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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.

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IS 3043 (1987, Reaffirmed 2005): Code of Practice for

Earthing (First Revision). UDC 621.316.99 : 006.76

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Indian Standard

(Reaff irmed 2006)

IS : 3043 -1987(Reaffirmed 2006)

CODE OF PRACTICE FOR EARTHING(First Revision)

Price Rs 650.00

Fourth Reprint JUNE 2007(Including Amendment No.1)

UDC 621316.99 : 006.76

Copyright 1988BUREAU OF INDIAN STANDARDSMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NE W DELHI 110002

September 1988

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AMENDMENT NO. 1 JANUARY 2006TO

IS 3043: 1987 CODE OF PRACTICE FOR EARTHING(First Revision)

(Page 19, clause 9.2.1) - Substitute the following for the existingformula:

(ET 20)

PR--.4

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AMENDMENT NO.2 JANUARY 2010TOIS 3043 : 1987 CODE OF PRACTICE FOR EARTHING

(First Revision)(Page 17, clause 8.6) - Add the following new sub-clause after 8.6:

8.6.1 Corrosion Allowance- On an average, steel corrodes about six times as fast as copper when placed insoil. The extent of corrosion depends upon the properties of soil. The generally accepted correlation between theelectrical resistivity of soil and its corrosivity is as indicated in the table below:

Soil Resistivity and CorrosionRange of Soil Resistivity (ClassofSoil)

(ohm-metres)Less than 25 Severely corrosive

25-50 Moderately corrosive50-100 Mildly corrosive

Above 100 Very mildly corrosive--

This following methods can be adopted to safeguard Conductor against excessive corrosion:a) Use of cathodic protection, andb) Use current conducting, corrosion resistant coating on steel (for example, zinc coating).

The zinc coa ting on the tubes shall be in accordance with IS 4736: 1986 'Hot dip zinc coatings onmild steel tubes (first revision) with coating thickness 150 microns, Min.a) Use steel conductor with large cross-section having allowance for corrosion.

Based on the results ofthe field studies on rates of corrosion, the following allowances in crosssectional area of the earthing conductor are recommended to take the dIect of corrosion intoaccount.Allowances in Cross-Sectional Area of the Earthing Conductor to Take the EfJect ofCorrosion into Account

Type of Laying of he Earth Conductor Allowances to beConsidered in Sizing

a) I Conductors laid to soils having resistivity o No allowance)greater then 100 ohm-metersb) Conductors laid II I soils having resistivity 15 percent

from 25 to 100 ohm-metersc)

I Conductor laid 111 soils having resistivity 30 percent

I

lower than 25 ohm-meters or where treatmentof soil around electrode is carried out

For the purpose of determining the allowance to be made for corrosion, the minimum resistivity ofthe soil encountered at the location of grounding electrodes to be considered The. resistivity will bethe minimum in wet weather. Thus, for very mildly corrosive soils, steel conductors meeting thestability and mechanical requirement are adequate. However, the steel conductors in the soil of othertypes should be at least 6 mm thick if it is steel flat and have a diameter of at least 16 mm if it is inthe form of steel rod.

Price Group 3

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Amend No.1 to IS 3043: 1987(Page 19, clause 9.2.1, para 1) - Substitute the following for the existing fonnula.

(Page 20, clause 9.2.2, para 1) - Substitute the following for the existing fonnula:IOOP I 2'If.:. 2 If I 0((.," d ohms

(Page 20, clause 9.2.2, para 4) - Substitute the following for the existing'Pipes may be of cast iron of not less than 100 mm diameter, 2.S to 3 m long and 13 mm thick. Such pipescannot be driven satisfactorily and may, therefore, be more expensive to install than plates for the same effectivearea. Alternatively, mild steel water-pipes of 38 to SO mm diameter are sometimes employed. These can bedriven but are less durable than copper rods. Alternatively, 40 mm diameter G 1 pipe in treated earth pit or 40mm diameter MS rod can be directly driven in virgin soil. The earth rod shall be placed at I.2S0 m belowground.'

(Page 21, clause 9.2.3, para 1) - Substitute the following for the existing fOffimla alongwith its tenus:I uo I' 4 JR ~ - log - o h m ~2n-1 . r ,

wherep = resistivity of soil (n.m) (assumed unifonn):I = length of the strip in cm; andt = width (strip) or twice the diameter (conductors) in cm

(Page 24, Fig. 14) - Substitute the figure given on page 3 of this Amendment for the existing:

(Page 2S, Fig. IS) - Substitute the figures given on pages 4 and S of this Amendment for the existing:(Page 49, clallse 20.6.2.2,./irst para, last sentence) - Substitute the following for the existing:

'It is recommended that the duration of earth fault current should be taken as one second for 66 kV and abovevoltage level substations; and 3 seconds while designing earth grids for all other voltage levels below 66 kV'

[Page 49, clause 20.6.2.3(a), secondsentence] - Substitute'I and 3 seconds'./or '3 seconds'[Page 49, clause 20.6.2.3(a)] - Add the following new sentence at the end:

'For corrosion allowance, see 8.6.1.'

2

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Amend No.1 to IS 3043 : 1987

NOTE - After laying the earth from the earth bus to the electrode through the PVC conduits at the pit entry conduits should be sealed withbitumen compound.

Al l dimensions in millimetres.FIG. 14 TYPICAL ARRANGEMENT OF PIPE ELECTRODE

3

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IS 3043 -1987Indian Standard

CODE OF PRACTICE FOR EARTHING

Members

(First Revision)Electrical Installations Sectional Committee, ETDC 20

ChairmanSHRI M. L. DONGRE

M- 3 Sat yam, 88 Sian Circle, Bombay 400022Representing

SHRI P ANANTHARAMAN Engineer-in-Chief's Branch, Army Headquarters (Ministry ofDefence), New DelhiSHRI S. K. SHANGARI (Alternate)

SHRI P. D. BAGADE Tata Consulting Engineers, BombaySHRI R. K. KAUL (Alrerl/ate)

SH RI V. S. BHATIA Siemens India Ltd, BombaySHRI M. M. SHETHNA (Alrernare)SHRI K. V. CHAUBAL Federation of Electricity Undertaking of India, BombaySHRI K. S. JOSHI (Alternate)

StIRI R. R. CHOUDHURI Larsen & Toubro (Construction Group), MadrasSIIRI N. BALASUBRAMANIAN (A l te rnate )CHIEF ELECTRICAL ENGINEER Railway Board (Ministry of Railways), Ne w DelhiDEPUTY DIRECTOR STANDARDS (ELEC)-DI,

RDSO (Alternate)C!lIEF ELECTRICAL INSPECTOR TO GOVERNMENT Chief Electrical Inspector to Government of Tamil Nadu, MadrasOF TAMIL NADU

ELECTRICAL INSPECTOR (TECHNICAL) TOGOVERNMENT o r TAMIL NADU (Al ternate)

CHIEF ENGINEER (ELEC)-I Central Public Works Department, New DelhiSUPERINTENDENT SURVEYOR WORKS

(E L EC) -I (Allernate)SHRI DEVENDER NATH Larsen & Toubro Ltd, Bombay

SHRI T. P. R. SARMA (Alternate)SH RI K. W. DHARMADHIKARI

DR V. N. MALLER (A/ternale)SH RI G. L. DUA

SHRI S. K. SETHI (Alrernate)SHRI R. C. KHANNA

SHRI P. S. SAWHNEY (Al ter l late )MEMBER (HYDRO-ELECTRIC)

DIRECTOR (HED)-I (Allernale)ER S. PANEERSELVAM

SHRI V. JANARDHANAN (Alternate)SHRI K P. R. PILLAI

SHRI C. R. R. MENON (Alternate)SIIRI V. RADHA KRISHNANSHRI H S. RAOPROF G. RAVEENDRAN NAIRSH RI S. R. SARDASHRI R. SATHIYABAL

SHRI K. K. MONDAL (AlTernate)SHRI H. K. SITARAM

SHRI S. K. PALI l (Alternate)SHRI P. SRINIVASA POTI

SHRI JOSEPH PHILOMENY (Alternale)SHRI D. S. TAWARESHRI S.J. HARIDAS (Al lemate)SHRI G. N. THADANI

SHRI S. K. GHOSH ( /I lrer l late)SHRI G. S. THAKURSHRI V. T. WARANG

SHRI R. P. PATEL (Alternate)SHRI S. P SACHDEV,

Director (Elec t ech)

Jyoti Ltd, VadodaraRural Electrification Corporation Ltd, New DelhiDelhi Electric Supply Undertaking, Ne w DelhiCentral Electricity Authority, Ne w DelhiTamil Nadu Electricity Board, MadrasFact Engineering and Design Organization, UdhyogamandalBharat Heavy Electricals Ltd, HyderabadCrompton Greaves Ltd, BombayChief Electrical Inspector to th e Government of Kerala, TrivandrumMaharashtra State Electricity Board. BombayTariff Advisory Committee (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 Madbya Pradesh, BhopalBombay Electric Supply :lnd Transport Undertaking, BombayDirector General, BI S (E .-officio Member)

Secrelat)'SHRI K. GANESH

Deputy Director (Elec tech) , B1S

(t! COp'w';ght 19R8(Conlinlled on page 2)

BUREAU OF INDIAN STANDARDSThis publication is protected under th e Indian Copyright Ac t (X I V 1957) an d production in whole or in part byan y meant except with written permission of the publisher shall be deemed to be an infringment of copyrightunder th e said Act.

