is 0732 (electrical wiring & installation)

7/22/2019 IS 0732 (Electrical Wiring & Installation)

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IS : 732 -1989( Reafffinned 199.5 )

I ndian StandardCODEOFPRACTTCEFORELECTRICALWIRINGINSTALLATIONS

( hird Revision )Second Reprint FEBRUARY 1999

UDC 621.315.3.696.6 : 006.76

0 Copyright 1989BUREAU OF INDIAN STANDARDSMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

Price Rs 225.00 November 1989

( Reaffirmed 2005 )


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I ndian St andardISt732-1989

CODE OF PRACTICE FORELECTRICAL WIRING INSTALLATIONS( Third Rev i si on

Electrical Installations Sectional Committee, ETDC 20Chuifmun

SHBI M. L. DONQ~EM-3 Satyam, 88 Sion Circle, Bombay 400 022Members Re#resenti&

SHRI P. ANANTHARAMAN Engineet-in-Chiefs Branch,Defence ), New Delhi Army Headquarters ( Ministry ofSH~I S. K. SHANQARI ( Altrrncte )SHRI P. D. BA~ADE Tata Consulting Engineers, BombaySHRI R. K. KAUL ( Allemote)SHRI V. S. BHATIA Siemens India Ltd, BombaySXRI M. M. SHETHNA ( Alternatr )SHRI K. V. CHAUBAL Federation of Electricity Undertaking of India, BombaySH~I KS. JOSHI ( Altesnute )SHRI R. R. CHOUDHURI Larsen & Toubro ( Construction Group ), MadraaSERI N. BALA~UBRAMANIAN ( Alternate )CHIEF ELEOTRICAL ENOINEER Railway Board ( Ministry of Railways ), New DelhiDEPUTY DIRECTOR S~ANDA~DB ( ELEO )-DI,RDSO ( At6ernate )CHIEF ELECTRICAL INSPECTORTO GOVEBNYIENT Chief Electrical Inspector to Government of Taml Nadu, MadrasOF TAMIL NADUELEGT~ICAL INSPECTOR ( TEOE~IOAL ) TOGOVERNMENT OF TAMIL NADU ( Alternate )CHIEF ENGINEER ( ELEC I-1 Central Public Works Department, New DelhiSUPEBINTEN~ENT SURVEYOFC ox WOBEB( ELEC )-I ( Alfcrnate )SHRI DEVENDER NATHSHBI T. P. R. SARYA ( Alternate )SHRI K. W. DEAR~Y~ADHIKARIDR V. N. MALLER ( Alternate )SERI G. L. DUASHBI S. K. SETHI ( Alternate )SHRI R. C. KHANNASHBI P. S. SAWHNEY (Altcmatr )MEMBER ( HYDRO-ELECTRIC )DIRECTOR ( HED )-I ( Alternate)En S. PANEERSELVAMSERI V. JANARDHANAN ( Alternate )SHRI K. P. R. PILLAISHRI C. R. R. MENON ( Altcrnute )

SHRI V. RADHA KRISHNANSHRI H. S. RAOPROF G. RAVEENDRAN NAIBSHRI S. R. SARDASHRI R. SATHIYABALSHRI K. K. MONDAL ( Altcrnatr )SERI H. K. SITARAMSHRI S. K. PALIT ( Alternate )SHRI P. SRINIVASA POTISHRI JOSEPH PHILOYENY ( Alternate )SHRI D. S. TAWARESHRI S. J . HARIDAS ( Alfernate )SHRJ G. N. THADANISH~I S. K. GHOST ( Alfernuts )SHRI G. S. THAKUB

Larsen & Toubro Ltd, BombayJyoti Ltd, VadodaraRural Electrification Corporation Ltd, New DelhiDelhi Electric Supply Undertaking, New DelhiCentral Electricity Authority, New DelhiTaml Nadu Electricity Board, MadrasFact Engineering and Design Organiiation, UdyogamandalBharat Heavy Electricals Ltd, HyderabadCrompton Greaves Ltd, BombayChief Electrical Inspector to the Government of Kerala, TrivandrumMaharashtra State Electricity Board, BombayTariff Advisory Commttee ( General Insurance ), BombayCalcutta Electric Supply Corporation Ltd, CalcuttaKarnataka Electricity Board, BangaloreElectrical Engineer to Government of Maharashtra, BombayEngineers India Ltd. New DelhiChief Electrical Inspector, Government of Madhya Pradesh, Bhopal

( Cot&& on pug8 2 )Q Copyright 1989

BUREAU OF INDIAN STANDARDSThis publication is protected under the Indian CopyrightAct ( XIV of1957 ) and production in whole or in part byany means except with written permssion of the publisher shall be deemed to be an infringement of copyrightunder the said Act. I


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?Sr7SZ-MM9 .( Continusd from puge 1 )

ChairmanSEW V. T. WARAN~SHRI R. P. PATEL ( Alternuts )SBRI S. P. SACEDIPV,Director (Elec tech )

Bombay Electric Supply and Trausport Undertaking, BombayDirector General, BIS ( Ex-O& O M ember )

s&r4ta?ySERI K. GAH~~SHDeputy Director ( Elec tech ), BIS

Panel for Electrical Wiring Installations, ETDC 20 : P30Convcnrr ,

SHRI R. K. SEEGALMmbm

SERI P. S. PANDYA ( A l kma t# toShri R. K. Sehgal )Crtxas EN~INBEB ( ELECT )-ISUPERINTENDINQ SWVEYOR OPWORKS( ELECT )-I ( Alftraetr )SHRI G. KRISHNASWA~~Y

Bombay Suburban Electric Supply Co Ltd, Bombay

Central Public Works Department, New Delhi

Srta~ A. G. LAK~H*IKABAYANAN ( Alfnnats )Best and Crompton Engineering Ltd, Madras&tar D. N. PUBAI~DAI~ESHRI SHIRISH S. J EAV~I ( A&act8 ) Electrical Contractors Association of Maharashtra, BombaySHRI K. P. R. PILLAISHBI A. 0. 00-n ( Atrrmotr ) Fact Engineering and Design Organization, UdyogamandalP~olr G. RAVE~DRAN NAIIC Chief Electrical Inspector to the Government of Kerala, TrivaudrumSHEX R. SATHIYABAL Tariff Advisory Commttee, BombaySHBI K. K. MONDAL ( Affemat6 )SHRI M. K. THADANI Engineer-in-Chiefs Branch, Army Headquarters, New DelhiSHRI R. K. Snar ( Al@rnefr )SEBI G. N. THADANI Engineers India Limted, New DelhiSHBI S. K. GHOSB ( dlwmzf~ )

2


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IS t 132 1989CONTENTS

0. FOREWORD1. SCOPE

Page. . . 5. . . 6

2.SECTION 1 TERMINOLOGY

TERMINOLOQY . . . 6

SECTION 2 ASSESSMENT OF GENERAL CHARACTERISTICSOF INSTALLATIONS

3. ASSESSMENTF CHARACTERISTICS GENERAL4. EXTERNAL NFLUENCES

SECTION 3 PROTECTION

. . . 12

. . . 13

FOR SAFETY5. REQUIREMENTS OR PROTECTION OR SAFETY ,.. 19

SECTION 4 DESIGN OF INSTALLATION, SELECTION ANDERECTION OF EQUIPMENT

6.7.8.9.

10.11.

FUNDAMENTAL EQUIREMENTS . . .COMMONRULES . . .CABLES,CONDUCTORS ND WIRING MATERIALS . . .SWITCHGEAR * .EARTHINGARRANQEMEMT ND PROTECTIVE ONDUCTORS . . .SUPPLIES OR SAFETY SERVICES . . .

394143495151

SECTION 5 INSPECTION AND TESTING12.13.

INITIAL INSPECTION ND TESTING . . .ALTERATIONS O INSTALLATIONS . . .

52545460

APPENDIX AAPPENDIX BAPPENDIX C

APPENDIX DAPPENDIX E

TYPES OF WIRING SYSTEMS ND THEIR SELECTION . . .METHODS OF INTERNALWIRINQGUIDELINES FOR SPECIFIC EQUIPMENT, FITTIN@ ANDACCESSORIES . . .SPECIFICGUIDANCE OF SELECTION OF EQUIPMENTWITHREGARD TO EXTERNAL INFLUENCES . . .CHECK LIST 0~ INITIAL NSPECTION . . .

687074


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As in the Original Standard, this Page is Intentionally Left Blank


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IS : 732 - 1989I ndian St andard

CODE OF PRACTICE FORELECTRICAL WIRING INSTALLATIONS( Third Revi si on0. FOREWORD

0.1 This Indian Standard was adopted by theBureau of Indian Standards on 25 January 1989,after the draft finalized by the Low VoltageSwitchgear and Controlgear Sectional Committeehad been approved by the Electrotechnical Divi-sion Council.0.2 The Indian Electricity Rules, together withthe supplementary regulations of the state electri-city departments and electricity undertakings,govern the electrical installation work in build-ings in this country. Regulations for the electricalequipment in buildings as recommended by theInstitution of Electrical Engineers, UK, have alsooften been followed in this work. Expanding useof electricity and increase in the number of elec-trical installations in buildings, necessitated thepreparation of a code of practice to guide andgovern installation of electrical wiring in build-ings, with particular reference to safety and goodengineering practice. This code was, therefore,first published in 1958 with the above objective.0.3 Since the first version of this code coveredelectrical installations only in buildings whichcould be considered as non-industrial locations,where the system voltage generally did not exceed650 volts, the need for having a similar code forindustrial locations was also felt and many addi-tional requirements had to be looked after. There-fore, in addition to the revision of this code, aseparate code on the latter subject was publishedas IS : 2274-1963.0.4 Experience in implementation of these stan-dards had proved that most of the industrialinstallations required references to guidelines forsystem of voltages not exceeding 650 V in theirdesign. Moreover, considerations such as layoutof electrical installations, measurement, etc, forwhich separate Indian Standard specificationsexist, require comprehensive reading, and it hasbeen felt that a single Indian Standard to providefor all aspects of wiring would serve as a com-prehensive reference guide on the subject.0.5 In the second version of IS : 732 brought outin 1982 in 3 parts, this fact has been taken into

