WIRINGMATTERS

Spring 2005

Radon GasSwimming Pools

Installing Recessed Luminaires

Part P comes into forceYour questions answered

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OverviewPart P of the Building Regulationscame into force on 1 January 2005. Part P doesn’t just apply to flats andhouses. Dwellings and businesspremises that have a common meteredsupply – for example, shops and publichouses with a flat above – are coveredtoo, along with common access areas inblocks of flats and shared amenitiessuch as laundries and gymnasiums.However, if the business unit isseparately metered to the dwelling itdoes not come under Part P. Thelegislation also extends to parts ofinstallations in or on associated land.This would include fixed lighting andpond pumps in gardens, or a supply tooutbuildings such as sheds, detachedgarages and greenhouses.

A clear distinction has to be madebetween residential accommodationthat are places of work such asuniversity halls of residence,residential care homes and dwellings.University halls of residence, andresidential care homes do not comeunder Part P since these are covered bythe Electricity at Work Regulations and

would be subject to HSE investigationsin the event of an incident. The localauthority Building Control officer oran approved inspector will be able toconfirm whether Part P of theBuilding Regulations apply in aspecific case.

Significant work, such as houserewires, new circuits, and any additionsto existing circuits in kitchens,bathrooms or outside the house will be‘notifiable’ , however, the local authorityBuilding Control officer or an approvedinspector will be able to confirmwhether work is notifiable in a specificcase. That means it will have to becertificated by a member of one of thecompetent person self-certificationschemes that have been approved by theGovernment or notified to the localauthority, which will then be responsiblefor inspection and testing. Part P coversthe fixed electrical installation i.e. fixedwiring and equipment. It is understoodthat equipment plugged into a 13A BS1363 socket outlet for example does notcome under Part P.

TYPICAL QUESTIONS

Work in a kitchen – Cooker

QIf I connect a new cooker to anexisting cooker control unit in a

kitchen do I have to notify the local authority?

ANo, because this is regarded as replacement work under

Part P.

Work in a bathroom – Shower

QIf I replace an existing electricshower with a new electric

shower connected to an existingshower circuit is this notifiable work?

PART P COMESINTO FORCE

By Geoff Cronshaw

IEE Wiring Matters | Spring 2005 | www.iee.org

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ANo, providing the shower is a likefor like replacement.

Light fitting

QIs the replacement of a light fitting in a bathroom

notifiable work?

ANo, providing that the lightfitting is a like for like

replacement. For example if a lightfitting was replaced by a number ofdown lighters this would be classedas alteration work rather thatreplacement work and would benotifiable.

Work outside – Wall mounted outside light

QIs the installation of a wallmounted outside light fitting

installed on the outside wall of ahouse notifiable work?

AThe general view of the ODPM isthat it is not notifiable. Even

though this work is outside the houseit is generally considered notnotifiable providing the supply istaken from an existing lightingcircuit and the connection is notmade in the kitchen or a speciallocation.

Extra low voltage wiring – Alarm wiring

QIs the installation of intruderalarm wiring notifiable?

ANo, providing the intruder alarmwiring is not in a special location.

Therefore intruder alarm wiring in,for example, a kitchen would not benotifiable. Telephone or extra lowvoltage wiring and equipment for thepurposes of communications,information technology, signallingcontrol and similar purposes that isnot in a special location need not benotified to Building Control bodies.

Caravans, mobile homes, and park homes

QDo caravans, mobile homes, andpark homes come under part P?

ACaravans, mobile homes, and parkhomes are treated as caravans under

legislation, and do not ordinarily fallwithin the definition of a building in theBuilding Regulations, and thereforewould not normally come under Part P.Also, to clarify the situation most two-unit caravans (those which are deliveredin two sections and bolted together onsite) fall within the definition ofcaravans as referred to above.

Published by IEE Publishing & Information Services Michael Faraday House, Six Hills Way, Stevenage, Herts, SG1 2AY, United KingdomTel: +44 (0)1438 313311 Fax: +44 (0)1438 313465

Sales and Project Coordinator K Hunton +44 (0)1438 767224 khunton@iee.org.uk | Editor G D Cronshaw +44 (0)1438 767384gcronshaw@iee.org.uk | Contributing Editors J Ware, W R Allan | Chief Sub Editor Jim Hannah | Design SaBle Media Solutions

IEE Wiring Matters is a quarterly publication from the Institution of Electrical Engineers (IEE). The IEE is not as a body responsible for theopinions expressed.

