power factor of the fault-current loop,for example, close to generators or large transformers.Figure H34 below extracted from IEC 60947-2 relates standardized values of cos ϕto industrial circuit-breakers according to their rated Icu.b Following an open - time delay - close/open sequence to test the Icu capacity of aCB, further tests are made to ensure that:v The dielectric withstand capabilityv The disconnection (isolation) performance andv The correct operation of the overload protectionhave not been impaired by the test.H15Icucos ϕ6 kA < Icu y 10 kA 0.510 kA < Icu y 20 kA 0.320 kA < Icu y 50 kA 0.2550 kA < Icu 0.2Fig. H34 : Icu related to power factor (cos ϕ) of fault-current circuit (IEC 60947-2)Familiarity with the following characteristics ofLV circuit-breakers is often necessary whenmaking a final choice.4.3 Other characteristics of a circuit-breakerRated insulation voltage (Ui)This is the value of voltage to which the dielectric tests voltage (generally greaterthan 2 Ui) and creepage distances are referred to.The maximum value of rated operational voltage must never exceed that of the ratedinsulation voltage, i.e. Ue y Ui.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

H - LV switchgear: functions & selection4 Circuit-breakerRated impulse-withstand voltage (Uimp)This characteristic expresses, in kV peak (of a prescribed form and polarity) the valueof voltage which the equipment is capable of withstanding without failure, under testconditions.t (s)Generally, for industrial circuit-breakers, Uimp = 8 kV and for domestic types,Uimp = 6 kV.Category (A or B) and rated short-time withstand current (Icw)H16ImFig. H35 : Category A circuit-breakert (s )I(A)As already briefly mentioned (sub-clause 4.2) there are two categories ofLV industrial switchgear, A and B, according to IEC 60947-2:b Those of category A, for which there is no deliberate delay in the operation of the“instantaneous” short-circuit magnetic tripping device (see Fig. H35), are generallymoulded-case type circuit-breakers, andb Those of category B for which, in order to discriminate with other circuit-breakerson a time basis, it is possible to delay the tripping of the CB, where the fault-currentlevel is lower than that of the short-time withstand current rating (Icw) of the CB(see Fig. H36). This is generally applied to large open-type circuit-breakers andto certain heavy-duty moulded-case types. Icw is the maximum current that the Bcategory CB can withstand, thermally and electrodynamically, without sustainingdamage, for a period of time given by the manufacturer.Rated making capacity (Icm)Icm is the highest instantaneous value of current that the circuit-breaker canestablish at rated voltage in specified conditions. In AC systems this instantaneouspeak value is related to Icu (i.e. to the rated breaking current) by the factor k, whichdepends on the power factor (cos ϕ) of the short-circuit current loop (as shown inFigure H37 ).Icu cos ϕ Icm = kIcu6 kA < Icu y 10 kA 0.5 1.7 x Icu10 kA < Icu y 20 kA 0.3 2 x Icu20 kA < Icu y 50 kA 0.25 2.1 x Icu50 kA y Icu 0.2 2.2 x IcuFig. H37 : Relation between rated breaking capacity Icu and rated making capacity Icm atdifferent power-factor values of short-circuit current, as standardized in IEC 60947-2ImFig. H36 : Category B circuit-breakerIIcwIcuI(A )Example: A Masterpact NW08H2 circuit-breaker has a rated breaking capacityIcu of 100 kA. The peak value of its rated making capacity Icm will be100 x 2.2 = 220 kA.© Schneider Electric - all rights reservedIn a correctly designed installation, a circuitbreakeris never required to operate at itsmaximum breaking current Icu. For this reasona new characteristic Ics has been introduced.It is expressed in IEC 60947-2 as a percentageof Icu (25, 50, 75, 100%)(1) O represents an opening operation.CO represents a closing operation followed by an openingoperation.Rated service short-circuit breaking capacity (Ics)The rated breaking capacity (Icu) or (Icn) is the maximum fault-current a circuitbreakercan successfully interrupt without being damaged. The probability of sucha current occurring is extremely low, and in normal circumstances the fault-currentsare considerably less than the rated breaking capacity (Icu) of the CB. On the otherhand it is important that high currents (of low probability) be interrupted under goodconditions, so that the CB is immediately available for reclosure, after the faultycircuit has been repaired. It is for these reasons that a new characteristic (Ics) hasbeen created, expressed as a percentage of Icu, viz: 25, 50, 75, 100% for industrialcircuit-breakers. The standard test sequence is as follows:b O - CO - CO (1) (at Ics)b Tests carried out following this sequence are intended to verify that the CB is in agood state and available for normal serviceFor domestic CBs, Ics = k Icn. The factor k values are given in IEC 60898 table XIV.In Europe it is the industrial practice to use a k factor of 100% so that Ics = Icu.Schneider Electric - Electrical installation guide 2009

H - LV switchgear: functions & selection4 Circuit-breakerMany designs of LV circuit-breakers featurea short-circuit current limitation capability,whereby the current is reduced and preventedfrom reaching its (otherwise) maximum peakvalue (see Fig. H38). The current-limitationperformance of these CBs is presented inthe form of graphs, typified by that shown inFigure H39, diagram (a)Fault-current limitationThe fault-current limitation capacity of a CB concerns its ability, more or lesseffective, in preventing the passage of the maximum prospective fault-current,permitting only a limited amount of current to flow, as shown in Figure H38.The current-limitation performance is given by the CB manufacturer in the form ofcurves (see Fig. H39).b Diagram (a) shows the limited peak value of current plotted against the rmsvalue of the AC component of the prospective fault current (“prospective” faultcurrentrefers to the fault-current which would flow if the CB had no current-limitingcapability)b Limitation of the current greatly reduces the thermal stresses (proportional I 2 t) andthis is shown by the curve of diagram (b) of Figure H39, again, versus the rms valueof the AC component of the prospective fault current.LV circuit-breakers for domestic and similar installations are classified in certainstandards (notably European Standard EN 60 898). CBs belonging to one class (ofcurrent limiters) have standardized limiting I 2 t let-through characteristics defined bythat class.In these cases, manufacturers do not normally provide characteristic performancecurves.a)Limitedcurrentpeak(kA)22Non-limited currentcharacteristicsb)4,5.105Limitedcurrent peak(A2 x s)H172.105Prospective ACcomponent (rms)150 kAProspective ACcomponent (rms)150 kAFig. H39 : Performance curves of a typical LV current-limiting circuit-breakerCurrent limitation reduces both thermal andelectrodynamic stresses on all circuit elementsthrough which the current passes, therebyprolonging the useful life of these elements.Furthermore, the limitation feature allows“cascading” techniques to be used (see 4.5)thereby significantly reducing design andinstallation costsIccProspecticefault-current peakLimitedcurrent peakLimitedcurrenttcFig. H38 : Prospective and actual currentsProspecticefault-currenttThe advantages of current limitationThe use of current-limiting CBs affords numerous advantages:b Better conservation of installation networks: current-limiting CBs strongly attenuateall harmful effects associated with short-circuit currentsb Reduction of thermal effects: Conductors (and therefore insulation) heating issignificantly reduced, so that the life of cables is correspondingly increasedb Reduction of mechanical effects: forces due to electromagnetic repulsion are lower,with less risk of deformation and possible rupture, excessive burning of contacts, etc.b Reduction of electromagnetic-interference effects:v Less influence on measuring instruments and associated circuits,telecommunication systems, etc.These circuit-breakers therefore contribute towards an improved exploitation of:b Cables and wiringb Prefabricated cable-trunking systemsb Switchgear, thereby reducing the ageing of the installationExampleOn a system having a prospective shortcircuit current of 150 kA rms, a Compact Lcircuit-breaker limits the peak current to less than 10% of the calculated prospectivepeak value, and the thermal effects to less than 1% of those calculated.Cascading of the several levels of distribution in an installation, downstream of alimiting CB, will also result in important savings.The technique of cascading, described in sub-clause 4.5 allows, in fact, substantialsavings on switchgear (lower performance permissible downstream of the limitingCB(s)) enclosures, and design studies, of up to 20% (overall).Discriminative protection schemes and cascading are compatible, in the CompactNSX range, up to the full short-circuit breaking capacity of the switchgear.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

H - LV switchgear: functions & selection4 Circuit-breakerH18The choice of a range of circuit-breakers isdetermined by: the electrical characteristics ofthe installation, the environment, the loads anda need for remote control, together with the typeof telecommunications system envisagedAmbienttemperatureSingle CBin free airFig. H40 : Ambient temperatureTemperature of airsurrouding thecircuit breakersCircuit breakers installedin an enclosureAmbienttemperature4.4 Selection of a circuit-breakerChoice of a circuit-breakerThe choice of a CB is made in terms of:b Electrical characteristics of the installation for which the CB is intendedb Its eventual environment: ambient temperature, in a kiosk or switchboardenclosure, climatic conditions, etc.b Short-circuit current breaking and making requirementsb Operational specifications: discriminative tripping, requirements (or not) forremote control and indication and related auxiliary contacts, auxiliary tripping coils,connectionb Installation regulations; in particular: protection of personsb Load characteristics, such as motors, fluorescent lighting, LV/LV transformersThe following notes relate to the choice LV circuit-breaker for use in distributionsystems.Choice of rated current in terms of ambient temperatureThe rated current of a circuit-breaker is defined for operation at a given ambienttemperature, in general:b 30 °C for domestic-type CBsb 40 °C for industrial-type CBsPerformance of these CBs in a different ambient temperature depends mainly on thetechnology of their tripping units (see Fig. H40).Circuit-breakers with uncompensated thermaltripping units have a trip current level thatdepends on the surrounding temperatureUncompensated thermal magnetic tripping unitsCircuit-breakers with uncompensated thermal tripping elements have a trippingcurrentlevel that depends on the surrounding temperature. If the CB is installedin an enclosure, or in a hot location (boiler room, etc.), the current required to tripthe CB on overload will be sensibly reduced. When the temperature in which theCB is located exceeds its reference temperature, it will therefore be “derated”. Forthis reason, CB manufacturers provide tables which indicate factors to apply attemperatures different to the CB reference temperature. It may be noted from typicalexamples of such tables (see Fig. H41) that a lower temperature than the referencevalue produces an up-rating of the CB. Moreover, small modular-type CBs mountedin juxtaposition, as shown typically in Figure H27, are usually mounted in a smallclosed metal case. In this situation, mutual heating, when passing normal loadcurrents, generally requires them to be derated by a factor of 0.8.ExampleWhat rating (In) should be selected for a C60 N?b Protecting a circuit, the maximum load current of which is estimated to be 34 Ab Installed side-by-side with other CBs in a closed distribution boxb In an ambient temperature of 50 °CA C60N circuit-breaker rated at 40 A would be derated to 35.6 A in ambient air at50 °C (see Fig. H41). To allow for mutual heating in the enclosed space, however, the0.8 factor noted above must be employed, so that, 35.6 x 0.8 = 28.5 A, which is notsuitable for the 34 A load.A 50 A circuit-breaker would therefore be selected, giving a (derated) current ratingof 44 x 0.8 = 35.2 A.© Schneider Electric - all rights reservedCompensated thermal-magnetic tripping unitsThese tripping units include a bi-metal compensating strip which allows the overloadtrip-current setting (Ir or Irth) to be adjusted, within a specified range, irrespective ofthe ambient temperature.For example:b In certain countries, the TT system is standard on LV distribution systems, anddomestic (and similar) installations are protected at the service position by a circuitbreakerprovided by the supply authority. This CB, besides affording protectionagainst indirect-contact hazard, will trip on overload; in this case, if the consumerexceeds the current level stated in his supply contract with the power authority. Thecircuit-breaker (y 60 A) is compensated for a temperature range of - 5 °C to + 40 °C.b LV circuit-breakers at ratings y 630 A are commonly equipped with compensatedtripping units for this range (- 5 °C to + 40 °C)Schneider Electric - Electrical installation guide 2009

H - LV switchgear: functions & selection4 Circuit-breakerC60a, C60H: curve C. C60N: curves B and C (reference temperature: 30 °C)Rating (A) 20 °C 25 °C 30 °C 35 °C 40 °C 45 °C 50 °C 55 °C 60 °C1 1.05 1.02 1.00 0.98 0.95 0.93 0.90 0.88 0.852 2.08 2.04 2.00 1.96 1.92 1.88 1.84 1.80 1.743 3.18 3.09 3.00 2.91 2.82 2.70 2.61 2.49 2.374 4.24 4.12 4.00 3.88 3.76 3.64 3.52 3.36 3.246 6.24 6.12 6.00 5.88 5.76 5.64 5.52 5.40 5.3010 10.6 10.3 10.0 9.70 9.30 9.00 8.60 8.20 7.8016 16.8 16.5 16.0 15.5 15.2 14.7 14.2 13.8 13.520 21.0 20.6 20.0 19.4 19.0 18.4 17.8 17.4 16.825 26.2 25.7 25.0 24.2 23.7 23.0 22.2 21.5 20.732 33.5 32.9 32.0 31.4 30.4 29.8 28.4 28.2 27.540 42.0 41.2 40.0 38.8 38.0 36.8 35.6 34.4 33.250 52.5 51.5 50.0 48.5 47.4 45.5 44.0 42.5 40.563 66.2 64.9 63.0 61.1 58.0 56.7 54.2 51.7 49.2Compact NSX100-250 N/H/L equippment with TM-D or TM-G trip unitsRating Temperature (°C)(A) 10 15 20 25 30 35 40 45 50 55 60 65 7016 18.4 18.7 18 18 17 16.6 16 15.6 15.2 14.8 14.5 14 13.825 28.8 28 27.5 25 26.3 25.6 25 24.5 24 23.5 23 22 2132 36.8 36 35.2 34.4 33.6 32.8 32 31.3 30.5 30 29.5 29 28.540 46 45 44 43 42 41 40 39 38 37 36 35 3450 57.5 56 55 54 52.5 51 50 49 48 47 46 45 4463 72 71 69 68 66 65 63 61.5 60 58 57 55 5480 92 90 88 86 84 82 80 78 76 74 72 70 68100 115 113 110 108 105 103 100 97.5 95 92.5 90 87.5 85125 144 141 138 134 131 128 125 122 119 116 113 109 106160 184 180 176 172 168 164 160 156 152 148 144 140 136200 230 225 220 215 210 205 200 195 190 185 180 175 170250 288 281 277 269 263 256 250 244 238 231 225 219 213H19Fig. H41 : Examples of tables for the determination of derating/uprating factors to apply to CBswith uncompensated thermal tripping units, according to temperatureElectronic tripping units are highly stable inchanging temperature levelsElectronic trip unitsAn important advantage with electronic tripping units is their stable performancein changing temperature conditions. However, the switchgear itself often imposesoperational limits in elevated temperatures, so that manufacturers generally providean operating chart relating the maximum values of permissible trip-current levels tothe ambient temperature (see Fig. H42).Moreover, electronic trip units can provide information that can be used for a bettermanagement of the electrical distribution, including energy efficiency and powerquality.Masterpact NW20 version 40°C 45°C 50°C 55°C 60°CH1/H2/H3 Withdrawable with In (A) 2,000 2,000 2,000 1,980 1,890horizontal plugs Maximum 1 1 1 0.99 0.95adjustment IrL1 Withdrawable with In (A) 2,000 200 1,900 1,850 1,800on-edge plugs Maximum 1 1 0.95 0.93 0.90adjustment IrCoeff.In (A)1 2,0000.95 1,8900.90 1,800NW20 withdrawable withhorizontal plugsNW20 L1 withdrawablewith on edge plugs20 25 30 35 40 45 50 55 60Fig. H42 : Derating of Masterpact NW20 circuit-breaker, according to the temperatureθ°C© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

H - LV switchgear: functions & selection4 Circuit-breakerSelection of an instantaneous, or short-time-delay, trippingthresholdFigure H43 below summarizes the main characteristics of the instantaneous orshort-time delay trip units.Type Tripping unit ApplicationsLow setting b Sources producing low short-circuitttype Bcurrent levels(standby generators)b Long lengths of line or cabletIStandard settingtype Cb Protection of circuits: general casetIHigh settingtype D or Kb Protection of circuits having high initialtransient current levels(e.g. motors, transformers, resistive loads)H20It12 In b Protection of motors in association withtype MAdiscontactors(contactors with overload protection)IFig. H43 : Different tripping units, instantaneous or short-time-delayedThe installation of a LV circuit-breaker requiresthat its short-circuit breaking capacity (or that ofthe CB together with an associated device) beequal to or exceeds the calculated prospectiveshort-circuit current at its point of installationSelection of a circuit-breaker according to the short-circuitbreaking capacity requirementsThe installation of a circuit-breaker in a LV installation must fulfil one of the twofollowing conditions:b Either have a rated short-circuit breaking capacity Icu (or Icn) which is equal to orexceeds the prospective short-circuit current calculated for its point of installation, orb If this is not the case, be associated with another device which is locatedupstream, and which has the required short-circuit breaking capacityIn the second case, the characteristics of the two devices must be co-ordinatedsuch that the energy permitted to pass through the upstream device must notexceed that which the downstream device and all associated cables, wires and othercomponents can withstand, without being damaged in any way. This technique isprofitably employed in:b Associations of fuses and circuit-breakersb Associations of current-limiting circuit-breakers and standard circuit-breakers.The technique is known as “cascading” (see sub-clause 4.5 of this chapter)© Schneider Electric - all rights reservedThe circuit-breaker at the output of the smallesttransformer must have a short-circuit capacityadequate for a fault current which is higherthan that through any of the other transformerLV circuit-breakersThe selection of main and principal circuit-breakersA single transformerIf the transformer is located in a consumer’s substation, certain national standardsrequire a LV circuit-breaker in which the open contacts are clearly visible such asCompact NSX withdrawable circuit-breaker.Example (see Fig. H44 opposite page)What type of circuit-breaker is suitable for the main circuit-breaker of an installationsupplied through a 250 kVA MV/LV (400 V) 3-phase transformer in a consumer’ssubstation?In transformer = 360 AIsc (3-phase) = 8.9 kAA Compact NSX400N with an adjustable tripping-unit range of 160 A - 400 A and ashort-circuit breaking capacity (Icu) of 50 kA would be a suitable choice for this duty.Schneider Electric - Electrical installation guide 2009

H - LV switchgear: functions & selection4 Circuit-breaker250 kVA20 kV/400 VCompactNSX400NFig. H44 : Example of a transformer in a consumer’s substationA1B1MVLVTr1CBMCBPA2B2Fig. H45 : Transformers in parallelEMVLVTr2CBMCBPA3B3MVLVTr3CBMSeveral transformers in parallel (see Fig. H45)b The circuit-breakers CBP outgoing from the LV distribution board must each becapable of breaking the total fault current from all transformers connected to thebusbars, viz: Isc1 + Isc2 + Isc3b The circuit-breakers CBM, each controlling the output of a transformer, must becapable of dealing with a maximum short-circuit current of (for example) Isc2 + Isc3only, for a short-circuit located on the upstream side of CBM1.From these considerations, it will be seen that the circuit-breaker of the smallesttransformer will be subjected to the highest level of fault current in thesecircumstances, while the circuit-breaker of the largest transformer will pass thelowest level of short-circuit currentb The ratings of CBMs must be chosen according to the kVA ratings of theassociated transformersNote: The essential conditions for the successful operation of 3-phase transformersin parallel may be summarized as follows:1. the phase shift of the voltages, primary to secondary, must be the same in all unitsto be paralleled.2. the open-circuit voltage ratios, primary to secondary, must be the same in all units.3. the short-circuit impedance voltage (Zsc%) must be the same for all units.For example, a 750 kVA transformer with a Zsc = 6% will share the load correctlywith a 1,000 kVA transformer having a Zsc of 6%, i.e. the transformers will be loadedautomatically in proportion to their kVA ratings. For transformers having a ratio of kVAratings exceeding 2, parallel operation is not recommended.Figure H46 indicates, for the most usual arrangement (2 or 3 transformers ofequal kVA ratings) the maximum short-circuit currents to which main and principalCBs (CBM and CBP respectively, in Figure H45) are subjected. It is based on thefollowing hypotheses:b The short-circuit 3-phase power on the MV side of the transformer is 500 MVAb The transformers are standard 20/0.4 kV distribution-type units rated as listedb The cables from each transformer to its LV circuit-breaker comprise 5 metres ofsingle core conductorsb Between each incoming-circuit CBM and each outgoing-circuit CBP there is1 metre of busbarb The switchgear is installed in a floormounted enclosed switchboard, in an ambientairtemperature of 30 °CMoreover, this table shows selected circuit-breakers of M-G manufacturerecommended for main and principal circuit-breakers in each case.Example (see Fig. H47 next page)b Circuit-breaker selection for CBM duty:For a 800 kVA transformer In = 1.126 A; Icu (minimum) = 38 kA (from Figure H46),the CBM indicated in the table is a Compact NS1250N (Icu = 50 kA)b Circuit-breaker selection for CBP duty:The s.c. breaking capacity (Icu) required for these circuit-breakers is given in theFigure H46 as 56 kA.A recommended choice for the three outgoing circuits 1, 2 and 3 would be currentlimitingcircuit-breakers types NSX400 L, NSX250 L and NSX100 L. The Icu rating ineach case = 150 kA.H21Number and kVA ratings Minimum S.C breaking Main circuit-breakers (CBM) Minimum S.C breaking Rated current In ofof 20/0.4 kV transformers capacity of main CBs total discrimination with out capacity of principal CBs principal circuit-breaker(Icu) kA going circuit-breakers (CBP) (Icu) kA (CPB) 250A2 x 400 14 NW08N1/NS800N 27 NSX250H3 x 400 28 NW08N1/NS800N 42 NSX250H2 x 630 22 NW10N1/NS1000N 42 NSX250H3 x 630 44 NW10N1/NS1000N 67 NSX250H2 x 800 19 NW12N1/NS1250N 38 NSX250H3 x 800 38 NW12N1/NS1250N 56 NSX250H2 x 1,000 23 NW16N1/NS1600N 47 NSX250H3 x 1,000 47 NW16N1/NS1600N 70 NSX250H2 x 1,250 29 NW20N1/NS2000N 59 NSX250H3 x 1,250 59 NW20N1/NS2000N 88 NSX250L2 x 1,600 38 NW25N1/NS2500N 75 NSX250L3 x 1,600 75 NW25N1/NS2500N 113 NSX250L2 x 2,000 47 NW32N1/NS3200N 94 NSX250L3 x 2,000 94 NW32N1/NS3200N 141 NSX250LFig. H46 : Maximum values of short-circuit current to be interrupted by main and principal circuit-breakers (CBM and CBP respectively), for several transformers in parallel© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

H - LV switchgear: functions & selection4 Circuit-breakerH22Short-circuit fault-current levels at any point inan installation may be obtained from tables400 ACBP1100 AFig. H47 : Transformers in parallelCBP23 Tr800 kVA20 kV/400 VCBM200 ACBP3These circuit-breakers provide the advantages of:v Absolute discrimination with the upstream (CBM) breakersv Exploitation of the “cascading” technique, with its associated savings for alldownstream componentsChoice of outgoing-circuit CBs and final-circuit CBsUse of table G40From this table, the value of 3-phase short-circuit current can be determined rapidlyfor any point in the installation, knowing:b The value of short-circuit current at a point upstream of that intended for the CBconcernedb The length, c.s.a., and the composition of the conductors between the two pointsA circuit-breaker rated for a short-circuit breaking capacity exceeding the tabulatedvalue may then be selected.Detailed calculation of the short-circuit current levelIn order to calculate more precisely the short-circuit current, notably, when the shortcircuitcurrent-breaking capacity of a CB is slightly less than that derived from thetable, it is necessary to use the method indicated in chapter G clause 4.Two-pole circuit-breakers (for phase and neutral) with one protected pole onlyThese CBs are generally provided with an overcurrent protective device on thephase pole only, and may be used in TT, TN-S and IT schemes. In an IT scheme,however, the following conditions must be respected:b Condition (B) of table G67 for the protection of the neutral conductor againstovercurrent in the case of a double faultb Short-circuit current-breaking rating: A 2-pole phase-neutral CB must, byconvention, be capable of breaking on one pole (at the phase-to-phase voltage) thecurrent of a double fault equal to 15% of the 3-phase short-circuit current at the pointof its installation, if that current is y 10 kA; or 25% of the 3-phase short-circuit currentif it exceeds 10 kAb Protection against indirect contact: this protection is provided according to therules for IT schemesInsufficient short-circuit current breaking ratingIn low-voltage distribution systems it sometimes happens, especially in heavy-dutynetworks, that the Isc calculated exceeds the Icu rating of the CBs available forinstallation, or system changes upstream result in lower level CB ratings beingexceededb Solution 1: Check whether or not appropriate CBs upstream of the CBs affectedare of the current-limiting type, allowing the principle of cascading (described in subclause4.5) to be appliedb Solution 2: Install a range of CBs having a higher rating. This solution iseconomically interesting only where one or two CBs are affectedb Solution 3: Associate current-limiting fuses (gG or aM) with the CBs concerned, onthe upstream side. This arrangement must, however, respect the following rules:v The fuse rating must be appropriatev No fuse in the neutral conductor, except in certain IT installations where a doublefault produces a current in the neutral which exceeds the short-circuit breaking ratingof the CB. In this case, the blowing of the neutral fuse must cause the CB to trip onall phases© Schneider Electric - all rights reservedThe technique of “cascading” uses theproperties of current-limiting circuit-breakersto permit the installation of all downstreamswitchgear, cables and other circuit componentsof significantly lower performance than wouldotherwise be necessary, thereby simplifying andreducing the cost of an installation4.5 Coordination between circuit-breakersCascadingDefinition of the cascading techniqueBy limiting the peak value of short-circuit current passing through it, a current-limitingCB permits the use, in all circuits downstream of its location, of switchgear andcircuit components having much lower short-circuit breaking capacities, and thermaland electromechanical withstand capabilities than would otherwise be necessary.Reduced physical size and lower performance requirements lead to substantialeconomy and to the simplification of installation work. It may be noted that, while acurrent-limiting circuit-breaker has the effect on downstream circuits of (apparently)increasing the source impedance during short-circuit conditions, it has no sucheffect in any other condition; for example, during the starting of a large motor (wherea low source impedance is highly desirable). The range of Compact NSX currentlimitingcircuit-breakers with powerful limiting performances is particularly interesting.Schneider Electric - Electrical installation guide 2009

H - LV switchgear: functions & selection4 Circuit-breakerIn general, laboratory tests are necessary toensure that the conditions of implementationrequired by national standards are met andcompatible switchgear combinations must beprovided by the manufacturerConditions of implementationMost national standards admit the cascading technique, on condition that theamount of energy “let through” by the limiting CB is less than the energy alldownstream CBs and components are able to withstand without damage.In practice this can only be verified for CBs by tests performed in a laboratory. Suchtests are carried out by manufacturers who provide the information in the form oftables, so that users can confidently design a cascading scheme based on thecombination of recommended circuit-breaker types. As an example, Figure H48indicates the cascading possibilities of circuit-breaker types C60, DT40N, C120 andNG125 when installed downstream of current-limiting CBs Compact NSX 250 N, Hor L for a 230/400 V or 240/415 V 3-phase installation.kA rmsShort-circuit 150 NSX250Lbreaking capacity 70 NSX250Hof the upstream(limiter) CBs50 NSX250NPossible short-circuit 150 NG125Lbreaking capacity of 70 NG125Lthe downstream CBs36 NG125N NG125N(benefiting from the30 C60N/H=40AH23Fig. H48 : Example of cascading possibilities on a 230/400 V or 240/415 V 3-phase installationAdvantages of cascadingThe current limitation benefits all downstream circuits that are controlled by thecurrent-limiting CB concerned.The principle is not restrictive, i.e. current-limiting CBs can be installed at any point inan installation where the downstream circuits would otherwise be inadequately rated.The result is:b Simplified short-circuit current calculationsb Simplification, i.e. a wider choice of downstream switchgear and appliancesb The use of lighter-duty switchgear and appliances, with consequently lower costb Economy of space requirements, since light-duty equipment have generally asmaller volumeDiscrimination may be total or partial, andbased on the principles of current levels, ortime-delays, or a combination of both. A morerecent development is based on the logictechniques.The Schneider Electric system takesadvantages of both current-limitation anddiscriminationPrinciples of discriminative tripping (selectivity)Discrimination is achieved by automatic protective devices if a fault condition, occurringat any point in the installation, is cleared by the protective device located immediatelyupstream of the fault, while all other protective devices remain unaffected (seeFig. H49).ABIsc0Total discriminationIscIr BIsc BPartial discrimination0B only opens A and B openIscIr B Is Isc BFig. H49 : Total and partial discriminationIs = discrimination limit© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

H - LV switchgear: functions & selection4 Circuit-breakerH24tB AIIr B Ir A Isc B Im AFig. H50 : Total discrimination between CBs A and BtB AIIr B Ir A Im A Is c B Is c AB only opens A and B openFig. H51 : Partial discrimination between CBs A and BDiscrimination between circuit-breakers A and B is total if the maximum value ofshort-circuit-current on circuit B (Isc B) does not exceed the short-circuit trip settingof circuit-breaker A (Im A). For this condition, B only will trip (see Fig. H50).Discrimination is partial if the maximum possible short-circuit current on circuit Bexceeds the short-circuit trip-current setting of circuit-breaker A. For this maximumcondition, both A and B will trip (see Fig. H51).Protection against overload : discrimination based on current levels(see Fig. H52a)This method is realized by setting successive tripping thresholds at stepped levels,from downstream relays (lower settings) towards the source (higher settings).Discrimination is total or partial, depending on particular conditions, as noted above.As a rule of thumb, discrimination is achieved when:b IrA/IrB > 2:Protection against low level short-circuit currents : discrimination based onstepped time delays (see Fig. H52b)This method is implemented by adjusting the time-delayed tripping units, such thatdownstream relays have the shortest operating times, with progressively longerdelays towards the source.In the two-level arrangement shown, upstream circuit-breaker A is delayedsufficiently to ensure total discrimination with B (for example: Masterpact withelectronic trip unit).Discrimination based on a combination of the two previous methods(see Fig. H52c)A time-delay added to a current level scheme can improve the overall discriminationperformance.The upstream CB has two high-speed magnetic tripping thresholds:b Im A: delayed magnetic trip or short-delay electronic tripb Ii: instantaneous stripDiscrimination is total if Isc B < Ii (instantaneous).Protection against high level short-circuit currents: discrimination based onarc-energy levelsThis technology implemented in the Compact NSX range (current limiting circuitbreaker)is extremely effective for achievement of total discrimination.Principle: When a very high level short-circuit current is detected by the two circuitsbreakerA and B, their contacts open simultaneously. As a result, the current is highlylimited.b The very high arc-energy at level B induces the tripping of circuit-breaker Bb Then, the arc-energy is limited at level A and is not sufficient to induce the trippingof AAs a rule of thumb, the discrimination between Compact NSX is total if the size ratiobetween A and B is greater than 2.5.a) tb)tAc) tBABABAIsc BIr BIr AIBIsc B∆tIIm AdelayedIi AinstantaneousI© Schneider Electric - all rights reservedFig. H52 : DiscriminationSchneider Electric - Electrical installation guide 2009

H - LV switchgear: functions & selection4 Circuit-breakerCurrent-level discriminationThis technique is directly linked to the staging of the Long Time (LT) tripping curvesof two serial-connected circuit-breakers.t D2 D1D1D2IIr2Ir1Isd 2 Isd1Fig. H53 : Current discriminationThe discrimination limit ls is:b Is = Isd2 if the thresholds lsd1 and lsd2 are too close or merge,b Is = Isd1 if the thresholds lsd1 and lsd2 are sufficiently far apart.As a rule, current discrimination is achieved when:b Ir1 / Ir2 < 2,b Isd1 / Isd2 > 2.The discrimination limit is:b Is = Isd1.H25Discrimination qualityDiscrimination is total if Is > Isc(D2), i.e. Isd1 > Isc(D2).This normally implies:b a relatively low level Isc(D2),b a large difference between the ratings of circuit-breakers D1 and D2.Current discrimination is normally used in final distribution.Discrimination based on time-delayed trippinguses CBs referred to as “selective” (in somecountries).Implementation of these CBs is relatively simpleand consists in delaying the instant of trippingof the several series-connected circuit-breakersin a stepped time sequenceTime discriminationThis is the extension of current discrimination and is obtained by staging over timeof the tripping curves. This technique consists of giving a time delay of t to the ShortTime (ST) tripping of D1.tD2D1D1D2Fig. H54 : Time discriminationIr2Ir1Isd 2 Isd1∆tIi1I© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

H - LV switchgear: functions & selection4 Circuit-breakerThe thresholds (Ir1, Isd1) of D1 and (Ir2, Isd2) comply with the staging rules ofcurrent discrimination.The discrimination limit ls of the association is at least equal to li1, the instantaneousthreshold of D1.H26Masterpact NT06630 ACompact NSX250 ACompact NSX100 AMulti 9C60Discrimination qualityThere are two possible applications:b on final and/or intermediate feedersA category circuit-breakers can be used with time-delayed tripping of theupstream circuit-breaker. This allows extension of current discrimination upto the instantaneous threshold li1 of the upstream circuit-breaker: Is = li1.If Isc(D2) is not too high - case of a final feeder - total discriminationcan be obtained.b on the incomers and feeders of the MSBAt this level, as continuity of supply takes priority, the installationcharacteristics allow use of B category circuit-breakers designed fortime-delayed tripping. These circuit-breakers have a high thermal withstand(Icw u 50% Icn for t = 1s): Is = Icw1.Even for high lsc(D2), time discrimination normally provides totaldiscrimination: Icw1 > Icc(D2).Note: Use of B category circuit-breakers means that the installation must withstandhigh electrodynamic and thermal stresses.Consequently, these circuit-breakers have a high instantaneous threshold li that canbe adjusted and disabled in order to protect the busbars if necessary.Practical example of discrimination at several levels with Schneider Electriccircuit-breakers (with electronic trip units)"Masterpact NT is totally selective with any moulded-case Compact NSX circuitbreaker, i.e., the downstream circuit-breaker will trip for any short-circuit value up toits breaking capacity. Further, all Compact NSX CBs are totally selective, as long asthe ration between sizes is greater than 1.6 and the ratio between ratings is greaterthan 2.5. The same rules apply for the total selectivity with the miniature circuitbreakersMulti9 further downstream (see Fig. H55).tBANon trippingtime of ACurrent-breakingtime for BIr BOnly B opensIcc BIIccFig. H55 : 4 level discrimination with Schneider Electric circuit breakers : Masterpact NTCompact NSX and Multi 9© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

H - LV switchgear: functions & selection4 Circuit-breakerEnergy discrimination with current limitationCascading between 2 devices is normally achieved by using the tripping of theupstream circuit-breaker A to help the downstream circuit-breaker B to break thecurrent. The discrimination limit Is is consequently equal to the ultimate breakingcurrent Icu B of circuit-breaker B acting alone, as cascading requires the tripping ofboth devices.The energy discrimination technology implemented in Compact NSX circuit-breakersallows to improve the discrimination limit to a value higher than the ultimate breakingcurrent Icu B of the downstream circuit-breaker. The principle is as follows:b The downstream limiting circuit-breaker B sees a very high short-circuit current.The tripping is very fast ( 1.6b The ratio of rated currents of the two circuit-breakers is > 2.5Logic discrimination or “Zone Sequence Interlocking – ZSI”This type of discrimination can be achieved with circuit-breakers equipped withspecially designed electronic trip units (Compact, Masterpact): only the Short TimeProtection (STP) and Ground Fault Protection (GFP) functions of the controlleddevices are managed by Logic Discrimination. In particular, the InstantaneousProtection function - inherent protection function - is not concerned.Settings of controlled circuit-breakersb time delay: there are no rules, but staging (if any)of the time delays of timediscrimination must be applied (ΔtD1 u ΔtD2 u ΔtD3),b thresholds: there are no threshold rules to be applied, but natural staging of theprotection device ratings must be complied with (IcrD1 u IcrD2 u IcrD3).Note: This technique ensures discrimination even with circuit-breakers of similarratings.PrinciplesActivation of the Logic Discrimination function is via transmission of information onthe pilot wire:b ZSI input:v low level (no downstream faults): the Protection function is on standby with areduced time delay (y 0,1 s),v high level (presence of downstream faults): the relevant Protection function movesto the time delay status set on the device.b ZSI output:v low level: the trip unit detects no faults and sends no orders,v high level: the trip unit detects a fault and sends an order.OperationA pilot wire connects in cascading form the protection devices of an installation(see Fig. H56). When a fault occurs, each circuit-breaker upstream of the fault(detecting a fault) sends an order (high level output) and moves the upstream circuitbreakerto its natural time delay (high level input). The circuitbreaker placed justabove the fault does not receive any orders (low level input) and thus trips almostinstantaneously.H27© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

H - LV switchgear: functions & selection4 Circuit-breakerDiscrimination qualityThis technique enables:b easy achievement as standard of discrimination on 3 levels or more,b elimination of important stresses on the installation, relating to timedelayedtripping of the protection device, in event of a fault directly on theupstream busbars.All the protection devices are thus virtually instantaneous,b easy achievement of downstream discrimination with non-controlledcircuit-breakers.4.6 Discrimination MV/LV in a consumer’ssubstationH28Fig. H57 : Example1,000t(s)Full-load current1,760 A3-phaseshort-circuitcurrent level31.4 kANS 2000set at1,800 A63 A1,250 kVA20 kV / 400 VCompactNS2000set at 1,800 AIn general the transformer in a consumer’s substation is protected by MV fuses,suitably rated to match the transformer, in accordance with the principles laid downin IEC 60787 and IEC 60420, by following the advice of the fuse manufacturer.The basic requirement is that a MV fuse will not operate for LV faults occurringdownstream of the transformer LV circuit-breaker, so that the tripping characteristiccurve of the latter must be to the left of that of the MV fuse pre-arcing curve.This requirement generally fixes the maximum settings for the LV circuit-breakerprotection:b Maximum short-circuit current-level setting of the magnetic tripping elementb Maximum time-delay allowable for the short-circuit current tripping element(see Fig. H57)b Short-circuit level at MV terminals of transformer: 250 MVAb Transformer MV/LV: 1,250 kVA 20/0.4 kVb MV fuses: 63 Ab Cabling, transformer - LV circuit-breaker: 10 metres single-core cablesb LV circuit-breaker: Compact NSX 2000 set at 1,800 A (Ir)What is the maximum short-circuit trip current setting and its maximum time delayallowable?The curves of Figure H58 show that discrimination is assured if the short-time delaytripping unit of the CB is set at:b A level y 6 Ir = 10.8 kAb A time-delay setting of step 1 or 2200100101 4 6Minimum pre-arcingcurve for 63 A HV fuses(current referred to thesecondary side of thetransformer)80.20.1Step 4Step 3Step 20.50Step 10.011,800 AIr10 kAIsc maxi31.4 kAI© Schneider Electric - all rights reservedFig. H58 : Curves of MV fuses and LV circuit-breakerSchneider Electric - Electrical installation guide 2009

Chapter JProtection against voltage surgesin LV1234ContentsGeneral1.1 What is a voltage surge? J21.2 The four voltage surge types J21.3 Main characteristics of voltage surges J41.4 Different propagation modes J5Overvoltage protection devices2.1 Primary protection devices (protection of installations J6against lightning)2.2 Secondary protection devices (protection of internal J8installations against lightning)Protection against voltage surges in LV3.1 Surge protective device description J113.2 Surge protective device standards J113.3 Surge protective device data according to IEC 61643-1 standard J113.4 Lightning protection standards J133.5 Surge arrester installation standards J13Choosing a protection device4.1 Protection devices according to the earthing system J144.2 Internal architecture of surge arresters J154.3 Coordination of surge arresters J164.4 Selection guide J174.5 Choice of disconnector J224.6 End-of-life indication of the surge arrester J234.7 Application example: supermarket J24J2J6J11J14J© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

J - Protection against voltage surges in LV1 General1.1 What is a voltage surge?A voltage surge is a voltage impulse or wave which is superposed on the ratednetwork voltage (see Fig. J1).VoltageLightning type impulse(duration = 100 µs)"Operating impulse"type dumped ring wave(F = 100 kHz to 1 MHz)IrmsFig. J1 : Voltage surge examplesJThis type of voltage surge is characterised by ( see Fig. J2):b The rise time (tf) measured in μsb The gradient S measured in kV/μsA voltage surge disturbs equipment and causes electromagnetic radiation.Furthermore, the duration of the voltage surge (T) causes a surge of energy in theelectrical circuits which is likely to destroy the equipment.Voltage (V or kV)U max50 %Rise time (tf)tVoltage surge duration (T)Fig. J2 : Main overvoltage characteristics1.2 The four voltage surge types© Schneider Electric - all rights reservedThere are four types of voltage surges which may disturb electrical installations andloads:b Atmospheric voltage surgesb Operating voltage surgesb Transient overvoltage at industrial frequencyb Voltage surges caused by electrostatic dischargeAtmospheric voltage surgesLightning risk – a few figuresBetween 2,000 and 5,000 storms are constantly forming around the earth. Thesestorms are accompanied by lightning which constitutes a serious risk for both peopleand equipment. Strokes of lightning hit the ground at a rate of 30 to 100 strokes persecond. Every year, the earth is struck by about 3 billion strokes of lightning.Schneider Electric - Electrical installation guide 2009

J - Protection against voltage surges in LV1 Generalb Throughout the world, every year, thousands of people are struck by lightning andcountless animals are killedb Lightning also causes a large number of fires, most of which break out on farms(destroying buildings or putting them out of use)b Lightning also affects transformers, electricity meters, household appliances, andall electrical and electronic installations in the residential sector and in industry.b Tall buildings are the ones most often struck by lightningb The cost of repairing damage caused by lightning is very highb It is difficult to evaluate the consequences of disturbance caused to computer ortelecommunications networks, faults in PLC cycles and faults in regulation systems.Furthermore, the losses caused by a machine being put out of use can have financialconsequences rising above the cost of the equipment destroyed by the lightning.Characteristics of lightning dischargeFigure J3 shows the values given by the lighting protection committee (TechnicalCommittee 81) of the I.E.C. As can be seen, 50 % of lightning strokes are of a forcegreater than 33 kA and 5 % are greater than 85 kA. The energy forces involved arethus very high.Beyond peak Current Gradient Total Number ofprobability peak duration dischargesP% I (kA) S (kA/μs) T (s) n95 7 9.1 0.001 150 33 24 0.01 25 85 65 1.1 6Fig. J3 : Lightning discharge values given by the IEC lightning protection committeeJLightning comes from the discharge of electricalcharges accumulated in the cumulo-nimbusclouds which form a capacitor with the ground.Storm phenomena cause serious damage.Lightning is a high frequency electricalphenomenon which produces voltage surgeson all conductive elements, and especially onelectrical loads and wires.It is important to define the probability of adequate protection when protecting a site.Furthermore, a lightning current is a high frequency (HF) impulse current reachingroughly a megahertz.The effects of lightningA lightning current is therefore a high frequency electrical current. As well asconsiderable induction and voltage surge effects, it causes the same effects as anyother low frequency current on a conductor:b Thermal effects: fusion at the lightning impact points and joule effect, due to thecirculation of the current, causing firesb Electrodynamic effects: when the lightning currents circulate in parallel conductors,they provoke attraction or repulsion forces between the wires, causing breaks ormechanical deformations (crushed or flattened wires)b Combustion effects: lightning can cause the air to expand and create overpressurewhich stretches over a distance of a dozen metres or so. A blast effect breaks windowsor partitions and can project animals or people several metres away from their originalposition. This shock wave is at the same time transformed into a sound wave: thunderb Voltage surges conducted after an impact on overhead electrical or telephone linesb Voltage surges induced by the electromagnetic radiation effect of the lightningchannel which acts as an antenna over several kilometres and is crossed by aconsiderable impulse currentb The elevation of the earth potential by the circulation of the lightning current in theground. This explains indirect strokes of lightning by step voltage and the breakdownof equipmentOperating voltage surgesA sudden change in the established operating conditions in an electrical networkcauses transient phenomena to occur. These are generally high frequency ordamped oscillation voltage surge waves (see Fig. J1).They are said to have a slow gradient: their frequency varies from several ten toseveral hundred kilohertz.Operating voltage surges may be created by:b The opening of protection devices (fuse, circuit-breaker), and the opening orclosing of control devices (relays, contactors, etc.)b Inductive circuits due to motors starting and stopping, or the opening oftransformers such as MV/LV substationsb Capacitive circuits due to the connection of capacitor banks to the networkb All devices that contain a coil, a capacitor or a transformer at the power supplyinlet: relays, contactors, television sets, printers, computers, electric ovens, filters, etc.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

J - Protection against voltage surges in LV1 GeneralTransient overvoltages at industrial frequency (see Fig. J4)These overvoltages have the same frequency as the network (50, 60 or 400 Hz); andcan be caused by:b Phase/frame or phase/earth insulating faults on a network with an insulated orimpedant neutral, or by the breakdown of the neutral conductor. When this happens,single phase devices will be supplied in 400 V instead of 230 V.b A cable breakdown. For example, a medium voltage cable which falls on a lowvoltage line.b The arcing of a high or medium voltage protective spark-gap causing a rise in earthpotential during the action of the protection devices. These protection devices followautomatic switching cycles which will recreate a fault if it persists.tNormal voltage230/400 VTransient overvoltageNormal voltage230/400 VJFig. J4 : Transient overvoltage at industrial frequencyVoltage surges caused by electrical dischargeIn a dry environment, electrical charges accumulate and create a very strongelectrostatic field. For example, a person walking on carpet with insulating soleswill become electrically charged to a voltage of several kilovolts. If the person walksclose to a conductive structure, he will give off an electrical discharge of severalamperes in a very short rise time of a few nanoseconds. If the structure containssensitive electronics, a computer for example, its components or circuit boards maybe damaged.Three points must be kept in mind:b A direct or indirect lightning stroke mayhave destructive consequences on electricalinstallations several kilometres away fromwhere it fallsb Industrial or operating voltage surges alsocause considerable damageb The fact that a site installation is undergroundin no way protects it although it does limit therisk of a direct strike1.3 Main characteristics of voltage surgesFigure J5 below sums up the main characteristics of voltage surges.Type of voltage surge Voltage surge Duration Front gradientcoefficientor frequencyIndustrial frequency y 1.7 Long Industrial frequency(insulation fault) 30 to 1,000 ms (50-60-400 Hz)Operation 2 to 4 Short Average1 to 100 ms 1 to 200 kHzAtmospheric > 4 Very short Very high1 to 100 μs 1 to 1,000 kV/μsFig. J5 : Main characteristics of voltage surges© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

J - Protection against voltage surges in LV1 General1.4 Different propagation modesCommon modeCommon mode voltage surges occur between the live parts and the earth:phase/earth or neutral/earth (see Fig. J6).They are especially dangerous for devices whose frame is earthed due to the risk ofdielectric breakdown.PhNImcEquipmentVoltage surgecommon modeImcFig. J6 : Common modeDifferential modeDifferential mode voltage surges circulate between live conductors: Phase to phaseor phase to neutral (see Fig. J7). They are especially dangerous for electronicequipment, sensitive computer equipment, etc.JPhNImdU voltage surgedifferential modeImdEquipmentFig. J7 : Differential mode© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

J - Protection against voltage surges in LV2 Overvoltage protection devicesTwo major types of protection devices are used to suppress or limit voltage surges:they are referred to as primary protection devices and secondary protection devices.2.1 Primary protection devices (protection ofinstallations against lightning)The purpose of primary protection devices is to protect installations against directstrokes of lightning. They catch and run the lightning current into the ground. Theprinciple is based on a protection area determined by a structure which is higherthan the rest.The same applies to any peak effect produced by a pole, building or very highmetallic structure.There are three types of primary protection:b Lightning conductors, which are the oldest and best known lightning protectiondeviceb Overhead earth wiresb The meshed cage or Faraday cageThe lightning conductorThe lightning conductor is a tapered rod placed on top of the building. It is earthed byone or more conductors (often copper strips) (see Fig. J8).JCopper stripdown conductorTest clamp© Schneider Electric - all rights reservedFig. J8 : Example of protection using a lightning conductorCrow-foot earthingSchneider Electric - Electrical installation guide 2009

J - Protection against voltage surges in LV2 Overvoltage protection devicesThe design and installation of a lightning conductor is the job of a specialist.Attention must be paid to the copper strip paths, the test clamps, the crow-footearthing to help high frequency lightning currents run to the ground, and thedistances in relation to the wiring system (gas, water, etc.).Furthermore, the flow of the lightning current to the ground will induce voltagesurges, by electromagnetic radiation, in the electrical circuits and buildings to beprotected. These may reach several dozen kilovolts. It is therefore necessary tosymmetrically split the down conductor currents in two, four or more, in order tominimise electromagnetic effects.Overhead earth wiresThese wires are stretched over the structure to be protected (see Fig. J9). They areused for special structures: rocket launch pads, military applications and lightningprotection cables for overhead high voltage power lines (see Fig. J10).Tin plated copper 25 mm 2d > 0.1 hMetal posthJFrame grounded earth beltFig. J9 : Example of lightning protection using overhead earth wiresii/2i/2LightningprotectioncablesFig. J10 : Lightning protection wires© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

J - Protection against voltage surges in LV2 Overvoltage protection devicesPrimary lightning conductor protection devicessuch as a meshed cage or overhead earthwires are used to protect against direct strokesof lighting.These protection devices do notprevent destructive secondary effects onequipment from occurring. For example, risesin earth potential and electromagnetic inductionwhich are due to currents flowing to the earth.To reduce secondary effects, LV surge arrestersmust be added on telephone and electricalpower networks.The meshed cage (Faraday cage)This principle is used for very sensitive buildings housing computer or integratedcircuit production equipment. It consists in symmetrically multiplying the number ofdown strips outside the building. Horizontal links are added if the building is high; forexample every two floors (see Fig. J11). The down conductors are earthed by frog’sfoot earthing connections. The result is a series of interconnected 15 x 15 m or10 x 10 m meshes. This produces better equipotential bonding of the building andsplits lightning currents, thus greatly reducing electromagnetic fields and induction.JFig. J11 : Example of protection using the meshed cage (Faraday cage) principleSecondary protection devices are classed intwo categories: Serial protection and parallelprotection devices.Serial protection devices are specific to asystem or application.Parallel protection devices are used for: Powersupply network, telephone network, switchingnetwork (bus).2.2 Secondary protection devices (protection ofinternal installations against lightning)These handle the effects of atmospheric, operating or industrial frequency voltagesurges. They can be classified according to the way they are connected in aninstallation: serial or parallel protection.Serial protection deviceThis is connected in series to the power supply wires of the system to be protected(see Fig. J12).Power supplyInstallation to be protectedSerialprotectionUp© Schneider Electric - all rights reservedFig. J12 : Serial protection principleTransformersThey reduce voltage surges by inductor effect and make certain harmonicsdisappear by coupling. This protection is not very effective.FiltersBased on components such as resistors, inductance coils and capacitors theyare suitable for voltage surges caused by industrial and operation disturbancecorresponding to a clearly defined frequency band. This protection device is notsuitable for atmospheric disturbance.Schneider Electric - Electrical installation guide 2009

J - Protection against voltage surges in LV2 Overvoltage protection devicesWave absorbersThey are essentially made up of air inductance coils which limit the voltage surges,and surge arresters which absorb the currents. They are extremely suitable forprotecting sensitive electronic and computing equipment. They only act againstvoltage surges. They are nonetheless extremely cumbersome and expensive.Network conditioners and static uninterrupted power supplies (UPS)These devices are essentially used to protect highly sensitive equipment, such ascomputer equipment, which requires a high quality electrical power supply. Theycan be used to regulate the voltage and frequency, stop interference and ensure acontinuous electrical power supply even in the event of a mains power failure (forthe UPS). On the other hand, they are not protected against large, atmospheric typevoltage surges against which it is still necessary to use surge arresters.Parallel protection deviceThe principleThe parallel protection is adapted to any installation power level (see Fig. J13).This type of overvoltage protection is the most commonly used.Power supplyParallelprotectionUpInstallation tobe protectedFig. J13 : Parallel protection principleJMain characteristicsb The rated voltage of the protection device must correspond to the network voltageat the installation terminalsb When there is no voltage surge, a leakage current should not go through theprotection device which is on standbyb When a voltage surge above the allowable voltage threshold of the installationto be protected occurs, the protection device abruptly conducts the voltage surgecurrent to the earth by limiting the voltage to the desired protection level Up(see Fig. J14).U (V)Up0 I (A)Fig. J14 : Typical U/I curve of the ideal protection deviceWhen the voltage surge disappears, the protection device stops conducting andreturns to standby without a holding current. This is the ideal U/I characteristic curve:b The protection device response time (tr) must be as short as possible to protect theinstallation as quickly as possibleb The protection device must have the capacity to be able to conduct the energycaused by the foreseeable voltage surge on the site to be protectedb The surge arrester protection device must be able to withstand the rated current In.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

J - Protection against voltage surges in LV2 Overvoltage protection devicesThe products usedb Voltage limitersThey are used in MV/LV substations at the transformer output, in IT earthing scheme.They can run voltage surges to the earth, especially industrial frequency surges(see Fig. J15)MV/LVOvervoltagelimiterPIMPermanentinsulationmonitorFig. J15 : Voltage limiterJ10b LV surge arrestersThis term designates very different devices as far as technology and use areconcerned. Low voltage surge arresters come in the form of modules to be installedinside LV switchboard. There are also plug-in types and those that protect poweroutlets. They ensure secondary protection of nearby elements but have a small flowcapacity. Some are even built into loads although they cannot protect against strongvoltage surgesb Low current surge arresters or overvoltage protectorsThese protect telephone or switching networks against voltage surges from theoutside (lightning), as well as from the inside (polluting equipment, switchgearswitching, etc.)Low current voltage surge arresters are also installed in distribution boxes orbuilt into loads.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

J - Protection against voltage surges in LV3 Protection against voltagesurges in LV3.1 Surge protective device descriptionA surge protective device (SDP) is a device that limits transient voltage surges andruns current waves to ground to limit the amplitude of the voltage surge to a safelevel for electrical installations and equipment.The surge protective device includes one or several non linear components.The surge protective device eliminates voltage surges:b In common mode: Phase to earth or neutral to earthb In differential mode: Phase to phase or phase to neutralWhen a voltage surge exceeds the Uc threshold, the surge protective device (SDP)conducts the energy to earth in common mode. In differential mode the divertedenergy is directed to another active conductor.The surge protective device has an internal thermal protection device which protectsagainst burnout at its end of life. Gradually, over normal use after withstandingseveral voltage surges, the Surge Protective Device degrades into a conductivedevice. An indicator informs the user when end-of-life is close.Some surge protective devices have a remote indication.In addition, protection against short-circuits is ensured by an external circuit-breaker.3.2 Surge protective device standardsInternational standard IEC 61643-1 ed. 02/2005Surge protective devices connected to low-voltage power distribution systems.Three test classes are defined:b Class I tests: They are conducted using nominal discharge current (In), voltageimpulse with 1.2/50 μs waveshape and impulse current Iimp.The class I tests is intended to simulate partial conducted lightning current impulses.SPDs subjected to class I test methods are generally recommended for locationsat points of high exposure, e.g., line entrances to buildings protected by lightningprotection systems.b Class II tests: They are conducted using nominal discharge current (In), voltageimpulse with 1.2/50 μs waveshapeb Class III tests: They are conducted using the combination waveform (1.2/50 and8/20 μs).SPDs tested to class II or III test methods are subjected to impulses of shorterduration. These SPDs are generally recommended for locations with lesser exposure.These 3 test classes cannot be compared, since each originates in a country andeach has its own specificities. Moreover, each builder can refer to one of the 3 testclasses.European standard EN 61643-11 2002Some requirements as per IEC 61643-1. Moreover SPDs are classified in threecategories:Type 1: SPD tested to Class IType 2: SPD tested to Class IIType 3: SPD tested to Class IIIJ113.3 Surge protective device data according toIEC 61643-1 standardb Surge protective device (SPD): A device that is intended to limit transientovervoltages and divert surge currents. It contains at least one nonlinear component.b Test classes: Surge arrester test classification.b In: Nominal discharge current; the crest value of the current through the SPDhaving a current waveshape of 8/20. This is used for the classification of the SPD forthe class II test and also for preconditioning of the SPD for class I and II tests.b Imax: Maximum discharge current for class II test; crest value of a current throughthe SPD having an 8/20 waveshape and magnitude according to the test sequenceof the class II operating duty test. Imax is greater than In.b Ic: Continuous operating current; current that flows in an SPD when supplied atits permament full withstand operating voltage (Uc) for each mode. Ic correspondsto the sum of the currents that flow in the SPD’s protection component and in all theinternal circuits connected in parallel.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

