AS 3007.21987

Australian Standard

Electrical installationsSurfacemines and associated processingplant

Part 2: General protectionrequirements

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This Australian standard was prepared by Committee EL/33, Electrical Installations forOutdoor Sites Under Heavy Conditions (Including Open-cast Mines and Quarries). Itwas approved on behalf of the Council of the Standards Association of Australia on27 February 1987 and published on 4 May 1987.

The following interests are represented on Committee EL/33:

Association of Consulting Engineers Australia

Australian Electrical and Electronic Manufacturers Association

Australian Institute of Mining and Metallurgy

Confederation of Australian Industry

Department of Industrial Relations, N.S.W.

Department of Mines, Qld

Department of Mines, Tas.

Electricity Supply Association of Australia

Mining Interests

Review of Australian Standards. To keep abreast of progress in industry, Australian Standards are subjectto periodic review and are kept up to date by the issue of amendments or new editions as necessary. It isimportant therefore that Standards users ensure that they are in possession of the latest edition, and anyamendments thereto.Full details of all Australian Standards and related publications wil l be found in the Standards AustraliaCatalogue of Publications; this information is supplemented each month by the magazine The AustralianStandard, which subscribing members receive, and which gives details of new publications, new edit ionsand amendments, and of withdrawn Standards.Suggestions for improvements to Australian Standards, addressed to the head off ice of Standards Australia,are welcomed. Noti fication of any inaccuracy or ambiguity found in an Australian Standard should be madewithout delay in order that the matter may be investigated and appropriate action taken.

This Standard was issued in draft form for comment as DR 85325.

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AS 3007.21987

Australian Standard

Electrical installationsSurfacemines and associated processingplantPart 2: General protectionrequirements

First published . . . . . . . . . . . . . . . . . . . . . . . . 1982Second edition . . . . . . . . . . . . . . . . . . . . . . . . 1987

PUBLISHED BY STANDARDS AUSTRALIA(STANDARDS ASSOCIATION OF AUSTRALIA)1 THE CRESCENT, HOMEBUSH, NSW 2140

ISBN 0 7262 4614 X

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AS 3007.21987 2

PREFACE

This standard was prepared by the Associations Committee on Electrical Installations for OutdoorSites Under Heavy Conditions (including Open-cast Mines and Quarries) to supersede AS 3007,Part 21982.It is essentially identical with IEC 621-2, as supplemented by IEC 621-2A, which were preparedby the corresponding IEC Technical Committee, i.e. TC 71. The alterations incorporated in thisnew edition stem primarily from several amendments to IEC 621-2 which have recently beenpublished or which are in the final stages of preparation, viz:(a) Amendment No 1 (1984) see Section 4 and Appendix B herein.(b) Amendment No 2 (1986) see Clause 2 and Table 2 herein.(c) A further amendment, in course of publication, based on IEC Document 71(Central Office)34

see Clause 7, Table 5 and Figs 1 to 4 herein.Where this standard deviates technically from IEC 621-2 (including the amendments describedabove) by way of different or additional requirements, this is indicated by a rule in the marginagainst the clause, or part thereof, affected. A summary of such technical variations is given in theAnnex.The Australian Committee (EL/33) has actively participated in the work of IEC TC 71 which hasas its objective the development of uniform and internationally acceptable rules for the safe use ofelectricity in open-cast mines, quarries, stockpiles and the like. Such applications presentparticularly onerous conditions for the electrical apparatus and systems, including continualalteration of the location of the apparatus and systems, extension of the operational area, andadverse environmental conditions. Because of the size of the plant and the need for mobility,supply is frequently at high voltage over long distances, by means of trailing cables. This shouldbe compared with other industries where the electrical installations are generally fixed.The AS 3007 series specifies requirements for the installation and operation of electrical apparatusand systems in the above mentioned locations, with the object of ensuring the safety of persons,livestock and property. AS 3007.1 outlines the scope of the AS 3007 series and provides definitionsfor some of the terms used. AS 3007.2 (this standard) specifies measures which are required forprotection against electric shock in normal service from direct contact with live parts, for protectionagainst electric shock from parts which may become live in the event of a fault (indirect contact),and for protection against the effects of overcurrent resulting from overload or short-circuitconditions. AS 3007.3 prescribes general requirements for equipment and ancillaries associated withthe electrical installation. AS 3007.4 sets out the requirements which are specific to particularinstallations, together with exemptions from the general requirements of AS 3007.2 and 3, whichapply for such installations. AS 3007.5 sets out the normal operating procedures which should becarried out to ensure the safety of personnel.The AS 3007 series recognizes several types of power supply system and specifies the protectivemeasures which are necessary for each system. Requirements for protection of persons fromindirect contact (see Section 2 of this standard) are based on the concept of permissible voltageversus time limits, which take into account the pathophysiological effects of electric current passingthrough the human body, typical industry conditions, and the probability of persons being in contactwith the plant. In this and other respects the AS 3007 series differs in approach from the practicallyevolved requirements of AS 3000, SAA Wiring Rules.It will therefore be necessary for the regulatory authorities concerned to clearly delineate therespective areas of application for the AS 3007 series and for AS 3000.

Copyright STANDARDS AUSTRALIAUsers of Standards are reminded that copyright subsists in all Standards Australia publications and software. Except where the Copyright Actallows and except where provided for below no publications or software produced by Standards Australia may be reproduced, stored in aretrieval system in any form or transmitted by any means without prior permission in writing from Standards Australia. Permission may beconditional on an appropriate royalty payment. Requests for permission and information on commercial software royalties should be directedto the head office of Standards Australia.

Standards Australia will permit up to 10 percent of the technical content pages of a Standard to be copied for use exclusively in-house by purchasers of the Standard without payment of a royalty or advice to Standards Australia.Standards Australia will also permit the inclusion of its copyright material in computer software programs for no royalty paymentprovided such programs are used exclusively in-house by the creators of the programs.

Care should be taken to ensure that material used is from the current edition of the Standard and that it is updated whenever the Standard isamended or revised. The number and date of the Standard should therefore be clearly identified.The use of material in print form or in computer software programs to be used commercially, with or without payment, or in commercialcontracts is subject to the payment of a royalty. This policy may be varied by Standards Australia at any time.

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3 AS 3007.21987

CONTENTS

Page

SCOPE OF PART . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

REFERENCED DOCUMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

SECTION 1. PROTECTION AGAINST DIRECT CONTACT1 GENERAL REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 COMPLETE PROTECTION BY MEANS OF BARRIERS OR ENCLOSURES . . . . 73 COMPLETE PROTECTION BY INSULATION OF LIVE PARTS . . . . . . . . . . . . . 94 PARTIAL PROTECTION BY PLACING LIVE PARTS OUT OF REACH . . . . . . . 95 PARTIAL PROTECTION BY THE PROVISION OF OBSTACLES . . . . . . . . . . . . 96 MINIMUM DISTANCES TO BE OBSERVED IN OPERATING AND

MAINTENANCE GANGWAYS FOR INDOOR INSTALLATIONS . . . . . . . . . . . . 97 MINIMUM CLEARANCES FOR OUTDOOR INSTALLATIONS . . . . . . . . . . . . . . 9

SECTION 2. PROTECTION AGAINST INDIRECT CONTACT A.C.8 GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 TN, TT AND IT SYSTEMS DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

10 PROTECTION MEASURES FOR TN SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . 1611 PROTECTION MEASURES FOR TT SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . 2212 PROTECTIVE MEASURES FOR IT SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . 2213 REQUIREMENTS FOR EARTH FAULT CURRENT LIMITATION DEVICES . . . 2314 EARTHING ARRANGEMENTS AND PROTECTIVE CONDUCTORS . . . . . . . . . 23

SECTION 3. PROTECTION AGAINST OVERCURRENT15 GENERAL RULE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2916 NATURE OF PROTECTIVE DEVICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2917 AUTOMATIC INTERRUPTION-PROTECTION AGAINST

OVERCURRENT DUE TO OVERLOAD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2918 AUTOMATIC INTERRUPTION-PROTECTION AGAINST

SHORT CIRCUITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3019 COORDINATION OF OVERLOAD AND SHORT-CIRCUIT PROTECTION . . . . . 3120 LIMITATION OF OVERCURRENT BY CHARACTERISTICS OF

SUPPLY OR LOAD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

SECTION 4. SELECTION OF PROTECTIVE DEVICES AND PROTECTION SYSTEMS21 BASIC REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3222 SELECTION PROCEDURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3223 DISCRIMINATION BETWEEN PROTECTIVE DEVICES . . . . . . . . . . . . . . . . . . 32

APPENDICESA SELECTION OF FACTOR k FOR CALCULATING THE MINIMUM

CROSS-SECTIONAL AREA OF PROTECTIVE CONDUCTORS . . . . . . . . . . . . . 35B DESCRIPTION OF CERTAIN TYPES OF PROTECTIVE DEVICES AND

THEIR USES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

ANNEX. SUMMARY OF TECHNICAL DEVIATIONS BETWEENTHIS STANDARD AND IEC 621-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