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IS: 3043 -1987(Continlledfj'ompage 1)

ConvenerSHRI N. BALASUBRAMAN1AN

MembersPROF G. RAVEENDRAM NAIRSHRI V. SATHYANATHANSHRI G. S. THAKURSHRI R. SATHIYABALSHRI K. P. R. PILLAI

Panel for the Revision of IS 3043, ETDe 20 : P38Representing

Larsen & Toubro (Construction Group), Madras

Chief Electrical Inspector to the Government of Kerala, TrivandrumTamil Nadu Electricity Board, MadrasChief Electrical Inspector, Government of Madhya Pradesh, BhopalTariff Advisory Committee, MadrasFact Engineering and Design Organization, Udyogamandal

2

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IS : 3043 - 1987

O. FOREWORDl. SCOPE

SECTION 1

CONTENTS

GENERAL GUIDELINES

Page56

2. TERMINOLOGY 73. EXCHANGE OF INFORMATION 84. STATUTORY PROVISIONS FOR EARTHING 95. FACTORS INFLUENCING THE CHOICE OF EARTHED AND UNEARTHED

SYSTEMS 106. SYSTEM EARTHING 117. EQUIPMENT EARTHING 15

SECTION 2 CONNECTIONS TO EARTH8. RESISTANCE TO EARTH 169. EARTH ELECTRODE 19

10. CURRENT DENSITY AT THE SURFACE OF AN EARTH ELECTRODE 2711. VOLTAGE GRADIENT AROUND EARTH ELECTRODES 2712. CONNECTIONS TO EARTl-I ELECTRODES - EARTHING AND PROTECTlVE

CONDUCTORS 27IJ. EARTHING ARRANGEMENT FOR PROTECTlVE PURPOSES 3214. EARTHING ARRANGEMENT FOR FUNCTIONAL PURPOSES 3215. EARTHING ARRANGEMENTS FOR COMBINED PROTECTIVE AND

FUNCTIONAL PURPOSES 3216. EQUIPOTENTIAL BONDING CONDUCTORS 3317. TYPICAL SCHEMATIC OF EARTHING AND PROTECTIVE CONDUCTORS 33

SECTION 3 EARTH FAULT PROTECTION ON CONSUMER'SPREMISES

18. EARTH FAULT PROTECTlON IN INSTALLATIONS 3419. SELECTION OF DEVICES FOR AUTOMATIC DISCONNECTION OF SUPPLY 39

SECTION 4 POWER ST ATJONS, SUBST AT IONS AN DOVERHEAD LINES

20. EARTHING IN POWER STATIONS AND SUBSTATIONS21. EARTHING ASSOCIATED WITH OVERHEAD POWER. LINES

SECTION 5 INDUSTRIAL PREMISES22. GUIDELINES FOR EARTHING IN INDUSTRIAL PREMISES

SECTION 6 STANDBY AN D OTHER PRIVATE GENERATINGPLANTS

23. EARTHING IN STANDBY AND OTHER PRIVATE GENERATING PLANTS

4352

53

(INCLUDING PORTABLE AND MOBILE GENERATORS) 56

3

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IS : 3043 - 1987

SECTION 7 MEDICAL ESTABUSHMENT24. PROTECTIVE MEASURES THROUGH EARTHING IN MEDICAL ESTABLISH

MENT25. SUPPLY CHARACTERISTICS AND PARAMETERS

Page

6465

SECTION 8 STATIC AND LIGHTNING PROTECTION EARTHING(U nder consideration. Clauses 26 and 27 reserved for Section 8 )

SECTION 9 MISCELLANEOUS INSTALLATIONS ANDCONSIDERATIONS28. EARTHING IN POTENTIALLY HAZARDOUS AREAS 6929. TELECOMMUNICATION CIRCUlTS AND APPARATUS 7030. :BUILDING SITES 7131. MINES AND QUARRIES 7l32. STREET LIGHTING AND OTHER ELECTRICALLY SUPPLIES STREET

FURNITURS 7333. EARTHING OF CONDUCTORS FOR SAFE WORKING 7434. MAINTENANCE OF EARTH ELECTRODES 76

SECTION 10 MEASUREMENTS AN D CALCULATIONS35. CALCULATION OF EARTH FAULT CURRENTS36. 'MEASUREMENT OF EARTH RESISTIVITY37. MEASUREMENT OF EARTH ELECTRODE RESISTANCE38. MEASUREMENT OF EARTH LOOP IMPEDANCE

SECTION 11 DATA PROCESSING INSTALLATIONS39. EARTHING REQUIREMENTS FOR INSTALLATIONS OF DATA PROCESSING

76777980

EQUIPMENT 8040. EXAMPLE OF US E OF TRANSFORMERS 83

4

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IS : 3043 - 1987

Indian StandardCODE OF PRACTICE FOR EARTHING

(First Revision)O. FOREWORD

0.1 This Indian Standard (First Revision) wasadopted by the Bureau of Indian Standards on6 August 1987, after the draft finalized by theElectrical Installations Sectional Committee, hadbeen approved by the Electrotechnical DivisionCouncil.0.2 The lndian Electricity Rules, together withthe supplementary regulations of the State Electricity Departments and Electricity Undertakings,govern the electrical installation work in generating stations, substations, industrial locations,buildings, etc, in the country. To ensure safetyof life and apparatus against earth faults, it wasfelt necessary to prepare a code of practice forearthing. This code of practice is intended toserve as a consolidated guide to all those whoare concerned with the design, installation, inspection an d maintenance of electrical systems an dapparatus.0.3 The subject of earthing covers the problemsrelating to conduction of electricity throughearth. The terms earth and earthing have beenused in this code irrespective of reliance beingplaced on th e earth itself as a low impedancereturn path of th e fault current. As a matter oftact, th e earth now rarely serves as a part of th ereturn circuit bu t is being used mainly forfixing th e voltage of system neutrals. The earthconnection improves service continuity an davoids damage to equipment and danger tohuman life.0.4 The object of an earthing system is to provideas nearly as possible a surface under and arounda station which shall be at a uniform potentialan d as nearly zero or absolute earth potential aspossible. The purpose of this is to ensure that, ingeneral, all parts of apparatus other than liveparts, shall be at earth potential, as well as toensure that operators and attendants shall be atearth potential at all times. Also by providingsuch an earth surface of uniform potential underan d surrounding the station, there can exist nodifference of potential in a short distance bi genough to shock or injure an attendant whenshort-circuits or other abnormal occurrences takeplace. The recommendations in this code aremade in order that these objects may be carriedout.

5

0.5 Earthing associated with current-carryingconductor is normally essential to the security ofthe system an d is generally known as systemearthing, while earthing of non-current carryingmetal work an d conductor is essential to the safetyof human life, animals and property, and is generally known as equipment earthing.0.6 Since th e publication of his standard in 1966,considerable experience has been gained throughthe implementation of it s various stipulations.Moreover, several new concepts have been introduced the world over, on the' understanding offunctional an d protective earthing with a view totake into account a variety of complex problemsencountered in actual practice. In the context ofincreased use of electric power an d th e associatedneed for sarety in the design of installations, itha d become necessary to prepare an overallrevision of the earlier version of the Code.0.7 In this Code, the terms 'earthing' an d'grounding' are used synonymously. However,this Code introduces several n ew terms (see 2.15,2.17, 2.28, etc) an d distinguishes earth ing 'conductor' from 'protective conductor'.0.8 This Code includes comprehensive guidelineson choosing the proper size of th e various components of the earthing system, particularlyearthing and protective conductors as well asearth electrodes. Guidance included on determination of relevant 'k' factor depending on (seeSec 2) material properties and boundary conditions, an d the associated minimum cross-sectionalarea would assist in a more scientific design of th eearthing system under various circumstances.0.9 Fo r th e first time, the Code also includescomprehensive guidelines on earth fault protection in consumers' premises to commensuratewith th e provisions of IE Rules 1956. It includesspecific guidelines on earth ing system design toachieve the desired degree of shock hazard protection from earth leakages. The rules given inSection 3 of the Code should be read in conjunction with corresponding regulations given in th ewiring code (see IS : 732).

0.9.1 Protection against shock, both in normalservice (direct contact) an d in case of fault(indirect contact) ca n be achieved by several

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IS : 3043 - 1987measures. Details of such protective measures an dguidance on their choice is the subject matter ofdebate in the process of revision oB IS : 732*.Earth fault/leakage protection sought to be achieved through equipotential bonding and automaticdisconnection of supply is envisaged to prevent atouch voltage from persisting for such a durationthat would be harmful to human beings. Guidance on achieving this protection is' covered inSec 3 of the Code.

0.9.2 While detailed guidelines are covered inspecific portions of the Code, the following shallbe noted:Ia) For solidly grounded systems, it shall besufficient to check whether the: characteristics of protective device for' automatic

disconnection, earthing arrangements an drelevant impedances of the !circuits areproperly coordinated to ensure that voltagesappearing between simultaneously accessible, exposed and extraneous conductiveparts are within the magnitudes that wouldnot cause danger;

b) For systems where the earthing is deemedto be adequate, it shall be checked whetherthe main overcurrent protecti v'e device iscapable of meeting the requirements in thewiring code; an d

c) Where the main overcurrent protectivedevice did not fulfil the requirements orwhere the earthing is considered inadequate, then a separate residual currentdevice would be necessary to be installed,the earth fault loop impedance and thetrippi ng characteristics so chosen that theycomply with safe touch voltage limits.

0.10 Th e revision of the Code aims at consolidating in one volume all the essential guidelinesneeded for preparing a good earthing design inan electrical installation. Th e revision alsoattempts to be more elaborate than the earlierversion, especially in areas of specific interestkeeping in view the need and wide experiencegained the world over.

*Code of practice for electrical wiring installation.

1. SCOPEl .l This code of practice gives guidance on themethods that may be adopted to earth an electrical system for the purpose of limiting the potential(with respect to the general mass of the earth)of current carrying conductors forming part ofthe system, that is, system earthin& and non-

6

0.11 For convenience of identifying areas of interest by any specific users of the Code, the information contained in this standard is divided intodifferent Sections as follows:

Section 1 General guidelines;Section 2Section 3Section 4Section 5Section 6

Connections to earth;Earth-fault protection 111 con-sumer's premises;Power stations, substations an doverhead lines;Industrial premises;Standby and other private generating plant;

Section 7 Medical establishments;Section 8 Static and lightning protectiongrounding;Section 9 Miscellaneous installations an dconsiderations;Section 10 Measurements and calculations;

an dSection 11 Data processing installations.