J - Protection against voltage surges in LV3 Protection against voltagesurges in LVb Iimp: Impulse current, it is defined by a current peak value Ipeak and the chargeQ. Tested according to the test sequence of the operating duty test. This is used forthe classification of the SPD for class I test.b Un: Rated network voltage.b Uc: Maximum continuous operating voltage; the maximum r.m.s. or d.c. voltagewhich may be continuously applied to the SPDs mode of protection. This is equal tothe rated voltage.b Up: Voltage protection level; a parameter that characterizes the performance ofthe SPD in limiting the voltage across its terminals, which is selected from a list ofpreferred values. This value shall be greater than the highest value of the measuredlimiting voltages.The most common values for a 230/400 V network are:1 kV - 1.2 kV - 1.5 kV - 1.8 kV - 2 kV - 2.5 kV.b Ures: Residual voltage, the peak value of the voltage that appears between theterminals of an SPD due to the passage of discharge current.The SPD is characterised by Uc, Up, In and Imax (see Fig. J16)b To test the surge arrester, standardized voltage and current waves have beendefined that are specific to each country:v Voltage wavee.g. 1.2/50 μs (see Fig. J17)v Current waveExample 8/20 μs (see Fig. J18)UJ12U pU c< 1 mAI nI maxIFig. J16 : Voltage/current characteristicsMaxi100 %50 %VMaxi100 %50 %I1,250t820tFig. J17 : 1.2/50 μs waveFig. J18 : 8/20 μs wavev Other possible wave characteristics:4/10 μs, 10/1000 μs, 30/60 μs, 10/350 μs...Comparison between different surge protective devices must be carried out using thesame wave characteristics, in order to get relevant results.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

J - Protection against voltage surges in LV3 Protection against voltagesurges in LV3.4 Lightning protection standardsThe IEC 62305 series (part 1 to 5) restructures and updates the publications ofIEC 61024 series, IEC 61312 series and IEC 61663 series.The need for protection, the economic benefits of installing protection measures andthe selection of adequate protection measures should be determined in terms of riskmanagement. Risk management is the subject of IEC 62305-2.The criteria for design, installation and maintenance of lightning protection measuresare considered in three separate groups:b The first group concerning protection measures to reduce physical damage and lifehazard in a structure is given in IEC 62305-3.b The second group concerning protection measures to reduce failures of electricaland electronic systems in a structure is given in IEC 62305-4.b The third group concerning protection measures to reduce physical damage andfailures of services connected to a structure (mainly electrical and telecommunicationlines) is given in IEC 62305-5.3.5 Surge arrester installation standardsb International: IEC 61643-12 selection and application principlesb International: IEC 60364 Electrical installations of buildingsv IEC 60364-4-443: protection for safetyWhen an installation is supplied by, or includes, an overhead line, a protection deviceagainst atmospheric overvoltages must be foreseen if the keraunic level of the sitebeing considered corresponds to the external influences condition AQ 1 (more than25 days per year with thunderstorms).v IEC 60364-4-443-4: selection of equipment in the installation.This section helps with the choice of the protection level Up for the surge arrester infunction of the loads to be protected.Rated residual voltage of protection devices must not be higher than the value in thevoltage impulse withstand category II (see Fig. J19):J13Nominal voltage of Required impulse withstand voltage forthe installation (1) V kVThree-phase Single-phase Equipment at Equipment of Appliances Speciallysystems (2) systems with the origin of distribution and protectedmiddle point the installation final circuits equipment(impulse (impulse (impulse (impulsewithstand withstand withstand withstandcategory IV) category III) category II) category I)120-240 4 2.5 1.5 0.8230/400 (2) - 6 4 2.5 1.5277/480 (2)400/690 - 8 6 4 2.51,000 - Values subject to system engineersFig. J19 : Choosing equipment for the installation according to IEC 60364(1) According to IEC 60038(2) In Canada and USA for voltages to earth higher than 300 V,the impulse withstand voltage corresponding to thenext higher voltage in column one applies.Category I is addressed to particular equipment engineering.Category II is addressed to product committees for equipmentfor connection to the mains.Category III is addressed to product committees of installationmaterial and some special product committees.Category IV is addressed to supply authorities and systemengineers (see also 443.2.2).© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

J - Protection against voltage surges in LV3 Protection against voltagesurges in LVv IEC 60364-5-534: choosing and implementing electrical equipmentThis section describes surge arrester installation conditions:- According to earthing systems: The maximum continuous operating voltage Ucof SPDs shall be equal to or higher than shown in Fig. J20.SPDs connectedbetweenLine conductor andneutral conductorEach line conductor andPE conductorNeutral conductor and PEconductorEach line conductor andPEN conductorSystem configuration of distribution networkTT TN-C TN-S IT withdistributedneutralIT withoutdistributedneutral1.1 Uo NA 1.1 Uo 1.1 Uo NA1.1 Uo NA 1.1 Uo 3Uo (1) Line-to-linevoltage (1)Uo (1) NA Uo (1) Uo (1) NANA 1.1 Uo NA NA NANA: not applicableNOTE 1: Uo is the line-to-neutral voltage of the low-voltage system.NOTE 2: This table is based on IEC 61643-1 amendment 1.Fig. J20 : Minimum required Uc of the SPD dependent on supply system configurationJ14- At the origin of the installation: if the surge arrester is installed at the source ofan electrical installation supplied by the utility distribution network, its rated dischargecurrent may be lower than 5 kA.If a surge arrester is installed downstream from an earth leakage protection device,an RCD of the s type, with immunity to impulse currents of less than 3 kA (8/20 μs),must be used.- Protection against overcurrent at 50 Hz and consequences of a SPD failure:protection against SPDs short-circuits is provided by the overcurrent protectivedevices F2 which are to be selected according to the maximum recommended ratingfor the overcurrent protective device given in the manufacturer's SPD instructions.- In the presence of lightning conductors: a surge arrester must be installed,additional specifications for surge arresters must be applied (see IEC 62305 part 4).© Schneider Electric - all rights reserved(1) These values are related to worst case fault conditions,therefore the tolerance of 10 % is not taken into accountSchneider Electric - Electrical installation guide 2009

J - Protection against voltage surges in LV4 Choosing a protection deviceWhen installing surge arresters, several elements must be considered, such as:b Cascadingb Positioning with respect to residual current devicesb The choice of disconnection circuit breakersThe earthing system must also be taken into account.4.1 Protection devices according to the earthingsystemb Common mode overvoltage: basic protection involves the installation of a commonmode surge arrester between phase and PE or phase and PEN, whatever type ofearthing system is used.b Differential mode overvoltage: in the TT and TN-S earthing systems, earthing theneutral leads to dissymmetry due to earthing impedances, which causes differentialmode voltages to appear, whereas the overvoltage induced by a lightning strike is acommon mode voltage.For example, let us consider a TT earthing system. A two-pole surge arrester isinstalled in common mode to protect the installation (see Fig. J21).IIIJ15IFig. J21 : Common mode protection onlyThe neutral earthing resistor R1 used for the pylons has a lower resistance than theearthing resistor R2 used for the installation. The lightning current will flow throughcircuit ABCD to earth via the easiest path. It will pass through varistors V1 and V2 inseries, causing a differential voltage equal to twice the residual voltage of the surgearrester (Up1 + Up2) to appear at the terminals of A and C at the entrance to theinstallation in extreme cases.To protect the loads between Ph and N effectively, the differential mode voltage(between A and C) must be reduced.Another earthing system is therefore used (see Fig. J22).The lightning current flows through circuit ABH which has a lower impedance thancircuit ABCD, as the impedance of the component used between B and H is null (gasfilled spark gap).In this case, the differential voltage is equal to the residual voltage of the surgearrester (Up2).IFig. J22 : Common + differentiel mode protectionII© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

J - Protection against voltage surges in LV4 Choosing a protection deviceMode Between TT TN-S TN-C ITDifferential phase and neutral yes yes - -Common phase and earth yes yes yes yesphase and earth yes yes - yes (if distributedneutral)Fig. J23 : Connections to be made according to the earthing systems used, in the case ofatmospheric overvoltages4.2 Internal architecture of surge arrestersb 2P, 3P, 4P surge arresters (see Fig. J24):v They provide protection against common-mode overvoltages onlyv They are appropriate for TN-C and IT earthing systems.J16Fig. J24 : 2P, 3P, 4P surge arrestersb 1P+N, 3P+N surge arresters (see Fig. J25):v They provide protection against common-mode and differential-mode overvoltagesv They are appropriate for TT, TN-S, and IT earthing systems.Fig. J25 : 1P+N, 3P+N surge arresters© Schneider Electric - all rights reservedPEEarthing conductorMain earth terminalFig. J26 : Connection exampleb Single-pole (1P) surge arresters (see Fig. J26):v They are used to satisfy the demand of different assemblies (according to themanufacturer’s instructions) by supplying only one product.However, special dimensioning will be required for N - PE protection(for example 1+N and 3P+N)v The assembly must be validated by means of the tests specified in EN 61643-11.Schneider Electric - Electrical installation guide 2009

J - Protection against voltage surges in LV4 Choosing a protection deviceCascading protection requires a minimumdistance of at least 10 m between the twoprotection devices.This is valid, whatever the field of application:domestic, tertiary or industrial.4.3 Coordination of surge arrestersThe overvoltage protection study of an installation may show that the site is highlyexposed and that the equipment to be protected is sensitive. The surge arrestermust be able to discharge high currents and have a low level of protection. This dualconstraint cannot always be handled by a single surge arrester. A second one willtherefore be required (see Fig. J27).The first device, P1 (incoming protection) will be placed at the incoming end of theinstallation.Its purpose will be to discharge the maximum amount of energy to earth with alevel of protection y 2000 V that can be withstood by the electrotechnical equipment(contactors, motors, etc.).The second device (fine protection) will be placed in a distribution enclosure, asclose as possible to the sensitive loads. It will have a low discharge capacity and alow level of protection that will limit overvoltages significantly and therefore protectsensitive loads (y 1500 V).IFig. J27 : Cascading of surge arrestersIIFig. J28 : Coordination of surge arrestersJ17The fine-protection device P2 is installed in parallel with the incoming protectiondevice P1.If the distance L is too small, at the incoming overvoltage, P2 with a protectionlevel of U2 = 1500 V will operate before P1 with a level of U1 = 2000 V. P2 will notwithstand an excessively high current. The protection devices must therefore becoordinated to ensure that P1 activates before P2. To do this, we shall experimentwith the length L of the cable, i.e. the value of the self-inductance between the twoprotection devices. This self-inductance will block the current flow to P2 and cause acertain delay, which will force P1 to operate before P2. A metre of cable gives a selfinductanceof approximately 1μH.The rule ∆U= Ldi causes a voltage drop of approximately 100 V/m/kA, 8/20 μsdtwave.For L = 10 m, we get UL1 = UL2 ≈ 1000 V.To ensure that P2 operates with a level of protection of 1500 V requiresU1 = UL1 + UL2 + U2 = 1000 + 1000 + 1500 V = 3500 V.Consequently, P1 operates before 2000 V and therefore protects P2.Note: if the distance between the surge arrester at the incoming end of theinstallation and the equipment to be protected exceeds 30 m, cascading the surgearresters is recommended, as the residual voltage of the surge arrester may riseto double the residual voltage at the terminals of the incoming surge arrester; as inthe above example, the fine protection surge arrester must be placed as close aspossible to the loads to be protected.Installation rules (see page Q12).© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

J - Protection against voltage surges in LV4 Choosing a protection device4.4 Selection guide1Estimate the value of the equipment to be protectedTo estimate its value, consider:b The cost of the equipment in financial termsb The economic impact if the equipment goes down.b Domestic equipment:v audio-video, computersv household appliancesv burglar alarm.b Sensitive equipment:v burglar alarmv fire alarmv access controlv video surveillance.b Professional equipment:v programmable machinev computer serverv sound or light control system.b Building equipment:v automated heating orair-conditioningv lift.b Heavy equipment:v medical infrastructurev production infrastructurev heavy computer processing.J1823Determine the electrical architecture of buildingsLightning protection can be calculated for an entire building or for part of abuilding that is electrically independentDepending on the size of the building and the extent of its electrical system, one ormore surge arresters must be used in the various switchboards in the installation.b Detached house.b Apartment, small semi-detached house.b Communal part of a building.b Professional premises.b Tertiary and industrial buildings:v single switchboard, main switchboardv distribution boardv sensitive equipment more than 30 m from the switchboard.Understand the risk of the impact of lightning on the siteLightning is attracted by high points that conduct electricity. They can be:b Natural: tall trees, mountain crest, wet areas, ferrous soilb Artificial: chimney, aerial, pylon, lightning conductor.Indirect effects can be incurred within a fifty metre radius around the point of impact.Location of the buildingIn an urban, peri-urban,grouped housing area.In an area where there is aparticular hazard (pylon, tree,mountainous region, mountaincrest, wet area or pond).© Schneider Electric - all rights reservedIn flat open country.In an exceptionally exposed area(lightning conductor on a buildingless than 50 metres away).Schneider Electric - Electrical installation guide 2009

J - Protection against voltage surges in LV4 Choosing a protection device1Equipment to beprotectedDomestic equipmentAudio-video, computers,household appliances,burglar alarm, etc.2Determine thearchitecture of thebuildingDetached house,ProfessionalpremisesApartment, smallsemi-detachedhouseCommunal part of abuilding3J19Risk level ofthe impact of alightning strikeChoice of type ofsurge arresterType 210 kAType 240 kAType 125 kA+Type 240 kAType 125 kA+Type 240 kAType 210 kAType 240 kAType 265 kAType 125 kA+Type 240 kAType 125 kA+Type 240 kANote:Type 1: very high discharge capacity surge arrester used with a lightning conductor with an impact level of and .Type 2: surge arrester used in cascade behind a type 1 surge arrester or alone in zone and .Fig. J32 : Domestic equipmentLightning also propagates throughtelecommunications networks.It can damage all the equipment connected tothese networks.Protection of telecommunications equipmentChoice of surge arrestersAnalogue telephone networks < 200 VPRCb© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

J - Protection against voltage surges in LV4 Choosing a protection device1Sensitive equipment:Building equipment:Equipment to beprotectedBurglar alarm,fire alarm,access control,video-surveillance, etc.Automated heating orair-conditioning,lift, etc.2Singleswitchboard,mainswitchboardDetermine thearchitecture of thebuildingDistributionboardDedicatedprotection,more than30 m from aswitchboardJ203Risk level ofthe impact of alightning strikeChoice of type ofsurge arresterType 220 kAType 240 kAType 240 kAType 125 kAor35 kA+Type 240 kAType 220 kAType 28 kANote:Type 1: very high discharge capacity surge arrester used with a lightning conductor with an impact level of and .Type 2: surge arrester used in cascade behind a type 1 surge arrester or alone in zone and .Fig. J33 : Sensitive equipment, Building equipment© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

J - Protection against voltage surges in LV4 Choosing a protection device1Equipment to beprotectedProfessional equipmentProgrammable machine,server,sound or light control system,etc.2Determine thearchitecture of thebuildingSingleswitchboard,mainswitchboardDistributionboardDedicatedprotection,more than30 m from aswitchboard3Risk level ofthe impact of alightning strikeJ21Choice of type ofsurge arresterType 240 kAType 265 kAType 265 kAType 125 kAor35 kA+Type 240 kAType 220 kAType 28 kANote:Type 1: very high discharge capacity surge arrester used with a lightning conductor with an impact level of and .Type 2: surge arrester used in cascade behind a type 1 surge arrester or alone in zone and .Fig. J34 : Professional equipment© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

J - Protection against voltage surges in LV4 Choosing a protection device1Equipment to beprotectedHeavy equipmentMedical, production,or heavy computerprocessing infrastructure,etc.2Singleswitchboard,mainswitchboardDetermine thearchitecture of thebuildingDistributionboardDedicatedprotection,more than30 m from aswitchboardJ223Risk level ofthe impact of alightning strikeChoice of type ofsurge arresterType 265 kAType 125 kA+Type 240 kAType 125 kAor35 kA+Type 240 kAType 125 kAor35 kA+Type 240 kAType 220 KAType 28 kANote:Type 1: very high discharge capacity surge arrester used with a lightning conductor with an impact level of and .Type 2: surge arrester used in cascade behind a type 1 surge arrester or alone in zone and .Fig. J35 : Heavy equipment© Schneider Electric - all rights reservedLightning can also propagate throughtelecommunications and computer networks.It can damage all the equipment connectedto these networks: telephones, modems,computers, servers, etc.Protection of telecommunications and computer equipmentChoice of surge arresters PRC PRIAnalogue telephone networks < 200 VDigital networks, analogue lines < 48 VDigital networks, analogue lines < 6 VVLV load supply < 48 VbbbSchneider Electric - Electrical installation guide 2009

J - Protection against voltage surges in LV4 Choosing a protection device4.5 Choice of disconnectorThe disconnector is necessary to ensure the safety of the installationb One of the surge arrester parameters is the maximum current (Imax 8/20 µswave) that it can withstand without degradation. If this current is exceeded, the surgearrester will be destroyed; it will be permanently short circuited and it is essential toreplace it.The fault current must therefore be eliminated by an external disconnector installedupstream.The disconnector provides the complete protection required by a surge arresterinstallation, i.e.:v It must be able to withstand standard test waves:- it must not trip at 20 impulses at In- it can trip at Imax without being destroyedv the surge arrester disconnects if it short-circuits.b The ready-to-cable surge arresters with an integrated disconnection circuit breakerare:v Combi PRF1v Quick PFv Quick PRD.Surge arrester / disconnection circuit breaker correspondencetableTypesType 1Type 2Surge arresternamesIscImax or Iimp6 kA 10 kA 15 kA 25 kA 36 kA 50 kA 70 kA 100 kAPRF1 Master 35 kA (1) Compact NSX160B 160A CompactNSX160F160APRD1 Master 25 kA (1) NG 125 N C 80A NG 125L C 80APRD1 25r NG 125 N C 80A NG 125L C 80APRF1Combi PRF1D125 DcurveIntegratedPRF1 12,5 r 12,5 kA (1) NG 125 N C 80A NG 125L C 80APF 65/ PRD 65r 65 kA (2) C60N 50A C curve C60H 50AC curvePF 40 / PRD 40r 40 kA (2) C60N 40A C curve C60H 40AC curveNG125L50A CcurveNG125L40A CcurveCompactNSX160N160AFuse NH 50A gL/gGQuick PRD 40r Integrated Contact usPF 20/ PRD 20r 20 kA (2) C60N 25A C curve C60H 25AC curveNG125L25A CcurveQuick PRD 20r Integrated Contact usQuick PF 10 10 kA (2) IntegratedPF 8/ PRD 8r 8 kA (2) C60N 20A C curve C60H 20AC curveNG125L 20A C curveQuick PRD 8 r Integrated Contact usFuse 22x58 40A gL/gGFuse 22x58 25A gL/gGJ23Isc: prospective short-circuit current at the point of installation.(1) Iimp.(2) Imax.Fig. J36 : Coordination table between SPD and its disconnector© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

J - Protection against voltage surges in LV4 Choosing a protection deviceJ24© Schneider Electric - all rights reservedFig. J37 : Example of indication for PRDFig. J39 : Example of indication for Quick PRD4.6 End-of-life indication of the surge arresterVarious indication devices are provided to warn the user that the loads are no longerprotected against atmospheric overvoltages.Type 1 surge arresters (with gas filled spark gap)PRF1 1P 260 V, Combi 1P+N and 3P+N and PRF1 MasterThese surge arresters have a light indicating that the module is in good workingorder. This indicator light requires a minimum operating voltage of 120 V AC.b The light does not come on:v if the operating voltage is y 120 V ACv if there is no network voltagev if the spark-over electronics are defective.Type 2 surge arresters (varistor, varistor + gas filled spark gap)PF, PRDAt end of life, the surge arrester or the cartridge are destroyed.b This can occur in two ways:v internal end-of-life disconnection: the accumulated electric shocks cause thevaristors to age, resulting in an increase in leakage current.Above 1 mA, a thermal runaway occurs and the surge arrester disconnects.v external end-of-life disconnection: this occurs in the event of an excessiveovervoltage (direct lightning strike on the line); above the discharge capacity of thesurge arrester, the varistor(s) are dead short-circuited to earth (or possibly betweenphase and neutral). This short-circuit is eliminated when the mandatory associateddisconnection circuit breaker opens.Quick PRD and Quick PFWhatever the hazards of the power supply network, Quick PRD and Quick PFincorporate a perfectly coordinated disconnector.b In the event of lightning strikes < Imax: like all surge arresters, they have internalanti-ageing protection.b In the event of a lightning strike > Imax: Quick PRD and Quick PF are selfprotectedby their integrated disconnector.b In the event of neutral disconnection or phase-neutral reversal occurring on thepower supply:Quick PRD and Quick PF are self-protected by their integrated disconnector.To simplify maintenance work, Quick PRD is fitted with local indicators and draw-outcartridges that are mechanically combined with the disconnector.Quick PRD has indicator lights on the cartridges and on the integrated disconnector,so that the work to be carried out can quickly be located.For safety reasons, the disconnector opens automatically when a cartridge isremoved. It cannot be set until the cartridge is plugged in.When changing the cartridge, a phase/neutral failsafe system ensures that it can beplugged in safely.Operating state continuous displayQuick PRD has an integrated reporting contact to send information about theoperating state of the surge arrester from a remote location.Monitoring the surge arresters installed throughout the installation makes it possibleto be continuously aware of their operating state and to ensure that the protectiondevices are always in good working order.b A reporting contact gives the alert:v at end of life of a cartridgev if a cartridge is missing, as soon as it has been removedv if a fault occurs on the line (short-circuit, neutral disconnection, phase-neutralreversal)v in the event of local manual operation (handle down).Quick PF has an optional indication reporting auxiliary (SR) that sends informationabout the operating state of the surge arrester from a remote location.Schneider Electric - Electrical installation guide 2009

J - Protection against voltage surges in LV4 Choosing a protection deviceMV/LV transformer160 kVAMainswitchboardC6040 APRD40 kASwitchboard 1Switchboard2C6020 APRD8 kAID"si"ID"si"C6020 APRD8 kAHeating Lighting Freezer RefrigeratorStoreroom lightingPower outletsFire-fighting system AlarmIT system CheckoutJ25Fig. J39 : Application example : supermarket4.7 Application example: supermarketSolutions and schematic diagramb The surge arrester selection guide has made it possible to determine the precisevalue of the surge arrester at the incoming end of the installation and that of theassociated disconnection circuit breaker.b As the sensitive devices (Uimp < 1.5 kV) are located more than 30 m from theincoming protection device, the fine protection surge arresters must be installed asclose as possible to the loads.b To ensure better continuity of service for cold room areas:v"si" type residual current circuit breakers will be used to avoid nuisance trippingcaused by the rise in earth potential as the lightning wave passes through.b For protection against atmospheric overvoltages:v install a surge arrester in the main switchboardv install a fine protection surge arrester in each switchboard (1 and 2) supplying thesensitive devices situated more than 30 m from the incoming surge arresterv install a surge arrester on the telecommunications network to protect the devicessupplied, for example fire alarms, modems, telephones, faxes.Fig. J40 : Telecommunications networkCabling recommendationsb Ensure the equipotentiality of the earth terminations of the building.b Reduce the looped power supply cable areas.Installation recommendationsb Install a surge arrester, Imax = 40 kA (8/20 µs) and a C60 disconnection circuitbreaker rated at 20 A.b Install fine protection surge arresters, Imax = 8 kA (8/20 µs) and the associatedC60 disconnection circuit breakers rated at 20 A.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Chapter KEnergy Efficiency in electricaldistribution123456ContentsIntroductionK2Energy efficiency and electricityK32.1 Regulation is pushing energy efficiency worldwide K32.2 How to achieve Energy Efficiency K4Diagnosis through electrical measurementK73.1 Physical value acquisition K73.2 Electrical data for real objectives K83.3 Measurement starts with the "stand alone product" solution K10Energy saving solutionsk134.1 Motor systems and replacement K134.2 Pumps, fans and variable speed drives K144.3 Lighting K184.4 Load management strategies K204.5 Power factor correction K224.6 Harmonic filtering K224.7 Other measures K234.8 Communication and Information System K234.9 Mapping of solutions K30How to value energy savingsK315.1 Introduction to IPMVP and EVO K315.2 Principles and options of IPMVP K315.3 Six qualities of IPMVP K325.4 IPMVP'S options K325.5 Fundamental points of an M&V plan K33From returns on investment to sustained performance K346.1 Technical support services K346.2 Operational support services K35K© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations1 IntroductionK1401201008060402002007200820092010201120122013BaseSC1SC2Fig. K1 : How to reach a fall in consumption of 20% by 2020While there are a number of factors influencing the attitudes and opinions towardsenergy efficiency – most notably the increasing cost of energy and a rising socialconscience – it is likely to be legislative drivers that have the greatest impact onchanging behaviours and practices. Respective governments internationally areintroducing energy saving targets and effecting regulations to ensure they are met.Reducing greenhouse gas emissions is a global target set at the Earth Summit inKyoto in 1997 and finally ratified by 169 countries in December 2006 enabling theAgreement’s enactment in February 2005.Under the Kyoto Protocol industrialised countries have agreed to reduce theircollective emissions of greenhouse gases by 5.2% by 2008-2012 compared to theyear 1990 (however, compared to the emissions levels expected by 2012 prior tothe Protocol, this limitation represents a 29% cut). The target in Europe is an 8%reduction overall with a target for CO 2 emissions to fall by 20% by 2020.Of the six greenhouse gases listed by Kyoto, one of the most significant by volumeof emissions is carbon dioxide (CO 2 ) and it is gas that is mainly emitted as a resultof electricity generation and use, as well as direct thermal losses in, for example,heating.Up to 50% of CO 2 emissions attributable to residential and commercial buildingsis from electricity consumption. Moreover, as domestic appliances, computers andentertainment systems proliferate; and other equipment such as air conditioning andventilation systems increase in use, electricity consumption is rising at a higher ratethan other energy usage.The ability to meet targets by simply persuading people to act differently or deploynew energy saving or energy efficient technology is unlikely to succeed. Justconsidering construction and the built environment, new construction is far less than2% of existing stock. If newly constructed buildings perform exactly as existing stockthe result by 2020 will be an increase in electricity consumption of 22%. On the otherhand, if all new construction has energy consumption of 50% less than existingstock, the result is still an increase of 18%.In order to reach a fall in consumption of 20% by 2020 the folllowing has to happen:b All new buildings constructed to consume 50% less energyb 1 in 10 existing buildings reduce consumption by 30% each year(see Fig.K1).Significantly, by 2020 in most countries 80% of all buildings will have already beenbuilt. The refurbishment of existing building stock and improving energy managementis vital in meeting emission reduction targets. Given that in the west, most buildingshave already undergone thermal insulation upgrades such as cavity wall insulation,loft insulation and glazing, the only potential for further savings is by reducing theamount of energy consumed.Action on existing built environment will almost certainly become compulsory to meettargets fixed for the coming years.As a result, governments are applying pressures to meet the ambitious targets. It isalmost certain that ever more demanding regulations will be enforced to address allenergy uses, including existing buildings and, naturally, industry. At the same timeenergy prices are rising as natural resources become exhausted and the electricalinfrastructure in some countries struggles to cope with increasing demand.Technology exists to help tackle energy efficiency on many levels from reducingelectrical consumption to controlling other energy sources more efficiently. Strongregulatory measures may be required to ensure these technologies are adoptedquickly enough to impact on the 2020 targets.The most important ingredient however, lies with the ability of those in control ofindustry, business and government to concentrate their hearts and minds on makingenergy efficiency a critical target. Otherwise, it might not be just the Kyoto targets onwhich the lights go out.The message to heed is that if those empowered to save energy don’t do sowillingly now, they will be compelled under legal threat to do so in the future.© Schneider Electric - all rights reserved20142015201620172018A minimum renovation of 10% per year of existing stock iscompulsory to reach less 20%Renovation =New =70% of the savings30% of the savingsSchneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations2 Energy efficiency and electricity2.1 Regulation is pushing Energy EfficiencyworldwideKyoto Protocol was the start of fixing quantitative targets and agenda in CO 2emissions reduction with clear government's commitments.Beyond Kyoto commitment (which covers only the period up to 2012) manycountries have fixed longer time frame and targets in line with the last GIEECrecommendations to UNFCC to stabilise the CO 2 concentration at a level of 450 ppm(this should require a division by 2 before 2050 of the CO 2 emission level based on1990).European Union is a good example and firm commitment with a target of Iess20% before 2020 has been taken by heads of EU member states in March 2007(known as the 3x20: it includes reduction of 20% of CO 2 emission, Improvement of20% of the Energy Efficiency level and reaching 20% of the energy produced fromrenewable).This commitment of Iess 20% in 2020 couId be extended to less 30% in2020 in case of post Kyoto international agreement.Some European Countries are planning commitment for the 2050 with level ofreduction up to 50%. All of this illustrates that Energy Efficiency Iandscape andpolicies will be present in a long time frame.Reaching these targets wiII require real change and regulations, legislation,standardisation are enablers governments are re inforcing everyday.All over the world Régulation/Législation is strengthening stakeholdersobligations and putting in place financial & fiscal schemesb In USv Energy Policy Act of 2005v Building Codesv Energy Codes (10CFR434)v State Energy prograrn (10CFR420)v Energy Conservation for Consumer Goods (10CFR430)b In European Unionv EU Emission Trading Schemev Energy Performance of Building Directivev Energy Using Product Directivev End use of energy & energy services directiveb In Chinav China Energy Conservation Lawv China Architecture law (EE in Building)v China Renewable Energy Lawv Top 1000 Industrial Energy Conservation ProgramKBuildingEnergyPerformanceEnergyLabelling ofDomesticAppliancesEmissionTradingSchemeCombinedHeat &PowerEnergyUsingProductsEnd use ofEnergy &Energy ServicesEEDedicateddirectivesDec 02EPB2002/91Jul 03ELDA2003/66Oct 03ETS2003/87Feb 04CHP2004/8July 05Eco Design2005/32April 06EUE & ES2006/32Fig. K2 : EE Dedicated directivesVarious legislative and financial-fiscal incentives schemes are developed atnational and regional levels such as:b Auditing & assessment schemesb Performance labelling schemesb Building Codesb Energy Performance Certificatesb Obligation to energy sellers to have their clients making energy savingsb Voluntary agreements in Industryb Financial-market mechanism (tax credit, accelerated depreciation, whitecertificates,...)b Taxation and incentive schemes© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations2 Energy efficiency and electricityAll sectors are concerned and regulations impact not only new constructionand installation but as well the existing buildings in industrial or infrastructureenvironment.In parallel Standardisation work has started with a lot of new standards beingissued or in progress.In building all energy use are concerned:b Lightingb Ventilationb Heatingb Cooling and ACFor industries as well as commercial companies Energy Management Systemsstandards ( in Iine with the well known ISO 9001 for quality and ISO 14001 forenvironment) are under process in Standardisation Bodies. Energy EfficiencyServices standards are as well at work.2.2 How to achieve Energy EfficiencyPassive EEb Efficient devices and efficient installation (10 to 15%)Low consumption devices, insulated building...KActive EEb Optimized usage of installation and devices (5 to 15%)Turn off devices when not needed, regulate motors orheating at the optimized level…b Permanent monitoring and improvement program (2 to 8%)Rigorous maintenance program, measureand react in case of deviationFig. K2 : 30% Savings are available today…© Schneider Electric - all rights reserved30% savings are available through existing EE solutions, but to really understandwhere these opportunities are, let’s understand first the main differences betweenPassive and Active EE.Passive EE is regarded as the installation of countermeasures against thermallosses, the use of low consumption equipment and so forth. Active Energy Efficiencyis defined as effecting permanent change through measurement, monitoring andcontrol of energy usage. It is vital, but insufficient, to make use of energy savingequipment and devices such as low energy lighting. Without proper control, thesemeasures often merely militate against energy losses rather than make a realreduction in energy consumed and in the way it is used.Everything that consumes power – from direct electricity consumption throughlighting, heating and most significantly electric motors, but also in HVAC control,boiler control and so forth – must be addressed actively if sustained gains are to bemade. This includes changing the culture and mindsets of groups of individuals,resulting in behavioural shifts at work and at home, but clearly, this need is reducedby greater use of technical controls.b 10 to 15% savings are achievable through passive EE measures such as installinglow consumption devices, insulating building, etc.b 5 to 15% can be achieved through such as optimizing usage of installation anddevices, turn off devices when not needed, regulating motors or heating at theoptimized level…v Up to 40% of the potential savings for a motor system are realized by the Drive &Automationv Up to 30% of the potential for savings in a building lighting system can be realizedvia the lighting control systemSchneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations2 Energy efficiency and electricityb And a further 2 to 8% can also be achieved through active EE measures such asputting in place a permanent monitoring and improvement programBut savings can be lost quickly if there is:b Unplanned, unmanaged shutdowns of equipment and processesb Lack of automation and regulation (motors, heating)b No continuity of behaviorsEnergy Efficiency : it's easy, just follow the 4 sustainability steps1 Measureb Energy metersb Power quality meters2 Fix the basics b Low consumption devicesb Insulation materialb Power qualityb Power reliability3 Automate4 Monitor and ImproveFig. K4 : The 4 sustainability stepsb Building management systemsb Lighting control systemsb Motor control systemsb Home control systemsb Variable speed driveb Energy management softwareb Remote monitoring systemsEnergy Efficiency is not different form other disciplines and we take a very rationalapproach to it, very similar to the 6Sigma DMAIC (Define, Measure, Analyze,Improve and Control) approach.As always, the first thing that we need to do is to measure in order to understandwhere are the main consumptions, what is the consumption pattern, etc. This initialmeasurement, together with some benchmarking information, will allow us see howgood or bad we are doing, to define the main improvement axis and an estimationof what can be expected in terms of gains. We can not improve what we can notmeasure.Then, we need to fix the basics or what is called passive EE. Change old endusedevices by Low consumption ones (bulbs, motors, etc), Improve the Insulation ofyour installations, and assure power quality reliability in order to be able to work in astable environment where the gains are going to sustainable over time.After that, we are ready to enter into the automation phase or Active Energyefficiency. As already highlighted, everything that consumes power must beaddressed actively if sustained gains are to be made.Active Energy Efficiency can be achieved not only when energy saving devicesand equipment are installed, but with all kind of end-use devices. It is this aspect ofcontrol that is critical to achieving the maximum efficiency. As an example, consider alow consumption bulb that is left on in an empty room. All that is achieved is that lessenergy is wasted compared to using an ordinary bulb, but energy is still wasted!Responsible equipment manufacturers are continually developing more efficientproducts. However, while for the most part the efficiency of the equipment is a fairrepresentation of its energy saving potential - say, in the example of a domesticwashing machine or refrigerator - it is not always the case in industrial andcommercial equipment. In many cases the overall energy performance of the systemis what really counts. Put simply, if an energy saving device is left permanentlyon stand-by it can be less efficient than a higher consuming device that is alwaysswitched off when not in use.Summarizing, managing energy is the key to maximizing its usefulness andeconomizing on its waste. While there are increasing numbers of products that arenow more energy efficient than their predecessors, controlling switching or reducingsettings of variables such as temperature or speed, makes the greatest impact.K© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations2 Energy efficiency and electricityThe key to sustainable savings100%70%b Up to 8% per year is lost withoutmonitoring and maintenance programb Up to 12% per year is lost withoutregulation and control systemsEnergyConsumptionEfficient devicesand installationOptimized usagevia automationMonitoring & MaintenanceTimeFig. K5 : Control and monitoring technologies will sustain the savingsAs you could see, 30% energy saving are available and quite easily achievabletoday but up to 8% per year can be lost without proper maintenance and diligentmonitoring of your key indicators. Information is key to sustaining the energy savings.You cannot manage what you cannot measure and therefore metering andmonitoring devices coupled with proper analysis provide the tools required to take onthat challenge successfully.KLifecycle approach to Energy EfficiencyEnergy Audit& Measurebuilding, industrialprocess…Fix the basicsLow consumptiondevices,Insulation materialPower factorcorrection…PassiveEnergy EfficiencyOptimize throughAutomation andregulationHVAC control,lighting control,variable speeddrives…Fig. K6 : Lifecycle solutions for Energy EfficiencyMonitor,maintain,improveActiveEnergy EfficiencyMeters installationMonitoring servicesEE analysis softwareControlImprove© Schneider Electric - all rights reservedEnergy Efficiency needs a structured approach in order to provide significant andsustainable savings. Schneider Electric take a customer lifecycle approach to tackleit. It starts with a diagnosis or audit on buildings and industrial processes… This willprovide us an indication of the situation and the main avenues to pursue savings. Butis not enough, it is just the beginning, what really counts is getting the results. Onlycompanies having the means to be active in the whole process can be there withtheir customers up to the real savings and results.Then, we will fix the basics, automate and finally monitor, maintain and improve.Then we are ready to start again and continue the virtuous cycle.Energy Efficiency is an issue where a risk sharing and a win-win relation shall beestablished to reach the goal.As targets are fixed over long timeframe (less 20% in 2020 , less 50% in 2050),for most of our customers EE programs are not one-shot initiatives and permanentimprovement over the time is key. Therefore, frame services contracts is the idealway to deal with these customer needs.Schneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations3 Diagnosis through electricalmeasurementThe energy efficiency performance in terms of electricity can only be expressed interms of fundamental physical measurements – voltage, current, harmonics, etc.These physical measurements are then reprocessed to become digital data and theninformation.In the raw form, data are of little use. Unfortunately, some energy managers becometotally immersed in data and see data collection and collation as their primary task.To gain value from data they must be transformed into information (used to supportthe knowledge development of all those managing energy) and understanding (usedto action energy savings).The operational cycle is based on four processes: data collection; data analysis;communication; and action (see Fig. K7). These elements apply to any informationsystem. The cycle works under condition that an adequate communication networkhas been set up.Communication(information tounderstanding)Data analysis(data to information)Action(understandingto results)Data collectionFig. K7 : The operational cycleKThe data processing level results in information that can be understood by therecipient profile: the ability to interpret the data by the user remains a considerablechallenge in terms of decision making.The data is then directly linked to loads that consume electricity – industrial process,lighting, air conditioning, etc. – and the service that these loads provide for thecompany – quantity of products manufactured, comfort of visitors to a supermarket,ambient temperature in a refrigerated room, etc.The information system is then ready to be used on a day to day basis by users toachieve energy efficiency objectives set by senior managers in the company.3.1 Physical value acquisitionThe quality of data starts with the measurement itself: at the right place, the righttime and just the right amount.Basically, electrical measurement is based on voltage and current going through theconductors. These values lead to all the others: power, energy, power factor, etc.Firstly we will ensure consistency of the precision class of current transformers,voltage transformers and the precision of the measurement devices themselves. Theprecision class will be lower for higher voltages: an error in the measurement of highvoltage for example represents a very large amount of energy.The total error is the quadratic sum of each error.2 2 2∑of error = error + error + ... + errorExample:a device with an error of 2% connected on a CT ’s with an error of 2% that means:2 2∑of error = ( 2) + ( 2) = 2,828% .That could mean a loss of 2,828 kWh for 100,000 kWh of consumption.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations3 Diagnosis through electricalmeasurementKA CT is defined by:b transformation ratio. For example: 50/5Ab precision class Cl. Example: Cl=0.5b precision power in VA to supply power tothe measurement devices on the secondary.Example: 1.25 VAb limit precision factor indicated as a factorapplied to In before saturation.Example: FLP (or Fs) =10 for measurementdevices with a precision power that is inconformity.PM700 measurement unitVoltage measurementIn low voltage, the voltage measurement is directly made by the measurementdevice. When the voltage level becomes incompatible with the device capacity, forexample in medium voltage, we have to put in voltage transformers.A VT (Voltage transformer) is defined by:b its primary voltage and secondary voltageb its apparent powerb its precision classCurrent measurementCurrent measurement is made by split or closed-core CT’s placed around the phaseand neutral conductors as appropriate.According to the required precision for measurement, the CT used for the protectionrelay also allows current measurement under normal conditions.Energy measurementTo measure energy, we consider two objectives:b A contractual billing objective, e.g. between an electricity company and its clientor even between an airport manager (sub-billing) and stores renting airport surfaceareas. In this case IEC 62053-21 for Classes 1 and 2 and IEC 62053-22 for Classes0.5S and 0.2S become applicable to measure active energy.The full measurement chain – CT, VT and measurement unit – can reach a precisionclass Cl of 1 in low voltage, Cl 0.5 in medium voltage and 0.2 in high voltage, or even0.1 in the future.b An internal cost allocation objective for the company, e.g. to break-down the costof electricity for each product produced in a specific workshop. In this case of aprecision class between 1 and 2 for the whole chain (CT, VT and measurementstation) is sufficient.It is recommended to match the full measurement chain precision with actualmeasurement requirements: there is no one single universal solution, but a goodtechnical and economic compromise according to the requirement to be satisfied.Note that the measurement precision also has a cost, to be compared with the returnon investment that we are expecting.Generally gains in terms of energy efficiency are even greater when the electricalnetwork has not been equipped in this way until this point. In addition, permanentmodifications of the electrical network, according to the company’s activity, mainlycause us to search for significant and immediate optimizations straight away.Example:A class 1 analogue ammeter, rated 100 A, will display a measurement of +/-1 Aat 100 A. However if it displays 2 A, the measurement is correct to within 1 A andtherefore there is uncertainty of 50%.A class 1 energy measurement station such as PM710 – like all other PowerMeter and Circuit Monitor Measurement Units – is accurate to 1% throughout themeasurement range as described in IEC standards 62053.Other physical measurements considerably enhance the data:b on/off, open/closed operating position of devices, etc.b energy metering impulseb transformer, motor temperatureb operation hours, quantity of switching operationsb motor loadb UPS battery loadb event logged equipment failuresb etc.3.2 Electrical data for real objectives© Schneider Electric - all rights reservedElectrical data is transformed into information that is usually intended to satisfyseveral objectives:b It can modify the behaviour of users to manage energy wisely and finally lowersoverall energy costsb It can contribute to field staff efficiency increaseb It can contribute to decrease the cost of Energyb It can contribute to save energy by understanding how it is used and how assetsand process can be optimized to be more energy efficientSchneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations3 Diagnosis through electricalmeasurementFig. K8 : Facility utility costs parallel the visualisation of anicebergb It may help in optimizing and increasing the life duration of the assets associated tothe electrical networkb And finally it may be a master piece in increasing the productivity of the associatedprocess (industrial process or even office, building management), by preventing, orreducing downtime, or insuring higher quality energy to the loads.Facility utility costs parallel the visualization of an iceberg (see Fig. K8). Whilean iceberg seems large above the surface, the size is completely overwhelmingbeneath the surface. Similarly, electrical bills are brought to the surface each monthwhen your power provider sends you a bill. Savings in this area are importantand can be considerable enough to be the only justification needed for a powermonitoring system. However, there are other less obvious yet more significantsavings opportunities to be found below the surface if you have the right tools at yourdisposal.Modify the behaviour of energy usersUsing cost allocation reports, you can verify utility billing accuracy, distribute billsinternally by department, make effective fact-based energy decisions and driveaccountability in every level of your organization. Then providing ownership ofelectricity costs to the appropriate level in an organization, you modify the behaviourof users to manage energy wisely and finally lowers overall energy costs.Increase field staff efficiencyOne of the big challenges of field staff in charge of the electrical network is to makethe right decision and operate in the minimum time.The first need of such people is then to better know what happens on the network,and possibly to be informed everywhere on the concerned site.This site-wise transparency is a key feature that enables a field staff to:b Understand the electrical energy flows – check that the network is correctly set-up,balanced, what are the main consumers, at what period of the day, or the week…b Understand the network behaviour – a trip on a feeder is easier to understandwhen you have access to information from downstream loads.b Be spontaneously informed on events, even outside the concerned site by usingtoday’s mobile communicationb Going straight forward to the right location on the site with the right spare part, andwith the understanding of the complete pictureb Initiate a maintenance action taking into account the real usage of a device, not tooearly and not too lateb Therefore, providing to the electrician a way to monitor the electrical network canappear as a powerful mean to optimize and in certain case drastically reduce thecost of power.Here are some examples of the main usage of the simplest monitoring systems:b Benchmark between zones to detect abnormal consumption.b Track unexpected consumption.b Ensure that power consumption is not higher that your competitors.b Choose the right Power delivery contract with the Power Utility.b Set-up simple load-shedding just focusing on optimizing manageable loads suchas lights.b Be in a position to ask for damage compensation due to non-quality deliveryfrom the Power Utilities – " The process has been stopped because of a sag on thenetworks".Implementing energy efficiency projectsThe Power monitoring system will deliver information that support a completeenergy audit of a factility. Such audit can be the way to cover not only electricitybut also Water, Air, Gas and Steam. Measures, benchmark and normalized energyconsumption information will tell how efficient the industrial facilities and processare. Appropriate action plans can then be put in place. Their scope can be as wideas setting up control lighting, Building automation systems, variable speed drive,process automation, etc.Optimizing the assetsOne increasing fact is that electrical network evolves more and more and then arecurrent question occurs : Will my network support this new evolution?This is typically where a Monitoring system can help the network owner in makingthe right decision.By its logging activity, it can archive the real use of the assets and then evaluatequite accurately the spare capacity of a network, or a switchboard, a transformer…A better use of an asset may increase its life duration.Monitoring systems can provide accurate information of the exact use of an assetand then the maintenance team can decide the appropriate maintenance operation,not too late, or not too early.In some cases also, the monitoring of harmonics can be a positive factor for the lifeduration of some assets (such as motors or transformers).K© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations3 Diagnosis through electricalmeasurementIncreasing the productivity by reducing the downtimeDowntime is the nightmare of any people in charge of an electrical network. It maycause dramatic loss for the company, and the pressure for powering up again in theminimum time – and the associated stress for the operator – is very high.A monitoring and control system can help reducing the downtime very efficiently.Without speaking of a remote control system which are the most sophisticatedsystem and which may be necessary for the most demanding application, a simplemonitoring system can already provide relevant information that will highly contributein reducing the downtime:b Making the operator spontaneously informed, even remote, even out of theconcerned site (Using the mobile communication such as DECT network or GSM/SMS)b Providing a global view of the whole network statusb Helping the identification of the faulty zoneb Having remotely the detailed information attached to each event caught by the fielddevices (reason for trip for example)Then remote control of a device is a must but not necessary mandatory. In manycases, a visit of the faulty zone is necessary where local actions are possible.Increasing the productivity by improving the Energy QualitySome loads can be very sensitive to electricity quality, and operators may faceunexpected situations if the Energy quality is not under control.Monitoring the Energy quality is then an appropriate way to prevent such event and /or to fix specific issue.K10Compact NSX with Micrologic trip unitION 6200 metering unitTeSys U motor controller3.3 Measurement starts with the “stand aloneproduct” solutionThe choice of measurement products in electrical equipment is made according toyour energy efficiency priorities and also current technological advances:b measurement and protection functions of the LV or MV electrical network areintegrated in the same device,Example: Sepam metering and protection relays, Micrologic tripping unit for CompactNSX and Masterpact, TeSys U motor controller, NRC12 capacitor bank controller,Galaxy UPSsb the measurement function is in the device, separate from the protection function,e.g. built on board the LV circuit breaker.Example: PowerLogic ION 6200 metering unitThe progress made in real time industrial electronics and IT are used in a singledevice:b to meet requirements for simplification of switchboardsb to reduce acquisition costs and reduce the number of devicesb to facilitate product developments by software upgrade procedures© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations3 Diagnosis through electricalmeasurementExample of solutions for a medium-sized site:Analysesample Ltd. is a company specialized in analyzing industrial samples fromregional factories: metals, plastics, etc., to certify their chemical characteristics.The company wants to carry out better control of its electrical consumption for theexisting electrical furnaces, its air conditioning system and to ensure quality ofelectrical supply for high-precision electronic devices used to analyze the samples.Electrical network protected and monitored via the Intranet siteThe solution implemented involves recovering power data via metering units thatalso allows measurement of basic electrical parameters as well as verification ofenergy power quality. Connected to a web server, an Internet browser allows to usethem very simply and export data in a Microsoft Excel type spreadsheet. Powercurves can be plotted in real time by the spreadsheet (see Fig. K9).Therefore no IT investment, either in software or hardware, is necessary to use thedata.For example to reduce the electricity bill and limit consumption during nighttimeand weekends, we have to study trend curves supplied by the measurement units(see Fig. K10).Fig. K9 : Example of electrical network protected andmonitored via the Intranet siteK11Fig. K10 : A Test to stop all lighting B Test to stop air conditioningHere consumption during non-working hours seems excessive, consequently two decisions were taken:b reducing night time lightingb stopping air conditioning during weekendsThe new curve obtained shows a significant drop in consumption.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations3 Diagnosis through electricalmeasurementBelow we give examples of measurements available via Modbus, RS485 or Ethernet(see Fig. K11):ExamplesKeep control over power consumptionMeasurement unitsPower Meter, CircuitMonitorMV protection andmeasurement relaysSepamLV protection andmeasurement relaysMasterpact &Compact Micrologictrip unitsCapacitor bankregulatorsVarlogicPower, inst., max., min. b b b b -Energy, reset capability b b b - -Power factor, inst. b b b - -Cos φ inst. - - - b -Insulation monitorsVigilohm SystemImprove power supply availabilityCurrent, inst., max., min., unbalance b b b b -Current, wave form capture b b b - -Voltage, inst., max., min., unbalance b b b b -Voltage, wave form capture b b b - -Device status b b b b -Faults history b b b - -Frequency, inst., max., min. b b b - -THDu, THDi b b b b -K12Manage electrical installation betterLoad temperature, load and devicethermal stateb b - b -Insulating resistance - - - - bMotor controllersLV variable speeddrivesLV softstarters MV softstarters UPSsExamples TeSys U ATV.1 ATS.8 Motorpact RVSS GalaxyKeep control over power consumptionPower, inst., max., min. - b - b bEnergy, reset capability - b b b -Power factor, inst. - - b b bImprove power supply availabilityCurrent, inst., max., min., unbalance b b b b bCurrent, wave form capture - - - b bDevice status b b b b bFaults history b b b b -THDu, THDi - b - - -© Schneider Electric - all rights reservedManage electrical installation betterLoad temperature, load and devicethermal stateb b b b bMotor running hours - b b b -Battery follow up - - - - bFig. K11 : Examples of measurements available via Modbus, RS485 or EthernetSchneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations4 Energy saving solutionsBased on the reports collected by the power monitoring system or energyinformation system, appropriate energy efficiency projects can be selected. Thereare various strategies for choosing which projects to implement:b Often organizations like to get started with relatively low-cost, easy projects togenerate some quick wins before making larger investments.b The simple payback period (the length of time the project will take to pay for itself)is a popular method to rank and choose projects. Its advantage is simplicity of theanalysis. The disadvantage is that this method may not take into account the fulllong-term impact of the project.b Other more complex methods such as net present value or internal rate of returncan also be used. Additional effort is required to make the analysis, but a truerindication of the full project benefits is obtained.Energy savings can be achieved in a number of ways:b Energy reduction measures that either use less energy to achieve the sameresults, or reduce energy consumption by ensuring that energy is not over-usedbeyond the real requirements. An example of the former is using high-efficiencylamps to provide the same illumination at lower energy cost. An example of the latteris reducing the number of lamps in over-illuminated areas to reduce lighting levels tothe required level.b Energy cost saving measures that do not reduce the total energy consumed, butreduce the per-unit cost. An example is scheduling some activities at night to takeadvantage of time-of-day electricity tariffs. Peak demand avoidance and demandresponse schemes are other examples.b Energy reliability measures that not only contribute to operational efficiency byavoiding downtime, but which also avoid the energy losses associated with restartsor reworking spoiled batches.ComprehensiveEnergy StrategyK13ReduceConsumptionOptimizeUtilityCostsImproveReliability &AvailabilityFig. K12 : Comprehensive Energy strategyEfficiency (%)9590858075EFF 14 poleEFF 2EFF 32 pole 2 & 4pole701 15 90Rated Power (kW)Fig. K13 : Definition of energy efficiency classes for LV motorsestablished by the European Commission and CEMEP(European Committee of Manufacturers of Electrical Machinesand Power Electronics)4.1 Motor systems and replacementSince in industry, 60% of consumed electricity is used to run motors, there is a highlikelihood that motor systems will appear strongly among the identified opportunities.Two reasons to consider replacing motors and thereby improve passive energyefficiency are:b to take advantage of new high-efficiency motor designsb to address oversizingDepending on horsepower, high efficiency motors operate between 1% and 10%more efficiently than standard motors. Motors that operate for long periods may begood candidates for replacement with high efficiency motors, especially if the existingmotor needs rewinding. Note that rewound motors are usually 3% – 4% less efficientthan the original motor. However, if the motor receives low to moderate use (e.g.under 3000 hours per year), replacement of standard efficiency motors (particularlythose that have not yet been re-wound) with high efficiency motors may not beeconomical. Also, it is important to ensure the critical performance characteristics(such as speed) of the new motor are equivalent to those of the existing motor.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations4 Energy saving solutionsMotors are most efficient when operated between about 60% and 100% of their fullratedload. Efficiency falls sharply when loading is below 50%. Historically, designershave tended to oversize motors by a significant safety margin in order to eliminateany risk of failure even under extremely unlikely conditions. Facility studies show thatabout one-third of motors are severely oversized and generally are running below50% of rated load (1) . Average loading of motors is around 60% (2) . Oversized motorsare not only inefficient but have higher initial purchase cost than correctly-sized units.Larger motors can also contribute to lower power factor, which may lead to reactivepower charges on the electricity bill. Replacement considerations should take thisinto account along with the remaining useful life of the motor. In addition, note thatsome motors may be oversized but still be so lightly loaded or infrequently used thatthey do not consume enough electricity to make it cost-effective to install a differentmotor.Clearly, wherever appropriate the two approaches should be combined to replaceover-sized standard motors with high-efficiency motors sized suitably for theapplication.Other tactics which can be applied to motor systems include:b Improve active energy efficiency by simply turn off motors when they are notrequired. This may require improvements in automatic control, or education,monitoring and perhaps incentives for operators. If the operator of the motor is notaccountable for its energy consumption, they are more likely to leave it running evenwhen not in use.b Check and if necessary correct shaft alignment, starting with the largest motors.Misaligned motor couplings waste energy and eventually lead to coupling failure anddowntime. An angular offset of 0.6 mm in a pin coupling can result in a power loss ofas much as 8%.4.2 Pumps, fans and variable speed drivesK1463% of energy used by motors is for fluid applications such as pumps and fans.Many of these applications run the motor at full speed even when lower levels of floware required. To obtain the level of flow needed, inefficient methods such as valves,dampers and throttles are often used. In a car, these methods would be equivalentto using the brake to control speed while keeping the gas or accelerator pedal fullydepressed. These are still some of the most common control methods used inindustry. Given that motors are the leading energy-consuming device, and pumpsand fans are the largest category of motor-driven equipment, these applications arefrequently among the top-ranked energy saving opportunities.An Altivar variable speed drive is an active EE approach that can provide the meansto obtain the variable output required from the fan or pump along with significantenergy savings and other benefits. Well-chosen projects can result in simple paybackperiods as short as ten months, with many useful projects in the range of paybacksup to three years. Variable speed drives (VSD) can be useful in many applications,including air compressors, plastic injection moulding machines, and other machines.© Schneider Electric - all rights reserved(1) Operations and Maintenance Manual for EnergyManagement - James E. Piper(2) US Department of Energy fact sheetFig. K14 : Examples of centrifugal pump and fan which can benefit from variable speed controlSchneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations4 Energy saving solutionsMost pumps are required either to move fluids between a source and a destination(e.g. filling a reservoir at a higher level) or to circulate liquid in a system (e.g.to transfer heat). Fans are required to move air or other gases, or to maintain apressure differential. To make the liquid or air flow at the required rate, pressure isrequired. Many pumping or ventilation systems require the flow or pressure to varyfrom time to time.To change the flow or pressure in the system, there are a number of possiblemethods. The suitability will depend on the design of the fan or pump, e.g. whethera pump is a positive displacement pump or rotodynamic pump, whether a fan is acentrifugal fan or axial fan.b Multiple pumps or fans: This leads to step increase when additional pumps or fansare switched in, making fine control difficult. Usually there are efficiency losses asthe real needs are somewhere between the possible steps.b Stop/start control: This is only practical where intermittent flow is acceptable.b Flow control valve: This uses a valve to reduce the flow by increased frictionalresistance to the output of the pump. This wastes energy since the pump isproducing a flow which is then cut back by the valve. In addition, pumps have apreferred operating range, and increasing the resistance by this method can forcethe pump to operate in a range where its efficiency is lower (wasting even moreenergy) and where its reliability is reduced.b Damper: Similar in effect to a flow control valve in a pumping system, this reducesthe flow by obstructing the output of the fan. This wastes energy since the fan isproducing a flow which is then cut back by the damper.b Bypass control: This technique keeps the pump running at full power and routessurplus fluid output from the pump back to the source. It allows a low value of flowto be achieved without risk of increasing the output pressure, but inefficiency is veryhigh since the energy used to pump the surplus fluid is entirely wasted.b Spillage valve: Similar in effect to a bypass control valve in a pumping system, thistechnique keeps the fan running at full power and vents surplus flow. Inefficiency isvery high since the energy used to move the vented air or gas is entirely wasted.b Variable pitch: Some fan designs allow the angle of the blades to be adapted tochange the output.b Inlet guide vane: these are structures using fins to improve or disrupt the routingof air or gas into a fan. In this way they increase or decrease the airflow going in andhence increase or decrease the output.K15actuatorsensormotorfan orpumpfixedshaft speed100% of nominaloutput100% ofnominaldamperor valvereduced output50% of nominalsensorVSDpowerconsumed12.5% ofnominalmotorfan orpumpvariableshaft speed50% of nominaloutput50% ofnominalopenunchanged output50% of nominalFig. K15 : Fan and pump control: in theoryWherever a fan or a pump has been installed for a range of required flow rates orpressure levels, it will have been sized to meet the greatest output demand. It willtherefore usually be oversized, and will be operating inefficiently for other duties.Combining this with the inefficiency of the control methods listed above means thatthere is generally an opportunity to achieve an energy cost saving by using controlmethods which reduce the power to drive the pump or fan during the periods ofreduced demand. However, a fan or pump that is not required to perform variableduties may be running at full speed without any of the above control methods, orwith those control methods present but unused (e.g. valves or dampers set to fullyopen). In this case the device will be operating at or close to its best efficiency and avariable frequency drive will not bring any improvement.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations4 Energy saving solutionsFor those fans and pumps which are required to generate varying levels of output,a variable frequency drive reduces the speed of the pump or fan and the power itconsumes. Among fans, effectiveness will vary depending on the design. Centrifugalfans offer good potential, both with forward curved and backward curved impellers.Axial fans have a greater intrinsic efficiency and normally do not offer enougheconomic potential for a VSD application. In pumps, the effectiveness will varydepending on a number of factors, including the ‘static head’ of the system (theeffects of a difference in height between the source and destination of the fluid) and‘friction head’ (the effects of the liquid moving in the pipes, valves and equipment).The variable frequency drive should always be matched with the safe operatingrange of the pump. Generally, variable speed drives bring greater benefits in systemswhere the friction head is the dominant effect. In some cases, replacing the fan orpump with a more efficient design may bring greater benefits than retrofit of a VSD.A fan or pump that is infrequently used, even if it is inefficient, may not generateenough savings to make replacement or VSD retrofit cost-effective. However notethat flow control by speed regulation is always more efficient than by control valve orbypass control.Fan and pump applications are governed by the affinity laws:b Flow is proportional to shaft speedv Half the shaft speed gives you half the flowb Pressure or head is proportional to the square of shaft speedv Half the shaft speed gives you quarter the pressureb Power is proportional to the cube of shaft speedv Half the shaft speed uses one–eighth of the powerv Hence half the flow uses one-eighth of the power120100K16P (%)8060402000 20 40 60 80 100 120Q (%)Fig. K16 : Theoretical power saving with a fan running at half speedTherefore, if you don’t need the fan or pump to run at 100% flow or pressure output,you can reduce the power consumed by the fan, and the amount of the reduction canbe very substantial for moderate changes in flow. Unfortunately in practice, efficiencylosses in the various components render the theoretical values not achievable.P (W)© Schneider Electric - all rights reserved00 Q (m 3 /s)Fig. K17 : Power versus flow rate for the different fan control methods: downstream damper, inletvanes, and variable speed (top to bottom).Schneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations4 Energy saving solutionsThe actual achievable savings depend on the design of the fan or pump, its inherentefficiency profile, the size of the motor, the number of hours used per year, and thelocal cost of electricity. These savings can be estimated using a tool such as ECO8,or can be accurately forecast by installing temporary metering and analyzing thedata obtained in the context of the appropriate curve.The drive can be integrated into a variety of possible control methods:b Control by fixing pressure but varying flow: This uses a pressure sensor connectedto the VSD which in turn varies the speed allowing the fan or pump to increase ordecrease the flow required by the system. This is a common method in water supplyschemes where constant pressure is required but water is required at differentflows dependant on the number of users at any given time. This is also common oncentralised cooling and distribution systems and in irrigation where a varying numberof spray heads or irrigation sections are involved.b Heating system control: In heating and cooling systems there is a requirement forflow to vary based on temperature. The VSD is controlled by a temperature sensor,which increases or decreases the flow of hot or cold liquid or air based on the actualtemperature required by the process. This is similar to pressure control, where theflow also varies, but a constant temperature requirement from a temperature sensorreplaces that from a pressure sensor.b Control by fixing flow but varying pressure: Constant flow may be required inirrigation and water supply systems. Since the water levels both upstream anddownstream of the pumping station can change, the pressure will be variable. Alsomany cooling, chiller, spraying and washing applications require a specific volume ofwater to be supplied even if the suction and delivery conditions vary. Typically suctionconditions vary when the height of a suction reservoir or tank drops and deliverypressure can change if filters blind or if system resistance increases occur throughblockages etc. A flowmeter is used to keep the flow rate constant, normally installedin the discharge line.The benefits achieved include:b Reduced energy consumption and hence cost savings by replacing inefficientcontrol methods or other obsolete components such as two-speed motorsb Better control and accuracy in achieving required flow and pressureb Reduced noise and vibration, as the inverter allows fine adjustment of the speedsand so prevents the equipment running at a resonant frequency of the pipes orductworkb Increased lifecycle and improved reliability, for example, pumps that are operatedin a throttled condition usually suffer from reduced useful lifeb Simplified pipe or duct systems (elimination of dampers, control valves & by-passlines)b Soft start & stop creates less risk of transient effects in the electrical network ormechanical stress on the rotating parts of the pump or fan. This also reduces waterhammer in pumps, because the drive provides smooth acceleration and decelerationinstead of abrupt speed variationsb Reduced maintenanceK17Without VSD With VSD Reduction % savingsAverage poweruse (2 motorsper fan)104 kW permotor40 kW per motor 64 kW per motor 62%Electricity costper fan£68.66 pertonne outputCO 2 rate 459,000 kg /yearAnnual runningcostPayback period£26.41 pertonne output175,541 kg /year£42.25 pertonne output283,459 kg /year£34,884 £13,341 £21,542Fig. K18 : Example of savings for variable speed driven pumps10 months with local capital allowances claimed14 months without local capital allowancesAdditionally, significant energy savings can be often be made simply by changingpulley sizes, to ensure a fan or pump runs at a more appropriate duty point. Thisdoesn’t provide the flexibility of variable speed control but costs very little, canprobably be done within the maintenance budget and doesn’t require capitalapproval.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations4 Energy saving solutions4.3 LightingLighting can represent over 35% of energy consumption in buildings depending onthe business. Lighting control is one of the easiest ways to save energy costs for lowinvestment and is one of the most common energy saving measures.K18Lamps and ballastsLighting design for commercial buildings is governed by standards, regulations andbuilding codes. Lighting not only needs to be functional but must meet occupationalhealth and safety requirements and be fit for purpose. In many instances, officelighting is over-illuminated, and substantial energy savings are possible by passiveEE: replacing inefficient, old technology lamps with high efficiency, low wattagelamps in conjunction with electronic ballasts.This is especially appropriate in areas where lighting is required constantly or forlong periods, because in such places there is less opportunity to save energy byturning lights off. Simple payback periods vary but many projects have paybacks ofaround two years.Depending on the needs, type and age of your lighting installation, more efficientlamps may be available. For example, 40-watt T12 fluorescent lamps may bereplaced by newer 32-watt T8 fluorescent lamps. (T designates a tubular lamp. Thenumber is the diameter in eights of an inch. T12 lamps are therefore 1.5 inches indiameter. Standards vary between countries.) Changing the lamp will also requirechanging the ballast.Fluorescent lamps contain gases that emit ultraviolet light when excited by electricity.The phosphor coating of the lamp converts the ultraviolet light into the visiblespectrum. If the electricity entering the lamp is not regulated, the light will continueto gain in intensity. A ballast supplies the initial electricity to create the light and thenregulates the current thereafter to maintain the correct light level. Ballasts are alsoused with arc lamps or mercury vapor lamps. New designs of electronic ballastsdeliver considerable savings compared with older electromagnetic ballast designs.T8 lamps with electronic ballasts will use from 32% to 40% less electricity than T12lamps with electromagnetic ballasts.Electronic ballasts do have a disadvantage compared to magnetic ballasts. Magneticballasts operate at line frequency (50 or 60 Hz), but electronic ballasts operateat 20,000 to 60,000 Hz and can introduce harmonic distortion or noise into theelectrical network. This can contribute to overheating or reduced life of transformers,motors, neutral lines, overvoltage trips and damage to electronics.Usually this is not a problem apart from facilities with heavy lighting loads and a largenumber of electronic ballasts. Most makes of electronic ballasts integrate passivefiltering within the ballast to keep the total harmonic distortion to less than 20 percentof fundamental current.If the facility has strict needs for power quality, (e.g. hospitals, sensitivemanufacturing environments, etc) electronic ballasts are available having totalharmonic distortion of five percent or less.Other types of lighting are also available and may be suitable depending on therequirements of the facility. An assessment of lighting needs will include evaluationof the activities taking place and the required degree of illumination and colourrendering. Many older lighting systems were designed to provide more light thancurrent standards require. Savings can be made by redesigning a system to providethe minimum necessary illumination.The use of high efficiency lamps in conjunction with electronic ballasts have anumber of advantages, firstly energy and cost savings can be easily qualified,modern lamps and electronic ballasts are more reliable leading to reducedmaintenance costs, lighting levels are restored to more appropriate levels foroffice space, whilst complying with relevant building codes, practices and lightingstandards, the incidence of ‘frequency beat” often associated with migraines andeye strain disappears and the color rendering of modern lamps produces a moreconducive working environment.© Schneider Electric - all rights reservedReflectorsA less common passive EE recommendation, but one which should be consideredalong with changing lamps and ballasts, is to replace reflectors. The reflector ina luminaire (light fixture) directs light from the lamps towards the area where itis intended to fall. Advances in materials and design have resulted in improvedreflector designs which can be retrofitted to existing luminaires. This results inincreased usable light, and may allow lamps to be removed, this saving energy whilemaintaining the needed level of lighting.Schneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations4 Energy saving solutions+ +Above: Around 70% of a fluorescent tube's light is directedsideways and upwards to the light fittings surfaces;Below: KW/2's silver surface is shaped to reflect the maximumamount of light downward.Fig. K19 : Overview on KW/2 principle+A KW2 high efficiency reflector has a spectral efficiency of over 90%. This means twolamps may be replaced by a single lamp. In this way it is possible to reduce energycosts attributed to lighting by 50% or more. Existing luminaires may be retrofittedwith the space age technology reflector, whilst maintaining spatial distance betweenluminaires, making retrofitting easy and cost effective, with minimal disruption to theexisting ceiling design.Lighting controlImproved lighting control is another method of increasing efficiency in lighting. Suchrecommendations are less common, but the simple payback period is typicallyshorter, between six and twelve months. By itself, passive EE from lamps, ballastsand reflectors does not maximize savings, since an energy efficient lamp will stillwaste energy if left on when not required. Although users can be sensitized toswitch off lights, in practice lapses are common, and automatic control is muchmore effective in obtaining and sustaining efficiency. The objective of lightingcontrol schemes is to provide the comfort and flexibility that users require, whilesimultaneously ensuring active EE, minimizing costs by ensuring lights are turnedoff promptly whenever they are not needed. The sophistication of such schemes canvary considerably.Some of the simplest methods include:b Timer switches to turn off lights after a fixed period has passed. Timers are bestdeployed in areas where occupancy is well defined (e.g. in hotel corridors where thetime for a person to pass through is predictable).b Occupancy sensors / movement detectors to turn off lights when no movement hasbeen detected for a certain period. Occupancy sensors are best deployed in offices,storerooms, stairwells, kitchens and bathrooms where the use of the facilities cannotbe predicted with a high degree of accuracy during the day.b Photoelectric cells / daylight harvesting sensors to control lights near windows.When bright exterior light is available, lamps are turned off or dimmed.b Programmable timers to switch lights on and off at predetermined times (e.g. shopfronts, ensure office lights are turned off at nights and weekends).b Dimmable lights to maintain a low level of illumination at off-peak periods (e.g. acar parking lot which needs to be fully illuminated during peak use, perhaps untilmidnight, but which can have lower ambient illumination from midnight until dawn)b Voltage regulators to optimize the power consumed. Ballasts perform this functionon fluorescent lighting. Voltage regulators are also available for other lighting typessuch as high pressure sodium lamps.K19US Dept of Energy Industrial Assessment Centers databaseFig. K20 : Examples of lighting control devices: timers, light detectors, movement detectors,...Schneider Electric - Electrical installation guide 2009© Schneider Electric - all rights reserved

