02. Ppt England

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Verification of

ElectricalInstallations

to BS 7671 & IEC 60364

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Verification of Electrical Installations

to BS 7671 & IEC 60364

1. Brief background to NAPIT

2. International Electrotechnical Commission

3. Part 6 Inspection & Testing

4. Continuity Testing

5. Insulation Resistance Testing

6. Earth Loop Impedance Testing

7. Zs and components8. Phase sequence testing

9. TN-C-S or as known in the UK PME

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National Association for Professional

Inspectors and Testers

NAPIT was formed in 1992 as the National Association for Professional

Inspectors and Testers, with the aim of setting standards for industry.

Since then NAPIT's role has evolved and expanded to be one of the fastest

growing Government Approved register holders for Part P Registered

Domestic Electrical Installers (both full and defined scope) while

continuing to serve the needs of those carrying out equipment testing and

electrical installation and testing in commercial and industrial sectors.

NAPIT believe in the individual competence of all personnel working with

the electrical sector and also across all schemes that we operate.

NAPIT have just under 10,000 members

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NAPIT Group has several different parts including:

NAPIT Registration, the holder of the registers of competent individualscovering the

Department for Communities and Local Government (DCLG) & Microgeneration Certification

Scheme (MCS) schemes, various other schemes, and external inspectorate including expert

witness cases,

NAPIT Trade Association for our members to provide industry and government with their

views,

NAPIT Registration, the holder of the registers of competent individualscovering the DCLG &

MCS schemes, various other schemes, and an external inspectorate including expert witness

cases,


views,



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views,

NAPIT Training and its network of training and assessment centres to provide our members

with professional development opportunities,

NAPIT Certification, a standard setting and monitoring body.

NAPIT Inspection, an internal assessment of the electrical operative as part of the company

assessment, our membership fee includes assessment for two individuals and for a reduced

rate for additional individual assessments. Anyone carrying out the work should be assessed as

competent.



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IEC 60364 & BS:7671

The International Electrotechnical Commission (IEC) is a worldwide organization forstandardization comprising all national electrotechnical committees (IEC National

Committees).

The object of IEC is to promote international co-operation on all questions concerning

standardization in the electrical and electronic fields. To this end and in addition to other

activities, IEC publishes International Standards, Technical Specifications, TechnicalReports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as IEC

Publication(s)).

Their preparation is entrusted to technical committees; any IEC National Committee

interested in the subject dealt with may participate in this preparatory work. International,

governmental and non-governmental organizations liaising with the IEC also participate in

this preparation.

IEC collaborates closely with the International Organization for Standardization (ISO) in

accordance with conditions determined by agreement between the two organizations.

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IEC 60364 & BS:7671

IEC 60364 Electr ical Installations for Buil dingsis the InternationalElectrotechnical Commission's international standardon electricalinstallations of bui ldings.

This standard is an attempt to harmonize national wiring standards in

an IECstandard.

The latest versions of many European wiring regulations (e.g., BS 7671in the UK) follow the section structure of IEC 60364 very closely, butcontain additional language to cater for historic national practice andto simplify field use and determination of compliance by electricaltradesmen and inspectors.

National codes and site guides are meant to attain the commonobjectives of IEC 60364, and provide rules in a form that allows forguidance of persons installing and inspecting electrical systems.

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http://en.wikipedia.org/wiki/International_Electrotechnical_Commissionhttp://en.wikipedia.org/wiki/International_Electrotechnical_Commissionhttp://en.wikipedia.org/wiki/International_standardhttp://en.wikipedia.org/wiki/International_Electrotechnical_Commissionhttp://en.wikipedia.org/wiki/BS_7671http://en.wikipedia.org/wiki/BS_7671http://en.wikipedia.org/wiki/International_Electrotechnical_Commissionhttp://en.wikipedia.org/wiki/International_standardhttp://en.wikipedia.org/wiki/International_Electrotechnical_Commissionhttp://en.wikipedia.org/wiki/International_Electrotechnical_Commission


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IEC 60364 & BS:7671

Within IEC 60364-6 there are differences on how we have adapted them inthe UK.

Clause 61 of IEC 60364 is titled Chapter 61 in the UK BS:7671 regulations

and this covers the Initial verification of new or additions to existing

installations.

Clause 62 of IEC 60364 is titled Chapter 62 in the UK BS:7671 regulations

and this covers the periodic verification of existing installations. In the UK we

term this Periodic Inspection and Testing as verification implies that the

design of the installation is being proven. For existing installations we are

trying to determine the installation is safe for continued use.