0.12 In the preparation of the Code, assistancehas been taken from the following:

IEC Pub 364 (and Parts) Electrical installations in buildings. International Electrotechnical Commission.

BS Document 84/21243 Draft standard codeof practice on earthing (revision of CP 1013:1965). British Standards Institution.ANSI/IEEE Std 142-1982 IEEE Recommended practice for grounding of industrial and

commercial power systems. AmericanNational Standards Institute (U SA).0.13 For the purpose of deciding whether a particular requirement of this standard is compliedwith, the final value, observed or calculated,expressing the result ofa test or analysis shall berounded off in accordance with IS : 2- I960*. Then umber of significant places retained in the rounded off value should be the same as that of thespecified value in this standard.

*Rules for rounding off numerical values ( revised).

current carrying metal work association withequipment, apparatus and appliance connectedto the system (that is, equipment earthing).

1.2 This Code applies only to land-based installations and it does not apply to ships, aircrafts oroffshore installations.

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IS : 3043 -1987SECTION 1 GENERAL GUIDELINES

2. TERMINOLOGY2.0 For the purpose of this standard, the following definitions shall apply.2.1 Arc-Suppression Coil (Peterson Co i l ) -An earthing reactor so designed that its reactance is such that the reactive current to earthunder fault conditions balances the capacitancecurrent to earth flowing from the lines so that theearth current at the fault is limited to practicallyzero.2.2 Bonding Conductor - A protective conductor providing equipotential bonding.2.3 Class I Equipment - Equipment in whichprotection against electric shock does not rely onbasic insulation only, but which includes meansfor the connection of exposed conductiv e parts toa protective conductor in the fixed wiring of theinstallation.

NOTE - For information on classification of equipment with regard to means provided for protectionagainst electric shock (see IS : 9409-1980*).2.4 Class ([ Equipment - Equipment in whichprotection against electric shock does not rely onbasic insulation only, but in which additionalsafety precautions such as supplementary insulation are provided, there being no provision forthe connection of exposed metalwork of the equipment to a protective conductor, and no relianceupon precautions to be taken in the fixed wiringof the installation.2.5 Dead - Th e term used to describe a deviceor circuit to indicate that a voltage is not applied.2.6 Double Insulation - Insulation comprisingboth basic and supplementary insulation.2.7 Earth - Th e conductive mass of the earth,whose electric potential at any point is conventionally taken as zero.2.8 Earth Electrode - A conductor or group ofconductors in intimate contact with and providingan electrical connection to earth.2.9 Earth Electrode Resistance - The resistance of an earth electrode to earth.2.10 Earth Fault Loop Impedance Theimpedance of the earth fault current loop (phaseto-earth loop) starting and ending at the pointof earth fault.2.11 Earth Leakage Current - A currentwhich flows to earth or to extraneous conductiveparts in a circuit which is electrically sound.

NOTE - This current may have a capacitive component including that resulting from the deliberate useof capacitors.*Classification of electrical and electronic equipmentwith regard to protection against electric shock.

2.12 Earthed Concentric Wiring - A wlrtngsystem in which one or more insulated conductorsare completely surrounded throughout their lengthby a conductor, for example, a sheath which actsas a PEN conductor.2.13 Earthing Conductor - A protective conductor connecting the main earthing terminal(see 2.2) (or the equipotential bonding conductor of an installation when there is no earth bus)to an earth electrode or to other means of earthing.2.14 Electrically Independent Earth Electrode s - Earth electrodes located at such a distancefrom one another that the maximum currentlikely to flow through one of them does not significantly affect the potential of the other(s).2.15 Equipotential Bonding - Electrical connection putting various exposed conductive partsand extraneous conductive parts at a substantiallyequal potential.

NOTE In a building installation, equipotentIalbonding conductors shall interconnect the followingconductive parts:a) Protective conductor;b) Earth continuity conductor; andc) Risers of air-conditioning systems and heatingsystems ( if any).

2.16 Exposed Conductive Par t - A conductivepart of equipment which can be touched andwhich is not a live part bu t which may becomelive under fault conditions.2.17 Extraneous Condctive Part - A conductive part liable to transmit a potential includingearth potential and not forming part of the electrical installation.2.18 Final Circui t - A circuit connected directly to current-using equipment or to a socketoutlet or socket outlets or other outlet points forthe connection of such equipment.

7

2.19 Functional Earthing - Connection toearth necessary for proper functioning of electricalequipment (see 29.1).2.20 Live Part - A conductor or conductivepart intended to be energized in normal useincluding a neutral conductor but, by convention,not a PEN conductor.2.21 Main Earthing Terminal - The terminalor bar (which is the equipotential bonding conductor) provided for the connection of protectiveconductors and the conductors of functional earthing, ifany, to the means of earthing.2.22 Neutral Conductor - A conductor connected to the neutral point of a system and capableof contributing to the transmission of electricalenergy.

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IS : 3043 - 19872.23 PEN Conductor - A conductor combining the functions of both protective conductor andneutral conductor.2.24 Portable Equipment - Equipment whichis moved while in operation or which can easilybe moved from one place to ano ther while connected to the supply.2.25 Potential Gradient (A t a Point) - Thepotential difference per unit length measured inthe direction in which it is maximum.

NOTE I - When an electric force is du e to potential difference, it is equal to the potential gradient.NOTE 2 - Potential gradient is expressed in voltsper unit length.

2.26 Protective Conductor - A conductor usedas a measure of protection against electric shockand intended for connecting any of the followingparts:a) Exposed conductive parts,

b) Extraneous conductive parts,c) Main earthing terminal, andd) Earthed point of the source or an artificialneutral.

2.27 Reinforced Insulation - Single insulationapplied to live parts, which provides a degree ofprotection against electric shock equivalent todouble insulation under the conditions specified inthe relevant standard.NOTE - Th e term 'single insulation' does not implythat the insulation has to be one homogeneolls piece. Itmay comprise several layers that cannot be tested singly

as supplementary or basIc insulation.2.28 Residual Current Device - A mechanical switching device or association of devicesintended to cause the opening of the contactswhen the residual current attains a given valueunder specified conditions.2.29 Residual Operating Current - Residualcurrent which causes the residual current deviceto operate under specified conditions.2.30 Resistance Area (For an Earth Electrode only) - The surface area of ground(around an earth electrode) on which a significant voltage gradient may exist.2.31 Safety Extra Low Voltage - See IS :9409-1980* .2.32 Simultaneously Accessible Parts -Con ductors or conductive parts which can be touchedsimultaneously by a person or, where applicable ,by livestock.

NOTE I Simultaneously accessible parts may be:a) live parts,b) exposed conductive parts,c) extraneous conductive parts,d) protective conductors, ande) earth electrodes.

*Classification of electrical and electronic equipmentwith regard to protection against electrical shock.

NOTE 2 - This term applies for liv estock in loca-tions specifically intended for these animals.2.33 Supplementary Insulation - Independent insulation applied in addition to basic insulation, in order to provide protection againstelectric shock in the event of a failure of basicinsulation.2.34 Switchgear - An assembly of main andauxiliary switching apparatus for operation, regulation, protection or other control of electricalinstallations.

NOTE A more comprehensive definition of theterm 'Switchgear' can be had from IS : 1885 (Part17 )-1979*.2.35 Voltage, Nomina l - Voltage by which aninstallation (o r part of an installation) is designated.2.36 Touch Voltage - The potential differencebetween a grounded metallic structure and a pointon the earth's surface separated by a distanceequal to the normal maximum horizontal reach,approximately one metre (see Fig. I).2.37 Step Voltage - The potential differencebetween two points on the earth's surface, separated by distance of one pace, that will be assumedto be one metre in the direction of maximumpotential gradient (see Fig. I).2.38 Equipotential Line or Contour - Thelocus of points having the same potential at agiven time.2.39 Mutual Resistance of Grounding Electrodes - Equal to the voltage change in one ofthem produced by a change of one ampere ofdirect current in the other and is expressed inohms.2.40 Earth Grid - A system of grounding electrodes consisting of inter-connected connectorsburied in the earth to provide a common groundfor electrical devices and metallic structures.

NOTE - The term 'earth grid' does not include'eatihmat'.2.41 Earth Mat - A grounding system formedby a grid of horizontally buried conductors andwhich serves to dissipate the earth fault current toearth and also as an equipotential bonding conductor system.3. EXCHANGE OF INFORIVIATION3.1 When the earthing of a consumer's installation is being planned, prior consultation shall takeplace between the consultant or contractor andthe supply authority. Where necessary, consultations with the Posts & Telegraphs Departmentshall also be carried out in order to avoid anyinterference with the telecommunication system.

*Electrotechnica1 vocabulaty: Part 17 Switchgear andcontrolgear (first revision).

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IS : 3043 - 1987

lPOTENTIAL RISE ABOVE REMOTEEARTH DURING SHORT CIRCUIT

STEP VOLTAGE AT t;ROUNDED STRUCTURE

POTENTIAL RISE ABOVE REMOTEEARTH DURING c)HOf

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IS : 3043 - 1987fault current or its duration until it has beenascertained that the existing arrangement of earthelectrodes, earth bus-bar, etc, are capable ofcarrying the new value of earth fault currentwhich may be obtained by this addition.4.9 No cut-out, link or switch other than a linkedswitch arranged to operate simultaneously on theearthed or earthed neutral conductor and the liveconductors, shall be inserted on any ' supplysystem. This, however, does not include the caseof a switch for use in controlling a generator ora transformer or a link for test purposes.4.10 All materials, fittings, etc, used in earthingshall conform to Indian Standard specifications,wherever these exist.5. FACTORS INFLUENCING THE CHOICE

OF EARTHED OR UNEARTHEDSYSTEM5.1 Service Continuity

5.1.1 A number of industrial plant systems havebeen operated unearthed at one or more voltagelevels. This is basically guided by the thought ofgaining an additional degree of service continuityvarying in its importance depending on the typeof plant. Earthed systems are in most cases designed so that circuit protective devices will removethe faulty circuit from the system regardless ofthe type of fault. However, experience has shownthat in a number of systems, greater service continuity may be obtained with earthed-neutral thanwith unearthed neutral systems.5.2 Multiple Faults to Ground

5.2.1 While a ground fault on one phase of anunearthed system generally does not cause aservice interruption, the occurrence of a secondground fault on a different phase before the firstfault is cleared, does result in an outage. Th elonger a ground fault is allowed to remain on anunearthed system, greater is the likelihood of asecond one occurring in another phase an d repairsare required to restore service. With an unearthed system, an organized maintenance programme is therefore extremely important so thatfaults are located and removed soon after detection.