K - Energy Efficiency in electrical installations4 Energy saving solutionsMethods may be combined, e.g. the ability to dim lights in the parking lot may becombined with movement detectors or override switches with a timer to increaseillumination when needed if a user requires access outside normal hours.More sophisticated and customizable schemes can be implemented with integratedlighting control systems. Aesthetic requirements can be incorporated, such as usingprogrammable lighting panels to record a variety of lighting setups which can bereproduced at the touch of a button (e.g. for boardrooms requiring different lightarrangements for meetings, presentations, demonstrations, etc). Wireless technologycan make retrofit applications simple and economical.Lighting control systems such as C-Bus and KNX offer the additional advantagethat they can be networked and integrated with the building management system,for greater flexibility of control, central monitoring and control function as well ascombination of lighting controls with other building services such as HVAC for evengreater energy savings.Lighting controls have the potential to realize energy savings of 30% but thisdepends very much on application. A lighting survey and energy audit can helpdefine the best lighting solution for the premises and activities performed as wellas identify areas for energy and cost savings. In addition to office space, Schneideroffers solutions for exterior, car parking and landscape lighting for optimum lightingand energy savings.4.4 Load management strategiesSince electricity has to be generated in response to immediate needs, and cannoteconomically be stored, suppliers are obliged to size their generating capacityaccording to peak needs, which may occur infrequently. At other times, that capacityis surplus and represents capital tied up in facilities and equipment that are idle andunused. Suppliers are therefore motivated to smooth out peaks in electricity demand.Load management requires an active EE approach, since even high-efficiencydevices will contribute to peak needs.K20Peak demand avoidanceOne way utilities encourage users to avoid peaks is by transferring the cost ofmaintaining the peak production capacity to those users who contribute most tothe peaks. Utilities structure their billing with various components. One is alwaysthe actual consumption in the billing period, but another component (the demandcharge) is normally based on the peak usage at some point during the precedingperiod, which could be twelve months or another period such as a season. Thedemand charge is a premium that large users pay each month for the utility to havethe extra generation capacity and infrastructure required to meet their peak demandlevels whenever they need it – even if they don’t use it very often. If a customercan avoid setting peaks in their energy usage, they can minimize the part of theirenergy bill driven by the peak consumption, even if their total consumption remainsthe same. Note that setting a new peak has a continuing economic impact, becauseit determines the demand charge not only for that month, but for each subsequentmonth during the period defined by the tariff, which may be as much as a year. Thismeans that a single short event that spikes consumption for as little as a few minutescan have a continuing effect on the electricity bill.kWPeak DemandPeak Usagerescheduledto fit underlower thresholdShaved PeakDemand© Schneider Electric - all rights reservedFig. K21 : Example of load management strategyTimeSchneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations4 Energy saving solutionsPeak demand avoidance applications are PLC controlled automatic electricaldistribution control systems. A demand interval is defined as a particular level ofconsumption in a period of time (e.g. kWh in a 15 minute period). The objective isto keep the total energy consumed in each period below the limit. If the customeris consuming a large amount of power in a given period, the system will detect thata peak is approaching. An alarm is activated, and unless an operator overrides thesystem, it will begin to shed non-essential loads in a predetermined order, until thealarm condition is cleared, or the demand interval ends. All loads in a facility aredefined in one of three categories: critical, essential, and non-essential loads. Usuallyonly non-essential loads are shed, and the order of shedding can be configured.kWPeak during month 2The peak set during month 2 willdictate the demand charge for thenext 12 months (or some other peirodset by the tariff).1 2 3 4 5Fig. K22 : Impact of peak demand on electricity billThe bill for month 4 will be based onthe consumption (green) and the peakset during month 2 (red line).Providing the customer has enough non-essential loads to be able to impact theirpeak consumption, it may be possible to reduce the demand charge by as much as10% to 30%. Demand charge can be up to 60% of the bill. The application usuallypays for itself in one year or less.K21Load schedulingUtilities often have different rates that apply for different times of the day. Duringnormal daily business hours, the rates are the highest. Many users shift, orreschedule loads to take advantage of lower rates. These are loads that are not timesensitive or critical.Demand response (curtailment)Another tactic is demand response (also known as demand curtailment). Demandresponse is a means to manage the demand from customers taking supplyconditions into account. Utilities may offer financial incentives to customers toreduce load during periods when the utility does not have the distribution capacity tohandle the total demand. Typically this will be during the hottest months of the year,when consumer and business needs for cooling and ventilation are high and drawa lot of electricity in addition to normal requirements. In some countries, third-partyaggregators may manage schemes that monitor the network capacity and the realtimeprice of electricity on the network. Participants in the scheme receive incentivesto shed load, creating capacity which the aggregator can sell into the network.In each case, the utility or aggregator offers a contract including an agreement fromthe customer to reduce the kW consumption at their site down to a predeterminedlevel when notified. These contracts may contain both emergency curtailments (whenthe participants in the scheme must comply or face penalties) and opt-in curtailments(where participants can evaluate the specific conditions for that particular curtailmentand decide whether or not to accept). Usually the contract limits the duration of thecurtailment (e.g. 2 to 6 hours) and the number of times per year the curtailmentcan be activated (3 to 5). Industrial customers tend to have more opportunity toparticipate, since building managers are less likely to be able to drop substantialloads without impacting the building occupants’ comfort.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations4 Energy saving solutionsA curtailment is activated following a notification by phone or via a signal outputfrom the utility revenue meter. Typically there is 30 to 60 minutes advance notice.The customer systematically reduces load until the curtailment level is obtained,either by manually reducing or shutting off loads or by an automated PLC controlledsystem. The utility or aggregator then signals the start of the curtailment period. Afterthe curtailment period is complete, the utility or aggregator signals the end of thecurtailment period. The customer may then re-establish normal facility loading andproduction.The return on investment from demand response schemes will vary depending onlocal tariff rates and electricity market. The incentive generally takes the form of acredit for the demand reduction during the response period. If the customer hasenough non-essential loads to be able to impact peak consumption, he may be ableto benefit from incentives that in effect reduce the cost per unit by as much as 30%.Automated demand response control applications usually pay for themselves in oneyear or less. Without such a scheme, loads have to be turned off manually, with asignificant chance of failure, for example, if a human operator does not act quicklyenough. Failing to comply with a curtailment brings financial penalties, and so anautomated application which can support both peak demand avoidance and demandcurtailment can be a very good investment.Together with the control applications, a demand response portal can makeparticipation in a demand response scheme much more convenient. Such a portalprovides a means for a utility or aggregator to notify the participants of emergencyor opt-in events. Participants can evaluate the conditions of an opt-in and view theircurrent consumption and what they would have to do in order to comply with therequest before accepting or rejecting the event. The portal also supports auditing orcompleted events to demonstrate compliance with the conditions.K22On-site generationOn-site generation increases the flexibility available to facility operators. Instead ofshedding loads, on-site generation can provide the power required to keep runningduring a period of peak avoidance or demand curtailment. The automated controlsystem can be extended to integrate control of on-site generation facilities into thescheme. If the customer is buying electricity from a supplier at a time-of-use rate,the control system can be configured to continuously monitor the current cost ofelectricity from the supplier and compare it to the cost of energy generated on siteusing another fuel source. When the cost of electricity rises above the cost of usingthe generator (replacing the fuel), the control scheme automatically shifts load to theon-site generation. When the cost falls, load is shifted back to the supply utility.However, in many places the local authorities only permit diesel generators to beused for a certain maximum number of hours per year, in order to limit emissions.This has to be taken into account as it limits the opportunities to make use of thegenerator.4.5 Power factor correctionIf the electricity supplier charges penalties for reactive power, implementing powerfactor correction has the potential to bring significant savings on the electricity bill.Power factor correction solutions are typically passive EE measures that operatetransparently once installed, and don’t require any changes to existing procedures orbehaviour of staff. Simple payback periods can be less than a year.Power factor correction is treated in detail in chapter L.4.6 Harmonic filtering© Schneider Electric - all rights reservedMany solutions to improve efficient use of electricity can have side effects, bringharmonics into the electrical network. High-efficiency motors, variable speed drives,electronic ballasts for fluorescent lights, and computers can all generate electricalpollution which can have significant effects. Harmonics can create transient overvoltageconditions that cause protection relays to trip and result in productiondowntime. They increase heat and vibration and thereby decrease efficiency andshorten life of neutral conductors, transformers, motors and generators. Power factorcorrection capacitors may magnify harmonics, and can suffer from overloading andpremature aging.Management of harmonics is treated in detail in chapter M.Schneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations4 Energy saving solutions4.7 Other measuresOutside the scope of the electrical installation, other energy savings measuresmay be available depending on the activities present on the site. Productivityenhancements in production such as reducing bottlenecks, eliminating defectsand reducing materials can generate further savings. Combustion systems (suchas furnaces, ovens, boilers) and thermal systems (such as steam systems, heatgeneration, containment and recovery, cooling towers, chillers, refrigerators, dryers)may also provide opportunities.4.8 Communication and Information SystemMost organisations will already have some level of energy information system, evenif it is not identified or managed as one. It should be appreciated that in a changingworking world, any information system will need to develop to meet its primeobjective - supporting management decision making: a key point is to make theenergy information visible at any level of the organization through the communicationinfrastructure.Energy data is important data, it is one of the company’s assets. The company hasIT managers who are already in charge of managing its other IT systems. Theseare important players in the power monitoring system and above all in that for dataexchange within the corporate organization.Communication network at product, equipment and site levelThe day-to-day working of the energy information system can be illustrated by aclosed loop diagram (see Fig. K23).Modbus*Intranet*UnderstandingK23InformationDataCommunicatingmeasurement device*Energy information systems* Communication networkFig. K23 : System hierarchyVarious resources are used to send data from metering and protection devicesinstalled in the user’s electrical cabinets, e.g. via Schneider ElectricTransparentReady.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations4 Energy saving solutionsThe Modbus communication protocolModbus is an industrial messaging protocol between equipment that isinterconnected via a physical transmission link e.g. RS 485 or Ethernet (via TCP/IP)or modem (GSM, Radio etc). This protocol is very widely implemented on meteringand protection products for electrical networks.Initially created by Schneider Electric, Modbus is now a public resource managedby an independent organization Modbus-IDA – enabling total opening up of itsspecification. An industrial standard since 1979, Modbus allows millions of productsto communicate with one another.The IETF, international authority managing the Internet, has approved the creationof a port (502) for products connected to the Internet/Intranet and using the EthernetModbus TCP/IP communication protocol.Modbus is a query/reply process between two pieces of equipment based on datareading and writing services (function codes).The query is emitted by a single “master”, the reply is sent only by the “slave”equipment identified in the query (see Fig. K24).Each “slave” product connected to the Modbus network is set by the user with an IDnumber, called the Modbus address, between 1 and 247.The “master” – for example a web server included in an electrical cabinet– simultaneously queries all of the products with a message comprising its target’saddress, function code, memory location in the product and quantity of information,at most 253 octets.Only a product set with the corresponding address answers the request for data.Exchange is only carried out on the initiative of the master (here the web server): thisis the master-slave Modbus operating procedure.This query procedure followed by a reply, implies that the master will have all of thedata available in a product when it is queried.The “master” manages all of the transaction queries successively if they are intendedfor the same product. This arrangement leads to the calculation of a maximumnumber of products connected to the master to optimize an acceptable responsetime for the query initiator, particularly when it is a low rate RS485 link.K24Fig. K24 : The function codes allow writing or reading of data.A transmission error software detection mechanism called CRC16 allows a message with anerror to be repeated and only the product concerned to respond.© Schneider Electric - all rights reservedYour Intranet networkData exchange from industrial data basically uses web technologies implementedpermanently on the corporate communication network, and more particularly on itsIntranet.The IT infrastructure manages the cohabitation of software applications: thecompany uses it to operate applications for the office, printing, data backup, for thecorporate IT system, accounting, purchasing, ERP, production facility control, API,MES, etc. The cohabitation of data on the same communication network does notpose any particular technological problem.When several PC’s, printers and servers are connected to one another in thecompany’s buildings, very probably using the Ethernet local network and webservices: this company is then immediately eligible to have energy efficiency datadelivered by its electrical cabinets. Without any software development, all they needis an Internet browser.Schneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations4 Energy saving solutionsThe data from these applications cross the local broadband Ethernet network up to1 Gb/s: the communication media generally used in this world is copper or optic fiber,which allows connection everywhere, in commercial or industrial buildings and inelectrical premises.If the company also has an internal Intranet communication network for emailingand sharing web servers data, it uses an extremely common standardizedcommunication protocol: TCP/IP.The TCP/IP communication protocol is designed for widely used web services suchas HTTP to access web pages, SMTP for electronic messaging between otherservices.Applications SNMP NTP RTPS DHCP TFTP FTP HTTP SMTP ModbusTransport UDP TCPLinkPhysicalIPEthernet 802.3 and Ethernet IIElectrical data recorded in industrial web servers installed in electrical cabinets aresent using the same standardized TCP/IP protocol in order to limit the recurrent ITmaintenance costs that are intrinsic in an IT network. This is the operating principleof Schneider Electric Transparent Ready TM for communication of data on energyefficiency. The electrical cabinet is autonomous without the need for any additional ITsystem on a PC, all of the data related to energy efficiency is recorded and can becirculated in the usual way via the intranet, GSM, fixed telephone link, etc.SecurityEmployees are well informed, more efficient and working in complete electricalsafety: they no longer need to go into electrical rooms or make standard checkson electrical devices - they just have to consult data. Under these conditions,communicative systems give the company’s employees immediate and significantgains and avoid worrying about making mistakes.It becomes possible for electricians, maintenance or production technicians, on-siteor visiting managers to work together in complete safety.According to the sensitivity of data, the IT manager will simply give users theappropriate access rights.Marginal impact on local network maintenanceThe company’s IT manager has technical resources to add and monitor equipmentto the local company network.Based on standard web services including the Modbus protocol on TCP/IP, anddue to the low level of bandwidth requirement characteristic in electrical networkmonitoring systems as well as the use of technologies that are not impacted byviruses and worldwide IT standards, the IT manager does not have to make anyspecific investment to preserve the local network performance level or to protectagainst any additional security problems (virus, hacking, etc.).Empowering external partnersAccording to the company’s security policy, it becomes possible to use supportservices of the usual partners in the electrical sector: contractors, utilities managers,panelbuilders, systems integrators or Schneider Electric Services can provideremote assistance and electrical data analysis to the company consuming electricity.The messaging web service can regularly send data by email or web pages can beremotely consulted using the appropriate techniques.K25© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations4 Energy saving solutionsFrom Network Monitoring and Control System to IntelligentPower EquipmentTraditionally and for years, monitoring and control systems have been centralizedand based on SCADA (Supervisory, Control and Data acquisition) automationsystems.Deciding on investing in such system – noted (3) in Figure K25 – was reallyreserved for high demanding installation, because either they were big powerconsumers, or their process was very sensitive to Power non quality.Based on automation technology, such systems were very often designed,customised by a system integrator, and then delivered on site. However the initialcost, the skills needed to correctly operate such system, and the cost of upgrades tofollow the evolutions of the network may have discouraged potential users to invest.Then based on a dedicated solution for electrician, the other approach noted (2)is much more fitting the electrical network specific needs and really increases thepayback of such system. However, due to its centralised architecture, the level costof such solution may still appear high.On some sites Type (2) and (3) can cohabit, providing the most accurate informationto the electrician when needed.Nowadays, a new concept of intelligent Power equipment – noted (1) – has come.considered as an entering step for going to level 2 or 3, due the ability of thesesolutions to co-exist on a site.FunctionlevelsGeneralpurposesitemonitoring3Eqt gatewayGeneralpurposemonitoringsystemK26PowerEquipmentOtherutilitiesProcessSpecialisednetworkmonitoring2Eqt gatewayPowerEquipmentSpecialisedmonitoringsuch asPower LogicION-EntrepriseWeb browserstandard1BasicmonitoringEqt serverIntelligentPowerEquipmentOtherutilitiesStandard network Sensitive electrical networks High demanding sitesSystemcomplexityFig. K26 : Monitoring system positioning© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations4 Energy saving solutionsb Level 1Intelligent equipment based architecture (see Fig. K26)This new architecture has appeared recently due to Web technology capabilities, andcan really be positioned as an entry point into monitoring systems.Based on Web technologies it takes the maximum benefits of standardcommunication services and protocols, and license-free software.The access to electricity information can be done from everywhere in the site, andelectrical staff can gain a lot in efficiency.Openness to the Internet is also offered for out of the site services.Standard remoteWeb browserInternetStandard localWeb browserIntranet (Ethernet/IP)Equipment serverGatewayIntelligence Power EquipmentModbus1 2 3Circuit breakersMeter 1Meter 2 Meter 3K27Fig. K26 : Intelligent equipment architectureb Level 2Electrician specialized centralised architecture (see Fig. K27)Dedicated to electrician, this architecture is based on a specific supervisioncentralised mean that fully match the needs for monitoring an electrical network.Then it offers naturally a lower level of skill to set up and maintain it – all ElectricalDistribution devices are already present in a dedicated library. Finally its purchasecost is really minimized, due the low level of system integrator effort.Dedicated supervisorfor electricianModbus (SL or Ethernet/IP)GatewayCommunicating Power Equipment1 2 3Circuit breakersFig. K27 : ED specialist monitoring systemModbusMeter 1 Meter 2 Meter 3© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations4 Energy saving solutionsb Level 3Conventional general purpose centralised architecture (see Fig. K28)Here is a typical architecture based on standard automation pieces such as SCADAsystems, and gateways.This architecture is typically used for high demanding installation which requires highavailability of electricity.In such case, real time performance is key, either to be achieved automatically orthrough 24/7 operation team on site.In order to comply with very high availability constraint, such system very oftenrequests to support transparently (i.e with no visible impact) a first fault of systemlevel components such as the SCADA itself, the communication infrastructure, ...Energy efficiency is also an important matter, and such solution should offer all themean to clearly master the energy consumption and quality on site. Electrical assetsprotection is then the 3d main matter, and such solution should offer a mean toprevent any damage of these very expensive electrical and process assets.Connectivity with the Process control system is also required, especially throughthe remote control of the operating mode of motors (MV and LV). Solutions such asPowerLogic SCADA (Modbus or IEC 61850 based) appear the most appropriate.ConventionalsupervisorModbus (SL or Ethernet/IP)GatewayCommunicating Power EquipmentK28Modbus1 2 3Circuit breakersMeter 1 Meter 2 Meter 3Fig. K28 : Real-time conventional monitoring and control system© Schneider Electric - all rights reservede-Support becomes accessibleThe setting up of an information system to support a global energy efficiencyapproach very quickly leads to economic gains, in general with an ROI of less than2 years for electricity.An additional benefit, that is still underestimated today, is the leverage that this leadsto in terms of information technologies in the electrical sector. The electrical networkcan be analyzed from time to time by third parties – in particular using externalcompetencies via the internet for very specific issues:b Electricity supply contracts. Changing of supplier at a given point in time, e.g.permanent economic analysis of the costs related to consumption becomes possiblewithout having to wait for an annual review.b Total management of electrical data – via internet – to transform it into relevantinformation that is fed back via a personalized web portal. Consumer usageinformation is now a value-added commodity, available to a wide range of users. It'seasy to post customer usage data on the Internet – making it useful to the users isanother matter.b Complex electrical fault diagnosis to call in an electrotechnical expert, a rareresource that is easily accessible on the web.b Monitoring of consumption and generating alerts in the case of abnormalconsumption peaks.b A maintenance service that is no more than necessary to meet pressure onoverheads via facility management services.Schneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations4 Energy saving solutionsEnergy efficiency is no longer an issue that the company has to face on its own,many e-partners can back up the approach as necessary – in particular when themeasurement and decision making assistance stage is reached, on condition thatthe electrical network is metered and communicative via internet.Implementation can be gradual starting by making a few key pieces of equipmentcommunicative and gradually extending the system so as to be more accurate or togive wider coverage of the installation.The company can choose its policy: ask one or more partners to analyze the data,do it itself or combine these options.The company may decide to manage its electrical energy itself, or ask a partner tomonitor the quality to ensure active monitoring of performances in terms of aging.Example:Schneider Electric proposes e-Services that offers load data visualization and analysisapplication in ASP mode. It simplifies processes for tenants with geographically diverse locationsby providing convenient integrated billing and usage information for all locations combined.The system turns customer usage data into useful information, easily accessible to all internalusers. It helps control costs by showing customers how their organizations use power.A wide range of functionality serves the needs of staff from the same platform:Data Access and Analysis , Historical and Estimated Bills, Rate Comparison, What-if Analysis- Assess the impact of operational changes, such as shifting energy between time periods orreducing usage by fixed amounts or percentages, Automatic Alarming, Memorized Reports,Benchmarking - Benchmark usage data from multiple facilities by applying normalization factorssuch as square footage, operating hours, and units of production. Multiple Commodities - Accessusage data for gas and water as well as electricity etc.New York Chicago Los Angeles SeattleEthernet/VPN Ethernet/VPNK29WEBWeather infoUtility tariffs & ratesWEBReal-time pricingElectricityWater & GasPower QualityReportsEnergy CostAnalysisNormalize data using:- Temperature- Occupancy rates- Rooms- Other parametersXMLCorporateDatabaseODBCStores data including:- Occupancy rates- Square footage- Other parametersFig. K29 : Typical solution example© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical installations4 Energy saving solutions4.9 Mapping of solutions:Energy savings Cost optimization Availability &ReliabilityVariable speed drives High efficiency motorsand transformersMV motor supplyPower factor correction Harmonic management Configuration of circuitsBack-up generators UPS (see page N11)Soft starters Protection coordinationiMCC Intelligent Equipmentbased architectureLevel 1Electrician specializedcentralised architectureLevel 2Conventional generalpurpose centralisedarchitectureLevel 3 K30Fig. K31 : Mapping of solutions© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical distribution5 How to value energy savingsIPMVP (International PerformanceMeasurement & Verification Protocol) is amethodology to value the energetic savings.Certain information in this chapter is taken fromthe IPMVP guide volume 1 published by EVOwww.evo-world.org5.1 Introduction to IPMVP and EVOToday, the interest in energy efficiency project, for whatever purpose, industrial orpublic, has never been greater. It is noticed that one of the most important barriersto a widespread implementation of energy efficiency projects is the lack of reliableand commercially-viable financing result. The more we invest for a project, the biggerthe need for a reliable proof is. Therefore, there is a continuing need for standardmethods to quantify the results of energy efficiency investments.That’s why Efficiency Valuation Organization (EVO) published IPMVP: InternationalPerformance Measurement and Verification Protocol, a guidance documentdescribing common practice in measuring, computing and reporting savingsachieved by energy efficiency projects at end user facilities.The first edition of IPMVP was published in March 1996 and the second in 2004.Until now, EVO has published three volumes of IPMVP:b Volume I : Concepts and Options for Determining Energy and Water Savingsb Volume II : Indoor Environmental Quality (IEQ) Issuesb Volume III : ApplicationsThe first volume is used by Schneider Electric in energy efficiency projects.This publication provides methods, with different levels of cost and accuracy, fordetermining savings either for the whole facility or for the energy efficiency actiononly.IPMVP also specifies the contents of a Measurement and Verification Plan(M&V Plan) which defines all activities necessary to demonstrate the short-termperformance of an industrial retrofit project and its result.5.2 Principles and options of IPMVPPrinciple of IPMVPEnergyUseBaselineenergyInreasedproductionSavingsAdjustedbaselineenergyK31SolutioninstallationReporting periodMeasured energyBaseline periodReporting periodTimeFig. K31 : Principle of baseline definitionBefore the installation of energy efficiency solution, a certain time interval is studiedto determine the relationship between energy use and conditions of production,this period is called baseline. We can do the measurement during this time ormore simply use the energy bill of the plant. Following the installation, this baselinerelationship was used to estimate how much energy the plant would have used ifthere had been no solution (called the “adjusted-baseline energy”). The savingsis the difference between the adjusted-baseline energy and the energy that wasactually metered during the reporting period.Savings = (Adjusted Baseline Period Use or Demand - Reporting-Period Use orDemand)OrSavings = Baseline Period Use or Demand - Reporting-Period Use or Demand± Adjustments© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical distribution5 How to value energy savings5.3 Six qualities of IPMVPWhen an M&V plan is drawn up for an IPMVP action, it must guarantee sixprinciples:b Accurate: M&V reports should be as accurate as the M&V budget will allow. M&Vcosts should normally be small relative to the monetary value of the savings beingevaluated.b Complete: The reporting of energy savings should consider all effects of a project.b Conservative: Where judgements are made about uncertain quantities, M&Vprocedures should be designed to under-estimate savings.b Consistent: The reporting of a project’s energy effectiveness should be consistentbetween:v different types of energy efficiency projects;v different energy management professionals for any one project;v different periods of time for the same project;v and energy efficiency projects and new energy supply projects.b Relevant: The determination of savings should measure the performanceparameters of concern, or least well known, while other less critical or predictableparameters may be estimated.b Transparent: All M&V activities should be clearly and fully disclosed.5.4 IPMVP’s optionsOption A Option B Option C Option DDefinitionRetrofit isolation: keyparameter measurementRetrofit isolation: all parametermeasurementWhole facilityCalibrated simulationK32DescriptionSavings are determined byfield measurement of the keyperformance parameter(s)which define the energy useof the system affected by theenergy efficiency solution.Parameters not selectedfor field measurement areestimated.Savings are determined by fieldmeasurement of the energyuse of the system affected bythe solution.Savings are determined bymeasuring energy use atthe whole facility or subfacilitylevel. Continuousmeasurements of the entirefacility’s energy use are takenthroughout the reporting period.Savings are determinedthrough simulation of theenergy use of the whole facility,or of a sub-facility. Simulationroutines are demonstratedto adequately model actualenergy performance measuredin the facility.Calculation of savingsEngineering calculation ofbaseline and reporting periodenergy from:- short-term or continuousmeasurements of key operatingparameter(s); and- estimated values.Short-term or continuousmeasurements of baseline andreporting period energyAnalysis of whole facilitybaseline and reporting perioddata.Routine adjustments arerequired, using techniquessuch as simple comparison orregression analysis.Energy use simulation,calibrated with hourly ormonthly utility billing data.When use this option?On one hand, this option cangive a result with considerableuncertainty because of theestimation of some parameters.On the other hand, it is notexpensive compared to theoption B.Option B is less cheap thanoption A as all parameters aremeasured. But if a customerasks for a high precision level,it would be a good choice.When there is a multifacetedenergy management programaffecting many systems in afacility, a choice of option C canhelp in saving money and work.Option D is used only whenthe baseline data is missed.Example: a facility where nometer existed before solution’sinstallation and the measure ofthe baseline period takes toomuch time and money.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical distribution5 How to value energy savingsOption selection processStartECMperformanceMeasure facility orECM performance?FacilityperformanceAble to isolateECM withmeter(s)?YesNeed fullperfomancedemonstration?YesInstall isolationmeters for allparameters andassess interactiveeffectsMissing baselineor reporting perioddata?NoNoNoInstall isolation metersfor key parametersassess interactive effects,and estimate well knowparametersMissing baselineor reporting perioddata?YesNoYesNoAnalysis ofmain meterdataExpectedsavings >10%?YesNeed toseparately assesseach ECM?YesSimulatesystem orfacilityCalibratesimulationSimulate with andwithout ECM(s)NoObtaincalibrationdataK33Option BRetrofit isolation:All parametermeasurementOption ARetrofit isolation:Key parametermeasurementOption CWhole facilityOption DCalibratedsimulationFig. K32 : Option selection process5.5 Fundamental points of an M&V planb Energy efficiency project’s intentb Selected IPMVP option and measurement boundaryb Baseline: period, energy and conditionsb Reporting period : duration and conditionb Basis for adjustmentb Analysis procedure: the data analysis procedures, algorithms and assumptions tobe used.b Energy pricesb Meter specificationsb Monitoring responsibilitiesb Expected accuracyb Budget for IPMVP activitiesb Report formatb Quality assuranceOur services with IPMVPSign theenergeticperformancecontractEstablishan M&VplanCollect thebaselineinformationProjectinstallationMeasure the reporting,report information andcalculate the savings© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical distribution6 From returns on investment tosustained performanceOnce energy audits have been conducted and energy savings measures are putin place with quantified return, it is imperative to implement follow up actions tosustain performance. Without an ongoing cycle of continuous improvement, energyperformance tends to revert to a level close to that before the implementation ofsavings measures.Energy Performance CurveSavings with On-going ServicesSavings without proper O&MEnergy Audit& ConsultingEnergyConservationMeasuresServicesContactK34The continuous improvement cycle requires the existence, productive use andmaintenance of a power monitoring system. Such system will be used for proactiveon-going analysis of site energy usage, as well as recommendations forimprovements to the electrical distribution system. In order to ensure optimalperformance of such system and the best use of the collected data, it is industrycommon practice to perform the technical and operational services described below.Schneider Electric experts can deliver such services upon request.6.1 Technical support servicesPower Monitoring systems which are not actively maintained tend to deteriorate for avariety of reasons.b The software can lose communications with devices resulting in lost data.b During the life of any software product upgrades, service packs and patches arereleased to address issues such as: uncovered bugs, operating system softwareupdates, new hardware product support etc.b Databases which are not maintained can become very large, unwieldy and evencorrupt.b The electrical distribution system itself may be changing so that the powermonitoring system no longer matches it.b Firmware updates for hardware devices are released periodically to address bugsor provide improved or additional functionality.Remote servicesSupport is provided by email, telephone and VPN or other remote connection fromthe support center to the customer’s server. Typical services available include:b Toll free hotline for troubleshooting assistanceb Senior support representative assigned to siteb Free software upgrades during the contract validityb Periodic remote system checks, maintenance and reportingb Remote software upgradesb 24/7 telephonic support© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

K - Energy Efficiency in electrical distribution6 From returns on investment tosustained performanceOn site servicesMonthly, quarterly, biannual or annual (as agreed) site visits for system maintenance.Typical services provided are:b Install all PowerLogic software upgradesb Perform firmware upgrades to all PowerLogic monitoring devicesb System troubleshooting to the device levelb Modification of graphic screens per customer inputb Modification of alarms and data logs per customer inputb Reconfiguration of system to match changes to the electrical distribution system6.2 Operational support servicesThese contracts are designed to meet the need for energy analysis and improvementrecommendations.Hosted systemsIn this scenario the user’s usage data is pushed to a Schneider Electric hostedserver. The user accesses his information via a web browser. Typical informationmade available is the following:b Energy consumption datab Carbon emissions datab Degree day analysisb Normalized performance indicatorsb Regression analysisb CUSUM analysis (Cumulative Sum)On site systemsHere the user has a server at one or multiple sites. Different software packages canbe in use depending on the need. The services include all the reports offered in thehosted system plus the following:b An up front site energy audit with improvement recommendationsb Direct line to an energy consultantb Periodic data analysis, reporting and recommendations (monthly, quarterly,biannual or annual as required)b Consolidated data from multiple facilitiesb Load profilesb Power quality reportingK35© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Chapter LPower factor correction andharmonic filtering12345678910ContentsReactive energy and power factor1.1 The nature of reactive energy L21.2 Equipment and appliances requiring reactive energy L21.3 The power factor L31.4 Practical values of power factor L4Why to improve the power factor?L52.1 Reduction in the cost of electricity L52.2 Technical/economic optimization L5How to improve the power factor?L73.1 Theoretical principles L73.2 By using what equipment? L73.3 The choice between a fixed or automatically-regulated bank L9of capacitorsWhere to install power factor correction capacitors? L104.1 Global compensation L104.2 Compensation by sector L104.3 Individual compensation L11How to decide the optimum level of compensation? L125.1 General method L125.2 Simplified method L125.3 Method based on the avoidance of tariff penalties L145.4 Method based on reduction of declared maximum apparentpower (kVA)L14Compensation at the terminals of a transformerL156.1 Compensation to increase the available active power output L156.2 Compensation of reactive energy absorbed by the transformer L16Power factor correction of induction motorsL187.1 Connection of a capacitor bank and protection settings L187.2 How self-excitation of an induction motor can be avoided L19Example of an installation before andL20after power-factor correctionThe effects of harmonicsL2L219.1 Problems arising from power-system harmonics L219.2 Possible solutions L219.3 Choosing the optimum solution L23Implementation of capacitor banksL2410.1 Capacitor elements L2410.2 Choice of protection, control devices and connecting cables L25L© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

L - Power factor correction andharmonic filtering1 Reactive energy and powerfactorLAlternating current systems supply two forms ofenergy:b “Active” energy measured in kilowatt hours(kWh) which is converted into mechanical work,heat, light, etcb “Reactive” energy, which again takes twoforms:v “Reactive” energy required by inductivecircuits (transformers, motors, etc.),v “Reactive” energy supplied by capacitivecircuits (cable capacitance, power capacitors,etc)1.1 The nature of reactive energyAll inductive (i.e. electromagnetic) machines and devices that operate on AC systemsconvert electrical energy from the power system generators into mechanical workand heat. This energy is measured by kWh meters, and is referred to as “active”or “wattful” energy. In order to perform this conversion, magnetic fields have to beestablished in the machines, and these fields are associated with another form ofenergy to be supplied from the power system, known as “reactive” or “wattless”energy.The reason for this is that inductive circuit cyclically absorbs energy from the system(during the build-up of the magnetic fields) and re-injects that energy into the system(during the collapse of the magnetic fields) twice in every power-frequency cycle.An exactly similar phenomenon occurs with shunt capacitive elements in a powersystem, such as cable capacitance or banks of power capacitors, etc. In this case,energy is stored electrostatically. The cyclic charging and discharging of capacitivecircuit reacts on the generators of the system in the same manner as that describedabove for inductive circuit, but the current flow to and from capacitive circuit in exactphase opposition to that of the inductive circuit. This feature is the basis on whichpower factor correction schemes depend.It should be noted that while this “wattless” current (more accurately, the “wattless”component of a load current) does not draw power from the system, it does causepower losses in transmission and distribution systems by heating the conductors.In practical power systems, “wattless” components of load currents are invariablyinductive, while the impedances of transmission and distribution systems arepredominantly inductively reactive. The combination of inductive current passingthrough an inductive reactance produces the worst possible conditions of voltagedrop (i.e. in direct phase opposition to the system voltage).For these reasons (transmission power losses and voltage drop), the power-supplyauthorities reduce the amount of “wattless” (inductive) current as much as possible.“Wattless” (capacitive) currents have the reverse effect on voltage levels and producevoltage-rises in power systems.The power (kW) associated with “active” energy is usually represented by the letter P.The reactive power (kvar) is represented by Q. Inductively-reactive power isconventionally positive (+ Q) while capacitively-reactive power is shown as anegative quantity (- Q).The apparent power S (kVA) is a combination of P and Q (see Fig. L1).Sub-clause 1.3 shows the relationship between P, Q, and S.S(kVA)Q(kvar)P(kW)Fig. L1 : An electric motor requires active power P and reactive power Q from the power system© Schneider Electric - all rights reservedFig. L2 : Power consuming items that also require reactiveenergy1.2 Equipement and appliances requiring reactiveenergyAll AC equipement and appliances that include electromagnetic devices, or dependon magnetically-coupled windings, require some degree of reactive current to createmagnetic flux.The most common items in this class are transformers and reactors, motors anddischarge lamps (with magnetic ballasts) (see Fig. L2).The proportion of reactive power (kvar) with respect to active power (kW) when anitem of equipement is fully loaded varies according to the item concerned being:b 65-75% for asynchronous motorsb 5-10% for transformersSchneider Electric - Electrical installation guide 2009

L - Power factor correction andharmonic filtering1 Reactive energy and powerfactorThe power factor is the ratio of kW to kVA.The closer the power factor approaches itsmaximum possible value of 1, the greater thebenefit to consumer and supplier.PF = P (kW) / S (kVA)P = Active powerS = Apparent power1.3 The power factorDefinition of power factorThe power factor of a load, which may be a single power-consuming item, or anumber of items (for example an entire installation), is given by the ratio of P/S i.e.kW divided by kVA at any given moment.The value of a power factor will range from 0 to 1.If currents and voltages are perfectly sinusoidal signals, power factor equals cos ϕ.A power factor close to unity means that the reactive energy is small compared withthe active energy, while a low value of power factor indicates the opposite condition.Power vector diagramb Active power P (in kW)v Single phase (1 phase and neutral): P = V I cos ϕv Single phase (phase to phase): P = U I cos ϕv Three phase (3 wires or 3 wires + neutral): P = 3U I cos ϕb Reactive power Q (in kvar)v Single phase (1 phase and neutral): P = V I sin ϕv Single phase (phase to phase): Q = U I sin ϕv Three phase (3 wires or 3 wires + neutral): P = 3 U I sin ϕb Apparent power S (in kVA)v Single phase (1 phase and neutral): S = V Iv Single phase (phase to phase): S = U Iv Three phase (3 wires or 3 wires + neutral): P = 3 U Iwhere:V = Voltage between phase and neutralU = Voltage between phasesI = Line currentϕ = Phase angle between vectors V and I.v For balanced and near-balanced loads on 4-wire systemsCurrent and voltage vectors, and derivation of the power diagramThe power “vector” diagram is a useful artifice, derived directly from the true rotatingvector diagram of currents and voltage, as follows:The power-system voltages are taken as the reference quantities, and one phaseonly is considered on the assumption of balanced 3-phase loading.The reference phase voltage (V) is co-incident with the horizontal axis, and thecurrent (I) of that phase will, for practically all power-system loads, lag the voltage byan angle ϕ.The component of I which is in phase with V is the “wattful” component of I and isequal to I cos ϕ, while VI cos ϕ equals the active power (in kW) in the circuit, if V isexpressed in kV.The component of I which lags 90 degrees behind V is the wattless component ofI and is equal to I sin ϕ, while VI sin ϕ equals the reactive power (in kvar) in thecircuit, if V is expressed in kV.If the vector I is multiplied by V, expressed in kV, then VI equals the apparent power(in kVA) for the circuit.The simple formula is obtained: S 2 = P 2 + Q 2The above kW, kvar and kVA values per phase, when multiplied by 3, can thereforeconveniently represent the relationships of kVA, kW, kvar and power factor for a total3-phase load, as shown in Figure L3 .LϕP = VI cos ϕ (kW)VFig. L3 : Power diagramQ = VI sin ϕ (kvar)S = VI (kVA)P = Active powerQ = Reactive powerS = Apparent power© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

L - Power factor correction andharmonic filtering1 Reactive energy and powerfactorAn example of power calculations (see Fig. L4 )Type of Apparent power Active power Reactive powercircuit S (kVA) P (kW) Q (kvar)Single-phase (phase and neutral) S = VI P = VI cos ϕ Q = VI sin ϕSingle-phase (phase to phase) S = UI P = UI cos ϕ Q = UI sin ϕExample 5 kW of load 10 kVA 5 kW 8.7 kvarcos ϕ = 0.5Three phase 3-wires or 3-wires + neutral S = 3 UI P = 3 UI cos ϕ Q = 3 UI sin ϕExample Motor Pn = 51 kW 65 kVA 56 kW 33 kvarcos ϕ = 0.86ρ = 0.91 (motor efficiency)Fig. L4 : Example in the calculation of active and reactive power1.4 Practical values of power factorThe calculations for the three-phase example above are as follows:Pn = delivered shaft power = 51 kWP = active power consumedP = Pn 56 kWρ = 510.91=S = apparent powerPS =cos ϕ = 56= 6 50.86kVASo that, on referring to diagram Figure L5 or using a pocket calculator, the value oftan ϕ corresponding to a cos ϕ of 0.86 is found to be 0.59Q = P tan ϕ = 56 x 0.59 = 33 kvar (see Figure L15).AlternativelyL2 2 2 2Q = S -P= 65 - 56 = 33 kvarAverage power factor values for the most commonly-used equipment andappliances (see Fig. L6)© Schneider Electric - all rights reservedP = 56 kWϕS = 65 kVAFig. L5 : Calculation power diagramQ = 33 kvarEquipment and appliances cos ϕ tan ϕb Common loaded at 0% 0.17 5.80induction motor 25% 0.55 1.5250% 0.73 0.9475% 0.80 0.75100% 0.85 0.62b Incandescent lamps 1.0 0b Fluorescent lamps (uncompensated) 0.5 1.73b Fluorescent lamps (compensated) 0.93 0.39b Discharge lamps 0.4 to 0.6 2.29 to 1.33b Ovens using resistance elements 1.0 0b Induction heating ovens (compensated) 0.85 0.62b Dielectric type heating ovens 0.85 0.62b Resistance-type soldering machines 0.8 to 0.9 0.75 to 0.48b Fixed 1-phase arc-welding set 0.5 1.73b Arc-welding motor-generating set 0.7 to 0.9 1.02 to 0.48b Arc-welding transformer-rectifier set 0.7 to 0.8 1.02 to 0.75b Arc furnace 0.8 0.75Fig. L6 : Values of cos ϕ and tan ϕ for commonly-used equipmentSchneider Electric - Electrical installation guide 2009

L - Power factor correction andharmonic filtering2 Why to improve the powerfactor?An improvement of the power factor of aninstallation presents several technical andeconomic advantages, notably in the reductionof electricity bills2.1 Reduction in the cost of electricityGood management in the consumption of reactive energy brings economicadvantages.These notes are based on an actual tariff structure commonly applied in Europe,designed to encourage consumers to minimize their consumption of reactive energy.The installation of power-factor correction capacitors on installations permits theconsumer to reduce his electricity bill by maintaining the level of reactive-powerconsumption below a value contractually agreed with the power supply authority.In this particular tariff, reactive energy is billed according to the tan ϕ criterion.As previously noted:tan ϕ =Q (kvarh)P (kWh)The power supply authority delivers reactive energy for free:b If the reactive energy represents less than 40% of the active energy (tan ϕ < 0.4)for a maximum period of 16 hours each day (from 06-00 h to 22-00 h) during themost-heavily loaded period (often in winter)b Without limitation during light-load periods in winter, and in spring and summer.During the periods of limitation, reactive energy consumption exceeding 40% ofthe active energy (i.e. tan ϕ > 0.4) is billed monthly at the current rates. Thus, thequantity of reactive energy billed in these periods will be:kvarh (to be billed) = kWh (tan ϕ > 0.4) where:v kWh is the active energy consumed during the periods of limitationv kWh tan ϕ is the total reactive energy during a period of limitationv 0.4 kWh is the amount of reactive energy delivered free during a period oflimitationtan ϕ = 0.4 corresponds to a power factor of 0.93 so that, if steps are taken to ensurethat during the limitation periods the power factor never falls below 0.93,the consumer will have nothing to pay for the reactive power consumed.Against the financial advantages of reduced billing, the consumer must balancethe cost of purchasing, installing and maintaining the power factor improvementcapacitors and controlling switchgear, automatic control equipment (where steppedlevels of compensation are required) together with the additional kWh consumed bythe dielectric losses of the capacitors, etc. It may be found that it is more economicto provide partial compensation only, and that paying for some of the reactive energyconsumed is less expensive than providing 100% compensation.The question of power-factor correction is a matter of optimization, except in verysimple cases.LPower factor improvement allows the use ofsmaller transformers, switchgear and cables,etc. as well as reducing power losses andvoltage drop in an installation2.2 Technical/economic optimizationA high power factor allows the optimization of the components of an installation.Overating of certain equipment can be avoided, but to achieve the best results, thecorrection should be effected as close to the individual inductive items as possible.Reduction of cable sizeFigure L7 shows the required increase in the size of cables as the power factor isreduced from unity to 0.4, for the same active power transmitted.Multiplying factor 1 1.25 1.67 2.5for the cross-sectionalarea of the cable core(s)cos ϕ 1 0.8 0.6 0.4Fig. L7 : Multiplying factor for cable size as a function of cos ϕ© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

L - Power factor correction andharmonic filtering2 Why to improve the powerfactor?Reduction of losses (P, kW) in cablesLosses in cables are proportional to the current squared, and are measured by thekWh meter of the installation. Reduction of the total current in a conductor by 10% forexample, will reduce the losses by almost 20%.Reduction of voltage dropPower factor correction capacitors reduce or even cancel completely the (inductive)reactive current in upstream conductors, thereby reducing or eliminating voltagedrops.Note: Over compensation will produce a voltage rise at the capacitor level.Increase in available powerBy improving the power factor of a load supplied from a transformer, the currentthrough the transformer will be reduced, thereby allowing more load to be added. Inpractice, it may be less expensive to improve the power factor (1) , than to replace thetransformer by a larger unit.This matter is further elaborated in clause 6.L© Schneider Electric - all rights reserved(1) Since other benefits are obtained from a high value ofpower factor, as previously noted.Schneider Electric - Electrical installation guide 2009