*Code of practice for electrical wiring installations( system voltage exceeding650 volts ).

account in that the information has been calledfrom various Indian Standard specifications andother literature available and presented as a singlecomprehensive code. Efforts were made to iden-tify gaps and the opportunity utilised to incor-porate the latest trends in wiring practice. It is,however, indicated that this revision was purelya temporary measure to meet the immediateneeds of the practising engineers and the ultimateaim was to bring out a comprehensive safety-oriented code on electrical installations in build-ings based on the international work in thisregard.0.6 Soon after the publication of the secondrevision, work on the preparation of NationalElectrical Code ( NEC ) began under the purviewof the National Electrical Code Sectional Commi-ttee, ETDC 56. This work, aimed as a compen-dium of all relevant information in IS Codesincluding IS : 732, concluded in 1985 when NECwas published. NEC besides drawing assistancefrom IS : 732, further elaborates the stipulationson wiring practice with reference to specificoccupancies.0.7 During the preparation of NEC it became.evident that IS : 732 would require considerableupdating in order to align with modified patternof power consumption and advancing technologyin installation design. There was also a strongneed to align the code with the work being accom-plished at the international level, namely, at thelevel of IEC/TC 64 Electrical Installations ofBuildings, which cover comprehensively the rele-vant issues. This revision of IS : 732 ( third ) isan attempt to improve the contents of the codeto meet this need.0.8 It is emphasized that the information con-tained in this code is oriented towards electricalsafety. The accent is on protection from thevarious hazards arising from use of electricity andthe rules relating to wiring practice are based onthe international guidelines on such matters. Itis in this respect that the present version of thisstandard differs from the earlier versions whichwere oriented towards design and constructionalaspects. However, a series of appendices havebeen added to this Code dealing with specific


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IS I 732.~1989guidelines on wiring practice as applicable todesign, construction and execution of work.Whenever necessary, the provisions of this Codeshall be read in conjunction with other Codessuch as those on earthing, lightning protection,etc,0.9 In the preparation of this standard, consider-able assistance has been derived from the follow-ing publications:

IEC Pub 364 ( in several parts ) ElectricalInstallations of Buildings. The InternationalElectrotechnical Commission ( IEG ) .IEC Dot: 64 ( Secretariat ) 437 ElectricalInstallations of Buildings. Part 2 Definitions.International Electrotechnical Commission( IEC ).IEC Dot: ( IEV 826 ,) ( Central Office ) 1193International Electrotechnional Vocabulary.Part 826 Electrical Installations of Buildings.

The International Electrotechnical Commission( IEC ).IEC Dot: 64 ( Secretariat ) 430. Pub 364Chapter 52 Selection and Erection of WiringSystems. The. International ElectrotechnicalCommission ( IEC ).IEE Wiring Regulations Regulations forelectrical installations 15th Edition ( 1981 )( as amended up to January 1985 ). The Insti-tution of Electrical Engineers ( UK ).

0.10 For the purpose of deciding whether aparticular requirement of this standard is compliedwith, the final value, observed or calculated,expressing the result of a test, shall be roundedoff in accordance with IS : 2-1960*. The numberof significant places retained in the rounded offvalue should be the same as that of the specifiedvalue in this standard.*Rules for rounding off numerical values ( revised ).

1. SCOPE,~I.~1his code covers the essential requirementsand precautions regarding wiring installations forensuring satisfactory and reliable service andsafety from all possible hazards from the use ofelectricity.1.2 This code applies to the design, selection,erection and inspection and testing of wiringinstallations whether permanent or temporary,in and about buildings,1.3 It relates generally to all wiring installationsin non-industrial and industrial locations, whe-ther the electric supply is derived from an externalsource or from a private generating plant.1.4 Installations utilizing the following nominalvoltage ranges are dealt with in this code:

a)b)

voltages normally not exceeding 50 V acor 120 V dc whether between conductorsor to earth.voltages normally exceeding extra-lowvoltage but not exceeding 1 000 V ac or1 500 V dc between conductors or 600 Vac or 900. V dc between conductors andearth.

1.5 This code covers all general guidelines appli-cable to installations operating within the rangesgiven in 1.4. Supplementary or additional pro-visions may be necessary to be complied with inrespect of specific occupancies depending on theirnature. For the purposes of guidelines on indi-vidual occupancies reference may be NationalElectrical Code ( SP : 30-1985 ).1.6 This code is not applicable to the following:

4b)44

Systems for distribution of energy to thepublic, or to power generation and trans-mission for such systems.Wiring installations in special locationssuch as mines or other areas where potenti-ally explosive atmosphere exists.Lightning conductors, telecommunicationsand alarm systems.Traction installations, motor vehicles, ins-tallations on board ships, aircraft oroffshore installations.

1.7 This code also does not apply to mattersconcerning specifications of individual items ofequipment and does not deal with requirementsfor the construction of prefabricated assemblies ofelectrical equipment.

SECTION 1 TERMINOLOGY2. TERMINOLOGY2.0 For the purposes of this standard, the follow-ing definitions shall apply.2.1 Accessory - A device, other than current-using equipment, associated with such equipmentor with the wiring of an installation.

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2.2 Ambient Temperature - The temperatureof the air or other medium where the equipmentis to be used.2.3 Appliance - An item of currentequipment other than a luminaire or anpendent motor.

usinginde-


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2.4 Arms Reach - A zone extending from anypoint on a surface where persons usually stand ormove about, to the limits which a person canreach with the hand in any direction withoutassistance.NOTE - Thir space is by convention, limited a~shownin ig. .

\1.25 m

I//////// LIMIT OF ARMS REACHS = Surface expected to be occupied by person

FIG. 1 ARMS Rt~ca2.5 Barrier - A part providing a defined degreeof protection against contact with live parts, fromany usual direction of access.2.6 Baeie Insulation - Insulation applied tolive parts to provide basic protection againstelectric shock.

Nom - Basic insulation ,does not necessarily in-clude insulation used exclusively for__functional pur-poses.2.7 Bonding Conductor - A protective con-ductor providing equipotential bonding.2.8 Building Voids - Space within the struc-ture or the components of a building accessibleonly at certain points.

NOT=1- Examples are: Space within partitions,suspended floors, ceilings and certain types of windowframe, door frame and architraves.

N-2 - Specially formed building voids arealso known as ducts.2.9 Buried Direct - A cable laid in the groundin intimate contact with the soil.2.10 Bonchtd - Cables are said to be bunchedwhen two or more are contained within a singleconduit, duct, ducking, or tnmking cr, if notenclosed, are not -rated from each &her:2.11 Cable BLnnntl - An enclosure situatedabove o; ,111he ground, open or ventilated orclo&; and having dimensions which do notprmit the access of persons but allow access tothe conductors and/or cabks throughout theirlength during and after installation.

NATE - A cable channelpart of the building construction may or may not form2.12 Cable Bracket - A cable support consist-ing of single devices fixed to elements of buildingor plant construction.2.13 Cable Coupler - A means enabling theconnection, at will, of two flexible cab& It con-sists ofa connector and a plug.2.14 Cable Ducting - A manufactured enclo-sure of metal or insulating material, other thanconduit or cable trunk& intended for tha protec-tion of cables which are drawn-in after erectionof the ducting, but which is not specificallyintendedto form part of a building structure.2.15 Cable Traaking - A factory made closedsupport and protection system into which con-ductors and/or cables are laid after removal of thecover.2.16 Cable Tunnel - An enclosure ( corridor )containing supporting structures for conductorsand/or cables and joints and whose dimensionsallo.w free access to persons throughout the entirelength.2.17 Cable Tray - A cable support consistingof a continuous base with raised edges and nocovering. A cable tray is considered to be non-perforate9 where less than 30 percent of thematerial IS removed from the base.218 Cable Ladder - A cable support occupy-in8 less than 10 percent of the plan area andcotisisting of a series of supporting elementsrigidly fixed to each other or to a main supportingmember or members.2.19 Cartridge Fuse Link - A device com-prising a fuse element or several fuse elementsconnected in parallel enclosed in a cartridgeusually filled with an arc-extinguishing mediumand connected to terminations. The fuse link isthe part of a fuse which requires replacing afterthe fuse has operated.2.20 Circuit - An assembly of electrical equipment supplied from the same origin and protectedagainst overcurrent by the same protective

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IS 1732 -1989,device(s). Certain types of circuit are categorisedas follows:

4

W

4

Category1 Circuit - A circuit ( other thana fire alarm or emergency lighting circuit )operating at low voltage and supplieddirectly from a mains supply system.Category 2 Circuit - With the exception offire alarm and emergency lighting circuits,any circuit for telecommunication ( forexample, radio, telephone, sound distr i-bution, intruder alarm, bell and call anddata transmission circuits ) which is sup-plied from a safety source.C&egory 3 Circuit - A fire alarm circuit oran emergency lighting circuit.

2.21 Circuit Breaker - A mechanical switchingdevice capable of making, carrying and breakingcurrents- under normal circuit conditions and alsoof making, carrying for a specified time, andbreaking currents under specified abnormalcircuit conditions such as those of short circtit.NOTE - A circuit breaker is usually intended tooperate infrequently, although some types are suitablefor frequent operation.

2.22 Class I Equipment - Equipment in whichprotection against electric shock does not rely onbasic iniulation only, but which indudes anadditional safety precaution in such a way thatmeans are provided for the connection of exposedconductive parts to a protective conductor in thefixed wiring of installation in such a way thataccessible conductive parts may not become livein the event of a failure of basic installation.NOTE For information on classification of equip-ment with regard to means ~~#M&d for protectionagainst electric shock,su IS : 9409-1980*.