©2005: The Institution of Electrical Engineers. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system,or transmitted in any form or by any means without the permission in writing of the publisher. Copying of articles is not permitted except forpersonal and internal use. Multiple copying of the content of this publication without permission is always illegal. Web-offset printing byWyndeham Heron, The Bentall Complex, Colchester Road, Heybridge, Maldon, Essex, UK

Co-operating Organisations The Institution of Electrical Engineers acknowledges the contribution made by the followingorganisations in the preparation of this publication: British Electrotechnical & Allied Manufacturers Association Ltd – R Lewington,P D Galbraith, M H Mullins | Office of the Deputy Prime Minister – K Bromley, I Drummond | Electrical Contractors Association – D Locke, S Burchell | City & Guilds of London Institute – H R Lovegrove | Energy Networks Association –D J Start | Electrical Contractors Association of Scotland SELECT – D Millar, N McGuiness | Health & Safety Executive – N Gove | National Inspection Council for Electrical InstallationContracting | The Radon Council B H Ahern

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Radon – a brief explanationRadon is a naturally occurring gas that has no colour, smellor taste. The gas comes from minute amounts of uraniumpresent in all earth materials such as rocks, soil, bricks andconcrete.

Radon is present in all parts of the UK, but in the mostpopulous areas the levels are quite low. Some of the highestlevels are found in the south west, but levels well aboveaverage have been found in some other parts of Englandand parts of Scotland, Wales and Northern Ireland.However, even in these areas most homes have low levels.Maps showing the areas of the country affected by radonare available from the National Radiological ProtectionBoard (NRPB). However, radon can be found in other areasand, even though levels may be low, isolated high levels canoccur. The only way to be sure is to conduct a radon test inthe building.

Basic methods of radon reduction The objective of all radon reduction schemes is to reduceradon levels within a building so that levels of exposure to occupants is reduced. It is not possible to remove radon entirely.

New BuildingsGiven that radon enters a building from the ground onwhich it is built, it follows that the most effective means ofreduction is to prevent it entering in the first place. Thiscan be achieved by placing a radon barrier over the entirefootprint of the building prior to construction. Providingthe barrier is gas tight and not perforated, very low indoorlevels can be achieved, even in areas known to have highlevels of radon.

Existing BuildingsThe majority of the housing stock in the UK consists ofexisting buildings, many of which are older and built usingtraditional methods. It has been necessary to designsuitable systems for radon reduction, once a building hasbeen found to have high levels. Available methods of radonreduction include mechanical ventilation. Three methods ofradon reduction using mechanical ventilation have provedto be effective and are described below.

1) Sump with extract fanThis is the most effective method so far devised for reducinghigh levels of radon. The sump is constructed either by

What is radon gas, and how can it be reduced?

RADON GAS

By John Ware

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vertical internal coring or external horizontal coringinto the sub-slab space beneath the damp proof coursemembrane. The sump is connected via ducting to an in-line fan that sucks out soil gases and exhausts themto atmosphere. The extract fan is mounted either insidethe building or, in most cases, externally on an outsidewall giving reduced noise and easier access.

Advantages: � Effective at high and very high radon levels.

Disadvantages: � The installation is frequently not effective for

timber (suspended) floors.� The installation is clearly visible in the case of the

external fan arrangement.

2) Positive pressurisationA building has an inherent negative pressurisationbecause warm air rises and the method of positivepressurisation partly overcomes this natural airflow.Positive pressurisation is achieved by fitting apurpose-built fan system in the attic space. The fanblows air downwards into the property through aceiling diffuser, usually above a stairwell. Suchsystems were initially used for reducing condensationbut have subsequently been found to be effective atreducing levels of radon. For reasons of reducingdraughts and noise the fan operates at low speed andpower level, hence it is only suitable in ‘air tight’properties with relatively low radon levels.

Advantages: � Easy and unobtrusive installation, condensation

reduction.

Disadvantages: � Only effective in certain properties and at fairly low

radon levels. Opening the windows and doors, insummer for example, reduces the effectiveness ofthe system.