L - Power factor correction andharmonic filtering3 How to improve the power factor?Improving the power factor of an installationrequires a bank of capacitors which acts as asource of reactive energy. This arrangement issaid to provide reactive energy compensationa) Reactive current components only flow patternIL - IC IC IL ILCLLoadb) When IC = IL, all reactive power is supplied from thecapacitor bankIL - IC = 0 IC IL ILCLc) With load current added to case (b)IRICCIR + ILILLLoadIRLoadFig. L8 : Showing the essential features of power-factorcorrectionϕ'ϕQcFig. L9 : Diagram showing the principle of compensation:Qc = P (tan ϕ - tan ϕ’)S'SQ'PRRRQ3.1 Theoretical principlesAn inductive load having a low power factor requires the generators andtransmission/distribution systems to pass reactive current (lagging the systemvoltage by 90 degrees) with associated power losses and exaggerated voltagedrops, as noted in sub-clause 1.1. If a bank of shunt capacitors is added to theload, its (capacitive) reactive current will take the same path through the powersystem as that of the load reactive current. Since, as pointed out in sub-clause1.1, this capacitive current Ic (which leads the system voltage by 90 degrees) isin direct phase opposition to the load reactive current (IL), the two componentsflowing through the same path will cancel each other, such that if the capacitor bankis sufficiently large and Ic = IL there will be no reactive current flow in the systemupstream of the capacitors.This is indicated in Figure L8 (a) and (b) which show the flow of the reactivecomponents of current only.In this figure:R represents the active-power elements of the loadL represents the (inductive) reactive-power elements of the loadC represents the (capacitive) reactive-power elements of the power-factor correctionequipment (i.e. capacitors).It will be seen from diagram (b) of Figure L9, that the capacitor bank C appearsto be supplying all the reactive current of the load. For this reason, capacitors aresometimes referred to as “generators of lagging vars”.In diagram (c) of Figure L9, the active-power current component has been added,and shows that the (fully-compensated) load appears to the power system as havinga power factor of 1.In general, it is not economical to fully compensate an installation.Figure L9 uses the power diagram discussed in sub-clause 1.3 (see Fig. L3) toillustrate the principle of compensation by reducing a large reactive power Q to asmaller value Q’ by means of a bank of capacitors having a reactive power Qc.In doing so, the magnitude of the apparent power S is seen to reduce to S’.Example:A motor consumes 100 kW at a power factor of 0.75 (i.e. tan ϕ = 0.88). To improvethe power factor to 0.93 (i.e. tan ϕ = 0.4), the reactive power of the capacitor bankmust be : Qc = 100 (0.88 - 0.4) = 48 kvarThe selected level of compensation and the calculation of rating for the capacitorbank depend on the particular installation. The factors requiring attention areexplained in a general way in clause 5, and in clauses 6 and 7 for transformers andmotors.Note: Before starting a compensation project, a number of precautions should beobserved. In particular, oversizing of motors should be avoided, as well as the noloadrunning of motors. In this latter condition, the reactive energy consumed by amotor results in a very low power factor (≈ 0.17); this is because the kW taken by themotor (when it is unloaded) are very small.3.2 By using what equipment?Compensation at LVAt low voltage, compensation is provided by:b Fixed-value capacitorb Equipment providing automatic regulation, or banks which allow continuousadjustment according to requirements, as loading of the installation changesNote: When the installed reactive power of compensation exceeds 800 kvar, and theload is continuous and stable, it is often found to be economically advantageous toinstal capacitor banks at the medium voltage level.L© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

L - Power factor correction andharmonic filtering3 How to improve the power factor?Compensation can be carried out by afixed value of capacitance in favourablecircumstancesFixed capacitors (see Fig. L10)This arrangement employs one or more capacitor(s) to form a constant level ofcompensation. Control may be:b Manual: by circuit-breaker or load-break switchb Semi-automatic: by contactorb Direct connection to an appliance and switched with itThese capacitors are applied:b At the terminals of inductive devices (motors and transformers)b At busbars supplying numerous small motors and inductive appliance for whichindividual compensation would be too costlyb In cases where the level of load is reasonably constantFig. L10 : Example of fixed-value compensation capacitorsLCompensation is more-commonly effected bymeans of an automatically-controlled steppedbank of capacitorsAutomatic capacitor banks (see Fig. L11)This kind of equipment provides automatic control of compensation, maintaining thepower factor within close limits around a selected level. Such equipment is applied atpoints in an installation where the active-power and/or reactive-power variations arerelatively large, for example:b At the busbars of a general power distribution boardb At the terminals of a heavily-loaded feeder cable© Schneider Electric - all rights reservedFig. L11 : Example of automatic-compensation-regulating equipmentSchneider Electric - Electrical installation guide 2009

L - Power factor correction andharmonic filtering3 How to improve the power factor?Automatically-regulated banks of capacitorsallow an immediate adaptation of compensationto match the level of loadThe principles of, and reasons, for using automaticcompensationA bank of capacitors is divided into a number of sections, each of which is controlledby a contactor. Closure of a contactor switches its section into parallel operation withother sections already in service. The size of the bank can therefore be increased ordecreased in steps, by the closure and opening of the controlling contactors.A control relay monitors the power factor of the controlled circuit(s) and is arrangedto close and open appropriate contactors to maintain a reasonably constantsystem power factor (within the tolerance imposed by the size of each step ofcompensation). The current transformer for the monitoring relay must evidentlybe placed on one phase of the incoming cable which supplies the circuit(s) beingcontrolled, as shown in Figure L12.A Varset Fast capacitor bank is an automatic power factor correction equipmentincluding static contactors (thyristors) instead of usual contactors. Static correctionis particularly suitable for a certain number of installations using equipment with fastcycle and/or sensitive to transient surges.The advantages of static contactors are :b Immediate response to all power factor fluctuation (response time 2 s or 40 msaccording to regulator option)b Unlimited number of operationsb Elimination of transient phenomena on the network on capacitor switchingb Fully silent operationBy closely matching compensation to that required by the load, the possibility ofproducing overvoltages at times of low load will be avoided, thereby preventingan overvoltage condition, and possible damage to appliances and equipment.Overvoltages due to excessive reactive compensation depend partly on the value ofsource impedance.CT In / 5 A cl 1VarmetricrelayLFig. L12 : The principle of automatic-compensation control3.3 The choice between a fixed or automaticallyregulatedbank of capacitorsCommonly-applied rulesWhere the kvar rating of the capacitors is less than, or equal to 15% of the supplytransformer rating, a fixed value of compensation is appropriate. Above the 15%level, it is advisable to install an automatically-controlled bank of capacitors.The location of low-voltage capacitors in an installation constitutes the mode ofcompensation, which may be global (one location for the entire installation), partial(section-by-section), local (at each individual device), or some combination of thelatter two. In principle, the ideal compensation is applied at a point of consumptionand at the level required at any instant.In practice, technical and economic factors govern the choice.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

L - Power factor correction andharmonic filtering4 Where to install correctioncapacitors?Where a load is continuous and stable, globalcompensation can be applied4.1 Global compensation (see Fig. L13)PrincipleThe capacitor bank is connected to the busbars of the main LV distribution board forthe installation, and remains in service during the period of normal load.AdvantagesThe global type of compensation:b Reduces the tariff penalties for excessive consumption of kvarsb Reduces the apparent power kVA demand, on which standing charges are usuallybasedb Relieves the supply transformer, which is then able to accept more load ifnecessaryCommentsb Reactive current still flows in all conductors of cables leaving (i.e. downstream of)the main LV distribution boardb For the above reason, the sizing of these cables, and power losses in them, arenot improved by the global mode of compensation.no.1L10Fig. L13 : Global compensationM M M M© Schneider Electric - all rights reservedCompensation by sector is recommendedwhen the installation is extensive, and where theload/time patterns differ from one part ofthe installation to anotherno. 1no. 2 no. 2M M M MFig. L14 : Compensation by sector4.2 Compensation by sector (see Fig. L14)PrincipleCapacitor banks are connected to busbars of each local distribution board, as shownin Figure L14.A significant part of the installation benefits from this arrangement, notably the feedercables from the main distribution board to each of the local distribution boards atwhich the compensation measures are applied.AdvantagesThe compensation by sector:b Reduces the tariff penalties for excessive consumption of kvarsb Reduces the apparent power kVA demand, on which standing charges are usuallybasedb Relieves the supply transformer, which is then able to accept more load ifnecessaryb The size of the cables supplying the local distribution boards may be reduced, orwill have additional capacity for possible load increasesb Losses in the same cables will be reducedCommentsb Reactive current still flows in all cables downstream of the local distribution boardsb For the above reason, the sizing of these cables, and the power losses in them,are not improved by compensation by sectorb Where large changes in loads occur, there is always a risk of overcompensationand consequent overvoltage problemsSchneider Electric - Electrical installation guide 2009

L - Power factor correction andharmonic filtering4 Where to install correctioncapacitors?Individual compensation should be consideredwhen the power of motor is significant withrespect to power of the installation4.3 Individual compensationPrincipleCapacitors are connected directly to the terminals of inductive circuit (notably motors,see further in Clause 7). Individual compensation should be considered when thepower of the motor is significant with respect to the declared power requirement(kVA) of the installation.The kvar rating of the capacitor bank is in the order of 25% of the kW rating of themotor. Complementary compensation at the origin of the installation (transformer)may also be beneficial.AdvantagesIndividual compensation:b Reduces the tariff penalties for excessive consumption of kvarsb Reduces the apparent power kVA demandb Reduces the size of all cables as well as the cable lossesCommentsb Significant reactive currents no longer exist in the installationL11© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

L - Power factor correction andharmonic filtering5 How to decide the optimum levelof compensation?5.1 General methodListing of reactive power demands at the design stageThis listing can be made in the same way (and at the same time) as that for thepower loading described in chapter A. The levels of active and reactive powerloading, at each level of the installation (generally at points of distribution and subdistributionof circuits) can then be determined.Technical-economic optimization for an existing installationThe optimum rating of compensation capacitors for an existing installation can bedetermined from the following principal considerations:b Electricity bills prior to the installation of capacitorsb Future electricity bills anticipated following the installation of capacitorsb Costs of:v Purchase of capacitors and control equipment (contactors, relaying, cabinets, etc.)v Installation and maintenance costsv Cost of dielectric heating losses in the capacitors, versus reduced losses in cables,transformer, etc., following the installation of capacitorsSeveral simplified methods applied to typical tariffs (common in Europe) are shownin sub-clauses 5.3 and 5.4.5.2 Simplified methodL12General principleAn approximate calculation is generally adequate for most practical cases, and maybe based on the assumption of a power factor of 0.8 (lagging) before compensation.In order to improve the power factor to a value sufficient to avoid tariff penalties (thisdepends on local tariff structures, but is assumed here to be 0.93) and to reducelosses, volt-drops, etc. in the installation, reference can be made to Figure L15 nextpage.From the figure, it can be seen that, to raise the power factor of the installation from0.8 to 0.93 will require 0.355 kvar per kW of load. The rating of a bank of capacitorsat the busbars of the main distribution board of the installation would beQ (kvar) = 0.355 x P (kW).This simple approach allows a rapid determination of the compensation capacitorsrequired, albeit in the global, partial or independent mode.ExampleIt is required to improve the power factor of a 666 kVA installation from 0.75 to 0.928.The active power demand is 666 x 0.75 = 500 kW.In Figure L15, the intersection of the row cos ϕ = 0.75 (before correction) withthe column cos ϕ = 0.93 (after correction) indicates a value of 0.487 kvar ofcompensation per kW of load.For a load of 500 kW, therefore, 500 x 0.487 = 244 kvar of capacitive compensationis required.Note: this method is valid for any voltage level, i.e. is independent of voltage.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

L - Power factor correction andharmonic filtering5 How to decide the optimum levelof compensation?Before kvar rating of capacitor bank to install per kW of load, to improve cos ϕ (the power factor) or tan ϕ,compensation to a given valuetan ϕ 0.75 0.59 0.48 0.46 0.43 0.40 0.36 0.33 0.29 0.25 0.20 0.14 0.0tan ϕ cos ϕ cos ϕ 0.80 0.86 0.90 0.91 0.92 0.93 0.94 0.95 0.96 0.97 0.98 0.99 12.29 0.40 1.557 1.691 1.805 1.832 1.861 1.895 1.924 1.959 1.998 2.037 2.085 2.146 2.2882.22 0.41 1.474 1.625 1.742 1.769 1.798 1.831 1.840 1.896 1.935 1.973 2.021 2.082 2.2252.16 0.42 1.413 1.561 1.681 1.709 1.738 1.771 1.800 1.836 1.874 1.913 1.961 2.022 2.1642.10 0.43 1.356 1.499 1.624 1.651 1.680 1.713 1.742 1.778 1.816 1.855 1.903 1.964 2.1072.04 0.44 1.290 1.441 1.558 1.585 1.614 1.647 1.677 1.712 1.751 1.790 1.837 1.899 2.0411.98 0.45 1.230 1.384 1.501 1.532 1.561 1.592 1.628 1.659 1.695 1.737 1.784 1.846 1.9881.93 0.46 1.179 1.330 1.446 1.473 1.502 1.533 1.567 1.600 1.636 1.677 1.725 1.786 1.9291.88 0.47 1.130 1.278 1.397 1.425 1.454 1.485 1.519 1.532 1.588 1.629 1.677 1.758 1.8811.83 0.48 1.076 1.228 1.343 1.370 1.400 1.430 1.464 1.497 1.534 1.575 1.623 1.684 1.8261.78 0.49 1.030 1.179 1.297 1.326 1.355 1.386 1.420 1.453 1.489 1.530 1.578 1.639 1.7821.73 0.50 0.982 1.232 1.248 1.276 1.303 1.337 1.369 1.403 1.441 1.481 1.529 1.590 1.7321.69 0.51 0.936 1.087 1.202 1.230 1.257 1.291 1.323 1.357 1.395 1.435 1.483 1.544 1.6861.64 0.52 0.894 1.043 1.160 1.188 1.215 1.249 1.281 1.315 1.353 1.393 1.441 1.502 1.6441.60 0.53 0.850 1.000 1.116 1.144 1.171 1.205 1.237 1.271 1.309 1.349 1.397 1.458 1.6001.56 0.54 0.809 0.959 1.075 1.103 1.130 1.164 1.196 1.230 1.268 1.308 1.356 1.417 1.5591.52 0.55 0.769 0.918 1.035 1.063 1.090 1.124 1.156 1.190 1.228 1.268 1.316 1.377 1.5191.48 0.56 0.730 0.879 0.996 1.024 1.051 1.085 1.117 1.151 1.189 1.229 1.277 1.338 1.4801.44 0.57 0.692 0.841 0.958 0.986 1.013 1.047 1.079 1.113 1.151 1.191 1.239 1.300 1.4421.40 0.58 0.665 0.805 0.921 0.949 0.976 1.010 1.042 1.076 1.114 1.154 1.202 1.263 1.4051.37 0.59 0.618 0.768 0.884 0.912 0.939 0.973 1.005 1.039 1.077 1.117 1.165 1.226 1.3681.33 0.60 0.584 0.733 0.849 0.878 0.905 0.939 0.971 1.005 1.043 1.083 1.131 1.192 1.3341.30 0.61 0.549 0.699 0.815 0.843 0.870 0.904 0.936 0.970 1.008 1.048 1.096 1.157 1.2991.27 0.62 0.515 0.665 0.781 0.809 0.836 0.870 0.902 0.936 0.974 1.014 1.062 1.123 1.2651.23 0.63 0.483 0.633 0.749 0.777 0.804 0.838 0.870 0.904 0.942 0.982 1.030 1.091 1.2331.20 0.64 0.450 0.601 0.716 0.744 0.771 0.805 0.837 0.871 0.909 0.949 0.997 1.058 1.2001.17 0.65 0.419 0.569 0.685 0.713 0.740 0.774 0.806 0.840 0.878 0.918 0.966 1.007 1.1691.14 0.66 0.388 0.538 0.654 0.682 0.709 0.743 0.775 0.809 0.847 0.887 0.935 0.996 1.1381.11 0.67 0.358 0.508 0.624 0.652 0.679 0.713 0.745 0.779 0.817 0.857 0.905 0.966 1.1081.08 0.68 0.329 0.478 0.595 0.623 0.650 0.684 0.716 0.750 0.788 0.828 0.876 0.937 1.0791.05 0.69 0.299 0.449 0.565 0.593 0.620 0.654 0.686 0.720 0.758 0.798 0.840 0.907 1.0491.02 0.70 0.270 0.420 0.536 0.564 0.591 0.625 0.657 0.691 0.729 0.769 0.811 0.878 1.0200.99 0.71 0.242 0.392 0.508 0.536 0.563 0.597 0.629 0.663 0.701 0.741 0.783 0.850 0.9920.96 0.72 0.213 0.364 0.479 0.507 0.534 0.568 0.600 0.634 0.672 0.712 0.754 0.821 0.9630.94 0.73 0.186 0.336 0.452 0.480 0.507 0.541 0.573 0.607 0.645 0.685 0.727 0.794 0.9360.91 0.74 0.159 0.309 0.425 0.453 0.480 0.514 0.546 0.580 0.618 0.658 0.700 0.767 0.9090.88 0.75 0.132 0.82 0.398 0.426 0.453 0.487 0.519 0.553 0.591 0.631 0.673 0.740 0.8820.86 0.76 0.105 0.255 0.371 0.399 0.426 0.460 0.492 0.526 0.564 0.604 0.652 0.713 0.8550.83 0.77 0.079 0.229 0.345 0.373 0.400 0.434 0.466 0.500 0.538 0.578 0.620 0.687 0.8290.80 0.78 0.053 0.202 0.319 0.347 0.374 0.408 0.440 0.474 0.512 0.552 0.594 0.661 0.8030.78 0.79 0.026 0.176 0.292 0.320 0.347 0.381 0.413 0.447 0.485 0.525 0.567 0.634 0.7760.75 0.80 0.150 0.266 0.294 0.321 0.355 0.387 0.421 0.459 0.499 0.541 0.608 0.7500.72 0.81 0.124 0.240 0.268 0.295 0.329 0.361 0.395 0.433 0.473 0.515 0.582 0.7240.70 0.82 0.098 0.214 0.242 0.269 0.303 0.335 0.369 0.407 0.447 0.489 0.556 0.6980.67 0.83 0.072 0.188 0.216 0.243 0.277 0.309 0.343 0.381 0.421 0.463 0.530 0.6720.65 0.84 0.046 0.162 0.190 0.217 0.251 0.283 0.317 0.355 0.395 0.437 0.504 0.6450.62 0.85 0.020 0.136 0.164 0.191 0.225 0.257 0.291 0.329 0.369 0.417 0.478 0.6200.59 0.86 0.109 0.140 0.167 0.198 0.230 0.264 0.301 0.343 0.390 0.450 0.5930.57 0.87 0.083 0.114 0.141 0.172 0.204 0.238 0.275 0.317 0.364 0.424 0.5670.54 0.88 0.054 0.085 0.112 0.143 0.175 0.209 0.246 0.288 0.335 0.395 0.5380.51 0.89 0.028 0.059 0.086 0.117 0.149 0.183 0.230 0.262 0.309 0.369 0.5120.48 0.90 0.031 0.058 0.089 0.121 0.155 0.192 0.234 0.281 0.341 0.484L13Value selected as an example on section 5.2Value selected as an example on section 5.4Fig. L15 : kvar to be installed per kW of load, to improve the power factor of an installation© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

L - Power factor correction andharmonic filtering5 How to decide the optimum levelof compensation?L14In the case of certain (common) types oftariff, an examination of several bills coveringthe most heavily-loaded period of the yearallows determination of the kvar level ofcompensation required to avoid kvarh (reactiveenergy)charges. The pay-back period of abank of power-factor-correction capacitorsand associated equipment is generally about18 months5.3 Method based on the avoidance of tariffpenaltiesThe following method allows calculation of the rating of a proposed capacitor bank,based on billing details, where the tariff structure corresponds with (or is similar to)the one described in sub-clause 2.1 of this chapter.The method determines the minimum compensation required to avoid these chargeswhich are based on kvarh consumption.The procedure is as follows:b Refer to the bills covering consumption for the 5 months of winter (in France theseare November to March inclusive).Note: in tropical climates the summer months may constitute the period of heaviestloading and highest peaks (owing to extensive air conditioning loads) so that aconsequent variation of high-tariff periods is necessary in this case. The remainder ofthis example will assume Winter conditions in France.b Identify the line on the bills referring to “reactive-energy consumed” and “kvarhto be charged”. Choose the bill which shows the highest charge for kvarh (afterchecking that this was not due to some exceptional situation).For example: 15,966 kvarh in January.b Evaluate the total period of loaded operation of the installation for that month, forinstance: 220 hours (22 days x 10 hours). The hours which must be counted arethose occurring during the heaviest load and the highest peak loads occurring onthe power system. These are given in the tariff documents, and are (commonly)during a 16-hour period each day, either from 06.00 h to 22.00 h or from 07.00 h to23.00 h according to the region. Outside these periods, no charge is made for kvarhconsumption.b The necessary value of compensation in kvar = kvarh billed/number of hours ofoperation (1) = QcThe rating of the installed capacitor bank is generally chosen to be slightly largerthan that calculated.Certain manufacturers can provide “slide rules” especially designed to facilitatethese kinds of calculation, according to particular tariffs. These devices andaccompanying documentation advice on suitable equipment and control schemes,as well as drawing attention to constraints imposed by harmonic voltages on thepower system. Such voltages require either over dimensioned capacitors (in terms ofheat-dissipation, voltage and current ratings) and/or harmonic-suppression inductorsor filters.© Schneider Electric - all rights reservedFor 2-part tariffs based partly on a declared valueof kVA, Figure L17 allows determination of thekvar of compensation required to reduce thevalue of kVA declared, and to avoid exceeding itϕ'ϕCos ϕ = 0.7Cos ϕ'= 0.95S = 122 kVAS' = 90 kVAQ = 87.1 kvarQc = 56 kvarQ' = 28.1 kvarS'SP = 85.4 kWFig. L16 : Reduction of declared maximum kVA by powerfactorimprovement(1) In the billing period, during the hours for whichreactive energy is charged for the case considered above:15,996 kvarhQc = = 73 kvar220 hQ'QcQ5.4 Method based on reduction of declaredmaximum apparent power (kVA)For consumers whose tariffs are based on a fixed charge per kVA declared, plus acharge per kWh consumed, it is evident that a reduction in declared kVA would bebeneficial. The diagram of Figure L16 shows that as the power factor improves, thekVA value diminishes for a given value of kW (P). The improvement of the powerfactor is aimed at (apart from other advantages previously mentioned) reducing thedeclared level and never exceeding it, thereby avoiding the payment of an excessiveprice per kVA during the periods of excess, and/or tripping of the the main circuitbreaker.Figure L15 (previous page) indicates the value of kvar of compensation perkW of load, required to improve from one value of power factor to another.Example:A supermarket has a declared load of 122 kVA at a power factor of 0.7 lagging, i.e.anactive-power load of 85.4 kW. The particular contract for this consumer was based onstepped values of declared kVA (in steps of 6 kVA up to 108 kVA, and 12 kVA stepsabove that value, this is a common feature in many types of two-part tariff). In thecase being considered, the consumer was billed on the basis of132 kVA. Referring to Figure L15, it can be seen that a 60 kvar bank of capacitorswill improve the power factor of the load from 0.7 to 0.95 (0.691 x 85.4 = 59 kvarin the figure). The declared value of kVA will then be 85.4 = 90 kVA , i.e. animprovement of 30%.0.95Schneider Electric - Electrical installation guide 2009

L - Power factor correction andharmonic filtering6 Compensation at the terminalsof a transformerThe installation of a capacitor bank can avoidthe need to change a transformer in the event ofa load increase6.1 Compensation to increase the available activepower outputSteps similar to those taken to reduce the declared maximum kVA, i.e. improvementof the load power factor, as discussed in subclause 5.4, will maximise the availabletransformer capacity, i.e. to supply more active power.Cases can arise where the replacement of a transformer by a larger unit, to overcomea load growth, may be avoided by this means. Figure L17 shows directly the power(kW) capability of fully-loaded transformers at different load power factors, fromwhich the increase of active-power output can be obtained as the value of powerfactor increases.tan ϕ cos ϕ Nominal rating of transformers (in kVA)00 160 250 315 400 500 630 800 1000 1250 1600 20000.00 1 100 160 250 315 400 500 630 800 1000 1250 1600 20000.20 0.98 98 157 245 309 392 490 617 784 980 1225 1568 19600.29 0.96 96 154 240 302 384 480 605 768 960 1200 1536 19200.36 0.94 94 150 235 296 376 470 592 752 940 1175 1504 18800.43 0.92 92 147 230 290 368 460 580 736 920 1150 1472 18400.48 0.90 90 144 225 284 360 450 567 720 900 1125 1440 18000.54 0.88 88 141 220 277 352 440 554 704 880 1100 1408 17600.59 0.86 86 138 215 271 344 430 541 688 860 1075 1376 17200.65 0.84 84 134 210 265 336 420 529 672 840 1050 1344 16800.70 0.82 82 131 205 258 328 410 517 656 820 1025 1312 16400.75 0.80 80 128 200 252 320 400 504 640 800 1000 1280 16000.80 0.78 78 125 195 246 312 390 491 624 780 975 1248 15600.86 0.76 76 122 190 239 304 380 479 608 760 950 1216 15200.91 0.74 74 118 185 233 296 370 466 592 740 925 1184 14800.96 0.72 72 115 180 227 288 360 454 576 720 900 1152 14401.02 0.70 70 112 175 220 280 350 441 560 700 875 1120 1400Fig. L17 : Active-power capability of fully-loaded transformers, when supplying loads at different values of power factorExample: (see Fig. L18 )An installation is supplied from a 630 kVA transformer loaded at 450 kW (P1) with a450mean power factor of 0.8 lagging. The apparent power S1= = 562kVA0.8The corresponding reactive power2 2Q1= S1 − P1 = 337 kvarThe anticipated load increase P2 = 100 kW at a power factor of 0.7 lagging.The apparent power 100 S 2 = = 143 kVAThe corresponding reactive 0.7 powerL15QP1S1SS2Q1Q2P2QQ mFig. L18 : Compensation Q allows the installation-loadextension S2 to be added, without the need to replace theexisting transformer, the output of which is limited to SP2 2Q2 = S2 − P2 = 102kvarWhat is the minimum value of capacitive kvar to be installed, in order to avoid achange of transformer?Total power now to be supplied:P = P1 + P2 = 550 kWThe maximum reactive power capability of the 630 kVA transformer when delivering550 kW is:2 2Qm = S − P Qm = 630 2 − 5502 = 307 kvarTotal reactive power required by the installation before compensation:Q1 + Q2 = 337 + 102 = 439 kvarSo that the minimum size of capacitor bank to install:Qkvar = 439 - 307 = 132 kvarIt should be noted that this calculation has not taken account of load peaks and theirduration.The best possible improvement, i.e. correction which attains a power factor of1 would permit a power reserve for the transformer of 630 - 550 = 80 kW.The capacitor bank would then have to be rated at 439 kvar.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

L - Power factor correction andharmonic filtering6 Compensation at the terminalsof a transformerL16Where metering is carried out at the MV sideof a transformer, the reactive-energy losses inthe transformer may need to be compensated(depending on the tariff)Perfect transformerPrimarywindingSecondarywindingFig. L19 : Transformer reactances per phaseLeakage reactanceMagnetizingreactanceThe reactive power absorbed by a transformercannot be neglected, and can amount to (about)5% of the transformer rating when supplyingits full load. Compensation can be provided bya bank of capacitors. In transformers, reactivepower is absorbed by both shunt (magnetizing)and series (leakage flux) reactances. Completecompensation can be provided by a bank ofshunt-connected LV capacitorsI sin'I sin'IESourceXLVLoadFig. L20 : Reactive power absorption by series inductanceIVEIXL6.2 Compensation of reactive energy absorbed bythe transformerThe nature of transformer inductive reactancesAll previous references have been to shunt connected devices such as those usedin normal loads, and power factor-correcting capacitor banks etc. The reason forthis is that shunt connected equipment requires (by far) the largest quantities ofreactive energy in power systems; however, series-connected reactances, such asthe inductive reactances of power lines and the leakage reactance of transformerwindings, etc., also absorb reactive energy.Where metering is carried out at the MV side of a transformer, the reactive-energylosses in the transformer may (depending on the tariff) need to be compensated. Asfar as reactive-energy losses only are concerned, a transformer may be representedby the elementary diagram of Figure L19. All reactance values are referred tothe secondary side of the transformer, where the shunt branch represents themagnetizing-current path. The magnetizing current remains practically constant (atabout 1.8% of full-load current) from no load to full load, in normal circumstances,i.e. with a constant primary voltage, so that a shunt capacitor of fixed value can beinstalled at the MV or LV side, to compensate for the reactive energy absorbed.Reactive-power absorption in series-connected(leakage flux) reactance XLA simple illustration of this phenomenon is given by the vector diagram ofFigure L20.The reactive-current component through the load = I sin ϕ so that QL = VI sin ϕ.The reactive-current component from the source = I sin ϕ’ so that QE = EI sin ϕ’.It can be seen that E > V and sin ϕ’ > sin ϕ.The difference between EI sin ϕ’ and VI sin ϕ gives the kvar per phase absorbedby XL.It can be shown that this kvar value is equal to I 2 XL (which is analogous to the I 2 Ractive power (kW) losses due to the series resistance of power lines, etc.).From the I 2 XL formula it is very simple to deduce the kvar absorbed at any load valuefor a given transformer, as follows:If per-unit values are used (instead of percentage values) direct multiplication of Iand XL can be carried out.Example:A 630 kVA transformer with a short-circuit reactance voltage of 4% is fully loaded.What is its reactive-power (kvar) loss?4% = 0.04 pu Ipu = 1loss = I 2 XL = 1 2 x 0.04 = 0.04 pu kvarwhere 1 pu = 630 kVAThe 3-phase kvar losses are 630 x 0.04 = 25.2 kvar (or, quite simply, 4% of 630 kVA).At half load i.e. I = 0.5 pu the losses will be0.5 2 x 0.04 = 0.01 pu = 630 x 0.01 = 6.3 kvar and so on...This example, and the vector diagram of Figure L20 show that:b The power factor at the primary side of a loaded transformer is different (normallylower) than that at the secondary side (due to the absorption of vars)b Full-load kvar losses due to leakage reactance are equal to the transformerpercentage reactance (4% reactance means a kvar loss equal to 4% of the kVA ratingof the transformer)b kvar losses due to leakage reactance vary according to the current(or kVA loading) squared© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

L - Power factor correction andharmonic filtering6 Compensation at the terminalsof a transformerTo determine the total kvar losses of a transformer the constant magnetizing-currentcircuit losses (approx. 1.8% of the transformer kVA rating) must be added to theforegoing “series” losses. Figure L21 shows the no-load and full-load kvar losses fortypical distribution transformers. In principle, series inductances can be compensatedby fixed series capacitors (as is commonly the case for long MV transmission lines).This arrangement is operationally difficult, however, so that, at the voltage levelscovered by this guide, shunt compensation is always applied.In the case of MV metering, it is sufficient to raise the power factor to a point wherethe transformer plus load reactive-power consumption is below the level at which abilling charge is made. This level depends on the tariff, but often corresponds to atan ϕ value of 0.31 (cos ϕ of 0.955).Rated power (kVA) Reactive power (kvar) to be compensatedNo loadFull load100 2.5 6.1160 3.7 9.6250 5.3 14.7315 6.3 18.4400 7.6 22.9500 9.5 28.7630 11.3 35.7800 20 54.51000 23.9 72.41250 27.4 94.51600 31.9 1262000 37.8 176Fig. L21 : Reactive power consumption of distribution transformers with 20 kV primary windingsAs a matter of interest, the kvar losses in a transformer can be completelycompensated by adjusting the capacitor bank to give the load a (slightly) leadingpower factor. In such a case, all of the kvar of the transformer is being supplied fromthe capacitor bank, while the input to the MV side of the transformer is at unity powerfactor, as shown in Figure L22.L17E (Input voltage)IϕV (Load voltage)IXLLoadcurrentI0 Compensation currentFig. L22 : Overcompensation of load to completely compensate transformer reactive-power lossesIn practical terms, therefore, compensation for transformer-absorbed kvar is includedin the capacitors primarily intended for powerfactor correction of the load, eitherglobally, partially, or in the individual mode. Unlike most other kvar-absorbing items,the transformer absorption (i.e. the part due to the leakage reactance) changessignificantly with variations of load level, so that, if individual compensation is appliedto the transformer, then an average level of loading will have to be assumed.Fortunately, this kvar consumption generally forms only a relatively small part of thetotal reactive power of an installation, and so mismatching of compensation at timesof load change is not likely to be a problem.Figure L21 indicates typical kvar loss values for the magnetizing circuit (“no-loadkvar” columns), as well as for the total losses at full load, for a standard range ofdistribution transformers supplied at 20 kV (which include the losses due to theleakage reactance).© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

L - Power factor correction andharmonic filtering7 Power factor correction ofinduction motorsIndividual motor compensation is recommendedwhere the motor power (kVA) is large withrespect to the declared power of the installation7.1 Connection of a capacitor bank and protectionsettingsGeneral precautionsBecause of the small kW consumption, the power factor of a motor is very low at noloador on light load. The reactive current of the motor remains practically constant atall loads, so that a number of unloaded motors constitute a consumption of reactivepower which is generally detrimental to an installation, for reasons explained inpreceding sections.Two good general rules therefore are that unloaded motors should be switched off,and motors should not be oversized (since they will then be lightly loaded).ConnectionThe bank of capacitors should be connected directly to the terminals of the motor.Special motorsIt is recommended that special motors (stepping, plugging, inching, reversing motors,etc.) should not be compensated.Effect on protection settingsAfter applying compensation to a motor, the current to the motor-capacitorcombination will be lower than before, assuming the same motor-driven loadconditions. This is because a significant part of the reactive component of the motorcurrent is being supplied from the capacitor, as shown in Figure L23.Where the overcurrent protection devices of the motor are located upstream of themotor capacitor connection (and this will always be the case for terminal-connectedcapacitors), the overcurrent relay settings must be reduced in the ratio:cos ϕ before compensation / cos ϕ after compensationFor motors compensated in accordance with the kvar values indicated in Figure L24(maximum values recommended for avoidance of self-excitation of standardinduction motors, as discussed in sub-clause 7.2), the above-mentioned ratiowill have a value similar to that indicated for the corresponding motor speed inFigure L25.L18BeforecompensationTransformerActivepowerAftercompensationPowermadeavailable3-phase motors 230/400 VNominal power kvar to be installedSpeed of rotation (rpm)kW hp 3000 1500 1000 75022 30 6 8 9 1030 40 7.5 10 11 12.537 50 9 11 12.5 1645 60 11 13 14 1755 75 13 17 18 2175 100 17 22 25 2890 125 20 25 27 30110 150 24 29 33 37132 180 31 36 38 43160 218 35 41 44 52200 274 43 47 53 61250 340 52 57 63 71280 380 57 63 70 79355 482 67 76 86 98400 544 78 82 97 106450 610 87 93 107 117CFigure L24 : Maximum kvar of power factor correction applicable to motor terminals without riskof self excitation© Schneider Electric - all rights reservedMMotorMReactivepowersuppliedby capacitorFig. L23 : Before compensation, the transformer supplies allthe reactive power; after compensation, the capacitor suppliesa large part of the reactive powerSpeed in rpmReduction factor750 0.881000 0.901500 0.913000 0.93Fig. L25 : Reduction factor for overcurrent protection after compensationSchneider Electric - Electrical installation guide 2009

L - Power factor correction andharmonic filtering7 Power factor correction ofinduction motorsWhen a capacitor bank is connected to theterminals of an induction motor, it is importantto check that the size of the bank is less thanthat at which self-excitation can occurFig. L26 : Connection of the capacitor bank to the motor7.2 How self-excitation of an induction motor can beavoidedWhen a motor is driving a high-inertia load, the motor will continue to rotate (unlessdeliberately braked) after the motor supply has been switched off.The “magnetic inertia” of the rotor circuit means that an emf will be generated in thestator windings for a short period after switching off, and would normally reduce tozero after 1 or 2 cycles, in the case of an uncompensated motor.Compensation capacitors however, constitute a 3-phase “wattless” load for thisdecaying emf, which causes capacitive currents to flow through the stator windings.These stator currents will produce a rotating magnetic field in the rotor which actsexactly along the same axis and in the same direction as that of the decayingmagnetic field.The rotor flux consequently increases; the stator currents increase; and the voltageat the terminals of the motor increases; sometimes to dangerously-high levels. Thisphenomenon is known as self-excitation and is one reason why AC generatorsare not normally operated at leading power factors, i.e. there is a tendency tospontaneously (and uncontrollably) self excite.Notes:1. The characteristics of a motor being driven by the inertia of the load are notrigorously identical to its no-load characteristics. This assumption, however, issufficiently accurate for practical purposes.2. With the motor acting as a generator, the currents circulating are largely reactive,so that the braking (retarding) effect on the motor is mainly due only to the loadrepresented by the cooling fan in the motor.3. The (almost 90° lagging) current taken from the supply in normal circumstances bythe unloaded motor, and the (almost 90° leading) current supplied to the capacitorsby the motor acting as a generator, both have the same phase relationshipto the terminalvoltage. It is for this reason that the two characteristics may besuperimposed on the graph.In order to avoid self-excitation as described above, the kvar rating of the capacitorbank must be limited to the following maximum value:Qc y 0.9 x Io x Un x 3 where Io = the no-load current of the motor and Un =phase-to-phase nominal voltage of the motor in kV. Figure L24 previous page givesappropriate values of Qc corresponding to this criterion.ExampleA 75 kW, 3,000 rpm, 400 V, 3-phase motor may have a capacitor bank no largerthan 17 kvar according to Figure L24. The table values are, in general, too small toadequately compensate the motor to the level of cos ϕ normally required. Additionalcompensation can, however, be applied to the system, for example an overall bank,installed for global compensation of a number of smaller appliances.High-inertia motors and/or loadsIn any installation where high-inertia motor driven loads exist, the circuit-breakers orcontactors controlling such motors should, in the event of total loss of power supply,be rapidly tripped.If this precaution is not taken, then self excitation to very high voltages is likely tooccur, since all other banks of capacitors in the installation will effectively be inparallel with those of the high-inertia motors.The protection scheme for these motors should therefore include an overvoltagetripping relay, together with reverse-power checking contacts (the motor will feedpower to the rest of the installation, until the stored inertial energy is dissipated).If the capacitor bank associated with a high inertia motor is larger than thatrecommended in Figure L24, then it should be separately controlled by a circuitbreakeror contactor, which trips simultaneously with the main motor-controllingcircuit-breaker or contactor, as shown in Figure L26.Closing of the main contactor is commonly subject to the capacitor contactor beingpreviously closed.L19© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

L - Power factor correction andharmonic filtering8 Example of an installationbefore and after power-factorcorrectionInstallation before P.F. correction kVA=kW+kvarkWkVA(1)kvarb kvarh are billed heavily above the declaredlevelb Apparent power kVA is significantly greaterthan the kW demandb The corresponding excess current causeslosses (kWh) which are billedb The installation must be over-dimensionedInstallation after P.F. correction kVA=kW+kvarkWkVAb The consumption of kvarh isv Eliminated, orv Reduced, according to the cos ϕ requiredb The tariff penaltiesv For reactive energy where applicablev For the entire bill in some cases areeliminatedb The fixed charge based on kVA demand isadjusted to be close to the active power kWdemand630 kVA400 VCharacteristics of the installation500 kW cos ϕ = 0.75b Transformer is overloadedb The power demand isP 500S = = = 665 kVAcos ϕ 0.75S = apparent power630 kVA400 VCharacteristics of the installation500 kW cos ϕ = 0.928b Transformer no longer overloadedb The power-demand is 539 kVAb There is 14% spare-transformer capacityavailableb The current flowing into the installationdownstream of the circuit breaker isI = P = 960 A3U cos ϕb The current flowing into the installationthrough the circuit breaker is 778 AL20b Losses in cables are calculated as afunction of the current squared: 960 2P=I 2 Rb The losses in the cables arereduced to7782 = 65% of the former value,960 2thereby economizing in kWh consumedcos ϕ = 0.75b Reactive energy is supplied through thetransformer and via the installation wiringb The transformer, circuit breaker, and cablesmust be over-dimensionedcos ϕ = 0.928b Reactive energy is supplied by the capacitorbank250 kvarCapacitor bank rating is 250 kvarin 5 automatically-controlled steps of 50 kvar.cos ϕ = 0.75workshopcos ϕ = 0.75workshop© Schneider Electric - all rights reservedFig. K27 : Technical-economic comparison of an installation before and after power-factor correction(1) The arrows denote vector quantities.(2) Particularly in the pre-corrected case.Schneider Electric - Electrical installation guide 2009Note: In fact, the cos ϕ of the workshop remains at 0.75 but cos ϕ for all theinstallation upstream of the capacitor bank to the transformer LV terminalsis 0.928.As mentioned in Sub-clause 6.2 the cos ϕ at the HV side of the transformerwill be slightly lower (2) , due to the reactive power losses in the transformer.

L - Power factor correction andharmonic filtering9 The effects of harmonics9.1 Problems arising from power-system harmonicsEquipment which uses power electronics components (variable-speed motorcontrollers, thyristor-controlled rectifiers, etc.) have considerably increased theproblems caused by harmonics in power supply systems.Harmonics have existed from the earliest days of the industry and were (and stillare) caused by the non-linear magnetizing impedances of transformers, reactors,fluorescent lamp ballasts, etc.Harmonics on symmetrical 3-phase power systems are generally odd-numbered: 3 rd ,5 th , 7 th , 9 th ..., and the magnitude decreases as the order of the harmonic increases.A number of features may be used in various ways to reduce specific harmonics tonegligible values - total elimination is not possible. In this section, practical means ofreducing the influence of harmonics are recommended, with particular reference tocapacitor banks.Capacitors are especially sensitive to harmonic components of the supply voltagedue to the fact that capacitive reactance decreases as the frequency increases.In practice, this means that a relatively small percentage of harmonic voltage cancause a significant current to flow in the capacitor circuit.The presence of harmonic components causes the (normally sinusoidal) wave formof voltage or current to be distorted; the greater the harmonic content, the greater thedegree of distortion.If the natural frequency of the capacitor bank/ power-system reactance combinationis close to a particular harmonic, then partial resonance will occur, with amplifiedvalues of voltage and current at the harmonic frequency concerned. In this particularcase, the elevated current will cause overheating of the capacitor, with degradationof the dielectric, which may result in its eventual failure.Several solutions to these problems are available. This can be accomplished byb Shunt connected harmonic filter and/or harmonic-suppression reactors orb Active power filters orb Hybrid filtersHarmonics are taken into account mainly byoversizing capacitors and including harmonicsuppressionreactors in series with themHarmonicgeneratorIharFilterFig. L28 : Operation principle of passive filter9.2 Possible solutionsPassive filter (see Fig. L28)Countering the effects of harmonicsThe presence of harmonics in the supply voltage results in abnormally high currentlevels through the capacitors. An allowance is made for this by designing for an r.m.s.value of current equal to 1.3 times the nominal rated current. All series elements,such as connections, fuses, switches, etc., associated with the capacitors aresimilarly oversized, between 1.3 to 1.5 times nominal rating.Harmonic distortion of the voltage wave frequently produces a “peaky” wave form,in which the peak value of the normal sinusoidal wave is increased. This possibility,together with other overvoltage conditions likely to occur when countering the effectsof resonance, as described below, are taken into account by increasing the insulationlevel above that of “standard” capacitors. In many instances, these two countermeasures are all that is necessary to achieve satisfactory operation.Countering the effects of resonanceCapacitors are linear reactive devices, and consequently do not generate harmonics.The installation of capacitors in a power system (in which the impedances arepredominantly inductive) can, however, result in total or partial resonance occurringat one of the harmonic frequencies.The harmonic order ho of the natural resonant frequency between the systeminductance and the capacitor bank is given byh o =SscQwhereSsc = the level of system short-circuit kVA at the point of connection of the capacitorQ = capacitor bank rating in kvar; and ho = the harmonic order of the naturalfrequency f o i.e. fo for a 50 Hz system, or fo for a 60 Hz system.5060L21© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

L - Power factor correction andharmonic filtering9 The effects of harmonicsFor example: h o =SscQmay give a value for h o of 2.93 which shows that theIharHarmonicgeneratorActivefilterIsIactLinearloadnatural frequency of the capacitor/system-inductance combination is close to the 3 rdharmonic frequency of the system.fFrom ho= oit can be seen that f o = 50 h o = 50 x 2.93 = 146.5 Hz50The closer a natural frequency approaches one of the harmonics present on thesystem, the greater will be the (undesirable) effect. In the above example, strongresonant conditions with the 3 rd harmonic component of a distorted wave wouldcertainly occur.In such cases, steps are taken to change the natural frequency to a value which willnot resonate with any of the harmonics known to be present. This is achieved by theaddition of a harmonic-suppression inductor connected in series with the capacitorbank.On 50 Hz systems, these reactors are often adjusted to bring the resonant frequencyof the combination, i.e. the capacitor bank + reactors to 190 Hz. The reactors areadjusted to 228 Hz for a 60 Hz system. These frequencies correspond to a valuefor h o of 3.8 for a 50 Hz system, i.e. approximately mid-way between the 3 rd and 5 thharmonics.In this arrangement, the presence of the reactor increases the fundamentalfrequency (50 Hz or 60 Hz) current by a small amount (7-8%) and therefore thevoltage across the capacitor in the same proportion.This feature is taken into account, for example, by using capacitors which aredesigned for 440 V operation on 400 V systems.L22Fig. L29 : Operation principle of active filterIharActivefilterIactIsActive filter (see Fig. L29)Active filters are based on power electronic technology. They are generally installedin parallel with the non linear load.Active filters analyse the harmonics drawn by the load and then inject the sameharmonic current to the load with the appropriate phase. As a result, the harmoniccurrents are totally neutralised at the point considered. This means they no longerflow upstream and are no longer supplied by the source.A main advantage of active conditioners is that they continue to guarantee efficientharmonic compensation even when changes are made to the installation. They arealso exceptionally easy to use as they feature:b Auto-configuration to harmonic loads whatever their order of magnitudeb Elimination of overload risksb Compatibility with electrical generator setsb Connection to any point of the electrical networkb Several conditioners can be used in the same installation to increase depollutionefficiency (for example when a new machine is installed)Active filters may provide also power factor correction.HarmonicgeneratorHybride filterFig. L30 : Operation principle of hybrid filterLinearloadHybrid filter (see Fig. L30)This type of filter combines advantages of passive and active filter. One frequencycan be filtered by passive filter and all the other frequencies are filtered by activefilter.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

L - Power factor correction andharmonic filtering9 The effects of harmonics9.3 Choosing the optimum solutionFigure L31 below shows the criteria that can be taken into account to select themost suitable technology depending on the application.Passive filter Active filter Hybrid filterApplications Industrial Tertiary Industrial… with total power of non greater than lower than greater thanlinear loads (variable speed 200 kVA 200 kVA 200 kVAdrive, UPS, rectifier…)Power factor correctionNoNecessity of reducing theharmonic distorsion involtage for sensitive loadsNecessity of reducingthe harmonic distorsionin current to avoid cableoverloadNecessity of being in Noaccordance with strictlimits of harmonicrejectedFig. L31 : Selection of the most suitable technology depending on the applicationFor passive filter, a choice is made from the following parameters:b Gh = the sum of the kVA ratings of all harmonic-generating devices (staticconverters, inverters, speed controllers, etc.) connected to the busbars from whichthe capacitor bank is supplied. If the ratings of some of these devices are quoted inkW only, assume an average power factor of 0.7 to obtain the kVA ratingsb Ssc = the 3-phase short-circuit level in kVA at the terminals of the capacitor bankb Sn = the sum of the kVA ratings of all transformers supplying (i.e. directlyconnected to) the system level of which the busbars form a partIf a number of transformers are operating in parallel, the removal from service of oneor more, will significantly change the values of Ssc and Sn. From these parameters,a choice of capacitor specification which will ensure an acceptable level of operationwith the system harmonic voltages and currents, can be made, by reference toFigure L32.L23b General rule valid for any size of transformerSscGh Ssc120Gh120i SscGh > Ssc7070Standard capacitors Capacitor voltage rating Capacitor voltage ratingincreased by 10% increased by 10%(except 230 V units) + harmonic-suppression reactorb Simplified rule if transformer(s) rating Sn y 2 MVAGh i 0.15 Sn 0.15 Sn < Gh i 0.25 Sn 0.25 Sn < Gh i 0.60 Sn Gh > 0.60 SnStandard capacitors Capacitor voltage rating Capacitor voltage rating Filtersincreased by 10% increased by 10%(except 230 V units) + harmonic suppressionreactorFig. L32 : Choice of solutions for limiting harmonics associated with a LV capacitor bank suppliedvia transformer(s)© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

L - Power factor correction andharmonic filtering10 Implementation of capacitorbanks10.1 Capacitor elementsTechnologyThe capacitors are dry-type units (i.e. are not impregnated by liquid dielectric)comprising metallized polypropylene self-healing film in the form of a two-film roll.They are protected by a high-quality system (overpressure disconnector used witha high breaking capacity fuse) which switches off the capacitor if an internal faultoccurs.The protection scheme operates as follows:b A short-circuit through the dielectric will blow the fuseb Current levels greater than normal, but insufficient to blow the fuse sometimesoccur, e.g. due to a microscopic flow in the dielectric film. Such “faults” often re-sealdue to local heating caused by the leakage current, i.e. the units are said to be “selfhealing”b If the leakage current persists, the defect may develop into a short-circuit, and thefuse will blowb Gas produced by vaporizing of the metallisation at the faulty location will graduallybuild up a pressure within the plastic container, and will eventually operate apressure-sensitive device to short-circuit the unit, thereby causing the fuse to blowCapacitors are made of insulating material providing them with double insulation andavoiding the need for a ground connection (see Fig. L33).a)HRC fuseDischargeresistorMetallicdiscOverpressure disconnectdeviceL24© Schneider Electric - all rights reserved(1) Merlin-Gerin designationb)Electrical characteristicsStandardFig. L33 : Capacitor element, (a) cross-section, (b) electrical characteristicsSchneider Electric - Electrical installation guide 2009IEC 60439-1, NFC 54-104, VDE 0560 CSAStandards, UL testsOperating range Rated voltage 400 VRated frequency50 HzCapacitance tolerance - 5% to + 10%Temperature range Maximum temperature 55 °C(up to 65 kvar) Average temperature over 45 °C24 hAverage annual 35 °CtemperatureMinimum temperature - 25 °CInsulation level50 Hz 1 min withstand voltage : 6 kV1.2/50 μs impulse withstand voltage : 25 kVPermissible current overload Classic range (1) Comfort range (1)30% 50%Permissible voltage overload 10% 20%

L - Power factor correction andharmonic filtering10 Implementation of capacitorbanks10.2 Choice of protection, control devices andconnecting cablesThe choice of upstream cables and protection and control devices depends on thecurrent loading.For capacitors, the current is a function of:b The applied voltage and its harmonicsb The capacitance valueThe nominal current In of a 3-phase capacitor bank is equal to:QIn =Un 3with:v Q: kvar ratingv Un: Phase-to-phase voltage (kV)The permitted range of applied voltage at fundamental frequency, plus harmoniccomponents, together with manufacturing tolerances of actual capacitance (for adeclared nominal value) can result in a 50% increase above the calculated value ofcurrent. Approximately 30% of this increase is due to the voltage increases, while afurther 15% is due to the range of manufacturing tolerances, so that1.3 x 1.15 = 1.5All components carrying the capacitor current therefore, must be adequate to coverthis “worst-case” condition, in an ambient temperature of 50 °C maximum. In thecase where temperatures higher than 50 °C occur in enclosures, etc. derating of thecomponents will be necessary.ProtectionThe size of the circuit-breaker can be chosen in order to allow the setting of longtime delay at:b 1.36 x In for Classic range (1)b 1.50 x In for Comfort range (1)b 1.12 x In for Harmony range (1) (tuned at 2.7 f) (2)b 1.19 x In for Harmony range (1) (tuned at 3.8 f)b 1.31 x In for Harmony range (1) (tuned at 4.3 f)Short time delay setting (short-circuit protection) must be insensitive to inrushcurrent. The setting will be 10 x In for Classic, Comfort and Harmony range (1) .Example 150 kvar – 400V – 50 Hz – Classic range50,000In = = 72 A( 400 x 1.732 )Long time delay setting: 1.36 x 72 = 98 AShort time delay setting: 10 x In = 720 AExample 250 kvar – 400V – 50 Hz – Harmony range (tuned at 4.3 f)In = 72 ALong time delay setting: 1.31 x 72 = 94 AShort time delay setting: 10 x In = 720 AL25Upstream cablesFigure L34 next page gives the minimum cross section area of the upstream cablefor Rectiphase capacitors.(1) Merlin-Gerin designation(2) Harmony capacitor banks are equipped with a harmonicsuppression reactor.Cables for controlThe minimum cross section area of these cables will be 1.5 mm 2 for 230 V.For the secondary side of the transformer, the recommended cross sectionarea is u 2.5 mm 2 .Schneider Electric - Electrical installation guide 2009© Schneider Electric - all rights reserved

L - Power factor correction andharmonic filtering10 Implementation of capacitorbanksBank power Copper Aluminium(kvar) crosssection cross- section230 V 400 V (mm 2 ) (mm 2 )5 10 2.5 1610 20 4 1615 30 6 1620 40 10 1625 50 16 2530 60 25 3540 80 35 5050 100 50 7060 120 70 9570 140 95 12090-100 180 120 185200 150 240120 240 185 2 x 95150 250 240 2 x 120300 2 x 95 2 x 150180-210 360 2 x 120 2 x 185245 420 2 x 150 2 x 240280 480 2 x 185 2 x 300315 540 2 x 240 3 x 185350 600 2 x 300 3 x 240385 660 3 x 150 3 x 240420 720 3 x 185 3 x 300Fig L34 : Cross-section of cables connecting medium and high power capacitor banks (1)L26© Schneider Electric - all rights reserved(1) Minimum cross-section not allowing for any correctionfactors (installation mode, temperature, etc.). The calculationswere made for single-pole cables laid in open air at 30 °C.Voltage transientsHigh-frequency voltage and current transients occur when switching a capacitorbank into service. The maximum voltage peak does not exceed (in the absence ofharmonics) twice the peak value of the rated voltage when switching unchargedcapacitors.In the case of a capacitor being already charged at the instant of switch closure,however, the voltage transient can reach a maximum value approaching 3 times thenormal rated peak value.This maximum condition occurs only if:b The existing voltage at the capacitor is equal to the peak value of rated voltage,andb The switch contacts close at the instant of peak supply voltage, andb The polarity of the power-supply voltage is opposite to that of the chargedcapacitorIn such a situation, the current transient will be at its maximum possible value, viz:Twice that of its maximum when closing on to an initially uncharged capacitor, aspreviously noted.For any other values of voltage and polarity on the pre-charged capacitor, thetransient peaks of voltage and current will be less than those mentioned above.In the particular case of peak rated voltage on the capacitor having the same polarityas that of the supply voltage, and closing the switch at the instant of supply-voltagepeak, there would be no voltage or current transients.Where automatic switching of stepped banks of capacitors is considered, therefore,care must be taken to ensure that a section of capacitors about to be energized isfully discharged.The discharge delay time may be shortened, if necessary, by using dischargeresistors of a lower resistance value.Schneider Electric - Electrical installation guide 2009

Chapter MHarmonic management12345678ContentsThe problem: why is it necessary to detectand eliminate harmonics?StandardsGeneralMain effects of harmonics in installations4.1 Resonance M64.2 Increased losses M64.3 Overloads on equipment M74.4 Disturbances affecting sensitive loads M94.5 Economic impact M10Essential indicators of harmonic distortionM11and measurement principles5.1 Power factor M115.2 Crest factor M115.3 Power values and harmonics M115.4 Harmonic spectrum and harmonic distortion M125.5 Total harmonic distortion (THD) M125.6 Usefulness of the various indicators M13Measuring the indicatorsM146.1 Devices used to measure the indicators M146.2 Procedures for harmonic analysis of distribution networks M146.3 Keeping a close eye on harmonics M15Detection devicesM16Solutions to attenuate harmonicsM2M3M4M6M178.1 Basic solutions M178.2 Harmonic filtering M188.3 The method M208.4 Specific products M20M© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