Experience has shown that multiple groundfaults are rarely, if ever, experienced on earthedneutral systems.5.3 Arcing Fault Burndowns

5.3.1 In typical cases, an arcing fault becomesestablished between two or more phase conductorsin an unearthed systems or between phase andground in a solidly earthed-neutral system. Thiswould result in severe damage or destruction toequipment. However, arcing fault current levelsmay be so low that phase overcurrent protectivedevices do not operate to remove the fault quickly.Such faults are characteristic of open or coveredfuses, particularly in switchgear or metal-enclosed

switching and motor control equipment. It is. generally recognized that protection under suchcircumstances is possible by fast an d sensitivedetection of the arcing fault current and interruption within 10-20 cycles. In sol idly earthedneutral systems, this is possible as an arcing faultwould produce a current in the ground path,thereby providing an easy means of detection andtripping against phase-to-ground arcing faultbreakdowns.5.4 Location of Faults

5.4.1 On an unearthed system, a ground faultdoes not open the circuit. Some means of detecting the presence of a ground fault requires to beinstalled. In earthed system, an accidental groundfault is both indicated at least partially locatedby an automatic interruption of the accidentallygrounded circuit or piece of equipment.5.5 Safety

5.5.1 Whether or not a system is grounded,protection of personnel and property from hazardsrequire thorough grounding of equipment andstructures. Proper grounding result s in less likelihood of accidents to personnel. Other hazards ofshock and fire may result from inadequate grounding of equipment in unearthed and earthedsystems. However, relatively high fault currentsassociated with solidly earthed system may present a hazard to workers from exposure to hotarc products and flying molten metal. This protection is, however, reduced because of use ofmetal-enclosed equipment.5.6 Abnormal Voltage Hazards

5.6.1 Th e possible over-voltages on th e unearthed system may cause more frequent failures ofequipment than is the system, if earthed. A faulton one phase of an unearthed or impedancegrounded system places a sustained increasedvoltage on the insulation of ungrounded phasesin a 3-phase system. This voltage is about 1.73times the normal voltage on the insulation. Thisor other sustained over-voltages on the unearthedsystem may not immediately cause failure ofinsulation but may tend to reduce the life of theinsulation. Some of the more common sources of.over-voltages on a power system are the follow-1l1g:

a) Lightning,b) Switching surges,c) Static,d) Contact with a high voltage system,e) Line-to-ground fault,f) Resonant conditions, an dg) Restriking ground faults.

5.6.2 Surge arresters are recommended forlightning protection. Grounding under such casesare separately discussed in Section 8. Neutral

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grounding is not likely to reduce the total magnitude of over-voltage produced by lightning orswitching surges. It can, however, distribute thevoltage between phases and reduce th e possibilityof excessive voltage stress on the phase-to-groundinsulation of a particular phase. A system groundconnection even of relatively high resistance caneffectively prevent static voltage build-up (seeSec 8). Even under conditions of an H V linebreaking and falling on an LV system, an effectively grounded LV system will hold the systemneutral close to the ground potential thus limitingthe over-voltage. An unearthed system will besubjected to resonant over-voltages. Field experience and theoretical studies have shown the worldover that arcing, restriking or vibrating groundfaults on unearthed systems can, under certainconditions, produce surge voltages as high as 6times the normal voltage. Neutral grounding iscffective in reducing transient build up by reducing the neutral displacement from ground potential and the destructiveness of any high frequencyvoltage oscillations following each arc initiationor restrike.5.7 Cost

5.7.1 Th e cost differential between earthedand unearthed neutral system will vary, depending on the method of grounding the degree ofprotection desired, and whether a new or anexisting system is to be earthed.6. SYSTEM EARTHING6.0 Basic Objectives

6.0.1 Earthing of system is designed primarilyto preserve the security of the system by ensuringthat the potential on each conductor is restrictedto such a value as is consistent with the level ofinsulation applied. From the point of view ofsafety, it is equally important that earthing shouldensure et1icient an d fast operation of protectivegear in the case of earth faults. Most high voltagepublic supply systems are earthed. Approval hasbeen given in recent years to unearthed overheadline systems in certain countries, bu t these haveonly been small 11 kV systems derived from33 kV mains, where the capacity earth current isless than 4 A an d circumstances are such that th esystem will not be appreciably extended.

6.0.2 Th e limitation of earthing to one pointon each system is designed to prevent the passageof current through the earth under normal conditions, and thus to avoid the accompanying risksof electrolysis an d interference with communication circuits. With a suitable designed system,properly operated an d maintained, earthing atseveral points may be permitted. This method ofearthing becomes economically essential in systems at 200 kV and upwards.

6.0.3 The system earth-resistance should besuch that, when any fault occurs against which

IS : 3043 - 1987earthing is designed to give protection, the protective gear will operate to make the faulty mainor plant harmless. In most cases, such operationinvolves isolation of th e faulty main or plant, forexample, by circuit-breakers or fuses.

6.0.4 In the case of underground systems, thereis no difficulty whatever but, for example, in thecase of overhead-line systems protected by fusesor circuit-breakers fitted with overcurrent protection only, there may be difficulty in arrangingthat th e value of the system earth-resistance issuch that a conductor falling an d making goodcontact with the ground results in operation ofthe protection. A low system-earth resistanceis required even in th e cases where an arcsuppression coil is installed, as its operation maybe frustrated by too high an earth-electroderesistance.

6.0.5 Earthing may not give protection againstfaults that are not essentially earth faults. Fo rexample, if a phase conductor on an overhead spurline breaks, and the part remote from the supplyfalls to the ground, it is unlikely that any protective gear relying on earthing, other than currentbalance protection at the substation, will operatesince the earth-fault current circuit includes theimpedance of th e load that would be high relativeto the rest of the circuit.

6.0.6 For th e purposes of this code of practice,it is convenient to consider a system as comprisinga source of energy and an installation; the formerincluding the supply cables to the latter.6.1 Classification of Systems Based onTypes of System Earthing

6.1.1 Internationally, it has been agreed toclassify the earthing systems as TN System. TTSystem and iT System. They are:

11

a) TN svstem - has one or more points of thesource of energy directly earthed, and theexposed and extraneous conductive partsof the installation are connected by meansof protective conductors to the earthedpoint(s) of the source, that is, there is ametallic path for earth fault currents toflow from the installation to the earthedpoint(s) of the source. TN systems arefurther sub-divided into TN-C, TN-S an dTN -C-S systems.

b) TT ,\ystem - - has on e or more points of thesource of energy directly earthed an d theexposed and extraneous conducti ve partsof the installation are connec ted to a localearth electrode or electrodes are electrically independent of the source earth( s) .

c) iT system - has the source either unearthed or earthed through a high impedanceand the exposed con ductive parts of theinstallation are connected to electricallyindependent earth electrodes.

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IS : 3043 - 19876.1.2 I t is also recognized that, in practice, a

system may be an admixture of type for the purposes of this code, earthing systems are designatedas follows:

couductor throughout the system ( forexample earthed concentric wiring (seeFig. 4).

d) TN-C-S S.vstem - The neutral an d protective functions are combined in a singleconductor but only in part of the system(see Fig 5).a) TN-S System (for 240 V single phase domestic!commercial supply) - Systems where there

are separate neutral and protective conductors throughout the system. A systemwhere the metallic path between theinstallation an d the source of energy is thesheath an d armouring of the supply cable(see Fig. 2).

e) T-TN-S s.ystem (for 6-6111 kV three-phasebulk SlIPPZV) - Th e consumers installation,a TN -S system receiving power at a captivesubstation through a delta connectedtransformer primary (see Fig. 6).b) Indian TN-S System (for 415 V three-phasedomestic commercial s u p p ~ v ) - An independen t earth electrode within the consumer'spremises is necessary (See Fig. 3).

f) TT System (for 415 V three-phase indus trialsupply) - Same as 6.1.1 (b) (see Fig 7.).c) Indian TN C-System - Th e neutral and pro

tective functons are combined in a singleg) IT System - Same as 6.1.1 (c) ( see

Fig. 8 ).SOURCE OF ENERGY- - __________________e-____________________________

~ - - - - - - - - - - - - - - - - - - ~ - - - - - - - - - - - - - - - - - - - - - - - - - L 2C = ~ - - - - - - - - - - - - - - - - - - - + - - - - - - - - - - - - - - - - - - - - - - - - - - L l__ - - - - - - - - - - - - - - - - - - - - - - - ~ ~ . _ - - - - - - - - - - - - - - - - - - - - - - - - H

. - - - - - - - - - - - - - - - - - - - - + - - + - - - ~ - - - - - - - - - - - - - - - - P ESOURCEEARTH

EQUIPMENT ININS ALLATION

r---I EXPOSEDI CONDUCTIVEI PART

ICONSUMERL_________.J INSTALLATIONNOTE - The protective conductor (P E) is the metallic covering (armour or load sheath ofthe cable supplyingthe installation or a separate conductor),All exposed conductive parts of an instal lation are connected to this protective conductor via main earthingterminal of the installation.

