7/28/2019 is.10118.2.1982

1/63

Disclosure to Promote the Right To Information

Whereas the Parliament of India has set out to provide a practical regime of right to

information for citizens to secure access to information under the control of public authorities,in order to promote transparency and accountability in the working of every public authority,

and whereas the attached publication of the Bureau of Indian Standards is of particular interest

to the public, particularly disadvantaged communities and those engaged in the pursuit of

education and knowledge, the attached public safety standard is made available to promote the

timely dissemination of this information in an accurate manner to the public.

! $ ' +-Satyanarayan Gangaram Pitroda

Invent a New India Using Knowledge

01 ' 5 Jawaharlal Nehru

Step Out From the Old to the New

1+, 1+Mazdoor Kisan Shakti Sangathan

The Right to Information, The Right to Live

! > 0 B BharthariNtiatakam

Knowledge is such a treasure which cannot be stolen

IS 10118 (Part 2) (1982, Reaffirmed 2006): Code of Practicefor Selection, Installation and Maintenance of Switchgearand Controlgear, Part 2: Selection. UDC 621.316.3/.7.004 :006.76

7/28/2019 is.10118.2.1982

2/63

7/28/2019 is.10118.2.1982

3/63

IS : 10118 ( Part 11)'982Indian Standard

CODE OF PRACTICE FORTHE SELECTION, INSTALLATION ANDMAINTENANCE OF SWITCHGEAR AND

CONTROLGEARPART II SELECTION

(Third Reprint JUNE 1992)

UDC 621"316'3/'7"004:006'76

Copyright 1982BUREAU OF INDIAN STANDARDSMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

IS : 10118 ( Part 11)'982Indian Standard

CODE OF PRACTICE FORTHE SELECTION, INSTALLATION ANDMAINTENANCE OF SWITCHGEAR AND

CONTROLGEARPART II SELECTION

(Third Reprint JUNE 1992)

UDC 621"316'3/'7"004:006'76

Copyright 1982BUREAU OF INDIAN STANDARDSMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

7/28/2019 is.10118.2.1982

4/63

IS : 10118 ( Par t n ) 1982

Indian StandardCODE OF PRACTICE FOR

THE SELECTION, INSTALLATION ANDMAINTENANCE OF SWITCHGEAR ANDCON'fROLGEARPART II SELECTION

Code of Practice for Power Installation and Maintenance Sectional" . Committee, ETDC 20

ChairmanSRRI K. K. BOSE

Members

RepresentingCalcutta Electric Supply C o r p o r a t i ~ m . Ltd,Calcutta

SHRI A. CHATTERJEE (Alternate toShri K. K. Bose)SHRI B. C. ALVA Karnataka Electricity Board, BangaloreSHRI T. N. R. RAO (Altmlate)SERI M. J. ANANDAMUHTliYELECTRIOAL INS P E 0 TOR(TECHNIOAL) TO THE

GOVERN:r.IENT Oll' TAMILNADU (Alternatl)SERIP.D.BAGADESHIll R. C. BAJPAL (Alternate)SHRI V. S. BHATIA

SHRI K. K. PANT (Alternate)SERI K. V. CEAUBAL.

Chief Electrical Inspector to the Government ofTamil Nadu, Madras

Tata Consulting Engineers, BombaySiemens India Ltd, BombayTh.e Federation of Electi:icity Undertakings ofIndia, Bombay

SHRI K. S. JOSHI ( Alternafe)CBlEF ELECTFICAL ENGINEER Railway Board, Ministry of RailwaysDEPu1'Y DIRECTOR S 1 ' A ~ D A R D S(ELEC)-lV, RDSe (Alternate)CHIEF ENGINEER (ELEC)-! Central Public Works Department, New DelhiSURVEYOR Oll' WORKS (ELEC)-I( Alternate)

( Continued on pag' 2 ):;l Copyright 1982

BUREAU OF INDIAN STANDARDSThilo publication is protected under the Indian Copyright Act (XIV of 1957) and

r ~ p r o d u c t i o n in whole or in part by any means except with written pp.rmis,ion of the. publisher shall be dt't'mf'd to be an infringemE'nt of copyright und"r tht" said Act.

IS : 10118 ( Par t n ) 1982

Indian StandardCODE OF PRACTICE FOR

THE SELECTION, INSTALLATION ANDMAINTENANCE OF SWITCHGEAR ANDCON'fROLGEARPART II SELECTION

Code of Practice for Power Installation and Maintenance Sectional" . Committee, ETDC 20

ChairmanSRRI K. K. BOSE

Members

RepresentingCalcutta Electric Supply C o r p o r a t i ~ m . Ltd,Calcutta

SHRI A. CHATTERJEE (Alternate toShri K. K. Bose)SHRI B. C. ALVA Karnataka Electricity Board, BangaloreSHRI T. N. R. RAO (Altmlate)SERI M. J. ANANDAMUHTliYELECTRIOAL INS P E 0 TOR(TECHNIOAL) TO THE

GOVERN:r.IENT Oll' TAMILNADU (Alternatl)SERIP.D.BAGADESHIll R. C. BAJPAL (Alternate)SHRI V. S. BHATIA

SHRI K. K. PANT (Alternate)SERI K. V. CEAUBAL.

Chief Electrical Inspector to the Government ofTamil Nadu, Madras

Tata Consulting Engineers, BombaySiemens India Ltd, BombayThe Federation of Electi:icity Undertakings ofIndia, Bombay

SHRI K. S. JOSHI ( Alternafe)CBlEF ELECTFICAL ENGINEER Railway Board, Ministry of RailwaysDEPu1'Y DIRECTOR S 1 ' A ~ D A R D S(ELEC)-lV, RDSe (Alternate)CHIEF ENGINEER (ELEC)-! Central Public Works Department, New DelhiSURVEYOR Oll' WORKS (ELEC)-I( Alternate)

( Continued on pag' 2 ):;l Copyright 1982

BUREAU OF INDIAN STANDARDSThilo publication is protected under the Indian Copyright Act (XIV of 1957) and

r ~ p r o d u c t i o n in whole or in part by any means except with written pp.rmis.ion of the. publisher shall be dt't'mf'd to be an infringemE'nt of copyright und"r tht" said Act.

7/28/2019 is.10118.2.1982

5/63

IS : 10118 ( Part n ) - 1982M6ITIIJlrs Represmting

SBBIB.L.DESHPANDE Electrical Engineer to the Goyernmem ofMaharashtra, BombaySRltI DEVENDER NATH Larsen & Toubro Ltd, BombaySltRI T. P. R. SARMA (Alternale)SHRI K. V. DHARMADHIKARI Jyoti Ltd, VadodaraSRRI P.J. HASTAK Maharashtra State Electricity Boards, Bombay

MEMBER (HYDRO-ELEOTRIO) Central Electricity Authority. New DelhiDIREOTOR (HED)-I (Alternate)

SBRI D. R. NEELAPPA REDDY NGEF Ltd. BangaloreSHRI S. S. N. MURTHY (Alternate)SlIRI K. P. R. PILLAI Fact Engineering & Design Organization.UdyogamandalSHBI C. R. R. MENON (Alternate)LT-COL B. B. RAJPAL Engineer-in-Chief's Branch. Army Headquarters( Ministry of Defence)SRRI S. K. SHANGARI ( Alternate) .SREI RANES RAY CHOUDHURI Engineering Construction Corporation Limited.BombaySRRI L. E. D. CRUZ ( Alternate)Smn B. M. SAMANT The Bombay Ele.ctric Supply & TransportUndertaking, BombaySREI S. R. UGRANXAR ( Alternate)SRRI I . C. SANGER Delhi Electric Supply Undertaking, New DelhiSRRI P. S. SAWHNBY (Alternate)Smu SARDUL SINGR Chief Electrical Inspector to the Government ofPunjab, ChandigarhSBRI D. S. UPPAL ( Altlrnate )SRRI V. SATRYANATRAN. Tamil Nadu Electricity Board, Madras

SRRI S. KRISHNARAJ ( Alternate)SRRl R. SATYABAL Tariff Advisory Committee, General InsuranceSHEI K. K. MAlfDAL ( Alternate) AssociatioD. of India, Bombay

SRRI R. K. SAXENA Rural Electrification Corporation Ltd, New DelhiSRItI G.L. DUA (Alternate)DB. T. C. SXDHANSBBI K. S. SUlIRABMANIYAMSHItI G. P. PAHWA (Alternate)

Chief Electrical Inspector to the Government ofKprala, TrivandrumBharat Heavy Electricals Ltd. SecunderabadS:E!RI'G. N. TJIADANI Engineers India Ltd, New Delhi

SBRX S. G. GORUALE ( Alternate)SBRI S. VAIDYANATHAN Kerala State Electrici ty Boards, TrivandrumSlUU R. VARADARAJAN (Alternate)SBRI S. P. SACHDEV. Director General. lSI (Ex-offjeiD Member)Director (Elec tech)

SecretarySHRX K. G A ~ E S HAssistant Director (Elec tech). lSI

( Continued 01'1 PilI' 60 )2

IS : 10118 ( Part n ) - 1982M6ITIIJlrs Represmting

Electrical Engineer to the Goyernmem ofMaharashtra, BombaySBBIB.L.DESHPANDESRltI DEVENDER NATH Larsen & Toubro Ltd, BombaySltRI T. P. R. SARMA (Alternale)SHRI K. V. DHARMADHIKARI Jyoti Ltd, VadodaraSRRI P.J . HASTAK Maharashtra State Electricity Boards, Bombay

MEMBER (HYDRO-ELEOTRIO) Central Electricity Authority. New DelhiDIREOTOR (HED) -I (Alternate)

SBRI D. R. NEELAPPA REDDY NGEF Ltd. BangaloreSHRI S. S. N. MURTHY (Alternate)SlIRI K. P. R. PILLAI Fact Engineering & Design Organization.UdyogamandalSHBI C. R. R. MENON (Alternate)LT-COL B. B. RAJPAL Engineer-in-Chief's Branch. Army Headquarters( Ministry of Defence)SRRI S. K. SHANGARI ( Alternate) .SREI RANES RAY CHOUDHURI Engineering Construction Corporation Limited.BombaySRRI L. E. D. CRUZ ( Alternate)Smn B. M. SAMANT The Bombay Ele.ctric Supply & TransportUndertaking, BombaySREI S. R. UGRANXAR ( Alternate)SRRI I . C. SANGER Delhi Electric Supply Undertaking, New DelhiSRRI P. S. SAWHNBY (Alternate)Smu SARDUL SINGR Chief Electrical Inspector to the Government of