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AS 3007.21987 4

Page

TABLES1 MINIMUM CLEARANCES BETWEEN FIELD INSTALLED BARE

CONDUCTORS AND BETWEEN SUCH CONDUCTORS ANDEARTHED PARTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2 RELATION BETWEEN DEGREES OF POLLUTION ANDCREEPAGE DISTANCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3 MINIMUM PROTECTION AGAINST DIRECT CONTACT BY BARRIERSOR ENCLOSURES (APPLICABLE TO LIVE PARTS ONLY) . . . . . . . . . . . . . . . 10

4 MINIMUM DISTANCES TO BE OBSERVED IN OPERATING ANDMAINTENANCE GANGWAYS FOR INDOOR INSTALLATIONS . . . . . . . . . . . 11

5 MINIMUM CLEARANCES FOR FIELD-INSTALLED BARE LIVE PARTS INOUTDOOR INSTALLATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

6 PROSPECTIVE TOUCH VOLTAGE/OPERATING TIME CHARACTERISTICSFOR SYSTEMS UP TO AND INCLUDING 1000 V . . . . . . . . . . . . . . . . . . . . . . 15

7 PROSPECTIVE TOUCH VOLTAGE/OPERATING TIME CHARACTERISTICSFOR SYSTEMS ABOVE 1000 V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

8 MINIMUM SIZE OF EARTHING CONDUCTORS . . . . . . . . . . . . . . . . . . . . . . . 249 SELECTION OF MINIMUM CROSS-SECTIONAL AREA FOR

PROTECTIVE CONDUCTORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2710 MINIMUM CROSS-SECTIONAL AREA OF AERIAL AND

SUSPENDED PROTECTIVE CONDUCTORS . . . . . . . . . . . . . . . . . . . . . . . . . . 2711 MINIMUM CROSS-SECTIONAL AREA OF SUPPLEMENTARY

EQUIPOTENTIAL BONDING CONDUCTORS . . . . . . . . . . . . . . . . . . . . . . . . . 2812 SUMMARY OF CRITERIA FOR PROTECTION AGAINST

INDIRECT CONTACT AND PROTECTIVE DEVICES ORPROTECTIVE MEASURES WHICH MAY BE USED . . . . . . . . . . . . . . . . . . . . . 33

13 VALUES OF FACTOR k FOR CALCULATING THE MINIMUMCROSS-SECTIONAL AREA OF PROTECTIVE CONDUCTORS . . . . . . . . . . . . . 35

14 SUGGESTED INITIAL AND FINAL TEMPERATURES FORPROTECTIVE CONDUCTORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

FIGURES1 CLEARANCES FROM LIVE PARTS AT THE OUTER BOUNDARY FENCE . . . 132 MINIMUM HEIGHT OF LIVE PARTS ABOVE ACCESSIBLE AREAS IN

OUTDOOR INSTALLATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 CLEARANCES FROM LIVE PARTS FOR OUTDOOR INSTALLATIONS

WITH VOLTAGES UP TO AND INCLUDING 30 kV . . . . . . . . . . . . . . . . . . . . 144 CLEARANCES FROM LIVE PARTS FOR OUTDOOR INSTALLATIONS

WITH VOLTAGES ABOVE 30 kV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 GRAPHICAL REPRESENTATION OF TABLE 6 . . . . . . . . . . . . . . . . . . . . . . . . 176 GRAPHICAL REPRESENTATION OF TABLE 7 . . . . . . . . . . . . . . . . . . . . . . . . 177 POWER SYSTEM TN WITH SEPARATE NEUTRAL AND

PROTECTIVE CONDUCTORS THROUGHOUT THE SYSTEM . . . . . . . . . . . . . 188 POWER SYSTEM TN WITH NEUTRAL AND PROTECTIVE FUNCTIONS

COMBINED IN A SINGLE CONDUCTOR IN A PART OF THE SYSTEM . . . . . 189 POWER SYSTEM TN WITH NEUTRAL AND PROTECTIVE FUNCTIONS

COMBINED IN A SINGLE CONDUCTOR THROUGHOUT THE SYSTEM . . . . . 1910 POWER SYSTEM TT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1911 POWER SYSTEM IT WITH INDEPENDENT EARTH ELECTRODES . . . . . . . . . 2012 POWER SYSTEM IT WITH COMMON EARTH ELECTRODE . . . . . . . . . . . . . . 2013 POWER SYSTEM IT USING EXTERNAL TT OR

TN SYSTEM AS A SOURCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2114 ILLUSTRATION OF THE ELEMENTS OF A

TYPICAL EARTHING ARRANGEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

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Page15 DIAGRAM FOR DETERMINING CONDUCTOR LENGTH ON LOAD SIDE

FOLLOWING REDUCTION IN CROSS-SECTIONAL AREA . . . . . . . . . . . . . . . 3116 CHART SHOWING THE PROCEDURE FOR THE SELECTION OF

PROTECTION SYSTEMS (INCLUDING APPLICABLE CRITERIA ANDEXAMPLES OF PROTECTIVE DEVICES WHICH MAY BE USED) . . . . . . . . . . 34

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AS 3007.21987 6

STANDARDS ASSOCIATION OF AUSTRALIA

Australian Standardfor

ELECTRICAL INSTALLATIONSSURFACE MINES ANDASSOCIATED PROCESSING PLANT

PART 2 GENERAL PROTECTION REQUIREMENTS

SCOPE OF PART

This standard prescribes general protection requirements for electrical installationswithin the scope of AS 3007.1. It outlines the measures which are required forprotection against electric shock in normal service from direct contact with live parts;for protection against electric shock from parts which may become live in the eventof a fault (indirect contact); and for protection against the effects of overcurrentresulting from overload or short-circuit conditions.

REFERENCED DOCUMENTS

The following standards are referred to in this standard:AS 1243 Voltage Transformers for Measurement and ProtectionAS 1675 Current Transformers for Measurement and ProtectionAS 1824.1 Insulation Coordination (Phase-to-earth and phase-to-phase, above 1 kV)

Part 1 Basic Principles, Standard Insulation Levels and TestProcedures

AS 1824.2 Insulation Coordination (Phase-to-earth and phase-to-phase, above 1 kV)Part 2 Application Guide

AS 1939 Classification of Degrees of Protection provided by Enclosures forElectrical Equipment

AS 2005 Fuses with Enclosed Fuse-Links (up to and including 1000 V a.c. and1500 V d.c.)Part 2 Fuses for Industrial Application

AS 3007.1 Electrical Installations Surface Mines and Associated Processing PlantPart 1 Scope and Definitions

AS 3007.4 Electrical Installations Surface Mines and Associated Processing PlantPart 4 Additional Requirements for Specific Applications

IEC 364 Electrical Installations of Buildings364-3 Part 3: Assessment of General Characteristics364-4-41 Part 4: Protection for Safety

Chapter 41: Protection Against Electric ShockIEC 815 Guide for the Selection of Insulators in Respect of Polluted ConditionsIEC XXX Protection (Protective) Systems (in preparation).

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7 AS 3007.21987

SECTION 1. PROTECTION AGAINST DIRECT CONTACT(Protection against electric shock in normal service)

INTRODUCTION. In this Section, the requirementsfor protection against direct contact are described forall installations with voltages up to and including1000 V and with those above 1000 V. Therequirements for installations for voltages up to1000 V are taken over essentially from IEC 364, asapplicable.

1 GENERAL REQUIREMENTS. Except asprovided in Clause 1.1, protection against directcontact shall be provided by compliance with therequirements contained in Clause 6 and in one of theClauses 2, 3, 4 or 5.1.1 Exceptions to the general requirements.

(a) Limitation of voltage. Protection against directcontact is deemed to be ensured where safetyextra-low voltage or functional extra-lowvoltage is used in accordance with therequirements of IEC 364-4-41.

(b) Limitation of discharge of energy. Protectionagainst direct contact is deemed to be ensuredwhere the energy available from the supplysource is limited to a safe value.

(c) Neutral and protective conductors . Protectionagainst direct contact for neutral and protectiveconductors is deemed to be ensured when suchconductors are installed in accordance with theapplicable clauses (see Clauses 8.1, 10.5, 11.1and 12.2).

2 COMPLETE PROTECTION BY MEANS OFBARRIERS OR ENCLOSURES.2.0 General. Barriers or enclosures are intended toprevent contact of persons or livestock with live partsof the electrical installation.The minimum clearance distances in air betweenfield-installed bare conductors and between suchconductors and earthed parts (such as barriers andenclosures) shall be in accordance with Table 1. Theclearance distances specified need not apply withinelectrical apparatus, wiring devices or manufacturedassemblies.The clearance distances in Table 1 have been derivedfrom Appendix D of AS 1824.2 based on the mostunfavourable conditions, viz. rod-structure electrodeconfiguration and highest category of impulsewithstand voltage. Smaller clearance distances thanthose specified in Table 1 may be adopted (a) where it is known that the lightning exposure

level is low; or(b) where surge protection limits impulse voltages to

lower values than specified in Appendix D ofAS 1824.2.