M - Harmonic management1 The problem: why is it necessaryto detect and eliminate harmonics?Disturbances caused by harmonicsHarmonics flowing in distribution networks downgrade the quality of electrical power.This can have a number of negative effects:b Overloads on distribution networks due to the increase in rms currentb Overloads in neutral conductors due to the cumulative increase in third-orderharmonics created by single-phase loadsb Overloads, vibration and premature ageing of generators, transformers and motorsas well as increased transformer humb Overloads and premature ageing of power-factor correction capacitorsb Distortion of the supply voltage that can disturb sensitive loadsb Disturbances in communication networks and on telephone linesEconomic impact of disturbancesHarmonics have a major economic impact:b Premature ageing of equipment means it must be replaced sooner unlessoversized right from the startb Overloads on the distribution network can require higher subscribed power levelsand increase lossesb Distortion of current waveforms provokes nuisance tripping that can stopproductionIncreasingly serious consequencesOnly ten years ago, harmonics were not yet considered a real problem becausetheir effects on distribution networks were generally minor. However, the massiveintroduction of power electronics in equipment has made the phenomenon far moreserious in all sectors of economic activity.In addition, the equipment causing the harmonics is often vital to the company ororganisation.Which harmonics must be measured and eliminated?The most frequently encountered harmonics in three-phase distribution networksare the odd orders. Harmonic amplitudes normally decrease as the frequencyincreases. Above order 50, harmonics are negligible and measurements are nolonger meaningful. Sufficiently accurate measurements are obtained by measuringharmonics up to order 30.Utilities monitor harmonic orders 3, 5, 7, 11 and 13. Generally speaking, harmonicconditioning of the lowest orders (up to 13) is sufficient. More comprehensiveconditioning takes into account harmonic orders up to 25.M© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

M - Harmonic management2 StandardsHarmonic emissions are subject to various standards and regulations:b Compatibility standards for distribution networksb Emissions standards applying to the equipment causing harmonicsb Recommendations issued by utilities and applicable to installationsIn view of rapidly attenuating the effects of harmonics, a triple system of standardsand regulations is currently in force based on the documents listed below.Standards governing compatibility between distribution networks andproductsThese standards determine the necessary compatibility between distributionnetworks and products:b The harmonics caused by a device must not disturb the distribution networkbeyond certain limitsb Each device must be capable of operating normally in the presence ofdisturbances up to specific levelsb Standard IEC 61000-2-2 for public low-voltage power supply systemsb Standard IEC 61000-2-4 for LV and MV industrial installationsStandards governing the quality of distribution networksb Standard EN 50160 stipulates the characteristics of electricity supplied by publicdistribution networksb Standard IEEE 519 presents a joint approach between Utilities and customersto limit the impact of non-linear loads. What is more, Utilities encourage preventiveaction in view of reducing the deterioration of power quality, temperature rise and thereduction of power factor. They will be increasingly inclined to charge customers formajor sources of harmonicsStandards governing equipmentb Standard IEC 61000-3-2 or EN 61000-3-2 for low-voltage equipment with ratedcurrent under 16 Ab Standard IEC 61000-3-12 for low-voltage equipment with rated current higher than16 A and lower than 75 AMaximum permissible harmonic levelsInternational studies have collected data resulting in an estimation of typicalharmonic contents often encountered in electrical distribution networks. Figure M1presents the levels that, in the opinion of many utilities, should not be exceeded.Odd harmonic orders Odd harmonic orders Even harmonic ordersnon-multiples of 3 multiples of 3Order h LV MV EMV Order h LV MV EMV Order h LV MV EMV5 6 6 2 3 5 2.5 1.5 2 2 1.5 1.57 5 5 2 9 1.5 1.5 1 4 1 1 111 3.5 3.5 1.5 15 0.3 0.3 0.3 6 0.5 0.5 0.513 3 3 1.5 21 0.2 0.2 0.2 8 0.5 0.2 0.217 2 2 1 > 21 0.2 0.2 0.2 10 0.5 0.2 0.219 1.5 1.5 1 12 0.2 0.2 0.223 1.5 1 0.7 > 12 0.2 0.2 0.225 1.5 1 0.7> 25 0.2 0.2 0.1+ 25/h + 25/h + 25/hMFig. M1 : Maximum permissible harmonic levels© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

M - Harmonic management3 GeneralThe presence of harmonics indicates a distorted current or voltage wave. Thedistortion of the current or voltage wave means that the distribution of electricalenergy is disturbed and power quality is not optimum.Harmonic currents are caused by non-linear loads connected to the distributionnetwork. The flow of harmonic currents causes harmonic voltages via distributionnetworkimpedances and consequently distortion of the supply voltage.Origin of harmonicsDevices and systems that cause harmonics are present in all sectors, i.e. industrial,commercial and residential. Harmonics are caused by non-linear loads (i.e. loadsthat draw current with a waveform that is not the same as that of the supply voltage).Examples of non-linear loads are:b Industrial equipment (welding machines, arc furnaces, induction furnaces,rectifiers)b Variable-speed drives for asynchronous or DC motorsb UPSsb Office equipment (computers, photocopy machines, fax machines, etc.)b Home appliances (television sets, micro-wave ovens, fluorescent lighting)b Certain devices involving magnetic saturation (transformers)Disturbances caused by non-linear loads: harmonic current and voltageNon-linear loads draw harmonic currents that flow in the distribution network.Harmonic voltages are caused by the flow of harmonic currents through theimpedances of the supply circuits (transformer and distribution network for situationssimilar to that shown in Figure M2).AZ hI hBNon-linearloadFig. M2 : Single-line diagram showing the impedance of the supply circuit for a harmonic of order hMThe reactance of a conductor increases as a function of the frequency of the currentflowing through the conductor. For each harmonic current (order h), there is thereforean impedance Zh in the supply circuit.When the harmonic current of order h flows through impedance Zh, it creates aharmonic voltage Uh, where Uh = Zh x Ih (Ohm law). The voltage at point B istherefore distorted. All devices supplied via point B receive a distorted voltage.For a given harmonic current, the distortion is proportional to the impedance in thedistribution network.Flow of harmonic currents in distribution networksThe non-linear loads can be considered to reinject the harmonic currents upstreaminto the distribution network, toward the source.Figures M3 and M4 next page show an installation disturbed by harmonics. FigureM3 shows the flow of the current at 50 Hz in the installation and Figure M4 showsthe harmonic current (order h).© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

M - Harmonic management3 GeneralZ lI 50 HzNon-linearloadFig. M3 : Installation supplying a non-linear load, where only the phenomena concerning the50 Hz frequency (fundamental frequency) are shownZ hI hNon-linearloadV hVh = Harmonic voltage= Z hx I hFig. M4 : Same installation, where only the phenomena concerning the frequency of harmonicorder h are shownSupply of the non-linear load creates the flow of a current I 50Hz (shown infigure M3), to which is added each of the harmonic currents Ih (shown in figure M4),corresponding to each harmonic order h.Still considering that the loads reinject harmonic current upstream into thedistribution network, it is possible to create a diagram showing the harmonic currentsin the network (see Fig. M5).Backup powersupplyGIh aRectifierArc furnaceWelding machinePower-factorcorrectionIh bVariable-speed driveMV/LVAIh dFluorescent ordischarge lampsMIh eDevices drawing rectifiedcurrent (televisions,computer hardware, etc.)Harmonicdisturbances todistribution networkand other users(do not createharmonics)Linear loadsNote in the diagram that though certain loads create harmonic currents in the distributionnetwork, other loads can absorb the harmonic currents.Fig. M5 : Flow of harmonic currents in a distribution networkHarmonics have major economic effects in installations:b Increases in energy costsb Premature ageing of equipmentb Production losses© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

M - Harmonic management4 Main effects of harmonics ininstallations4.1 ResonanceThe simultaneous use of capacitive and inductive devices in distribution networksresults in parallel or series resonance manifested by very high or very lowimpedance values respectively. The variations in impedance modify the current andvoltage in the distribution network. Here, only parallel resonance phenomena, themost common, will be discussed.Consider the following simplified diagram (see Fig. M6) representing an installationmade up of:b A supply transformerb Linear loadsb Non-linear loads drawing harmonic currentsb Power factor correction capacitorsFor harmonic analysis, the equivalent diagram (see Fig. M7) is shown below.Impedance Z is calculated by:Z=jLsω1-LsCω2neglecting R and where:Ls = Supply inductance (upstream network + transformer + line)C = Capacitance of the power factor correction capacitorsR = Resistance of the linear loadsIh = Harmonic currentResonance occurs when the denominator 1-LsCw 2 tends toward zero. Thecorresponding frequency is called the resonance frequency of the circuit. At thatfrequency, impedance is at its maximum and high amounts of harmonic voltagesappear with the resulting major distortion in the voltage. The voltage distortion isaccompanied, in the Ls+C circuit, by the flow of harmonic currents greater thanthose drawn by the loads.The distribution network and the power factor correction capacitors are subjected tohigh harmonic currents and the resulting risk of overloads. To avoid resonance, antiharmoniccoils can be installed in series with the capacitors.4.2 Increased lossesI hLosses in conductorsMCThe active power transmitted to a load is a function of the fundamental component I1of the current.When the current drawn by the load contains harmonics, the rms value of thecurrent, Irms, is greater than the fundamental I1.The definition of THD being:Non-linearloadCapacitorbankLinearloadTHD =2⎛ Irms⎞⎜ ⎟ −1⎝ I1⎠Fig. M6 : Diagram of an installationLs C R Ihit may be deduced that: Irms = I1 1+ THD 2Figure M8 (next page) shows, as a function of the harmonic distortion:b The increase in the rms current Irms for a load drawing a given fundamentalcurrentb The increase in Joule losses, not taking into account the skin effect(The reference point in the graph is 1 for Irms and Joules losses, the case whenthere are no harmonics)The harmonic currents provoke an increase in the Joule losses in all conductors inwhich they flow and additional temperature rise in transformers, devices, cables, etc.© Schneider Electric - all rights reservedZFig. M7 : Equivalent diagram of the installation shown inFigure M6Losses in asynchronous machinesThe harmonic voltages (order h) supplied to asynchronous machines provoke in therotor the flow of currents with frequencies higher than 50 Hz that are the cause ofadditional losses.Schneider Electric - Electrical installation guide 2009

M - Harmonic management4 Main effects of harmonics ininstallations2.221.81.61.41.210.8 THD0 20 40 60 80 100 120 (%)Joules lossesIrmsFig. M8 : Increase in rms current and Joule losses as a function of the THDOrders of magnitudeb A virtually rectangular supply voltage provokes a 20% increase in lossesb A supply voltage with harmonics u5 = 8% (of U1, the fundamental voltage),u7 = 5%, u11 = 3%, u13 = 1%, i.e. total harmonic distortion THDu equal to 10%,results in additional losses of 6%Losses in transformersHarmonic currents flowing in transformers provoke an increase in the “copper”losses due to the Joule effect and increased “iron” losses due to eddy currents. Theharmonic voltages are responsible for “iron” losses due to hysteresis.It is generally considered that losses in windings increase as the square of the THDiand that core losses increase linearly with the THDu.In utility-distribution transformers, where distortion levels are limited, losses increasebetween 10 and 15%.Losses in capacitorsThe harmonic voltages applied to capacitors provoke the flow of currentsproportional to the frequency of the harmonics. These currents cause additionallosses.ExampleA supply voltage has the following harmonics:Fundamental voltage U1, harmonic voltages u5 = 8% (of U1), u7 = 5%, u11 = 3%,u13 = 1%, i.e. total harmonic distortion THDu equal to 10%. The amperage of thecurrent is multiplied by 1.19. Joule losses are multiplied by 1.19 2 , i.e. 1.4.M4.3 Overloads on equipmentGeneratorsGenerators supplying non-linear loads must be derated due to the additional lossescaused by harmonic currents.The level of derating is approximately 10% for a generator where the overall loadis made up of 30% of non-linear loads. It is therefore necessary to oversize thegenerator.Uninterruptible power systems (UPS)The current drawn by computer systems has a very high crest factor. A UPS sizedtaking into account exclusively the rms current may not be capable of supplying thenecessary peak current and may be overloaded.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

M - Harmonic management4 Main effects of harmonics ininstallationsTransformersb The curve presented below (see Fig. M9) shows the typical derating required for atransformer supplying electronic loadskVA(%)10090807060504030201000 20 40 60 80 100%ElectronicloadFig. M9 : Derating required for a transformer supplying electronic loadsExampleIf the transformer supplies an overall load comprising 40% of electronic loads, it mustbe derated by 40%.b Standard UTE C15-112 provides a derating factor for transformers as a function ofthe harmonic currents.k =1⎛ 40 ⎞1.6 21+0.1 ⎜ ∑hT h ⎟⎝ h=2 ⎠MT h = I Ih1Typical values:b Current with a rectangular waveform (1/h spectrum (1) ): k = 0.86b Frequency-converter current (THD ≈ 50%): k = 0.80Asynchronous machinesStandard IEC 60892 defines a weighted harmonic factor (Harmonic voltage factor)for which the equation and maximum value are provided below.HVF =13Uh∑ i 0.02 h2h=2ExampleA supply voltage has a fundamental voltage U1 and harmonic voltages u3 = 2% ofU1, u5 = 3%, u7 = 1%. The THDu is 3.7% and the MVF is 0.018. The MVF valueis very close to the maximum value above which the machine must be derated.Practically speaking, for supply to the machine, a THDu of 10% must not beexceeded.© Schneider Electric - all rights reserved(1) In fact, the current waveform is similar to a rectangularwaveform. This is the case for all current rectifiers (three-phaserectifiers, induction furnaces).CapacitorsAccording to IEC 60831-1 standard, the rms current flowing in the capacitors mustnot exceed 1.3 times the rated current.Using the example mentioned above, the fundamental voltage U1, harmonic voltagesvoltages u5 = 8% u5 (of = U1), 8% u7 (of = U1), 5%, u7 u11 = 5%, = 3%, u11 u13 = 3%, = 1%, u13 i.e. = total 1%, harmonic i.e. total harmonicdistortion THDu equal to 10%, the result is I rmsI1 = 1 . 19 ,, at at the the rated voltage. For For avoltage equal equal to to 1.1 1.1 times the the rated voltage, the current limit I rmsI1 = 1 . 3is reachedand it is necessary to resize the capacitors.Schneider Electric - Electrical installation guide 2009

M - Harmonic management4 Main effects of harmonics ininstallationsNeutral conductorsConsider a system made up of a balanced three-phase source and three identicalsingle-phase loads connected between the phases and the neutral (see Fig. M10).Figure M11 shows an example of the currents flowing in the three phases and theresulting current in the neutral conductor.In this example, the current in the neutral conductor has an rms value that is higherthan the rms value of the current in a phase by a factor equal to the square root of 3.The neutral conductor must therefore be sized accordingly.Ir(A)tIstIttInMt020 40t (ms)Fig. M11 : Example of the currents flowing in the various conductors connected to a three-phaseload (In = Ir + Is + It)I rLoadI sI tI nLoadLoadFig. M10 : Flow of currents in the various conductorsconnected to a three-phase source4.4 Disturbances affecting sensitive loadsEffects of distortion in the supply voltageDistortion of the supply voltage can disturb the operation of sensitive devices:b Regulation devices (temperature)b Computer hardwareb Control and monitoring devices (protection relays)Distortion of telephone signalsHarmonics cause disturbances in control circuits (low current levels). The level ofdistortion depends on the distance that the power and control cables run in parallel,the distance between the cables and the frequency of the harmonics.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

M - Harmonic management4 Main effects of harmonics ininstallations4.5 Economic impactEnergy lossesHarmonics cause additional losses (Joule effect) in conductors and equipment.Higher subscription costsThe presence of harmonic currents can require a higher subscribed power level andconsequently higher costs.What is more, utilities will be increasingly inclined to charge customers for majorsources of harmonics.Oversizing of equipmentb Derating of power sources (generators, transformers and UPSs) means they mustbe oversizedb Conductors must be sized taking into account the flow of harmonic currents.In addition, due the the skin effect, the resistance of these conductors increaseswith frequency. To avoid excessive losses due to the Joule effect, it is necessary tooversize conductorsb Flow of harmonics in the neutral conductor means that it must be oversized as wellReduced service life of equipmentWhen the level of distortion in the supply voltage approaches 10%, the durationof the service life of equipment is significantly reduced. The reduction has beenestimated at:b 32.5% for single-phase machinesb 18% for three-phase machinesb 5% for transformersTo maintain the service lives corresponding to the rated load, equipment must beoversized.Nuisance tripping and installation shutdownCircuit-breakers in the installation are subjected to current peaks caused byharmonics.These current peaks cause nuisance tripping with the resulting production losses, aswell as the costs corresponding to the time required to start the installation up again.M10ExamplesGiven the economic consequences for the installations mentioned below, it wasnecessary to install harmonic filters.Computer centre for an insurance companyIn this centre, nuisance tripping of a circuit-breaker was calculated to have cost100 k€ per hour of down time.Pharmaceutical laboratoryHarmonics caused the failure of a generator set and the interruption of a longdurationtest on a new medication. The consequences were a loss estimated at17 M€.Metallurgy factoryA set of induction furnaces caused the overload and destruction of threetransformers ranging from 1500 to 2500 kVA over a single year. The cost of theinterruptions in production were estimated at 20 k€ per hour.Factory producing garden furnitureThe failure of variable-speed drives resulted in production shutdowns estimated at10 k€ per hour.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

M - Harmonic management5 Essential indicators of harmonicdistortion and measurementprinciplesA number of indicators are used to quantify and evaluate the harmonic distortionin current and voltage waveforms, namely:b Power factorb Crest factorb Distortion powerb Harmonic spectrumb Harmonic-distortion valuesThese indicators are indispensable in determining any necessary corrective action.5.1 Power factorDefinitionThe power factor PF is the ratio between the active power P and the apparentpower S.PF =P SAmong electricians, there is often confusion with:P1cos ϕ =S1WhereWhereP1 = active power of the fundamentalS1 = apparent power of the fundamentalThe cos ϕ concerns exclusively the fundamental frequency and therefore differsfrom the power factor PF when there are harmonics in the installation.Interpreting the power factorAn initial indication that there are significant amounts of harmonics is a measuredpower factor PF that is different (lower) than the measured cos ϕ.5.2 Crest factorDefinitionThe crest factor is the ratio between the value of the peak current or voltage (Im orUm) and its rms value.b For a sinusoidal signal, the crest factor is therefore equal to 2.b For a non-sinusoidal signal, the crest factor can be either greater than or lessthan 2.In the latter case, the crest factor signals divergent peak values with respect to therms value.M11Interpretation of the crest factorThe typical crest factor for the current drawn by non-linear loads is much higherthan 2. It is generally between 1.5 and 2 and can even reach 5 in critical cases.A high crest factor signals high transient overcurrents which, when detected byprotection devices, can cause nuisance tripping.5.3 Power values and harmonicsActive powerThe active power P of a signal comprising harmonics is the sum of the activepowers resulting from the currents and voltages of the same order.Reactive powerReactive power is defined exclusively in terms of the fundamental, i.e.Q = U1 x I1 x sinϕ1Distortion powerWhen harmonics are present, the distortion power D is defined asD = (S 2 - P 2 - Q 2 ) 1/2 where S is the apparent power.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

M - Harmonic management5 Essential indicators of harmonicdistortion and measurementprinciples5.4 Harmonic spectrum and harmonic distortionPrincipleEach type of device causing harmonics draws a particular form of harmonic current(amplitude and phase displacement).These values, notably the amplitude for each harmonic order, are essential foranalysis.Individual harmonic distortion (or harmonic distortion oforder h)The individual harmonic distortion is defined as the percentage of harmonics fororder h with respect to the fundamental.( ) =u % 100 U hhU1orIi h % 100 h( ) =I1Harmonic spectrumBy representing the amplitude of each harmonic order with respect to its frequency, itis possible to obtain a graph called the harmonic spectrum.Figure M12 shows an example of the harmonic spectrum for a rectangular signal.Rms valueThe rms value of the voltage and current can be calculated as a function of the rmsvalue of the various harmonic orders.U(t)Irms=andUrms=∞∑Ih 2h=1∞∑Uh 2h=115.5 Total harmonic distortion (THD)M12tThe term THD means Total Harmonic Distortion and is a widely used notion indefining the level of harmonic content in alternating signals.Definition of THDFor a signal y, the THD is defined as:© Schneider Electric - all rights reserved1003320H %012 3 4 5 6Fig. M12 : Harmonic spectrum of a rectangular signal, for avoltage U (t)h∞∑yh 2h=2THD =y1This complies with the definition given in standard IEC 61000-2-2.Note that the value can exceed 1.According to the standard, the variable h can be limited to 50. The THD is the meansto express as a single number the distortion affecting a current or voltage flowing at agiven point in the installation.The THD is generally expressed as a percentage.Current or voltage THDFor current harmonics, the equation is:∞∑Ih 2h=2THD i =I1Schneider Electric - Electrical installation guide 2009

M - Harmonic management5 Essential indicators of harmonicdistortion and measurementprinciples1.210.80.60.40.2PFcos ϕ050Figure L13 Fig. shows M13 : a Variation graph of inTHDu = 0PFcosϕ100150THDi(%)as a function of THDI.as a function of the THDi, whereThe equation below is equivalent to the above, but easier and more direct when thetotal rms value is available:THD i = ⎛ 2I ⎞⎝ ⎜ rms⎟ −1I1⎠For voltage harmonics, the equation is:THDu=∞∑Uh 2h=2U1Relation between power factor and THD (see Fig. M13)When the voltage is sinusoidal or virtually sinusoidal, it may be said that:P ≈ P1 = U 1. I1.cosϕ1Consequently : PF = P U 1. I1.cosϕ≈1S U 1.Irmsas:II1 =rmshence: PF ≈121+ THDicosϕ 121+ THDiFigure M13 L13 shows a graph ofPFcosϕas a function of THDi. THDI.5.6 Usefulness of the various indicatorsThe THDu characterises the distortion of the voltage wave.Below are a number of THDu values and the corresponding phenomena in theinstallation:b THDu under 5% - normal situation, no risk of malfunctionsb 5 to 8% - significant harmonic pollution, some malfunctions are possibleb Higher than 8% - major harmonic pollution, malfunctions are probable. In-depthanalysis and the installation of attenuation devices are requiredThe THDi characterises the distortion of the current wave.The disturbing device is located by measuring the THDi on the incomer and eachoutgoer of the various circuits and thus following the harmonic trail.Below are a number of THDi values and the corresponding phenomena in theinstallation:b THDi under 10% - normal situation, no risk of malfunctionsb 10 to 50% - significant harmonic pollution with a risk of temperature rise and theresulting need to oversize cables and sourcesb Higher than 50% - major harmonic pollution, malfunctions are probable. In-depthanalysis and the installation of attenuation devices are requiredPower factor PFUsed to evaluate the necessary oversizing for the power source of the installation.Crest factorUsed to characterise the aptitude of a generator (or UPS) to supply highinstantaneous currents. For example, computer equipment draws highly distortedcurrent for which the crest factor can reach 3 to 5.Spectrum (decomposition of the signal into frequencies)It provides a different representation of electrical signals and can be used to evaluatetheir distortion.M13© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

M - Harmonic management6 Measuring the indicators6.1 Devices used to measure the indicatorsDevice selectionThe traditional observation and measurement methods include:b Observations using an oscilloscopeAn initial indication on the distortion affecting a signal can be obtained by viewing thecurrent or the voltage on an oscilloscope.The waveform, when it diverges from a sinusoidal, clearly indicates the presence ofharmonics. Current and voltage peaks can be viewed.Note, however, that this method does not offer precise quantification of the harmoniccomponentsb Analogue spectral analysersThey are made up of passband filters coupled with an rms voltmeter. They offermediocre performance and do not provide information on phase displacement.Only the recent digital analysers can determine sufficiently precisely thevalues of all the mentioned indicators.Functions of digital analysersThe microprocessors in digital analysers:b Calculate the values of the harmonic indicators (power factor, crest factor,distortion power, THD)b Carry out various complementary functions (corrections, statistical detection,measurement management, display, communication, etc.)b In multi-channel analysers, supply virtually in real time the simultaneous spectraldecomposition of the currents and voltagesAnalyser operation and data processingThe analogue signals are converted into a series of numerical values.Using this data, an algorithm implementing the Fast Fourier Transform (FFT)calculates the amplitudes and the phases of the harmonics over a large number oftime windows.Most digital analysers measure harmonics up to order 20 or 25 when calculating theTHD.Processing of the successive values calculated using the FFT (smoothing,classification, statistics) can be carried out by the measurement device or by externalsoftware.M146.2 Procedures for harmonic analysis of distributionnetworksMeasurements are carried out on industrial or commercial site:b Preventively, to obtain an overall idea on distribution-network status (network map)b In view of corrective action:v To determine the origin of a disturbance and determine the solutions required toeliminate itv To check the validity of a solution (followed by modifications in the distributionnetwork to check the reduction in harmonics)© Schneider Electric - all rights reservedOperating modeThe current and voltage are studied:b At the supply sourceb On the busbars of the main distribution switchboard (or on the MV busbars)b On each outgoing circuit in the main distribution switchboard (or on theMV busbars)For the measurements, it is necessary to know the precise operating conditionsof the installation and particularly the status of the capacitor banks (operating, notoperating, the number of disconnected steps).Analysis resultsb Determine any necessary derating of equipment in the installation orb Quantify any necessary harmonic protection and filtering systems to be installed inthe distribution networkb Enable comparison between the measured values and the reference values of theutility (maximum harmonic values, acceptable values, reference values)Schneider Electric - Electrical installation guide 2009

M - Harmonic management6 Measuring the indicatorsUse of measurement devicesMeasurement devices serve to show both the instantaneous and long-term effects ofharmonics. Analysis requires values spanning durations ranging from a few secondsto several minutes over observation periods of a number of days.The required values include:b The amplitudes of the harmonic currents and voltagesb The individual harmonic content of each harmonic order of the current and voltageb The THD for the current and voltageb Where applicable, the phase displacement between the harmonic voltage andcurrent of the same harmonic order and the phase of the harmonics with respect to acommon reference (e.g. the fundamental voltage)6.3 Keeping a close eye on harmonicsThe harmonic indicators can be measured:b Either by devices permanently installed in the distribution networkb Or by an expert present at least a half day on the site (limited perception)Permanent devices are preferableFor a number of reasons, the installation of permanent measurement devices in thedistribution network is preferable.b The presence of an expert is limited in time. Only a number of measurements atdifferent points in the installation and over a sufficiently long period (one week to amonth) provide an overall view of operation and take into account all the situationsthat can occur following:v Fluctuations in the supply sourcev Variations in the operation of the installationv The addition of new equipment in the installationb Measurement devices installed in the distribution network prepare and facilitate thediagnosis of the experts, thus reducing the number and duration of their visitsb Permanent measurement devices detect any new disturbances arising followingthe installation of new equipment, the implementation of new operating modes orfluctuations in the supply networkTake advantage of built-in measurement and detection devicesMeasurement and detection devices built into the electrical distribution equipment:b For an overall evaluation of network status (preventive analysis), avoid:v Renting measurement equipmentv Calling in expertsv Having to connect and disconnect the measurement equipment.For the overall evaluation of network status, the analysis on the main low-voltagedistribution switchboards (MLVS) can often be carried out by the incoming deviceand/or the measurement devices equipping each outgoing circuitb For corrective action, are the means to:v Determine the operating conditions at the time of the incidentv Draw up a map of the distribution network and evaluate the implemented solutionThe diagnosis is improved by the use of equipment intended for the studied problem.M15© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

M - Harmonic management7 Detection devicesM16PowerLogic System with Power Meter andCircuit Monitor, Micrologic offer a completerange of devices for the detection of harmonicdistortionFig. M14 : Circuit monitorMeasurements are the first step in gaining control over harmonic pollution.Depending on the conditions in each installation, different types of equipmentprovide the necessary solution.Power-monitoring unitsPower Meter and Circuit Monitor in the PowerLogic SystemThese products offer high-performance measurement capabilities for low andmedium-voltage distribution networks. They are digital units that include powerqualitymonitoring functions.PowerLogic System is a complete offer comprising Power Meter (PM) and CircuitMonitor (CM). This highly modular offer covers needs ranging from the most simple(Power Meter) up to highly complex requirements (Circuit Monitor). These productscan be used in new or existing installations where the level of power quality must beexcellent. The operating mode can be local and/or remote.Depending on its position in the distribution network, a Power Meter provides an initialindication on power quality. The main measurements carried out by a Power Meter are:b Current and voltage THDb Power factorDepending on the version, these measurements can be combined with timestampingand alarm functions.A Circuit Monitor (see Fig. M14) carries out a detailed analysis of power qualityand also analyses disturbances on the distribution network. The main functions of aCircuit Monitor are:b Measurement of over 100 electrical parametersb Storage in memory and time-stamping of minimum and maximum values for eachelectrical parameterb Alarm functions tripped by electrical parameter valuesb Recording of event datab Recording of current and voltage disturbancesb Harmonic analysisb Waveform capture (disturbance monitoring)Micrologic - a power-monitoring unit built into the circuit-breakerFor new installations, the Micrologic H control unit (see Fig. M15), an integral partof Masterpact power circuit-breakers, is particularly useful for measurements at thehead of an installation or on large outgoing circuits.The Micrologic H control unit offers precise analysis of power quality and detaileddiagnostics on events. It is designed for operation in conjunction with a switchboarddisplay unit or a supervisor. It can:b Measure current, voltage, active and reactive powerb Measure current and voltage THDb Display the amplitude and phase of current and voltage harmonics up to the 51 st orderb Carry out waveform capture (disturbance monitoring)The functions offered by the Micrologic H control unit are equivalent to those of aCircuit Monitor.© Schneider Electric - all rights reservedFig. M15 : Micrologic H control unit with harmonic metering forMasterpact NT and NW circuit-breakersOperation of power-monitoring unitsSoftware for remote operation and analysisIn the more general framework of a distribution network requiring monitoring,the possibility of interconnecting these various devices can be offered in acommunication network, thus making it possible to centralise information and obtainan overall view of disturbances throughout the distribution network.Depending on the application, the operator can then carry out measurements in realtime, calculate demand values, run waveform captures, anticipate on alarms, etc.The power-monitoring units transmit all the available data over either a Modbus,Digipact or Ethernet network.The essential goal of this system is to assist in identifying and planning maintenancework. It is an effective means to reduce servicing time and the cost of temporarilyinstalling devices for on-site measurements or the sizing of equipment (filters).Supervision software SMSSMS is a very complete software used to analyse distribution networks, in conjunctionwith the products in the PowerLogic System. Installed on a standard PC, it can:b Display measurements in real timeb Display historical logs over a given periodb Select the manner in which data is presented (tables, various curves)b Carry out statistical processing of data (display bar charts)Schneider Electric - Electrical installation guide 2009

M - Harmonic management8 Solutions to attenuateharmonicsThere are three different types of solutions to attenuate harmonics:b Modifications in the installationb Special devices in the supply systemb Filtering8.1 Basic solutionsTo limit the propagation of harmonics in the distribution network, different solutionsare available and should be taken into account particularly when designing a newinstallation.Position the non-linear loads upstream in the systemOverall harmonic disturbances increase as the short-circuit power decreases.All economic considerations aside, it is preferable to connect the non-linear loads asfar upstream as possible (see Fig. M16).Z 2SensitiveloadsZ 1Non-linearloadsWhere impedanceZ 1< Z 2Fig. M16 : Non-linear loads positioned as far upstream as possible (recommended layout)Group the non-linear loadsWhen preparing the single-line diagram, the non-linear devices should be separatedfrom the others (see Fig. M17). The two groups of devices should be supplied bydifferent sets of busbars.M17SensitiveloadsYesLine impedancesNoNon-linearload 1Non-linearload 2Fig. M17 : Grouping of non-linear loads and connection as far upstream as possible(recommended layout)Create separate sourcesIn attempting to limit harmonics, an additional improvement can be obtained bycreating a source via a separate transformer as indicated in the Figure M18 nextpage.The disadvantage is the increase in the cost of the installation.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

M - Harmonic management8 Solutions to attenuateharmonicsNon-linearloadsMVnetworkLinearloadsFig. M18 : Supply of non-linear loads via a separate transformerTransformers with special connectionsDifferent transformer connections can eliminate certain harmonic orders, asindicated in the examples below:b A Dyd connection suppresses 5 th and 7 th harmonics (see Fig. M19)b A Dy connection suppresses the 3 rd harmonicb A DZ 5 connection suppresses the 5 th harmonich11, h13h5, h7, h11, h13h5, h7, h11, h13Fig. M19 : A Dyd transformer blocks propagation of the 5 th and 7 th harmonics to the upstreamnetworkInstall reactorsWhen variable-speed drives are supplied, it is possible to smooth the currentby installing line reactors. By increasing the impedance of the supply circuit, theharmonic current is limited.Installation of harmonic suppression reactors on capacitor banks increases theimpedance of the reactor/capacitor combination for high-order harmonics.This avoids resonance and protects the capacitors.M18Select the suitable system earthing arrangementTNC systemIn the TNC system, a single conductor (PEN) provides protection in the event of anearth fault and the flow of unbalance currents.Under steady-state conditions, the harmonic currents flow in the PEN. The latter,however, has a certain impedance with as a result slight differences in potential (afew volts) between devices that can cause electronic equipment to malfunction.The TNC system must therefore be reserved for the supply of power circuits at thehead of the installation and must not be used to supply sensitive loads.TNS systemThis system is recommended if harmonics are present.The neutral conductor and the protection conductor PE are completely separate andthe potential throughout the distribution network is therefore more uniform.8.2 Harmonic filtering© Schneider Electric - all rights reservedIn cases where the preventive action presented above is insufficient, it is necessaryto equip the installation with filtering systems.There are three types of filters:b Passiveb Activeb HybridSchneider Electric - Electrical installation guide 2009

M - Harmonic management8 Solutions to attenuateharmonicsI harNon-linearloadFig. M20 : Operating principle of a passive filterI harNon-linearloadFilterAHCFig. M22 : Operating principle of a hybrid filterIsIactFig. M21 : Operating principle of an active filterI harNon-linearloadAHCIactHybride filterLinearloadIsLinearloadPassive filtersTypical applicationsb Industrial installations with a set of non-linear loads representing more than200 kVA (variable-speed drives, UPSs, rectifiers, etc.)b Installations requiring power-factor correctionb Installations where voltage distortion must be reduced to avoid disturbing sensitiveloadsb Installations where current distortion must be reduced to avoid overloadsOperating principleAn LC circuit, tuned to each harmonic order to be filtered, is installed in parallel withthe non-linear load (see Fig. M20). This bypass circuit absorbs the harmonics, thusavoiding their flow in the distribution network.Generally speaking, the passive filter is tuned to a harmonic order close to the orderto be eliminated. Several parallel-connected branches of filters can be used if asignificant reduction in the distortion of a number of harmonic orders is required.Active filters (active harmonic conditioner)Typical applicationsb Commercial installations with a set of non-linear loads representing less than200 kVA (variable-speed drives, UPSs, office equipment, etc.)b Installations where current distortion must be reduced to avoid overloads.Operating principleThese systems, comprising power electronics and installed in series or parallel withthe non-linear load, compensate the harmonic current or voltage drawn by the load.Figure M21 shows a parallel-connected active harmonic conditioner (AHC)compensating the harmonic current (Ihar = -Iact).The AHC injects in opposite phase the harmonics drawn by the non-linear load, suchthat the line current Is remains sinusoidal.Hybrid filtersTypical applicationsb Industrial installations with a set of non-linear loads representing more than200 kVA (variable-speed drives, UPSs, rectifiers, etc.)b Installations requiring power-factor correctionb Installations where voltage distortion must be reduced to avoid disturbing sensitiveloadsb Installations where current distortion must be reduced to avoid overloadsb Installations where strict limits on harmonic emissions must be metOperating principlePassive and active filters are combined in a single system to constitute a hybrid filter(see Fig. M22). This new filtering solution offers the advantages of both types offilters and covers a wide range of power and performance levels.Selection criteriaPassive filterIt offers both power-factor correction and high current-filtering capacity.Passive filters also reduce the harmonic voltages in installations where the supplyvoltage is disturbed. If the level of reactive power supplied is high, it is advised to turnoff the passive filter at times when the percent load is low.Preliminary studies for a filter must take into account the possible presence of apower factor correction capacitor bank which may have to be eliminated.Active harmonic conditionersThey filter harmonics over a wide range of frequencies and can adapt to any type ofload.On the other hand, power ratings are low.Hybrid filtersThey combine the performance of both active and passive filters.M19© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

M - Harmonic management8 Solutions to attenuateharmonicsA complete set of services can be offered toeliminate harmonics:b Installation analysisb Measurement and monitoring systemsb Filtering solutions8.3 The methodThe best solution, in both technical and financial terms, is based on the results of anin-depth study.Harmonic audit of MV and LV networksBy calling on an expert, you are guaranteed that the proposed solution will produceeffective results (e.g. a guaranteed maximum THDu).A harmonic audit is carried out by an engineer specialised in the disturbancesaffecting electrical distribution networks and equipped with powerful analysis andsimulation equipment and software.The steps in an audit are the following:b Measurement of disturbances affecting current and phase-to-phase and phaseto-neutralvoltages at the supply source, the disturbed outgoing circuits and thenon-linear loadsb Computer modelling of the phenomena to obtain a precise explanation of thecauses and determine the best solutionsb A complete audit report presenting:v The current levels of disturbancesv The maximum permissible levels of disturbances (IEC 61000, IEC 34, etc.)b A proposal containing solutions with guaranteed levels of performanceb Finally, implementation of the selected solution, using the necessary means andresources.The entire audit process is certified ISO 9002.M208.4 Specific productsPassive filtersPassive filters are made up of coils and capacitors set up in resonant circuits tunedto the specific harmonic order that must be eliminated.A system may comprise a number of filters to eliminate several harmonic orders.Suitable for 400 V three-phase voltages, the power ratings can reach:b 265 kvar / 470 A for harmonic order 5b 145 kvar / 225 A for harmonic order 7b 105 kvar / 145 A for harmonic order 11Passive filters can be created for all voltage and current levels.Active filtersb SineWave active harmonic conditionersv Suitable for 400 V three-phase voltages, they can deliver between 20 and 120 Aper phasev SineWave covers all harmonic orders from 2 to 25. Conditioning can be total ortarget specific harmonic ordersv Attenuation: THDi load / THDi upstream greater than 10 at rated capacityv Functions include power factor correction, conditioning of zero-sequenceharmonics, diagnostics and maintenance system, parallel connection, remotecontrol, Ibus/RS485 communication interfaceb Accusine active filtersv Suitable for 400 and 480 V three-phase voltages, they can filter between 50 and 30A per phasev All harmonic orders up to 50 are filteredv Functions include power factor correction, parallel connection, instantaneousresponse to load variationsHybrid filtersThese filters combine the advantages of both a passive filter and the SineWaveactive harmonic conditioner in a single system.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Chapter NCharacteristics of particularsources and loads12345ContentsProtection of a LV generator setand the downstream circuits1.1 Generator protection N21.2 Downstream LV network protection N51.3 The monitoring functions N51.4 Generator Set parallel-connection N10Uninterruptible Power Supply units (UPS)N112.1 Availability and quality of electrical power N112.2 Types of static UPSs N122.3 Batteries N152.4 System earthing arrangements for installations comprising UPSs N162.5 Choice of protection schemes N182.6 Installation, connection and sizing of cables N202.7 The UPSs and their environment N222.8 Complementary equipment N22Protection of LV/LV transformersN243.1 Transformer-energizing inrush current N243.2 Protection for the supply circuit of a LV/LV transformer N243.3 Typical electrical characteristics of LV/LV 50 Hz transformers N253.4 Protection of LV/LV transformers, using Merlin Gerincircuit-breakersN25Lighting circuitsN274.1 The different lamp technologies N274.2 Electrical characteristics of lamps N294.3 Constraints related to lighting devices and recommendations N344.4 Lighting of public areas N42Asynchronous motorsN455.1 Functions for the motor circuit N455.2 Standards N475.3 Applications N495.4 Maximum rating of motors installed for consumers supplied at LV N545.5 Reactive-energy compensation (power-factor correction) N54N2N© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads1 Protection of a LV generator setand the downstream circuitsMost industrial and large commercial electrical installations include certain importantloads for which a power supply must be maintained, in the event that the utilityelectrical supply fails:b Either, because safety systems are involved (emergency lighting, automatic fireprotectionequipment, smoke dispersal fans, alarms and signalization, and so on…) orb Because it concerns priority circuits, such as certain equipment, the stoppage ofwhich would entail a loss of production, or the destruction of a machine tool, etc.One of the current means of maintaining a supply to the so-called “priority” loads, inthe event that other sources fail, is to install a diesel generator set connected, via achange-over switch, to an emergency-power standby switchboard, from which thepriority services are fed (see Fig. N1).HVLVGChange-over switchNon-priority circuitsPriority circuitsFig N1 : Example of circuits supplied from a transformer or from an alternator1.1 Generator protectionFigure N2 below shows the electrical sizing parameters of a Generator Set. Pn, Unand In are, respectively, the power of the thermal motor, the rated voltage and therated current of the generator.Un, InNThermalmotorPnRSTt (s)Fig N2 : Block diagram of a generator setN© Schneider Electric - all rights reserved1,000100121073210IIn0 1.1 1.2 1.5 2 3 4 5OverloadsFig N3 : Example of an overload curve t = f(I/In)Overload protectionThe generator protection curve must be analysed (see Fig. N3).Standards and requirements of applications can also stipulate specific overloadconditions. For example:I/Int1.1 > 1 h1.5 30 sThe setting possibilities of the overload protection devices (or Long Time Delay) willclosely follow these requirements.Note on overloadsb For economic reasons, the thermal motor of a replacement set may be strictly sizedfor its nominal power. If there is an active power overload, the diesel motor will stall.The active power balance of the priority loads must take this into accountb A production set must be able to withstand operating overloads:v One hour overloadv One hour 10% overload every 12 hours (Prime Power)Schneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads1 Protection of a LV generator setand the downstream circuitsShort-circuit current protectionMaking the short-circuit currentThe short-circuit current is the sum:b Of an aperiodic currentb Of a damped sinusoidal currentThe short-circuit current equation shows that it is composed of three successivephases (see Fig. N4).I rms1 2 31 - Subtransient conditions2 - Transient conditions3 - Steady state conditions≈ 3 InGenerator with compoundexcitation or over-excitationIn≈ 0.3 In0010 to 20 msFault appears0.1 to 0.3 sGenerator with serialexcitationt (s)Fig N4 : Short-circuit current level during the 3 phasesb Subtransient phaseWhen a short-circuit appears at the terminals of a generator, the current is first madeat a relatively high value of around 6 to 12 In during the first cycle (0 to 20 ms).The amplitude of the short-circuit output current is defined by three parameters:v The subtransient reactance of the generatorv The level of excitation prior to the time of the fault andv The impedance of the faulty circuit.The short-circuit impedance of the generator to be considered is the subtransientreactance x’’d expressed in % by the manufacturer. The typical value is 10 to 15%.We determine the subtransient short-circuit impedance of the generator:2U x′′dX′′ d(ohms) = n where S = 3 Un In100 Sb Transient phaseThe transient phase is placed 100 to 500 ms after the time of the fault. Starting fromthe value of the fault current of the subtransient period, the current drops to 1.5 to2 times the current In.The short-circuit impedance to be considered for this period is the transientreactance x’d expressed in % by the manufacturer. The typical value is 20 to 30%.b Steady state phaseThe steady state occurs after 500 ms.When the fault persists, the output voltage collapses and the exciter regulation seeksto raise this output voltage. The result is a stabilised sustained short-circuit current:v If generator excitation does not increase during a short-circuit (no fieldoverexcitation) but is maintained at the level preceding the fault, the current stabilisesat a value that is given by the synchronous reactance Xd of the generator. The typicalvalue of xd is greater than 200%. Consequently, the final current will be less than thefull-load current of the generator, normally around 0.5 In.v If the generator is equipped with maximum field excitation (field overriding) or withcompound excitation, the excitation “surge” voltage will cause the fault current toincrease for 10 seconds, normally to 2 to 3 times the full-load current of the generator.N© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads1 Protection of a LV generator setand the downstream circuitsCalculating the short-circuit currentManufacturers normally specify the impedance values and time constants requiredfor analysis of operation in transient or steady state conditions (see Fig. N5).(kVA) 75 200 400 800 1,600 2,500x”d 10.5 10.4 12.9 10.5 18.8 19.1x’d 21 15.6 19.4 18 33.8 30.2xd 280 291 358 280 404 292Fig N5 : Example of impedance table (in %)Resistances are always negligible compared with reactances. The parameters for theshort-circuit current study are:b Value of the short-circuit current at generator terminalsShort-circuit current amplitude in transient conditions is:In1Isc3 =(X’d in ohms)X ′ d 3orInIsc3 = 100 (x’d in%)x ′ dUn is the generator phase-to-phase output voltage.Note: This value can be compared with the short-circuit current at the terminals of atransformer. Thus, for the same power, currents in event of a short-circuit close to agenerator will be 5 to 6 times weaker than those that may occur with a transformer(main source).This difference is accentuated still further by the fact that generator set power isnormally less than that of the transformer (see Fig. N6).Source 1MV2,000 kVALVGS500 kVA42 kANC2.5 kAND1NCMain/standbyNOD2Non-priority circuitsPriority circuitsNC: Normally closedNO: Normally open© Schneider Electric - all rights reservedFig N6 : Example of a priority services switchboard supplied (in an emergency) from a standbygenerator setWhen the LV network is supplied by the Main source 1 of 2,000 kVA, the short-circuitcurrent is 42 kA at the main LV board busbar. When the LV network is supplied by theReplacement Source 2 of 500 kVA with transient reactance of 30%, the short-circuitcurrent is made at approx. 2.5 kA, i.e. at a value 16 times weaker than with the Mainsource.Schneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads1 Protection of a LV generator setand the downstream circuits1.2 Downstream LV network protectionPriority circuit protectionChoice of breaking capacityThis must be systematically checked with the characteristics of the main source(MV/LV transformer).Setting of the Short Time Delay (STD) tripping currentb Subdistribution boardsThe ratings of the protection devices for the subdistribution and final distributioncircuits are always lower than the generator rated current. Consequently, except inspecial cases, conditions are the same as with transformer supply.b Main LV switchboardv The sizing of the main feeder protection devices is normally similar to that of thegenerator set. Setting of the STD must allow for the short-circuit characteristic of thegenerator set (see “Short-circuit current protection” before)v Discrimination of protection devices on the priority feeders must be providedin generator set operation (it can even be compulsory for safety feeders). It isnecessary to check proper staggering of STD setting of the protection devices ofthe main feeders with that of the subdistribution protection devices downstream(normally set for distribution circuits at 10 In).Note: When operating on the generator set, use of a low sensitivity ResidualCurrent Device enables management of the insulation fault and ensures very simplediscrimination.Safety of peopleIn the IT (2 nd fault) and TN grounding systems, protection of people against indirectcontacts is provided by the STD protection of circuit-breakers. Their operation ona fault must be ensured, whether the installation is supplied by the main source(Transformer) or by the replacement source (generator set).Calculating the insulation fault currentZero-sequence reactance formulated as a% of Uo by the manufacturer x’o.The typical value is 8%.The phase-to-neutral single-phase short-circuit current is given by:Un 3I f =2 X′ d + X′oThe insulation fault current in the TN system is slightly greater than the threephase fault current. For example, in event of an insulation fault on the system in theprevious example, the insulation fault current is equal to 3 kA.1.3 The monitoring functionsDue to the specific characteristics of the generator and its regulation, the properoperating parameters of the generator set must be monitored when special loads areimplemented.The behaviour of the generator is different from that of the transformer:b The active power it supplies is optimised for a power factor = 0.8b At less than power factor 0.8, the generator may, by increased excitation, supplypart of the reactive powerNCapacitor bankAn off-load generator connected to a capacitor bank may self-excite, consequentlyincreasing its overvoltage.The capacitor banks used for power factor regulation must therefore be disconnected.This operation can be performed by sending the stopping setpoint to the regulator(if it is connected to the system managing the source switchings) or by opening thecircuit-breaker supplying the capacitors.If capacitors continue to be necessary, do not use regulation of the power factor relayin this case (incorrect and over-slow setting).Motor restart and re-accelerationA generator can supply at most in transient period a current of between 3 and 5 timesits nominal current.A motor absorbs roughly 6 In for 2 to 20 s during start-up.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads1 Protection of a LV generator setand the downstream circuitsIf the sum of the motor power is high, simultaneous start-up of loads generates ahigh pick-up current that can be damaging. A large voltage drop, due to the highvalue of the generator transient and subtransient reactances will occur (20% to30%), with a risk of:b Non-starting of motorsb Temperature rise linked to the prolonged starting time due to the voltage dropb Tripping of the thermal protection devicesMoreover, all the network and actuators are disturbed by the voltage drop.Application (see Fig. N7)A generator supplies a set of motors.Generator characteristics: Pn = 130 kVA at a power factor of 0.8,In = 150 Ax’d = 20% (for example) hence Isc = 750 A.b The Σ Pmotors is 45 kW (45% of generator power)Calculating voltage drop at start-up:Σ PMotors = 45 kW, Im = 81 A, hence a starting current Id = 480 A for 2 to 20 s.Voltage drop on on the the busbar for for simultaneous motor starting:∆U ⎛ Id− In⎞= ⎜ ⎟ in %U ⎝ Isc− In⎠ΔU ∆U = 55%which is is not not tolerable for for motors (failure to to start).b the Σ Pmotors is 20 kW (20% of generator power)Calculating voltage drop at start-up:Σ PMotors = 20 kW, Im = 35 A, hence a starting current Id = 210 A for 2 to 20 s.Voltage drop on the busbar:∆U ⎛ Id− In⎞= ⎜ ⎟ in %U ⎝ Isc− In⎠ΔU ∆U = 10%which is high but tolerable (depending on the type of loads).PLCGNFNRemote control 1F F FRemote control 2MotorsResistive loadsFig N7 : Restarting of priority motors (ΣP > 1/3 Pn)© Schneider Electric - all rights reservedRestarting tipsb If the Pmax of the largest motor > 1 Pn, , a progressive soft starter must starter bemust be3installed on this motorIf the Pmax of the b largest If Σ Pmotors > 1 Pn, , a motor progressive cascade starter restarting must must be be managed by a PLC3b If Σ Pmotors < 1 3 Pn , there are no restarting problemsSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads1 Protection of a LV generator setand the downstream circuitsNon-linear loads – Example of a UPSNon-linear loadsThese are mainly:b Saturated magnetic circuitsb Discharge lamps, fluorescent lightsb Electronic convertersb Information Technology Equipment: PC, computers, etc.These loads generate harmonic currents: supplied by a Generator Set, this cancreate high voltage distortion due to the low short-circuit power of the generator.Uninterruptible Power Supply (UPS) (see Fig. N8)The combination of a UPS and generator set is the best solution for ensuring qualitypower supply with long autonomy for the supply of sensitive loads.It is also a non-linear load due to the input rectifier. On source switching, the autonomyof the UPS on battery must allow starting and connection of the Generator Set.Electrical utilityHV incomerGNCNOMains 1feederMains 2feederBy-passUninterruptiblepower supplyNon-sensitiveloadSensitive feedersFig N8 : Generator set- UPS combination for Quality energyNUPS powerUPS inrush power must allow for:b Nominal power of the downstream loads. This is the sum of the apparent powersPa absorbed by each application. Furthermore, so as not to oversize the installation,the overload capacities at UPS level must be considered (for example: 1.5 In for1 minute and 1.25 In for 10 minutes)b The power required to recharge the battery: This current is proportional to theautonomy required for a given power. The sizing Sr of a UPS is given by:Sr = 1.17 x PnFigure N9 next page defines the pick-up currents and protection devices forsupplying the rectifier (Mains 1) and the standby mains (Mains 2).© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads1 Protection of a LV generator setand the downstream circuitsNominal power Current value (A)Pn (kVA) Mains 1 with 3Ph battery Mains 2 or 3Ph application400 V - I1 400 V - Iu40 86 60.560 123 9180 158 121100 198 151120 240 182160 317 243200 395 304250 493 360300 590 456400 793 608500 990 760600 1,180 912800 1,648 1,215Fig N9 : Pick-up current for supplying the rectifier and standby mainsGenerator Set/UPS combinationb Restarting the Rectifier on a Generator SetThe UPS rectifier can be equipped with a progressive starting of the charger toprevent harmful pick-up currents when installation supply switches to the GeneratorSet (see Fig. N10).Mains 1GS startingt (s)UPS chargerstartingN20 ms5 to 10 sFig N10 : Progressive starting of a type 2 UPS rectifier© Schneider Electric - all rights reservedb Harmonics and voltage distortionTotal voltage distortion τ is defined by:τ(%) =ΣU h 2U1where Uh is the harmonic voltage of order h.This value depends on:v The harmonic currents generated by the rectifier (proportional to the power Sr ofthe rectifier)v The longitudinal subtransient reactance X”d of the generatorv The power Sg of the generatorWe define U′ Rcc(%) = X′′d Srthe generator relative short-circuit voltage, brought toSgrectifier power, i.e. t = f(U’Rcc).Schneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads1 Protection of a LV generator setand the downstream circuitsNote 1: As subtransient reactance is great, harmonic distortion is normally too highcompared with the tolerated value (7 to 8%) for reasonable economic sizing of thegenerator: use of a suitable filter is an appropriate and cost-effective solution.Note 2: Harmonic distortion is not harmful for the rectifier but may be harmful for theother loads supplied in parallel with the rectifier.ApplicationA chart is used to find the distortion τ as a function of U’Rcc (see Fig. N11).τ (%) (Voltage harmonic distortion)181716151413121110987654321001 23 4 5 6 7 8 9 10 11 12Without filterWith filter(incorporated)U'Rcc = X''d SrSgFig N11 : Chart for calculating harmonic distorsionThe chart gives:b Either τ as a function of U’Rccb Or U’Rcc as a function of τFrom which generator set sizing, Sg, is determined.Example: Generator sizingb 300 kVA UPS without filter, subtransient reactance of 15%The power Sr of the rectifier is Sr = 1.17 x 300 kVA = 351 kVAFor a τ < 7%, the chart gives U’Rcc = 4%, power Sg is:Sg =351 x15 4≈ 1,400 kVANcb 300 kVA UPS with filter, subtransient reactance of 15%For τ = 5%, the calculation gives U’Rcc = 12%, power Sg is:Sg = 351 x15 ≈ 500 kVA12Note: With an upstream transformer of 630 kVA on the 300 kVA UPS without filter,the 5% ratio would be obtained.The result is that operation on generator set must be continually monitored forharmonic currents.If voltage harmonic distortion is too great, use of a filter on the network is the mosteffective solution to bring it back to values that can be tolerated by sensitive loads.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads1 Protection of a LV generator setand the downstream circuits1.4 Generator Set parallel-connectionParallel-connection of the generator set irrespective of the application type - Safetysource, Replacement source or Production source - requires finer management ofconnection, i.e. additional monitoring functions.MV incomerParallel operationAs generator sets generate energy in parallel on the same load, they must besynchronised properly (voltage, frequency) and load distribution must be balancedproperly. This function is performed by the regulator of each Generator Set (thermaland excitation regulation). The parameters (frequency, voltage) are monitored beforeconnection: if the values of these parameters are correct, connection can take place.Insulation faults (see Fig. N12)An insulation fault inside the metal casing of a generator set may seriously damagethe generator of this set if the latter resembles a phase-to-neutral short-circuit. Thefault must be detected and eliminated quickly, else the other generators will generateenergy in the fault and trip on overload: installation continuity of supply will no longer beguaranteed. Ground Fault Protection (GFP) built into the generator circuit is used to:b Quickly disconnect the faulty generator and preserve continuity of supplyb Act at the faulty generator control circuits to stop it and reduce the risk of damageThis GFP is of the “Residual Sensing” type and must be installed as close aspossible to the protection device as per a TN-C/TN-S (1) system at each generator setwith grounding of frames by a separate PE. This kind of protection is usually called“Restricted Earth Fault”.FHV busbarFGGenerator no. 1Generator no. 2ProtectedareaRSRSPELVFig N13 : Energy transfer direction – Generator Set as ageneratorUnprotectedareaPEPENPEPENPhasesNN10MV incomerPEFig N12 : Insulation fault inside a generatorFHV busbarFGGenerator Set operating as a load (see Fig. N13 and Fig. N14)One of the parallel-connected generator sets may no longer operate as a generatorbut as a motor (by loss of its excitation for example). This may generate overloadingof the other generator set(s) and thus place the electrical installation out of operation.To check that the generator set really is supplying the installation with power(operation as a generator), the proper flow direction of energy on the coupling busbarmust be checked using a specific “reverse power” check. Should a faultoccur, i.e. the set operates as a motor, this function will eliminate the faulty set.© Schneider Electric - all rights reservedLVFig N14 : Energy transfer direction – Generator Set as a load(1) The system is in TN-C for sets seen as the “generator” andin TN-S for sets seen as “loads”Grounding parallel-connected Generator SetsGrounding of connected generator sets may lead to circulation of earth fault currents(triplen harmonics) by connection of neutrals for common grounding (groundingsystem of the TN or TT type). Consequently, to prevent these currents from flowingbetween the generator sets, we recommend the installation of a decouplingresistance in the grounding circuit.Schneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads2 Uninterruptible Power Supplyunits (UPS)2.1 Availability and quality of electrical powerThe disturbances presented above may affect:b Safety of human lifeb Safety of propertyb The economic viability of a company or production processDisturbances must therefore be eliminated.A number of technical solutions contribute to this goal, with varying degrees ofeffectiveness. These solutions may be compared on the basis of two criteria:b Availability of the power suppliedb Quality of the power suppliedThe availability of electrical power can be thought of as the time per year that poweris present at the load terminals. Availability is mainly affected by power interruptionsdue to utility outages or electrical faults.A number of solutions exist to limit the risk:b Division of the installation so as to use a number of different sources rather thanjust oneb Subdivision of the installation into priority and non-priority circuits, where thesupply of power to priority circuits can be picked up if necessary by another availablesourceb Load shedding, as required, so that a reduced available power rating can be usedto supply standby powerb Selection of a system earthing arrangement suited to service-continuity goals, e.g.IT systemb Discrimination of protection devices (selective tripping) to limit the consequencesof a fault to a part of the installationNote that the only way of ensuring availability of power with respect to utility outagesis to provide, in addition to the above measures, an autonomous alternate source, atleast for priority loads (see Fig. N15).2.5 kA GAlternate sourceN11Non-priority circuitsPriority circuitsFig. N15 : Availability of electrical powerThis source takes over from the utility in the event of a problem, but two factors mustbe taken into account:b The transfer time (time required to take over from the utility) which must beacceptable to the loadb The operating time during which it can supply the loadThe quality of electrical power is determined by the elimination of the disturbances atthe load terminals.An alternate source is a means to ensure the availability of power at the loadterminals, however, it does not guarantee, in many cases, the quality of the powersupplied with respect to the above disturbances.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads2 Uninterruptible Power Supplyunits (UPS)Today, many sensitive electronic applications require an electrical power supplywhich is virtually free of these disturbances, to say nothing of outages, withtolerances that are stricter than those of the utility.This is the case, for example, for computer centers, telephone exchanges and manyindustrial-process control and monitoring systems.These applications require solutions that ensure both the availability and quality ofelectrical power.The UPS solutionThe solution for sensitive applications is to provide a power interface between theutility and the sensitive loads, providing voltage that is:b Free of all disturbances present in utility power and in compliance with the stricttolerances required by loadsb Available in the event of a utility outage, within specified tolerancesUPSs (Uninterruptible Power Supplies) satisfy these requirements in terms of poweravailability and quality by:b Supplying loads with voltage complying with strict tolerances, through use of aninverterb Providing an autonomous alternate source, through use of a batteryb Stepping in to replace utility power with no transfer time, i.e. without any interruptionin the supply of power to the load, through use of a static switchThese characteristics make UPSs the ideal power supply for all sensitive applicationsbecause they ensure power quality and availability, whatever the state of utility power.A UPS comprises the following main components:b Rectifier/charger, which produces DC power to charge a battery and supply aninverterb Inverter, which produces quality electrical power, i.e.v Free of all utility-power disturbances, notably micro-outagesv Within tolerances compatible with the requirements of sensitive electronic devices(e.g. for Galaxy, tolerances in amplitude ± 0.5% and frequency ± 1%, compared to± 10% and ± 5% in utility power systems, which correspond to improvement factorsof 20 and 5, respectively)b Battery, which provides sufficient backup time (8 minutes to 1 hour or more) toensure the safety of life and property by replacing the utility as requiredb Static switch, a semi-conductor based device which transfers the load from theinverter to the utility and back, without any interruption in the supply of power2.2 Types of static UPSsN12© Schneider Electric - all rights reservedTypes of static UPSs are defined by standard IEC 62040.The standard distinguishes three operating modes:b Passive standby (also called off-line)b Line interactiveb Double conversion (also called on-line)These definitions concern UPS operation with respect to the power source includingthe distribution system upstream of the UPS.Standard IEC 62040 defines the following terms:b Primary power: power normally continuously available which is usually supplied byan electrical utility company, but sometimes by the user’s own generationb Standby power: power intended to replace the primary power in the event ofprimary-power failureb Bypass power: power supplied via the bypassPractically speaking, a UPS is equipped with two AC inputs, which are called thenormal AC input and bypass AC input in this guide.b The normal AC input, noted as mains input 1, is supplied by the primary power, i.e.by a cable connected to a feeder on the upstream utility or private distribution systemb The bypass AC input, noted as mains input 2, is generally supplied by standbypower, i.e. by a cable connected to an upstream feeder other than the one supplyingthe normal AC input, backed up by an alternate source (e.g. by an engine-generatorset or another UPS, etc.)When standby power is not available, the bypass AC input is supplied with primarypower (second cable parallel to the one connected to the normal AC input).The bypass AC input is used to supply the bypass line(s) of the UPS, if theyexist. Consequently, the bypass line(s) is supplied with primary or standby power,depending on the availability of a standby-power source.Schneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads2 Uninterruptible Power Supplyunits (UPS)BatteryChargerInverterNormal modeBattery backup modeAC inputLoadFig. N16 : UPS operating in passive standby modeBatteryIf only one AC inputInverterStaticswitchNormal modeBattery backup modeBypass modeNormalAC inputLoadFig. N17 : UPS operating in line-interactive modeFilter/conditionerBypassAC inputBypassUPS operating in passive-standby (off-line) modeOperating principleThe inverter is connected in parallel with the AC input in a standby (see Fig. N16).b Normal modeThe load is supplied by utility power via a filter which eliminates certain disturbancesand provides some degree of voltage regulation (the standard speaks of “additionaldevices…to provide power conditioning”). The inverter operates in passive standbymode.b Battery backup modeWhen the AC input voltage is outside specified tolerances for the UPS or the utilitypower fails, the inverter and the battery step in to ensure a continuous supply ofpower to the load following a very short (