SBRI D. S. UPPAL ( Altlrnate ) Punjab, ChandigarhSRRI V. SATRYANATRAN. Tamil Nadu Electricity Board, MadrasSRRI S. KRISHNARAJ ( Alternate)SRRl R. SATYABAL Tariff Advisory Committee, General InsuranceSHEI K. K. MAlfDAL ( Alternate) AssociatioD. of India, BombaySRRI R. K. SAXENA Rural Electrification Corporation Ltd, New DelhiSRItI G.L. DUA (Alternate)

DB. T. C. SXOHANSBBI K. S. SUlIRABMANIYAMSHItI G. P. PAHWA (Alternate)

Chief Electrical Inspector to the Government ofKprala, TrivandrumBharat Heavy Electricals Ltd. SecunderabadS:E!RI'G. N. TJIADANI Engineers India Ltd, New Delhi

SBRX S. G. GO:S:BALE ( Alternate)SBRI S. VAIDYANATHAN Kerala State Electricity Boards, TrivandrumSlUU R. VARADARAJAN (Alternate)SBRI S. P. SACHDEV. Director General. lSI (Ex-offjeiD Member)Director (Elec tech)

SecretarySHRX K. G I \ . ~ E S HAssistant Director (Elec tech). lSI

( Continued 01'1PilI' 60 )2

7/28/2019 is.10118.2.1982

6/63

IS : 10118 ( Par t n ) 1982Indian Standard

CODE OF PRACTICE FORTHE SELECTION, INSTALLATION ANDMAINTENANCE OF SWItCHGEAR ANDCONTROLGEAR

PART II SELECTION

o. FOR E WO R D0.1 This Indian Standard (Part I I) was adopted by the IndianStandards Institution on 3 March 1982, after the draft finalized by theCode of Practice for Power Installation and Maintenance SectionalCommittee had been approved by the Electrotechnical Division Council.

The object of this standard ( Part II) is to provide guidelines for theselection of switchgear and controlgear and the associated auxiliaryequipment.0.3 It has been generally felt that the requirements of the switchgear vfdifferent voltage ratings can be conveniently covered in a single standard.Keeping this in view, the Indian Standard IS: 3072-1975* was broughtout to cover equipments for indoor and outdbor use. Equipment socovered included circuit-breakers, isolators and other switches operatingon ac or dc. Separate Indian Standards had been formulated asfollows, for detailed codes of practices for fuses, ac induction motorstarters, high voltage ac circuit-breakers and other switches:

IS : 3106-1966 Code of practice for selection, installation andmaintenance of fuses ( voltage not exceeding 650 volts)

IS : 3914--1967 Code of practice for selection of ac induction motorstarters ( voltage not exceeding I 000 volts) .IS : 5124-1969 Code of practice for installation and maintenance ofac induction motor starters ( voltage not exceeding I 000 V )

IS: 5987-1970 Code of practice for selection of switches (voltagenot exceeding 1 000 V ) .IS: 7987-1976 Guide for selection of high voltage ac circuit-breakers

Code of practice fol!' installation and mainte!laDCe of :switchgear (first revision).3

IS : 10118 ( Par t n ) 1982Indian Standard

CODE OF PRACTICE FORTHE SELECTION, INSTALLATION ANDMAINTENANCE OF SWItCHGEAR ANDCONTROLGEAR

PART II SELECTION

o. FOR E WO R D0.1 This Indian Standard (Part II) was adopted by the IndianStandards Institution on 3 March 1982, after the draft finalized by theCode of Practice for Power Installation and Maintenance SectionalCommittee had been approved by the Electrotechnical Division Council.

O ~ 2 The object of this standard ( Part II) is to provide guidelines for theselection of switchgear and controlgear and the associated auxiliaryequipment.0.3 It has been generally felt that the requirements of the switchgear vfdifferent voltage ratings can be conveniently covered in a single standard.Keeping this in view, the Indian Standard IS: 3072-1975* was broughtout to cover equipments for indoor and outdbor use. Equipment socovered included circuit-breakers, isolators and other switches operatingon ac or dc. Separate Indian Standards had been formulated asfollows, for detailed codes of practices for fuses, ac induction motorstarters, high voltage ac circuit-breakers and other switches:

IS : 3106-1966 Code of practice for selection, installation andmaintenance of fuses ( voltage not exceeding 650 volts)

IS: 39J4.-1967 Code of practice for selection of ac induction motorstarters ( voltage not exceeding I 000 volts) .IS: 5124-1969 Code of practice for installation and maintenance ofac induction motor starters ( voltage not exceeding I 000 V )

IS : 5987-1970 Code of practice for selection of switches (voltagenot exceeding 1 000 V ) .IS: 7987-1976 Guide for selection of high voltage ac circuit-breakers

Code of practice fol!' installation and mainte!laDCe of :switchgear (first revision).3

7/28/2019 is.10118.2.1982

7/63

IS : 10118 ( Par t II) - 19820.4 This standard is being brought out with a view to presenting in acogent fashion, the codes of practice for the various types of switchgearand control gear used in electric power system, filling up the gapsbetween these specifications, utilizing the latest in concepts introduced inthe product specifications.0.5 This standard presents the subject product-wise, bringing out therelevant good practices recommended for L T and HT applicationsseparately. This standard 'is being brought out in four parts, namely:

Part I General,Part II Selection,Part III Installation, andPart IV Maintenance.All these parts shall be read in conjunction with each other.

0.6 In the preparation of this standard, considerable assistance has beenderived from the information contained in the Indian Standards listedin 0.3. On publication of this standard (Parts I to IV), the IndianStandards in 0.3 would stand withdrawn.0.7 During the preparation of various parts of this standard, the expertPanel, responsible for the sarne, had kept in view the fact that thestandard could at best give guidance on the bulk of the equipment usedin the country and should be understood in the ma.nner; that aspectsrelating to selection, installation or maintenance of EHV equipment aswell as thuse intended for very special application would have to besupplemented with additional data, not attempted by the present series.0.8 For the purpose of deciding whether a particular requirement of thisstandard is complied with, the final value, observed or calculated,expressing the result of a test, shall be rounded off in accordance with IS:2-1960*. The number of significant places retained in the rounded offvalue should be the same as that of the specified value in this standard.

1. SCOPE1.1 This standard (Par t I I ) covers guidelines for selection of all types ofswitchgear and controlgear for indoor and outdoor use,1.2 The requirements provided here shall be read in conjunction withthose in Part I of this standard.

-Rules for rounding off numerical values ( revised).4

IS : 10118 ( Par t II) - 19820.4 This standard is being brought out with a view to presenting in acogent fashion, the codes of practice for the various types of switchgearand control gear used in electric power system, filling up the gapsbetween these specifications, utilizing the latest in concepts introduced inthe product specifications.0.5 This standard presents the subject product-wise, bringing out therelevant good practices recommended for L T and HT applicationsseparately. This standard 'is being brought out in four parts, namely:

Part I General,Part II Selection,Part III Installation, andPart IV Maintenance.All these parts shall be read in conjunction with each other.

0.6 In the preparation of this standard, considerable assistance has beenderived from the information contained in the Indian Standards listedin 0.3. On publication of this standard (Parts I to IV), the IndianStandards in 0.3 would stand withdrawn.0.7 During the preparation of various parts of this standard, the expertPanel, responsible for the sarne, had kept in view the fact that thestandard could at best give guidance on the bulk of the equipment usedin the country and should be understood in the ma.nner; that aspectsrelating to selection, installation or maintenance of EHV equipment aswell as thuse intended for very special application would have to besupplemented with additional data, not attempted by the present series.0.8 For the purpose of deciding whether a particular requirement of thisstandard is complied with, the final value, observed or calculated,expressing the result of a test, shall be rounded off in accordance with IS:2-1960*. The number of significant places retained in the rounded offvalue should be the same as that of the specified value in this standard.

1. SCOPE1.1 This standard (Par t I I ) covers guidelines for selection of all types ofswitchgear and controlgear for indoor and outdoor use,1.2 The requirements provided here shall be read in conjunction withthose in Part I of this standard.

-Rules for rounding off numerical values ( revised).4

7/28/2019 is.10118.2.1982

8/63

IS a 10118 ( Par t II) - 1982SECTION 1 GENERAL

2. GENERAL CRITERIA FOR SELECTION2.0 The information collected on the nature of the installation and theavailability of equipment combined with the characteristics of the same asconforming to the relevant Indian Standard shall guide optimum choice.2.1 The selection of equipment shall be based on criteria, such as thefunction of the equipment, type of the equipment, enclosures, dimensions,rating and operational characteristics, type of duty envisaged and otherrelevant considerations as listed in this standard.

N O T E - For -the purposes of this standard, the term 'equipment' is used todenote any type of switchgear or controlgear.2.2 The service conditions for which an equipment is suitable are definedin the respective product'standards. These normlllly include ambienttemperature conditions and the reference ambient temperature, altitude,atmospheric pressure, humidity, degree of toler a ble pollution and suchother conditions under which the design of the equipment is expected toguarantee the declared performance.

The actual service conditions at the location of installation of theequipment shall be studied to assess any correction factors to be employed .This should be of consideration while selecting the equipment. Guidanceon the same shall be obtained from the relevant Indian Standards orfrom manufacturer's instructions.SECTION 2 SPECIFIC GUIDELINES FOR LOW

VOLTAGE EQUIPMENT3, SPECIFIC GUIDELINES FOR SELECTION OF EQUIPMENTFOR VOLTAGES UP TO AND INCLUDING 1 000 V ae or 1200

Vde3.1 Fuses

3.1.1 Function - A fuse in an electric circuit stands guard at all timesto protect the circuit and the equipment connected to it from damagewithin the limits of its rating,3.1.2 Classifiration - Fuses for low voltage application' can be classifiedaccording to the:

a) type of contacts of the fuse-link,b) principle of replacement of the fuse-link,c) principle of operation, andd) degree of protection against contacts and influences.

5

IS a 10118 ( Par t I I) - 1982SECTION 1 GENERAL

2. GENERAL CRITERIA FOR SELECTION2.0 The information collected on the nature of the installation and theavailability of equipment combined with the characteristics of the same asconforming to the relevant Indian Standard shall guide optimum choice.2.1 The selection of equipment shall be based on criteria, such as thefunction of the equipment, type of the equipment, enclosures, dimensions,rating and operational characteristics, type of duty envisaged and otherrelevant considerations as listed in this standard.