Appropriate guidance may be obtained by referenceto AS 1824.1 and AS 1824.2.For equipment with a designed impulse withstandvoltage, equipment dimensions may result in

clearances of less than those in Table 1 at theconductor terminations; consequently, conductors inthe connection zone may need to be insulated.Where the conductor under consideration isimmediately adjacent to a conductor of a highervoltage, the clearance distance applicable to thehigher voltage shall apply between the conductors.Constructional or environmental conditions such asconductor swing due to wind or short circuit,construction tolerances, the likelihood of snow or ice,may necessitate the use of clearance distances inexcess of those specified in Table 1.The creepage distances between field-installed liveconductors and earthed parts, such as barriers andenclosures, shall be not less than the value specifiedin Table 2 appropriate to the degree of pollutionexpected.The creepage distances given in Table 2 shall bemultiplied by the ratio U phase-to-phase/ U phase-to-earth (3 for a three-phase system) for the followingcases:

(a) Where IT systems are used.(b) Where insulators are used between phases, e.g.

phase spacers.

TABLE 1MINIMUM CLEARANCES BETWEEN FIELD

INSTALLED BARE CONDUCTORS ANDBETWEEN SUCH CONDUCTORS AND

EARTHED PARTSSystem voltage Minimum clearance

distanceNominal voltage Highest voltagekV, r.m.s. kV, r.m.s. mm

1.13.36.6

1.23.67.2

406090

112233

122436

120220320

66110150

72.5123170

63011001500

220 245 2100

2.1 Protection from live parts. All live parts shallbe inside enclosures or behind barriers providing atleast the degrees of protection in accordance withTable 3.2.2 Strength and stability of barriers andenclosures. Barriers and enclosures shall be firmlysecured in place. Taking into account their nature,size and arrangement, they shall have sufficientstability and durability to resist the strains andstresses likely to occur in normal service.

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AS 3007.21987 8

TABLE 2RELATION BETWEEN DEGREES OF POLLUTION AND CREEPAGE

DISTANCES

Pollution degree Significant characteristics(see Notes 1, 2 and 3)Minimum specific nominal creepage

distance between phase and earth(see Notes 4 and 5)

mm/phase-to-phase kV

ILight

No pollution or only dry, non-conductivepollution occurs. The pollution has noinfluence.

16

IIMedium

Normally, only non-conductive pollutionoccurs. Occasionally, however, atemporary conductivity caused bycondensation must be expected.

20

IIIHeavy

Conductive pollution occurs, or dry,non-conductive pollution occurs whichbecomes conductive due to condensation.

25

IVVery heavy

The pollution generates persistentconductivity caused, for instance, byconductive dust or by rain or snow.

31

NOTES:1. It should be realized that any tabulation of pollution characteristics cannot cover the complete range of

pollution possible and hence it may be necessary, in particular cases, to increase creepage distances forthe special pollution encountered. Consideration should also be given to the possibility of varyingpollution levels due to seasonal changes and exceptional climatic conditions.

2. Except for Pollution degree I, condensation of water must always be considered arising from either (a) the temperature of the insulation surface falling below the dew-point of the surrounding air; or(b) hygroscopic dust or salt contamination causing moisture to deposit at low relative humidity.

3. Conductive dusts may originate from the environment (e.g. material being mined or processed), orfrom within an enclosure (e.g. dust from carbon or metallic brushes).

4. The creepage distances in Table 2 have been derived from test data for normal porcelain and glassinsulators. For more detailed guidance on the selection of insulators, see IEC 815.

5. The voltage corresponds to the system highest voltage (phase-to-phase).

2.3 Access to installation. Where it is necessary tomake provision for the removal of barriers, the openingof enclosures, or the withdrawal of parts of enclosures(doors, casings, lids, covers and the like), this shall be inaccordance with one of the following items:(a) Key or tool. Removal, opening or withdrawal shall

necessitate the use of a key or tool.(b) Interlocking device. An interlocking device shall be

provided so that removal, opening or withdrawalwithout the use of a key or tool necessitatesprevious switching off of all live parts behind thebarrier or enclosure which might be touchedaccidentally. Restoration of supply shall be possibleonly after replacement or reclosure of the barriers orenclosures.Provision shall be made for the discharge of storedenergy in capacitors or cable systems where theyare likely to give rise to the risk of electric shock.

(c) Automatic disconnection. Removal, opening orwithdrawal without the use of a key or tool shallinitiate automatic switching off before live partsbehind the barrier or enclosure can be touchedaccidentally. Restoration of supply shall be possibleonly after replacement or reclosure of the barriers orenclosures.

(d) Internal interposing screen. An internal interposingscreen shall be positioned so that none of the liveparts can be touched while the barrier or enclosureis removed. The screen shall meet the requirements

in Clause 2.1 (except as provided in Item (e) below)and Clause 2.2; it may be either firmly secured inplace or slid into place at the moment the barrier orenclosure is removed. It shall not be removableexcept by means of a tool or key.Such a screen may be a protective shutter which, inthe case of a disconnectable assembly, slides intoplace in front of the feed line contacts.

(e) Access to fuses or lamps. Where any parts behindthe barrier or enclosure need occasional handling(such as the replacement of a lamp or of afuse-link) the removal, opening or withdrawalwithout the use of a key or tool and withoutswitching off shall be possible only if the followingconditions are simultaneously fulfilled:(i) A second barrier shall be provided inside that

barrier or enclosure so as to prevent personsfrom coming accidentally into contact withlive parts not protected by another protectivemeasure.

However, this second barrier need not preventpersons from coming intentionally into contactwith live parts by bypassing it with the hand.Nevertheless, it shall not be possible toremove the second barrier except through theuse of a key or tool.

(ii) The voltage of all live parts behind the secondbarrier shall not exceed 1000 V.

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3 COMPLETE PROTECTION BY INSULATIONOF LIVE PARTS. The insulation is intended toprevent any contact of persons or livestock with liveparts of the electrical installation.3.1 Degree of insulation. Live parts shall becompletely covered with insulation which can beremoved only by destruction.3.2 Type of insulation. The insulation shall complywith the relevant requirements for the electricalequipment.4 PARTIAL PROTECTION BY PLACING LIVEPARTS OUT OF REACH. Placing out of reach isdesigned to prevent unintentional contact with live parts(see Table 3).Protection against shock in normal service by placinglive parts so as to be out of reach from all directions isconsidered to be ensured if no simultaneously accessiblelive parts are at distances less than the minimum statedin Table 4, for the appropriate voltage.If the extent of locations normally occupied by personsis limited by an obstacle which affords a degree ofprotection less than IP2X (see AS 1939), the distancespecified shall extend from this obstacle.Examples of such obstacles are handrails, open meshscreens and partial protective barriers.5 PARTIAL PROTECTION BY THE PROVISIONOF OBSTACLES. Partial protection by theinterposition of obstacles is designed to preventunintentional contact with live parts, but not intentionalcontact such as may result when a person deliberatelytries to circumvent the obstacles with his hand (seeTable 3).Protection against electric shock in normal service by theprovision of obstacles is considered to be ensured if suchobstacles prevent either (a) an unintentional bodily approach to live parts, this

being achieved by, for example, protective barriers,handrails or similar partitions; or

(b) an unintentional contact with live parts when liveequipment is handled during operation, for example,by the provision of screens or by protective handleson fuses.

The obstacle may be removable without the use of a toolor key, but it shall be secured in place in such a manneras to prevent involuntary removal.6 MINIMUM DISTANCES TO BE OBSERVED INOPERATING AND MAINTENANCE GANGWAYSFOR INDOOR INSTALLATIONS. Minimumdistances are intended to provide protection against directcontact while permitting access to and from gangwaysfor operating and maintenance purposes.6.1 Minimum distances. The minimum distances to beobserved in operating and maintenance gangways shallbe in accordance with Table 4. (Sec also Clause 6.2.)6.2 Minimum width. If it is not practicable to achievethe specified clearances, values less than the widthsshown in Table 4 may be used provided the degree ofprotection is equal to or greater than IP4X. In such casesthe minimum width may be reduced to 375 mm forrestricted gangways for lengths up to 2 m.6.3 Access. Access to and from maintenance andoperating gangways shall be in accordance with thefollowing:

(a) For voltages up to and including 1000 V. Forinstallations having a nominal voltage of not morethan 1000 V, operating and maintenance gangwaysof a length exceeding 20 m shall be accessible fromboth ends. For gangways shorter than 20 m butexceeding 6 m, access from both ends isrecommended.

(b) For voltages above 1000 V. For installationshaving a nominal voltage greater than 1000 V,operating and maintenance gangways of a lengthexceeding 6 m shall be accessible from both ends.For very long gangways, additional access ways arerecommended.

(c) Access doors. It is recommended that access doorsto gangways should (i) swing outwards;(ii) open without the use of hands; and(iii) have a free space outside the door of at least

1.5 m2 with width and length of approximatelyequal dimensions.

NOTE: Pressurized rooms and other special rooms may requiredoors to swing inwards.

7 MINIMUM CLEARANCES FOR OUTDOORINSTALLATIONS.7.1 Application. This clause specifies minimumclearances for outdoor installations from field-installedbare live parts to (a) boundary fences enclosing such live parts (see

Clause 7.2);(b) areas within the boundary fence to which persons

normally have access (see Clause 7.3); and(c) barriers installed within the boundary fence to

restrict the access of persons to the live parts (seeClause 7.4).