FIG. 2 TN-S SYSTEM SEPARATE NEUTRAL AND PROTECTIVE CONDUCTORS THROUGHOUT THE SYSTEM,230V SIMPLE PHASE. DOMESTIC/COMMERCIAL SUPPLY FOR 3 ~ T N - S (See FIG. 3)SOURCE OF ENERGV

L - ~ - - - - - - - - - - - - - - - - - - - - ~ ~ - - - - - - - - - - - - - - - - - - - - - l l~ ~ - - - - - - - - - - - - - - - - - - 4 - ~ ~ - - - - - - - - - - - - - - - - - - - - L 2

L - ~ - - - - - - - - - - - - - - - ' - - + - ~ - - - - - - - - - - - - - - - - - - - - - - l 3. - - - - - - - - - - - - - - - - - - + - - ~ - - ~ ~ - - - - - - - - - - - - - - - - - - - N

e - - - - - - - - - - - - - ~ - - - + - - ~ - - ~ ~ - - - - - - - - - - - - - - - - - - - P E.-........._-,

II tII . ,L ...__ __ .-._ .... __ ..............................415 V Three phase Domestic/Commercial supply having 3 - and 1 - loads.All exposed conductive parts ofthe installation are connected to protective conductor via the main earthingterminal of the installation. An independent earth electrode within the consumer's permises is necessary.

FIG. 3 INDIAN TN-S SYSTEM12

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SOURCE OF ENERGY UC = ~ - - - - - - ~ ' - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - l 2

C = ~ - - - - - - ~ ~ - - - - - - - - - - - - ~ ~ - - - - - - - - - - - - - - l Je - - - - - - - - - ~ ~ ~ - - - - - - - - - - - - ~ ~ - - - - - - ~ ~ - - - C O M 8 J N E O,..--SOURCE IEARTH :

ItI1 ~ C O N ; u ~ ~ ; l -

PE .. N--, CON Due TORI ADOITIONALI SOURCE: EARTH: (MAY BE PROVIOEO)

I ~ INS TAlLATlON

IS : 3043 - 1987

All exposed conductive parts are connected to the PEN conductor. For 3 - consumer, local earth electrode hasto be provided in addition.FIG. 4 INDIAN TN-C SYSTEM (NEUTRAL AND PROTECTIVE FUNCTIONS COMBINED IN

A SINGLE CONDUCTOR THROUGHOUT SYSTEM)

C = ~ - - - - - - 4 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - L l~ ~ - - - - - - ~ ' - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - L 2~ ~ - - - - - 4 ~ ~ - - - - - - - - - - - - - - - - - - - - - - - - - - - - l l

6 - - - - - - - - - ~ 4 - ~ ~ - - - - ~ . _ - - - - - - - - - - - - - - - - - - - - C O M 8 I N E OP( &. N---, CONOUCT"R,t II IL _________ J

The usual fOJ-m of a TN-C-S system is as shown, where the supply is TN-C and the arrangement in theinstallations in TN-S.

This type of distribution is known also as Protective Multiple Earthing and the PEN conductor is refelTl'fl to asthe combined neutral and earth (CNE) Conductor.The supply system PEN conductor is earthed at several points and an earth electr ode may be necessary at orncar a consumer's installation.All exposed conductive parts of an installation are connected to the PEN conductor via the main earthingterminal and the neutral terminal, these terminals being linked together.The protective neutral bonding (P NB) is a variant of TN-C-S with single point earthing.FIG. 5 TN-C-S SYSTEM, NEUTRAL AND PROTECTIVE FUNCTIONS COMBINED IN A SINGLECONDUCTOR IN A PART OF THE SYSTEM

13

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IS : 3043 - 1987souRCr OF INERGY

C : ~ - - - - - - - - - - - - ~ ~ - - - - - - - - - - - - 1 - - - - - - - L '~ ~ - - - - - - - - - - - 4 - + - - - - - - - - - - ~ ~ - - - - - - - L 2~ ~ - - - - - - - - - - e - + - + - - - - - - - - - - ' ~ ~ - - ~ - - - l lr-r-

CONSUMER I' N S T A L L ~ T l O N :...............---.

CONSUMERINSTALLATION,"-- ~ - - - - - - - - - 1 ~ - - - P &......----- ......- - t - - - lL-_ _ _ _ _ _ _ _ _ _ ~ - - ~ - - - - 2

~ ~ - - - - - - ~ ~ _ + - - _ r - - - - l

6-6111 kY Three phase bulk supply.FIG.6 T -TN -S SYSTEM

SOURCE OF' ENERGY- ~--. - ., .RCEOUEAR

r------I 4> U ) 4t I IH I I 6 b I

SOMER IlALLATION I ICONINS

~ ) ~ ) ~ J

I I

Lll2IIH---..,l

JI\ INSTAllEARTAllONH

ODEELECTRI

415 V Three phase industrial supply having 3 and 1 - loads.All exposed conductive parts of the installation are connected to an earth electrode which is electrically inde-pendent of the source earth. Single phase TT system not present in India.

SOURCE OFE ~ E R G V

FIG. 7 TT SYSTEM

~ ~ - - - - - - ~ - - - - - - - - - - - - - - - - - - - - - - - - - - - - ~ - - - - - ~ I~ ~ - - - - ~ ~ ~ - - - - - - - - - - - - - - - 1 ~ - - - - - - - - - - - l 2

~ ~ - - - - - - r - r - ' - - - - - - - - - - - - - ~ ~ ~ - - - - - - - - - l 3i --IIt ; I'------_ _ _ _ J

rItII I'----_ _ _ _ _ J

All exposed conductive parts of an installation are connected to an earth electrode.Th e source is either connected to earth through a deliberately introduced earthing impedance or IS isolatedfrom earth.

FIG. 8 IT SYSTEM14

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6.2 Marking of Earthing/Protective Conductor6.2.1 The earthing and protective conductor

shall be marked as given II I Table 1 (see alsoIS: 11353-1986*).TABLE 1 MARKING OF CONDUCTORS

DESIGNATION orCONDUCTOR

Earth

Protectiveconductor

IDENTIFICATION BYr----------,AlphanumericNotationE

PB

GraphicalSymbol

COLOUR

No colour otherthan colour ofthe bare conductorGreen and yellow

6.2.2 Use of Bi-Colollr Combination - Green andYellow - Th e bi-colour combination, green an dyellow (green/yellow), shall be used for identifying the protective conductor and for no otherpurpose. This is the only colour code recognizedfor identifying the protective conductor.

Bare conductors or busbars, used as protectiveconductors, shall be coloured by equally broadgreen and yellow stripes, each 15 mm up to 100mm wide, close together, either throughout thelength of each conductor or in each compartmentor unit or at each accessible position. I f adhesivetape is used, only bi-coloured tape shall beapplied.

For insulated conductors, the combination ofthe colours, green an d yellow, shall be such that,on any 15 mm length of insulated conductor, oneof these colours covers at least 30 percent an dnot more than 70 percent of the surface of theconductor, the other colour covering the remainde r of that surface.

NOTE - Where the protective conductor can beeasily identified from it s shape, construction or position,for example, a concentric conductor, then colourcoding throughout its length is not necessary but th eends or accessible positions should be clearly identifiedby a symbol or the bi-colour combination, green andyellow.

7. EQUIPMENT EARTHING7.0 Basic Objectives

7.0.1 Th e basic objectives of equipmentgrounding are:

1) to ensure freedom from dangerous electric*Guide for uniform system of marking and identifica

tion of conductors and apparatus terminals.

IS : 3043 - 1987shock voltages exposure to persons in thearea;

2) to provide current carrying capability, bothin magnitude and duration, adequate toaccept the ground fault current permittedby the overcurrent protective system withou t creating a fire or explosive hazard tobuilding ar contents; an d

3) to contribute to better performance of theelectrical system.7.0.2 Voltage E-rposlire - When there IS un

intentional contact between an energized electricconductor and the metal frame or structure thatencloses it (0 r is adjacent, the frame or structuretends to become energized to the same voltagelevel as exists on the energized conductor. Toavoid this appearance of this dangerous, exposedshock hazard voltage, the equipment groundingconductor must present a low impedance pathfrom the stricken frame to the zero potentialground junction. Th e impedance should also besufficiently low enough to accept the full magnitude of the line-ta-ground fault current withoutcreating an impedance voltage drop large enoughto be dangerous.

7.0.3 Avoidance of Thermal Distress - Th eearthing conductor nlust also function to conductthe full ground fault current (both magnitudeand duration) without excessively raising thetemperature of the earthing conductor or causingthe expulsion of arcs and sparks that could initiatea fire or explosion. The total impedance of thefault circuit including the grounding conductorshould also permit the required current amplitudeto cause operation of the protective system.

7.0.4 Preservation o f System PeJ.iormance - Th eearthing conductor must return the ground faultcurrent on a circuit without introducing enoughadditional impedance to an extent that wouldimpair the operating performance of the overcurr-'ent protective device, that is, a higher thannecessary ground-circuit impedance would beacceptable if there is no impairment of the performance characteristics of the protective system.7.1 Classification of Equipment with R egardto Protection Against Electric Shock

7.1.1 Table 2 gives the principal characteristics of equipment according to this classificationand indicates the precautions necessary for safetyin the event of failure of the basic insulation.

TABLE 2 CLASSIFICATION OF EQUIPMENT

Principalcharacteristicsof equipment

Precautions forsafety

CLASS 0No means of

protectiveearthing

Earth freeenvironment

CLASII IProtective

earthing meansprovided

Connection toth e protectiveearthing

15

CLASS IIAdditional insula

tion an d no meansfor protectiveeartingNone necessary

CLASS IIIDesigned for supply

at safety extralow voltageConnection to safety

extra low voltage

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IS : 3043 - 1987SECTION 2 CONNECTIONS TO EARTH

8. RESISTANCE TO EARTH8.0 Nature of Earthing Resistance

8.0.1 The earthing resistance of an electrode ismade up of:

a) resistance of the (meta I) electrode,b) contact resistance between the electrodeand the soil, an dc) resistance of the soil from the electrode surface outward in the geometry set up for the

tlow of current outward from the electrodeto infinite earth.Th e first two factors are very small fractions of

an oh m and can be neglected for all practical pur"'"poses. Th e factor of soil resistivity is discussedin 8.1.8.1 Soil Resistivity

8.1.1 Th e resistance to earth of a given electrode depends upon the electrical resistivity ofthe soil in which it is installed. This factor is,therefore, important in deciding which of manyprotective systems to adopt.