2.23 Class II Equipment - Equipment inwhich protection against electric shock does notrely on basic insulation only, but in which additio-nal safety precautions, such as double or reinforcedinsulation are provided, there being no prQvisionfor the connection of exposed metalwork of theequipment to a protective conductor, and noreliantie upon precautions to be taken in the fixedwiring of the installation.2.24 Conduit - A part of a closed wiring systema circular or non-circular cross section for conduc-tors and/or cables in electrical installations,allowing them to be drawn in and/or replaced.

Conduits should be sufficiently closed-jointedso that the conductors can only be drawh in andnot inserted laterally.2.25 Confined LConductive Location - Alocation having surfaces which are mainly com-posed of extraneous condutive parts and whichare of such dimensions that movement is restrictedto such an extent that contact with surfaces isdifficult to avoid ( for example, in a boiler ).*Classificationof electrical and electronic equipmentwith regardto protectionagainstelectric shock.

8

2.26 Connector - The part of a cable coupleror of an appliance coupler which is providedwith female contact and is intended to be attachedto the flexible cable connected to the supply.2.27 Conventional Touch Voltage Limit -Maximum value of the touch voltage which ispermitted to be maintained indefinitely in specifiedconditions of external influences.2.28 Conventional Operating Cu r r en t ( of aProtective Device )- A specified value of thecurrent which causes tht protective device tooperate within a specifiqd time,conventional time. designated

NOTE - For fuses this current is called the con-ventional fusing current . For circuit breakers thiscurrent ia called the conventional operating current .The conventional operating current is greater thanthe rated current or current setting of the device andthe conventional time varies according to the type andrated current of the protective device.

2.29 Current Carrying Capacity of a Con-ductor - The maximum current which can bdcarried by a conductor under specified conditionswithout i ts steady state temperature exceeding aspecified value.2.39 Current Using Equipment - Equipmentwhich converts electrical energy into anotherform of energy, such as light, heat, or motivepower.2 . 3 1 Danger - Danger to health or danger tolife or limb from shock, burn or injury frommechanical movement to persons ( and livestockwhere present ), or from fire attendent upon theuse of electrical energy.2.32 Design Current ( of a Circtlit ) - Themagnitude of the current intended to be carr iedby the circuit in normal service.2.33 Direct Contact - Contact of persons orlivestock with live parts which may result inelectric shock.2.34 Distribution Circuit ( of Buildings )- Acircuit supplying a distributing board.2.35 Double Insulation - Insulation compris-ing both basic insulation and supplementaryinsulation.2.36 Duct - A closed passage way formedunderground or in a structure and intended toreceive one or more cables which may be drawnin.2.37 Ducting - See2.14.2.38 Earth - The conductive mass of the earth,whose electric potential at any point is conven-tionally taken as zero.2.39 Earth Electrode - A conductor or groupof conductors in intimate contact with and provid-ing an electrical connection to earth.


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2.40 Earth Electrode Resistance - The resis;tance of an earth electrode to earth.2.41 Earth Fault Loop Impedance - Theimpedance of the earth fault current loop ( phaseto earth loop ) starting and ending at the point ofearth fault.2.42 Earth Leakage Current - A currentwhich flows to earth, or to extraneous conductiveparts, in a circuit which is electrically sound.

NOW - This current may have a capacitive com-ponent including that resulting from the deliberateuse of capacitors.2.43 Earthing Resistance, Total - The resis-tance between the main earthing terminal andthe earth.2.44 Earthed Concentric Wiring - A wiringsystem in which one or more insulated conduc-tors are completely surrounded throughout theirlength by a conductor, for example a sheath,which acts as a PEN conductor.2.45 Earthing Conductor-A protective conduc-tor connecting the main earth terminal ( orequipotential bonding conductor of an installationwhen there is no earth bus ) to an earth elec-trode or to other means of earthing.2.46 Electric Shock - A dangerous patho-physiological effect resulting from the passing ofan electric current through a human body or ananimal.2.47 Elect&al Equipment ( 466: Equip-ment ) - Any item for such purposes as genera-tion, conversion, transmission, distribution orutilization of electrical energy, such as machines,transformers, apparatus, measuring instruments,protective devices, wiring materials, accessories,and appliances.2.48 Elect&al Inrtallation (of a Building) -An assembly of associated electrical equipment tofulfil a specific purpose or purposes and havingcoordinated characteristics.2.49 Electrically Independent Earth Elec-trades - Earth electrodes located at such adistance from one another that the maximumcurrent likely to flow through one of them doesnot significantly affect the potential of theother(s).2.50 Electrode Boiler (or Electrode WaterHeater ) - Equipment for the electrical heatingof water or electrolyte by the passage of anelectric current between electrodes immersed inthe water or electrolyte.2.51 Emergency Switching - Rapid cuttingoff of electrical energy .to remove any hazard topersons, livestock, or property which may occurunexpectedly.

IS t 732 - 19892.52 Enclorure - A part providing protection ofequipment againstc ertain external influences and,in any direction, protection against direct contact.2.53 Equipment - See2.47.2.54 Equipotential Bonding - Electrical con-nection putting various exposed conductive partsand extraneousconductive parts at a substantiallyequal potential.

NOTE In a building installation equipotentialbonding conductors ahall interconnect the followingconductive parts:a) Protective conductor,b) Earth continuity conductor, andc) Risers of air-conditioning system and beatingsystems ( if any ).

2.55 Exposed Conductive Part - A conductivepart of electrical equipment, which can be touchedand which is not normally live, but which maybecome live under fault conditions.2.56 External InBuence - Any influence exter-nal to an electrical nstallation which affects thedesign and safe operation of that installation.2.57 Extramourn Conductive Part - A con-ductive part pot forming part of the electricalinstallation a/id liable to introduce a potential,generally the karth potential.2.58 Factory Built Assembly ( of LV Switch-y;T;*and Controlgear ) - Seu S : 862 (Part l)-2.59 Final Circuit - A circuit connected direct-ly to current using equipment, or to a socketoutlets or other outlet points for the connection ofsuch equipment.2.60 Fixed Equipment - Equipment fastenedto a support or otherwise secured.2.61 Functional Earthing - Connection toearth necessary for proper functioning of electricalequipment.2.62 Fare Element - A part of a fuse designedto melt when the fuse operates.2.63 Fuse Lkk - A part of fuse, including thefwe element(s), which requires replacement by anew or renewable fuse link after the fuse hasoperated and before the fuse is put back intoservice.2.64 Hand-Held Equipment - Portable equip-ment intended to be held in the hand duringnormal use, in which the motor, if any, forms anintegral part of the equipment.

NOTE- A hand-held equipment is an item ofequipment, the functioning of which requires constantmanual support or guidance.*Specification for factory built assemblies of switchgear

and controlgear for voltac and I 200 volt dc: es upto and including 1 000~ voltP 3 t 1 General requirements.9


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IS:732:19892.90 Residual Cyrrent Device ( RCD ) - Amechanical switchrng device or association ofdevices intended to cause the opening of the con-tacts when the residual current attains a givenvalue under specified conditions.2.91 Residual Operating Current - ResiduaIcurrent which causes the residual current deviceto operate under specified conditions.2.92 Resistance Area (for an Earth Electrodeonly) - The surface area of ground ( around anearth electrode ) on which a significant voltagegradient may exist.2.93 Ring Pinal Circuit - A final circuitarranged in the form of a ring and connected toa single point of supply.2.94 Shock Current-A current passing throughthe body of a person or an animal and havingcharacteristics likely to cause dangerous pathophy-siological effects.2.95 Short-Circuit Current - An overcurrentresulting from a fault of negligible impedance be-tween live conductors having a difference inpotential under normal operating conditions.2.96 Simultaneously Accessible Parts - Con-ductors or conductive parts which can be touchedsimultaneously by a person or, where applicableby livestock.

Norx - 1x1 the context of protection against directcontacts a live part may be accessible with:a) qnother live part, orb) an exposed conductive pert, orc) an extraneous conductive part, ord) a protective conductor.

The following may constitute simultaneouslyaccessible parts in the context of protection.against indirect contacts:a) Exposed conductive parts,b) Extraneous conductive parts, andc) Protective conductors.It should be noted that the word touchedsignifies any contact with any part of the body( hand, foot, head, etc ).

2.97 Socket Outlet - A device, provided withfemale contacts, which is intended to be installedwith the fixed wiring, and intended to receive aplug. NOTE A lumnaire track system is not regardedas a socket outlet system.2.98 Space Factor - The ratio ( expressed as apercentage ) of the sum of the overall cross-sectional areas of cables (including insulation andsheath ) to the internal cross-sectional area of theconduit or other cable enclosure in which theyare installed. The effective overall cross-sectionalarea of a non-circular cable is taken as that of a

circle of diameter equal to the major axis of thecable.2.99 Spur - A branch cable connected to a ringor radial final circuit.2.100 Standby Supply System - A systemintended to maintain supply to the installation orpart thereof, in case of interruption of the normalsupply, for reasons other than safety of persons.

NOTE - Standby supplies are necessary, for exam-ple, to avoid interruption of continuous industrialprocesses or data processing.2.101 Stationary Equipment - Either fixedequipment or equipment not -provided with acarrying handle and having such a mass that itcannot easily be moved.2.102 Supplementary Insulation - Indepen-dent insulation applied in addition to basicinsulation in order to provide protection againstelectric shock in the event of a failure of basicinsulation.2.103 Switch - A mechanical switching devicecapable of making, carrying and breaking currentunder normal circuit conditions, which mayinclude specified operating overload conditions,and also of carrying for a specified time currentsunder specified abnormal circuit conditions suchas those of short circuit.