The minimum clearances are based on persons with areach of 2440 mm from ground and may not prevent aperson from reaching into the flashover area.Where the live parts consist of overhead linesprecautions shall be taken to ensure that minimumclearance distances are not reduced by conductor sag,wind forces, short-circuit forces, or insulator rupturewhen using multiple parallel insulator strings.7.2 Minimum clearances to boundary fences.Boundary fences enclosing bare live parts shall be of aheight of not less than 1800 mm. The boundary fenceshall be so located that the live parts are outside the zoneprescribed by Fig. 1 and Table 5, taking into account thetype of fencing used.

NOTE: The minimum height of the boundary fence and theminimum clearances from live parts are based on considerations ofprotection against direct contact. Additional measures may benecessary to restrict access.

7.3 Minimum clearances from accessible areas.Within areas that are accessible to persons such aspermanent walkways, platforms or other surfaces onwhich persons may normally stand, bare live conductorsshall be installed either (a) at a height above the area concerned of not less

than the appropriate value specified in Column 3 ofTable 5, or

(b) behind barriers which restrict access of persons tothe live parts in accordance with Clause 7.4.

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AS 3007.21987 10

In areas where heavy snow is experienced, the clearancesrequired by (a) shall be increased by the expectedcompacted depth of snow accumulation.

NOTE: See Fig. 2 for an illustration of the requirement of (a) above.7.4 Minimum clearances to barriers. Where bare liveparts within the boundary fence are at a height which is

less than the minimum value required by Clause 7.3(a),barriers shall be installed to restrict the access of personsto such live parts. The type, height and location of thebarrier shall be such that the live parts are outside therelevant zone prescribed in Figs 3 or 4 and Table 5. Theheight of the barrier shall in any event be not less than1100 mm.

TABLE 3MINIMUM PROTECTION AGAINST DIRECT CONTACT BY BARRIERS OR ENCLOSURES

(APPLICABLE TO LIVE PARTS ONLY)Voltage band

(a.c.) Within operating areasWithin electrical operating

areasWithin closed electrical

operating areas50 < U 1000 V Complete protection IP2X or IP4X

for top surfaces or barriers orenclosures which are readilyaccessible. This applies inparticular to those parts ofenclosures which might serve as astanding surface.

The use of floor plug and socketconnectors is not precluded butsuch sockets shall be covered whennot in use.

Partial protection IP1X ifU 600 V or no simultaneouslyaccessible parts at different voltagesare situated within arms reach.

No protection IP0X if live parts areplaced out of reach or obstacles,e.g. protective barriers or handrails,are interposed (see Clauses 4and 5).

Complete protection IP2X ifU < 600 V or IP4X if U > 600 Vfor top surfaces or barriers orenclosures which are readilyaccessible. This applies inparticular to those parts ofenclosures which might serve as astanding surface.

The use of floor plug and socketconnectors is not precluded butsuch sockets shall be covered whennot in use.

No protection IP0X if (a) U 600 V, or(b) live parts are placed out of

reach or obstacles, e.g.protective barriers orhandrails, are interposed (seeClauses 4 and 5).

Partial protection IP1X ifU > 600 V or no simultaneouslyaccessible parts at different voltagesare situated within arms reach.

The use of floor plug and socketconnectors is not precluded butsuch sockets shall be covered whennot in use.

U > 1000 V Complete protection IP5X withinarms reach.

Partial protection IP2X beyondarms reach.

Complete protection IP5X withinarms reach.

Partial protection IP1X beyondarms reach.

No protection IP0X if live parts areplaced out of reach or obstacles,e.g. protective barriers or handrails,are interposed (see Clauses 4and 5).

Partial protection IP1X.No protection IP0X if live parts areplaced out of reach or obstacles,e.g. protective barriers or handrails,are interposed (see Clauses 4and 5).

U = the nominal voltage of the installation between lines.

NOTES:1. See AS 1939 for details of the IP classifications. The IP classifications specified in Table 3 are only intended to specify the

degree of protection required against contact with live parts. Additional protection may be required for protection from contactwith moving parts or to prevent ingress of solid foreign bodies, such as dust.

2. For d.c. voltages, the voltage bands in Table 3 may be increased in the ratio of 1:1.5, namely up to 1500 V and above.

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11 AS 3007.21987

TABLE 4MINIMUM DISTANCES TO BE OBSERVED IN OPERATING AND MAINTENANCE GANGWAYS FOR INDOOR INSTALLATIONS

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

System voltageMinimum distances, mm

Complete protection as required in Table 3 Partial protection as required in Table 3

Nominalvoltage

Highestvoltage

Heightbelow

barriersor

enclosures

Width betweenobstacles or switchhandles and wall

Width betweenobstacles or switch

handles

Live parts on one side with IP1X protection Live parts on both sides with IP1X protection

Height oflive parts

abovefloorlevel*

Width between walland live part

Free pasage in frontof controls

Height oflive parts

abovefloorlevel*

Width between liveparts and conductors

on both sides

Free passagebetween controls

kV,r.m.s

kV,r.m.s. Maint. Opn Maint. Opn Maint. Opn Maint. Opn Maint. Opn Maint. Opn

1.13.36.6

1.23.67.2

200020002000

700800800

70010001000

70010001000

70012001200

230025002500

100010001000

100011651190

700800800

70010001000

230025002500

100013301380

120015301580

90010001000

110012001200

112233

122436

200020002000

800800800

100010001000

100010001000

120012001200

250025002550

101511151225

121513151425

800800800

100010001000

250025002550

143016301850

163018302050

100010001000

120012001200

66110

72.5123

20002000

800800

10001000

10001000

12001200

28003250

16002000

18002200

800800

10001000

28003250

26003400

28003600

10001000

12001200

* Where live part s are installed at or above the minimum height specified, no addit ional protection is required.

NOTE: Minimum distances for voltages above 110 kV are under consideration.Maint. = maintenance.Opn = operation.

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AS 3007.21987 12

TABLE 5MINIMUM CLEARANCES FOR FIELD-INSTALLED BARE LIVE PARTS IN OUTDOOR INSTALLATIONS1 2 3 4 5 6 7

System voltage H Horizontal clearances from live parts to barrierswithin the instsallation (Figs 3 and 4)

Horizontal clearances from live parts toouter fencing (Fig. 1)

Nominalvoltage

Highestvoltage

Minimum height oflive parts aboveaccessible areas(Figs 2, 3 and 4)

AFor solid barriers*

with a minimum heightof 1800 mm

BFor wire mesh or

screen barriers with aminimum beight of

1800 mm

CFor solid fences*with a minimum

height of 1800 mm

DFor wire mesh or

screen fences with aminimum height of

1800 mm

kV,r.m.s.

kV,r.m.s.

H = d + 2440mm

A = dmm

B = d + 100mm

C = d + 1000mm

D = d + 1500mm

3.66.6

11

3.67.2

12

250025302560

6090

120

160190220

106010901120

156015901620

223366

243672.5

266027603070

220320630

320420730

122013201630

172018202130

110150220

123170245

354037404540

110013002100

120014002200

210023003100

260028003600

* For solid barriers and fences, the horizontal clearances shall be measured from the face nearest to the live parts.d = The applicable minimum clearance distance specif ied in Table 1.

NOTE: The minimum clearances specif ied in Table 5 assume the lightning impulse withstand voltages given in Table 4.1 and 5.1 of AS 1824.2.

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13 AS 3007.21987

Live parts must be outside dotted zone

LEGEND:H = minimum clearance for overhead power linesC, D = minimum clearance required by Columns 6 and 7 respectively in Table 5d = minimum clearance specified in Table 1

Fig. 1. CLEARANCES FROM LIVE PARTS AT THE OUTER BOUNDARY FENCE

LEGEND:H = minimum clearance of live parts above accessible areas required by Column 3 of

Table 5. The clearance may need to be increased to take into account the conditionsreferred to in Clause 7.1 and 7.3.

Fig. 2. MINIMUM HEIGHT OF LIVE PARTS ABOVE ACCESSIBLE AREAS IN OUTDOOR INSTALLATIONS

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AS 3007.21987 14

Live parts must be outside dotted zone

(a) Solid barrier (b) Wire mesh or screen barr ierLEGEND:H = minimum clearance of live parts above accessible areas required by Column 3 of Table 5.

The clearance may need to be take into account the condit ions referred to in Clauses 7.1and 7.3

A & B = minimum clearances required by Columns 4 and 5 respectively in Table 5

DIMENSIONS IN MILLIMETRES

Fig. 3. CLEARANCES FROM LIVE PARTS FOR OUTDOOR INSTALLATIONS WITH VOLTAGES UP TO ANDINCLUDING 30 kV

Live parts must be outside dotted zone

(a) Solid barrier (b) Wire mesh or screen barr ier

LEGEND:H = minimum clearance of live parts above accessible areas required by Column 3 of

Table 5. The clearance may need to be take into account the condit ions referred to inClauses 7.1 and 7.3

A & B = minimum clearances required by Columns 4 and 5 respectively in Table 5d = minimum clearance specif ied in Table 1

DIMENSIONS IN MILLIMETRES

Fig. 4. CLEARANCES FROM LIVE PARTS FOR OUTDOOR INSTALLATIONSWITH VOLTAGES ABOVE 30 kV

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15 AS 3007.21987

SECTION 2. PROTECTION AGAINST INDIRECT CONTACT A.C.(Protection against electric shock in case of a fault)

INTRODUCTION. The protective measures specifiedare intended to prevent a touch voltage from persistingfor such a length of time after the occurrence of a faultthat danger to persons or livestock could arise. Themeasures have been developed from experience and fromconsideration of the probability of persons or livestockbeing in an indirect contact situation and of the nature ofthe plant involved in the fault situation.Protection shall be afforded in the case of an earth faultby either automatic disconnection of supply withinspecified conditions of voltage and time, or limitation ofindirect contact voltage below the conventional voltagelimit at which disconnection of the supply is notrequired.In this Section, the protective measures against indirectcontact with a protective conductor for all installationswith voltages up to and including 1000 V and thoseabove 1000 V are described. The requirements forinstallations for voltages up to and including 1000 V aretaken over essentially from IEC 364 as applicable.