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IEC 60364 & BS:7671

The UK have adopted the intent of the requirements of IEC 60364-6 andalthough the wording may differ the inherent safety requirements have been

met in full.

This provides designers, installers and verifiers of electrical installations with

a document which fully details the means of achieving a safe and reliableelectrical wiring system.

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IEC 60364 & BS:7671

General

The IEC commences with regulation 61.1.1 where the UK version starts at 610.1

61.1.1 Every installation shall be verified during erection, as far as reasonably practicable, and on

completion, before being put into service by the user.

610.1 Every installation shall, during erection and on completion before being put into service, be

inspected and tested to verify, so far as is reasonably practicable, that the requirements of the

Regulations have been met. Precautions shall be taken to avoid danger to persons and livestock, and to

avoid damage to property and installed equipment, during inspection and testing.

Within the BS:7671 we have amended some wording where this provides a clearer message to thereader

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IEC 60364 & BS:7671

Inspection

The IEC Regulation starts at 61.2.1 where the UK version starts at 611.1

61.2.1 Inspection shall precede testing and shall normally be done prior to energizing the installation.

611.1 Inspection shall precede testing and shall normally be done with that part of the installation underinspection disconnected from the supply.

Within the BS:7671 we have additional wording to make clear that areas under test should be

isolated from the supply to increase the safety to the operatives and users of the electrical system

The UK have also include several more items as an example for the inspection than the IEC 60364

requires.

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IEC 60364 & BS:7671

Testing

The IEC Regulation starts at 61.3.1 where the UK version starts at 612.1

61.3.2 Continuity of conductors

A continuity test shall be made on

a) protective conductors, including main and supplementary equipotential bonding conductors, and

b) in the case of ring final circuits, live conductors.

612.2.1 Continuity of protective conductors, including main and supplementary equipotential bonding

A continuity test shall be made. It is recommended that the test be carried out with a supply having a no-

load voltage between 4 V and 24 V, d.c. or a.c., and a short-circuit current of not less than 200 mA.

612.2.2 Continuity of ring final circuit conductors

A test shall be made to verify the continuity of each conductor, including the protective conductor, of

every ring final circuit.

.

The UK have included some additional requirements to include the test instrument requirements and

also extending the types of conductors to include the protective conductor

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IEC 60364 & BS:7671 - Continuity Testing

One method of carrying out testing of a Main Earth Conductor in

compliance with BS:7671 Regulation 612.2.1 and IEC 61.3.2

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IEC 60364 & BS:7671 - Continuity Testing

One method of carrying out testing of a Circuit Protective Conductor in

compliance with BS:7671 Regulation 612.2.1 and IEC 61.3.2

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Testing of a Line Conductor of a ring circuit in compliance with BS:7671

Regulation 612.2.1, 612.2.2 and IEC 61.3.2

IEC 60364 & BS:7671Ring Continuity Testing

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Testing of a Circuit Protective Conductor of a ring circuit in compliance

with BS:7671 Regulation 612.2.1, 612.2.2 and IEC 61.3.2

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Confirming that there are no bridge connections between Line &

Neutral on the ring circuit, although not listed in BS:7671 or IEC 60364-

6 it is an essential test to confirm correct installation

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IEC 60364 & BS:7671Ring Continuity TestingTo confirm there are no

bridge connections in the

ring circuit, connect the

start of the line conductor to

the return neutral conductor,

the return of the line

conductor and the start of

the neutral conductor. Then

measure the

resistance between the line

and neutral at each socket-

outlet as illustrated in

fig 6.3.2e. The resistance

values obtained should be

substantially the same,

with readings being

approximately of the r1rn

value.

This is not listed in BS:7671 or IEC 60364-6 it is an

essential test to confirm correct installation

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IEC 60364 & BS:7671Insulation Testing

This test is to verify

that the insulation of

circuit conductors,electrical

accessories and

equipment is

satisfactory and there

is no unwanted

leakage between live

conductors (line and

neutral).

BS:7671 and IEC

60364-6 this is an

essential test to

confirm correct

installation

Testing of Insulation resistance in a Lighting circuit in compliance


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IEC 60364 & BS:7671Insulation TestingThis test is to verify

that the insulation of

circuit conductors,electrical

accessories and

equipment is

satisfactory and there

is no unwanted

leakage between live

conductors and earth.