Th e type of soil largely determines its resistivity and examples are given in Table 3. Earthconductivity is, however, essentially electrolyticin nature and is affected, by th e moisture contentof the soil an d by the chemical composition an d

concentration of salts dissolved in the containedwater. Grain size and distribution, and closenessof packing are also contri butory factors since theycontrol the manner in which th e moisture is heldin the soil. Many of these factors vary locally andsome seasonally so that the table should only betaken as a general guide.

Local values should be verified by actual measurement, and this is especi ally important whereth e soil is stratified as, owing to the dispersion ofthe earth current, the efTective resistivity dependsnot only on the surface layers but also on theunderlying geological formation.

It should also be noted that soil temperaturehas some effect (see 8.7), bu t is only importantnear and below freezing point, necessitating theinstallation of earth electrodes at depths to whichfrost will not penetrate. It is, therefore, recommended that the first metre of any earth electrodeshould not be regarded as being effective underfrost condi tions.

While the fundamental nature and propertiesof a soil in a given area cannot be changed, usecan be made of purely local conditions in choosingsuitable electrode sites an d methods of preparingthe site selected to secure the optimum resistivity.These measures may be summarized as in 8.2to 8.7.

TABLE 3 EXAMPLES OF SOIL RESISTIVITYTYPE OF SOIL

(I )

Alluvium and lighter claysClays (excluding al luvium)Marls (for example, keuper marl )Porous limestone (for example, chalk)Porolls sandstone (for example, keupersandstone and clay shales)Quartzites, compact an d crystalline

limestone (for example, carboniferOllS marble, etc)Clay slates and slatey shalesGraniteFossile slates, schists gneiss igneous

rocks*Depends on water level of locality.

CLIMATIC CONDITION, - . - - - - - - - - - - ------- - - " - - - - - - ._----------""""Normal and High Low Rainfall and Underground

Rainfall (for Desert Condition (F or WatersExample, Greater Examples, Less than (Sal ids)than 500 mm a Year ) 250 111111 a Year), - - - - - - - - ----.------"------------_. ------Probable Range of Range of Range of

value values values valuesencountered encountered encountered

(2) (3) (4) (5)n. m

5102050

100300

1 000I 000

2 000

16

n. m*

5 to 2010 to 30

30 to 10030 to 300100 to I 000

300 to 3 000

1000 upwards

n. m Q.m* I to 5

10 to 10050 to 300

I 000 upwards 30 to 100

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8.2 Where there is any option, a site should bechosen in one of the following types of soil in theorder of preference given:

a) Wet marshy ground (see 8 .3) ;b) Clay, loamy soil, arable land, clayey soil,clayey soil or loam mixed with small quantities of sand;c) Clay and loam mixed with varying proportions of sand, gravel and stones;d) Damp an d wet sand, peat.Dry sand, gravel chalk, limestone, granite and

any very stony ground should be avoided, and alsoall locations where virgin rock is very close to thesurface.8.3 A site should be chosen that is not naturallywell-drained. A water-logged situation is not,however, essential, unless the soil is sand or gravel, as in general no advantage results from anincrease in moisture content above about 15 to 20percent. Care should be taken to avoid a site keptmoist by water flowing over it (for example, thebed of a stream) as the beneficial salts may beentirely removed from the soil in such situations.8.4 Where building has taken place, the site conditions may be altered by disturbance of the localstratification and natural geological formationwhen the electrodes have to be installed in thisdisturbed area.

If a cut and fill exercise has been carried outthen the top layer may be similar to the naturalformation but increased in depth, whether it isgood or bad in terms of resistivity.If an imported fill exercise has been carriedout, the conditions of the upper layers may bealtered considerably.

In these cases, deeper driving of the electrodemay be necessary to reach layers of reasonableresistivity and also to reach stable ground, suchthat the value of the electrode resistance remainsstable if the top layers of the ground dry out.8.5 Soil treatment to improve earth electrode contact resistance may be applied in special or difficult locations, but migration and leaching ofapplied chemicals over a period of time reducesthe efficiency of the system progressively, requiringconstant monitoring and replacement of the additives. Ecological considerations are inherent before such treatment is commenced an d any deleterious effect upon electrode material has to betaken into account. However, for some temporaryelectrical installations in areas of high ground resistivity, this may be the most economic method forobtaining satisfactory earth contact over a shortperiod of working. If a greater degree of permanence is envisaged, earth electrodes packaged inmaterial such as bentonite are preferable.

Bentonite or similar material may be used toadvantage in rocky terrain. Where holes are bored

IS : 3043 - 1987for the insertion of vertical electrodes or wherestrip electrodes are laid radially under shallowareas of low resistivity overlaying rock strata, ben-otonite packing will increase the contact efficiencywith the general mass of ground.8.6 Effect of Moisture Content on EarthResistivity - Moisture content is one of thecontrolling factors in earth resistivity. Figure 9shows the variation of resistivity of red clay soilwith percentage of moisture. Th e moisture contentis expressed in percent by weight of the dry soil.Dry earth weighs about I 440 kg per cubic metreand thus 10 percent moisture content is equivalentto 144 kg of water per cubic metre of dry soil. Itwill be seen from Fig. 9 that above about 20 percent moisture, th e resistivity is very little affected,while below 20 percent the resistivity increasesvery abruptly with the decrease in moisture content. A difference of a few percent moisture willtherefore, make a very marked difference in theeffectiveness of earth connection if the moisturecontent falls below 20 p ercent. Th e normal moisture content of soils ranges from 10 percent in dryseasons to 35 percent in wet seasons, an d an ap proximate average may be perhaps 16 to 18 percent.

It should be recognized, however, that moisture alone is not the predominant factor in the lowresistivity of soils; for example, earth electrodesdriven directly in the beds of rivers or mountainstreams may present very high resistance to earth.ff the water is relatively pure, it will be high resistivity and unless the soil contains sufficientnatural elements to form a conducting electrolyte,the abundance of water will not provide the soilwith adequate conductivity. Th e value of highmoisture content in soils is advantageous in increasing the solubility of existing natural elements inthe soil, and in providing for the solubility of ingredients which may be artificially introduced toimprove the soil conductivity.8.7 Effect of Temperature on Earth Resistance - The temperature coefficient of resistivityfor soil is negative, but is neglig ible for temperatures above freezing point. At about 20C, theresistivity change is about 9 percent per degreeCelsius. Below OC the water in the soil begins tofreeze and introduces a tremendous increase in thetemperature coefficient, so that as the temperaturebecomes lower the resistivity rises enormously. Itis, therefore, recommended that in areas wherethe temperature is expected to be quite low, theearth electrodes should be installed well below thefrost line. Where winter seasons are severe, thismay be about 2 metres below the surface, whereasin mild climates the frost may penetrate only afew centimetres or perhaps the ground may notfreeze at all. Earth electrodes which are not drivenbelow the first depth may have a very great variation in resistance throughout the seasons of theyear. Even when driven below the frost line, thereis some variation, because the upper soil, when

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IS : 3043 - 1987frozen, presents a decided increase in soil resisti-vity an d has the effect of shortening th e activelength of electrode in contact with soil of normalresistivity.8.8 Artificial Treatment of Soil - Multiplerods, even in large number, ma y sometime fail to

produce an adequately low resistance to earth.This condition arises in installations involving

soils of high resistivity. The alternative is to reducethe resistivity of the soil immediately surroundingthe earth electrode. To reduce the soil resistivity,it is necessary to dissolve in the moisture, norm-ally contained in the soil, some substance which ishighly conductive in its water solution. The mostcommonly used substances are sodium chloride(N a C I), also known as common salt, calciumchloride (CaCI 2 ), sodium carbonate (Na2C03) ,copper sulphate (CUS04) ' sait, and soft coke, an dsalt an d charcoal in suitable proportions.

400

300

\AIa:::...W~

~ 200r:l~

~a-t :.-'"})~

tOO

\,~

8.8.1 With average or high moisture content,these agents form a conducting electrolyte through-ou t a wide region surrounding the earth elec-trode. Approximately 90 percent of the resistancebetween a driven rod an d earth lies within a radi-us of about two metres from the rod. This shouldbe kept in mind when applying the agents forartificial treatment of soil. The simplest applica-tion is by excavating a shallow basin around thetop of the rod, one metre in diameter and about30 em deep, and applying the artificial agent inthis basin. The basin should subsequently be filledseveral times with water, which should be allowedeach time to soak into the ground, thus carryingthe artificial treatment, in electrolyte form, to con-siderable depths and allowing the artificial agentto become diffused throughout the greater partof the effective cylinder of earth surrounding thedriven rod.

o 5 I ) 15 20 2S 30 35 40 45 50 55 60 65 70MOISTURE IN SOIL.PERCENT

FIG. 9 VARIATION OF SOIL RESISTIVITY WITH MOISTURE CONTENT

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8.8.2 The reduction in soil reSIstIVIty effect edby salt is shown by the curve in Fig. 10. Th e saltcontent is expressed in percent by weight of thecontained moisture. It will be noted that thecurve flattens of f at about 5 percent salt content anda further increase in salt gives but little decreasein the soil resistivi ty. The effect of salt will bedifferent for different kinds of soil an d for variousmoisture contents but the curve will convey anidea of ho w the soil conductivity can be impro-ved. Decreasing the soil resistivity causes a corres-ponding decrease in the resistance of a drivenearth electrode.

400

! ,tor lOOI lSGg zooti l... '100.- 1005;; 10iiiw'"

\ ~ ~ ...o 2 , 10 12 1. ""AC!MT 0 ' SA",'T IN tIIIOISTUA!FIG. 10 VARIATION OF SOIL RESISTIVITY WITH

SALT (N ac I) CONTENT, CLAY SoILHAVING 3 PERCENT MOISTURE

8.8.3 In close texture soils, the artificial treat-ment may be effective over a period of many years.However, it is recommended that annual or bi-annual measurements of earth resistivity shouldbe made to find ou t if additional treatment isneeded.