8 GENERAL.8.1 Use of protective conductors. All exposedconductive parts shall be connected to a protectiveconductor except (a) where any of the protective measures described in

Clause 8.4 are used, or(b) where specifically exempted in Clause 8.8.The earthable point of the power system, if earthed, shallbe connected to an earth electrode near the respectivepower transformer or generator.Where a protective conductor is required to be separatelyearthed, the connection to earth shall be made remotefrom the power system earth electrode. If good earthingfacilities or points are available, the protective conductorshall preferably be connected to them at as many placesas possible. Multiple earthing at points distributed asevenly as possible may be necessary in order to ensurethat the potential of the protective conductor remains asclose as possible to the earth potential in case of fault.The protective conductor may be a bare conductor, thatis, without a covering of insulating material.8.2 Automatic disconnection of supply. A protectivedevice shall automatically disconnect the supply to thatpart of the electrical installation protected by the device,if, following a fault in that part, the touch voltage cannotbe maintained at any point of the installation at a valueequal to or less than the conventional voltage limit UL,where UL = 50 V (r.m.s.).*

NOTE: In certain configurations of IT systems (see Clause 12),automatic disconnection may not be required on the occurrence ofa first fault.

8.3 Characteristics of protection. Thecharacteristics of the protective device or theprotective measures shall comply with the following:

(a) For voltages up to and including 1000 V seeTable 6.

(b) For voltages above 1000 V see Table 7.NOTE: See Figs 5 and 6 respectively for graphical representationsof the requirements of Tables 6 and 7.

TABLE 6PROSPECTIVE TOUCH

VOLTAGE/OPERATING TIMECHARACTERISTICS FOR SYSTEMS UP TO

AND INCLUDING 1000 VProspective touch voltage

(a.c., r.m.s.)Maximum operating

timeV s

505075

51

90110150

0.50.20.1

220280

0.050.03

TABLE 7PROSPECTIVE TOUCH

VOLTAGE/OPERATING TIMECHARACTERISTICS FOR SYSTEMS ABOVE

1000 VProspective touch voltage

(a.c., r.m.s.)Maximum operating

timeV s

5080

120

51

150180300

0.50.40.1

420550

0.050.03

8.4 Protective measures other than use of protectiveconductors. The protective requirements without aprotective conductor are in IEC 364-4-41, namely (a) protection by supplementary or reinforced

insulation;(b) protection by non-conducting locations;(c) protection by electrical separation; and(d) protection by safety extra-low voltage.8.5 Distinction of supply to fixed and portable ormobile apparatus. In particular installations (forexample, systems supplying motors) up to and including1000 V where a clear and permanent distinction can bemade between (a) those parts of the installation which supply only

equipment installed at a fixed point; and

* It may be necessary to specify lower values for certain applications or locations, for example, wet and conductive environments.

In the case of power generation, distr ibution and power suppliers, where there is a low probabil ity of exposure to hazard, values in excessof those in Table 6 and 7 may be permitted.

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AS 3007.21987 16

(b) those parts intended to supply portable and mobileapparatus having exposed conductive parts likely tobe held in the hand;

then the disconnecting time for the fixed installation shallnot exceed 5 s.

NOTE: Clear distinction means that a fault in a fixed installationdoes not impair the safety of portable or mobile apparatus, for whichthe disconnecting time of Table 6 is relevant.

8.6 Disconnection time for systems above 1000 V. Itmust be recognized in systems above 1000 V that a finitetime is required to disconnect under a fault condition,and that during this time under some special situations,higher prospective touch voltages may exist during thedisconnection process. In such situations, disconnectionmust take place in the shortest practical time.8.7 Coordination of protection. The protectivemeasures necessitate coordination of (a) the power system type in relation to earthing

(Clause 9); and(b) the characteristics of the protective devices.8.8 Exemption from use of protective conductors.Protective conductors are not required for the exposedconductive parts of individual components providedthat(a) each component is mounted on a conductive part

which is directly connected to a protectiveconductor or which is a protective conductor ;

(b) the conductance between each component and thepart on which it is mounted is at least equal to thatresulting from the application of Clause 14.6.2, and

(c) the electrical continuity is assured, either byconstruction or by suitable connections, in such away as to be protected against mechanical, chemicalor electrochemical deterioration.

Where the equipment is required to operate undercorrosive conditions or extreme vibration, a separateprotective conductor shall be connected to thecomponents.

9 TN, TT AND IT SYSTEMS DESCRIPTION.9.1 General. The codes used in the description of thesystems have the following meaning:(a) First letter. The relationship of the earthable point

of the power system to earth, as follows:(i) T = direct electrical connection (minimum

practical impedance) to earth.(ii) I = no connection (all live parts isolated

from earth) or connected to earththrough an impedance (resistor orreactor) or equivalent circuit.

NOTE: In three-phase systems, the earthable point is commonlythe neutral point of the generator or transformer.

(b) Second letter. The relationship of the exposedconductive parts of the electrical installation toearth, as follows:(i) T = direct electrical connection (minimum

practical impedance) to earth,independently of any connection to theearthable point of the power system.

(ii) N = direct electrical connection (minimumpractical impedance) to the earthablepoint of the power system.

Where the characteristics of the system of earthingof the supply to the electrical installation are notknown they should be ascertained from the powersupplier.

9.2 Description of the systems. The followingdistinction is made with regard to the system of earthing:

(a) TN system (Figs 7, 8 and 9). Power systems havingthe earthable point directly connected to earth andthe exposed conductive parts of the installationbeing connected by protective conductors to theearthable point of the power system.

(b) TT system (Fig. 10). Power systems having theearthable point directly connected to earth, theexposed conductive parts of the installation beingconnected to earth electrodes which are electricallyindependent of the earth electrodes of the powersystem.

(c) IT system (Figs 11, 12 and 13). Power systemshaving the earthable point not connected to earth, orconnected to earth through an impedance (resistoror reactor), the exposed conductive parts of theinstallation being connected to earth electrodeswhich may be the same as those used for theearthing resistor or reactor.

Power systems deriving supply from other systems (TTor TN) through a three-phase reactor (zero sequencereactor) offering a high impedance to earth fault (zerosequence) currents with neutral displacement (seeClause 13.3).

10 PROTECTIVE MEASURESFOR TN SYSTEMS.

10.0 General. In TN systems the earthable point (inthree-phase systems commonly the neutral point of thepower system) and exposed conductive parts areinterconnected by a protective conductor. In the case ofa short circuit from a phase conductor to the protectiveconductor or exposed conductive parts, the resultant faultcurrent initiates, through a protective device,disconnection of the supply to the defective equipment.

To ensure that in case of a fault (to exposed conductiveparts or to earth), the potential of the protectiveconductor and of the exposed conductive parts connectedto it differs as little as possible from the earth potential,the protective conductor shall be connected to a numberof earthing points distributed so as to obtain the lowestpractical earthing impedance. In the event of a faultbetween a phase conductor and an exposed conductivepart, the touch voltage shall be limited as specified inClause 8.

10.1 Bonding of exposed conductive parts. Allexposed conductive parts of the electrical installationshall be connected to the earthable point of the powersystem by protective conductors.

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17 AS 3007.21987

Fig. 5. GRAPHICAL REPRESENTATION OF TABLE 6

Fig. 6. GRAPHICAL REPRESENTATION OF TABLE 7

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AS 3007.21987 18

* Recommended colour (see Clause 10.6)Fig. 7. POWER SYSTEM TN WITH SEPARATE NEUTRAL AND PROTECTIVE CONDUCTORS THROUGHOUT

THE SYSTEM

* Recommended colour (see Clause 10.6)Fig. 8. POWER SYSTEM TN WITH NEUTRAL AND PROTECTIVE FUNCTIONS COMBINED IN A SINGLE

CONDUCTOR IN A PART OF THE SYSTEM

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19 AS 3007.21987

* Recommended colour (see Clause 10.6)Fig. 9. POWER SYSTEM TN WITH NEUTRAL AND PROTECTIVE FUNCTIONS COMBINED IN A SINGLE

CONDUCTOR THROUGHOUT THE SYSTEM

* Recommended colour (see Clause 10.6)Fig. 10. POWER SYSTEM TT

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AS 3007.21987 20

Fig. 11. POWER SYSTEM IT WITH INDEPENDENT EARTH ELECTRODES

Fig. 12. POWER SYSTEM IT WITH COMMON EARTH ELECTRODE

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21 AS 3007.21987

Fig. 13. POWER SYSTEM IT USING EXTERNAL TT OR TN SYSTEM AS A SOURCE

10.2 Disconnection following fault. The protectivedevices and the cross-sectional area of the conductorsshall be chosen in such a way that, if a short circuitoccurs at any point between a phase conductor and theprotective conductor or an exposed conductive partconnected to it, disconnection will be effected within aspecified time.This requirement is met if the following condition isfulfilled:

Zs Ial Uowhere

Zs = fault loop impedanceIal = current ensuring the operation of the

disconnecting device within 5 s in thecase of the particular installationsdescribed in Clause 8.5 or theappropriate time specified in Tables 6or 7

Uo = phase to neutral voltage.NOTES:1. In a given installation Zs may be calculated or determined by

measurement.2. The value of the prospective touch voltage depends on the

voltage of the system and on the relationship between theimpedance of the protective circuit and the phase conductorplus source impedance.