N O T E - For -the purposes of this standard, the term 'equipment' is used todenote any type of switchgear or controlgear.2.2 The service conditions for which an equipment is suitable are definedin the respective product'standards. These normlllly include ambienttemperature conditions and the reference ambient temperature, altitude,atmospheric pressure, humidity, degree of toler a ble pollution and suchother conditions under which the design of the equipment is expected toguarantee the declared performance.

The actual service conditions at the location of installation of theequipment shall be studied to assess any correction factors to be employed .This should be of consideration while selecting the equipment. Guidanceon the same shall be obtained from the relevant Indian Standards orfrom manufacturer's instructions.SECTION 2 SPECIFIC GUIDELINES FOR LOW

VOLTAGE EQUIPMENT3, SPECIFIC GUIDELINES FOR SELECTION OF EQUIPMENTFOR VOLTAGES UP TO AND INCLUDING 1 000 V ae or 1200

Vde3.1 Fuses

3.1.1 Function - A fuse in an electric circuit stands guard at all timesto protect the circuit and the equipment connected to it from damagewithin the limits of its rating,3.1.2 Classifiration - Fuses for low voltage application' can be classifiedaccording to the:

a) type of contacts of the fuse-link,b) principle of replacement of the fuse-link,c) principle of operation, andd) degree of protection against contacts and influences.

5

7/28/2019 is.10118.2.1982

9/63

IS : 10118 ( Part I I ) Ao 1982The broadly accepted classification is therefore:a) Rewirable type(see IS : 2086-1963*)

( reversible type,-< non-reversible type, andLsliding typeb) Cartridge type r D-type(see IS: 8l87-1976t)I {With knife-blade contacts,i for bolted connection, and, with cylindrical capsI Link-type { { gl } d[ see IS : 9224 General purpose gIl ,anl (Part I )-1979tJ Back-up fuse links ( aM)NOTE 1-The fuses should be used in each live conductor of the distributionsystem. They should not be used in the neutral conductor or a conductor which' isalways "arthed while the system live. The various points to be consiCiered for theselection of the appropriate type and rating of the fuse are explained further.NO'rE 2- If protective devices are discriminative, then the fault is localized andonly the faulty portion is disconnected. The rewirable fuses do not offer reliablediscrimination. The fuse-element of the rewirable fuse is exposed to atmosphere; itoxidizes with the time and, therefore, it results in premature operation of the fuse.Further its characteristics are easily affectpd by the fluctuation in the ambienttemperature or by the improper handling during installation., Due to the ageingeffects, the rewirable f u s , ~ s cannot be calibrated accurately. dartridge fuses, bothD-type and link-type, on the other hand, have definite characteristics.

3.1.3 Rating and Operational Characteristics3.1.3.0 The selection of fuses, for voltages below 1 000 V, shall be inrespect of the parameters listed below:

a) Rated voltage;b) Rated current and rated frequency, if applicable;c) Breaking capacity;

'd) Cut-off h a r a c t e r i ~ t i c s ; ande) Time-current charatteristics., NOTE - Type oj Supply - The f u s e ~ are designed for ac Or dc application or forboth. It is not necessary that the fuses d e s i g n ~ d for ac should also be suitable forUse on dc systems or vice versa.

" 'Specification for carriers and bases used in rewirable type electric fUlea up to 650, volts ( revISed).t;;pecification for D-type fuses.~ S p e c i f i c a t l o n for low voltage fuses: Part I General requirements.

6

IS : 10118 ( Part I I ) Ao 1982The broadly accepted classification is therefore:a) Rewirable type(see IS : 2086-1963*)

( reversible type,-< non-reversible type, andLsliding typeb) Cartridge type r D-type(see IS: 8l87-1976t)I {With knife-blade contacts,i for bolted connection, and, with cylindrical capsI Link-type { { gl } d[ see IS : 9224 General purpose gIl ,anl (Part I )-1979tJ Back-up fuse links ( aM)NOTE 1-The fuses should be used in each live conductor of the distributionsystem. They should not be used in the neutral conductor or a conductor which' isalways "arthed while the system live. The various points to be consiCiered for theselection of the appropriate type and rating of the fuse are explained further.NO'rE 2- If protective devices are discriminative, then the fault is localized andonly the faulty portion is disconnected. The rewirable fuses do not offer reliablediscrimination. The fuse-element of the rewirable fuse is exposed to atmosphere; itoxidizes with the time and, therefore, it results in premature operation of the fuse.Further its characteristics are easily affectpd by the fluctuation in the ambienttemperature or by the improper handling during installation., Due to the ageingeffects, the rewirable f u s , ~ s cannot be calibrated accurately. dartridge fuses, bothD-type and link-type, on the other hand, have definite characteristics.

3.1.3 Rating and Operational Characteristics3.1.3.0 The selection of fuses, for voltages below 1 000 V, shall be inrespect of the parameters listed below:

a) Rated voltage;b) Rated current and rated frequency, if applicable;c) Breaking capacity;

'd) Cut-off h a r a c t e r i ~ t i c s ; ande) Time-current charatteristics., NOTE - Type oj Supply - The f u s e ~ are designed for ac Or dc application or forboth. It is not necessary that the fuses d e s i g n ~ d for ac should also be suitable forUse on dc systems or vice versa.

" 'Specification for carriers and bases used in rewirable type electric fUlea up to 650, volts ( revISed).t;;pecification for D-type fuses.~ S p e c i f i c a t l o n for low voltage fuses: Part I General requirements.

6

7/28/2019 is.10118.2.1982

10/63

IS : 10118 ( Part II) - 19823.1.3.1 Ratd voltage - T h e rated voltage of the fuse should always beequal to or hi,gher than:

a) the,.voltage of the cir'cuit in single-phase ac or 2-wire dc circuit;anci'b) the line voltage or the voltage between the outer conductors, inthree-phase ac or 3-wire dc circuits.

NOTE I - When two or more phase circuits are in the same enclosure, it shouldbe considered as a three-phase system.NOTE 2 - Fuses rated for a particular voltage can, however, be used on lowervoltage systems but care Ihould be taken to check that the arc vohagc g .nerated bythe fuse during ils operation is not more than the system insulation capability.

Example:When a 415 V fuse is to be used on a 60 V system, theswitching voltage shall not exceed the value corresponding tothe system voltage [see IS: 9224 ( Part 1)-1979* J. This shallbe guaranteed by the manufacturer.

3.1.3.2 Rated current' and rated frequency (for at) - Since thecharacteristics of fuses are related to the rated current, the selection ofappropriate rated current of a fuse for a particular insta.llation will mainlydepend upon the fuse characteristics and the type of load (see 5.2.1 ).Further, manufacturer should be' consulted for any derating factor forinstallation of the fuse unit at higher surround n:.; ai r temperattJre, alsotaking into consideration the type of enclosure and the presence of anyother heat generating source in close vicinity of the fuse.The rewirable fuses are standardized for rated currents up to 100 AIbut the link-type cartridge fuses are standardized for currents as high as1 250 A. The fuse-links (fuse wire in case of rewirable fuses) areavailable in a range of rated currents for flexibility of selection. On theother hand only a few sizes of the fuse-bases and carriers are standardized,each permitting the use of a number of fuse-links of different ratings.Under certain circumstances, such as in cable distribution pillars of

electric supply undertakings, it may be preferable to select the fuse-baseof such a design which permits installation of fllse-links of maximumnumber of ratings for the sake of flexibility. However, adequate careshall be taken to ensure that during replacements, the correct ratings ofthe fuse link be chosen. 'The electrical apparatus and the connecting cables and wires havespecific thermal capacity to withstand overloads and short-circuit

'Specification for low voltage fuses: Part I General requiremenu.

7

IS : 10118 ( Part II) - 19823.1.3.1 Ratd voltage - T h e rated voltage of the fuse should always beequal to or hi,gher than:

a) the,.voltage of the cir'cuit in single-phase ac or 2-wire dc circuit;anci'b) the line voltage or the voltage between the outer conductors, inthree-phase ac or 3-wire dc circuits.

NOTE I - When two or more phase circuits are in the same enclosure, it shouldbe considered as a three-phase system.NOTE 2 - Fuses rated for a particular voltage can, however, be used on lowervoltage systems but care Ihould be taken to check that the arc vohagc g .nerated bythe fuse during ils operation is not more than the system insulation capability.

Example:When a 415 V fuse is to be used on a 60 V system, theswitching voltage shall not exceed the value corresponding tothe system voltage [see IS: 9224 ( Part 1)-1979* J. This shallbe guaranteed by the manufacturer.

3.1.3.2 Rated current' and rated frequency (for at) - Since thecharacteristics of fuses are related to the rated current, the selection ofappropriate rated current of a fuse for a particular insta.llation will mainlydepend upon the fuse characteristics and the type of load (see 5.2.1 ).Further, manufacturer should be' consulted for any derating factor forinstallation of the fuse unit at higher surround n:.; air temperattJre, alsotaking into consideration the type of enclosure and the presence of anyother heat generating source in close vicinity of the fuse.The rewirable fuses are standardized for rated currents up to 100 AIbut the link-type cartridge fuses are standardized for currents as high as1 250 A. The fuse-links (fuse wire in case of rewirable fuses) areavailable in a range of rated currents for flexibility of selection. On theother hand only a few sizes of the fuse-bases and carriers are standardized,each permitting the use of a number of fuse-links of different ratings.Under certain circumstances, such as in cable distribution pillars of

electric supply undertakings, it may be preferable to select the fuse-baseof such a design which permits installation of fllse-links of maximumnumber of ratings for the sake of flexibility. However, adequate careshall be taken to ensure that during replacements, the correct ratings ofthe fuse link be chosen. 'The electrical apparatus and the connecting cables and wires havespecific thermal capacity to withstand overloads and short-circuit

'Specification for low voltage fuses: Part I General requiremenu.

7

7/28/2019 is.10118.2.1982

11/63

IS t 10118 ( Part U) - 1982currents of certain duration. The fuses used for protection shal l thereforebe so selected that they are rated to operate before the thermal capacitylimit of the electrical apparatus is reached. The manufacturer of theapparatus shall state the maximum rating of the fuse that should not beexceeded.