Both BS:7671 and

IEC 60364-6 require

this an essential test

to confirm correct

installation

Testing of Insulation resistance in a Lighting circuit in compliance


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IEC 60364 & BS:7671Insulation Testing The terrible consequences of not carrying out verification correctly were

highlighted by the death of a young mother, Emma Shaw at her first floor flat in

West Bromwich in 2007. The seven-day Inquest into her death at Sandwell Coroners Court concluded, on 20

December 2011, that the cause of death was electrocution and that she had beenkilled unlawfully. She leaves behind a son who, at the time of her death, wastwenty-three months old.

Emma was just 22 when she received a fatal electric shock while mopping upwater on the floor of a hallway cupboard.

The leakage of water was caused by a fault on a hot water boiler, the installation ofwhich came under criticism. The inquest concluded that the installation work onthe boiler was, not adequate and criticised its, poor layout and poor design.

The electrical installation had been left in a dangerous state due to a plasterboardscrew having gone through a cable, bridging the line conductor and the metal studpartitioning, making it live.

It was said in court that the electrical fault had not been detected because testingwas, not carried out to a professional standard if at all. It was also stated thatsome test results on the electrical certificate had been fabricated.

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The work had been carried out the previous year by an company working underthe Qualifying supervisor system, based in Staffordshire, which was wound up justover a year after Miss Shaws death.

The company had allowed an electricians mate to work alone at the property.

This person stated that he had been asked to carry out the inspection and testingof the installation but felt uncomfortable about it. A friend of his tested andapproved the wiring. The testing was described in court as, farcical by anindependent expert. The completion of the test certificate was said to be full oferrors yet it had supposedly been checked by the companys Qualified Supervisor.The company bosses claimed in court that the electricians mate was there toassist in testing only but they could not explain why he was allowed to work aloneat the flat.

The coroner concluded that there was a, failure by the company to assess thecapabilities of their workforce and constantly monitor their development.

The Crown Prosecution Service (CPS) had originally decided not to prosecute

anyone over Miss Shaws death. However, following the Inquest, they have now instructed their lawyers to carry

out a full and detailed case review on this decision. The review could agree withthe original decision or it could lead to a decision to bring charges.

IEC 60364 & BS:7671Insulation Testing

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IEC 60364 & BS:7671Earth Loop Testing

External loop impedance Ze The external loop impedance value may be measured using a line-earth

loop tester. The main switch on the consumer unit should be turned offand made secure to isolate the installation from the source of supply. Theearthing conductors on TN-S and TN-C-S supply systems are disconnectedfrom the main earthing terminals and the earth fault loop impedancetester connected between the incoming supply line conductor and the end

of the earthing conductor, as illustrated below: An alternative method of obtaining a value of Ze is to make enquires from

the electrical supplier. Typical Maximum values are:

TN-S system 0.8& Prospective Fault Current of 16kA

TN-C-S system 0.35& Prospective Fault Current of 16kA

Note: the measured value must be obtained to ensure compliance

These figures and the figure for the maximum prospective fault current(16kA) are incompatible.

This can be seen by doing an Ohms Law equation, using 230V.

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My understanding is that these values came into play when

the 15thEdition off the IEE Wiring Regulations which whenpublished placed more emphasis was put on disconnectiontimes and earth fault loop impedance.

The ENA guidance material and 14thand 15thEditions ofRegs do not have any reference to the source of the 0.35

and 0.8values. It is believed that they were cited by the Electricity

Association c.1981 and had been adopted uniformly.

Note that the latest IET Wiring Regulations On Site Guidenow states these values as Typical maximum values thiscame from discussion with Energy Networks Association.

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Earth Loop impedance Zs Knowledge of the earth fault loop impedance

(Zs ) is an essential factor where the most

commonly used protective measure -automatic disconnection of the supplyis

used

The formulae for the Earth Fault LoopImpedance is as follows:

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IEC 60364 & BS:7671

Regulation 612.9 of BS 7671 permits the Zs value to be determined by

measuring it on a live installation with a suitable test instrument or by

using an alternative method, such as calculation.The value obtained is then compared with the appropriate tabulated

maximum value of Zs as given in Tables 41.2, 41.3 and 41.4 of BS 7671,

after making allowance for the 0.8 temperature correction factor as

indicated in Appendix 14.

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When measuring Zs, inaccurate measurements often occur where the Zs

value being measured is very low.