If this condition cannot be fulfilled, then supplementarybonding in accordance with Clause 14 shall be provided.10.3 Single conductor as combined protective andneutral conductor. A single conductor may combinethe functions of a protective and neutral conductor,subject to the following:(a) The conductor shall be non-flexible and in a fixed

electrical installation.(b) The cross-sectional area of the conductor shall be

not less than 10 mm2.(c) The conductor shall not be supplied through a

residual current operated protective device.

In those instances where the conductor may be bare, i.e.without insulation, it may be necessary to insulate theconductor for reasons other than protection againstindirect contact, e.g. fire risk.10.4 Interruption of combined protective and neutralconductor. The protective conductor shall not beinterrupted in service. Overcurrent-operated protectivedevices are admissible in a combined protective andneutral conductor only where they also interrupt thephase conductors.10.5 Separation of protective conductor from acombined protective and neutral conductor. If, fromany point of the electrical installation, the neutral andprotective conductors are separated, it is inadmissible toconnect these two conductors to each other from thatpoint on toward the load.The neutral conductor shall be insulated and installed inthe same manner as a phase conductor.10.6 Conductor identification. Conductors shall beidentified in accordance with the following requirements:(a) Protective conductor. The protective conductor

shall have a colour coding of green/yellow.(b) Combined conductor identification. The combined

conductor shall have the same colour coding as theprotective conductor green/yellow. Theterminations shall also be identified to show jointneutral function.

(c) Neutral conductor identification. Where a neutralconductor has no other function the colour lightblue is recommended for identification purposes.

10.7 Protective devices. The use of the followingprotective devices is recommended.(a) Overcurrent-operated protective devices.(b) Residual-current-operated protective devices, exceptwhere a combined protective and neutral conductor isused (see Clause 10.3). However, in three-phaseinstallations where the unbalanced (neutral) current islow compared with the phase currents, a device whichsenses unbalance in the three-phase currents can provideprotection against earth faults.

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AS 3007.21987 22

10.8 Residual-current-operated protective devices.Where residual-current-operated protective devices areused, the exposed conductive parts need not beconnected to the protective conductor provided they areconnected to an earth electrode the resistance of whichis adapted to the operating current of theresidual-current-operated protective device. The circuitprotected by this residual-current-operated protectivedevice is then considered as a TT system and theconditions of Clause 11 shall apply.If, however, no separate earth electrode exists, theconnection of the exposed conductive parts to theprotective conductor shall be made on the source side ofthe residual-current-operated protective device.10.9 Voltage balance. In certain cases for TN systemsup to and including 1000 V in which a direct faultbetween a phase conductor and earth can occur (e.g.systems with overhead lines), the following conditionshall be fulfilled in order to prevent the protectiveconductor, or any parts connected thereto, reaching avoltage relative to earth in excess of UL:

whereRB = total earthing resistanceRE = prospective lowest earth contact

resistance of conductive parts notconnected to the protective conductor,wherever an earth-contact of a phaseconductor appears

Uo = phase-to-neutral voltageUL = conventional voltage limit.

Protective measures recommended are as follows:(a) A cradle connected to the protective conductor

under an overhead line.(b) Structural parts connected to the protective

conductor.

11 PROTECTIVE MEASURES FOR TT SYSTEMS.11.0 General. In TT systems, the earthable point(neutral point) is directly connected to an earth electrodewith no impedance (other than the impedance of theprotective conductor) being inserted between theearthable point and the earth electrode.The exposed conductive parts are connected, eitherindividually, in groups, or as a whole, to one or severalearth electrodes independent of the earth electrode of theearthable point.For systems wholly contained within movable or mobileapparatus, the metallic structure shall form the earthelectrode and the earthable point shall be connected tothe metallic structure.In the event of a fault between a phase conductor and anexposed conductive part, the touch voltage shall belimited in accordance with Clause 8.11.1 Neutral conductor insulation and installation.The neutral conductor, if any, shall be insulated andinstalled in the same manner as a phase conductor.11.2 Bonding of exposed conductive parts. Allexposed conductive parts of electrical equipment

protected by a common protective device shall beinterconnected and connected by a protective conductorto a common earth electrode. If several protectivedevices are used in series, this requirement applies toeach group of exposed conductive parts protected by thesame device.Exposed conductive parts which are simultaneouslyaccessible shall be connected to a common earthelectrode.11.3 Conditions to be fulfilled following a fault. Inorder to comply with the requirements of Clause 8.3, thefollowing condition shall be fulfilled:

Ia RA Uwhere

Ia = current ensuring operation of thedisconnecting device within theappropriate time for the prospectivetouch voltage maximum operatingtime curve, in accordance withClause 8.3If a residual-current-operated device isused, Ia is equal to the rated operatingresidual current I D n

U = conventional voltage limit (UL) orprospective touch voltage as the casemay be

RA = resistance of the earth electrode of theexposed conductive parts.

If this condition cannot be satisfied, supplementaryequipotential bonding, in accordance with Clause 14,shall be installed.11.4 Protective devices. The use of the followingprotective devices is recommended:(a) Residual-current operated protective devices.(b) Overcurrent operated protective devices.However, the use of fault voltage operated protectivedevices is not excluded for systems up to and including1000 V.

12 PROTECTIVE MEASURES FOR IT SYSTEMS.12.0 General. In IT systems, the earthable point of thepower system is either isolated from earth or earthedthrough an impedance, and the exposed conductive partsare connected to one or several earth electrodes eitherindividually, in groups or as a whole. Where the faultcurrent, in the event of a single fault to exposedconductive parts, is of sufficiently low value, and theconventional voltage limit UL is not exceeded,disconnection of the source of supply may not berequired. Measures shall be taken to avoid danger in caseof the occurrence of two simultaneous earth faults (phaseto earth to phase).A system in which supply is taken from a TN or TTpower system through an earth fault current limitingneutral displacement reactor (zero sequence reactor)restricting the earth fault current to a low value, complieswith the definition of an IT system.Where neutral displacement is to be achieved through theapplication of earth fault current limiting devices, suchdevices shall comply with the special requirements ofClause 13.

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12.1 Isolation or earthing of the power systemearthable point. The earthable point may be eitherisolated from earth or earthed through an impedance (insuch cases, it is the neutral point that is connected toearth via an impedance).The use of artificial earthable points is recognized.

NOTE: Such earths may be necessary in order to reduce over-voltage or oscillations.

12.2 Neutral conductor insulation and installation.The neutral conductor, if any, shall be insulated andinstalled in the same manner as a phase conductor. It isstrongly recommended that the neutral conductor shouldnot be used for the connection of loads.12.3 Bonding of exposed conductive parts. Allexposed conductive parts shall be earthed individually, ingroups, or as a whole and may be connected directly tothe earth (see Figs 11 and 12).The total earthing resistance RA of all exposed conductiveparts connected by the protective conductor to an earthelectrode shall meet the following requirement:

Id RA ULwhere

Id = fault current in the case of the first deadfault between a phase conductor and anexposed conductive part. The value of Idtakes into account the leakage currentsand the total earthing impedance of theelectrical installation

UL = prospective touch voltage.12.4 Operation of the protective devices under faultcondition.(a) On the occurrence of first fault. Where the

prospective touch voltage (Clause 12.3) exceeds UL(Clause 8.2), the protective device shall disconnectthe supply to the circuit in accordance withClause 8.3.Where the prospective touch voltage does notexceed UL (Clause 8.2), operation may be continuedsubject to the following:(i) The protective measures shall be designed to

disconnect in the event of a subsequent fault(phase to earth to phase) in accordance withthe requirements of Clause 12.4(b).

(ii) An insulation monitoring device or othersuitable protective device shall be provided toindicate the occurrence of a first fault toexposed conductive parts or to earth from alive part of the electrical installation. (Forexemptions, refer to Clause 12.4(b).)This device shall give an audible and/or visualsignal in order to permit elimination of thefault without delay.It is recommended that a device orcombination of devices be provided to indicatethe area of the fault with sufficient accuracy tofacilitate disconnection of the faulty branch ofthe circuit.

(iii) Such continued operation is subject toconsideration of the risk of fire. Whenoperating a mobile machine with a powersystem as shown in Fig. 12, it is recommendedthat operation be terminated as soon aspossible or practical after occurrence of thefirst fault.