NOTE - A switch may also be capable of making,but not breaking, rhort-circuit currents.2.104 Switch, Linked - A switch the contactsof which are so arranged as to make or break allpoles simultaneously or in a definite sequence.2.105 Switchboard - An assembly of switchgearwith or without instruments, but the term does notapply to a group of local switches in a finalcircuit.

NOTE - The term switchboard includes a distri-bution board.2.106 Switchgear - An assembly of main andauxiliary switching apparatus for operation, regu-lation, protection or other control of electricalinstallations.

NOTE For more comprehensive definitions of theterms in 2.103 to 2.106 ( ICI IS : 1885 ( Part 17 )-1987*.

2.107 System - An electrical system consistingof a single source of electrical energy and aninstallation.NOTE - The types of systems depending upon therelationship to the source and of the exposed conductiveparts of the installation to earth are defined inIS : 3043-1987t.

2.108 Touch Voltage - The potential differencebetween a grounded metallic structure and a point+Electrotechnical vocabulary:Part 17 Switchgear andcontrolgear (J irsl raoision ) .tCode of practice for earthing.

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on the earths surface separated by a distance 2.109 Voltage, Nominal (of an Installation)-equal to the normal maximum horizontal reach Voltage by which an installation or part of anapproximately 1 metre. installation is designated.

SECTION 2 ASSESSMENT OF GENERAL CHARACTERISTICS OF INSTALLATIONS3. ASSESSMENT OF CHARACTERISTICS3.0 An assessment shall be made of the followingcharacteristics of the installation in accordancewith the clauses indicated:

a) The purpose for which the installation isintended to be used, its general structure,and its supplies (3.1 );b) The external influences to which it is to beexposed ( 3.2 );c) T?l?$ compatibility of its equipment ( 3.3 );d) Its maintainability ( 3.4 ).These characteristics shall be taken intoaccount in the choice of methods of protectionfor safety ( see Section 3 ) and the selection anderection of equipment ( see Section 4 ).

3.1 Purposes, Sapplies and Structure3.1.1 Maximum Demand - The maximumdemand of the installation, expressed as a currentvalue, shall be assessed.3.1.2 Diversity - In determining the maximumdemand of an installation or parts thereof, diver-

sity may be taken into account.3.1.3 Ar rangement of L ive Conductors and Tyke ofEarthing

3.1.3.1 General - The characteristics men-tioned in 3.1.3.2 and 3.1.3.3 shall be ascertainedin order to determine which methods of protectionfor safety, will be appropriate.3.1.3.2 .Number and types of live conductorsThe number and types of live conductors ( forexample single-phase two-wire ac, three-phasefour-wire ac ) shall be assessed, both for thesource of energy and for the circuits to be used

within the installation. Where the source ofenergy is provided by a supply undertaking, thatundertakings shall be consulted, if necessary.3.1.3.3 Typos of earthing anangement - Thetype of earthing arrangement or arrangements tobe used for the installation shall be determined.

3.1;4 .hG&reof Sr#!y3.1.4.1 General - The following character-istics of the supply or supplies shall be ascertainedfor an external supply and shall be determinedfor a private source:

a) Nominal voltage(s);b) Nature of current and frequency;

c) Prospective short-circuit current at theorigin of the installation;d) Type and rating of the overcurrent protec-tive device acting at the origin of thee>f>

installation;Suitability for the requirements of theinstallation, including the maximumdemand; andThe earth loop impedance of that part ofthe system external to the installation.

NOTE As regardsitem (f), it may only be possi-ble to ascertain an expected maximum value.3.1.4.2 Su@lies for safety services and standbypur poses - Where a supply for safety services orstandby purposes is specified, the characteristicsof the sources of any such supply shall be assessed.Such supplies shall have adequate capacity, relia-bility and rating and appropriate changeovertime for the operation specified.Where the normal source of energy is to beprovided by a supply undertaking, the supplyundertaking shall be consulted regarding switchingarrangements for safety and standby supplies,especially where the various sources are intended

to operate in parallel.NOTE For further reqtiitementsfor suppliesforsafety services ee .4.

3.1.5 I nstallation Circuit Arr angements3.1.5.1 Every installation shall be dividedinto circuits as necessary to:

a) avoid danger and minimise inconveniencein the event of a fault, andb) facilitate safe operation, inspection, testing,and maintenance.

3.1.5.2 Separate circuits shall be providedfor parts of the installation which need to beseparately controlled, in such a way that thesecircuits are not affected by failure of othercircuits.

3.1.5.3 The number of final circuits requi-red, and the number of points supplied by anyfinal circuit, shall be such as to comply with therequirements for overcurrent protection, for isola-tion and switching, and as regards current-carrying capacities of onductors.3.1.5.4 Where an installation comprisesmore than one final circuit, each final circuit shallbe connected to a separate way in a distribution

board. The wiring of each final circuit shall be12


14/79

clecttically separate from that of every other finalcircuit, so as to prevent indirect energisation of afinal circuit intended to be isolated.3.2 Compatibility .

3.2.1 An assessment shall be made of anycharacter@@ .ofequi$ment likely to have harmfuleffects upon other electrical equipment or otherservices, or likely to impair the supply. Thecharacteristics include, for example:

4b)4d)transient overvoltages;rapidly fluctuating loads;starting currents;

e>f)!3)h)j)

harmonic currents ( such as with fluores-cent lighting loads and thyristor drives );mutual inductance;dc feedback;high frequency oscillations;earth leakage currents; andany need for additional connections toearth ( for example, for equipment needinga connection with earth independent ofthe main means of earthing of the installa-tion, for the avoidance of interference withits operation ).

NOTII For an external source of energy it iseaaential that the supply undertaking be consultedregarding any equipment of the installation having acharacterirtic likely to have a significant influence onthe supply, for example, having heavy startingcurrents.3.3 Maintainability

3.3.1 An assessment shall be made of the fre-.quency and quality of maintenance that the ins-tallation can reasonably be expected to receiveduring its intended life. This assessment shall,wherever practicable, include consultation withthe person or body who will be responsible forthe operation and maintenance of the installation.Having regard to the frequency and quality ofmaintenance expected, the requirements of thisCode shall be applied so that:4

b)4

any periodic inspection, testing, mainten-ance and repairs likely to be necessaryduring the intended life can be readilyand sefely carried out;the protective measures for safety remaineffective during the intended life; and

the reliability of equipment is appropriateto the intended life.3.4 Supplies for Safety Services

NOTE The need for safety services and theirnature are frequently regulated by statutory authoritiwwhose requirements have to be observed.3.4.1 General- The following sources forsafety services are recognized:a) storage batteries,b) primary cells,

Cld)

18873291%?9generator sets independent of the normalsupp1.y anda separate feeder effectively independentof the normal feeder.NOTE The use of separate independent feeders

should be based on an assessment that the two suppliesare unlikely to fail concurrently.3.4.2 ClassiJication - A safety service is either:

a non-automatic supply, the starting ofwhich is initiated by an operator, oran automatic supply, the starting olwhich is independent of an operator.

An automatic supply is classified according tochangeover time:a) no-break - an automatic supply which canensure a continuous supply within specifiedconditions during the period of transition,for example, as regards variations in volt-age and frequency;b) oery short break: an automatic supply avail-able within 0.15 second;c) short brsak: an automatic supply availablewithin 0.5 second;d) medium break: an automatic supply avail-able within 15 seconds; ande) long break: an automatic supply available inmore than 15 seconds.

4. EXTERNAL INFLUENCES4.1 Identification of External Influences onthe Electrical Installrrtion4.1.1 The characteristics of the followingexternal influences shall be assessed:1) Environments

a) Ambient temperature,b) Atmospheric humidity,c) Altitude,d) Presence of water,e) Presence of foreign solid bodies,f) Presence of corrosive or polluting subs-tances,g) Mechanical stresses,h) Presence of flora and/or mouid growth,j) Presence of fauna,k) Electromagnetic,influences, electrostatic or ionizing

m) Solar radiation,n) Seismic effects,p) Lightning, andq) Wind.

2) Utilizationa) Capability of persons,b) Electrical resistance of human body,

13


15/79

JS t 732 - 1989c) Contact of persons with earth potential,d) y;;ditions of evacuation in an emergency,e) Nature of processed or stored material.

3) Construction of Buildingsa) Constructional materials, andb) Building design.

4.1.2 Table I suggests the classification andcodification of external influences which requireassessment in-the design and erection of electricalinstallation.NOTE1 - Each condition of external influence isdesignated by a code comprising a group of two capitallettersand a number as follows:ThaJirSt letter relates to rhe general category of externalinJkence :A - environmentB = utilizationC = construction of buildingsThe second leltcr relates to the nature of the exxlnnalit&mca:A . .B...C . . .The number relates lo the class within each external

inJt#ncc :1 . .2 . . .3 . .For example, the code AC 2 signifies:

A - environmentAC = environment altitude

AC2 = environment altitude > 2 000 m.The code given here is not intended to he used formarking equipment.NOTE 2 - The characteristics defined for electricalinstallations are those accepted by the IEC and asapplicable for electrical installations in buildinga.Influences on outdoor installations are separately defy-ned in the respective parts of the Code.

For the time being, the characteristics of influences.( co1 2, Table 1 ) are given in descriptive laagu8geonly. Codification for the same .( SW Note 1 above ),as recommended by IEC are given in co1 4 for infor-mation. It is hoped that in due course the users of theCode would be familiar with the codification in terma-ofwhich the requirements would be stated in futureeditions.

4.2 Compatibility - An assessment shall be-made of any characteristics of equipment likelyto have .harmful effects upon other electrical.equipment or other services or likely to impairthe supply. Those characteristics include, forexample:a) transient overvoltages,b) rapidly fluctuating loads,c) starting currents,d) harmonic currents,e) dc feedback,f ) high-frequency oscillations, andg) earth leakage currents.