N - Characteristics of particular sources and loads2 Uninterruptible Power Supplyunits (UPS)b Bypass modeThis type of UPS is generally equipped with a static bypass, sometimes referred toas a static switch (see Fig. N18).The load can be transferred without interruption to the bypass AC input (suppliedwith utility or standby power, depending on the installation), in the event of thefollowing:v UPS failurev Load-current transients (inrush or fault currents)v Load peaksHowever, the presence of a bypass assumes that the input and output frequenciesare identical and if the voltage levels are not the same, a bypass transformer isrequired.For certain loads, the UPS must be synchronized with the bypass power to ensureload-supply continuity. What is more, when the UPS is in bypass mode, a disturbanceon the AC input source may be transmitted directly to the load because the inverterno longer steps in.Note: Another bypass line, often called the maintenance bypass, is available formaintenance purposes. It is closed by a manual switch.NormalAC inputBypassAC inputIf only one AC inputBatteryInverterStaticswitch(staticbypass)ManualmaintenancebypassLoadN14Normal modeBattery backup modeBypass modeFig. N18 : UPS operating in double-conversion (on-line) mode© Schneider Electric - all rights reservedUsageIn this configuration, the time required to transfer the load to the inverter is negligibledue to the static switch.Also, the output voltage and frequency do not depend on the input voltage andfrequency conditions. This means that the UPS, when designed for this purpose, canoperate as a frequency converter.Practically speaking, this is the main configuration used for medium and highpower ratings (from 10 kVA upwards).The rest of this chapter will consider only thisconfiguration.Note: This type of UPS is often called “on-line”, meaning that the load is continuouslysupplied by the inverter, regardless of the conditions on the AC input source. Thisterm is misleading, however, because it also suggests “supplied by utility power”,when in fact the load is supplied by power that has been reconstituted by the doubleconversionsystem. That is why standard IEC 62040 recommends the term “doubleconversion”.Schneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads2 Uninterruptible Power Supplyunits (UPS)2.3 BatteriesSelection of battery typeA battery is made up of interconnected cells which may be vented or of therecombination type.There are two main families of batteries:b Nickel-cadmium batteriesb Lead-acid batteriesb Vented cells (lead-antimony): They are equipped with ports tov Release to the atmosphere the oxygen and hydrogen produced during the differentchemical reactionsv Top off the electrolyte by adding distilled or demineralized waterb Recombination cells (lead, pure lead, lead-tin batteries): The gas recombinationrate is at least 95% and they therefore do not require water to be added duringservice lifeBy extension, reference will be made to vented or recombination batteries(recombination batteries are also often called “sealed” batteries).The main types of batteries used in conjunction with UPSs are:b Sealed lead-acid batteries, used 95% of the time because they are easy tomaintain and do not require a special roomb Vented lead-acid batteriesb Vented nickel-cadmium batteriesThe above three types of batteries may be proposed, depending on economic factorsand the operating requirements of the installation, with all the available service-lifedurations.Capacity levels and backup times may be adapted to suit the user’s needs.The proposed batteries are also perfectly suited to UPS applications in that they arethe result of collaboration with leading battery manufacturers.Selection of back up timeSelection depends on:b The average duration of power-system failuresb Any available long-lasting standby power (engine-generator set, etc.)b The type of applicationThe typical range generally proposed is:b Standard backup times of 10, 15 or 30 minutesb Custom backup timesThe following general rules apply:b Computer applicationsBattery backup time must be sufficient to cover file-saving and system-shutdownprocedures required to ensure a controlled shutdown of the computer system.Generally speaking, the computer department determines the necessary backuptime, depending on its specific requirements.b Industrial processesThe backup time calculation should take into account the economic cost incurred byan interruption in the process and the time required to restart.N15Selection tableFigure N19 next page sums up the main characteristics of the various types ofbatteries.Increasingly, recombination batteries would seem to be the market choice for thefollowing reasons:b No maintenanceb Easy implementationb Installation in all types of rooms (computer rooms, technical rooms not specificallyintended for batteries, etc.)In certain cases, however, vented batteries are preferred, notably for:b Long service lifeb Long backup timesb High power ratingsVented batteries must be installed in special rooms complying with preciseregulations and require appropriate maintenance.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads2 Uninterruptible Power Supplyunits (UPS)Service life Compact Operating- Frequency Special Costtemperature of roomtolerances maintenanceSealed lead-acid 5 or 10 years + + Low No Low mediumVented lead-acid 5 or 10 years + ++ Medium Yes LowNickel-cadmium 5 or 10 years ++ +++ High no HighFig. N19 : Main characteristics of the various types of batteriesFig. N20 : Shelf mountingInstallation methodsDepending on the UPS range, the battery capacity and backup time, the battery is:b Sealed type and housed in the UPS cabinetb Sealed type and housed in one to three cabinetsb Vented or sealed type and rack-mounted. In this case the installation method may bev On shelves (see Fig. N20)This installation method is possible for sealed batteries or maintenance-free ventedbatteries which do not require topping up of their electrolyte.v Tier mounting (see Fig. N21)This installation method is suitable for all types of batteries and for vented batteriesin particular, as level checking and filling are made easy.v In cabinets (see Fig. N22)This installation method is suitable for sealed batteries. It is easy to implement andoffers maximum safety.2.4 System earthing arrangements for installationscomprising UPSsN16Fig. N21 : Tier mountingFig. N22 : Cabinet mountingApplication of protection systems, stipulated by the standards, in installationscomprising a UPS, requires a number of precautions for the following reasons:b The UPS plays two rolesv A load for the upstream systemv A power source for downstream systemb When the battery is not installed in a cabinet, an insulation fault on the DC systemcan lead to the flow of a residual DC componentThis component can disturb the operation of certain protection devices, notablyRCDs used for the protection of persons.Protection against direct contact (see Fig. N23)All installations satisfy the applicable requirements because the equipment is housedin cabinets providing a degree of protection IP 20. This is true even for the batterywhen it is housed in a cabinet.When batteries are not installed in a cabinet, i.e. generally in a special room, themeasures presented at the end of this chapter should be implemented.Note: The TN system (version TN-S or TN-C) is the most commonly recommendedsystem for the supply of computer systems.© Schneider Electric - all rights reservedType of arrangement IT system TT system TN systemOperation b Signaling of first insulation fault b Disconnection for first b Disconnection for first insulation faultb Locating and elimination of first fault insulation faultb Disconnection for second insulation faultTechniques for protection b Interconnection and earthing of b Earthing of conductive parts b Interconnection and earthing ofof persons conductive parts combined with use of RCDs conductive parts and neutral imperativeb Surveillance of first fault using an b First insulation fault results in b First insulation fault results ininsulation monitoring device (IMD) interruption by detecting leakage interruption by detecting overcurrentsb Second fault results in circuit interruption currents (circuit-breaker or fuse)(circuit-breaker or fuse)Advantages and b Solution offering the best continuity of b Easiest solution in terms of design b Low-cost solution in terms of installationdisadvantages service (first fault is signalled) and installation b Difficult designb Requires competent surveillance b No insulation monitoring device (calculation of loop impedances)personnel (location of first fault) (IMD) required b Qualified operating personnel requiredb However, each fault results in b Flow of high fault currentsinterruption of the concerned circuitFig. N23 : Main characteristics of system earthing arrangementsSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads2 Uninterruptible Power Supplyunits (UPS)Essential points to be checked for UPSsFigure N24 shows all the essential points that must be interconnected as well as thedevices to be installed (transformers, RCDs, etc.) to ensure installation conformitywith safety standards.T0 neutralT0IMD 1CB0Earth 1CB1CB2T1 neutralT1T2T2 neutralBypassneutralQ1Q4SQ3BPUPS exposedconductivepartsNQ5NUPS outputIMD 2N17DownstreamneutralEarth 2CB3LoadexposedconductivepartsEarth3Fig. N24 : The essential points that must be connected in system earthing arrangements© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads2 Uninterruptible Power Supplyunits (UPS)2.5 Choice of protection schemesThe circuit-breakers have a major role in an installation but their importance oftenappears at the time of accidental events which are not frequent. The best sizing ofUPS and the best choice of configuration can be compromised by a wrong choice ofonly one circuit-breaker.Circuit-breaker selectionFigure N25 shows how to select the circuit-breakers.100IrdownstreamIrupstreamSelect the breaking capacities ofCB1 and CB2 for the short-circuitcurrent of the most powerful source(generally the transformer)GECB2 curveCB3 curveTripping time (in seconds)1010.1ImdownstreamImupstreamGeneratorshort-circuitThermal limitof static powerHowever, CB1 and CB2 musttrip on a short-circuit suppliedby the least powerful source(generally the generator)CB2 must protect the UPS staticswitch if a short circuit occursdownstream of the switchCB1CB20.01CB2The overload capacity of the staticswitch is 10 to 12 In for 20 ms,where In is the current flowingthrough the UPS at full rated loadCB30.0010.1 110 100Energizing ofa transformerEnergizing of allloads downstreamof UPSI/In of upstreamcircuit breakerN18The Im current of CB2 must be calculated for simultaneousenergizing of all the loads downstream of the UPSThe trip unit of CB3 muqt be set not to trip for the overcurrent when the load is energizedCB3If bypass power is not used to handle overloads, the UPS current must trip the CB3 circuitbreaker with the highest rating© Schneider Electric - all rights reservedFor distant short-circuits, the CB3 unit setting must not result in a dangerous touch voltage.If necessary, install an RCDFig. N25 : Circuit-breakers are submitted to a variety of situationsIrdownstreamUcSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads2 Uninterruptible Power Supplyunits (UPS)RatingThe selected rating (rated current) for the circuit-breaker must be the one just abovethe rated current of the protected downstream cable.Breaking capacityThe breaking capacity must be selected just above the short-circuit current that canoccur at the point of installation.Ir and Im thresholdsThe table below indicates how to determine the Ir (overload ; thermal or longtime)and Im (short-circuit ; magnetic or short time) thresholds to ensure discrimination,depending on the upstream and downstream trip units.Remark (see Fig. N26)b Time discrimination must be implemented by qualified personnel because timedelays before tripping increase the thermal stress (I 2 t) downstream (cables, semiconductors,etc.). Caution is required if tripping of CB2 is delayed using the Imthreshold time delayb Energy discrimination does not depend on the trip unit, only on the circuit-breakerType of downstream Ir upstream / Im upstream / Im upstream /circuit Ir downstream Im downstream Im downstreamratio ratio ratioDownstream trip unit All types Magnetic ElectronicDistribution > 1.6 >2 >1.5Asynchronous motor >3 >2 >1.5Fig. N26 : Ir and Im thresholds depending on the upstream and downstream trip unitsSpecial case of generator short-circuitsFigure N27 shows the reaction of a generator to a short-circuit.To avoid any uncertainty concerning the type of excitation, we will trip at the firstpeak (3 to 5 In as per X”d) using the Im protection setting without a time delay.Irms3 InGenerator withover-excitationN19In0.3 InGenerator withseries excitationtSubtransientconditions 10 to 20 msTransient conditions100 to 300 msFig. N27 : Generator during short-circuit© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads2 Uninterruptible Power Supplyunits (UPS)2.6 Installation, connection and sizing of cablesReady-to-use UPS unitsThe low power UPSs, for micro computer systems for example, are compact readyto-useequipement. The internal wiring is built in the factory and adapted to thecharacteristics of the devices.Not ready-to-use UPS unitsFor the other UPSs, the wire connections to the power supply system, to the batteryand to the load are not included.Wiring connections depend on the current level as indicated in Figure N28 below.IuMains 1SWStatic switchIuI1Rectifier/chargerInverterLoadMains 2IbBatterycapacity C10Fig.N28 : Current to be taken into account for the selection of the wire connectionsCalculation of currents I1, Iub The input current Iu from the power network is the load currentb The input current I1 of the charger/rectifier depends on:v The capacity of the battery (C10) and the charging mode (Ib)v The characteristics of the chargerv The efficiency of the inverterb The current Ib is the current in the connection of the batteryThese currents are given by the manufacturers.N20Cable temperature rise and voltage dropsThe cross section of cables depends on:b Permissible temperature riseb Permissible voltage dropFor a given load, each of these parameters results in a minimum permissible crosssection. The larger of the two must be used.When routing cables, care must be taken to maintain the required distances betweencontrol circuits and power circuits, to avoid any disturbances caused by HF currents.© Schneider Electric - all rights reservedTemperature risePermissible temperature rise in cables is limited by the withstand capacity of cableinsulation.Temperature rise in cables depends on:b The type of core (Cu or Al)b The installation methodb The number of touching cablesStandards stipulate, for each type of cable, the maximum permissible current.Voltage dropsThe maximum permissible voltage drops are:b 3% for AC circuits (50 or 60 Hz)b 1% for DC circuitsSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads2 Uninterruptible Power Supplyunits (UPS)Selection tablesFigure N29 indicates the voltage drop in percent for a circuit made up of 100 metersof cable. To calculate the voltage drop in a circuit with a length L, multiply the value inthe table by L/100.b Sph: Cross section of conductorsb I n : Rated current of protection devices on circuitThree-phase circuitIf the voltage drop exceeds 3% (50-60 Hz), increase the cross section of conductors.DC circuitIf the voltage drop exceeds 1%, increase the cross section of conductors.a - Three-phase circuits (copper conductors)50-60 Hz - 380 V / 400 V / 415 V three-phase, cos ϕ = 0.8, balanced system three-phase + NIn Sph (mN 2 )(A) 10 16 25 35 50 70 95 120 150 185 240 30010 0.915 1.220 1.6 1.125 2.0 1.3 0.932 2.6 1.7 1.140 3.3 2.1 1.4 1.050 4.1 2.6 1.7 1.3 1.063 5.1 3.3 2.2 1.6 1.2 0.970 5.7 3.7 2.4 1.7 1.3 1.0 0.880 6.5 4.2 2.7 2.1 1.5 1.2 0.9 0.7100 8.2 5.3 3.4 2.6 2.0 2.0 1.1 0.9 0.8125 6.6 4.3 3.2 2.4 2.4 1.4 1.1 1.0 0.8160 5.5 4.3 3.2 3.2 1.8 1.5 1.2 1.1 0.9200 5.3 3.9 3.9 2.2 1.8 1.6 1.3 1.2 0.9250 4.9 4.9 2.8 2.3 1.9 1.7 1.4 1.2320 3.5 2.9 2.5 2.1 1.9 1.5400 4.4 3.6 3.1 2.7 2.3 1.9500 4.5 3.9 3.4 2.9 2.4600 4.9 4.2 3.6 3.0800 5.3 4.4 3.81,000 6.5 4.7For a three-phase 230 V circuit, multiply the result by eFor a single-phase 208/230 V circuit, multiply the result by 2b - DC circuits (copper conductors)In Sph (mN2)(A) - - 25 35 50 70 95 120 150 185 240 300100 5.1 3.6 2.6 1.9 1.3 1.0 0.8 0.7 0.5 0.4125 4.5 3.2 2.3 1.6 1.3 1.0 0.8 0.6 0.5160 4.0 2.9 2.2 1.6 1.2 1.1 0.6 0.7200 3.6 2.7 2.2 1.6 1.3 1.0 0.8250 3.3 2.7 2.2 1.7 1.3 1.0320 3.4 2.7 2.1 1.6 1.3400 3.4 2.8 2.1 1.6500 3.4 2.6 2.1600 4.3 3.3 2.7800 4.2 3.41,000 5.3 4.21,250 5.3N21Fig. N29 : Voltage drop in percent for [a] three-phase circuits and [b] DC circuitsSpecial case for neutral conductorsIn three-phase systems, the third-order harmonics (and their multiples) of singlephaseloads add up in the neutral conductor (sum of the currents on the threephases).For this reason, the following rule may be applied:neutral cross section = 1.5 x phase cross section© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads2 Uninterruptible Power Supplyunits (UPS)ExampleConsider a 70-meter 400 V three-phase circuit, with copper conductors and a ratedcurrent of 600 A.Standard IEC 60364 indicates, depending on the installation method and the load, aminimum cross section.We shall assume that the minimum cross section is 95 mm 2 .It is first necessary to check that the voltage drop does not exceed 3%.The table for three-phase circuits on the previous page indicates, for a 600 A currentflowing in a 300 mm 2 cable, a voltage drop of 3% for 100 meters of cable, i.e. for70 meters:3 x 70 = 2.1 %100Therefore less than 3%A identical calculation can be run for a DC current of 1,000 A.In a ten-meter cable, the voltage drop for 100 meters of 240 mN 2 cable is 5.3%, i.e.for ten meters:5.3 x 10 = 0.53 %100Therefore less than 3%2.7 The UPSs and their environmentThe UPSs can communicate with electrical and computing environment. They canreceive some data and provide information on their operation in order:b To optimize the protectionFor example, the UPS provides essential information on operating status to thecomputer system (load on inverter, load on static bypass, load on battery, low batterywarning)b To remotely controlThe UPS provides measurement and operating status information to inform andallow operators to take specific actionsb To manage the installationThe operator has a building and energy management system which allow to obtainand save information from UPSs, to provide alarms and events and to take actions.This evolution towards compatibilty between computer equipment and UPSs has theeffect to incorporate new built-in UPS functions.2.8 Complementary equipmentN22TransformersA two-winding transformer included on the upstream side of the static contactor ofcircuit 2 allows:b A change of voltage level when the power network voltage is different to that of theloadb A change of system of earthing between the networksMoreover, such a transformer :b Reduces the short-circuit current level on the secondary, (i.e load) side comparedwith that on the power network sideb Prevents third harmonic currents which may be present on the secondary sidefrom passing into the power-system network, providing that the primary winding isconnected in delta.© Schneider Electric - all rights reservedAnti-harmonic filterThe UPS system includes a battery charger which is controlled by thyristors ortransistors. The resulting regularly-chopped current cycles “generate” harmoniccomponents in the power-supply network.These indesirable components are filtered at the input of the rectifier and for mostcases this reduces the harmonic current level sufficiently for all practical purposes.Schneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads2 Uninterruptible Power Supplyunits (UPS)In certain specific cases however, notably in very large installations, an additionalfilter circuit may be necessary.For example when :b The power rating of the UPS system is large relative to the MV/LV transformersuppllying itb The LV busbars supply loads which are particularly sensitive to harmonicsb A diesel (or gas-turbine, etc,) driven alternator is provided as a standby powersupplyIn such cases, the manufacturer of the UPS system should be consultedCommunication equipmentCommunication with equipment associated with computer systems may entail theneed for suitable facilities within the UPS system. Such facilities may be incorporatedin an original design (see Fig. N30a ), or added to existing systems on request(see Fig. N30b ).Fig. N30a : Ready-to-use UPS unit (with DIN module)Fig. N30b : UPS unit achieving disponibility and quality of computer system power supplyN23© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads3 Protection of LV/LV transformersThese transformers are generally in the range of several hundreds of VA to somehundreds of kVA and are frequently used for:b Changing the low voltage level for:v Auxiliary supplies to control and indication circuitsv Lighting circuits (230 V created when the primary system is 400 V 3-phase3-wires)b Changing the method of earthing for certain loads having a relatively highcapacitive current to earth (computer equipment) or resistive leakage current(electric ovens, industrial-heating processes, mass-cooking installations, etc.)LV/LV transformers are generally supplied with protective systems incorporated,and the manufacturers must be consulted for details. Overcurrent protection must,in any case, be provided on the primary side. The exploitation of these transformersrequires a knowledge of their particular function, together with a number of pointsdescribed below.Note: In the particular cases of LV/LV safety isolating transformers at extra-lowvoltage, an earthed metal screen between the primary and secondary windingsis frequently required, according to circumstances, as recommended in EuropeanStandard EN 60742.3.1 Transformer-energizing inrush currentAt the moment of energizing a transformer, high values of transient current (whichincludes a significant DC component) occur, and must be taken into account whenconsidering protection schemes (see Fig. N31).It5 sI 1 st peak10 to 25 In20msIrRMS value ofthe 1 st peakImIiIInFig N31 : Transformer-energizing inrush currenttN24Fig N32 : Tripping characteristic of a Compact NS type STR(electronic)tThe magnitude of the current peak depends on:b The value of voltage at the instant of energizationb The magnitude and polarity of the residual flux existing in the core of thetransformerb Characteristics of the load connected to the transformerThe first current peak can reach a value equal to 10 to 15 times the full-load r.m.s.current, but for small transformers (< 50 kVA) may reach values of 20 to 25 timesthe nominal full-load current. This transient current decreases rapidly, with a timeconstant θ of the order of several ms to severals tens of ms.3.2 Protection for the supply circuit of aLV/LV transformer© Schneider Electric - all rights reservedInRMS value ofthe 1 st peak10In 14InFig N33 : Tripping characteristic of a Multi 9 curve DIThe protective device on the supply circuit for a LV/LV transformer must avoid thepossibility of incorrect operation due to the magnetizing inrush current surge, notedabove.It is necessary to use therefore:b Selective (i.e. slighly time-delayed) circuit-breakers of the type Compact NS STR(see Fig. N32) orb Circuit-breakers having a very high magnetic-trip setting, of the types Compact NSor Multi 9 curve D (see Fig. N33)Schneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads3 Protection of LV/LV transformersFig N34 : ExampleNS250NTrip unitSTR 22E3 x 70 mm 2400/230 V125 kVAExampleA 400 V 3-phase circuit is supplying a 125 kVA 400/230 V transformer (In = 180 A)for which the first inrush current peak can reach 12 In, i.e. 12 x 180 = 2,160 A.This current peak corresponds to a rms value of 1,530 A.A compact NS 250N circuit-breaker with Ir setting of 200 A and Im setting at 8 x Irwould therefore be a suitable protective device.A particular case: Overload protection installed at the secondary side of thetransformer (see Fig. N34)An advantage of overload protection located on the secondary side is that the shortcircuitprotection on the primary side can be set at a high value, or alternatively acircuit-breaker type MA (magnetic only) can be used. The primary side short-circuitprotection setting must, however, be sufficiently sensitive to ensure its operation inthe event of a short-circuit occuring on the secondary side of the transformer.Note: The primary protection is sometimes provided by fuses, type aM. This practicehas two disadvantages:b The fuses must be largely oversized (at least 4 times the nominal full-load ratedcurrent of the transformer)b In order to provide isolating facilities on the primary side, either a load-break switchor a contactor must be associated with the fuses.3.3 Typical electrical characteristics of LV/LV 50 Hztransformers3-phasekVA rating 5 6.3 8 10 12.5 16 20 25 31.5 40 50 63 80 100 125 160 200 250 315 400 500 630 800No-load 100 110 130 150 160 170 270 310 350 350 410 460 520 570 680 680 790 950 1160 1240 1485 1855 2160losses (W)Full-load 250 320 390 500 600 840 800 1180 1240 1530 1650 2150 2540 3700 3700 5900 5900 6500 7400 9300 9400 11400 13400losses (W)Short-circuit 4.5 4.5 4.5 5.5 5.5 5.5 5.5 5.5 5 5 4.5 5 5 5.5 4.5 5.5 5 5 4.5 6 6 5.5 5.5voltage (%)1-phasekVA rating 8 10 12.5 16 20 25 31.5 40 50 63 80 100 125 160No-load losses (W) 105 115 120 140 150 175 200 215 265 305 450 450 525 635Full-load losses (W) 400 530 635 730 865 1065 1200 1400 1900 2000 2450 3950 3950 4335Short-circuit voltage (%) 5 5 5 4.5 4.5 4.5 4 4 5 5 4.5 5.5 5 53.4 Protection of LV/LV transformers, usingMerlin Gerin circuit-breakersMulti 9 circuit-breakerTransformer power rating (kVA) Cricuit breaker Size230/240 V 1-ph 230/240 V 3-ph 400/415 V 3-ph curve D or K (A)400/415 V 1-ph0.05 0.09 0.16 C60, NG125 0.50.11 0.18 0.32 C60, NG125 10.21 0.36 0.63 C60, NG125 20.33 0.58 1.0 C60, NG125 30.67 1.2 2.0 C60, NG125 61.1 1.8 3.2 C60, C120, NG125 101.7 2.9 5.0 C60, C120, NG125 162.1 3.6 6.3 C60, C120, NG125 202.7 4.6 8.0 C60, C120, NG125 253.3 5.8 10 C60, C120, NG125 324.2 7.2 13 C60, C120, NG125 405.3 9.2 16 C60, C120, NC100, NG125 506.7 12 20 C60, C120, NC100, NG125 638.3 14 25 C120, NC100, NG125 8011 18 32 C120, NC100, NG125 10013 23 40 C120, NG125 125N25© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads3 Protection of LV/LV transformersCompact NSX100 to NSX250 circuit-breakers with TM-D trip unitsTransformer power rating (kVA) Circuit-breaker Trip unit230/240 V 1-ph 230/240 V 3-ph 400/415 V 3-ph400/415 V 1-ph3 5…6 9…12 NSX100B/F/N/H/S/L TM16D5 8…9 14…16 NSX100B/F/N/H/S/L TM25D7…9 13…16 22…28 NSX100B/F/N/H/S/L TM40D12…15 20…25 35…44 NSX100B/F/N/H/S/L TM63D16…19 26…32 45…56 NSX100B/F/N/H/S/L TM80D18…23 32…40 55…69 NSX160B/F/N/H/S/L TM100D23…29 40…50 69…87 NSX160B/F/N/H/S/L TM125D29…37 51…64 89…111 NSX250B/F/N/H/S/L TM160D37…46 64…80 111…139 NSX250B/F/N/H/S/L TM200DCompact NSX100 to NS1600 / Masterpact circuit-breakers with Micrologic tripunitsTransformer power rating (kVA) Circuit-breaker Trip unit Setting230/240 V 1-ph 230/240 V 3-ph 400/415 V 3-ph Ir max400/415 V 1-ph4…7 6…13 11…22 NSX100B/F/N/H/S/L Micrologic 2.2 or 6.2 40 0.89…19 16…30 27…56 NSX100B/F/N/H/S/L Micrologic 2.2 or 6.2 100 0.815…30 5…50 44…90 NSX160B/F/N/H/S/L Micrologic 2.2 or 6.2 160 0.823…46 40…80 70…139 NSX250B/F/N/H/S/L Micrologic 2.2 or 6.2 250 0.837…65 64…112 111…195 NSX400F/N/H/S Micrologic 2.3 or 6.3 400 0.737…55 64…95 111…166 NSX400L Micrologic 2.3 or 6.3 400 0.658…83 100…144 175…250 NSX630F/N//H/S/L Micrologic 2.3 or 6.3 630 0.658…150 100…250 175…436 NS630bN/bH NT06H1 Micrologic 5.0/6.0/7.0 174…184 107…319 222…554 NS800N/H - NT08H1- NW08N1/H1 Micrologic 5.0/6.0/7.0 190…230 159…398 277…693 NS1000N/H - NT10H1- NW10N1/H1 Micrologic 5.0/6.0/7.0 1115…288 200…498 346…866 NS1250N/H - NT12H1 - NW12N1/H1 Micrologic 5.0/6.0/7.0 1147…368 256…640 443…1,108 NS1600N/H - NT16H1 - NW16N1/H1 Micrologic 5.0/6.0/7.0 1184…460 320…800 554…1,385 NW20N1/H1 Micrologic 5.0/6.0/7.0 1230…575 400…1,000 690…1,730 NW25H2/H3 Micrologic 5.0/6.0/7.0 1294…736 510…1,280 886…2,217 NW32H2/H3 Micrologic 5.0/6.0/7.0 1N26© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads4 Lighting circuitsA source of comfort and productivity, lighting represents 15% of the quantity ofelectricity consumed in industry and 40% in buildings. The quality of lighting (lightstability and continuity of service) depends on the quality of the electrical energythus consumed. The supply of electrical power to lighting networks has thereforeassumed great importance.To help with their design and simplify the selection of appropriate protection devices,an analysis of the different lamp technologies is presented. The distinctive featuresof lighting circuits and their impact on control and protection devices are discussed.Recommendations relative to the difficulties of lighting circuit implementation are given.4.1 The different lamp technologiesa -b -Fig. N35 : Compact fluorescent lamps [a] standard,[b] inductionArtificial luminous radiation can be produced from electrical energy according to twoprinciples: incandescence and electroluminescence.Incandescence is the production of light via temperature elevation. The mostcommon example is a filament heated to white state by the circulation of an electricalcurrent. The energy supplied is transformed into heat by the Joule effect and intoluminous flux.Luminescence is the phenomenon of emission by a material of visible or almostvisible luminous radiation. A gas (or vapors) subjected to an electrical dischargeemits luminous radiation (Electroluminescence of gases).Since this gas does not conduct at normal temperature and pressure, the dischargeis produced by generating charged particles which permit ionization of the gas. Thenature, pressure and temperature of the gas determine the light spectrum.Photoluminescence is the luminescence of a material exposed to visible or almostvisible radiation (ultraviolet, infrared).When the substance absorbs ultraviolet radiation and emits visible radiation whichstops a short time after energization, this is fluorescence.Incandescent lampsIncandescent lamps are historically the oldest and the most often found in commonuse.They are based on the principle of a filament rendered incandescent in a vacuum orneutral atmosphere which prevents combustion.A distinction is made between:b Standard bulbsThese contain a tungsten filament and are filled with an inert gas (nitrogen andargon or krypton).b Halogen bulbsThese also contain a tungsten filament, but are filled with a halogen compoundand an inert gas (krypton or xenon). This halogen compound is responsible for thephenomenon of filament regeneration, which increases the service life of the lampsand avoids them blackening. It also enables a higher filament temperature andtherefore greater luminosity in smaller-size bulbs.The main disadvantage of incandescent lamps is their significant heat dissipation,resulting in poor luminous efficiency.Fluorescent lampsThis family covers fluorescent tubes and compact fluorescent lamps. Theirtechnology is usually known as “low-pressure mercury”.In fluorescent tubes, an electrical discharge causes electrons to collide withions of mercury vapor, resulting in ultraviolet radiation due to energization of themercury atoms. The fluorescent material, which covers the inside of the tubes, thentransforms this radiation into visible light.Fluorescent tubes dissipate less heat and have a longer service life thanincandescent lamps, but they do need an ignition device called a “starter” and adevice to limit the current in the arc after ignition. This device called “ballast” isusually a choke placed in series with the arc.Compact fluorescent lamps are based on the same principle as a fluorescent tube.The starter and ballast functions are provided by an electronic circuit (integrated inthe lamp) which enables the use of smaller tubes folded back on themselves.Compact fluorescent lamps (see Fig. N35) were developed to replace incandescentlamps: They offer significant energy savings (15 W against 75 W for the same level ofbrightness) and an increased service life.Lamps known as “induction” type or “without electrodes” operate on the principle ofionization of the gas present in the tube by a very high frequency electromagneticfield (up to 1 GHz). Their service life can be as long as 100,000 hrs.N27© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads4 Lighting circuitsFig. N36 : Discharge lampsDischarge lamps (see Fig. N36)The light is produced by an electrical discharge created between two electrodes withina gas in a quartz bulb. All these lamps therefore require a ballast to limit the current inthe arc. A number of technologies have been developed for different applications.Low-pressure sodium vapor lamps have the best light output, however the colorrendering is very poor since they only have a monochromatic orange radiation.High-pressure sodium vapor lamps produce a white light with an orange tinge.In high-pressure mercury vapor lamps, the discharge is produced in a quartz orceramic bulb at high pressure. These lamps are called “fluorescent mercury dischargelamps”. They produce a characteristically bluish white light.Metal halide lamps are the latest technology. They produce a color with a broad colorspectrum. The use of a ceramic tube offers better luminous efficiency and better colorstability.Light Emitting Diodes (LED)The principle of light emitting diodes is the emission of light by a semi-conductoras an electrical current passes through it. LEDs are commonly found in numerousapplications, but the recent development of white or blue diodes with a high lightoutput opens new perspectives, especially for signaling (traffic lights, exit signs oremergency lighting).LEDs are low-voltage and low-current devices, thus suitable for battery-supply.A converter is required for a line power supply.The advantage of LEDs is their low energy consumption. As a result, they operateat a very low temperature, giving them a very long service life. Conversely, a simplediode has a weak light intensity. A high-power lighting installation therefore requiresconnection of a large number of units in series and parallel.Technology Application Advantages DisadvantagesStandard - Domestic use - Direct connection without - Low luminous efficiency andincandescent - Localized decorative intermediate switchgear high electricity consumptionlighting - Reasonable purchase price - Significant heat dissipation- Compact size - Short service life- Instantaneous lighting- Good color renderingHalogen - Spot lighting - Direct connection - Average luminous efficiencyincandescent - Intense lighting - Instantaneous efficiency- Excellent color renderingFluorescent tube - Shops, offices, workshops - High luminous efficiency - Low light intensity of single unit- Outdoors - Average color rendering - Sensitive to extreme temperaturesN28Compact - Domestic use - Good luminous efficiency - High initial investmentfluorescent lamp - Offices - Good color rendering compared to incandescent lamps- Replacement ofincandescent lampsHP mercury vapor - Workshops, halls, hangars - Good luminous efficiency - Lighting and relighting time- Factory floors - Acceptable color rendering of a few minutes- Compact size- Long service lifeHigh-pressure - Outdoors - Very good luminous efficiency - Lighting and relighting timesodium - Large halls of a few minutesLow-pressure - Outdoors - Good visibility in foggy weather - Long lighting time (5 min.)sodium - Emergency lighting - Economical to use - Mediocre color renderingMetal halide - Large areas - Good luminous efficiency - Lighting and relighting time- Halls with high ceilings - Good color rendering of a few minutes- Long service lifeLED - Signaling (3-color traffic - Insensitive to the number of - Limited number of colorslights, “exit” signs and switching operations - Low brightness of single unitemergency lighting)- Low energy consumption- Low temperature© Schneider Electric - all rights reservedTechnology Power (watt) Efficiency (lumen/watt) Service life (hours)Standard incandescent 3 – 1,000 10 – 15 1,000 – 2,000Halogen incandescent 5 – 500 15 – 25 2,000 – 4,000Fluorescent tube 4 – 56 50 – 100 7,500 – 24,000Compact fluorescent lamp 5 – 40 50 – 80 10,000 – 20,000HP mercury vapor 40 – 1,000 25 – 55 16,000 – 24,000High-pressure sodium 35 – 1,000 40 – 140 16,000 – 24,000Low-pressure sodium 35 – 180 100 – 185 14,000 – 18,000Metal halide 30 – 2,000 50 – 115 6,000 – 20,000LED 0.05 – 0.1 10 – 30 40,000 – 100,000Fig. N37 : Usage and technical characteristics of lighting devicesSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads4 Lighting circuitsa]3002001000-100-200-3000b]3002001000-100-2000.01 0.02-3000 0.01 0.02t (s)t (s)Fig. N38 : Shape of the voltage supplied by a light dimmer at50% of maximum voltage with the following techniques:a] “cut-on control”b] “cut-off control”4.2 Electrical characteristics of lampsIncandescent lamps with direct power supplyDue to the very high temperature of the filament during operation (up to 2,500 °C),its resistance varies greatly depending on whether the lamp is on or off. As the coldresistance is low, a current peak occurs on ignition that can reach 10 to 15 times thenominal current for a few milliseconds or even several milliseconds.This constraint affects both ordinary lamps and halogen lamps: it imposes areduction in the maximum number of lamps that can be powered by devices such asremote-control switches, modular contactors and relays for busbar trunking.Extra Low Voltage (ELV) halogen lampsb Some low-power halogen lamps are supplied with ELV 12 or 24 V, via atransformer or an electronic converter. With a transformer, the magnetizationphenomenon combines with the filament resistance variation phenomenon atswitch-on. The inrush current can reach 50 to 75 times the nominal current for a fewmilliseconds. The use of dimmer switches placed upstream significantly reduces thisconstraint.b Electronic converters, with the same power rating, are more expensive thansolutions with a transformer. This commercial handicap is compensated by a greaterease of installation since their low heat dissipation means they can be fixed on aflammable support. Moreover, they usually have built-in thermal protection.New ELV halogen lamps are now available with a transformer integrated in theirbase. They can be supplied directly from the LV line supply and can replace normallamps without any special adaptation.Dimming for incandescent lampsThis can be obtained by varying the voltage applied to the lampereThis voltage variation is usually performed by a device such as a Triac dimmerswitch, by varying its firing angle in the line voltage period. The wave form of thevoltage applied to the lamp is illustrated in Figure N38a. This technique knownas “cut-on control” is suitable for supplying power to resistive or inductive circuits.Another technique suitable for supplying power to capacitive circuits has beendeveloped with MOS or IGBT electronic components. This techniques varies thevoltage by blocking the current before the end of the half-period (see Fig. N38b) andis known as “cut-off control”.Switching on the lamp gradually can also reduce, or even eliminate, the current peakon ignition.As the lamp current is distorted by the electronic switching, harmonic currentsare produced. The 3 rd harmonic order is predominant, and the percentage of 3 rdharmonic current related to the maximum fundamental current (at maximum power)is represented on Figure N39.Note that in practice, the power applied to the lamp by a dimmer switch can only varyin the range between 15 and 85% of the maximum power of the lampere50.045.040.035.030.025.020.015.010.05.00i3 (%)0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0 100.0Fig. N39 : Percentage of 3 rd harmonic current as a function of the power applied to anincandescent lamp using an electronic dimmer switchPower (%)N29© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads4 Lighting circuitsAccording to IEC standard 61000-3-2 setting harmonic emission limits for electric orelectronic systems with current y 16 A, the following arrangements apply:b Independent dimmers for incandescent lamps with a rated power less than orequal to 1 kW have no limits appliedb Otherwise, or for incandescent lighting equipment with built-in dimmer or dimmerbuilt in an enclosure, the maximum permissible 3 rd harmonic current is equal to2.30 AFluorescent lamps with magnetic ballastFluorescent tubes and discharge lamps require the intensity of the arc to be limited,and this function is fulfilled by a choke (or magnetic ballast) placed in series with thebulb itself (see Fig. N40).This arrangement is most commonly used in domestic applications with a limitednumber of tubes. No particular constraint applies to the switches.Dimmer switches are not compatible with magnetic ballasts: the cancellation of thevoltage for a fraction of the period interrupts the discharge and totally extinguishesthe lampereThe starter has a dual function: preheating the tube electrodes, and then generatingan overvoltage to ignite the tube. This overvoltage is generated by the opening of acontact (controlled by a thermal switch) which interrupts the current circulating in themagnetic ballast.During operation of the starter (approx. 1 s), the current drawn by the luminaire isapproximately twice the nominal current.Since the current drawn by the tube and ballast assembly is essentially inductive, thepower factor is very low (on average between 0.4 and 0.5). In installations consistingof a large number of tubes, it is necessary to provide compensation to improve thepower factor.For large lighting installations, centralized compensation with capacitor banks is apossible solution, but more often this compensation is included at the level of eachluminaire in a variety of different layouts (see Fig. N41).a] Ballast b] C Ballast c]BallastLampaCLampaLampaCBallastLampN30Compensation layout Application CommentsWithout compensation Domestic Single connectionParallel [a]Offices, workshops, Risk of overcurrents for control devicessuperstoresSeries [b]Choose capacitors with highoperating voltage (450 to 480 V)Duo [c]Avoids flickerFig. N41 : The various compensation layouts: a] parallel; b] series; c] dual series also called“duo” and their fields of applicationThe compensation capacitors are therefore sized so that the global power factor isgreater than 0.85. In the most common case of parallel compensation, its capacityis on average 1 µF for 10 W of active power, for any type of lampere However, thiscompensation is incompatible with dimmer switches.© Schneider Electric - all rights reservedFig. N40 : Magnetic ballastsConstraints affecting compensationThe layout for parallel compensation creates constraints on ignition of the lampereSince the capacitor is initially discharged, switch-on produces an overcurrent.An overvoltage also appears, due to the oscillations in the circuit made up of thecapacitor and the power supply inductance.The following example can be used to determine the orders of magnitude.Schneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads4 Lighting circuitsAssuming an assembly of 50 fluorescent tubes of 36 W each:b Total active power: 1,800 Wb Apparent power: 2 kVAb Total rms current: 9 Ab Peak current: 13 AWith:b A total capacity: C = 175 µFb A line inductance (corresponding to a short-circuit current of 5 kA): L = 150 µHThe maximum peak current at switch-on equals:-6Cx 10Ic = Vmax= 230 2 175 = 350 AL-6150 x 10The theoretical peak current at switch-on can therefore reach 27 times the peakcurrent during normal operation.The shape of the voltage and current at ignition is given in Figure N42 for switchclosing at the line supply voltage peak.There is therefore a risk of contact welding in electromechanical control devices(remote-control switch, contactor, circuit-breaker) or destruction of solid stateswitches with semi-conductors.(V)6004002000t (s)-200-400-60000.02 0.04 0.06(A)3002001000-100-200t (s)N31-30000.02 0.04 0.06Fig. N42 : Power supply voltage at switch-on and inrush currentIn reality, the constraints are usually less severe, due to the impedance of the cables.Ignition of fluorescent tubes in groups implies one specific constraint. When a groupof tubes is already switched on, the compensation capacitors in these tubes whichare already energized participate in the inrush current at the moment of ignition ofa second group of tubes: they “amplify” the current peak in the control switch at themoment of ignition of the second group.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads4 Lighting circuitsThe table in Figure N43, resulting from measurements, specifies the magnitude ofthe first current peak, for different values of prospective short-circuit current Isc. It isseen that the current peak can be multiplied by 2 or 3, depending on the number oftubes already in use at the moment of connection of the last group of tubes.Number of tubes Number of tubes Inrush current peak (A)already in use connected Isc = 1,500 A Isc = 3,000 A Isc = 6,000 A0 14 233 250 32014 14 558 556 57528 14 608 607 62442 14 618 616 632Fig. N43 : Magnitude of the current peak in the control switch of the moment of ignition of asecond group of tubesNonetheless, sequential ignition of each group of tubes is recommended so as toreduce the current peak in the main switch.The most recent magnetic ballasts are known as “low-loss”. The magnetic circuit hasbeen optimized, but the operating principle remains the same. This new generationof ballasts is coming into widespread use, under the influence of new regulations(European Directive, Energy Policy Act - USA).In these conditions, the use of electronic ballasts is likely to increase, to thedetriment of magnetic ballasts.N32Fluorescent lamps with electronic ballastElectronic ballasts are used as a replacement for magnetic ballasts to supply powerto fluorescent tubes (including compact fluorescent lamps) and discharge lamps.They also provide the “starter” function and do not need any compensation capacity.The principle of the electronic ballast (see Fig. N44) consists of supplying the lamparc via an electronic device that generates a rectangular form AC voltage with afrequency between 20 and 60 kHz.Supplying the arc with a high-frequency voltage can totally eliminate the flickerphenomenon and strobe effects. The electronic ballast is totally silent.During the preheating period of a discharge lamp, this ballast supplies the lamp withincreasing voltage, imposing an almost constant current. In steady state, it regulatesthe voltage applied to the lamp independently of any fluctuations in the line voltage.Since the arc is supplied in optimum voltage conditions, this results in energysavings of 5 to 10% and increased lamp service life. Moreover, the efficiency of theelectronic ballast can exceed 93%, whereas the average efficiency of a magneticdevice is only 85%.The power factor is high (> 0.9).The electronic ballast is also used to provide the light dimming function. Varying thefrequency in fact varies the current magnitude in the arc and hence the luminousintensity.Inrush currentThe main constraint that electronic ballasts bring to line supplies is the highinrush current on switch-on linked to the initial load of the smoothing capacitors(see Fig. N45).© Schneider Electric - all rights reservedFig. N44 : Electronic ballastTechnology Max. inrush current DurationRectifier with PFC 30 to 100 In y 1 msRectifier with choke 10 to 30 In y 5 msMagnetic ballast y 13 In 5 to 10 msFig. N45 : Orders of magnitude of the inrush current maximum values, depending on thetechnologies usedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads4 Lighting circuitsIn reality, due to the wiring impedances, the inrush currents for an assembly of lampsis much lower than these values, in the order of 5 to 10 In for less than 5 ms.Unlike magnetic ballasts, this inrush current is not accompanied by an overvoltage.Harmonic currentsFor ballasts associated with high-power discharge lamps, the current drawn fromthe line supply has a low total harmonic distortion (< 20% in general and < 10% forthe most sophisticated devices). Conversely, devices associated with low-powerlamps, in particular compact fluorescent lamps, draw a very distorted current(see Fig. N46). The total harmonic distortion can be as high as 150%. In theseconditions, the rms current drawn from the line supply equals 1.8 times the currentcorresponding to the lamp active power, which corresponds to a power factor of 0.55.(A)0.60.40.20t (s)-0.2-0.4-0.600.02Fig. N46 : Shape of the current drawn by a compact fluorescent lampIn order to balance the load between the different phases, lighting circuits are usuallyconnected between phases and neutral in a balanced way. In these conditions,the high level of third harmonic and harmonics that are multiple of 3 can cause anoverload of the neutral conductor. The least favorable situation leads to a neutralcurrent which may reach 3 times the current in each phase.Harmonic emission limits for electric or electronic systems are set by IEC standard61000-3-2. For simplification, the limits for lighting equipment are given here only forharmonic orders 3 and 5 which are the most relevant (see Fig. N47).Harmonic Active input Active input power y 25Worder power > 25W one of the 2 sets of limits apply:% of fundamental % of fundamental Harmonic current relativecurrent current to active power3 30 86 3.4 mA/W5 10 61 1.9 mA/WN33Fig. N47 : Maximum permissible harmonic currentLeakage currentsElectronic ballasts usually have capacitors placed between the power supplyconductors and the earth. These interference-suppressing capacitors are responsiblefor the circulation of a permanent leakage current in the order of 0.5 to 1 mA perballast. This therefore results in a limit being placed on the number of ballasts thatcan be supplied by a Residual Current Differential Safety Device (RCD).At switch-on, the initial load of these capacitors can also cause the circulation of acurrent peak whose magnitude can reach several amps for 10 µs. This current peakmay cause unwanted tripping of unsuitable devices.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads4 Lighting circuitsHigh-frequency emissionsElectronic ballasts are responsible for high-frequency conducted and radiatedemissions.The very steep rising edges applied to the ballast output conductors cause currentpulses circulating in the stray capacities to earth. As a result, stray currents circulatein the earth conductor and the power supply conductors. Due to the high frequencyof these currents, there is also electromagnetic radiation. To limit these HF emissions,the lamp should be placed in the immediate proximity of the ballast, thus reducingthe length of the most strongly radiating conductors.The different power supply modes (see Fig. N48)Technology Power supply mode Other deviceStandard incandescent Direct power supply Dimmer switchHalogen incandescentELV halogen incandescent Transformer Electronic converterFluorescent tube Magnetic ballast and starter Electronic ballastElectronic dimmer +ballastCompact fluorescent lamp Built-in electronic ballastMercury vapor Magnetic ballast Electronic ballastHigh-pressure sodiumLow-pressure sodiumMetal halideFig. N48 : Different power supply modesN344.3 Constraints related to lighting devices andrecommendationsThe current actually drawn by luminairesThe riskThis characteristic is the first one that should be defined when creating aninstallation, otherwise it is highly probable that overload protection devices will tripand users may often find themselves in the dark.It is evident that their determination should take into account the consumption ofall components, especially for fluorescent lighting installations, since the powerconsumed by the ballasts has to be added to that of the tubes and bulbs.The solutionFor incandescent lighting, it should be remembered that the line voltage can be morethan 10% of its nominal value, which would then cause an increase in the currentdrawn.For fluorescent lighting, unless otherwise specified, the power of the magneticballasts can be assessed at 25% of that of the bulbs. For electronic ballasts, thispower is lower, in the order of 5 to 10%.The thresholds for the overcurrent protection devices should therefore be calculatedas a function of the total power and the power factor, calculated for each circuit.© Schneider Electric - all rights reservedOvercurrents at switch-onThe riskThe devices used for control and protection of lighting circuits are those such asrelays, triac, remote-control switches, contactors or circuit-breakers.The main constraint applied to these devices is the current peak on energization.This current peak depends on the technology of the lamps used, but also on theinstallation characteristics (supply transformer power, length of cables, number oflamps) and the moment of energization in the line voltage period. A high currentpeak, however fleeting, can cause the contacts on an electromechanical controldevice to weld together or the destruction of a solid state device with semiconductors.Schneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads4 Lighting circuitsTwo solutionsBecause of the inrush current, the majority of ordinary relays are incompatible withlighting device power supply. The following recommendations are therefore usuallymade:b Limit the number of lamps to be connected to a single device so that their totalpower is less than the maximum permissible power for the deviceb Check with the manufacturers what operating limits they suggest for the devices.This precaution is particularly important when replacing incandescent lamps withcompact fluorescent lampsBy way of example, the table in Figure N49 indicates the maximum number ofcompensated fluorescent tubes that can be controlled by different devices with16 A rating. Note that the number of controlled tubes is well below the numbercorresponding to the maximum power for the devices.Tube unit power Number of tubes Maximum number of tubes that can berequirement corresponding controlled by(W) to the power Contactors Remote Circuit-6 A x 230 V GC16 A control breakersCT16 A switches C60-16 ATL16 A18 204 15 50 11236 102 15 25 5658 63 10 16 34Fig. N49 : The number of controlled tubes is well below the number corresponding to themaximum power for the devicesBut a technique exists to limit the current peak on energization of circuits withcapacitive behavior (magnetic ballasts with parallel compensation and electronicballasts). It consists of ensuring that activation occurs at the moment when the linevoltage passes through zero. Only solid state switches with semi-conductors offerthis possibility (see Fig. N50a). This technique has proved to be particularly usefulwhen designing new lighting circuits.More recently, hybrid technology devices have been developed that combine a solidstate switch (activation on voltage passage through zero) and an electromechanicalcontactor short-circuiting the solid state switch (reduction of losses in the semiconductors)(see Fig. N50b).N35a b cFig. N50 : “Standard” CT+ contactor [a], CT+ contactor with manual override, pushbutton forselection of operating mode and indicator lamp showing the active operating mode [b], and TL +remote-control switch [c] (Merlin Gerin brand)© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads4 Lighting circuitsModular contactors and impulse relays donot use the same technologies. Their rating isdetermined according to different standards.For example, for a given rating, an impulserelay is more efficient than a modularcontactor for the control of light fittings witha strong inrush current, or with a low powerfactor (non-compensated inductive circuit).Choice of relay rating according to lamp typeb Figure 51 below shows the maximum number of light fittings for each relay,according to the type, power and configuration of a given lamp. As an indication, thetotal acceptable power is also mentioned.b These values are given for a 230 V circuit with 2 active conductors (single-phasephase/neutral or two-phase phase/phase). For 110 V circuits, divide the values in thetable by 2.b To obtain the equivalent values for the whole of a 230 V three-phase circuit,multiply the number of lamps and the total acceptable power:v by 3 (1.73) for circuits without neutral;v by 3 for circuits with neutral.Note: The power ratings of the lamps most commonly used are shown in bold.N36© Schneider Electric - all rights reservedTypeof lampUnit powerand capacitance of power factorcorrection capacitorMaximum number of light fittings for a single-phase circuitand maximum power output per circuitTL impulse relayCT contactor16 A 32 A 16 A 25 A 40 A 63 ABasic incandescent lampsLV halogen lampsReplacement mercury vapour lamps (without ballast)40 W60 W75 W4025201500 Wto1600 W10666534000 Wto4200 W3830251550 Wto2000 W5745382300 Wto2850 W11585704600 Wto5250 W125100100 W 16 42 19 28 50 73150 W 10 28 12 18 35 50200 W 8 21 10 14 26 37300 W 5 1500 W 13 4000 W 7 2100 W 10 3000 W 18 5500 W500 W 3 8 4 6 10 to 151000 W 1 4 2 3 6 6000 W 81500 W 1 2 1 2 4 5ELV 12 or 24 V halogen lampsWith ferromagnetic transformer 20 W 70 1350 W 180 3600 W 15 300 W 23 450 W 42 850 W50 W 28 to 74 to 10 to 15 to 27 to 4275 W 19 1450 W 50 3750 W 8 600 W 12 900 W 23 1950 W 35100 W 14 37 6 8 18 27With electronic transformer 20 W 60 1200 W 160 3200 W 62 1250 W 90 1850 W 182 3650 W50 W 25 to 65 to 25 to 39 to 76 to 11475 W 18 1400 W 44 3350 W 20 1600 W 28 2250 W 53 4200 W 78100 W 14 33 16 22 42 60Fluorescent tubes with starter and ferromagnetic ballast1 tube15 W 83 1250 W 213 3200 W 22 330 W 30 450 W 70 1050 Wwithout compensation (1)18 W 70to186to22to30to70to1001300 W 3350 W 850 W 1200 W 2400 W20 W 62 160 22 30 70 10036 W 35 93 20 28 60 9040 W 31 81 20 28 60 9058 W 21 55 13 17 35 5665 W 20 50 13 17 35 5680 W 16 41 10 15 30 48115 W 11 29 7 10 20 321 tube15 W 5 µF 60 900 W 160 2400 W 15 200 W 20 300 W 40 600 Wwith parallel compensation (2) 18 W 5 µF 50 133 15 to 20 to 40 to 6020 W 5 µF 45 120 15 800 W 20 1200 W 40 2400 W 6036 W 5 µF 25 66 15 20 40 6040 W 5 µF 22 60 15 20 40 6058 W 7 µF 16 42 10 15 30 4365 W 7 µF 13 37 10 15 30 4380 W 7 µF 11 30 10 15 30 43115 W 16 µF 7 20 5 7 14 202 or 4 tubes2 x 18 W 56 2000 W 148 5300 W 30 1100 W 46 1650 W 80 2900 Wwith series compensation4 x 18 W 28 74 16to24to44to681500 W 2400 W 3800 W2 x 36 W 28 74 16 24 44 682 x 58 W 17 45 10 16 27 422 x 65 W 15 40 10 16 27 422 x 80 W 12 33 9 13 22 342 x 115 W 8 23 6 10 16 25Fluorescent tubes with electronic ballast1 or 2 tubes 18 W 80 1450 W 212 3800 W 74 1300 W 111 2000 W 222 4000 W36 W 40 to 106 to 38 to 58 to 117 to 17658 W 26 1550 W 69 4000 W 25 1400 W 37 2200 W 74 4400 W 1112 x 18 W 40 106 36 55 111 1662 x 36 W 20 53 20 30 60 902 x 58 W 13 34 12 19 38 57Fig. N51 : Maximum number of light fittings for each relay, according to the type, power and configuration of a given lamp (Continued on opposite page)172 6900 Wto7500 W25 7500 Wto8000 W63 1250 Wto2850 W275 5500 Wto6000 W100 1500 Wto3850 W60 900 Wto3500 W123 4450 Wto5900 W333 6000 Wto6600 WSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads4 Lighting circuitsTypeof lampUnit powerand capacitance of power factorMaximum number of light fittings for a single-phase circuitand maximum power output per circuitcorrection capacitorTL impulse relayCT contactor16 A 32 A 16 A 25 A 40 A 63 ACompact fluorescent lampsWith external electronic ballast 5 W 240 1200 W 630 3150 W 210 1050 W 330 1650 W 670 3350 W not tested7 W 171 to 457 to 150 to 222 to 478 to9 W 138 1450 W 366 3800 W 122 1300 W 194 2000 W 383 4000 W11 W 118 318 104 163 32718 W 77 202 66 105 21626 W 55 146 50 76 153With integral electronic ballast 5 W 170 850 W 390 1950 W 160 800 W 230 1150 W 470 2350 W 710 3550 W(replacement for incandescent 7 W 121 to 285 to 114 to 164 to 335 to 514 tolamps)9 W 100 1050 W 233 2400 W 94 900 W 133 1300 W 266 2600 W 411 3950 W11 W 86 200 78 109 222 34018 W 55 127 48 69 138 21326 W 40 92 34 50 100 151High-pressure mercury vapour lamps with ferromagnetic ballast without ignitorReplacement high-pressure sodium vapour lamps with ferromagnetic ballast with integral ignitor (3)Without compensation (1) 50 W not tested,15 750 W 20 1000 W 34 1700 W 53 2650 W80 W infrequent use10 to 15 to 27 to 40 to125 / 110 W (3) 8 1000 W 10 1600 W 20 2800 W 28 4200 W250 / 220 W (3) 4 6 10 15400 / 350 W (3) 2 4 6 10700 W 1 2 4 6With parallel compensation (2) 50 W 7 µF 10 500 W 15 750 W 28 1400 W 43 2150 W80 W 8 µF 9 to 13 to 25 to 38 to125 / 110 W (3) 10 µF 9 1400 W 10 1600 W 20 3500 W 30 5000 W250 / 220 W (3) 18 µF 4 6 11 17400 / 350 W (3) 25 µF 3 4 8 12700 W 40 µF 2 2 5 71000 W 60 µF 0 1 3 5Low-pressure sodium vapour lamps with ferromagnetic ballast with external ignitorWithout compensation (1) 35 W not tested,5 270 W 9 320 W 14 500 W 24 850 W55 W infrequent use5 to 9 to 14 to 24 to90 W 3 360 W 6 720 W 9 1100 W 19 1800 W135 W 2 4 6 10180 W 2 4 6 10With parallel compensation (2) 35 W 20 µF 38 1350 W 102 3600 W 3 100 W 5 175 W 10 350 W 15 550 W55 W 20 µF 24 63 3 to 5 to 10 to 15 to90 W 26 µF 15 40 2 180 W 4 360 W 8 720 W 11 1100 W135 W 40 µF 10 26 1 2 5 7180 W 45 µF 7 18 1 2 4 6High-pressure sodium vapour lampsMetal-iodide lampsWith ferromagnetic ballast with 35 W not tested,16 600 W 24 850 W 42 1450 W 64 2250 Wexternal ignitor, without 70 W infrequent use8 12 to 20 to 32 tocompensation (1)150 W 4 7 1200 W 13 2000 W 18 3200 W250 W 2 4 8 11400 W 1 3 5 81000 W 0 1 2 3With ferromagnetic ballast with 35 W 6 µF 34 1200 W 88 3100 W 12 450 W 18 650 W 31 1100 W 50 1750 Wexternal ignitor and parallel 70 W 12 µF 17 to 45 to 6 to 9 to 16 to 25 tocompensation (2)150 W 20 µF 8 1350 W 22 3400 W 4 1000 W 6 2000 W 10 4000 W 15 6000 W250 W 32 µF 5 13 3 4 7 10400 W 45 µF 3 8 2 3 5 71000 W 60 µF 1 3 1 2 3 52000 W 85 µF 0 1 0 1 2 3With electronic ballast 35 W 38 1350 W 87 3100 W 24 850 W 38 1350 W 68 2400 W 102 3600 W70 W 29 to 77 to 18 to 29 to 51 to 76 to150 W 14 2200 W 33 5000 W 9 1350 W 14 2200 W 26 4000 W 40 6000 WN37(1) Circuits with non-compensated ferromagnetic ballasts consume twice as much current for a given lamp power output. This explains the small number of lamps in thisconfiguration.(2) The total capacitance of the power factor correction capacitors in parallel in a circuit limits the number of lamps that can be controlled by a contactor. The totaldownstream capacitance of a modular contactor of rating 16, 25, 40 or 63 A should not exceed 75, 100, 200 or 300 µF respectively. Allow for these limits to calculate themaximum acceptable number of lamps if the capacitance values are different from those in the table.(3) High-pressure mercury vapour lamps without ignitor, of power 125, 250 and 400 W, are gradually being replaced by high-pressure sodium vapour lamps with integralignitor, and respective power of 110, 220 and 350 W.Fig. N51 : Maximum number of light fittings for each relay, according to the type, power and configuration of a given lamp (Concluded)© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads4 Lighting circuitsProtection of lamp circuits: Maximum number of lamps and MCB rating versuslamp type, unit power and MCB tripping curveDuring start up of discharge lamps (with their ballast), the inrush current drawn byeach lamp may be in the order of:b 25 x circuit start current for the first 3 msb 7 x circuit start current for the following 2 sFor fluorescent lamps with High Frequency Electronic control ballast, the protectivedevice ratings must cope with 25 x inrush for 250 to 350 µs.However due to the circuit resistance the total inrush current seen by the MCB islower than the summation of all individual lamp inrush current if directly connected tothe MCB.The tables below (see Fig. N52 to NXX) take into account:b Circuits cables have a length of 20 meters from distribution board to the first lampand 7 meters between each additional fittings.b MCB rating is given to protect the lamp circuit in accordance with the cable crosssection, and without unwanted tripping upon lamp starting.b MCB tripping curve (C = instantaneous trip setting 5 to 10 In, D = instantaneoustrip setting 10 to 14 In).Lamppower (W)Number of lamps per circuit1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20MCB rating C & D tripping curve14/18 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 614 x2 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 614 x3 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 10 10 1014 x4 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 10 10 10 1018 x2 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 618 x4 6 6 6 6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10 1021/24 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 621/24 x2 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 628 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 628 x2 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 10 10 1035/36/39 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 635/36 x2 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 10 10 10 10 1038/39 x2 6 6 6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10 10 1040/42 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 640/42 x2 6 6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10 10 10 1649/50 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 649/50 x2 6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10 16 16 16 1654/55 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 10 1054/55 x2 6 6 6 6 6 6 6 6 10 10 10 10 10 10 16 16 16 16 16 1660 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 10 10 10 10N38Fig. N52 : Fluorescent tubes with electronic ballast - Vac = 230 V© Schneider Electric - all rights reservedLamppower (W)Number of lamps per circuit1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20MCB rating C & D tripping curve6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 69 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 611 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 613 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 614 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 615 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 616 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 617 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 618 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 620 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 621 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 623 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 625 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 10Fig. N53 : Compact fluorescent lamps - Vac = 230 VSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads4 Lighting circuitsLamppower (W)Number of lamps per circuit1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20MCB rating C tripping curve50 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 10 10 10 1080 6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10 10 16 16 16125 6 6 6 10 10 10 10 10 10 10 10 16 16 16 16 16 16 16 20 20250 6 10 10 16 16 16 16 16 16 20 20 25 25 25 32 32 32 32 40 40400 6 16 20 25 25 32 32 32 32 32 32 40 40 40 50 50 50 50 63 631000 16 32 40 50 50 50 50 63 63 - - - - - - - - - - -MCB rating D tripping curve50 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 10 10 10 1080 6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10 10 16 16 16125 6 6 6 6 6 6 10 10 10 10 10 16 16 16 16 16 16 16 20 20250 6 6 10 10 10 10 16 16 16 20 20 25 25 25 32 32 32 32 40 40400 6 10 16 16 20 20 25 25 25 32 32 40 40 40 50 50 50 50 63 631000 10 20 25 32 40 40 50 63 63 - - - - - - - - - - -Fig. N54 : High pressure mercury vapour (with ferromagnetic ballast and PF correction) - Vac = 230 VLamppower (W)Number of lamps per circuit1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20MCB rating C tripping curveFerromagnetic ballast18 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 626 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 635/36 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 655 6 6 6 6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10 1091 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10 10 16 16 16 16131 6 6 6 10 10 10 10 10 10 10 10 10 16 16 16 16 16 16 16 20135 6 6 6 10 10 10 10 10 10 10 10 16 16 16 16 16 16 20 20 20180 6 6 10 10 10 10 10 10 16 16 16 16 20 20 20 20 25 25 25 25Electronic ballast36 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 655 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 666 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 10 10 1091 6 6 6 6 6 10 10 10 10 10 10 10 10 10 10 10 16 16 16 16MCB rating D tripping curveFerromagnetic ballast18 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 626 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 635/36 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 655 6 6 6 6 6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 1091 6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10 16 16 16 16131 6 6 6 6 6 6 6 10 10 10 10 10 16 16 16 16 16 16 16 20135 6 6 6 6 6 6 10 10 10 10 10 16 16 16 16 16 16 20 20 20180 6 6 6 6 10 10 10 10 16 16 16 16 20 20 20 20 25 25 25 25Electronic ballast36 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 655 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 666 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 10 10 1091 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10 10 16 16 16 16N39Fig. N55 : Low pressure sodium (with PF correction) - Vac = 230 V© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads4 Lighting circuitsLamppower (W)Number of lamps per circuit1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20MCB rating C tripping curveFerromagnetic ballast50 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 10 10 10 1070 6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10 10 16 16 16100 6 6 6 6 6 6 6 6 10 10 10 10 10 16 16 16 16 16 16 16150 6 6 10 10 10 10 10 10 6 16 16 16 16 16 16 20 20 20 25 25250 6 10 16 16 16 20 20 20 20 20 20 25 25 25 32 32 32 32 40 40400 10 16 20 25 32 32 32 32 32 32 32 40 40 40 50 50 50 50 63 631000 16 32 40 50 50 50 50 63 63 - - - - - - - - - - -Electronic ballast35 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 650 6 6 6 6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10 10100 6 6 6 6 6 6 6 6 10 10 10 10 10 10 16 16 16 16 16 16MCB rating D tripping curveFerromagnetic ballast50 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 10 10 10 1070 6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10 10 16 16 16100 6 6 6 6 6 6 6 6 10 10 10 10 10 16 16 16 16 16 16 16150 6 6 6 6 6 10 10 10 10 16 16 16 16 16 16 20 20 20 25 25250 6 6 10 10 16 16 16 16 16 20 20 25 25 25 32 32 32 32 40 40400 6 10 16 16 20 20 25 25 25 32 32 40 40 40 50 50 50 50 63 631000 10 20 32 32 40 40 50 63 63 - - - - - - - - - - -Electronic ballast35 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 650 6 6 6 6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10 10100 6 6 6 6 6 6 6 6 10 10 10 10 10 10 16 16 16 16 16 16Fig. N56 : High pressure sodium (with PF correction) - Vac = 230 VN40Lamppower (W)Number of lamps per circuit1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20MCB rating C tripping curveFerromagnetic ballast35 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 670 6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10 10 16 16 16150 6 6 10 10 10 10 10 10 10 16 16 16 16 16 16 20 20 20 25 25250 6 10 16 16 16 20 20 20 20 20 20 25 25 25 32 32 32 32 40 40400 6 16 20 25 25 32 32 32 32 32 32 40 40 40 50 50 50 50 63 631000 16 32 40 50 50 50 50 63 63 63 63 63 63 63 63 63 63 63 63 631800/2000 25 50 63 63 63 - - - - - - - - - - - - - - -Electronic ballast35 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 670 6 6 6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10 10 10150 6 6 6 10 10 10 10 10 10 10 16 16 16 16 16 16 16 20 20 20MCB rating D tripping curveFerromagnetic ballast35 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 670 6 6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10 16 16 16150 6 6 6 6 6 10 10 10 10 16 16 16 16 16 16 20 20 20 25 25250 6 6 10 10 16 16 16 16 16 20 20 25 25 25 32 32 32 32 40 40400 6 10 16 16 20 20 25 25 25 32 32 40 40 40 50 50 50 50 63 631000 16 20 32 32 40 50 50 63 63 - - - - - - - - - - -1800 16 32 40 50 63 63 - - - - - - - - - - - - - -2000 20 32 40 50 63 - - - - - - - - - - - - - - -Electronic ballast35 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 670 6 6 6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10 10 10150 6 6 6 6 6 6 6 10 10 10 16 16 16 16 16 16 16 20 20 20Fig. N57 : Metal halide (with PF correction) - Vac = 230 V© Schneider Electric - all rights reservedLamppower (W)Number of lamps per circuit1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20MCB rating C tripping curve1800 16 32 40 50 50 50 50 63 63 - - - - - - - - - - -2000 16 32 40 50 50 50 50 63 63 - - - - - - - - - - -MCB rating D tripping curve1800 16 20 32 32 32 32 50 63 63 - - - - - - - - - - -2000 16 25 32 32 32 32 50 63 - - - - - - - - - - - -Fig. N58 : Metal halide (with ferromagnetic ballast and PF correction) - Vac = 400 VSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads4 Lighting circuitsOverload of the neutral conductorThe riskIn an installation including, for example, numerous fluorescent tubes with electronicballasts supplied between phases and neutral, a high percentage of 3 rd harmoniccurrent can cause an overload of the neutral conductor. Figure N59 below gives anoverview of typical H3 level created by lighting.Lamp type Typical power Setting mode Typical H3 levelIncandescend lamp 100 W Light dimmer 5 to 45 %with dimmerELV halogen lamp 25 W Electronic ELV 5 %transformerFluorescent tube 100 W Magnetic ballast 10 %< 25 W Electronic ballast 85 %> 25 W + PFC 30 %Discharge lamp 100 W Magnetic ballast 10 %Electrical ballast 30 %Fig. N59 : Overview of typical H3 level created by lightingThe solutionFirstly, the use of a neutral conductor with a small cross-section (half) should beprohibited, as requested by Installation standard IEC 60364, section 523–5–3.As far as overcurrent protection devices are concerned, it is necessary to provide4-pole circuit-breakers with protected neutral (except with the TN-C system for whichthe PEN, a combined neutral and protection conductor, should not be cut).This type of device can also be used for the breaking of all poles necessary to supplyluminaires at the phase-to-phase voltage in the event of a fault.A breaking device should therefore interrupt the phase and Neutral circuitsimultaneously.Leakage currents to earthThe riskAt switch-on, the earth capacitances of the electronic ballasts are responsible forresidual current peaks that are likely to cause unintentional tripping of protectiondevices.Two solutionsThe use of Residual Current Devices providing immunity against this type of impulsecurrent is recommended, even essential, when equipping an existing installation(see Fig. N60).For a new installation, it is sensible to provide solid state or hybrid control devices(contactors and remote-control switches) that reduce these impulse currents(activation on voltage passage through zero).N41OvervoltagesThe riskAs illustrated in earlier sections, switching on a lighting circuit causes a transient statewhich is manifested by a significant overcurrent. This overcurrent is accompanied by astrong voltage fluctuation applied to the load terminals connected to the same circuit.These voltage fluctuations can be detrimental to correct operation of sensitive loads(micro-computers, temperature controllers, etc.)The SolutionIt is advisable to separate the power supply for these sensitive loads from the lightingcircuit power supply.Fig. N60 : s.i. residual current devices with immunity againstimpulse currents (Merlin Gerin brand)Sensitivity of lighting devices to line voltage disturbancesShort interruptionsb The riskDischarge lamps require a relighting time of a few minutes after their power supplyhas been switched off.b The solutionPartial lighting with instantaneous relighting (incandescent lamps or fluorescenttubes, or “hot restrike” discharge lamps) should be provided if safety requirements sodictate. Its power supply circuit is, depending on current regulations, usually distinctfrom the main lighting circuit.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads4 Lighting circuitsVoltage fluctuationsb The riskThe majority of lighting devices (with the exception of lamps supplied by electronicballasts) are sensitive to rapid fluctuations in the supply voltage. These fluctuationscause a flicker phenomenon which is unpleasant for users and may even causesignificant problems. These problems depend on both the frequency of variationsand their magnitude.Standard IEC 61000-2-2 (“compatibility levels for low-frequency conducteddisturbances”) specifies the maximum permissible magnitude of voltage variations asa function of the number of variations per second or per minute.These voltage fluctuations are caused mainly by high-power fluctuating loads (arcfurnaces, welding machines, starting motors).b The solutionSpecial methods can be used to reduce voltage fluctuations. Nonetheless, it isadvisable, wherever possible, to supply lighting circuits via a separate line supply.The use of electronic ballasts is recommended for demanding applications(hospitals, clean rooms, inspection rooms, computer rooms, etc).Developments in control and protection equipmentThe use of light dimmers is more and more common. The constraints on ignition aretherefore reduced and derating of control and protection equipment is less important.New protection devices adapted to the constraints on lighting circuits are beingintroduced, for example Merlin Gerin brand circuit-breakers and modular residualcurrent circuit-breakers with special immunity, such as s.i. type ID switches andVigi circuit-breakers. As control and protection equipment evolves, some now offerremote control, 24-hour management, lighting control, reduced consumption, etc.4.4 Lighting of public areasNormal lightingRegulations governing the minimum requirements for buildings receiving the public inmost European countries are as follows:b Installations which illuminates areas accessible to the public must be controlledand protected independently from installations providing illumination to other areasb Loss of supply on a final lighting circuit (i.e. fuse blown or CB tripped) must notresult in total loss of illumination in an area which is capable of accommodating morethan 50 personsb Protection by Residual Current Devices (RCD) must be divided amongst severaldevices (i.e. more than on device must be used)N42Emergency lighting and other systemsWhen we refer to emergency lighting, we mean the auxiliary lighting that is triggeredwhen the standard lighting fails.Emergency lighting is subdivided as follows (EN-1838):Safety lightingIt originates from the emergency lighting and is intended to provide lighting for people toevacuate an area safely or for those who try to fi nish a potentially dangerous operation beforeleaving the area. It is intended to illuminate the means of evacuation and ensure continuousvisibility and ready usage in safety when standard or emergency lighting is needed.Safety lighting may be further subdivided as follows:© Schneider Electric - all rights reservedSafety lighting for escape routesIt originates from the safety lighting, and isintended to ensure that the escape meanscan be clearly identifi ed and used safelywhen the area is busy.Anti-panic lighting in extended areasIt originates from the safety lighting, and isintended to avoid panic and to provide thenecessary lighting to allow people to reacha possible escape route area.Emergency lighting and safety signs for escape routesThe emergency lighting and safety signs for escape routes are very important for allthose who design emergency systems. Their suitable choice helps improve safetylevels and allows emergency situations to be handled better.Schneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads4 Lighting circuitsStandard EN 1838 ("Lighting applications. Emergency lighting") gives somefundamental concepts concerning what is meant by emergency lighting for escaperoutes:"The intention behind lighting escape routes is to allow safe exit by the occupants,providing them with suffi cient visibility and directions on the escape route …"The concept referred to above is very simple:The safety signs and escape route lighting must be two separate things.Functions and operation of the luminairesThe manufacturing specifi cations are covered by standard EN 60598-2-22,"Particular Requirements - Luminaires for Emergency Lighting", which must be readwith EN 60598-1, "Luminaires – Part 1: General Requirements and Tests".DurationA basic requirement is to determine the duration required for the emergency lighting.Generally it is 1 hour but some countries may have different duration requirementsaccording to statutory technical standards.OperationWe should clarify the different types of emergency luminaires:b Non-maintained luminairesv The lamp will only switch on if there is a fault in the standard lightingv The lamp will be powered by the battery during failurev The battery will be automatically recharged when the mains power supply isrestoredb Maintained luminairesv The lamp can be switched on in continuous modev A power supply unit is required with the mains, especially for powering the lamp,which can be disconnected when the area is not busyv The lamp will be powered by the battery during failure.DesignThe integration of emergency lighting with standard lighting must comply strictly withelectrical system standards in the design of a building or particular place.All regulations and laws must be complied with in order to design a system which isup to standard (see Fig. N61).The main functions of an emergency lighting systemwhen standard lighting fails are the following:b Clearly show the escaperoute using clear signs.b Provide sufficient emergencylighting along the escape pathsso that people can safely findtheir ways to the exits.N43b Ensure that alarms andthe fire safety equipmentpresent along the way outare easily identifiable.Fig. N61 : The main functions of an emergency lighting systemEuropean standardsThe design of emergency lighting systems is regulated by a number of legislativeprovisions that are updated and implemented from time to time by newdocumentation published on request by the authorities that deal with European andinternational technical standards and regulations.Each country has its own laws and regulations, in addition to technical standards© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads4 Lighting circuitswhich govern different sectors. Basically they describe the places that must beprovided with emergency lighting as well as its technical specifi cations. Thedesigner's job is to ensure that the design project complies with these standards.EN 1838A very important document on a European level regarding emergency lighting is theStandard EN 1838, "Lighting applications. Emergency lighting".This standard presents specifi c requirements and constraints regarding theoperation and the function of emergency lighting systems.CEN and CENELEC standardsWith the CEN (Comité Européen de Normalisation) and CENELEC standards(Comité Européen de Normalisation Electrotechnique), we are in a standardisedenvironment of particular interest to the technician and the designer. A numberof sections deal with emergencies. An initial distinction should be made betweenluminaire standards and installation standards.EN 60598-2-22 and EN-60598-1Emergency lighting luminaires are subject to European standard EN 60598-2-22, "Particular Requirements - Luminaires for Emergency Lighting", which is anintegrative text (of specifi cations and analysis) of the Standard EN-60598-1,Luminaires – "Part 1: General Requirements and Tests".N44© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads5 Asynchronous motorsThe asynchronous (i.e. induction) motor isrobust and reliable, and very widely used.95% of motors installed around the world areasynchronous. The protection of these motorsis consequently a matter of great importancein numerous applications.The consequence of an incorrectly protected motor can include the following:b For persons:v Asphyxiation due to the blockage of motor ventilationv Electrocution due to insulation failure in the motorv Accident due to non stopping of the motor following the failure of the control circuitin case of incorrect overcurrent protectionb For the driven machine and the processv Shaft couplings and axles, etc, damaged due to a stalled rotorv Loss of productionv Manufacturing time delayedb For the motorv Motor windings burnt out due to stalled rotorv Cost of dismantling and reinstalling or replacement of motorv Cost of repairs to the motorTherefore, the safety of persons and goods, and reliability and availability levels arehighly dependant on the choice of protective equipment.In economic terms, the overall cost of failure must be considered. This costis increasing with the size of the motor and with the difficulties of access andreplacement. Loss of production is a further, and evidently important factor.Specific features of motor performance influence the power supply circuits requiredfor satisfactory operationA motor power-supply circuit presents certain constraints not normally encounteredin other (common) distribution circuits, owing to the particular characteristics, specificto motors, such as:b High start-up current (see Fig. N62) which is mostly reactive, and can therefore bethe cause of important voltage dropb Number and frequency of start-up operations are generally highb The high start-up current means that motor overload protective devices must haveoperating characteristics which avoid tripping during the starting period5.1 Functions for the motor circuittd1 to 10s20 to30 mstI" = 8 to 12 InId = 5 to 8 InIn = rated current of the motorIn Id I"Fig. N62 : Direct on-line starting current characteristics of aninduction motorIFunctions generally provided are:b Basic functions including:v Isolating facilityv Motor control (local or remote)v Protection against short-circuitsv Protection against overloadb Complementary protections including:v Thermal protection by direct winding temperature measurementv Thermal protection by indirect winding temperature determinationv Permanent insulation-resistance monitoringv Specific motor protection functionsb Specific control equipment including:v Electromechanical startersv Control and Protective Switching devices (CPS)v Soft-start controllersv Variable speed drivesBasic functionsIsolating facilityIt is necessary to isolate the circuits, partially or totally, from their power supplynetwork for satety of personnel during maintenance work. “Isolation” function isprovided by disconnectors. This function can be included in other devices designedto provide isolation such as disconnector/circuit-breaker.Motor controlThe motor control function is to make and break the motor current. In case of manualcontrol, this function can be provided by motor-circuit-breakers or switches.In case of remote control, this function can be provided by contactors, starters or CPS.The control function can also be initiated by other means:b Overload protectionb Complementary protectionb Under voltage release (needed for a lot of machines)The control function can also be provided by specific control equipment.N45© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads5 Asynchronous motorsProtection against short-circuitsb Phase-to-phase short-circuitThis type of fault inside the machine is very rare. It is generally due to mechanicalincident of the power supply cable of the motor.b Phase-to-earth short-circuitThe deterioration of winding insulation is the main cause. The resulting fault currentdepends on the system of earthing. For the TN system, the resulting fault current isvery high and in most cases the motor will be deteriorated. For the other systems ofearthing, protection of the motor can be achieved by earth fault protection.For short-circuit protection, it is recommended to pay special attention to avoidunexpected tripping during the starting period of the motor. The inrush current of astandard motor is about 6 to 8 times its rated current but during a fault the currentcan be as high as 15 times the rated current. So, the starting current must not beseen as a fault by the protection. In addition, a fault occuring in a motor circuit mustnot disturb any upstream circuit. As a consequence, discrimination/selectivity ofmagnetic protections must be respected with all parts of the installation.Protection against overloadMechanical overloads due to the driven machine are the main origins of the overloadfor a motor application. They cause overload current and motor overheating. The lifeof the motor can be reduced and sometimes, the motor can be deteriorated. So, it isnecessary to detect motor overload. This protection can be provided by:b Specific thermal overload relayb Specific thermal-magnetic circuit-breaker commonly referred to as “motor circuitbreaker”b Complementary protection (see below) like thermal sensor or electronicmultifunction relayb Electronic soft start controllers or variable speed drives (see below)N46© Schneider Electric - all rights reservedComplementary protectionsb Thermal protection by direct winding temperature measurementProvided by thermal sensors incorporated inside the windings of the motor andassociated relays.b Thermal protection by indirect winding temperature determinationProvided by multifunction relays through current measurement and taking intoaccount the characteristics of the motors (e.g.: thermal time constant).b Permanent insulation-resistance monitoring relays or residual current differentialrelaysThey provide detection and protection against earth leakage current and short-circuitto earth, allowing maintenance operation before destruction of the motor.b Specific motor protection functionsSuch as protection against too long starting period or stalled rotor, protectionagainst unbalanced, loss or permutation of phases, earth fault protection, no loadprotection, rotor blocked (during start or after)…; pre alarm overheating indication,communication, can also be provided by multifunction relays.Specific control equipmentb Electromechanical starters (star-delta, auto-transformer, rheostatic rotorstarters,…)They are generally used for application with no load during the starting period (pump,fan, small centrifuge, machine-tool, etc.)v AdvantagesGood torque/current ratio; great reduction of inrush current.v DisadvantagesLow torque during the starting period; no easy adjustment; power cut off during thetransition and transient phenomenon; 6 motor connection cables needed.b Control and Protective Switching devices (CPS)They provide all the basic functions listed before within a single unit and also somecomplementary functions and the possibility of communication. These devices alsoprovide continuity of service in case of short-circuit.b Soft-start controllersUsed for applications with pump, fan, compressor, conveyor.v AdvantagesReduced inrush current, voltage drop and mechanical stress during the motor start;built-in thermal protection; small size device; possibility of communicationv DisadvantagesLow torque during the starting period; thermal dissipation.Schneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads5 Asynchronous motorsb Variable speed drivesThey are used for applications with pump, fan, compressor, conveyor, machine withhigh load torque, machine with high inertia.v AdvantagesContinuous speed variation (adjustment typically from 2 to 130% of nominal speed),overspeed is possible; accurate control of acceleration and deceleration; hightorque during the starting and stopping periods; low inrush current, built-in thermalprotection, possibility of communication.v DisadvantagesThermal dissipation, volume, cost.5.2 StandardsThe motor control and protection can be achieved in different way:b By using an association of a SCPD (Short-Circuit-Protective-Device) andelectromechanical devices such asv An electromechanical starters fulfilling the standard IEC 60947-4-1v A semiconductor starter fulfilling the standard IEC 60947-4-2v A variable speed drives fulfilling the standard series IEC 61800b By using a CPS, single device covering all the basic functions, and fulfilling thestandard IEC 60947-6-2In this document, only the motor circuits including association of electromechanicaldevices such as, starters and protection against short-circuit, are considered. Thedevices meeting the standard 60947-6-2, the semiconductor starters and the variablespeed drives will be considered only for specific points.A motor circuit will meet the rules of the IEC 60947-4-1 and mainly:b The co-ordination between the devices of the motor circuitb The tripping class of the thermal relaysb The category of utilization of the contactorsb The insulation co-ordinationNote: The first and last points are satisfied inherently by the devices meeting theIEC 60947-6-2 because they provide a continuity of service.Standardization of the association circuit-breaker + contactor+ thermal relayControl devices categoriesThe standards in the IEC 60947 series define the utilisation categoriesaccordingto the purposes the control gear is designed for (see Fig. N63). Each category ischaracterised by one or more operating conditions such as:b Currentsb Voltagesb Power factor or time constantb And if necessary, other operating conditionsN47Type of current Operating categories Typical usesAlternating current AC-1 Non inductive or slightly inductive load, resistance furnace.Power distribution (lighting, generators, etc.).AC-2AC-3AC-4Brush motor: starting, breaking.Heavy duty equipment (hoisting, handling, crusher, rolling-mill train, etc.).Squirrel cage motor: starting, switching off running motors. Motor control (pumps, compressors, fans, machinetools,conveyors,presses, etc.).Squirrel cage motor: starting, plugging, inching. Heavy-duty equipment (hoisting, handling, crusher, rolling-milltrain, etc.).Direct current DC-1 Non inductive or slightly inductive load, resistance furnace.DC-3DC-5Shunt wound motor: starting, reversing, counter-current breaking, inching.Dynamic breaking for direct currentmotors.Series wound motor: starting, reversing, counter-current breaking, inching.Dynamic breaking for direct currentmotors.* Category AC-3 can be used for the inching or reversing, counter-current breaking for occasional operations of a limited length of time, such as for theassembly ofa machine. The number of operations per limited length of time normally do not exceed five per minute and ten per 10 minutes.Fig. N63 : Contactor utilisation categories based on the purposes they are designed for, according to IEC 60947-1© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads5 Asynchronous motorsThe following is also taken into consideration:b Circuit making and breaking conditionsb Type of load (squirrel cage motor, brush motor, resistor)b Conditions in which making and breaking take place (motor running,motor stalled,starting process, counter-current breaking, etc.)Coordination between protections and controlIt is coordination, the most efficient combination of the different protections(againstshort circuits and overloads) and the control device (contactor) which make up amotor starter unit.Studied for a given power, it provides the best possible protection of the equipmentcontrolled by this motor starter unit (see Fig. N64).It has the double advantage of reducing equipment and maintenance costsas thedifferent protections complement each other as exactly as possible,with no uselessredundancy.Trip curve overload relayFuseTrip of the overload relay aloneThermal limit of the breakerOverload relay limitBreaking current with SCPD (1) (1).Magnetic tripping of the breakerN48Fig. N64 : The basics of coordination© Schneider Electric - all rights reservedThere are different types of coordinationTwo types of coordination (type 1 and type 2) are defined by IEC 60947-4-1.b Type 1 coordination:The commonest standard solution. It requires that in event of a short circuit, thecontactor or the starter do not put people or installations in danger. It admits thenecessity of repairs or part replacements before service restoration.b Type 2 coordination:The high performance solution. It requires that in the event of a short circuit, thecontactor or the starter do not put people or installations in danger and that itis able to work afterwards. It admits the risk of contact welding. In this case, themanufacturer must specify the measures to take for equipment maintenance.b Some manufacturers offer:The highest performance solution, which is “Total coordination”.This coordination requires that in the event of a short circuit, the contactor orthe starter do not put people or installations in danger and that it is able to workafterwards. It does not admit the risk of contact welding and the starting of the motorstarter unit must be immediate.Schneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads5 Asynchronous motorsControl and protection switching gear (CPS)CPS or “starter-controllers” are designed to fulfil control and protection functionssimultaneously (overload and short circuit). In addition, they are designed to carryout control operations in the event of a short circuit.They can also assure additional functions such as insulation, thereby totally fulfillingthe function of “motor starter unit”. They comply with standard IEC 60947-6-2, whichnotably defines the assigned values and utilisation categories of a CPS, as dostandards IEC 60947-1 and 60947-4-1.The functions performed by a CPS are combined and coordinated in such a way asto allow for uptime at all currents up to the Ics working short circuit breaking capacityof the CPS. The CPS may or may not consist of one device, but its characteristics areassigned as for a single device. Furthermore, the guarantee of “total” coordination ofall the functions ensures the user has a simple choice with optimal protectionwhich is easy to implement.Although presented as a single unit, a CPS can offer identical or greater modularitythan the “three product” motor starter unit solution. This is the case with the “Tesys U”starter-controller (see Fig. N65).Fig. N65 : Example of a CPS modularity (Tesys Ustarter controller by Telemecanique)N49This starter-controller can at any time bring in or change a control unit with protectionand control functions for motors from 0.15A to 32A in a generic “base power” or“base unit” of a 32 A calibre.Additional functionality’s can also be installed with regard to:b Power, reversing block, limiterb Controlv Functions modules, alarms, motor load, automatic resetting, etc,v Communication modules: AS-I, Modbus, Profibus, CAN-Open, etc,v Auxiliary contact modules, added contacts.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads5 Asynchronous motorsCommunications functions are possible with this system (see Fig. N66).Available functions: Standard Control units: Upgradeable MultifunctionStarter status (ready, running, with default)Alarms (overcurrents…)Thermal alarmRemote resetting by busIndication of motor loadDefaults differentiationParameter setting and protection function reference“Log file” function“Monitoring” functionStart and Stop controlsInformation conveyed by bus (Modbus) and functions performedFig. N66 : Tesys U Communication functionsWhat sort of coordination does one choose?The choice of the coordination type depends on the operation parameters.It should be made to achieve the best balance of user needs and installation costs.b Type 1Acceptable when uptime is not required and the system can be reactivated afterreplacing the faulty parts.In this case the maintenance service must be efficient (available andcompetent).The advantage is reduced equipment costs.b Type 2To be considered when the uptime is required.It requires a reduced maintenance service.When immediate motor starting is necessary, “Total coordination”mustbe retained.No maintenance service is necessary.The coordinations offered in the manufacturers’ catalogues simplify the users’ choiceand guarantees that the motor starter unit complies with the standard.5.3 ApplicationsN50© Schneider Electric - all rights reservedThe control and protection of a motor can consist of one, two, three or four differentdevices which provide one or several functions.In the case of the combination of several devices, co-ordination between themis essential in order to provide optimized protection of the motor application.To protect a motor circuit, many parameters must be taken into account. Theydepend on:b The application (type of driven machine, safety of operation, number of operations,etc.)b The continuity performance requested by the applicationb The standards to be enforced to provide security and safety.The electrical functions to be provided are quite different:b Start, normal operation and stop without unexpected tripping while maintainingcontrol requirements, number of operations, durability and safety requirements(emergency stops), as well as circuit and motor protection, disconnection (isolation)for safety of personnel during maintenance work.Schneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads5 Asynchronous motorsAmong the many possible methods ofprotecting a motor, the association of acircuit breaker + contactor + thermal relay (1)provides many advantagesBasic protection schemes: circuit-breaker + contactor+ thermal relayAvantagesThe combination of devices facilitates installation work, as well as operation andmaintenance, by:b The reduction of the maintenance work load: the circuit-breaker avoids the need toreplace blown fuses and the necessity of maintaining a stock (of different sizes andtypes)b Better continuity performance: the installation can be re-energized immediatelyfollowing the elimination of a fault and after checking of the starterb Additional complementary devices sometimes required on a motor circuit areeasily accomodatedb Tripping of all three phases is assured (thereby avoiding the possibility of “singlephasing”)b Full load current switching possibility (by circuit-breaker) in the event of contactorfailure, e.g. contact weldingb Interlockingb Diverse remote indicationsb Better protection for the starter in case of overcurrent and in particular for impedantshort-circuit (2) corresponding to currents up to about 30 times In of motor (see Fig. N67).b Possibility of adding RCD:v Prevention of risk of fire (sensitivity 500 mA)v Protection against destruction of the motor (short-circuit of laminations) by theearly detection of earth fault currents (sensitivity 300 mA to 30 A)tCircuitbreaker1.05 to 1.20 InMagneticrelayEnd ofstart-upperiodOperating curveof thermal relayContactorThermalrelay1 to10 sCable thermal withstand limitLimit of thermal relay constraintCableMotor20 to30 msInIsI" magn.Short circuit current breaking capacityof the association (CB + contactor)Operating curve of theMA type circuit breakerIShort circuit current breaking capacityof the CBN51Fig. N67 : Tripping characteristics of a circuit-breaker + contactor + thermal relay (1)ConclusionThe combination of a circuit-breaker + contactor + thermal relay for the control andprotection of motor circuits is eminently appropriate when:b The maintenance service for an installation is reduced, which is generally the casein tertiary and small and medium sized industrial sitesb The job specification calls for complementary functionsb There is an operational requirement for a load breaking facility in the event of needof maintenance.(1) The combination of a contactor with a thermal relay iscommonly referred to as a “discontactor”.(2) In the majority of cases, short-circuit faults occur at themotor, so that the current is limited by the cable and the wiringof the starter and are called impedant short-circuits© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads5 Asynchronous motorsKey points in the successful combination of a circuit-breakerand a discontactorStandards define precisely the elements which must be taken into account toachieve a correct coordination of type 2:b Absolute compatibility between the thermal relay of the discontactor and themagnetic trip of the circuit-breaker. In Figure N68 the thermal relay is protected ifits limit boundary for thermal withstand is placed to the right of the circuit-breakermagnetic trip characteristic curve. In the case of a motor control circuit-breakerincorporating both magnetic and thermal relay devices, coordination is provided bydesign.b The overcurrent breaking capability of the contactor must be greater than thecurrent corresponding to the setting of the circuit-breaker magnetic trip relay.b When submitted to a short-circuit current, the contactor and its thermal relay mustperform in accordance with the requirements corresponding to the specified type ofco-ordination.Compacttype MAt21 Operating curve of the MA type circuit breaker2 Operating curve of thermal relay3 Limit of thermal relay constraintIcc ext.13Fig. N68 : The thermal-withstand limit of the thermal relay must be to the right of the CBmagnetic-trip characteristicIN52It is not possible to predict the short-circuitcurrent-breaking capacity of a circuit-breaker+ contactor combination. Only laboratory testsby manufacturers allow to do it. So, SchneiderElectric can give table with combination ofMulti 9 and Compact type MA circuit-breakerswith different types of startersShort-circuit current-breaking capacity of a circuit-breaker+ contactor combinationAt the selection stage, the short-circuit current-breaking capacity which must becompared to the prospective short-circuit current is:b Either, that of the circuit-breaker + contactor combination if the circuit-breakerand the contactor are physically close together (see Fig. N69) (same drawer orcompartment of a motor control cabinet). A short-circuit downstream of thecombination will be limited to some extent by the impedances of the contactor andthe thermal relay. The combination can therefore be used on a circuit for whichthe prospective short-circuit current level exceeds the rated short-circuit currentbreakingcapacity of the circuit-breaker. This feature very often presents a significanteconomic advantageb Or that of the circuit-breaker only, for the case where the contactor is separated(see Fig. N70) with the risk of short-circuit between the contactor and the circuitbreaker.© Schneider Electric - all rights reservedMFig. N69 : Circuit-breaker and contactor mounted side by sideFig. N70 : Circuit-breaker and contactor mounted separatelyMSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads5 Asynchronous motorsChoice of instantaneous magnetic-trip relay for the circuitbreakerThe operating threshold must never be less than 12 In for this relay, in order to avoidunexpected tripping due to the first current peak during motor starting.Complementary protectionsComplementary protections are:b Thermal sensors in the motor (windings, bearings, cooling-air ducts, etc.)b Multifunction protections (association of functions)b Insulation-failure detection devices on running or stationary motorThermal sensorsThermal sensors are used to detect abnormal temperature rise in the motor by directmeasurement. The thermal sensors are generally embedded in the stator windings(for LV motors), the signal being processed by an associated control device acting totrip the contactor or the circuit-breaker (see Fig. N71).Fig. N71 : Overheating protection by thermal sensorsMutifunction motor protection relayThe multifunction relay, associated with a number of sensors and indication modules,provides protection for motor and also for some functions, protection of the drivenmachine such as:b Thermal overloadb Stalled rotor, or starting period too longb Overheatingb Unbalanced phase current, loss of one phase, inverse rotationb Earth fault (by RCD)b Running at no-load, blocked rotor on startingThe avantages are essentially:b A comprehensive protection, providing a reliable, high performance and permanentmonitoring/control functionb Efficient monitoring of all motor-operating schedulesb Alarm and control indicationsb Possibility of communication via communication busesExample: Telemecanique LT6 relay with permanent monitoring/control functionand communication by bus, or multifunction control unit LUCM and communicationmodule for TeSys model U.Preventive protection of stationary motorsThis protection concerns the monitoring of the insulation resistance level of astationary motor, thereby avoiding the undesirable consequences of insulation failureduring operation such as:b Failure to start or to perform correctly for motor used on emergency systemsb Loss of productionThis type of protection is essential for emergency systems motors, especially wheninstalled in humid and/or dusty locations. Such protection avoids the destruction ofa motor by short-circuit to earth during starting (one of the most frequently-occuringincidents) by giving a warning informing that maintenance work is necessary torestore the motor to a satisfactory operationnal condition.N53© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads5 Asynchronous motorsExample of application:Motors driving pumps for “sprinklers” fire-protection systems or irrigation pumps forseasonal operation.A Vigilohm SN21 (Merlin Gerin) monitors the insulation of a motor, and signalsaudibly and visually any abnormal reduction of the insulation resistance level.Furthermore, this relay can prevent any attempt to start the motor, if necessary(see Fig. N72).SM21M E R LIN G E R INSM20IN OUTFig. N72 : Preventive protection of stationary motorsN54Limitative protectionsResidual current diffential protective devices (RCDs) can be very sensitive anddetect low values of leakage current which occur when the insulation to earth of aninstallation deteriorates (by physical damage, contamination, excessive humidity,and so on). Some versions of RCDs, with dry contacts, specially designed for suchapplications, provide the following:b To avoid the destruction of a motor (by perforation and short-circuiting of thelaminations of the stator) caused by an eventual arcing fault to earth. This protectioncan detect incipient fault conditions by operating at leakage currents in the range of300 mA to 30 A, according to the size of the motor (approx sensitivity: 5% In)b To reduce the risk of fire: sensitivity y 500 mAFor example, RH99M relay (Merlin Gerin) provides (see Fig. N73):b 5 sensitivities (0.3; 1; 3; 10; 30 A)b Possibility of discrimination or to take account of particular operation by virtue of 3possible time delays (0, 90, 250 ms)b Automatic breaking if the circuit from the current transformer to the relay is brokenb Protection against unwanted trippingsb Protection against DC leakage currents (type A RCD)RH99M© Schneider Electric - all rights reservedFig. N73 : Example using relay RH99MM E R LIN G E R INSchneider Electric - Electrical installation guide 2009