(b) On the occurrence of a subsequent fault (phase toearth to phase). After the occurrence of the firstearth fault, protection shall be provided todisconnect the supply in the case of the second fault.The conditions of protection and disconnection arethose specified for TN or TT systems, depending onwhether or not all exposed conductive parts areinterconnected by a protective conductor.The use of an insulation monitoring device isstrongly recommended.

12.5 Protective devices. The use of the followingprotective devices is recommended:(a) Insulation monitoring devices.(b) Overcurrent-operated protective devices.(c) Residual-current-operated protective devices.(d) Residual-voltage-operated protective devices (only

for special applications).13 REQUIREMENTS FOR EARTH FAULTCURRENT LIMITATION DEVICES.13.0 General. In IT systems, where earth fault currentlimitation devices affording system neutral displacementare used, the forms listed below are recognized with thefollowing preferred values of earth fault currentlimitation:(a) For voltages up to and including 1000 V: 10 A,

15 A, 25 A.(b) For voltages above 1000 V: 10 A, 15 A, 25 A,

50 A.The rated insulation voltage of these devices shall beat least the phase-to-neutral voltage of the system.

13.1 Neutral earthing resistors. Special requirementsare under consideration.13.2 Neutral earthing reactors and arc suppressioncoils. Reactors may be used to limit earth fault currentalone or to act as arc suppression coils, compensating forcapacitive current in the case of single phase to earthfaults in the system.Such arc suppression coils may be provided with aseparate winding for connection of a resistor.13.3 Three-phase earth fault current limiting neutraldisplacement reactor (zero sequence reactor). Anearth fault current limiting neutral displacement reactor isintended for use in series with a three-phase system. Theearthable point (the neutral point in this case) is earthed,providing low impedance to load current but highimpedance to zero sequence currents in order to limit toa specified value the current which would occur under asingle phase to earth fault.Normally reactors of this type are used only on systemsabove 1000 V.Such a reactor may be used in lieu of an isolatingtransformer for the purpose of restricting earth faultcurrents.The preferred values of earth fault current limitation forthese reactors are similar to those provided elsewhere inthis clause.

14 EARTHING ARRANGEMENTS ANDPROTECTIVE CONDUCTORS.14.1 General requirements.14.1.1 Performance of earthing arrangements. Theperformance of the earthing arrangements shall satisfy thesafety and functional requirements of the electricalinstallation and the equipment of that installation. The

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earthing arrangements may be used jointly or separatelyfor protective or functional purposes according to therequirements of the installation.14.1.2 Required components. The earthing arrangementsshall include earth electrode(s), protective conductor(s)and other components necessary to comply with thisstandard.

NOTES:1. An illustration of the elements of a typical earthing arrangement

is provided in Fig. 14. It should be noted that not all of theelements illustrated need be present in every earthingarrangement. Additional elements may be required in someinstallations, and some elements may have a combined function.

2. This clause should not be interpreted as requiring the use ofseparate earthing arrangements or protective conductor(s) wherethe requirements can be complied with by other means (seeAS 3007.4).

14.1.3 Design, selection and installation. The design,selection and installation of the earthing arrangementsshall be such as will ensure the following:(a) The requirements prescribed in Section 2 herein for

protection against indirect contact are compliedwith.

(b) The requirements for proper functioning ofprotective devices are complied with.

(c) The earth electrode(s) and protective conductor(s)are designed and installed so that the protective andfunctional requirements are complied with under theexpected conditions.

(d) Earth fault currents (including currents resultingfrom phase-earth-phase faults in the case of ITsystems) and earth-leakage currents can be carriedwithout danger, particularly from thermal,thermomechanical and electromechanical stresses.

(e) It is adequately robust or has additional mechanicalprotection appropriate to the assessed conditions ofexternal influence.

(f) The value of earthing resistance is in accordancewith the protective and functional requirements ofthe installation and is expected to be continuouslyeffective.

14.1.4 Precautions against damage due to electrolysis.Precautions shall be taken to minimize damage to othermetallic parts through electrolysis.14.2 Earth electrodes.14.2.1 Acceptable types. The following types of earthelectrodes may be used:(a) Rod(s) or pipe(s).(b) Tape(s) or wire(s).(c) Plate(s) or mat(s).(d) Electrode(s) embedded in foundations.(e) Metallic reinforcement of concrete.(f) Other suitable underground structures.One or more earth electrodes suitable for the soilconditions and value of earth resistance required shall beselected.For movable and mobile installations, the metallicstructure shall be considered as being the earth electrodefor electrical systems which are isolated from an externalpower supply or which are obtained from aself-contained power supply.

NOTES:1. The efficacy of any earth electrode depends on local soil

conditions. Where conditions preclude satisfactory electricalcontact, the use of techniques such as blasting and/or the additionof chemical fillers may be advantageous.

2. In some cases separate earth electrode arrangements may berequired. See Clause 14.5.

14.2.2 Material and cross-sectional area. The materialand total cross-sectional area of the earth electrode(s)shall be such as to provide a conductance of not lessthan that of the earthing conductor required inaccordance with Clause 14.3.1.14.2.3 Type and embedded depth. The type andembedded depth of earth electrodes shall be such thatsoil drying and freezing will not increase the earthresistance of the earth electrodes above the requiredvalue. Where practicable, the earth electrodes shall beembedded below permanent moisture level, except forelectrodes which are used for gradient control.14.2.4 Design of electrodes. The design of theelectrodes shall take into consideration the type,temperature and moisture content of the soil as well asthe magnitude and duration of expected current flow soas to prevent soil dryness in the vicinity of theelectrodes.14.2.5 Allowance for deterioration. The design,selection of materials and construction of earth electrodesshall take into consideration the possible deteriorationand increase of resistance due to corrosion over theexpected period of use of the installation.14.2.6 Measurement of earth resistance. The earthresistance shall be measured when the electrode isinitially installed and shall be periodically checkedthereafter.14.2.7 Use of metallic pipe systems. Metallic pipesystems for water or other services (e.g. flammableliquids or gases, heating systems) shall not be used asearth electrodes for protective or functional purposes.

NOTE: This requirement does not preclude connections to metallicpipe systems for equipotential bonding.

14.2.8 Use of metallic coverings of cables. Leadsheaths and other metallic coverings of cables shall notbe used as earth electrodes for protective or functionalpurposes.14.3 Earthing conductors.14.3.1 Minimum cross-sectional area. Every earthingconductor shall have a cross-sectional area of not lessthan that determined in accordance with Clause 14.6.2,but the cross-sectional area shall in no case be less thanthe appropriate value specified in Table 8.

TABLE 8MINIMUM SIZE OF EARTHING

CONDUCTORS

Corrosionprotection

Minimum cross-sectional areaMechanically

protectedMechanicallyunprotected

Protected againstcorrosion

As determined byClause 14.6.2

16 mm2 for copperand ferrousmaterials

Not protectedagainst corrosion

25 mm2 for copper50 mm2 for ferrous materials

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1 Earthing conductor2 Main protective conductor3 Protective conductor4 Main equipotential bonding conductor5 Supplementary equipotential bonding conductor

T Earth electrodeB Main earthing terminalM Exposed conductive partC Extraneous conductive partP Main metallic water pipe

Fig. 14. ILLUSTRATION OF THE ELEMENTS OF A TYPICAL EARTHING ARRANGEMENT

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14.3.2 Connections to earth electrodes. The connectionof an earthing conductor to an earth electrode shall besoundly made and shall provide satisfactory electricalcontinuity. Where a clamp is used it shall not damagethe electrode, e.g. a pipe, or the earthing conductor.Connections between earthing conductors and earthelectrodes shall be protected against mechanical damageand corrosion.

NOTE: In certain installations it may be necessary to use more thanone electrode and in these circumstances it may be desirable for thepoints of connection to the electrodes to be accessible for testingpurposes.

14.4 Main earthing terminals or bars.14.4.1 Recommended connection facilities. It isrecommended that a main earthing terminal(s) or bar(s)be provided for the interconnection of (a) protective conductors;(b) main equipotential bonding conductors;(c) functional earthing conductors, if required; andfor their connection to the earthing conductor.14.4.2 Means of disconnection. Means shall beprovided in an accessible position for disconnecting theearthing conductor. Such means may conveniently becombined with the main earthing terminal or bar, topermit measurement of the resistance of the earthingarrangements. This joint shall be disconnectable only bymeans of a tool, shall be mechanically strong, and shallensure the maintenance of electrical continuity.14.4.3 Current carrying capacity. The current carryingcapacity of a main earthing terminal or bar shall be notless than that of the largest conductor connected to it.14.5 Interconnection with earthing arrangements ofother systems.14.5.1 High voltage systems.(Requirements yet to be established)14.5.2 Lightning protection systems.(Requirements yet to be established)14.6 Protective conductors.14.6.1 Types of protective conductor. Protectiveconductors may comprise the following:(a) Conductors in multicore cables.(b) Insulated or bare conductors in a common enclosure

with phase conductors.(c) Separate bare or insulated conductors.(d) Metal coverings for conductors or cables, for

example, sheaths, screens, or armouring.(e) Suitable metallic enclosures for conductors.(f) Suitable structural parts as permitted in AS 3007.4

and in other cases where similar conditions exist.14.6.2 Minimum cross-sectional area.14.6.2.1 Basic requirements. The cross-sectional areaof the protective conductor shall be selected to ensure (a) that it will withstand the thermal conditions which

may be experienced in the case of a fault (seeClause 14.6.2.2); and

(b) that it has adequate mechanical strength to ensurethe integrity of the conductor under the expectedconditions (see Clause 14.6.2.3).