4.3 Maintainability - An assessment shall bemade of the frequency and quality of mainten-ance the installation can reasonably be expectedto receive, during its intended life. Where anauthority is to be responsible for the operation ofthe installation, that authority shall be consulted.Those characteristics are to be taken into accountin applying the requirements of this code so Xhat,having regard to the frequency and quality ofmaintenance expected:

a) any periodic inspection and testing andmaintenance and repairs likely to benecessary during the intended life can bereadily and safely carried out,b) the effectiveness of the protective measuresfor safety during the intended life is ensur-ed, andc) the reliability of equipment for proper func-tioning of the installation is appropriate tothe intended life.

14


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IS : 732 - 1989TABLE 1 ASSESSMENT OF GENERAL CHA&UICTERISTICS OF BUILDINGS

( Clam 4.1.2 )CLA~SDESIONATION

(1)1) Ambienttemperature

.2) Atmospherichumidity3) AltitudeI4) Presence of water

Negligible

CHARAOTERISTIC~(2) Environment

APPLICATION AND EXAXPLES(3)

CODZI(4)

The ambient temperature to beconsidered for the equipment isthe temperature at the placewhere the equipment is to beinstalled resulting from theinfluence of all other equipmentin the same location, whenoperating, not taking into acco-unt the thermal contribution ofthe equipment to be installed.Lower and upper limits of rangesof ambient temperature:

- 60%- 40% $1:Y: -i-5%0 +40c

::E+ 40%0 f6OCThe average temperature over a24 hour period must not exceed5C below the upper limts.

Combination of two ranges todefine some environments maybe necessary. Installations sub-ject to temperatures outsidethe ranges require special con-sideration.

AA1AA2AA3AA4AA5AA6

under considerationC2000m AC1>2OOOm AC2Probability of presence of water isnegligible

Free-fallingdrops Possibility of vertically fallingdrops

Sprays

Splashes

Possibility of water falling as sprayat an angle up to 60C from theverticalPossibility of splashes from anydirection

Jets Possibility ofjets of water fromany direction

WavesImmersion

Possibility of water wavesPossibility of intermttent partialor total covering by water

Submersion Possibility, of permanent and totalcovering by water

Locations in which the walls do notgenernlly show traces of waterbut may do so for short periods,for example, in the form ofvapour which good ventilationdries rapidly

Locations in which water vapouroccasionally condenses as dropsor where steam may occasionallybe presentLocations in which sprayed waterforms a continuous film on fIoorsand/or wallsLocations where equipment may besubjected to splashed water, thisapplies, for example, to certainexternal lighting fittings, conatru-ction site equipment, etc.Locations where bosewater is used

regularly ( yardr, car-washingbays )Seashore locations such as piers,beaches, quays, etc.Locations which may be flooded and/or where water may be at leaat150 mm above the highest pointof equipment, the lowest part ofequipment being not more than1 m below the water surfaceLocations such as swimmng poolswhere electrical equipment ia per-manent!y and totally covered withwater under a pressure greaterthanwl bar

AD1

AD2

AD3

AD4

AD5

AD6AD?

AD&?

( Continwd )

15


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IS:732-1889

TABLE 1 ASSESSMENT OF GENERAL CHARACTERISTICS OF BUILDINGS - ContdCLASS DESIUNATION CHABACTERISTICS

(1) (2)5) Presence of foreign

solid bodies:Negligible The quantity of nature of dust orforeign solid bodies is not signi-ficant

Small Objects Presence of foreign solid bodieswhere the smallest dimension isnot less than 2.5 mmVery small Presence of foreign solid bodiesobjects where the smallest dtmensionis not less than 1 mm

Nom - In conditions AEIand AE3, dust may be presentbut is not significant to operationof the electrical equipment

Dust Presence of dust is significantquantity

6) Presence ofcorrosive or pol-luting subtances:Negligible The quantity or nature of corrosiveor polluting substances is notsignificantAtmospheric The presence of corrosive orpolluting substance of atmos-pheric origin is significant

Intermittent Intermittent or accidental subjec-or accidental tion to corrosive or pollutingchemical substances being usedor produced

Continuous Continuously subject to corrosiveor polluting chemical rubs-tances in substantial quantity7) Mechanical Stresses:

a) ImpactLow severityMedium severityHigh severity

NOTES Provisional classili-cation. Quantitative expressionof impact severities is under-onsiderationb) Vibration

Low severity

Medium severityHigh severity

NOTE - Provisional classifi-cation. Quantitative expressionof vibration severities is underconsideration

APPLICATIONS AND EXAMPLES CODE(3) (4)

AEl

Tools and small objects are exam-ples of foreign solid bodies ofwhich the smallest dimension isat least 25 mm

AE2

Wires are examples of foreign solidbodies of which the smallestdimension is not less than 1 mm.AE3

AE4

Installations situated by the sea orindustrial aones producing seriousatmospheric pollution, such aschemical works and cementworks; this type of pollution arisesespecially in the production ofabrasive, insulating or conductivedusts

Locations where some chemicalproducts are handled in smallquantities and where these pro-ducts may come only accidentallyinto contact with electrical equip-ment; such conditions are foundin factory, laboratories, otherlaboratories, or in locations wherehydro-carbons are used ( boiler-rooms, garages, etc ).

For example, chemical works

Household and similar conditions AGlUsual industrial conditions AG2Severe industrial conditions AG3

AFI

AFZ

AF3

AF4

Household and similar conditionswhere the effects of vibration aregenerally negligible

Usual industrial conditionsIndustrial installations subject tosevere conditions

AH1

AH2AH3

( Confinusd )16


18/79

ISr732-Ml9-

TABLE I ASSESSMENT OF GENERAL CHARACTERISTICS OF BUILDINGS - CodCLASS DESIONATION CHAEACTERISTICS

c) Other mechanicalstresses8) Presence of fungusand/or mould growth:

No hazardHazard

9) Presence of vermin:No hazardHazard

10) Electromagnetic,electrostatic orionizing influences:Negligible

Stray currentsElectromagneticsIonizationElectrostaticsInduction

11) Solar radiationNegligibleSignificant

12) Seismic effectsNegligibleLow severityMedium severityHigh severity

No hazard of fungus and/or mouldgrowthhazard of fungus and/or mouldgrowth

No hazardHazard from fauna ( insects, birds,small animals )

No harmful effects from straycurrents, electromagnetic radia-tion, electrostatic fields, ionizingradiation or inductionHarmful hazards of stray currentsHarmful presence of electromag-netic radiationHarmful presence

radiationof ionizing

Ha;eyA;l presence of electrostaticHarmful presence of inducedcurrents

Solar radiation of harmful intensityand/or duration

Up to 30 Gal ( 1 Gal = 1 cm/s1 )Over 30 up to and including 300GalOv;l300 up to and including 600aGreater than 600 Gal

APPLICATIONS AND EXAYPL~S(3)

Under consideration

The hazard depends on local condi-tions and the nature of fungus.Distinction should be made be-tween harmful growth of vegeta-tion or conditions for promotionof mould growth

The hazard.depends on the natureof the vermin. Distinction shouldbe made between:- presence of insects in harmful

quantity or of an aggressivenature- presence of small animals orbirds in harmful quantity or ofan aggressive nature

Vibration which may cause thedestruction of the building is out-side the classificationFrequency is not taken into accountin the classification; however, ifthe seismic wave resonates withthe building, seismic effects mustbe sprciallv considered. Ingeneral, the frequency of seismicacceleration is between 0 and10 Hz

CODE(41AJ

AK1AK2

AL1AL2

AM1

AM2AM3AM4AM5AM6

ANIAN2

APIAP2AP3AP4

( Confinwd

17


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20/79

IIt1989TABLET ASS- OF GENERAL CHARACTERISTICS 01 BUILDINGS - Cmtd

CLASSDnaerotrr~xow(1)

5) Nature of processedor atored m8teriialrNo rigni6cant risks

CHABACTBBlSTIOS(2)

-Fire risks

Rxplosion risk

Contaminationrisks

Manufacture,processing or storageof flamtnab+e materials includingprebnce of dustProcessing or storage of explosiveor low flashpoint materialsincluding presence of explosivedustsPresence of unprotected foodstuffs,

Bharmaceutics, and similar pro-ucts without protection

1) ConstructionalmaterialsNon-comburtibleCombustible

2) Building designNegligible riskPropagation of fire

Movement

Flexible orunstable

Conotnnctious of BuMbg

Buildings mainly constructed ofcombustible materials

Buildings of which the shape anddimensions facilitate the spreadof fire ( for example, chimneyeffectr )Risks due to structaral movement(for example, diiplacemeat be-tween a building and the ground,

or rettlement of ground or build-ing foundations )Structures which are weak or sub-jects to movement ( for example,cscill8tion )

hPLICATIOIW AND tiAXPLlES CODE43) (4)

Ba~~~o;exi-working shops, paperaOil refinerier, hydrocarbon stores

Foodstuff industries, kitchensNOTS- Certain prec8utionsmay be necessary, in the event offruit, to prevent processedmaterials being contaminated byelectrical equipment, for exam-ple, by broken lamps

Wooden buildings

High-rise buildings, forced ventila-tion systems

Buildiogs of considerable length orerected on unstable groundContraction or expansion jointsTents, air-suppoat structures. falseceilings. removable partition1Flexible wiring, installatioos needingsPpo*

BE1BE2

BE3

BE4

CA1CA2

CBlCB2

CB3

CM

SECTION 3 PROTECTION FOR SAFETY5. REQUIREMENTS FOR PROTECTIONFOR SAFETY5.0 Fundamental Reqdremmts for Safety -The rquirements for protection for safety ofpcraons, livestock and property involve protectionagainst electric shock, thermal effects, overcurrent,overvoltage and undervoltage and a measure ofisolation and switching of electric circuits. Theprotective measures may be applicable to theentire installation or a part or an item of equip-ment. The requirements stated below in thisSection are based on the following basic princi-ples.

SO.1 Protection Against Dirrct Contact - Personsaod livestock shall be protected against dangersthat may arise 6om watact with live parts of theinstallation.