In the absence of any marking regarding rated frequency on acfuses, it implies that the fuse meets the conditions for frequencies between45 and 62 Hz only.3.1.3.3 Breaking capacity - The fuses used in a particular installationshould have a breaking capacity rating equal to or more than theprospective short-circuit current at the point of installation. Therefore,when calculating the prospective short-circuit current and the breakingcapacity rating of the fuses to be used, it is recommended that due

allowance should be made for potential increase of the prospective shortcircuit current available as a result of the natural growth of the system orinstallation.Rewirable fuses up to 16 A rated current shQuld not be used inlocations where short-circuit level exceeds 2 kA -and those of higherratings should be used in such locations where the short-circuit level is4 kA (see IS : 2 0 8 6 - 1 9 6 3 ~ ) : D-type or link-type cartridge fuses shouldbe used for higher breaking capacities. Cartridge f u s ~ s are nowavailable with breaking capacity exceeding 100 kA.Breaking capacitY of a fuse is expressed in modern times in kiloamperes (rms) and is applicable for a given voltage. IS: 9224(Part II )-1979t specifies for industrial appHcations, a minimumbreaking capacity of 50 kA.

3.1.3.4 Time-current characteristics - For the sake of comparison oftwo fuses, it may be necessary to compare the time-current characteristicsof the fuses ( see 5.2.1). This is a curve giving the virtual time (forexample, pre-arcing time or operating time) as a function of theprospective breaking current under stated conditions of. operation.Together with the cut-off characteristics and the Pt (joule Integral)characteristics, it gives a clear picture of the behaviour of the fuse undera given condition. The standard zones of time-current characteristicsbased on an amhient temperature of 270 and on a maximum ratedvoltage of 500 V acare given in IS : 9224 (Part II )-1979t for ;ink typecartridge fuses Specification for carriers and bases used in rewirable type electric fuses up to650 volts ( revised).tSpecification for low voltage fuses: Part II Supplementary requirements for fuseswith high breaking capacity for industrial applications (superseding IS : 2208 ).

8

IS t 10118 ( Part U) - 1982currents of certain duration. The fuses used for protection shal l thereforebe so selected that they are rated to operate before the thermal capacitylimit of the electrical apparatus is reached. The manufacturer of theapparatus shall state the maximum rating of the fuse that should not beexceeded.

In the absence of any marking regarding rated frequency on acfuses, it implies that the fuse meets the conditions for frequencies between45 and 62 Hz only.3.1.3.3 Breaking capacity - The fuses used in a particular installationshould have a breaking capacity rating equal to or more than theprospective short-circuit current at the point of installation. Therefore,when calculating the prospective short-circuit current and the breakingcapacity rating of the fuses to be used, it is recommended that due

allowance should be made for potential increase of the prospective shortcircuit current available as a result of the natural growth of the system orinstallation.Rewirable fuses up to 16 A rated current shQuld not be used inlocations where short-circuit level exceeds 2 kA -and those of higherratings should be used in such locations where the short-circuit level is4 kA (see IS : 2 0 8 6 - 1 9 6 3 ~ ) : D-type or link-type cartridge fuses shouldbe used for higher breaking capacities. Cartridge f u s ~ s are nowavailable with breaking capacity exceeding 100 kA.Breaking capacitY of a fuse is expressed in modern times in kiloamperes (rms) and is applicable for a given voltage. IS: 9224(Part II )-1979t specifies for industrial appHcations, a minimumbreaking capacity of 50 kA.

3.1.3.4 Time-current characteristics - For the sake of ,::,omparison oftwo fuses, it may be necessary to compare the time-current characteristicsof the fuses ( see 5.2.1). This is a curve giving the virtual time (forexample, pre-arcing time or operating time) as a function of theprospective breaking current under stated conditions of . operation.Together with the cut-off characteristics and the Pt (joule Integral)characteristics, i t gives a clear picture of the behaviour of the fuse undera given condition. The standard zones of time-current characteristicsbased on an amhient temperature of 27C and on a maximum ratedvoltage of 500 V acare given in IS : 9224 (Part II )-1979t for ;ink typecartridge fuses

Specification for carriers and bases used in rewirable type electric fuses up to650 volts ( revised).tSpecification for low voltage fuses: Part II Supplementary requirements for fuseswith high breaking capacity for industrial applications (superseding IS : 2208 ).8

7/28/2019 is.10118.2.1982

12/63

IS : 10118 (Par t II ) - 1982General purpose fuse-links are those capable of breaking underspedfied conditions all currents which cause melting of the fuse-elementup to its rated breaking capacity. The standard time-current zones andthe limits for general purpose f ~ s e - l i n k s of rated currents of 100 A to

1 000 A are identical to gI and gIl.Back-up fuse-links are those capabJe of breaking all currents betweenthe lowest current on its time-current characteristicts and its rated breakingcurrent. These are generally used to provide short-circuit protection.Standard time current zones for back-up fuse-links are given inIS : 9224 ( Part II )-1979*.3.1.3.5 Cut-oJ! characteristics - Cut-off characteristics give the cut-offcurrent as a function of the prospective breaking current under statedconditions of operation .. These represent the highest va lues of currentlikely to be experienced in service. At high prospective short-circuit

currents, the fuses exhibit cut-off properly for pre-arcing times less than5 millisecond and thereby prevent the heavy short-circuit currents toreach their crest value ( see Fig. 1). The rewirable type of fuses do notpossess this property. The cut-off property of the fuses is very helpfulsince it p r o t ~ c t s the connected equipment from the thermal and dynamiceffects of heavy short-circuit currents which would have otherwise beenapplied. The manufacturers should be contacted for the cut-off valuesof fuses of different ratings at various prospective short-circuit currents.Ic

SHORT-CIRCUIT CURRENTWITH DC COMPONENT

t. = Pre-arcing .timet, = Arcing timeFIG. I OSCILLOGRAM SHOWING CUT-OFF

Specification fc.r low voltag" f l l s r ~ : Part TI Sttpplementarv r l ' q l l i r " m ( ' n r ~ for fns"swith high breaking capacity for industrial applications (slIpemdillg IS : 220!l ).

IS : 10118 (Par t II ) - 1982General purpose fuse-links are those capable of breaking underspedfied conditions all currents which cause melting of the fuse-elementup to its rated breaking capacity. The standard time-current zones andthe limits for general purpose f ~ s e - l i n k s of rated currents of 100 A to

1 000 A are identical to gI and gIl.Back-up fuse-links are those capabJe of breaking all currents betweenthe lowest current on its time-current characteristicts and its rated breakingcurrent. These are generally used to provide short-circuit protection.Standard time current zones for back-up fuse-links are given inIS : 9224 ( Part II )-1979*.3.1.3.5 Cut-oJ! characteristics - Cut-off characteristics give the cut-offcurrent as a function of the prospective breaking current under statedconditions of operation .. These represent the highest va lues of currentlikely to be experienced in service. At high prospective short-circuit

currents, the fuses exhibit cut-off properly for pre-arcing times less than5 millisecond and thereby prevent the heavy short-circuit currents toreach their crest value ( see Fig. 1). The rewirable type of fuses do notpossess this property. The cut-off property of the fuses is very helpfulsince it p r o t ~ c t s the connected equipment from the thermal and dynamiceffects of heavy short-circuit currents which would have otherwise beenapplied. The manufacturers should be contacted for the cut-off valuesof fuses of different ratings at various prospective short-circuit currents.Ic

SHORT-CIRCUIT CURRENTWITH DC COMPONENT

t. = Pre-arcing .timet, = Arcing timeFIG. I OSCILLOGRAM SHOWING CUT-OFF

Specification fc.r low voltag" f l l s r ~ : Part TI Sttpplementarv r l ' q l l i r " m ( ' n r ~ for fns"swith high breaking capacity for industrial applications (slIpemdillg IS : 220!l ).

7/28/2019 is.10118.2.1982

13/63

IS : 10118 (Part n ) d 1982Generally, the information is provided in the form of curves asshown in Fig. 2. I t should be noted that the cut-off current is expressedin peak value. On the abscissa, the initial symmetrical prospectivecurrent I in kA ( rms) is plotted in the logarithmic scale and the maximumcurrent peak Ie in kA on the ordinate as an instantaneous value. The

influence of the de component on the crest value in short-circuit paths isseen from the straight lines running at an angle of 45. The maximumvalue of current ( crest value of the first half wave ) is represented bythe straight line belonging to the particular dc component.To determine the peak current ie, the ordinate should be drawnover the value calculated for the initial symmetrical short-circuit current.

I t always intersects the straight line of the de component concerned, andin most cases also that of the fuse,' The value of the ordinate of thispoint of intersection or the smaller value, if there are two points ofintersection, is the maximum peak current ie in kA.In normal low voltage systems, a de component up to approximately50 percent may be expected. Within the range above the 0 percent linein Fig. 2, that is, as soon as a de component is present, current limitationtakes place even with pre-arcing times above 5 millisecond (up to 10millisecond). For dc, no general values can be laid down for thecurrent limitation, since in the event of a short-circuit, the inductance inthe particular system greatly affects the current rise. Similar valuesapply under normal conditions also.An example showing the cut-off property of fuses is given below:Example:Fuse-links of 200 A rated current are to be installed. Initialsymmetrical short-circuit current I = "20 kA (computedrms value) (see Fig. 2 ).dc component - 50 percent ( assumed value)Without fuses: Current peak - 40 kA (the ordinate I = 20 ItAintersects the 50 percent line at point A )With fuses : Limited current peak = 14'5 kA (the ordinate

3.2 Switches

I = +0 kA intersects the characteristic line of the200 A fuse at point B ).

3.2.1 Function - The basic function of a switch is to connect or isolateor select a circuit. The fuses in the composite unit of switches and fuses,additionally serve to protect the equipment connected in the circuitmainly against short-circuit.10

IS : 10118 (Part n ) d 1982Generally, the information is provided in the form of curves asshown in Fig. 2. I t should be noted that the cut-off current is expressedin peak value. On the abscissa, the initial symmetrical prospectivecurrent I in kA ( rms) is plotted in the logarithmic scale and the maximumcurrent peak Ie in kA on the ordinate as an instantaneous value. The

influence of the dc component on the crest value in short-circuit paths isseen from the straight lines running at an angle of 45. The maximumvalue of current ( crest value of the first half wave ) is represented bythe straight line belonging to the particular dc component.To determine the peak current ie, the ordinate should be drawnover the value calculated for the initial symmetrical short-circuit current.