8.8.4 In using artificial treatment, the possiblecorrosive effect of the salt on the driven rods andconnections should be considered. Th e possiblecontamination of the domestic water supply shouldalso be considered.9. EARTH ELECTRODES9.1 Effect of Shape on Electrode Resistance

9.1.1 With al l electrodes other than extendedsystems, the greater part of the fall in potentialoccurs in the soil within a few feet of the electrodesurface, since it is here that the current density ishighest. To obtain a low overall resistance thecurrent density should be as low as possible in themedium adjacent to the electrode, which shouldbe so designed as to cause the current density todecrease rapidly with distance from the electrode.This requirement is met by making the dimensi-ons in one direction large compared with those in

IS : 3043 - 1987the other two, thus a pipe, rod or strip has a muchlower resistance than a plate of equal surface area.Th e resistance is not, however, inversely propor-tional to th e surface area of the electrode.9.2 Resistance of Com mo n Types of Earth-Electrodes

9.2.1 Plates - The approximate resistance toearth of a plate can be calculated from:

R- V ~ ohm.where

p = resistivity of th e soil (assumed uni-form) (i n n.m); an dA = area of both sides of the plate (i n m 2 ) .

Where the resistance of a single plate is higherthan the required value, two or more plates maybe used in parallel and the total resistance is thaninversely proportional to the number employed,provided that each plate is installed outside theresistance area of any other. This normally requi-res a separation of about 10 m bu t for sizes of plategenerally employed, a separation of 2 m is sufficient to ensure that the total resistance will notexceed the value obtained from the above formulaby more than 20 percent. Even at the latter spac-ing, it is generally more economical to use tw oplates in parallel, each of a given size, than one oftwice that size. Th e size employed is, therefore,normally not greater than 12 x 1'2 m.

Plate electrodes shall be of the size at least 60em x 60 cm. Plates are generally of cast iron notless than 12 mm thick and preferably ribbed. Theearth connection should bejoined to the plate atnot less than two separate points. Plate electrodes,when made of GI or steel, shall be not less than63 mm in thickness. Plate electrodes of eu shallbe no t less than 3 15 mm in thickness.

Suitable methods of jointing are a taper pindriven into a reamed hole and riveted over or acopper stud screwed into a tapped hole an d rive-ted. Such joints should be protected by a heavycoat of bitumen. The connection between th eearth plate and the disconnecting link should be setvertically and the depth of setting should be suchas to ensure that th e surrounding soil is alwaysdamp. Th e minimum cover should be 600 mm ex-cept that where the underlying stratum is solid,for example, chalk or sandstone and near the sur-face, the top of the plate should be level with thetop of the solid stratum. Sufficient solid stratumshould be removed an d replaced with fine sailorother suit able infill to ensure as Iowa resistanceas possible.

Th e use of coke breeze as an infill is no trecommended as it ma y result in rapid corrosionnot only of the electrode itselfbut also of cablesheaths, etc, to which it ma y be bonded.

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IS : 3043 - 1987Th e resistance R (i n Q) ofa 12 m x 12 m

plate is given approximately by the formula:pR - T-75

Fo r conventional sizes, the resistance is approximately inversely proportional to th e linear di-,mensions, not the surface area, that is a 09 m x09 m plate would have a resistance approximately25 percent higher than a 12 x 12 m plate. Th ecurrent loading capacity of a 12 m x 12 m plateis of the order of I 600 A for 2 sand 1 300 A for3 s.

Plate electrodes shall be buried such that its to pedge is at a depth not less than 1 5m from th esurface of the ground. However, the depth atwhich plates ar e set should be such as to ensurethat the surrounding soil is always damp. Whereth e underlying stratum is solid, for example chalkor sandstone and near the surface, the top of th eplate should be approximately level with the topof the solid stratum.

9.2.2 Pipes or Rods ~ Th e resistance of a pipeor rod electrode is given by:

100 p 41R - fiT logo T ohmswhere

I = length of rod or pipe (in cm),d = diameter of rod or pipe in cm, an dp = resistivity of the soil (in Q.m)

(assumed uniform).Th e curves of Fig. 11 are calculated from this

equation for electrodes of 13, 25 an d 100 mm diameter respectively in a soil of 100Q.m respectively.Change of diameter has a relatively minor effectan d size of pipe is generally governed by resistance to bending or splitting. It is apparent thatthe resistance diminishes rapidly with the first fewfeet of driving, bu t less so at depths greater than2 to 3 m in soil of uniform resistivity.

A number of rods or pipes may be connectedin parallel an d the resistance is then practicallyproportional to the reciprocal of th e number employed so long as each is situated outside the resistance area of an y other. In practice, this is satisfied by a mutual separation equal to the drivendepth. Little is to be gained by separation beyondtwice the driven depth. A substantial gain iseffected even at 2 m separation.

Pipes may be of cast iron of not less than 100mm diameter, 25 to 3 m long and 13 mm thick.Such pipes cannot be driven satisfactorily an dmay, therefore, be more expensive to instal thanplates for the same effective area. Alternatively,mild steel water-pipes of38 to 50 mm diameter aresometimes employed. These can be driven but areless durable than copper rods.

20

Driven rods generally consist of round copper,steel-cored copper or galvanized steel (see 9.2.8)13, 16 or 19 mm in diameter from I 220 to 2 440mm in length.

250CUJ 200 til 25 mmuz....

I150

VIwa::0UJ....

c.t

50:;)U.....Ic.tu a 12 24 )6LENGTH OF PIPE (1'1'\)

...

FIG. 11 EFFECT OF LENGTH OF PIP E ELECTRODEON CALCULATED RESISTANCE FOR SOIL

RESISTIVITY OF 100 n m (ASSUMED UNIFORM)Cruciform and star shaped sections are also

available and are more rigid while being driven,but the apparent additional surface does no t confer a noticeable advantage in current-carryingcapacity or reduction of resistance. In circumstances where it is convenient to do so, the additionof radial strips will be advantageous.

Such rods may be coupled together to givelonger lengths. Except in special conditions, anumber of rods in parallel are to be preferred toa single long rod. Deeply driven rods are, howver, effective where the soil resistivity decreaseswith depth or where substrata of low resistivityoccur at depths greater than those with rods, foreconomic reasons, are normally driven. In suchcases the decrease of resistance with depth of driving may be very considerable as is shown by themeasurements plotted in Fig. 12 for a number ofsites; for curves AI an d A2, it wa s knownfrom previously sunk boreholes that the soildown to a depth between 6 an d 9 m consisted ofballast, sand an d gravel below which occurredLondon clay. Th e rapid reduction in resistance,when the electrodes penetrated the latter, wasvery marked. Th e mean resistivity up to a depthof 8 m in one case wa s l50.Qm; at 11 m the meanvalue for the whole depth was 20 Q m moving toth e low resistivity of the clay stratum. Similarlyfor curve C, the transition from gravely soil toclayey at a depth of about 15 m wa s very effective. In the case of curve B, however, no such marked effect occurred, although there wa s a gradual

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IS : 3043 - 1987

30 0200 ,100 ,80 "1 "0 ......"40 "\\c:; \

I.LI 20 ,u \4: ,0- lD ,I) ,en 8 ,w ,ex: 6,

20 1 6 9LENGTH OF DRIVEN ELtC'TRODE m

.....

F[G. [2 CALCULATED AND EXPER[MENTAL CURVES OF RES [STANCE OF [3 mm DIADR[VEN ELECTRODES

reduction in average resistivity with increase indepth, as can be seen by comparison with the dotted curves, which are calculated on the assumptionof uniform resistivity.

Other factors that affect a decision whether todrive deep electrodes or to employ several rods orpipes in parallel are the steep rise in the energyrequired to drive them with increase in depth an dthe cost of couplings. Th e former can be offset byreducing the diameter of the rods, since a 13 mmdiameter rod can be driven to considerable depthswithout deformation or bending if th e techniqueof using a large number of comparatively lightblows is adopted rather than a smaller number ofblows with a sledge hammer. Power-driven hammers suitable for this purpose are available.

In cases where impenetrable strata or highresistivity soil occur at relatively small depths, considerable advantage ma y result from driving rodsat an angle of about 30 to the horizontal, thusincreasing th e length installed for a given depth.

9.2.3 Strip or Conductor Electrodes - Thesehave special advantages where high resistivity soilunderlies shallow surface layers of low resistivity.Th e minimum cross-sectional area of strip electro-

21

des shall be according to 12.1.1. Ifround conductors are used as earth electrodes, their crosssectional area shall not be less than the sizesrecommended for strip electrodes. Th e resistanceR is given by:

R:::: lOrp loge ~ ohms!!'rtl . w twhere

p resistivity of th e soil ( in Q.m) (assumed uniform);

I = length of the strip 111 cm;w = depth of burial of the electrode in cm;

andt = width (i n the case of s tr i p) or twice

the diameter (fir conductors) in cm.Care should be taken in positioning these elec

trodes, especially to avoid damage by agriculturaloperations.

Figure 13 shows the variation of calculatedearth-resistance of strip or conductor electrodes

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IS : 3043 - 1987with length for a soil reslsttv ity of 100 n.m. Theeffect of conductor size an d depth over the rangenormally used is very small.

If several strip electrodes are required for connection in parallel in order to reduce the resistance, they may be installed in parallel lines or theymay radiate from a point. In the former case, theresistance of two strips at a separation of 2.4 m isless than 65 percent of the individual resistance ofeither of them.

a 12

\""Z'10cft/ \ 8iiiwQ:: 6 \a I':i , f...J:::>u. . . j

21fu0 60 120 180 2' 0 )0 0

LENG1H(m)

FIG. 13 EFFECT OF LENGTH OF STRIP ORCONDUCTOR ELECTRODES IN CALCULATED

RESISTANCE FOR SOIL RESISTIVITY OF IDa Qm(ASSUMED UNIFORM)

9.2.4 Water Pipes - Water pipes shall not beused as consumer earth electrodes.NOTE - In urban districts and other areas where

piped water supply is available th e use of water pipesfor consumers' earth electrodes has been common in th epast. Though this was generally very effective whenconsumers' pipes and water-mains to which they wereconnected were al l metal-to-metaljoints, the use ofpublic water-pipes for this purpos e has not been acceptable for many years because of the use of nonconducting material fo r pipes on new installations and forreplacement purposes. Jointing techniques now beingused do not ensure electrical continuity of metallicpipes.