This generally occurs in two situations:

1. when the measurement is carried out close to the supply transformer

2. when the measurement is carried out on circuits which are protected by

overcurrent devices with a rating in excess of 50 amps.

As the prospective fault current figure is based upon the Zsmeasurement

(whether carried out as an internal calculation by the instrument or by

manual calculation), it can also be affected significantly by small variations

in Zsvalues.

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After the result is measured it must be compared against the tabulated

values to ensure compliance and to meet disconnection times

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This diagrams demonstrates the route of the Zs path made up the different

components which include Ze , R1 impedance of the Line, R2 impedance

of the Circuit Protective conductor and the earth connections back to the

supply.

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This test is carried out to ensure that the incoming supply has an earth

connection.

Using an earth loop impedance tester, measure the loop impedance of

each phase at the origin Ze, in compliance with BS:7671 Regulation 612.9

and IEC 61.3.6

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This test is carried out to ensure that the required disconnection times for

each circuit in an installation will be achieved if a fault to Earth occurs.

Using an earth loop impedance tester, measure the loop impedance of

each radial circuit at the furthest point Zs, in compliance with BS:7671

Regulation 612.9 and IEC 61.3.6

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This test is carried out to ensure that the required disconnection times for

each circuit in an installation will be achieved if a fault to Earth occurs.

Using an earth loop impedance tester, measure the loop impedance of each radial circuit

at the furthest point Zs, in compliance with BS:7671 Regulation 612.9 and IEC 61.3.6

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IEC 60364 & BS:7671Phase Sequence Testing

For multi phase circuits the phase sequence shall be verified, in

compliance with BS:7671 Regulation 612.12 and IEC 61.3.9

Electricians have

been known in orderto save time, to

change the direction

of rotation of

three phase motors

by changing over two

of the line conductorsat the distribution

board feeding those

motors. This is

instead of changing

two line conductor

connections over ineach three phase

motor.

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IEC 60364 & BS:7671Documentation

Documentation for Initial work

IEC refers to this as a report where BS:7671

refers to this as a certificate

Persons carrying this work shall be competent

in verification

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Documentation for Periodic Inspection & Testing

IEC refers to this as Verification where BS:7671

refers to this as an Electrical Installation

Condition Report

IEC states that -Persons carrying this work

shall be a skilled person competent in

verification but the BS:7671 statesby a

competent person

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Requirements for Initial Inspection & Testing

On completion of an electrical installation, an

Electrical Installation Certificate (EIC) should

provide to the owner/occupier of the building

but the electrical contractor, this will detail the

work that has been carried out including

Inspection, Testing and Verification.

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Requirements for Initial Inspection & Testing

Electricity suppliers must be satisfied that theelectrical installation complies with BS 7671 at

the time of connection. The electricitysupplier must be provided with evidence tothis effect, in the form of the EIC. The EIC isthe normal method of providing confirmation

that the installation is satisfactory to be putinto service.

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Requirements for Periodic Inspection & Testing

The Institution of Engineering and Technology

(IET) publishes industry-agreed guidance on

how to comply with BS 7671. One such

document, Guidance Note 3, Inspection and

Testing, gives specific guidance on how

inspection and testing should be carried out.

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IEC 60364 & BS:7671Legal Requirements

Requirements for Periodic Inspection & Testing

Unfortunately there is no legal requirement to carry out PeriodicInspection & Testing of premises within the UK

Often there is a requirement that is imposed by Local Government vialicensing for entertainment purposes

Insurance companies can request an inspection prior to providing coverfor the premises

The majority of companies carry out this as part of their health & safetyduties but often this is kept to a minimum level of around 10-20% of theinstallation

Initiatives to introduce this as an enforced standard has been met withresistance by business and government as it places a financial burden oncompanies

Electrical contracting companies are normally registered with bodies suchas the NAPIT, Niceic or ECA, the terms of which oblige memberscompanies to abide by certain codes of professional conduct and also besubjected to assessment of their work normally on an annual basis.

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IEC 60364 & BS:7671

TN-C-S or as it is known in the UK PME In normal operation, the current drawn by the installation will flow from the main fuse in the

cut-out box through the installation, back to the incoming PEN conductor and then back tothe supply source.

Fig. 1 shows that a proportion of this returning neutral current from the installation will flowalong the main earthing conductor to the main earthing terminal (MET), then to anyincoming extraneous-conductive-parts via the main bonding conductors.

Some of this current will then return to the substation through the ground.