N - Characteristics of particular sources and loads5 Asynchronous motorsThe importance of limiting the voltage drop at the motor terminals duringstart-upIn order to have a motor starting and accelerating to its normal speed in theappropriate time, the torque of the motor must exceed the load torque by at least70%. However, the starting current is much higher than the full-load current ofthe motor. As a result, if the voltage drop is very high, the motor torque will beexcessively reduced (motor torque is proportional to U 2 ) and it will result, for extremecase, in failure to start.Example:b With 400 V maintained at the terminals of a motor, its torque would be 2.1 timesthat of the load torqueb For a voltage drop of 10% during start-up, the motor torque would be2.1 x 0.9 2 = 1.7 times the load torque, and the motor would accelerate to its ratedspeed normallyb For a voltage drop of 15% during start-up, the motor torque would be2.1 x 0.85 2 = 1.5 times the load torque, so that the motor starting time wouldbe longer than normalIn general, a maximum allowable voltage drop of 10% is recommended duringstart-up of the motor.5.4 Maximum rating of motors installed forconsumers supplied at LVThe disturbances caused on LV distribution networks during the start-up of largedirect-on-line AC motors can cause considerable nuisance to neighbouringconsumers, so that most power-supply utilities have strict rules intended to limit suchdisturbances to tolerable levels. The amount of disturbance created by a given motordepends on the “strength” of the network, i.e. on the short-circuit fault level at thepoint concerned. The higher the fault level, the “stronger” the system and the lowerthe disturbance (principally voltage drop) experienced by neibouring consumers. Fordistribution networks in many countries, typical values of maximum allowable startingcurrents and corresponding maximum power ratings for direct-on-line motors areshown in Figures N74 and N75 below.Type of motor Location Maximum starting current (A)Overhead-line network Underground-cable networkSingle phase Dwellings 45 45Others 100 200Three phase Dwellings 60 60Others 125 250Fig. N74 : Maximum permitted values of starting current for direct-on-line LV motors (230/400 V)LocationType of motorSingle phase 230 V(kW)Three phase 400 VDirect-on-line starting Other methodsat full load (kW) of starting (kW)Dwellings 1.4 5.5 11Others Overhead 3 11 22line networkUnderground 5.5 22 45cable networkN55Fig. N75 : Maximum permitted power ratings for LV direct-on-line starting motorsSince, even in areas supplied by one power utility only, “weak” areas of the networkexist as well as “strong” areas, it is always advisable to secure the agreement of thepower supplier before acquiring the motors for a new project.Other (but generally more costly) alternative starting arrangements exist, whichreduce the large starting currents of direct-on-line motors to acceptable levels; forexample, star-delta starters, slip-ring motor, “soft start” electronic devices, etc.5.5 Reactive-energy compensation (power-factorcorrection)The method to correct the power factor is indicated in chapter L.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Chapter PResidential and other speciallocations123ContentsResidential and similar premises1.1 General P21.2 Distribution boards components P21.3 Protection of people P41.4 Circuits P61.5 Protection against overvoltages and lightning P7Bathrooms and showersP82.1 Classification of zones P82.2 Equipotential bonding P112.3 Requirements prescribed for each zone P11Recommendations applicable to special installations P12and locationsP2P© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

P - Residential and other special locations1 Residential and similar premisesElectrical installations for residential premisesneed a high standard of safety and reliabilityThe power distribution utility connects the LVneutral point to its MV/LV distribution tranformerto earth.All LV installations must be protected by RCDs.All exposed conductive parts must be bondedtogether and connected to the earth.1.1 GeneralRelated standardsMost countries have national regulations and-or standards governing the rulesto be strictly observed in the design and realization of electrical installations forresidential and similar premises. The relevant international standard is the publicationIEC 60364.The power networkThe vast majority of power distribution utilities connect the low voltage neutral pointof their MV/LV distribution transformers to earth.The protection of persons against electric shock therefore depends, in such case, onthe principle discussed in chapter F. The measures required depend on whether theTT, TN or IT scheme of earthing is adopted.RCDs are essential for TT and IT earthed installations. For TN installations, highspeed overcurrent devices or RCDs may provide protection against direct contactof the electrical circuits. To extend the protection to flexible leads beyond the fixedsocket outlets and to ensure protection against fires of electrical origin RCDs shallbe installed.The quality of electrical equipment used inresidential premises is commonly ensured by amark of conformity situated on the front of eachitem1.2 Distribution boards components (see Fig. P1)Distribution boards (generally only one in residential premises) usually includethe meter(s) and in some cases (notably where the supply utilities impose a TTearthing system and/or tariff conditions which limit the maximum permitted currentconsumption) an incoming supply differential circuit-breaker which includes anovercurrent trip. This circuit-breaker is freely accessible to the consumer.EnclosureService connectionLightning protectionIncoming-supplycircuit breakerDistribution boardCombi surge arresterPOvercurrentprotectionand isolationProtection againstdirect and indirectcontact,and protectionagainst fireRemote controlMCB phase and neutralDifferentialMCBRemote control switchTL 16 ADifferential loadswitch© Schneider Electric - all rights reservedFig. P1 : Presentation of realizable functions on a consumer unitEnergy managementProgrammable thermostatTHPProgrammable time switchIHPLoad shedding switchCDStContactors, off-peakor manual control CTSchneider Electric - Electrical installation guide 2009

P - Residential and other special locations1 Residential and similar premisesOn installations which are TN earthed, the supply utilities usually protect theinstallation simply by means of sealed fuse cut-outs immediately upstream of themeter(s) (see Fig. P2). The consumer has no access to these fuses.MeterFuse …or …Circuit breakerdepending onearthing systemDistributionboardFig. P2 : Components of a control and distribution boardFig. P3 : Incoming-supply circuit-breakerFig. P4 : Control and distribution boardIf, in a TT scheme, the value of 80 Ω for theresistance of the electrode can not be met then,30 mA RCDs must be installed to take over thefunction of the earth leakage protection of theincoming supply circuit-breakerThe incoming supply circuit-breaker (see Fig. P3)The consumer is allowed to operate this CB if necessary (e.g to reclose it if thecurrent consumption has exceeded the authorized limit; to open it in case ofemergency or for isolation purposes).The rated residual current of the incoming circuit-breaker in the earth leakageprotection shall be 300 mA.If the installation is TT, the earth electrode resistance shall be less than50 VR 300 mA 166 . In practice, the earth electrode resistance of a new installationshall be less than 80 Ω Ω ( R 2 ). .The control and distribution board (consumer unit) (see Fig. P4)This board comprises:b A control panel for mounting (where appropriate) the incoming supply circuitbreakerand other control auxiliaries, as requiredb A distribution panel for housing 1, 2 or 3 rows (of 24 multi 9 units) or similar MCBsor fuse units, etc.b Installation accessories for fixing conductors, and rails for mounting MCBs, fusesbases, etc, neutral busbar and earthing bar, and so onb Service cable ducts or conduits, surface mounted or in cable chases embedded inthe wallNote: to facilitate future modifications to the installation, it is recommended to keepall relevant documents (photos, diagrams, characteristics, etc.) in a suitable locationclose to the distribution board.The board should be installed at a height such that the operating handles,indicating dials (of meters) etc., are between 1 metre and 1.80 metres from the floor(1.30 metres in situations where handicapped or elderly people are concerned).Lightning arrestersThe installation of lightning arresters at the service position of a LV installation isstrongly recommended for installations which include sensitive (e.g electronic)equipment.These devices must automatically disconnect themselves from the installation incase of failure or be protected by a MCB. In the case of residential installations, theuse of a 300 mA differential incoming supply circuit-breaker type S (i.e slightly timedelayed)will provide effective earth leakage protection, while, at the same time, willnot trip unnecessarily each time a lightning arrester discharges the current (of anovervoltage-surge) to earth.Resistance value of the earth electrodeIn the case where the resistance to earth exceeds 80 Ω, one or several 30 mA RCDsshould be used in place of the earth leakage protection of the incoming supplycircuit-breaker.P© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

P - Residential and other special locations1 Residential and similar premisesWhere utility power supply systems andconsumers’ installations form a TT earthedsystem, the governing standards impose the useof RCDs to ensure the protection of persons1.3 Protection of peopleOn TT earthed systems, the protection of persons is ensured by the followingmeasures:b Protection against indirect contact hazards by RCDs (see Fig. P5) of mediumsensitivity (300 mA) at the origin of the installation (incorporated in the incomingsupply circuit-breaker or, on the incoming feed to the distribution board). Thismeasure is associated with a consumer installed earth electrode to which must beconnected the protective earth conductor (PE) from the exposed conductive parts ofall class I insulated appliances and equipment, as well as those from the earthingpins of all socket outletsb When the CB at the origin of an installation has no RCD protection, the protectionof persons shall be ensured by class II level of insulation on all circuits upstreamof the first RCDs. In the case where the distribution board is metallic, care shall betaken that all live parts are double insulated (supplementary clearances or insulation,use of covers, etc.) and wiring reliably fixedb Obligatory protection by 30 mA sensitive RCDs of socket outlet circuits, andcircuits feeding bathroom, laundry rooms, and so on (for details of this latterobligation, refer to clause 3 of this chapter)300 mA30 mA 30 mADiversecircuitsSocket-outletscircuitBathroom and/orshower roomFig. P5 : Installation with incoming-supply circuit-breaker having instantaneous differentialprotectionPIncoming supply circuit-breaker with instantaneous differentialrelayIn this case:b An insulation fault to earth could result in a shutdown of the entire installationb Where a lightning arrester is installed, its operation (i.e. discharging a voltagesurge to earth) could appear to an RCD as an earth fault, with a consequentshutdown of the installationRecommendation of suitable Merlin Gerin componentsb Incoming supply circuit-breaker with 300 mA differential andb High sensitivity 30 mA RCD (for example differential circuit-breaker 1P + N typeDeclic Vigi) on the circuits supplying socket outletsb High sensitivity 30 mA RCD (for example differential load switch type ID’clic) oncircuits to bathrooms, shower rooms, laundry rooms, etc. (lighting, heating, socketoutlets)© Schneider Electric - all rights reservedIncoming supply circuit-breaker with type S time delayeddifferential relayThis type of CB affords protection against fault to earth, but by virtue of a short timedelay, provides a measure of discrimination with downstream instantaneous RCDs.Tripping of the incoming supply CB and its consequences (on deep freezers, forexample) is thereby made less probable in the event of lightning, or other causes ofvoltage surges. The discharge of voltage surge current to earth, through the surgearrester, will leave the type S circuit-breaker unaffected.Schneider Electric - Electrical installation guide 2009