For new installations, therefore, a public waterpipe may not be used as a means of earthing.Metallic pipe systems of services other than waterservice (for example, for flammable liquids orgases, heating systems, etc) shall not be used asearth electrodes for protective purposes. Bondingof the water service with the exposed metalworkof the electrical installation (0 n the consumers'side of any insulating insert) and any other extraneous metalwork to th e installation earthingterminal is, however, permissible and indeed ne-

cessary in most circumstances subject to the proVISIOn of earthing facilities that are satisfactorybefore these bonding connections are made.

For existing installations in which a water pipeis used as a sole earth electrode; an independentmeans of earthing should be provided at the firstpracticable opportunity.

9.2.5 Cable Sheaths - Where an extensiveunderground cable system is available, the leadsheath and armour form a most effective earthelectrode. In the majority of cases, the resistanceto earth of such a system is less than I n.A freshlyinstalled jute or hessian served cable is insulatedfrom earth, but the insulation resistance of thejute deteriorates according to the moisture contentand nature of the soil. However, cable sheaths arcmore commonly used to provide a metalli c pathto th e fault current returning to the neutral.

9.2.6 Structural Steelwork - The resistance toearth of steel frames or reinforced concrete buildings will vary considerably according to the typeof soil and its moisture content, and the design ofthe stanch ion bases. For this reason, it is essentialto measure th e resistance to earth of any structural steetwork that it is employing and at frequentintervals thereafter.

NOTE - Special care is necessary where the construction includes prestressed concrete.

9.2.7 Reinforcement of Piles - At power stationsand large substations, it is often possible to securean effective earth-electrode by making use of thereinforcement in concrete piles. The earth strapshould be bonded to a minimum of four piles andall the piles between the bonds should be bondedtogether. Each set of four piles should be connected to the mai nngearthi-strap of the substation.

22

9.2.8 Calhodicallv ProtectedStructures- Cathodicprotection is n o r m ~ d l y applied to ferrous structures in order to counteract electrolytic corrosionat a metal to electrolyte interface.

The electrolyte IS generally the ground 111which the structure is either wholly or partiallyburied an d the protection system relies uponmaintaining the metalwork at a slightly morenegative potential than it would exhibit by halfcell measurements, if no corrective action hadbeen taken.

Th e application of cathodic protection variesaccording to circumstances between bare metal incontact with ground and metal that has been

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deliberately coated or wrapped against corrosion.In the latter case, cathodic protection is used tosupplement the coating and guard against localizedcorrosion due to coating flaws or faults. Protectivesystem current drain is proportional to the area ofbare metal in earth contact and if a normalearthing electrode is attached to a cathodicallyprotected structure, the increased drain currenttaken by the electrode could be .completely unacceptable. This is especially true where the systemhas been designed to protect a well wrapped orcoated structure.

Nevertheless, there may be a necessity to connect earth electrodes to cathodically protectedstructures, especially where the coating or wrapping tends to electrically insulate the structure fromground, for example:a) diversion of earth fault currents from electrical apparatus mounted on the structure;b) diversion ofstray current to ground, a problem often met where well coated pipelinesare substantially parallel to the route of ahigh voltage overhead line;c) prevention of elevated voltages where structures encroach into hazardous (f1ammab Ie) areas; andd) Prevention of power surges into the apparatus providing cathodic protection, or similarinvasion of delicate low current instrumentation circuits.Tn addition to the guidance given in 9.3,selection of metals for earth electrodes and determination of their ground contact area is mostimportant where cathodically protected structuresare involved.The material selected should exhibit a galvanicpotential with respect to ground as nearly equalto that exhibited by the structure in its naturalor unprotected condition. For ferrous structures,austenitic iron (austenitic cast nickel chromiumalloy with spheroidal graphite present) is oftenused. Vertically driven rods of this material arepreferred in order to minimize contact area andthus reduce cathodic protection drain, whilstobtaining optimum performance fi:om the electro

de. Copper should be avoided, wherever possible,not only for its increased drain but also for itsability to become cathodi c to the protected structure. Magnesium or zinc electrodes have beenused successfully, but are anodic to the protectedstructure and thus sacrificial in action.9.3 Selection of Metals for Earth-Electrodes- Although electrode material does not affect initial earth resistance, care should be taken to selecta material that is resistant to corrosion in the typeof soil in which it will be used. Tests in a widevariety of soils have shown that copper, whether

23

IS : 3043 - 1987tinned or not, is entirely satisfactory (subject tothe precautions given in this subclause), the average loss in weight of specimens 150 mm x 25mm x 3 mm buried for 12 years in no case exceed0-2 percent per year. COiTesponding averagelosses for unprotected ferrous specimens (forexample, cast iron, wrought iron or mild steel) usedin the tests were as high as 22 percent per year.Considerable and apparently permanent protectionappears to be given to mild steel by galvanizing,the test showing galvanized mild steel to be littleinferior to copper with an average loss not greaterthan 05 percent per year. Only in a few caseswas there any indication in all these tests tha tcorrosion was accelerating and in these cases theindications were not very significant.

The possibility on damage to cables and otherunderground services and structural metalwork inthe vicinity of earth-electrode due to electrolyticaction between dissimilar materials should not beoverlooked when the material for earth-electrodesis selected. Materials compatible with other metalstructures in the vicinity should be selected orother remedial action taken.

It may be essential to use materials of typesother than those mentioned earlier in special circumstances, when cathodically protected structuressuch as pipelines are encountered.A modem high pressure gas pipeline, wrappedand cathodically protected may have a galvanicpotential of - 0-5 V, the accepted material of cop

per for an earth electrode with a galvanic potentialof -0 2 V decreases the total galvanic voltage andincreases the need for current from the corrosionprotection impressed current system, when theearth electrode is connected to the pipeline.An earth electrode with a galvanic potentialnearer to the protected structure has to be used toovercome the above and be certain the pipeline isbeing protected. Such a material is termed anaustenitic iron and is an austenitic cast nickelchromium alloy, with spheroidal graphite present.It may be necessary to earth the pipeline forone or more of the following reasons:a) It should not on its own be a carrier of anylow voltage fault current,b) It may have low voltage equipment connected to it, for example, for the purpose ofvalve operation;c) It may have instrumentation connected toit that require it to be earthed for this purpose and to provide a signal reference earthas well as for earthing requirement relativeto electrical equipment used in hazardousareas; and

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IS : 3043 - 1987d) It may require connection to earth atpoints to discharge unwanted induced currents and voltages from other sources suchas overhead lines.These four points lead to a compromisebetween the need to have a low earth value for instrumentation reference purposes, which mayrequire a lot of buried metal, and a reasonableearth value for electrical purposes against the corrosion protection requirement to have a minimum of

buried bare metal connected to the pipeline, an dthus drawing a corrosion protection current thatmay be required by the pipeline.9.4 Typical installations of pipe earth electrodeand plate earth electrode are shown in Fig. 14and 15.9.5T.vpical j\1ethod or Jointing ofConductors-Methods of jointing conductors are shown inFig. 16.

2 400

. . 6S PVCCONDUITEMBEDDED

DETAIL A

2SQ

A HOMOGE.NOUSLAYER OF ' COKE ICHARCOAL, SALTAND SAND

NOTE - After l aying the earth from the earth bus to the electrode through the PVG conduits at the pi tentry conduits should be sealed with bitumin compound.

All dimensions in millimetres.FIG. 14 TYPICAL ARRANGEMENT OF PIPE ELECTRODE

24

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c

WU,D

lOOOdOOx600INSPECTIONCHAMBER

1200 II 1200 1112CI PLATE61 BOLT LENGTH

DETAIL

D E T A I ~ 8

A

IS : 3043 - 1987

fJ; 12'116 LONG G I BOLTS" NUTS,CHECK NurTWASHER CAfTER FIXING"THE. OUTSIOE SURfAC.SHOULO It COVERED'HI T H aITUMIN)

12 60 LONG G I BOL.TS II. NUTS"CHECK NUT &. WASHER (ArTERf iXING, THE OUTER SURfACE SHOULDBE COVERlO WITH B,T'UMIN)

. . . . -=-.:..::::..--41J14 \25 _19" GI PLATE FOR ClAt.4PSO mm Q 100 rn (AFTERFIXING, THE OUTSIDESURFACE SHOULO IeCOVERED WITH BITUMIN) DETAIL C

All dimensions in millimetres,FIG. 15 TYPICAL ARRANGEMENT OF PLATE ELECTRODE

PUSH B U T T O ~Sf AflON ISTAfHE R

16A Earthing Arrangement for Motors with Push Button Station/Starter Earth Connections toStarter Looped from Earth Connections of MotorFIG 16. TYPICAL EARTHING CONNECTION DETAILS - Contd

25

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IS : 3043 - 1987

GI BOLTS AND NUTS,FLATWAS HER AND G I SPRINGWASHER lAFTER FIXING,THEOUT SIO SURFACE SHOULD8E COVERED WITH BITUMINOR GREASE)EQUIPMEf\&-T ISTRIP

168 Arrangement of Double Earth Connection to Equipments (Strip to Conductor Connection)

BRAZING FOR COPPER AND WELDINGF OR ALUMINIUM

16C Straight Joint (Strips) 160 'T' Joint (Strips)

FLAT WASHER AND SPRING WASHER{GIJTO BE CONNECTED USfNG G I SOlTSAND NUTS--------_

16E Arrangement of Strip to Strip and Stripto Equipment Connection

2_ mm TfNNE 0 COPPER81NDING WIRE ANO THEJOINT TO 8E SOLDEREDALUMINIUMI COPPERCONDUCTOR

16F Conductor to Conductor Joint(Round Conductors)FIG. 16 TYPICAL EARTHING CONNECTION DETAILS

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10. CURRENT DENSITY AT THE SURFACEOF AN EARTH-ELECTRODE10.1 An earth electrode should