In addition, the protective conductor, as an element of theearthing arrangement, shall satisfy, either alone or inconjunction with other elements of the earthingarrangement, the requirements of Section 2 of thisstandard, for protection against indirect contact and forthe proper operation of protective devices.14.6.2.2 Minimum cross-sectional area based on thermalconsiderations. The cross-sectional area of the protectiveconductor shall be either calculated or selected inaccordance with the procedure described in (a) or (b)below, as applicable:(a) Calculation procedure. The cross-sectional area

shall be not less than the value determined by thefollowing equation (applicable only fordisconnection times less than 5 s):

A =

whereA = the cross-sectional area, in square

millimetresI = the value (a.c., r.m.s.) of fault

current for a fault of negligibleimpedance, which can flow throughthe protective device, in amperes

t = the operating time of thedisconnecting device, in seconds.

NOTE: Account should be taken of the current limitingeffect of the circuit impedances and the limiting capability(I2t) of the protective device.k = a factor dependent on the material

of the protective conductor,insulating and other parts, and theinitial and final temperatures

k1 = a factor which takes into accountthe effect of asymmetrical faultcurrents for short operating times.It is recommended that a factor of1 be used for operating times of0.2 s or greater, and 1.3 foroperating times of less than 0.2 s.

The value of k for the calculation shall be selectedin accordance with Appendix A.If application of the equation produces non-standardsizes, conductors of the next largest standardcross-sectional area shall be used.

(b) Selection procedure. The cross-sectional area of theprotective conductor shall be not less than theappropriate value shown in Table 9. If theapplication of this table produces non-standardsizes, conductors having the next largest standardcross-sectional area shall be used.Where the cross-sectional area of the protectiveconductor is determined in accordance with theabove procedure, checking of compliance withItem (a) above is not necessary.The values in Table 9 are valid only if theprotective conductor is made of the same metal asthe phase conductors. If this is not so, thecross-sectional area of the protective conductor shallbe determined in a manner which produces aconductance equivalent to that which results fromthe application of Table 9.

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TABLE 9SELECTION OF MINIMUM

CROSS-SECTIONAL AREA FORPROTECTIVE CONDUCTORS

Cross-sectional areaof phaseconductors

of the installations (Ap)Minimum cross-sectional

areaof the corresponding

protective conductor (A)mm2 mm2

Ap 16 Ap16 < Ap 35 16

Ap > 35 Ap/2

14.6.2.3 Minimum cross-sectional area based onmechanical strength. Notwithstanding the size ofprotective conductor determined in accordance withClause 14.6.2.2, the cross-sectional area shall be not lessthan the appropriate value prescribed below in Items (a)to (d) inclusive to ensure that it has adequate mechanicalstrength. The cross-sectional areas prescribed are basedon the use of copper conductors; where other conductormaterials are used, equivalent strength shall be provided.(a) Separately installed protective conductors. The

cross-sectional area of every protective conductorwhich does not form part of the cable or cableenclosure shall be not less than (i) 2.5 mm2 if mechanical protection is provided;

and(ii) 4.0 mm2 if mechanical protection is not

provided.(b) Protective conductors installed with phase

conductors. Where the protective conductor isinstalled in the same cable, conduit, sheathing orother protective covering as the phase conductors ofsize not greater than 2.5 mm2, the protectiveconductor shall have the same cross-sectional areaas the phase conductors.

(c) Protective conductors of high voltage installations.Where the phase conductors are supplied at above1000 V the cross-sectional area of the associatedprotective conductor shall be not less than 16 mm2.

(d) Aerial and suspended protective conductors. Aerialand suspended protective conductors shall be notless than the relevant cross-sectional area prescribedin Table 10 according to the length of span and typeof conductor. Conductors of larger cross-sectionalarea may be required for severe icing or windconditions.

TABLE 10MINIMUM CROSS-SECTIONAL AREA OFAERIAL AND SUSPENDED PROTECTIVE

CONDUCTORS

Type of protective conductorSpan Minimum cross-

sectional aream mm2

Weatherproof rubber insulatedor thermoplastic insulatedcables with annealedconductors

10 4

Bare or covered hard drawnconductors

25> 25 50> 50 75

46

16

14.6.3 Preservation of electrical continuity of protectiveconductors.14.6.3.1 Required protection. Protective conductorsshall be suitably protected against mechanical andchemical deterioration and electrodynamic effects.14.6.3.2 Accessibility of connections. Connections ofprotective conductors shall be accessible for inspectionand testing except for compound-filled or encapsulatedjoints.14.6.3.3 Use of switching devices. No switching deviceshall be inserted in the protective conductor, but jointswhich can be disconnected for testing purposes by use ofa tool may be provided. If it is a combined neutral andprotective (PEN) conductor, then a switching device ispermitted provided that it is linked with the main poles.

NOTE: For switching devices in combined neutral and protective(PEN) conductors, see Clause 10.4.

14.6.3.4 Connection of earth continuity monitoringdevices. Where electrical monitoring of earth-continuityis used, the operating coils shall not be inserted inprotective conductors.14.6.3.5 Monitoring protective conductor continuity intrailing cables. It is recommended that continuouscontinuity monitoring be provided for the protectiveconductor of trailing cables of the external power supplyto mobile installations.14.6.3.6 Use of exposed conductive parts of apparatus.Exposed conductive parts of apparatus shall not be usedto form part of the protective conductor of otherequipment.14.7 Earthing arrangements for protective purposes.

NOTE: For protective measures for TN, TT and IT systems ofearthing, see Clauses 10, 11 and 12.

14.7.1 Protective conductors used with overcurrent-operated protective devices. Where overcurrent-operatedprotective devices are used for protection against indirectcontact in alternating current systems, the protectiveconductors shall follow the same magnetic path as thephase conductors.14.7.2 Earthing and protective conductors for fault-voltage-operated protective devices.(Requirements yet to be established).14.8 Equipotential bonding.14.8.1 Main equipotential bonding. Whereverpracticable, a main equipotential bonding conductorshould be installed to connect extraneous conductiveparts which are embedded in the earth (e.g. mainmetallic water pipes, metallic structures, metallicreinforcement of foundations) to the main earthingterminal or equivalent point (see Fig.14).The main equipotential bonding conductor(s) shall havea current-carrying capacity of not less than that of themain protective conductor of the installation. However,for IT systems of up to and including 1000 V, the cross-sectional area of the conductor need not exceed 25 mm2if of copper or a cross-sectional area affording equivalentcurrent carrying capacity in other metals.

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14.8.2 Supplementary equipotential bonding.14.8.2.1 Conditions of use. If, in an installation or partof an installation, the specified conditions for protectionagainst indirect contact in the event of a fault cannot befulfilled, then local bonding, known as supplementaryequipotential bonding, shall be provided. This may beachieved by the use of additional conductors, additionalstructural parts, or both. Supplementary equipotentialbonding may involve the entire installation, a part of theinstallation, or an item of apparatus. In addition, thebonding of metallic parts may be necessary in hazardouslocations, e.g. fuel storage areas, to minimize the risk ofexplosion.14.8.2.2 Components to be connected. Supplementaryequipotential bonding shall connect the following:(a) Simultaneously accessible exposed conductive parts,

e.g. frames of equipment, covers, exposed cablearmour.

(b) Exposed conductive parts simultaneously accessibleto extraneous conductive parts, e.g. ladders,walkways.

14.8.2.3 Minimum cross-sectional area. Thecross-sectional area of supplementary equipotentialbonding conductors shall be in accordance with therequirements of (a) or (b) below, as appropriate, but shallbe not less than the relevant value specified in Table 11.(a) Conductors connecting two exposed conductive

parts shall have a cross-sectional area not less thanthat of the smaller protective conductor connectedto the exposed conductive parts.

(b) Conductors connecting exposed conductive parts toextraneous conductive parts shall have across-sectional area not less than half of thecross-sectional area of the corresponding protectiveconductor.

14.8.2.4 Check of effectiveness. Where doubt existsregarding the effectiveness of supplementaryequipotential bonding it shall be confirmed that theimpedance Z between simultaneously accessible exposedconductive parts and extraneous conductive parts fulfillsthe following condition:

Z

whereU = prospective touch voltage (see Table 6

or Table 7)Ia = operating current of the protective device

ensuring disconnection within theappropriate time specified in Table 6 orTable 7.

Where supplementary equipotential bonding is installedbetween exposed conductive parts of apparatus which areconnected to separate supplies, the above condition shallbe fulfilled for each of the supplies involved.Where fuses are used, it is sufficient to confirm that thecondition is fulfilled for the conventional voltage limitUL and for the current ensuring the operation of the fusewithin 5 s.

TABLE 11MINIMUM CROSS-SECTIONAL AREA OF

SUPPLEMENTARY EQUIPOTENTIALBONDING CONDUCTO