I t always intersects the straight line of the dc component concerned, andin most cases also that of the fuse,' The value of the ordinate of thispoint of intersection or the smaller value, if there are two points ofintersection, is the maximum peak current ie in kA.In normal low voltage systems, a dc component up to approximately50 percent may be expected. Within the range above the 0 percent linein Fig. 2, that is, as soon as a dc component is present, current limitationtakes place even with pre-arcing times above 5 millisecond (up to 10millisecond). For dc, no general values can be laid down for thecurrent limitation, since in the event of a short-circuit, the inductance inthe particular system greatly affects the current rise. Similar valuesapply under normal conditions also.An example showing the cut-off property of fuses is given below:Example:Fuse-links of 200 A rated current are to be installed. Initialsymmetrical short-circuit current I = "20 kA (computedrms value) (see Fig. 2 ).dc component - 50 percent ( assumed value)Without fuses: Current peak - 40 kA (the ordinate I = 20 ItAintersects the 50 percent line at point A )With fuses : Limited current peak = 14'5 kA (the ordinate

3.2 Switches

I = +0 kA intersects the characteristic line of the200 A fuse at point B ).

3.2.1 Function - The basic function of a switch is to connect or isolateor select a circuit. The fuses in the composite unit of switches and fuses,additionally serve to protect the equipment connected in the circuitmainly against short-circuit.10

7/28/2019 is.10118.2.1982

14/63

1006040

~

- -....-: ~/ ./

l' ~ -"~ . ,/ V., --"r-- VV " --~ ,.

/A .,,,:,,"

" I / ~ ~n:.,~ B 1--~ ~ ., -".......I .......f - rII

!

I

IS : 10118 (Par t II) - 198250/. 0'/.L' "/ ~~ - 'r -

l,...-'"

C COMPONENT6430AOOA

200A FUSERATINGV k-" 1OOAVV 63A....- I---"'"

25.A

, 2 4 8 15 20 40 100INITIAL SHORT-CIRCUIT CURRENT I IN kA ( rms)

FIG. 2. CUT-OFF CHARACTERISTIC OF CARTRIDGE FUSES3.2.2 Classificatio1l

3.2.2.1 According to the method of operation of manually operatedequipment, switches are classjfied as having:

a) Dependent manual operation [sile 2.1.5.3 of IS : 4064(Part I )-1978*]b) Independent manual operation [see 2.1.5.5 of IS.: 4064-( Part I )-1978*]

*Sp('cificatioll for air break switches, air-brpak disconnrctors, air-brpak switchd i ~ c o n n r c l O r s and fllse' combination units for voltagl's not exceeding 1 000 V ac ort 200 V de: Part I General requirements (first rtIJi.ion ).J 1

1006040

~

-.....-: ~/ , /

l' ~ --~ / ' V~ i--"r--" V~ ........--- ,.

/A ...... !:""

~ , / I-"~ : ..-[19 .--~ ~ ~n .--~ I

I

!

I

IS : 10118 (Par t II) - 198250/. 0'/. C COMPONENTL' l - '

/ --......... 630AOOA~ 4~V

V ~V 1--"f.-" I---

200A1OOA63A25.A

FUSERATING

, 2 4 8 15 20 40 100INITIAL SHORT-CIRCUIT CURRENT I IN kA ( rms)

FIG. 2. CUT-OFF CHARACTERISTIC OF CARTRIDGE FUSES3.2.2 Classificatio1l

3.2.2.1 According to the method of operation of manually operatedequipment, switches are classjfied as having:

a) Dependent manual operation [sile 2.1.5.3 of IS: 4064(Part I )-1978*]b) Independent manual operation [see 2.1.5.5 of IS.: 4064-( Part I )-1978*]

*Sp('cificatioll for air break switches, air-brpak disconnrctors, air-brpak switchd i ~ c o n n r c l O r s and fllse' combination units for voltagl's not exceeding 1 000 V ac ort 200 V de: Part I General requiremcnts (first rtIJi.ion ).J 1

7/28/2019 is.10118.2.1982

15/63

IS : 10118 (Par t n ) 19823.2.2.2 According to the degree of protection provided by theenclosure, distinction is made in a.ccordance with IS : 2147-19152*.3.2.2.3 The type of equipment can also be characterized by thefollowing:

a) Number of poles,b) Number of positions ( if mOre than two ), andc). Kind of current ( ac or dc) and in the case of ac number ofphases and rated frequency.

3.2.2.4 Switches are also further categorized depending on theseverity of the .duty, they can withstand, namely, the utilisation category,and as detailed in IS : 4064 ( Part I )-1978t.

NI l ' I 'E - Control ~ w i t c h e s , which serve th e purpose of controlling the operationof switchgear or control gear include manual control switches, electromagneticallyop raled colltrol sWitches and pilot switches. '3.2.3 Rating and Operational Characteristics

3.2.3.0 The selection of switches shall be based on the parametersindicated below:

a) Utilisation category,b) Frequency of operation,c) Rated voltages,d) Rated currents,e) Making and breaking capacities, andf) Number of poles.

3.2.3.1 Utilisation categ')ry - The utilisation categories of switches havebeen specified and defined in the following standards:a) Switches [see IS : 4034 (Part I ) - 1978t ],b) Di5connectors and switch dis connectors [ set' IS : 4061- (Part 1 )-1978t], and

*Sp"cilication for degrees of protection provided by enclosures for low-voltageswitchgear and controlgear.tSp"cificalion lor air-break s w i t c h e ~ , air-break disconnectors. air-break switchdis

7/28/2019 is.10118.2.1982

16/63

IS : 10118 ( Part II ) - 1982c) Switches for motor duty [SCI! IS : 40li4 (Part 1I)-1978*].The switches should be selected to suit the duty they are requiredto perform.

3.2.3.2 Frequency if operation - Isolators and switches covered in IS :4064 ( Part I )-1978', are designed fot' normally, operation once in a while.In case of very frequent operation, either motor control switches coveredby IS : 4064 (Part II )-1978* shall be used or the manufacturerconsulted.3.2.3.3 Rated voltage - An equipment is defined by the following:a) Rated operational voltage ( Uc ) , andb) Rated insulation voltage ( U j ).The rated voltage of the switch shall be so selected as to suit therated operational voltage of the system in which it will be used.

3.2.3.4 Rated currents - An equipment is defined by the followingrated currents [see 4.3.2 of IS : 4064 ( Part I )-1978t ]:a) Rated thermal current (Ith ) , andb) Rated .operational current (Ie ).Whjle deciding the rated operationa I current of the switch, both the

making and breaking capacity (see 3.2.3.5) and the temperature-risepermissible shall be borne in mind.3.2.3.5 Making and breaking capacity - With respect to making andbreaking capacities the switches are classified according to the utilizationcategory given in the relevant ISS.Where switches are used for direct control of motors [see 5.1.2.3(a)], the making and breaking capacity should correspond to thosespecified in IS : 4064 (Part II )-1978*. .

3.2.3.6 I t is very essential to keep the making and breaking capacityin mind while selecting the units as has been explained in 5."'Specification for a i r - h r ~ a k switches, air-break disconnectors, air-brE;>ak switchdisconnt'clors and fus!' combination units for voltagrs not c x c e ~ d i n g 1000 V ac or 1200V de: Part II Specific requirements for the direct switching of individual motor$ (firstrevision) .tSpecification for air-brE;>uk switches, ai r break disconnectors, air-break switchdis("onn('crors and fllsC'-combination units for voltages no t exceeding 1000 V ac or1 200.V dc: Part I. General r.equirements (firs, revis/oil).

13

IS : 10118 ( Part II ) - 1982c) Switches for motor duty [SCI! IS : 40li4 (Part 1I)-1978*].The switches should be selected to suit the duty they are requiredto perform.

3.2.3.2 Frequency if operation - Isolators and switches covered in IS :4064 ( Part I )-1978', are designed fot' normally, operation once in a while.In case of very frequent operation, either motor control switches coveredby IS : 4064 (Part II )-1978* shall be used or the manufacturerconsulted.3.2.3.3 Rated voltage - An equipment is defined by the following:a) Rated operational voltage ( Uc ) , andb) Rated insulation voltage ( U j ).The rated voltage of the switch shall be so selected as to suit therated operational voltage of the system in which it will be used.

3.2.3.4 Rated currents - An equipment is defined by the followingrated currents [see 4.3.2 of IS : 4064 ( Part I )-1978t ]:a) Rated thermal current (Ith ) , andb) Rated .operational current (Ie ).Whjle deciding the rated operationa I current of the switch, both the

making and breaking capacity (see 3.2.3.5) and the temperature-risepermissible shall be borne in mind.3.2.3.5 Making and breaking capacity - With respect to making andbreaking capacities the switches are classified according to the utilizationcategory given in the relevant ISS.Where switches are used for direct control of motors [see 5.1.2.3(a)], the making and breaking capacity should correspond to thosespecified in IS : 4064 (Part II )-1978*. .

3.2.3.6 I t is very essential to keep the making and breaking capacityin mind while selecting the units as has been explained in 5."'Specification for a i r - h r ~ a k switches, air-break disconnectors, air-brE;>ak switchdisconnt'clors and fus!' combination units for voltagrs not c x c e ~ d i n g 1000 V ac or 1200V de: Part II Specific requirements for the direct switching of individual motor$ (firstrevision) .tSpecification for air-brE;>uk switches, ai r break disconnectors, air-break switchdis("onn('crors and fllsC'-combination units for voltages no t exceeding 1000 V ac or1 200.V dc: Part I. General r.equirements (firs, revis/oil).

13

7/28/2019 is.10118.2.1982

17/63

IS : 10118 ( Part n ) 19823.2.3.7 Short-circuit rating - It is important to select a switch ofsufficient capacity depending upon the prospective value of the faultcurrt;nt expected at the point of installation, and the factors given below:

a) Short time withstand capacity - The switches should be of sufficientcapacity to withstand the thermal and dynamic effects of shortcircuit current. While deciding the withstand capacity, oneshould take due consideration of the protective device used inseries with the switches for the protection against short circuit,that is, the tripping time of the circuit breakers, the operatingtime of the fuses an4 their cut-off characteristics, if any.

b) Short-current making capacity - For certain application, it may beunavoidable that switches (never disconnector) are closed on an, existing fault. In such cases, it should be ensured that switcheshave sufficient making capacity so that they do not get damagedbefore the fault is cleared by the protective device installed inseries.NOTE - Neither isolators nor switches are intended to break the circuits onshort circuit. No short-circuit breaking capacity is assigned to them.

3.2.4 Combination Units oj Switches and Fuses - See IS : 4064 ( Part I )-1978*3.2.4.1 Arrangement oj switches and fuses - The composite unit ofswitches and fuses may have the fuses either incorporated on the movingmem ber of the switch or installed separately. In the former case, thecomposite units are termed as 'fuse switch' and in the latter case as

'switch-fuse'. These terms are only by way of differentiatiOn althoughthere is no difference in their performance, requirements, tests, etc, aslaid down in the corresponding Indian Standards.It is possible to have different rating for the switch and fuse in acombination unit. However, excepting under special conditions, therating of the fuse should not exceed the rating of the switch.