A factor determining the magnitude of this current is the effectiveness of the connectionwith Earth of the extraneous-conductive-parts.

The PEN conductor in the underground supply cable carries the returning neutral currentfrom all the other consumers supplied by that cable back to the source of supply.

Again looking at Fig. 1, we might well ask whether some of this returning neutral current canalso flow into consumers premises and return to Earth via the main earthing conductor, theMET, the main bonding conductors and bonded extraneous-conductive-parts. However, thiscurrent will find the easiest route (in terms of impedance) to return to Earth and theimpedance of the PEN conductor in the supply cable is generally much lower than the

impedance of other paths. Therefore, in normal operation, the MET in PME systems will be at some potential relative to

Earth. This potential would clearly also be on the exposed-conductive-parts and theextraneous-conductive-parts which are connected to the MET. Hence the vital need for mainprotective bonding. (See the section below on main protective bonding)

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IEC 60364 & BS:7671

TN-C-S or as it is known in the UK PME

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IEC 60364 & BS:7671


The PME systemwith a line to Earth fault inan installation (Fig.2)

Under line to Earth fault conditions within an installation

forming part of a PME system, the fault current will flow to

the MET and from there, most of it will flow to Earth along themain earthing conductor, operating the appropriate

overcurrent device in the process.

However, a proportion of the fault current may also flow to

Earth via the main protective bonding conductor(s) and theextraneous-conductive-parts. (The same would be true of a

TN-S system)

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IEC 60364 & BS:7671


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IEC 60364 & BS:7671


The PME systemwith an open-circuit PENconductor (Fig. 3)

The fault condition of most concern in PMEsystems is an open circuit in the PEN conductor ofthe distribution system. This may result in adangerous potential appearing between themetallic parts connected to the PME mainearthing terminal and the general mass of Earth.

To prevent such a condition, electricity suppliersconnect the PEN conductor to Earth at variouspoints along its length to provide a path to Earthduring a fault current situation.

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IEC 60364 & BS:7671


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IEC 60364 & BS:7671

TN-C-S or as it is known in the UK PMEMain protective bonding

The purpose of main protective bonding is to maintain the exposed-conductive-parts and the extraneous-conductive-parts within premises at substantially the same potential(an equipotential zone). By thismeans, the likelihood of dangerous potential differenceswhich can give rise to electric shock - appearingbetween such items of metalwork is reduced.

The equipotential zone will be maintained under the following conditions:

normal operating conditions

line to Earth fault conditions

open-circuit PEN conductors in PME supplies

The point was made above that, in PME systems which are operating normally, a proportion of thecurrent can flow along the main protective bonding conductors to the extraneous-conductive-parts, whichmay, for example, be underground service pipes.

If other consumers on the PME network are also connected to these same metallic underground servicepipes, via their main bonding conductors, each premises will contribute some current to this bondedmetalwork. As a result, these service pipes, on entering each premises, could well be at some potentialrelative to Earth. Such voltage differences are normally too low to be of concern, however there aresometimes cases where this is an issue. It is of the utmost importance therefore that such metalwork ismain bonded in accordance with Regulation 544.1.1 of BS 7671.

The current which each main protective bonding conductor will have to carry in the event of a faultwhether a line to Earth fault or a broken PEN conductor - cant be known unless the relative impedances ofthe paths to Earth are known. This means that the sizes for the main bonding conductors given inRegulation 544.1.1 of BS 7671 are somewhat arbitrary.

However, as the fault current is likely to be substantial, Regulation 544.1.1 of BS 7671 requires a largercross-sectional area for main bonding conductors in PME installations, compared to TN-S and TTinstallations, with this possibility in mind.

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IEC 60364 & BS:7671

TN-C-S or as it is known in the UK PME Restrictions on the use of PME systems

As the main earthing terminal of PME systems is at some potential relativeto Earth, clearly then, any metallic item which is connected to such anMET will also be at some potential relative to Earth. It is for this reasonthat Regulation 9(4) of the Electricity Safety, Quality and ContinuityRegulations 2002 (ESQCR) prohibits the use of TN-C-S (PME) systems forthe supply to a caravan or boat or anything having a similar construction.

For example, caravans must not use PME main earthing terminals. Otherrestrictions on the use of PME main earthing terminals which arementioned in BS 7671 include supplies to:

temporary buildings, such as exhibitions, shows and stands.

construction sites, except for the supply to a fixed building of theconstruction site.

mobile or transportable units. marinas.

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