P - Residential and other special locations1 Residential and similar premisesRecommendation of suitable Merlin Gerin components (see Fig. P6)b Incoming supply circuit-breaker with 300 mA differential type S andb High sensitivity 30 mA RCD (for example differential circuit-breaker 1P + N typeDeclic Vigi) on the circuits supplying washing machines and dish-washing machineb High sensitivity 30 mA RCD (for example differential load switch type ID’clic) oncircuits to bathrooms, shower rooms, laundry rooms, etc. (lighting, heating, socketoutlets)300 mA - type S12DiversecircuitsHigh-risk location(laundry room)30 mA 30 mA 30 mASocketoutletcircuitBathroom and/orshower roomFig. P6 : Installation with incoming-supply circuit-breaker having short time delay differentialprotection, type S5 3 4Diversecircuits300 mA 30 mA 30 mA 30 mAHigh-risk circuit(dish-washingmachine)Socket-outletcircuitBathroom and/orshower roomFig. P7 : Installation with incoming-supply circuit-breakerhaving no differential protectionIncoming supply circuit-breaker without differential protectionIn this case the protection of persons must be ensured by:b Class II level of insulation up to the downstream terminals of the RCDsb All outgoing circuits from the distribution board must be protected by 30 mA or300 mA RCDs according to the type of circuit concerned as discussed in chapter F.Where a voltage surge arrester is installed upstream of the distribution board(to protect sensitive electronic equipment such as microprocessors, videocassetterecorders, TV sets, electronic cash registers, etc.) it is imperative that thedevice automatically disconnects itself from the installation following a rare (butalways possible) failure. Some devices employ replaceable fusing elements; therecommended method however as shown in Figure P7, is to use a circuit-breaker.Recommendation of suitable Merlin Gerin componentsFigure P7 refers:1. Incoming-supply circuit-breaker without differential protection2. Automatic disconnection device (if a lightning arrester is installed)3. 30 mA RCD (for example differential circuit-breaker 1P + N type Declic Vigi) oneach circuit supplying one or more socket-outlets4. 30 mA RCD (for example differential load swith type ID’clic) on circuits tobathrooms and shower rooms (lighting, heating and socket-outlets) or a 30 mAdifferential circuit-breaker per circuit5. 300 mA RCD (for example differential load swith) on all the other circuitsP© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

P - Residential and other special locations1 Residential and similar premisesThe distribution and division of circuits providescomfort and facilitates rapid location of fault1.4 CircuitsSubdivisionNational standards commonly recommend the subdivision of circuits according to thenumber of utilization categories in the installation concerned (see Fig. P8):b At least 1 circuit for lighting. Each circuit supplying a maximum of 8 lighting pointsb At least 1 circuit for socket-outlets rated 10/16 A, each circuit supplying a maximumof 8 sockets. These sockets may be single or double units (a double unit is made upof two 10/16 A sockets mounted on a common base in an embedded box, identicalto that of a single unitb 1 circuit for each appliance such as water heater, washing machine, dish-washingmachine, cooker, refrigerator, etc. Recommended numbers of 10/16 A (or similar)socket-outlets and fixed lighting points, according to the use for which the variousrooms of a dwelling are intended, are indicated in Figure P9SocketoutletsLightingHeatingWashingmachineCookingapparatusRoom function Minimum number Minimum numberof fixed lighting points of 10/16 A socket-outletsLiving room 1 5Bedroom, lounge, 1 3bureau, dining roomKitchen 2 4 (1)Bathroom, shower room 2 1 or 2Entrance hall, box room 1 1WC, storage space 1 -Laundry room - 1(1) Of which 2 above the working surface and 1 for a specialized circuit: in additionan independent socket-outlet of 16 A or 20 A for a cooker and a junction box orsocket-outlet for a 32 A specialized circuitFig. P8 : Circuit division according to utilizationFig P9 : Recommended minimum number of lighting and power points in residential premisesThe inclusion of a protective conductor in allcircuits is required by IEC and most nationalstandardsProtective conductorsIEC and most national standards require that each circuit includes a protectiveconductor. This practice is strongly recommended where class I insulated appliancesand equipment are installed, which is the general case.The protective conductors must connect the earthing-pin contact in each socketoutlet,and the earthing terminal in class I equipment, to the main earthing terminalat the origin of the installation.Furthermore, 10/16 A (or similarly sized) socket-outlets must be provided withshuttered contact orifices.PCross-sectional-area (c.s.a.) of conductors (see Fig. P10)The c.s.a. of conductors and the rated current of the associated protective devicedepend on the current magnitude of the circuit, the ambient temperature, the kind ofinstallation, and the influence of neighbouring circuits (refer to chapter G)Moreover, the conductors for the phase wires, the neutral and the protectiveconductors of a given circuit must all be of equal c.s.a. (assuming the same materialfor the conductors concerned, i.e. all copper or all aluminium).© Schneider Electric - all rights reservedFig. P10 : Circuit-breaker 1 phase + N - 2 x 9 mm spacesSchneider Electric - Electrical installation guide 2009

P - Residential and other special locations1 Residential and similar premisesFigure P11 indicates the c.s.a. required for commonly-used appliancesProtective devices 1 phase + N in 2 x 9 mm spaces comply with requirements forisolation, and for marking of circuit current rating and conductor sizes.Type of circuit c. s. a. of the Maximum power Protective devicesingle-phase 230 Vconductors1 ph + N or 1 ph + N + PEFixed lighting 1.5 mm 2 2,300 W Circuit-breaker 16 A(2.5 mm 2 ) Fuse 10 A10/16 A 2.5 mm 2 4,600 W Circuit-breaker 25 A(4 mm 2 ) Fuse 20 AIndividual-load circuitsWater heater 2.5 mm 2 4,600 W Circuit-breaker 25 A(4 mm 2 ) Fuse 20 ADish-washing machine 2.5 mm 2 4,600 W Circuit-breaker 25 A(4 mm 2 ) Fuse 20 AClothes-washing machine 2.5 mm 2 4,600 W Circuit-breaker 25 A(4 mm 2 ) Fuse 20 ACooker or hotplate (1) 6 mm 2 7,300 W Circuit-breaker 40 A(10 mm 2 ) Fuse 32 AElectric space heater 1.5 mm 2 2,300 W Circuit-breaker 16 A(2.5 mm 2 ) Fuse 10 A(1) In a 230/400 V 3-phase circuit, the c. s. a. is 4 mm 2 for copper or 6 mm 2 for aluminium, and protection is provided by a 32 Acircuit-breaker or by 25 A fuses.Fig. P11 : C. s. a. of conductors and current rating of the protective devices in residential installations (the c. s. a. of aluminium conductors are shown in brackets)1.5 Protection against overvoltages and lightningThe choice of surge arrester is described in chapter JInstallation rulesThree principal rules must be respected:1 - It is imperative that the three lengths of cable used for the installation of the surgearrester each be less than 50 cm i.e.:b the live conductors connected to the isolating switchb from the isolating switch to the surge arresterb from the surge arrester to the main distribution board (MDB) earth bar (notto be confused with the main protective-earth (PE) conductor or the main earthterminal for the installation.The MDB earth bar must evidently be located in thesame cabinet as the surge arrester.2 - It is necessary to use an isolating switch of a type recommended by themanufacturer of the surge arrester.3 - In the interest of a good continuity of supply it is recommended that thecircuit-breaker be of the time-delayed or selective type.P© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

P - Residential and other special locations2 Bathrooms and showersBathrooms and showers rooms are areas of high risk, because of the very lowresistance of the human body when wet or immersed in water.Precaution to be taken are therefore correspondingly rigorous, and the regulationsare more severe than those for most other locations.The relevant standard is IEC 60364-7-701.Precautions to observe are based on three aspects:b The definition of zones, numbered 0,1, 2, 3 in which the placement (or exclusion)of any electrical device is strictly limited or forbidden and, where permitted, theelectrical and mechanical protection is prescribedb The establishment of an equipotential bond between all exposed and extraneousmetal parts in the zones concernedb The strict adherence to the requirements prescribed for each particular zones, astabled in clause 32.1 Classification of zonesSub-clause 701.32 of IEC 60364-7-701 defines the zones 0, 1, 2, 3 as shown in thefollowing diagrams (see Fig. P12 below to Fig P18 opposite and next pages):Zone 1*Zone 0Zone 2 Zone 3Zone 1*Zone 0Zone 2 Zone 30.60 m 2.40 m0.60 m2.40 mZone 1Zone 2Zone 3Zone 12.25 mZone 0P0.60 m2.40 m(*) Zone 1 is above the bath as shown in the vertical cross-sectionFig. P12 : Zones 0, 1, 2 and 3 in proximity to a bath-tub© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

2 Bathrooms and showersZone 0Zone 1 Zone 2Zone 0Zone 3 Zone 1 Zone 2 Zone 30.60 m2.40 m0.60 m2.40 mZone 1 Zone 2Zone 3Zone 12.25 mZone 00.60 m2.40 mFig. P13 : Zones 0, 1, 2 and 3 in proximity of a shower with basinZone 1Zone 2Fixed showerhead (1)0.60 m 0.60 mZone 10.60 m0.60 mZone 2Fixed showerhead (1)Zone 32.40 mZone 32.40 mZone 1Zone2Zone 32.25 m(1) When the shower head is at the end of a flexible tube, the vertical central axis ofa zone passes through the fixed end of the flexible tubeFig. P14 : Zones 0, 1, 2 and 3 in proximity of a shower without basinP0.60 mPrefabricatedshowercabinet0.60 mFig. P15 : No switch or socket-outlet is permitted within 60 cm of the door opening of a showercabinet© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

P - Residential and other special locations2 Bathrooms and showersClassesof externalinfluencesClassesof externalinfluencesAD 3BB 2BC 3AD 3BB 3BC 3AD 7BB 3BC 3Fig. P16 : Individual showers with dressing cubiclesZone 3Dressing cubicles (zone 2)Shower cabinets (zone 1)AD 3BB 2BC 3WCAD 3BB 2BC 3Classesof externalinfluencesClassesof externalinfluencesh < 1.10mAD 51.10m < h < 2.25mAD 3BB 3BC 3Dressing cubiclesZone 2h < 1.10mAD 51.10m < h < 2.25mAD 3BB 3BC 3AD 7BB 3BC 3Zone 1WCAD 3BB 2BC 3Fig. P17 : Individual showers with separate individual dressing cubiclesClassesof externalinfluencesAD 3BB 2BC 3Dressing roomZone 2Classesof externalinfluencesh < 1.10mAD 51.10m < h < 2.25mAD 3BB 3BC 3h < 1.10mAD 51.10m < h < 2.25mAD 3BB 3BC 3Zone 2Zone 1AD 7BB 3BC 3P10Fig. P18 : Communal showers and common dressing roomNote: Classes of external influences (see Fig. E46).© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

P - Residential and other special locations2 Bathrooms and showers2.2 Equipotential bonding (see Fig. P19)To the earthelectrodeMetallic pipesh i 2 mWater-drainagepipingSocket-outletGazRadiatorLightingMetal bathEquipotential conductorsfor a bathroomMetaldoor-frameFig. P19 : Supplementary equipotential bonding in a bathroom2.3 Requirements prescribed for each zoneThe table of clause 3 describes the application of the principles mentioned in theforegoing text and in other similar or related casesP11© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

P - Residential and other special locations3 Recommendations applicable tospecial installations and locationsFigure P20 below summarizes the main requirements prescribed in many nationaland international standards.Note: Section in brackets refer to sections of IEC 60364-7P12© Schneider Electric - all rights reservedLocations Protection principles IP Wiring Switchgear Socket-outlets Installationlevel and cables materialsDomestic dwellings b TT or TN-S systems 20 Switch operating handles Protection byand other habitations b Differential protection and similar devices on 30 mA RCDsv 300 mA if the earth electrodedistribution panels,resistance is y 80 ohms instantaneousto be mountedor short time delay (type S)between 1 metre andv 30 mA if the earth electrode1.80 metre above the floorresistance is u 500 ohmsb surge arrester at the origin of theinstallation ifv supply is from overhead line with bareconductors, and ifv the keraunic level > 25b a protective earth (PE) conductoron all circuitsBathrooms or shower Supplementary equipotential bondingrooms (section 701) in zones 0, 1, 2 and 3Zone 0 SELV 12 V only 27 Class II Special applianceslimited tostrict minimumZone 1 SELV 12 V 25 Class II Special apllianceslimited toWater heaterstrict minimumZone 2 SELV 12 V or 30 mA RCD 24 Class II Special applianceslimited toWater heaterstrict minimumClass II luminairesZone 3 21 Only socket-outlets protected by :b 30 mA RCD orb Electrical separation orb SELV 50 VSwimming baths Supplementary equipotential bonding(section 702) in zones 0, 1, and 2Zone 0 SELV 12 V 28 Class II Special applianceslimited tostrict minimumZone 1 25 Class II Special applianceslimited tostrict minimumZone 2 22 Only socket-outlets protected by :(indoor)b 30 mA RCD or24 b electrical separation or(outdoor)b SELV 50 VSaunas 24 Class II Adapted to temperature(section 703)Work sites Conventional voltage limit UL 44 Mechanically Protection by(section 704) reduced to 25 V protected 30 mA RCDsAgricultural and Conventional voltage limit UL 35 Protection byhorticultural reduced to 25 V 30 mA RCDsestablishments Protection against fire risks(section 705)by 500 mA RCDsRestricted conductive 2x Protection of:locations (section 706)b Portable tools by:v SELV orv Electrical separationb Hand-held lampsv By SELVb Fixed equipement byv SELVv Electrical separationv 30 mA RCDsv Special supplementaryequipotential bondingFig. P20 : Main requirements prescribed in many national and international standards (continued on opposite page)Schneider Electric - Electrical installation guide 2009

P - Residential and other special locations3 Recommendations applicable tospecial installations and locationsLocations Protection principles IP Wiring Switchgear Socket-outlets Installationlevel and cables materialsFountainsProtection by 30 mA RCDs and(section 702)equipotential bonding of all exposedand extraneous conductive partsData processing TN-S system recommended(section 707)TT system if leakage current is limited.Protective conductor 10 mm 2 minimumin aluminium. Smaller sizes (in copper)must be doubled.Caravan park 55 Flexible cable of Socket-outlets(section 708) 25 metres shall be placedlengthat a height of0.80 m to 1.50 mfrom the ground.Protection ofcircuits by30 mA RCDs(one per 6socket-outlets)Marinas and pleasure The cable length for connection to Protection ofcraft (section 709) pleasure craft must not exceeded 25 m circuits by30 mA RCDs(one per 6socket-outlets)Medical locations IT medical system equipotential Only magnetic Protection of circuitsGroup 2 : Operating grouding, limited to one operating protection for the by thermal-magnetictheatres and similar theatre and not exceeding 10 kVA primary of LV/LV protection only. One(section 710) transformer. Monitoring to three per circuit.of secondary loadsand transformertemperatureMedical locations TT or TNS Protection byGroup 1 :30 mA RCDsHospitalization andsimilar (section 710)Exhibitions, shows and TT or TN-S systems 4x Protection bystands (section 711)30 mA RCDsBalneotherapy Individual: see section 701(cure-centre baths) (volumes 0 and 1)Collective: see section 702(volumes 0 and 1)Motor-fuel filling Explosion risks in security zones Limited to thestationsnecessary minimumMotor vehicules Protection by RCDs or byelectrical separationExternal lighting 23 Protection byinstallations30 mA RCDs(section 714)Mobile or transportable The use of TN-C system is not30 mA RCDsunits (section 717) permitted inside any unit must be used forall socket-outletssupplyingequipmentoutside the unitFig. P20 : Main requirements prescribed in many national and international standards (concluded)P13© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Chapter QEMC guidelines12345ContentsElectrical distributionEarthing principles and structuresImplementationQ53.1 Equipotential bonding inside and outside buildings Q53.2 Improving equipotential conditions Q53.3 Separating cables Q73.4 False floor Q73.5 Cable running Q83.6 Implementation of shielded cables Q113.7 Communication networks Q113.8 Implementation of surge arrestors Q123.9 Cabinet cabling Q153.10 Standards Q15Coupling mechanisms and counter-measuresQ164.1 General Q164.2 Common-mode impedance coupling Q174.3 Capacitive coupling Q184.4 Inductive coupling Q194.5 Radiated coupling Q20Wiring recommendationsQ225.1 Signal classes Q225.2 Wiring recommendations Q22Q2Q3Q© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Q - EMC guidelines1 Electrical distributionThe system earthing arrangement must be properly selected to ensure thesafety of life and property. The behaviour of the different systems with respectto EMC considerations must be taken into account. Figure Q1 below presents asummary of their main characteristics.European standards (see EN 50174-2 § 6.4 and EN 50310 § 6.3) recommend theTN-S system which causes the fewest EMC problems for installations comprisinginformation-technology equipment (including telecom equipment).TT TN-S IT TN-CSafety of persons Good GoodRCD mandatory Continuity of the PE conductor must be ensured throughout the installationSafety of property Good Poor Good PoorMedium fault current High fault current Low current for first fault High fault current(< a few dozen amperes) (around 1 kA) (< a few dozen mA), (around 1 kA)but high for second faultAvailability of energy Good Good Excellent GoodEMC behaviour Good Excellent Poor (to be avoided) Poor- Risk of overvoltages - Few equipotential - Risk of overvoltages (should never be used)- Equipotential problems - Common-mode filters - Neutral and PE areproblems - Need to manage and surge arrestors the same- Need to manage devices with high must handle the phase- - Circulation of disturbeddevices with high leakage currents to-phase voltages currents in exposedleakage currents - High fault currents - RCDs subject to conductive parts (high(transient disturbances) nuisance tripping if magnetic-field radiation)common-mode - High fault currentscapacitors are present (transient disturbances)- Equivalent toTN system for secondfaultFig. Q1 : Main characteristics of system earthingWhen an installation includes high-power equipment (motors, air-conditioning, lifts,power electronics, etc.), it is advised to install one or more transformers specificallyfor these systems. Electrical distribution must be organised in a star system and alloutgoing circuits must exit the main low-voltage switchboard (MLVS).Electronic systems (control/monitoring, regulation, measurement instruments, etc.)must be supplied by a dedicated transformer in a TN-S system.Figure Q2 below illustrate these recommendations.Transformer© Schneider Electric - all rights reservedQDisturbingdevicesSensitivedevicesDisturbingdevicesSensitivedevicesDisturbingdevicesNot recommended Preferable ExcellentFig. Q2 : Recommendations of separated distributionsLightingAir conditioningSensitivedevicesSchneider Electric - Electrical installation guide 2009

Q - EMC guidelines2 Earthing principles andstructuresThis section deals with the earthing and equipotential bonding of information-technologydevices and other similar devices requiring interconnections for signalling purposes.Earthing networks are designed to fulfil a number of functions. They can beindependent or operate together to provide one or more of the following:b Safety of persons with respect to electrical hazardsb Protection of equipment with respect to electrical hazardsb A reference value for reliable, high-quality signalsb Satisfactory EMC performanceThe system earthing arrangement is generally designed and installed in view ofobtaining a low impedance capable of diverting fault currents and HF currents awayfrom electronic devices and systems. There are different types of system earthingarrangements and some require that specific conditions be met. These conditionsare not always met in typical installations. The recommendations presented in thissection are intended for such installations.For professional and industrial installations, a common bonding network (CBN) maybe useful to ensure better EMC performance with respect to the following points:b Digital systems and new technologiesb Compliance with the EMC requirements of EEC 89/336 (emission and immunity)b The wide number of electrical applicationsb A high level of system safety and security, as well as reliability and/or availabilityFor residential premises, however, where the use of electrical devices is limited, anisolated bonding network (IBN) or, even better, a mesh IBN may be a solution.It is now recognised that independent, dedicated earth electrodes, each serving aseparate earthing network, are a solution that is not acceptable in terms of EMC,but also represent a serious safety hazard. In certain countries, the national buildingcodes forbid such systems.Use of a separate “clean” earthing network for electronics and a “dirty” earthingnetwork for energy is not recommended in view of obtaining correct EMC, evenwhen a single electrode is used (see Fig. Q3 and Fig. Q4). In the event of a lightningstrike, a fault current or HF disturbances as well as transient currents will flow in theinstallation. Consequently, transient voltages will be created and result in failures ordamage to the installation. If installation and maintenance are carried out properly,this approach may be dependable (at power frequencies), but it is generally notsuitable for EMC purposes and is not recommended for general use.Surge arrestors"Clean"earthing networkElectricalearthing networkSeparate earth electrodesFig. Q3 : Independent earth electrodes, a solution generally not acceptable for safety and EMCreasonsQSurge arrestors"Clean"earthing networkElectricalearthing networkSingle earth electrodeFig. Q4 : Installation with a single earth electrode© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Q - EMC guidelines2 Earthing principles andstructuresThe recommended configuration for the earthing network and electrodes is two orthree dimensional (see Fig. Q5). This approach is advised for general use, bothin terms of safety and EMC. This recommendation does not exclude other specialconfigurations that, when correctly maintained, are also suitable.Equipotential bonding required formulti-level buildingsSurge arrestors"Electrical" and "communication"earthing as neededMultiple interconnected earth electrodesFig. Q5 : Installation with multiple earth electrodesFig. Q6 : Each level has a mesh and the meshes areinterconnected at several points between levels. Certainground-floor meshes are reinforced to meet the needs ofcertain areasIn a typical installation for a multi-level building, each level should have itsown earthing network (generally a mesh) and all the networks must be bothinterconnected and connected to the earth electrode. At least two connections arerequired (built in redundancy) to ensure that, if one conductor breaks, no section ofthe earthing network is isolated.Practically speaking, more than two connections are made to obtain better symmetryin current flow, thus reducing differences in voltage and the overall impedancebetween the various levels in the building.The many parallel paths have different resonance frequencies. If one path has a highimpedance, it is most probably shunted by another path with a different resonancefrequency. On the whole, over a wide frequency spectrum (dozens of Hz and MHz), alarge number of paths results in a low-impedance system (see Fig. Q6).Each room in the building should have earthing-network conductors for equipotentialbonding of devices and systems, cableways, trunking systems and structures. Thissystem can be reinforced by connecting metal pipes, gutters, supports, frames, etc.In certain special cases, such as control rooms or computers installed on false floors,ground reference plane or earthing strips in areas for electronic systems can be usedto improve earthing of sensitive devices and protection interconnection cables.Q© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Q - EMC guidelines3 Implementation3.1 Equipotential bonding inside and outsidebuildingsThe fundamental goals of earthing and bonding are the following:b SafetyBy limiting the touch voltage and the return path of fault currentsb EMCBy avoiding differences in potential and providing a screening effect.Stray currents are inevitably propagated in an earthing network. It is impossible toeliminate all the sources of disturbances for a site. Earth loops are also inevitable.When a magnetic field affects a site, e.g. the field created by lightning, differences inpotential are created in the loops formed by the various conductors and the currentsflowing in the earthing system. Consequently, the earthing network is directlyaffected by any counter-measures taken outside the building.As long as the currents flow in the earthing system and not in the electronic circuits,they do no damage. However, when earthing networks are not equipotential, e.g.when they are star connected to the earth electrode, the HF stray currents will flowwherever they can, including in control wires. Equipment can be disturbed, damagedor even destroyed.The only inexpensive means to divide the currents in an earthing system andmaintain satisfactory equipotential characteristics is to interconnect the earthingnetworks. This contributes to better equipotential bonding within the earthingsystem, but does not remove the need for protective conductors. To meet legalrequirements in terms of the safety of persons, sufficiently sized and identifiedprotective conductors must remain in place between each piece of equipment andthe earthing terminal. What is more, with the possible exception of a building with asteel structure, a large number of conductors for the surge-arrestor or the lightningprotectionnetwork must be directly connected to the earth electrode.The fundamental difference between a protective conductor (PE) and a surgearrestordown-lead is that the first conducts internal currents to the neutral of theMV/LV transformer whereas the second carries external current (from outside theinstallation) to the earth electrode.In a building, it is advised to connect an earthing network to all accessible conductingstructures, namely metal beams and door frames, pipes, etc. It is generally sufficientto connect metal trunking, cable trays and lintels, pipes, ventilation ducts, etc. atas many points as possible. In places where there is a large amount of equipmentand the size of the mesh in the bonding network is greater than four metres, anequipotential conductor should be added. The size and type of conductor are not ofcritical importance.It is imperative to interconnect the earthing networks of buildings that have sharedcable connections. Interconnection of the earthing networks must take place via anumber of conductors and all the internal metal structures of the buildings or linkingthe buildings (on the condition that they are not interrupted).In a given building, the various earthing networks (electronics, computing, telecom,etc.) must be interconnected to form a single equipotential bonding network.This earthing-network must be as meshed as possible. If the earthing network isequipotential, the differences in potential between communicating devices will be lowand a large number of EMC problems disappear. Differences in potential are alsoreduced in the event of insulation faults or lightning strikes.If equipotential conditions between buildings cannot be achieved or if the distancebetween buildings is greater than ten metres, it is highly recommended to useoptical fibre for communication links and galvanic insulators for measurement andcommunication systems.These measures are mandatory if the electrical supply system uses the IT orTN-C system.Q3.2 Improving equipotential conditionsBonding networksEven though the ideal bonding network would be made of sheet metal or a finemesh, experience has shown that for most disturbances, a three-metre mesh size issufficient to create a mesh bonding network.Examples of different bonding networks are shown in Figure Q7 next page. Theminimum recommended structure comprises a conductor (e.g. copper cable or strip)surrounding the room.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Q - EMC guidelines3 ImplementationIBNPEMesh BNMesh IBNMesh BNTrunkLocal meshLocal meshIBNTree structureIBNStar (IBN)CBNBN: Bonding networkCBN: Common bonding networkIBN: Isolated bonding networkFig. Q7 : Examples of bonding networksThe length of connections between a structural element and the bonding networkdoes not exceed 50 centimetres and an additional connection should be installedin parallel at a certain distance from the first. The inductance of the connectionbetween the earthing bar of the electrical enclosure for a set of equipment and thebonding network (see below) should be less than one µHenry (0.5 µH, if possible).For example, it is possible to use a single 50 cm conductor or two parallel conductorsone meter long, installed at a minimum distance from one another (at least 50 cm) toreduce the mutual inductance between the two conductors.Where possible, connection to the bonding network should be at an intersection todivide the HF currents by four without lengthening the connection. The profile of thebonding conductors is not important, but a flat profile is preferable. The conductorshould also be as short as possible.© Schneider Electric - all rights reservedQParallel earthing conductor (PEC)The purpose of a parallel earthing conductor is to reduce the common-mode currentflowing in the conductors that also carry the differential-mode signal (the commonmodeimpedance and the surface area of the loop are reduced).The parallel earthing conductor must be designed to handle high currents when itis used for protection against lightning or for the return of high fault currents. Whencable shielding is used as a parallel earthing conductor, it cannot handle such highcurrents and the solution is to run the cable along metal structural elements orcableways which then act as other parallel earthing conductors for the entire cable.Another possibility is to run the shielded cable next to a large parallel earthingconductor with both the shielded cable and the parallel earthing conductor connectedat each end to the local earthing terminal of the equipment or the device.For very long distances, additional connections to the network are advised forthe parallel earthing conductor, at irregular distances between the devices. Theseadditional connections form a shorter return path for the disturbing currents flowingthrough the parallel earthing conductor. For U-shaped trays, shielding and tubes, theadditional connections should be external to maintain the separation with the interior(“screening” effect).Bonding conductorsBonding conductors may be metal strips, flat braids or round conductors. For highfrequencysystems, metal strips and flat braids are preferable (skin effect) because around conductor has a higher impedance than a flat conductor with the same crosssection. Where possible, the length to width ratio should not exceed 5.Schneider Electric - Electrical installation guide 2009

Q - EMC guidelines3 Implementation3.3 Separating cablesThe physical separation of high and low-current cables is very important for EMC,particularly if low-current cables are not shielded or the shielding is not connectedto the exposed conductive parts (ECPs). The sensitivity of electronic equipment is inlarge part determined by the accompanying cable system.If there is no separation (different types of cables in separate cableways, minimumdistance between high and low-current cables, types of cableways, etc.),electromagnetic coupling is at its maximum. Under these conditions, electronicequipment is sensitive to EMC disturbances flowing in the affected cables.Use of busbar trunking systems such as Canalis or busbar ducts for high powerratings is strongly advised. The levels of radiated magnetic fields using these types oftrunking systems is 10 to 20 times lower than standard cables or conductors.The recommendations in the “Cable running” and “Wiring recommendations”sections should be taken into account.3.4 False floorsThe inclusion of the floors in the mesh contributes to equipotentiality of the area andconsequently to the distribution and dilution of disturbing LF currents.The screening effect of a false floor is directly related to its equipotentiality. If thecontact between the floor plates is poor (rubber antistatic joints, for example) or ifthe contact between the support brackets is faulty (pollution, corrosion, mildew, etc.or if there are no support brackets), it is necessary to add an equipotential mesh. Inthis case, it is sufficient to ensure effective electrical connections between the metalsupport columns. Small spring clips are available on the market to connect the metalcolumns to the equipotential mesh. Ideally, each column should be connected, butit is often sufficient to connect every other column in each direction. A mesh 1.5 to2 metres is size is suitable in most cases. The recommended cross-sectional area ofthe copper is 10 mm 2 or more. In general, a flat braid is used. To reduce the effects ofcorrosion, it is advised to use tin-plated copper (see Fig. Q8).Perforated floor plates act like normal floor plates when they have a cellular steelstructure.Preventive maintenance is required for the floor plates approximately every five years(depending on the type of floor plate and the environment, including humidity, dustand corrosion). Rubber or polymer antistatic joints must be maintained, similar to thebearing surfaces of the floor plates (cleaning with a suitable product).False floorQSpring clipsMetal support columnsFig. Q8 : False floor implementationu 10 mm 2© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Q - EMC guidelines3 Implementation3.5 Cable runningSelection of materials and their shape depends on the following criteria:b Severity of the EM environment along cableways (proximity of sources ofconducted or radiated EM disturbances)b Authorised level of conducted and radiated emissionsb Type of cables (shielded?, twisted?, optical fibre?)b EMI withstand capacity of the equipment connected to the wiring systemb Other environmental constraints (chemical, mechanical, climatic, fire, etc.)b Future extensions planned for the wiring systemNon-metal cableways are suitable in the following cases:b A continuous, low-level EM environmentb A wiring system with a low emission levelb Situations where metal cableways should be avoided (chemical environment)b Systems using optical fibresFor metal cableways, it is the shape (flat, U-shape, tube, etc.) rather than the crosssectionalarea that determines the characteristic impedance. Closed shapes arebetter than open shapes because they reduce common-mode coupling. Cablewaysoften have slots for cable straps. The smaller the better. The types of slots causingthe fewest problems are those cut parallel and at some distance from the cables.Slots cut perpendicular to the cables are not recommended (see Fig. Q9).Mediocre OK BetterFig. Q9 : CEM performance of various types of metal cablewaysIn certain cases, a poor cableway in EMI terms may be suitable if theEM environment is low, if shielded cables or optical fibres are employed, or separatecableways are used for the different types of cables (power, data processing, etc.).It is a good idea to reserve space inside the cableway for a given quantity ofadditional cables. The height of the cables must be lower than the partitions of thecableway as shown below. Covers also improve the EMC performance of cableways.In U-shaped cableways, the magnetic field decreases in the two corners.That explains why deep cableways are preferable (see Fig. Q10).Q© Schneider Electric - all rights reservedNO!Fig. Q10 : Installation of different types of cablesYES!Area protected against external EM fieldDifferent types of cables (power and low-level connections) should not be installed inthe same bundle or in the same cableway. Cableways should never be filled to morethan half capacity.Schneider Electric - Electrical installation guide 2009

Q - EMC guidelines3 ImplementationIt is recommended to electromagnetically separate groups from one another, eitherusing shielding or by installing the cables in different cableways. The quality of theshielding determines the distance between groups. If there is no shielding, sufficientdistances must be maintained (see Fig. Q11).The distance between power and control cables must be at least 5 times the radiusof the larger power cable.Forbidden Correct IdealPower cablesAuxiliary circuits (relay contacts)Control (digital)Measurements (analogue)Note: All metal parts must be electrically interconnectedFig. Q11 : Recommendation to install groups of cables in metal cablewaysMetal building components can be used for EMC purposes. Steel beams (L, H, Uor T shaped) often form an uninterrupted earthed structure with large transversalsections and surfaces with numerous intermediate earthing connections. Cablesshould if possible be run along such beams. Inside corners are better than theoutside surfaces (see Fig. Q12).RecommendedAcceptableNot recommendedFig. Q12 : Recommendation to install cables in steel beamsBoth ends of metal cableways must always be connected to local earth electrodes.For very long cableways, additional connections to the earthing system arerecommended between connected devices. Where possible, the distance betweenthese earthing connections should be irregular (for symmetrical wiring systems) toavoid resonance at identical frequencies. All connections to the earthing systemshould be short.Metal and non-metal cableways are available. Metal solutions offer betterEMC characteristics. A cableway (cable trays, conduits, cable brackets, etc.) mustoffer a continuous, conducting metal structure from beginning to end.An aluminium cableway has a lower DC resistance than a steel cableway of thesame size, but the transfer impedance (Zt) of steel drops at a lower frequency,particularly when the steel has a high relative permeability µ r . Care must be takenwhen different types of metal are used because direct electrical connection is notauthorised in certain cases to avoid corrosion. That could be a disadvantage in termsof EMC.When devices connected to the wiring system using unshielded cables are notaffected by low-frequency disturbances, the EMC of non-metal cableways can beimproved by adding a parallel earthing conductor (PEC) inside the cableway. Bothends must be connected to the local earthing system. Connections should be madeto a metal part with low impedance (e.g. a large metal panel of the device case).The PEC should be designed to handle high fault and common-mode currents.Q© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Q - EMC guidelines3 ImplementationImplementationWhen a metal cableway is made up of a number of short sections, care is required toensure continuity by correctly bonding the different parts. The parts should preferablybe welded along all edges. Riveted, bolted or screwed connections are authorised aslong as the contact surfaces conduct current (no paint or insulating coatings) and areprotected against corrosion. Tightening torques must be observed to ensure correctpressure for the electrical contact between two parts.When a particular shape of cableway is selected, it should be used for the entirelength. All interconnections must have a low impedance. A single wire connectionbetween two parts of the cableway produces a high local impedance that cancels itsEMC performance.Starting at a few MHz, a ten-centimetre connection between two parts of the cablewayreduces the attenuation factor by more than a factor of ten (see Fig. Q13).NO!NOT RECOMMENDEDYES!Fig. Q13 : Metal cableways assemblyEach time modifications or extensions are made, it is very important to make surethey are carried out according to EMC rules (e.g. never replace a metal cableway bya plastic version!).Covers for metal cableways must meet the same requirements as those applying tothe cableways themselves. A cover should have a large number of contacts along theentire length. If that is not possible, it must be connected to the cableway at least atthe two ends using short connections (e.g. braided or meshed connections).When cableways must be interrupted to pass through a wall (e.g. firewalls), lowimpedanceconnections must be used between the two parts (see Fig. Q14).Q10© Schneider Electric - all rights reservedMediocre OK BetterFig. Q14 : Recommendation for metal cableways assembly to pass through a wallSchneider Electric - Electrical installation guide 2009

Q - EMC guidelines3 Implementation3.6 Implementation of shielded cablesWhen the decision is made to use shielded cables, it is also necessary to determinehow the shielding will be bonded (type of earthing, connector, cable entry, etc.),otherwise the benefits are considerably reduced. To be effective, the shielding shouldbe bonded over 360°. Figure Q15 below show different ways of earthing the cableshielding.For computer equipment and digital links, the shielding should be connected at eachend of the cable.Connection of the shielding is very important for EMC and the following points shouldbe noted.If the shielded cable connects equipment located in the same equipotential bondingarea, the shielding must be connected to the exposed conductive parts (ECP) atboth ends. If the connected equipment is not in the same equipotential bonding area,there are a number of possibilities.b Connection of only one end to the ECPs is dangerous. If an insulation fault occurs,the voltage in the shielding can be fatal for an operator or destroy equipment. Inaddition, at high frequencies, the shielding is not effective.b Connection of both ends to the ECPs can be dangerous if an insulation faultoccurs. A high current flows in the shielding and can damage it. To limit this problem,a parallel earthing conductor (PEC) must be run next to the shielded cable. The sizeof the PEC depends on the short-circuit current in the given part of the installation.It is clear that if the installation has a well meshed earthing network, this problemdoes not arise.All bonding connections must be made to bare metalNot acceptableAcceptableCollar, clamp, etc.Bonding wireBonding barconnectedto the chassisPoorly connected shielding = reduced effectivenessCorrectCollar, clamp, etc.IdealEquipotential metal panelCable gland = circumferential contact toequipotential metal panelFig. Q15 : Implementation of shielded cablesQ113.7 Communication networksCommunication networks cover large distances and interconnect equipmentinstalled in rooms that may have distribution systems with different system earthingarrangements. In addition, if the various sites are not equipotential, high transientcurrents and major differences in potential may occur between the various devicesconnected to the networks. As noted above, this is the case when insulationfaults and lightning strikes occur. The dielectric withstand capacity (between liveconductors and exposed conductive parts) of communication cards installed inPCs or PLCs generally does not exceed 500 V. At best, the withstand capacity canreach 1.5 kV. In meshed installations with the TN-S system and relatively smallcommunication networks, this level of withstand capacity is acceptable. In all cases,however, protection against lightning strikes (common and differential modes) isrecommended.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Q - EMC guidelines3 ImplementationThe type of communication cable employed is an important parameter. It mustbe suited to the type of transmission. To create a reliable communication link, thefollowing parameters must be taken into account:b Characteristic impedanceb Twisted pairs or other arrangementb Resistance and capacitance per unit lengthb Signal attenutation per unit lengthb The type(s) of shielding usedIn addition, it is important to use symmetrical (differential) transmission links becausethey offer higher performance in terms of EMC.In environments with severe EM conditions, however, or for wide communicationnetworks between installations that are not or are only slightly equipotential, inconjunction with IT, TT or TN-C systems, it is highly recommended to use opticalfibre links.For safety reasons, the optical fibre must not have metal parts (risk of electric shockif the fibre links two areas with different potentials).3.8 Implementation of surge arrestorsConnectionsThey must be as short as possible. In fact, one of the essential characteristicsfor equipment protection is the maximum level of voltage that the equipment canwithstand at its terminals. A surge arrester with a protection level suitable for theequipment to be protected should be chosen (see Fig. 16). The total length of theconnections is L = L1 + L2 + L3. It represents an impedance of roughly 1 µH/m forhigh frequency currents.Application of the rule ∆U = L didtwith an 8/20 µs wave and a current of 8 kA leads to a voltage of 1,000 V peak permetre of cable.∆U = 1.10 -6 x 8.10 3 = 1,000 V8.10 -6 U equipmentL1L = L1 + L2 + L3 < 50 cmdisconnectioncircuit-breakerL2surge arresterU1Upload to beprotectedL3U2Q12Fig. Q16 : Surge arrester connection: L < 50 cmThis gives U equipment = Up + U1 + U2.If L1 + L2 + L3 = 50 cm, this will result in a voltage surge of 500 V for a current of8 kA.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Q - EMC guidelines3 ImplementationWiring rulesb Rule 1The first rule to be respected is not to exceed a distance of 50 cm when connectingthe surge arrester to its disconnection circuit-breaker. The surge arrester connectionsare shown in Figure Q17.d1d1disconnectord2Quick PRDSPDd3SPDImax: 65kA (8/20)In: 20kA (8/20)Up: 1,5kVUc: 340Vad3d1 + d2 + d3 y 50 cmd1 + d2 + d3 35 cmFig. Q17 : SPD with separate or integrated disconnectorb Rule 2The outgoing feeders of the protected conductors must be connected right at theterminals of the surge arrester and disconnection circuit-breaker (see Fig. Q18).Power supplyProtected feedersL < 35 cmQuick PRDFig. Q18 : Connections are right at the SPD's terminalsQ13© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Q - EMC guidelines3 Implementationb Rule 3The phase, neutral and PE incoming wires must be tightly coupled to reduce the loopsurfaces (see Fig. Q19).Clean cables polluted byneighbouring polluted cablesClean cable paths separatedfrom polluted cable pathsprotectedoutgoingfeedersNOIntermediateearth terminalLargeframeloopsurfaceSmallframeloopsurfaceYESIntermediateearthterminalL NMain earthterminalL NMain earthterminalFig. Q19 : Example of wiring precautions to be taken in a box (rules 2, 3, 4, 5)b Rule 4The surge arrester's incoming wires must be moved away from the outgoing wires toavoid mixing the polluted cables with the protected cables (see Fig. Q19).b Rule 5The cables must be flattened against the metallic frames of the box in order tominimise the frame loops and thus benefit from a disturbance screening effect.If the box is made of plastic and the loads particularly sensitive, it must be replacedby a metal box.In all cases, you must check that the metallic frames of the boxes or cabinets areframe grounded by very short connections.Finally, if screened cables are used, extra lengths which serve no purpose("pigtails"), must be cut off as they reduce screening effectiveness.Q14© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Q - EMC guidelines3 Implementation3.9 Cabinet cabling (Fig. Q20)Each cabinet must be equipped with an earthing bar or a ground reference metalsheet. All shielded cables and external protection circuits must be connected to thispoint. Anyone of the cabinet metal sheets or the DIN rail can be used as the groundreference.Plastic cabinets are not recommended. In this case, the DIN rail must be used asground reference.PotentialReference PlateFig. Q20 : The protected device must be connected to the surge-arrestor terminals3.10 StandardsIt is absolutely essential to specify the standards and recommendations that must betaken into account for installations.Below are several documents that may be used:b EN 50174-1b EN 50174-2Information technology - Cabling installation.Part 1: Specification and quality assuranceInformation technology - Cabling installation.Part 2: Installation planning and practices inside buildingsQ15© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Q - EMC guidelines4 Coupling mechanisms andcounter-measures4.1 GeneralAn EM interference phenomenon may be summed up in Figure Q21 below.SourceOrigin ofemitted disturbancesExample:CouplingMeans by whichdisturbances aretransmittedVictimEquipment likelyto be disturbedRadiated wavesWalkie-talkieTV setFig. Q21 : EM interference phenomenonQ16The different sources of disturbances are:b Radio-frequency emissionsv Wireless communication systems (radio, TV, CB, radio telephones, remote controls)v Radarb Electrical equipmentv High-power industrial equipment (induction furnaces, welding machines, statorcontrol systems)v Office equipment (computers and electronic circuits, photocopy machines, largemonitors)v Discharge lamps (neon, fluorescent, flash, etc.)v Electromechanical components (relays, contactors, solenoids, current interruptiondevices)b Power systemsv Power transmission and distribution systemsv Electrical transportation systemsb Lightningb Electrostatic discharges (ESD)b Electromagnetic nuclear pulses (EMNP)The potential victims are:b Radio and television receivers, radar, wireless communication systemsb Analogue systems (sensors, measurement acquisition, amplifiers, monitors)b Digital systems (computers, computer communications, peripheral equipment)The different types of coupling are:b Common-mode impedance (galvanic) couplingb Capacitive couplingb Inductive couplingb Radiated coupling (cable to cable, field to cable, antenna to antenna)© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Q - EMC guidelines4 Coupling mechanisms andcounter-measures4.2 Common-mode impedance couplingDefinitionTwo or more devices are interconnected by the power supply and communicationcables (see Fig. Q22). When external currents (lightning, fault currents, disturbances)flow via these common-mode impedances, an undesirable voltage appears betweenpoints A and B which are supposed to be equipotential. This stray voltage candisturb low-level or fast electronic circuits.All cables, including the protective conductors, have an impedance, particularly athigh frequencies.StrayovervoltageDevice 1Z sign.Device 2I2ECPsSignal lineECPsZ1I1Z2The exposed conductive parts (ECP) of devices 1 and 2 are connected to a commonearthing terminal via connections with impedances Z1 and Z2.The stray overvoltage flows to the earth via Z1. The potential of device 1 increasesto Z1 I1. The difference in potential with device 2 (initial potential = 0) results in theappearance of current I2.I2Z1Z1 I1= ( Zsign + Z2) I2⇒ =I1Zsign + Z2( )I Current I2, present on the signal line, disturbs device 2.Fig. Q22 : Definition of common-mode impedance couplingExamples (see Fig. Q23)b Devices linked by a common reference conductor (e.g. PEN, PE) affected by fastor intense (di/dt) current variations (fault current, lightning strike, short-circuit, loadchanges, chopping circuits, harmonic currents, power factor correction capacitorbanks, etc.)b A common return path for a number of electrical sourcesDevice 1 Device 2Signal cableDisturbedcableFaultcurrentsLightningstrikeQ17DisturbingcurrentDifference inpotentialZMCFig. Q23 : Example of common-mode impedance coupling© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Q - EMC guidelines4 Coupling mechanisms andcounter-measuresCounter-measures (see Fig. Q24)If they cannot be eliminated, common-mode impedances must at least be as low aspossible. To reduce the effects of common-mode impedances, it is necessary to:b Reduce impedances:v Mesh the common references,v Use short cables or flat braids which, for equal sizes, have a lower impedance thanround cables,v Install functional equipotential bonding between devices.b Reduce the level of the disturbing currents by adding common-mode filtering anddifferential-mode inductorsStrayovervoltageDevice 1Z sign.Device 2I2Z sup.PECZ1I1Z2If the impedance of the parallel earthing conductor PEC (Z sup) is very lowcompared to Z sign, most of the disturbing current flows via the PEC, i.e. notvia the signal line as in the previous case.The difference in potential between devices 1 and 2 becomes very low and thedisturbance acceptable.Fig. Q24 : Counter-measures of common-mode impedance couplingQ18© Schneider Electric - all rights reservedUVsourceVvictimFig. Q25 : Typical result of capacitive coupling (capacitivecross-talk)tt4.3 Capacitive couplingDefinitionThe level of disturbance depends on the voltage variations (dv/dt) and the value ofthe coupling capacitance between the disturber and the victim.Capacitive coupling increases with:b The frequencyb The proximity of the disturber to the victim and the length of the parallel cablesb The height of the cables with respect to a ground referencing planeb The input impedance of the victim circuit (circuits with a high input impedance aremore vulnerable)b The insulation of the victim cable (ε r of the cable insulation), particularly for tightlycoupled pairsFigure Q25 shows the results of capacitive coupling (cross-talk) between two cables.Examples (see Fig. Q26 opposite page)b Nearby cables subjected to rapid voltage variations (dv/dt)b Start-up of fluorescent lampsb High-voltage switch-mode power supplies (photocopy machines, etc.)b Coupling capacitance between the primary and secondary windings oftransformersb Cross-talk between cablesSchneider Electric - Electrical installation guide 2009

Q - EMC guidelines4 Coupling mechanisms andcounter-measuresDifferential modeCommon modeSourceVictimVsDMIvDMVsCMIvCMSourceVictimMetal shieldingVs DM: Source of the disturbing voltage (differential mode)Iv DM: Disturbing current on victim side (differential mode)Vs CM: Source of the disturbing voltage (common mode)Iv CM: Disturbing current on victim side (common mode)Fig. Q26 : Example of capacitive couplingSourceFig. Q27 : Cable shielding with perforations reduces capacitivecouplingCVictimCounter-measures (see Fig. Q27)b Limit the length of parallel runs of disturbers and victims to the strict minimumb Increase the distance between the disturber and the victimb For two-wire connections, run the two wires as close together as possibleb Position a PEC bonded at both ends and between the disturber and the victimb Use two or four-wire cables rather than individual conductorsb Use symmetrical transmission systems on correctly implemented, symmetricalwiring systemsb Shield the disturbing cables, the victim cables or both (the shielding must bebonded)b Reduce the dv/dt of the disturber by increasing the signal rise time where possible4.4 Inductive couplingDefinitionThe disturber and the victim are coupled by a magnetic field. The level of disturbancedepends on the current variations (di/dt) and the mutual coupling inductance.Inductive coupling increases with:b The frequencyb The proximity of the disturber to the victim and the length of the parallel cables,b The height of the cables with respect to a ground referencing plane,b The load impedance of the disturbing circuit.Examples (see Fig. Q28 next page)b Nearby cables subjected to rapid current variations (di/dt)b Short-circuitsb Fault currentsb Lightning strikesb Stator control systemsb Welding machinesb InductorsQ19© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Q - EMC guidelines4 Coupling mechanisms andcounter-measuresiDisturbingcableHVictim pairiDisturbingcableHVictim loopVictim loopDifferential modeCommon modeFig. Q28 : Example of inductive couplingCounter-measuresb Limit the length of parallel runs of disturbers and victims to the strict minimumb Increase the distance between the disturber and the victimb For two-wire connections, run the two wires as close together as possibleb Use multi-core or touching single-core cables, preferably in a triangular layoutb Position a PEC bonded at both ends and between the disturber and the victimb Use symmetrical transmission systems on correctly implemented, symmetricalwiring systemsb Shield the disturbing cables, the victim cables or both (the shielding must bebonded)b Reduce the dv/dt of the disturber by increasing the signal rise time where possible(series-connected resistors or PTC resistors on the disturbing cable, ferrite rings onthe disturbing and/or victim cable)4.5 Radiated couplingDefinitionThe disturber and the victim are coupled by a medium (e.g. air). The level ofdisturbance depends on the power of the radiating source and the effectivenessof the emitting and receiving antenna. An electromagnetic field comprises both anelectrical field and a magnetic field. The two fields are correlated. It is possible toanalyse separately the electrical and magnetic components.The electrical field (E field) and the magnetic field (H field) are coupled in wiringsystems via the wires and loops (see Fig. Q29).E fieldH fieldiQ20VField-to-cable couplingField-to-loop coupling© Schneider Electric - all rights reservedFig. Q29 : Definition of radiated couplingSchneider Electric - Electrical installation guide 2009

Q - EMC guidelines4 Coupling mechanisms andcounter-measuresWhen a cable is subjected to a variable electrical field, a current is generated in thecable. This phenomenon is called field-to-cable coupling.Similarly, when a variable magnetic field flows through a loop, it creates a counterelectromotive force that produces a voltage between the two ends of the loop. Thisphenomenon is called field-to-loop coupling.Examples (see Fig. Q30)b Radio-transmission equipment (walkie-talkies, radio and TV transmitters, mobileservices)b Radarb Automobile ignition systemsb Arc-welding machinesb Induction furnacesb Power switching systemsb Electrostatic discharges (ESD)b LightingE fieldEM fieldiSignalcableDevice 1 Device 2DevicehhArea of theearth loopGround reference planeExample of field-to-cable couplingExample of field-to-loop couplingFig. Q30 : Examples of radiated couplingCounter-measuresTo minimise the effects of radiated coupling, the measures below are required.For field-to-cable couplingb Reduce the antenna effect of the victim by reducing the height (h) of the cable withrespect to the ground referencing planeb Place the cable in an uninterrupted, bonded metal cableway (tube, trunking, cabletray)b Use shielded cables that are correctly installed and bondedb Add PECsb Place filters or ferrite rings on the victim cableFor field-to-loop couplingb Reduce the surface of the victim loop by reducing the height (h) and the lengthof the cable. Use the solutions for field-to-cable coupling. Use the Faraday cageprinciple.Radiated coupling can be eliminated using the Faraday cage principle. A possiblesolution is a shielded cable with both ends of the shielding connected to the metalcase of the device. The exposed conductive parts must be bonded to enhanceeffectiveness at high frequencies.Radiated coupling decreases with the distance and when symmetrical transmissionlinks are used.Q21© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Q - EMC guidelines5 Wiring recommendations5.1 Signal classes (see Fig. Q31)1 - Power connections(supply + PE)2 - RelayconnectionsUnshielded cables ofdifferent groupsShielded cables ofdifferent groupsDeviceeNO!hYES!Groundreferenceplane4 - Analogue link(sensor)3 - Digital link(bus)Risk of cross-talk in common mode if e < 3 hFig. Q31 : Internal signals can be grouped in four classesSensitivecableDisturbingcableNO!SensitivecableDisturbingcable30 cm u 1 mYES!Cross incompatiblecables at right anglesFig. Q32 : Wiring recommendations for cables carryingdifferent types of signalsNO!YES!Four classes of internal signals are:b Class 1Mains power lines, power circuits with a high di/dt, switch-mode converters, powerregulationcontrol devices.This class is not very sensitive, but disturbs the other classes (particularly incommon mode).b Class 2Relay contacts.This class is not very sensitive, but disturbs the other classes (switching, arcs whencontacts open).b Class 3Digital circuits (HF switching).This class is sensitive to pulses, but also disturbs the following class.b Class 4Analogue input/output circuits (low-level measurements, active sensor supplycircuits). This class is sensitive.It is a good idea to use conductors with a specific colour for each class tofacilitate identification and separate the classes. This is useful during design andtroubleshooting.Standard cableTwo distinct pairs5.2 Wiring recommendationsQ22Poorly implementedribbon cableDigital connectionAnalogue pairBonding wiresFig. Q33 : Use of cables and ribbon cableCorrectly implementedribbon cableCables carrying different types of signals must be physically separated(see Fig. Q32 above)Disturbing cables (classes 1 and 2) must be placed at some distance from thesensitive cables (classes 3 and 4) (see Fig. Q32 and Fig. Q33)In general, a 10 cm separation between cables laid flat on sheet metal is sufficient(for both common and differential modes). If there is enough space, a distance of30 cm is preferable. If cables must be crossed, this should be done at right angles toavoid cross-talk (even if they touch). There are no distance requirements if the cablesare separated by a metal partition that is equipotential with respect to the ECPs.However, the height of the partition must be greater than the diameter of the cables.© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Q - EMC guidelines5 Wiring recommendationsA cable should carry the signals of a single group (see Fig. Q34)If it is necessary to use a cable to carry the signals of different groups, internalshielding is necessary to limit cross-talk (differential mode). The shielding, preferablybraided, must be bonded at each end for groups 1, 2 and 3.It is advised to overshield disturbing and sensitive cables (see Fig. Q35)The overshielding acts as a HF protection (common and differential modes) if itis bonded at each end using a circumferential connector, a collar or a clampereHowever, a simple bonding wire is not sufficient.NO!ElectroniccontroldeviceShielded pairUnshielded cable for stator controlElectromechanicaldeviceSensorElectroniccontroldeviceYES!Shielded pair + overshieldingShielded cable for stator controlBonded using a clampElectromechanicaldeviceSensorFig. Q35 : Shielding and overshielding for disturbing and/or sensitive cablesPower +analogueNO!Digital +relay contactsPower connectionsRelay I/O connectionsPower +relay contactsShieldingYES!Digital +analogueDigital connectionsAnalogue connectionsAvoid using a single connector for different groups (see Fig. Q36)Except where necessary for groups 1 and 2 (differential mode). If a single connectoris used for both analogue and digital signals, the two groups must be separated by atleast one set of contacts connected to 0 V used as a barrier.All free conductors (reserve) must always be bonded at each end(see Fig. Q37)For group 4, these connections are not advised for lines with very low voltageand frequency levels (risk of creating signal noise, by magnetic induction, at thetransmission frequencies).Fig. Q34 : Incompatible signals = different cablesNO!YES!NO!YES!ElectronicsystemElectronicsystemWires notequipotentiallybondedQ23Digital connectionsAnalogue connectionsFig. Q36 : Segregation applies to connectors as well!Equipotential sheet metal panelFig. Q37 : Free wires must be equipotentially bondedEquipotential sheet metal panel© Schneider Electric - all rights reservedSchneider Electric - Electrical installation guide 2009

Q - EMC guidelines5 Wiring recommendationsThe two conductors must be installed as close together as possible(see Fig. Q38)This is particularly important for low-level sensors. Even for relay signals with acommon, the active conductors should be accompanied by at least one commonconductor per bundle. For analogue and digital signals, twisted pairs are a minimumrequirement. A twisted pair (differential mode) guarantees that the two wires remaintogether along their entire length.NO!YES!PCB withrelay contactI/OsArea ofloop too largePCB withrelay contactI/Os- +Power supply- +Power supplyFig. Q38 : The two wires of a pair must always be run close togetherGroup-1 cables do not need to be shielded if they are filteredBut they should be made of twisted pairs to ensure compliance with the previoussection.Cables must always be positioned along their entire length against the bondedmetal parts of devices (see Fig. Q39)For example: Covers, metal trunking, structure, etc. In order to take advantage of thedependable, inexpensive and significant reduction effect (common mode) and anticross-talkeffect (differential mode).NO!YES!Chassis 1Chassis 1Chassis 2Chassis 2NO!YES!Metal trayChassis 3Chassis 3Q24PowersupplyI/O interfacePowersupplyI/O interfacePower or disturbing cablesRelay cablesMeasurement or sensitive cablesAll metal parts (frame, structure, enclosures, etc.) are equipotentialFig. Q39 : Run wires along their entire length against the bonded metal parts© Schneider Electric - all rights reservedFig. Q40 : Cable distribution in cable traysThe use of correctly bonded metal trunking considerably improvesinternal EMC (see Fig. Q40)Schneider Electric - Electrical installation guide 2009

Make the most of your energyISBN 978-2-9531643-0-59 782953 164305Schneider Electric Industries SASHead Office89, bd Franklin RooseveltF-92506 Rueil-Malmaison CedexFRANCEAs standarts, specifications and designs change from time to time, please ask for confirmationof the information given in this pubication.This document has beenprinted on ecological paperEIGED306001ENART.82292012/2008

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