3.2.4.2 Fuse combination units are characterised by the rated fusedshort-circuit current [ see IS : 4064 ( Part I )-1978* ].3.3 Circuit Breakers -See IS : 2516 (Parts I and II/Sec 1 )-1977t.

3.3.1 Function - The basic function of a circuit-breaker is to protect thecircuit and the equipment connected to it, make carry and break the"'Specification for air-break switches, air-break disconnectors, ai r-break switchdisconnectors and fusc-combination units for voltages not exceeding 1000 Vac or

1. 200 V dc: Part I General requirements (jir$t r4uislon ).tSpecificatioil for alternating current circuit-breakers: Parts I and II Requirementsaud tests, Section 1 Voltages not ~ x c e e d i n g 1000 V ac or 1200 V dc (jirst revision).14

IS : 10118 ( Part n ) 19823.2.3.7 Short-circuit rating - It is important to select a switch ofsufficient capacity depending upon the prospective value of the faultcurrt;nt expected at the point of installation, and the factors given below:

a) Short time withstand capacity - The switches should be of sufficientcapacity to withstand the thermal and dynamic effects of shortcircuit current. While deciding the withstand capacity, oneshould take due consideration of the protective device used inseries with the switches for the protection against short circuit,that is, the tripping time of the circuit breakers, the operatingtime of the fuses an4 their cut-off characteristics, if any.

b) Short-current making capacity - For certain application, it may beunavoidable that switches (never disconnector) are closed on an, existing fault. In such cases, it should be ensured that switcheshave sufficient making capacity so that they do not get damagedbefore the fault is cleared by the protective device installed inseries.NOTE - Neither isolators nor switches are intended to break the circuits onshort circuit. No short-circuit breaking capacity is assigned to them.

3.2.4 Combination Units oj Switches and Fuses - See IS : 4064 ( Part I )-1978*3.2.4.1 Arrangement oj switches and fuses - The composite unit ofswitches and fuses may have the fuses either incorporated on the movingmem ber of the switch or installed separately. In the former case, thecomposite units are termed as 'fuse switch' and in the latter case as

'switch-fuse'. These terms are only by way of differentiatiOn althoughthere is no difference in their performance, requirements, tests, etc, aslaid down in the corresponding Indian Standards.It is possible to have different rating for the switch and fuse in acombination unit. However, excepting under special conditions, therating of the fuse should not exceed the rating of the switch.

3.2.4.2 Fuse combination units are characterised by the rated fusedshort-circuit current [ see IS : 4064 ( Part I )-1978* ].3.3 Circuit Breakers -See IS : 2516 (Parts I and II/Sec 1 )-1977t.

3.3.1 Function - The basic function of a circuit-breaker is to protect thecircuit and the equipment connected to it, make carry and break the"'Specification for air-break switches, air-break disconnectors, air-break switchdisconnectors and fusc-combination units for voltages not exceeding 1000 Vac or

1. 200 V dc: Part I General requirements (jir$t rl!uislon ).tSpecificatioil for alternat ing current circuit-breakers: Parts I and II Requirementsaud tests, Section 1 Voltages not ~ x c e e d i n g 1000 V ac or 1200 V dc (jirst revision).14

7/28/2019 is.10118.2.1982

18/63

IS : 10118 ( Par t II ) 19Mrated current satisfactorily at the rated voltage, as well as at abnormalsystem conditions. It shall also be capable of making on to fault up toits rated making capacity and breaking any short circuit up to its ratedb r ~ a k i n g capacity without any difficulty.

3.3.2 Classification - According to the method of control of the closingoperation, circuit breakers are designated as having:a) dependent manual closing,b) independent manual closing,c) depende.nt power closing, andd) stored energy closing.According to the interrupting medium, they are divided into:a) ~ t i r - b r e a k , andb) oil immersed break.According to the degree of protection provided by the enclosuredistinction is made in accordance with IS : 2147-1962*.The type of equipment is also further characterized by:a) number. of poles,b) kind of current,c) method of closing,d) method of opening, ande) provision for maintenance.NOTE - Circuit breakers are also classified depending on their short-circuitperformance category.

3.3.3 Rating and Operational Characteristics3.3.3.0 The selection of circuit breaker shaH be made based on theparameters given below:

a) Rated voltages,b) Rated currents,c) Rated frequency,d) Rated short-circuit making and breaking capacities,nRated short-time withstand current, andg) S ~ o r t - c i r c u i t performance categories.

Specification. for d ~ g r e e s of protection provided by enc10surel .for low-voltageIwitchgear and controlgear .15

IS : 10118 ( Par t I I) 19Mrated current satisfactorily at the rated voltage, as well as at abnormalsystem conditions. It shall also be capable of making on to fault up toits rated making capacity and breaking any short circuit up to its ratedb r ~ a k i n g capacity without any difficulty.

3.3.2 Classification - According to the method of control of the closingoperation, circuit breakers are designated as having:a) dependent manual closing,b) independent manual closing,c) depende.nt power closing, andd) stored energy closing.According to the interrupting medium, they are divided into:a) ~ t i r - b r e a k , andb) oil immersed break.According to the degree of protection provided by the enclosuredistinction is made in accordance with IS : 2147-1962*.The type of equipment is also further characterized by:a) number. of poles,b) kind of current,c) method of closing,d) method of opening, ande) provision for maintenance.NOTE - Circuit breakers are also classified depending on their short-circuitperformance category.

3.3.3 Rating and Operational Characteristics3.3.3.0 The selection of circuit breaker shaH be made based on theparameters given below:

a) Rated voltages,b) Rated currents,c) Rated frequency,d) Rated short-circuit making and breaking capacities,nRated short-time withstand current, andg) S ~ o r t - c i r c u i t performance categories.

Specification. for d ~ g r e e s of protection provided by enc10surel .for low-voltageIwitchgear and controlgear .15

7/28/2019 is.10118.2.1982

19/63

IS : 10Ils ( Part II) - 1982The characteristics of the circuit breaker also includes:a) control circuits and air supply systems,b) types and characteristics of releases, andc) characteristics of auxiliary switches.

3.3.3.1 Rated volta!{p.s - A circuit breaker is defined by the followingrated voltages [ see 4.3.1 of IS : 2516 ( Parts I and II/Sec 1 )-1977* J:a) Rated operational voltage ( Ue ) , andb) Rated insulation voltage ( Vi ).The rated voltage of the circuit breaker shall be so selected as tosuit the rated operational voltage of the system in which it will be used.

3.3.3.2 Rated currentr - A circuit breaker is defined by the followingrated currents [see 4.3.2 ofIS : 2516 ( Parts I and II/Sec 1 )-1977* J:a) Rated thermal current (Ith), andb) Rated uninterrupted current (Iu ).

3.3.3.3 Rated frequency - The rated frequency of the equipment shallbe so chosen as to suit the service frequency.3.3.3.4 Rated short-circuit m a ~ i n g and breaking capacities - The assignedvalues of short-circuit making and breaking capacities imply that theequipment is capable of making and breaking the current up to andincluding the rated capacity at an applied voltage and recovery voltagerespectively, corresponding to 110 percent of the rated operational volt-age.3.3.3.5 Short-circuit peiformance category - The short-circuit performancecategory of the equipment states the rated operating sequence and thecondition of the circuit-breaker aftet' performing this sequence at the ratedshort-circuit making and breaking capacities. For the same i r c u i t - b r e ~ ~ e r ,the values of the rated short-circuit breaking and corresponding makingcapacities may be different for different short-circuit performancecategories.

"'Specification for alternating current circuit-breakers:. Paris I and II Requirementsand tests, Section 1 o l t a g ~ s not exceeding 1000 V ac or 1200 V dc (first r ~ i J i s i o l t ) .16

IS : 10Ils ( Part II) - 1982The characteristics of the circuit breaker also includes:a) control circuits and air supply systems,b) types and characteristics of releases, andc) characteristics of auxiliary switches.

3.3.3.1 Rated volta!{p.s - A circuit breaker is defined by the followingrated voltages [ see 4.3.1 of IS : 2516 ( Parts I and II/Sec 1 )-1977* J:a) Rated operational voltage ( Ue ) , andb) Rated insulation voltage ( Vi ).The rated voltage of the circuit breaker shall be so selected as tosuit the rated operational voltage of the system in which it will be used.

3.3.3.2 Rated currentr - A circuit breaker is defined by the followingrated currents [see 4.3.2 ofIS : 2516 ( Parts I and II/Sec 1 )-1977* J:a) Rated thermal current (Ith), andb) Rated uninterrupted current (Iu ).

3.3.3.3 Rated frequency - The rated frequency of the equipment shallbe so chosen as to suit the service frequency.3.3.3.4 Rated short-circuit m a ~ i n g and breaking capacities - The assignedvalues of short-circuit making and breaking capacities imply that theequipment is capable of making and breaking the current up to andincluding the rated capacity at an applied voltage and recovery voltagerespectively, corresponding to 110 percent of the rated operational volt-age.3.3.3.5 Short-circuit peiformance category - The short-circuit performancecategory of the equipment states the rated operating sequence and thecondition of the circuit-breaker aftet' performing this sequence at the ratedshort-circuit making and breaking capacities. For the same i r c u i t - b r e ~ ~ e r ,the values of the rated short-circuit breaking and corresponding makingcapacities may be different for different short-circuit performancecategories.

"'Specification for alternating current circuit-breakers: . Paris I and II Requirementsand tests, Section 1 o l t a g ~ s not exceeding 1000 V ac or 1200 V dc (first r ~ i J i s i o l t ) .16

7/28/2019 is.10118.2.1982

20/63

IS : 10118 ( Par t II) - 19823.3.3.6 The following characteristics should also be considered whileselecting the circuit-breaker:

a) For control circuits - Rated control supply voltage andkind of currentb) For air-supply systems - Rated pressure and its limits andvolumes of air at atfllosphericpressure req uired for each closingand each opening operationc) For shunt release and - Rated voitage and kind of currentunder voltage released) For over-current release - Rated thermal current, kind ofcurrent and range of settingse) For auxiliary switches - As in IS: 6875 (Part 1)-1973*.