This protection can be achieved by one of thefollowing methods:a) Preventing a current Gem passing throughthe body of any pcraon or any livestock;andb) Limiting the current which can pass thro-ugh a body to a value lower than the shockcurrent.

5.0.2 Protection Against I ndir ect Contact - Pcr-sons and livestock shah be protected againstdangers that may arise from contact with exposedconductive parts.This protection can be achieved by one of thefollowing methods:a) Preventing a fault current from passingthrough the body of any person or anylivestock;

19


21/79

IS:732 -1989b) Limiting the fault current which can passthrough a body to a value lower than theshock current; andc) Automatic disconnection of the supply onthe occurrence of a fault likely to cause acurrent to flow through a body in contact

with exposed conductive parts, where thevalue of that current is equal to or greaterthan the shock current.5.0.3 Protection Against Thermal E@cts in .NonalService - The electrical installation shall be soarranged that there is no risk of melting besidesignition of flammable materials due to high tem-perature or electric arc. Also during normaloperation of the electrical equipment, there shallbe no risk of persons or livestock suffering burns.5.0.4 Protection Against Overcurrent - Persons or

livestock shall be protected against injury andproperty shall be protected against damage due toexcessive temparatures or electromechanicalstresses caused by any overcurrents likely to arisein live conductors.This protection can be achieved by one of thefollowing methods:a) Automatic disconnection on the occurrenceof an overcurrent before this overcurrentattains a dangerous value taking intoaccount its duration; andb) Limiting the maximum overcurrent to a

safe value and duration.5.0.4.1 Overcurrent grotection devices - Wherenecessary to, prevent danger, every installationand every circuit thereof shall be protected againstovercurrent by devices which:

a) will operate automatically at values ofcurrent which are suitably related to thesafe current ratings of the circuit;b) are of adequate breaking capacity and,where appropriate, making capacity; andc) are suitably located and are constructed SO

as to prevent danger from overheating,arcing or the scattering of hot particleswhen they come into operation and topermit ready restoration of the supply with-out danger.NOTE - Where the supply undertaking pro-vides switchgear or fusegear-at the origin of-theinstallation it may not be necessary to duplicatethe means of overcurrent protection for that partof the installation between its origin and the maindistribution point of the installation where thenext step for overcurrent protection is provided.In domestic installations the protection and isolat-ing functions are combined in the same device.

5.0.5 Protection Against Fault Currents - Conduc-tors, other than live conductors, and any otherparts intended to carry a fault current shall be

capable of carrying that current without assumingexcessive temperature, until the protective gearoperates.NOTE 1 - Particular attention should be given toearth fault currents.NOTE 2 - For live conductors, compliance with 5assures their protection against any fault currents,including overcurrents.

5.0.5.1 Precautions against earth leokoge andearth fault currents -Where metalwork of electricalequipment, other than current-carrying conduc-tors, may become charged with electricity in sucha manner as to cause danger if the insulation of aconductor should become defective or if a faultshould occur in any equipment:a>b)

the metalwork shall be earthed in such amanner as will cause discharge of electricalenergy without danger, orother equally effective precautions shall betaken to prevent danger.

Every circuit shall be arranged so as to preventthe persistence of dangerous earth leakagecurrents.Where metalwork is earthed, the circuitsconcerned shall be protected against the persis-tence of dangerous earth fault currents by:a) the overcurrent protective devices requiredby 5.0.4.1, orb) a residual current operated device orequally effective device.The method described in (b) above shall beused whenever the prospective earth fault currentis insufficient to cause prompt optration of theovercurrent protective devices.Where necessary to prevent danger and wheremetalwork of electrical equipment is earthed forcompliance with (a) above and is accessiblesimultaneously with substantial exposed metalparts of other services, the latter parts shall beeffectively connected to the main earthing termi-nal of the installation.

5.0.6 Protection Against Overvoltage - Persons orlivestock shall be protected against injury andproperty shall be protected against any harmfuleffects of a fault between live parts of circuitssupplied at different voltages.Persons or livestock shall be protected against

injury and property *shall be protected againstdamage from any excessive voltages likely to arisedue to other causes ( for example, atmosphericphenomena or switching voltages ).


22/79

IS I 732 - 1989SECTION 3A PROTECTION AGAINST ELECTRIC SHOCK

-5.1 R&@ements for Protection Against intentionally be connected to any ofElect& sho.& the following:5.1.1 Proi&Zon Against Both Direct and bdirectContact

5J.l.I General +Qne of the follotiing .basicprotective measures for protection Against bothdirect contact and indirect contact shall be used:a) Protection by safety extra low voltage,b) Protection by functional extra low voltage,andc) Protection. by limitation of discharge ofenergy.

5.1.1.2 Protection by safety extra low voltage -Protection against electric shock is provided whenall the following requirements are fulfilled:

4b)4

The nominal voltage of the circuit concer-ned does not exceed extra low voltage.The supply is from one of the safety sourceslisted in (1) below.The conditions of (2) below are fulfilled.

NOTE - Lower voltage limits may berequiredfor certain conditions of external influences.1) Safety sources - The safety source shall beone of the following:

9 A class II safety isolating transformer,the secondary-winding being isolatedfrom earth.ii) A source of current providing a degreeof safety equivalent to that of the safetyisolating transformer specified in (a)above ( for example, a motor generatorwith windings providing equivalentisolation ).

iii) An electrochemical source ( for exam-ple, a battery ) or another sourceindependent of a higher voltage circuit( for example, a engine-driven genera-tor ).iv) Electronic devices where measures havebeen taken so that even in the case ofan internal fault the voltage at the out-going terminals cannot exceed extralow voltage.

2) Arrangement of Circuitsi)

ii)

Live parts of safety extra low voltagecircuits shall not be connected to earthor to live parts or protective conductorforming part of other circuits.Exposed conductive parts of safetyextra low voltage circuits shall not

21

iii)

iv)

1) Earth,2) Protective conductors or exposedconductive parts of another system,or3) Extraneous conductive parts, exceptthat where electrical equipment isinherently required to be connectedto extraneous conductive parts it

shall be verified that those parts can-not attain a voltage exceeding thelimit of the safety .extra low voltagecircuit. If the exposad conductiveparts of safety extra low voltagecircuits are liable to come into con-tact fortuitously with exposedconductive parts of other circuits,the protection no longer dependssolely on the measure for protectionby safety extra low voltage and shallbe in accordance with the require-ments for the measures applicable tothe latter exposed condactive parts.

Live parts of safety extra low voltageequipment other than cables shall beelectrically separate from those ofhigher voltage circuits. The electricalseparation between live parts of safetyextra low voltage circuits and highervoltage circuits shall be not less thanthat between the input and outputwindings of safety isolating transfor-mers.Safety extra low voltage circuit conduc-tors shall preferably be physicallyseparated from those of any othercircuit. Where this requirement is im-practicable, one of the followingarrangements is required:1) Safety extra low voltage circuitconductors shall be insulated in

accordance with the requirements ofthis code for the highest voltagepresent.2) Safety extra low voltage circuitcables shall be non-metallic sheathedcables.3) Conductors of circuits at differentvoltages shall be separated fromthose at safety extra low voltage byan earthed metallic screen or anearthed metallic sheath.4) Circuits at different voltages may becontained in a multicore cable or

other grouping of conductors but theconductors of safety extra low


23/79


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ii) Insulation corresponding to the mini-mum test voltage required for theprimary circuit.In addition, protection againstindirect contact shall be provided inaccordance with (d) below.The extra low voltage circuit may beused to supply factory built equipmentwhose insulation does not comply withthe minimum test voltage required forthe primary circuit provided that theaccessible insulation of that equipmentis reinforced during erection to with-stand a test voltage of 1 500 V rms forone minute.

If the primary circuit of the functionalextra low voltage source is protected byautomatic disconnection, exposed conduc-tive parts of the equipment in the function-al extra low voltage circuit shall beconnected to the protective conductor ofthe primary circuit.

NOTE - Thii doer not exclude the nossibilitvof connecting a conductor of the functi6nal ext&low voltage circuit to the protective conductor ofthe primary circuit.If the primary circuit of the functionalextra low voltage source is protected byelectrical separation, the exposed conduc-

tive parts of equipment in the functionalextra low voltage circuit shall be connectedto the non-earthed protective conductor ofthe primary circuit.N~T~G- This latter requirement does not con-travene 5.1.5.5(c), the combination of theelectrically separated circuit and lhe extra lowvoltage circuit being regarded as one electricallyseparated circuit.

The socket outlet of functional extra lowvoltage systems shall not admit plugs inten-ded for use with other systems in use in thesame premises.

Application of Protective Measure -Functional extra-low voltageWhere, for functional reasons, t& a-low

voltage s ustd but:i)

ii)&c pont of the extra-low voltage cir cuit isrequi red to be earthed, orLive pcrtts or exposed conducti ve parts of theextra-l ow vol tage ircuit art conntctcd o tht

prottc fiive condu& rs qf other ys& ns (wht tk a:those protective conductor s art earthed or not);or

iii) The i nsulation between the extra-low voltagtcircui ts and other circuits is not equivalent tothat provi ded by a safety source.The syskm shall be t reated as a unctionalextra-low voltage system Fnd 5.1.1.3 applg.

5.1.1.4 Prokction by limitation of discharge ofenergy - For equipment complying with theappropriate standard, protection against electricshock is afforded when the equipment incorporatesmeans of limiting the current which can passthrough the body of a person or livestock to avalue lower than the shock current. Circuits rely-ing on this protective measure shall be separatedfrom other circuits in a manner similar to thatspecified in !5.1.1.2(2)(iii) and (iv) for safety extralow voltage circuits.