3.4 Mo tor Starters3.4.1 Function - The motor starter comprises the main switching devicestogether with protective devices and the control and auxiliary devices,such as, push buttons, limit switches and pilot lamps.A motor starter has the following functions to perform:a) Start and stop the motor. This is the fundamental job of everystarter. I t shall be capable of switching the motor ON a,nd OFFthe line repeatedly, safely, quickly and dependably;b) Limit motor inrush current, where necessary. Thi:; may ne

achieved by actual reduction of voltage at m9tor termin,ds;temporary reconnection of t a ~ o r winding; connecting resista:lcein the rotor circuit either temporarily or permanently or byother suitable means;c) Permit automatic control when required;d) Protect motor and other connected equipment; ande) Under voltage protection ( if required ).

3.4.2 Classification3.4.2.1 The following are the main types of motor starters in use:a) Direct-on-line starters (see IS : 8544 (Part I )-1977tJ.

*Sppcificaskn for control switches (switching devices for control and auxiliarvcircuits including contractor r c \ ! ! . ~ s) for voitag's up to and iucluding 1000 V ac and1 200 V de: Part 1" Genrral rpquiremmts and tests.tSpecification for motor starters for voltages nOt exceeding 1000 V: Part I Direct-online ac starters.

17

IS : 10118 ( Par t II) - 19823.3.3.6 The following characteristics should also be considered whileselecting the circuit-breaker:

a) For control circuits - Rated control supply voltage andkind of currentb) For air-supply systems - Rated pressure and its limits andvolumes of air at atfllosphericpressure req uired for each closingand each opening operationc) For shunt release and - Rated voitage and kind of currentunder voltage released) For over-current release - Rated thermal current, kind ofcurrent and range of settingse) For auxiliary switches - As in IS: 6875 (Part 1)-1973*.

3.4 Mo tor Starters3.4.1 Function - The motor starter comprises the main switching devicestogether with protective devices and the control and auxiliary devices,such as, push buttons, limit switches and pilot lamps.A motor starter has the following functions to perform:a) Start and stop the motor. This is the fundamental job of everystarter. I t shall be capable of switching the motor ON a,nd OFFthe line repeatedly, safely, quickly and dependably;b) Limit motor inrush current, where necessary. Thi:; may ne

achieved by actual reduction of voltage at m9tor termin,ds;temporary reconnection of t a ~ o r winding; connecting resista:lcein the rotor circuit either temporarily or permanently or byother suitable means;c) Permit automatic control when required;d) Protect motor and other connected equipment; ande) Under voltage protection ( if required ).

3.4.2 Classification3.4.2.1 The following are the main types of motor starters in use:a) Direct-on-line starters (see IS: 8544 (Part I )-1977tJ.

*Sppcificaskn for control switches (switching devices for control and auxiliarvcircuits including contractor r c \ ! ! . ~ s) for voitag's up to and iucluding 1000 V ac and1 200 V de: Part 1" Genrral rpquiremmts and tests.tSpecification for motor starters for voltages nOt exceeding 1000 V: Part I Direct-online ac starters.

17

7/28/2019 is.10118.2.1982

21/63

IS : 10118 ( Part U) 1982b) Reduced voltage starters ( Star-delta starters [see IS : 8544I (Part II )-1977*]i Auto-transformer starters [ seeL IS : 8544 ( Part IV )-1979t]c) Rheostat ic rotor starterS [see IS : 8544 (Part III/Sec 2 )-1979t]3.4.2.2 These types of starters are further classified as follows:a) According to the method of control:

1) auto,matic ( by pilot switch or sequence control );2) non-automatic ( by hand-operation, push-buttons, etc);

b) According to the method of operation:1) manual;2) electromagnetic;3) motor-operated;4) pneumatic; and5) electro pneumatic.

c) According to the interrupting medium:1) air-break; and2) oilimmersed break.

d) According to the degree of protection provided by enclosures asin IS 2147-1962.

3.4.2.3 Star-delta starters in addition to 3.4.2.2 are further classifieddepending on the method of change-over from star to delta, as follows:a) Automatic changeover Controlled by a timer or byunder current relays,andb) Non-automatic changeover Controlled by hand or by push-buttons.

. "Spedfication for motor starters for voltages not exceeding 1 000, V: Part II Stardelta ~ t a r t e r s ."{Specification for motor starters for voltages not exceeding 1000 V: Part IVReduced voltage ac starters; twostep auto transformer t a r t c r s ~tSpecification for motor starters for voltages not exceeding ! 000 V: Part ,IIIRheostalic rOlor starlers, Section 2 Additional, requirements fOI" ac rheostatic rotorcontrollers.Sp(!r,ilication for degrees of protection provided by enclosures for low-voltageawi,chgear and comrolgear.

18

IS : 10118 ( Part U) 1982b) Reduced voltage starters ( Star-delta starters [see IS : 8544I (Part II )-1977*]i Auto-transformer starters [ seeL IS : 8544 ( Part IV )-1979t]c) Rheostat ic rotor starterS [see IS : 8544 (Part III/Sec 2 )-1979t]3.4.2.2 These types of starters are further classified as follows:a) According to the method of control:

1) auto,matic ( by pilot switch or sequence control );2) non-automatic ( by hand-operation, push-buttons, etc);

b) According to the method of operation:1) manual;2) electromagnetic;3) motor-operated;4) pneumatic; and5) electro pneumatic.

c) According to the interrupting medium:1) air-break; and2) oilimmersed break.

d) According to the degree of protection provided by enclosures asin IS 2147-1962.

3.4.2.3 Star-delta starters in addition to 3.4.2.2 are further classifieddepending on the method of change-over from star to delta, as follows:a) Automatic changeover Controlled by a timer or byunder current relays,andb) Non-automatic changeover Controlled by hand or by push-buttons.

. "Spedfication for motor starters for voltages not exceeding 1 000, V: Part II Stardelta ~ t a r t e r s ."{Specification for motor starters for voltages not exceeding 1000 V: Part IVReduced voltage ac starters; twostep auto transformer t a r t c r s ~tSpecification for motor starters for voltages not exceeding ! 000 V: Part ,IIIRheostalic rOlor starlers, Section 2 Additional, requirements fOI" ac rheostatic rotorcontrollers.Sp(!r,ilication for degrees of protection provided by enclosures for low-voltageawi,chgear and comrolgear.

18

7/28/2019 is.10118.2.1982

22/63

IS : 10118 ( Par t n ) - 19823.4.2.4 Auto-transformer starters in addition to 3.4.2.2 are furtherclassified:

a) According to method of changing from the starting position tothe FULL ON position:1) automatic changeover - Controlled by a timer or byunder current relays2) non-automatic changeover - Controlled by hand or by pushbut ton.

b) According to the method of connecting the auto-transformer:1) open transition starters; and2) closed transition starters.

c) According to the method of cooling the auto-transformer:I) air-cooled by connection, and2) cooled by immersion in oil.

3.4.2.5 Rheostatic rotor starters, in addition to 3.4.2.2 are furtherclassified as follows:a) According to the method of changing starting steps:

1) automaic changeover - Controlled by a timer by anunder current relays2) non-automatic changeover - Controlled by hand by pushabuttons.3) semi-automatic changeover.

b) According to the means of cooling of resistors:I) cooled by connection,2) ('ooled by forced air, and3) 'cooled by immersion in oil.

3.4.2.6 The following feautures of the switching device in the maincircuit shall also be considered while selecting the equipment:

a) number of poles;b) interrupting medium ( air, oil, etc);c) method of operation [for example, dependent manualoperation, dependent power operation ( co.ntactor ), stc, ed enel'gyoperation, etc]; aI.d.d) rated values.

19

IS : 10118 ( Par t n ) - 19823.4.2.4 Auto-transformer starters in addition to 3.4.2.2 are furtherclassified:

a) According to method of changing from the starting position tothe FULL ON position:1) automatic changeover - Controlled by a timer or byunder current relays2) non-automatic changeover - Controlled by hand or by pushbut ton.

b) According to the method of connecting the auto-transformer:1) open transition starters; and2) closed transition starters.

c) According to the method of cooling the auto-transformer:I) air-cooled by connection, and2) cooled by immersion in oil.

3.4.2.5 Rheostatic rotor starters, in addition to 3.4.2.2 are furtherclassified as follows:a) According to the method of changing starting steps:

1) automaic changeover - Controlled by a timer by anunder current relays2) non-automatic changeover - Controlled by hand by pushabuttons.3) semi-automatic changeover.

b) According to the means of cooling of resistors:I) cooled by connection,2) ('ooled by forced air, and3) 'cooled by immersion in oil.

3.4.2.6 The following feautures of the switching device in the maincircuit shall also be considered while selecting the equipment:

a) number of poles;b) interrupting medium ( air, oil, etc);c) method of operation [for example, dependent manualoperation, dependent power operation ( co.ntactor ), stc, ed enel'gyoperation, etc]; aI.d.d) rated values.

19

7/28/2019 is.10118.2.1982

23/63

IS : 10118 ( Par t II ) 19823.4.2.7 The starter may be provided with one or more of thefollowing relays or releases. Some of these types requires consultationbetween the manufacturer and the user while selecting the equipment:

a) Release with shunt coil (shunt trip ),b) Overload time-delay relay (which may be dependent orindependent of previous load),c) Under voltage opening relay or release,d) Instantaneous overcurrent relay or release, ande) Other relays or releases.The types and characteristics of automatic changeover devices forstar-delta type starters would also have a bearing on selection. These

are:a) timers (for example, specified time all-or-nothing relays), andb) under current relays.

3.4.3 Rating and Operari(Jnal Characteristics3.4.3.0 The selection or motor starters shall be based on theparameters given below:

a) Rated voltages,b) Rated currents,c) Rated frequency,d) Inrush current criteria 'and overload settings,e) Making and bearing capacity,f) Utilization category,g) Frequency of operation,h) Number and type of auxiliary contact, andk) Co-ordination with short-circuit protective d('vices ,( see 5.2.4.1 ).

3.4.3.1 Rated voltage and frequencya) A starter may have different rated voltages corresponding tothose of main circuit (rated operational voltage ( U. ;. and ratedinsulation voltage ( Ui)] , control circuit and auxiliary circuit.Further, the making and breaking capacities of the main andauxiliary contacts are stated at different rated voltages.

20

IS : 10118 ( Par t II ) 19823.4.2.7 The starter may be provided with one or more of thefollowing relays or releases. Some of these types requires consultationbetween the manufacturer and the user while selecting the equipment:

a) Release with shunt coil (shunt trip ),b) Overload time-delay relay (which may be dependent orindependent of previous load),c) Under voltage opening relay or release,d) Instantaneous overcurrent relay or release, ande) Other relays or releases.The types and characteristics of automatic changeover devices forstar-delta type starters would also have a bearing on selection. These

are:a) timers (for example, specified time all-or-nothing relays), andb) under current relays.

3.4.3 Rating and Operari(Jnal Characteristics3.4.3.0 The selection or motor starters shall be based on theparameters given below:

a) Rated voltages,b) Rated currents,c) Rated frequency,d) Inrush current criteria 'and overload settings,e) Making and bearing capacity,f) Utilization category,g) Frequency of operation,h) Number and type of auxiliary contact, andk) Co-ordination with short-circuit protective d('vices ,( see 5.2.4.1 ).

3.4.3.1 Rated voltage and frequencya) A starter may have different rated voltages corresponding tothose of main circuit (rated operational voltage ( U. ;. and ratedinsulation voltage ( Ui)] , control circuit and auxiliary circuit.Further, the making and breaking capacities of the main andauxiliary contacts are stated at different rated voltages.

20

7/28/2019 is.10118.2.1982

24/63

IS : 10118 ( Part II) - 1982b) The control circuit voltage has extra significance in defining:

1) the limits of voltage in which the starter shall close positively,and

2) the drop-off voltage.c) In accordance with IS : 2959-1975* and IS : 8544 (Part 1)-1977t, the contactors and starters shall close positively between85 to 110 percent of the rated control voltage. Thus, if there isa starter for the rated coil voltage of 415 V, it should positivelyclose between 353 to 456 V. In case a 415 V starter is used for400 V the limits available to take care of the voltage fluctuationswould be:

353 456400" = 88'2 percent and -400 = 114 percent.d) The standard starters with ac coils are designed for operation onsupply with a frequency of 50 Hz.

NOTE - I f the coil of th e starter has to be used on any frequency otherthan 50 Hz, the manufacturer of the starter should be consulted.e) When exceptionally quiet operation is required or other systemconditions necessitate, ac contactors or starters may be providedwith dc coils.

3.4.3.2 Rated currentsa) Unlike other products, the term 'rated current' that is, themaximum current with which the starter may be loadedcontinuously without the temperature-rise" of the equipmentexceeding the maximum permissible limits, generally does notprove sufficient to bring out clearly all the capabilities of thestarters. I t is, also necessary to consider the type of duty cyciQ.

To make the matter clear, the value of current which fi:--:es .the temperature-rise is known as rated thermal current ( Itl!) andis based on the standard ( 8 hours) duty. On the other hand,the value of current in terms of which the making and breakingcapacity is specified is known as rated operational current ( Ie ).b) For uninterrupted duty, a starter may have to be derated for Ill!.

In case of starters with silver contacts, which do not requiresel f-cleaning, there is generally no derating necessary foruninterrupted duty. High ambier)t temperature shall, howevf!r,be considered and .derating factors obtained from themanufacturers.Specification for contactors fo r valtages not ~ x c c e d i n g I 000 V ac or 1 200 V de.(first relli.don )"tSpcdfication for motor starters for voltages not exceeding I 000 V: Part I Directon-line ac starters.

21

IS : 10118 ( Part II) - 1982b) The control circuit voltage has extra significance in defining:

1) the limits of voltage in which the starter shall close positively,and

2) the drop-off voltage.c) In accordance with IS : 2959-1975* and IS : 8544 (Part 1)-1977t, the contactors and starters shall close positively between85 to 110 percent of the rated control voltage. Thus, if there isa starter for the rated coil voltage of 415 V, it should positivelyclose between 353 to 456 V. In case a 415 V starter is used for400 V the limits available to take care of the voltage fluctuationswould be:

353 456400" = 88'2 percent and -400 = 114 percent.d) The standard starters with ac coils are designed for operation onsupply with a frequency of 50 Hz.

NOTE - I f the coil of the starter has to be used on any frequency otherthan 50 Hz, the manufacturer of the starter should be consulted.e) When exceptionally quiet operation is required or other systemconditions necessitate, ac contactors or starters may be providedwith dc coils.

3.4.3.2 Rated currentsa) Unlike other products, the term 'rated current' that is, themaximum current with which the starter may be loadedcontinuously without the temperature-rise" of the equipmentexceeding the maximum permissible limits, generally does notprove sufficient to bring out clearly all the capabilities of thestarters. I t is, also necessary to consider the type of duty cyciQ.

To make the matter clear, the value of current which fi:--:es .the temperature-rise is known as rated thermal current ( Itl!) andis based on the standard ( 8 hours) duty. On the other hand,the value of current in terms of which the making and breakingcapacity is specified is known as rated operational current ( Ie ).b) For uninterrupted duty, a starter may have to be derated for Ill!.

In case of starters with silver contacts, which do not requiresel f-cleaning, there is generally no derating necessary foruninterrupted duty. High ambier)t temperature shall, howevf!r,be considered and .derating factors obtained from themanufacturers.Specification for contactors for valtages not ~ x c c e d i n g I 000 V ac or 1 200 V de.(first relli.don )"tSpcdfication for motor starters fo r voltages not exceeding I 000 V: Part I Directon-line ac starters.

21

7/28/2019 is.10118.2.1982

25/63

' . ':.

IS, : 10118 ( Part II) 19823.4.3.3 Inrurh-current criteria - While starting a motor direct-on-line,it draws a heavy inrush-current from the supply system. This may causevoltage drop likely to interfere with other equipment on the system.Further from the point of view of load connected, it may become

necessary to make the stalting smooth. I ~ case of the above t,woconditions, it would be necessary to limit the inrush current particuladyfor bigger capacity motors. The starters which connect the, motordirectly across the lines are called direct-on-line starters and thoseemploying current limitation for squirrel cage' induction motors aregenerally star-delta, primary resistance, reactor or auto-transformer type.NOTE - There are usually limitations on direct-on-line starting of motors. Themaximum rating of motor for direct-on-line starting varies from placl1\ to place andshould be ascertained from the distribution authorities.

3.4.3.4 Making and breaking capacity and utilization categorya) The making and breaking capacity of a starter depends on thevoltage, freq uency and the type of the load. ACmotorstartershave been classified into two categories with typical applicationsas given in Table 1 orrs : 8544 (Part I H 977*.

NOTE - The requirements and test conditions for making and breakingcapacity of starters of these categories have also been specified therein.b) Table 2 of IS: 8544 ( Part I )-1977* prescribe conditions andrequirements for making and breaking capacities of motorstarters corresponding to different utilization categories, and also

details of the conditions and requirements for normal loadoperation of motor starters corresponding_ to different utilizationcategories. These should be referred to for selection of a starterfor any particular utilization category.c) A starter may even be uprated for operational current, forexample, AC3 category starter may be used at higher operationalcurrent while performing AC2 duty provided the value does notexceed the rated thermal current (Ith). Similarly, such startersmay have to be derated while performing AC, duty.d)

.,(

Making and breaking capacity and the rated thermal currentare two different things altogether and both shall be taken intoconsideration for selecting a suitable starter. I f a starter has arated thermal current of lOA, it is not at al l necessary that itmay start a motor also rated for lOA. It a,lso depends uponits making capacity, which shall be at least 60A (six times fullload current) to start the motor direct-on-line rated for lOA.

, "".'Specificali l)n for motor starters for voltages not exceeding 1 000 V: Part I 'Direct,o.. l i ~ e :ac starters.22

' . ':.

IS, : 10118 ( Part II) 19823.4.3.3 Inrurh-current criteria - While starting a motor direct-on-line,it draws a heavy inrush-current from the supply system. This may causevoltage drop likely to interfere with other equipment on the system.Further from the point of view of load connected, it may become

necessary to make the stalting smooth. I ~ case of the above t,woconditions, it would be necessary to limit the inrush current particuladyfor bigger capacity motors. The starters which connect the, motordirectly across the lines are called direct-on-line starters and thoseemploying current limitation for squirrel cage' induction motors aregenerally star-delta, primary resistance, reactor or auto-transformer type.NOTE - There are usually limitations on direct-on-line star ting of motors. Themaximum rating of motor for direct-on-line starting varies from placl1\ to place andshould be ascertained from the distribution authorities.

3.4.3.4 Making and breaking capacity and utilization categorya) The making and breaking capacity of a starter depends on thevoltage, freq uency and the type of the load. ACmotorstartershave been classified into two categories with typical applicationsas given in Table 1 orrs : 8544 (Part I H 977*.

NOTE - The requirements and test conditions for making and breakingcapacity of starters of these categories have also been specified therein.b) Table 2 of IS: 8544 ( Part I )-1977* prescribe conditions andrequirements for making and breaking capacities of motorstarters corresponding to different utilization categories, and also

details of the conditions and requirements for normal loadoperation of motor starters corresponding_ to different utilizationcategories. These should be referred to for selection of a starterfor any particular utilization category.c) A starter may even be uprated for operational current, forexample, AC3 category starter may be used at higher operationalcurrent while performing AC2 duty provided the value does notexceed the rated thermal current (Ith). Similarly, such startersmay have to be derated while performing AC, duty.d)

.,(

Making and breaking capacity and the rated thermal currentare two different things altogether and both shall be taken intoconsideration for selecting a suitable starter. I f a starter has arated thermal current of lOA, it is not at al l necessary that itmay start a motor also rated for lOA. It a,lso depends uponits making capacity, which shall be at least 60A (six times fullload current) to start the motor direct-on-line rated for lOA.

, "".'Specificali l)n for motor starters for voltages not exceeding 1 000 V: Part I 'Direct,o.. l i ~ e :ac starters.22

7/28/2019 is.10118.2.1982

26/63

IS : 10118 (Par t II) 19823.4.3.5 Frequency i f operation

a) In the relevant ISS, the starters are classified according todifferent intermittenf duty ratings also.

b) For certain devices, s u c ~ as machine tools and rolling mills, astarter may have to operate very frequently. Such an operationhas the following effects:1) Greater mechanical wear and tear,2) Higher breaking capacity requirements,3) Higher temperature-rise, and4) Reduction in the life of contacts.

c) It is not only important to know the number of o p e r ~ t i o n s perhour, but also the period in each cycle for which the starterremains closed and open. This is determined from the followingexpression:On-load Factor = Switching-in period 100Total period per cycle X

Thus, for example, a starter carrying 100 A for 4 minutes in every10 minutes shall be termed as:, Intermittent duty 100 A, 4 minutesflO minutes' or'Intermittent duty 100 A, 6 operations per hour, 40 percent' (seeFig. 3).

TIME IN ),oiINUTESFIG. 3 INTERMITTENT LOADING CYCLE

23

IS : 10118 (Par t II) 19823.4.3.5 Frequency i f operation

a) In the relevant ISS, the starters are class