Application of protective measure-Limitationof discharge of energyThi s measure shall be applied only o individualitems of curr ent-using equipment complying wi th an

appropriate I ndian Standard, where the equipmentincorporates means of limiting to a saje value the cur rentthat can Jlow rom lhe equipment through he body of aperron or ivestock. The appli cation of this measure maybe extended to a part of an installati on derived rom suchitems of cqulpment, where the relevant I ndian Standardconcerned provi des specz$all y for thi s, for example, toelectr ic ences suppl ied rom electr ic ence controll ers.

5.1.2 Protection Against Di rect Contact5.1.2.0 General - One or more of the fGllow-ing basic protective measures for protection against

direct contact shall be used:a) Protection by insulation ofiive parts,b) Protection by barriers or enclosures,c) Protection by obstacles, andd) Protection by placing out of reach.

5.1.2.1 Pro& li on by insul ation of li zlt parts -Live parts shall be completely covered with insu-lation which can only be removed by destructionand which is capable of durably withstanding.themechanical, electrical, thermal and che&alstresses to which it may be subjected in service.NOTE1- Where insulation is app)ied during theerection of the installation. the aualitv of the insulationshould be confirmed by iests km&r to &se whichensure the quality of the insulation of simlar factorybuilt equipment.NOT~P - General purpose, paints, varnishes, lac-quers and simlar products without additional insulationdo not provide adequate insulation for protectionagainst direcf contact.

Application of protective measure - Insulationof live parts

Thi s measur e elates to basic insul ation , and is inten-ded to prevent contact with li ve parts. 4, i s generall yapplicable or protection against dir ect contact, n conjunc-tion with a measure for procction tiganst indirectcontad.


25/79

IS : 732 - 19895.1.2.2 Protection by barri ers or enclosur es

4

b)

4

4

Live parts shall be inside enclosures orbehind barriers providing at least thedegree of protection IP 2X except that,where an opening larger than that admittedfor IP 2X is necessary to allow the replace-ment of parts or to avoid interferencewith the proper functioning of electricalequipment both of the following require-ments apply:

i) Suitable precautions shall be taken toprevent persons or livestock fromunintentionally touching live parts,andii) It shall be established as far as practi-cable, that persons will be aware thatlive parts can be touched through theopening and should not be touched.

Horizontal top surfaces of barriers orenclosures which are readily accessible shallprovide a degree of protection of at leastIP 4x.Barriers and enclosures shall be firmlysecured in place and have sufficient stabilityand durability to maintain the requireddegrees of protection and appropriate sepa-ration from live parts in the known condi-tions of normal service.Where it is necessary to remove barriers orto open enclosures or to remove parts ofenclosures, one or more of the followingrquirements shall be satisfied:

i) The removal or opening shall be possi-ble only by use of a key or tool,ii) The removal or opening shall be possi-ble only after disconnection of thesupply to live parts against which thebarriers or enclosures afford protection,restoration of the supply being possibleonly after replacement or reclosure ofthe barriers or enclosures, andiii) An intermediate barrier shall be provi-ded to prevent contact with live parts,such barrier affording a degree of pro-tection of at least IP 2X and removableonly by the use of a tool.

This requirement does not apply to ceilingroses or to ceiling switches operated by a cord.Application of Protective Measure - Barriersor enclosuresa) Thi s measure is in tended to prevent or deter anycontact with liveparts I t i sgenerally appli cablefor protectiun against direct contact in conjuncti on-wir h a measure for protection against tndi rectcontact.b) The exception in 5.1.2.2(a) allowing for open-ings larger than I P 2X in barri ers or cndosuresshall be appli ed only to items of equipment or

accessori es complying with an I ndian Standardwhere comjL iance with the general it y of 5.1.2.2(a)is imbracticable by reason of the function ofthose tems, for exam@, to ampholder; . Where-ver hat exception is used, the opening shall be assmall as is consistent with the requir ements orproper uncti onin g and or replacement of parts.5.1.2.3 Protection by obstacles

a) Obstacles shall prevent, as appropriate, thefollowing:i) Unintentional bodily approach to liveparts, or

ii) Unintentional contact with live partswhen operating equipment live innormal use.b) Obstacles shall be so secured as to preventunintentional removal but may be remov-able without using a key or tool.Application of Protective Measure-ObstaclesThi s measure is in tended to prevent uni ntentional

contact with Live arts, but not i ntentional contact bydeli berate cir cumvention af the obstacles. I t shall be usedonly or protection against dir ect contact n areas accessi-ble only to skilled persons, or nstructed persons underdir ect supervision .5.1.2.4 Protection by placing out of reach

a) Bare or PVC covered overhead lines fordistribution between buildings and struc-tures shall be installed in accordance withgood practice.b) Bare live parts shall not be within armsreach.c) Where bare live parts other than overheadlines are out of arms reach but neverthelessmay be accessible, they shall not be within2.5 m of any of the following:

d)

4

i) Exposed conductive parts,ii) Extraneous conductive parts, and

iii) Bare live parts of other circuits.If a normally occupied position is restrictedin the horizontal plane by an obstacle ( forexample, handrail mesh screen ) affordinga degree of protection less than IP 2X,arms reach shall extend from that obstacle.In the overhead direction, arms reach is2.5 m from the surface S not taking intoaccount any intermediate obstacle provid-ing a degree of protection less than IP 2X( see Fig. 1 ).

NOTE - The values of arms reach refer tobare hands witbout any assistance, for example,from tools or a ladder.I n places where bulky or long conductingobjects are normally handled, the distancesrequired by (b) to (d) shall be increasedaccordingly.


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IS : 732 - 1989Application of Protective Measure - Placingout of reach

This measure is intended only to prevent unintentionalcontact with live parts and shall be applied only forprotection against direct contact. The applicatien of theprovisions of 5.1.2.4(b) to (d) shall be limited to loca-tions accessible only to skilled jersons, or instructedpersons under direct supervision.

5.1.3 Protection Against Indirect Contact5.1.3.0 General - One or more of the follow-ing basic protective measures for protection againstindirect contact shall be used:

4b)C>44

Earthed equipotential bonding and auto-matic disconnection of supply,Use of Class I I equipment or equivalentinsulation,Non-conducting location,Earth free local equipotential bonding,andElectrical separation.

5.1.3.1 Protection by earfhed equipotential bondingand automatic disconnection of supplra) General

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ii)

In each installation main equipotentialbonding conductors complying withIS : 3043-1987* shall connect extrane-ous conductive parts including thefollowing to the main earthing termi-nal for that insulation:1) Main water pipes,2) Main gas pipes,3) Other service pipes and ducting,4) Risers of central heating and air-conditioning systems, and5) Exposed metallic parts of the build-ing structure.

NOTE 1- This bonding is intended tocreate a ione in which any voltages be-tween exposed conductive parts and extra-neous conductive parts are mnimsed.NOTE 2 - Compliance with (a) (i) will

normally satisfy the relevant requirementsof the protective multiple earthing.NOTE 3 - Additional equipotentialbonding may be required [see 5.1.3.1(a)(v)].

The characteristics of the protectivedevices for automatic disconnection,the earthing arrangements for theinstallation and the relevant impe-dances of the circuits concerned shall becoordinated so that during an earthfault the voltages between simultane-ously accessible exposed and extrane-ous conductive parts occurring anyeCode of practice for earthing ( jrtirrt&fort ). *Code of practicefor earthing.

where in the installation shall be ofsuch magnitude and duration as notto cause danger.NATE 1 - For information on types ofearthing arrangements, SI I IS : 3043-1987..NOTE - For the conditions of connectionof exposed conductive parts SII 5.1.3.1(b) to(d) and as appropriate to the earthingarrangement concerned.

ii i) The provisions of (ii) above are consi-dered to be satisfied if the automaticdisconnection provided for occurs with-in the duration not permitting thetouch voltage to exceed the safe value.iv) Where protection is afforded by anovercurrent protective device, and thenominal voltage to earth (V, ) is240 V rms ac, the earth fault loop im-pedance ( & ), for compliance with(iiiesabove, shall not exceed safev) Where compliance with the disconnec-tion times of (ii i) above is afforded bya residual current device in an installa-tion, the product of the rated residualoperating current in amperes and theearth fault loop impedance in ohmsshall not exceed the values given inIS : 3043-198i* for different types ofsystem earthing.

vi) Within the zone formed by the mainequipotential bonding, local supple-mentary bonding connections shall bemade to metal parts, to maintain theequipotential zone, where those parts:1) are extraneous conductive parts,2) are simultaneously accessible withexposed conductive parts or otherextraneous conductive parts, and3) are not electrically connected to themain equipotential bonding bypermanent and reliable metal-to-metal joints of negligibleimpedance.

NOTE - Where local equipotentialbondinn is nrovided in accordance with (vi)above, meialwork which may be requiredto be bonded includes baths and exposedmetal pipes, sinks, taps, tanks and radiatorsand, where practicable, accessible struc-tural metalwork.b) Installations which are part of a TN system:

i) All exposed conductive parts of theinstallation shall be connected by pro-tective conductors to the main earthingterminal of the installation and thatterminal shall be connected to theearthed point of the supply source inaccordance with IS : 3043-1987*.

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IS:732-1989ii) The protective devices shall be of oneor more of the following type:

1) Overcurrent protective devices, and2) Residual current devices.

Provided that where the neutraland the protective functions are combi-ned in one conductor (PEN conductor)a residual current device shall not beused.

c) Installations which are part of a TT system:i) Where protection is afforded by over-current protective devices or residualcurrent devices, exposed conductiveparts shall be connected by protectiveconductors individually, in groups orcollectively to an earth electrode orelectrodes.

ii) The protective dt.4ces shall be of oneor more of the following types:1) Residual current devices, and2) Overcurrent protective devices.

d) Installations which are part of an ITsystem:i) No live conductor of the installationshall be directly connected to earth.

ii)

iii)iv)

v)

NOTE -To reduce overvoltage or to dampvoltage oscillations, it may be necessary to pro-vide earthing through impedances or artificialneutral points and the characteristics of theseshould be appropriate to the requirements ofthe installation.Exposed conductive parts shall beearthed either individually, in groups orcollectively. Simultaneously accessibleexposed conductive parts and associatedextraneous conductive parts shall beconnected only to an earth electrodecommon to those parts.The protective devices shall be residualcurrent devices.An insulation monitoring device shallbe provided to indicate the occurrenceof first fault from a live part to exposedconductive parts or to earth. The deviceshall automatically disconnect thesupply, or initiate an audible and/orvisual signal.

NOTE First fault should be eliminated asquickly aa practicable.After the occurrence of first fault, condi-tions for disconnection of supply, asspecified for TN and TT systems, shallapply*

Application of protective measure - Automa-tic disconnection of supplya) This measure is gensrally appli cable, and isint ended t o prevent t he occurr ence of vol t age of

b)

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d)

such magnit ude and durat ion betw een simul t ane-ously accessi ble conduct iv e part s tha t danger couldarise. Il includesall methods invol vi ng the earth-ing of exposed conductiv e parts. The li mit ingval ues of eart h faul t loop im pedance speciJiedi n 5.1.3.1 (a)(iv) shall be appli ed. w here t hecondit ions are such that conventi onall y normalbody resist ance appl ies. I n condit ion s w herereduced or v ery low body resist ance i s to beexpected, eit her t he eart h faul t loop im pedanceval ues shall be appropr iat ely reduced or anot herprot ecti ve measure shall be used.

NOTE -Conventionally normal body resistancerelates to a contact involvine cjne band and bothfeet, the skin being dry or Goist with perspiration( but not wet ). Reduced body resistance may beexpected in situations where tile hands and/or. feetare likely to be w&or where the shock currentpath may not.& through the extremities. and verylow body resistance (of the order of one quarter ofthe conventionally normal body resistance ) is tobe expected m locations where a person is immer-sed in a water or working in confined conductivelocations.The li mit ing v alues of eart h ault loop mpedancespe@ed in 5.1.3.lj a)(iv ) are aqpl icabl e onlyw here t he exposed conduct iv e parts af t he equip-ment concerned and any extraneous conductiveparts are situat ed wi thi n t he cane created by t hemai n equip ot ent ia l bondi ng [ see 5.1.3.1 (a) (i)].

Where a circpit ori ginati ng in that zone isspeciji cally int ended to supply equipment t o beused outsid e he zone, and t hat equi pment may betouched by a person i n contact dir ectly w it h thdgeneral mass of eart h, th e oll ow ing requirement sapply:i) For solidl y grounded system it shall be suji-

cient t o check w heth er de provi sions of5.1.3.1 are compli ed w it h in general ;

ii) It shall be veriJed w het her the mai n ov er-current prot ecti on drvi ce afords t he degree ofprot ecti on envi saged by 5.1.3.1 (a) (iv);

iii)

iv)

Where t he overcurrent prot ecti ve devi ce did notaford t he degree of protecti on i n 5.1.3.1(a)(iv) and w here the eart hi ng i s inadequate, aseparat e residual current devi ce shall be *i ns-tal led, afordind a prot ection in complianceGt h 5.1.3.l(a)(iv); andThe aut omat ic di sconnect in g devi ce shall beso instal led hat proper di scri minat ion betw eenthe circuit s being prot ected is avail able.

Where t he measure i s used i n a househsl d orsimi lar instal lat ion orming part of a TT systemor w here the eart hi ng i s not effecti ve, every socketoutl et circuit shall be prot ected by a residualcurrent devi ce havi ng a rat ed resid ual operati ngcurrent not exceedi ng 30 mA .Automatic disconnection using residual currentdevi ces shall not be appli ed to circuit s it lcorpordt -in g a PENoenductor. The measure i s ot herw isegenerally applicable, provided that the deviee isselected t o have a resid ual operati ng current

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ISr732-1989ensuring compliance with 5.1.3.1 (a)(ii) and(v). The use of s&h devices is preferred wherethe value of earth fault loop impedance preventsthe use of overeurrent devices to obtain compli-ance with the disconnection times specifiedin 5.1.3.l(a)(iii).

NOTE - If a residual current device affordingprotection against indirect contact has a ratedresidual current equal to or less than 30 mA andan operating time of 40 msor less at a residualcurrent of 250 mA, it may also be used to reducethe risk associated with direct contact in case offailure of other protective measures. Such a devicecannot be used as a sole means of protectionagainst direct contact and does not obviate theneed to apply one of the protective measure speci-fied in 5.1.2.0.e) Automatic disconnection using fault voltage opera-tedprotective devices is recogniscdfor use in TTand IT systems and is suitabte where the impe-dance of the earth fault loop prevents compliance

with 5.1.2.2(b) and (c) by theuse of overcurrentprotective devices.

The insulating enclosure shall be capableof resisting the mechanical, electrical andthermal stresses to which it is likely to besubjected.NOTE - Coatings of paint, varnish and similarproducts are generally considered not to complywith (d).

e) If the insulating enclosure has not previ-ously been tested, a suitable test shall becarried out ( see Section 5 ).f)

5.1.3.2 Protection by use of Class II equipmentor by equivalent insulationa) Protection shall be provided by one ormore of the following:

The insulating enclosure shall not bepierced by conductive parts, other thancircuit conductors, likely to transmit apotential. The insulating enclosure shall notcontain any screws of insulating material,the replacement of which by metallicscrews could impair the insulation providedby the enclosure.i) Electrical equipment of the followingtypes, type tested and marked to therelevant standards:

1) Electrical equipment having &oubleor reinforced insulatiofi ( Class IIequipment ).

NOTE-Where the insulating enclorure must bepierced by mechanical oints or connections ( forexample, for operating h andlea of bui:t-in equip-ment, and for fixing screws ) these should bearranged in such a way that protection againstindirect contact is not impaired.2) Factory built assemblies of electricalequipment having total insulation.

ii) Supplementary insulation applied toelectrical equipment having basic insu-lation only, as a process in the erectionof an electrical installation, providing adegree of safety equivalent to that ofelectrical equipment accor$ing to (i) (1.);:;J; and compiymg with (b) to (J).

f3)Where lids or doors in the insulating enclo-sure can be opened without the use of atool or key, all conductive parts which areaccessible if the lid or door is open shall bebehind an insulating barrier which preventpersons from coming into contact with thoseparts; this insulating barrier shall provide adegree of protection of at least XP 2X andbe removable only by use of a tool.h)

iii) Reinforced insulation applied to uninsu-lated live parts, as a process in the erec-tion of an electrical installation,providing a degree of safety equivalentto electrical equipment according to(i)(l) above and complying with (b) to(j), such insulation being recognizedonly where constructional featuresprevent the application of double insu-lation.

Conductive parts enclosed in the insulatingenclosure shall not be connected to a pro-tective conductor. However, provision maybe made fur connecting protective conduc-tors which necessarily run through theenclosure in order to serve other items ofelectrical equipment whose supply circuitalso runs through the enclosure. Inside thatenclosure, any such conductors and theirterminals or joints shall be insulated asthough they were live parts and their ter-minals shall be appropriately marked.b) The installation of equipment described initem (a) (i) above ( for example the fixingand connection of conductors ) shall beeffected in such a way as not to impair the

j) The enclosure provided for this measureshall not adversely affect the operation ofthe equipment protected.Application of protective measure - Class II. _protection afforded in compliance with theequipment specification, Class 11 equipment equipment or equivalent insulitionshall be so installed that basic insulation is a) This measure is intended to prevent !he appearancenet the only protection between live parts of a dangerous voltage on the exposed metalwork

4

4

of the installation and exposed metalworkof that equipment.The electrical equipment being ready foroperation, all conductive parts separatedfrom live parts by basic insulation onlyshall be contained in an insulatingenclosures affording at least the degree ofprotection IP 2X.

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b)

4

IS ; 732 - 1989of elect ri cal equipment through a ault in t he basicinsulat ion. It is general ly appli cable to it ems ofequipment, ei t her by t he sel ecti on of equipmentcomplyi ng wi th an appropriat e Indian Standardw here that standard provi des for the use ofClass N constr ucti on or total nsulati on, or by t heapplication of suitable supplementary insulationduri ng erecti on.Where a circuit supplies it ems of Class I I equip-ment, a means of connection to the prot ecti veconductor of the circuit shall nevertheless be provi -ded at every point or the supply of current-u singequi pment l ik ely t o be changed by t he user, andat terminat ions or accessories similarly likely tobe changed by t he user. Thi s requi rement neednot be observ ed where (c) below appl ies.

NOTE Exposed metalwork of Class II equip-ment should preferably be mounted so that it isnot in electrical contact with any part of the ins-tallation connected to a protective conductor. Sucha contact may impair the Class II protectionprovided by the equipment specification.Where t hi s measure is to be used as a sole meansof prot ection against indi rect contact ( that s,w here a whole i nstal lat ion or circuit i s intendedto consist enti rely of Class I I equipment or theequiv alent ), i t shall be verifi ed hat t he install a-ti on or circuit concerned w il l be under ejecti vesupervision in normal use so that no. change ismade that would impair the efl ectiveness of theClass I f or equivalent i nsulation. The measureshal l not therefore be so appli ed to any crr cui twhich includes socket outl ets or where a user maychange items of equipment without authori sation.Cables having a non-metalli c sheath OY a non-metalli c enclosure shal l not be descri bed as beingof Class N constiti .on. However , the use of suchcables install ed in accordance with relevantstandard is considered to aford satisfactory pro-tection against dir ect and indi rect contact.

5.1.3.3 Prot ecti on by non-conducti ng locati on4

b)

4

Exposed conductive parts shall be arrangedso that under ordinary circumstances aperson will not come into simultaneouscontact with:i) two exposed conductive parts, or

ii) an exposed conductive part and anyextraneous conductive part,if these parts a

is 0732 (electrical wiring & installation)

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