3) DilutionRadon levels in properties with suspended timberfloors can be reduced by increasing the air-flowbeneath the floor. Increased air flow is achieved by theuse of an in-line fan forcing air from one side of thebuilding and exhausting via airbricks on the other.

Advantages: � The fan can be mounted beneath the floor and would

be unobtrusive.

A sump is excavated under the property and an extract fan exhausts gases to the outside air

Disadvantages: � Not always successful and fan noise can be a problem.

Recommendations applicable to fan-operated radonreduction systemsThe fan of a fan-operated radon reduction systemshould be supplied by a permanent connection to thefixed wiring of the installation. A fan should not be

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connected via a 13A plug and socket arrangement orother removable means.

The supply for a fan-operated radon reductionsystem should be supplied by one of the following:� An independent circuit at the dwelling’s main

distribution board, in which case no other electricalequipment should be connected to the circuit andRCD protection should not be provided, unlessnecessary for reasons of electrical safety.

� A separate electrically-protected regularly-usedlocal lighting or ring or radial final circuit.The use of moulded, non-conductive fan assemblies

is recommended.

Prior to making an alteration or addition to anelectrical installationNo addition or alteration, temporary or permanent,can be made to an existing electrical installationunless it has been ascertained that the rating andcondition of any existing equipment is adequate forthe altered circumstances and that the earthing andbonding arrangements are adequate (Regulation 130-07-01 of BS 7671 refers).

In the case of a fan-operated radon reductionsystem, the additional load of the fan placed on anexisting circuit will not be large. The installer mustascertain that the rating and condition of the existingcircuit is adequate, that the protective device for theexisting circuit is suitable and will provide protectionfor the modified circuit and any other relevant safetyprovisions are satisfactory.

The installer is also required to check that theinstallation’s earthing and bonding arrangements areadequate. The presence and adequacy of a means ofearthing for the installation must be checked as mustthe equipotential bonding arrangements.

Sump and similar ventilation systems using a fanmounted inside the buildingProviding the protective device for the existing circuitis suitable and provides protection for the modifiedcircuit, and that other relevant safety provisions aresatisfactory, the fan should be supplied from anexisting ring or radial final circuit via a fused spur.Isolation at the consumer unit would permit fanreplacement or maintenance as necessary.

Sump and similar ventilation systems using a fanmounted outside the buildingThe external fan selected should be in a dustprotected, splash proof housing to IP54 or better. Thefan should be mounted on an external wall and due

Air from the attic space is blown downwards into the building

consideration should be taken of external influencessuch as the possibility of mechanical damage or theingress of water, for example, due to leakingrainwater gutters and downpipes. External wiringshould be minimised. Electrical connection should bemade within the building to an existing local ringfinal or radial circuit via a fused spur. Isolation at theconsumer unit would permit fan replacement ormaintenance as necessary.

Loft mounted positive pressurisation systemThe fan should be wired into the existing lightingcircuit. A local double pole isolating switch should beprovided to permit isolation of the supply so that thefan can be replaced or maintained as necessarywithout the need to switch off the lighting circuit.Alternatively, such maintenance could be performedby isolating the entire installation at the main switchin the consumer unit.

Inspection, testing and certificationIt must be verified that every alteration or addition toan electrical installation complies with therequirements of BS 7671 (Regulation 721-01-02 of thatStandard refers). Inspection and testing must beperformed. (Chapter 71 refers). Inspection includes

checking that installed electrical equipment is suitable,correctly installed, not damaged so as to impair safetyand that the detailed requirements of BS 7671 have beenmet (Refer to Regulation 712-01-03). Requirements fortesting are detailed in Regulation 713 and shouldinclude, as a minimum, tests of continuity, insulation,polarity and earth fault loop impedance.

The electrical installer must issue either anElectrical Installation Certificate or DomesticElectrical Installation Certificate if the work involvesa new circuit or a Minor Works certificate providedthat the alteration or addition to the installation isminor and does not include the provision of a newcircuit. A Minor Works certificate could be issued forthe addition of a fused spur to an existing ring orradial final circuit or for the addition of a point to anexisting lighting circuit.

User instructionsIt is important that appropriate documentation andinstructions are given to the user of the installation.Such instructions should include:� An explanation of radon gas and its effects� An explanation of the need to keep the fan operational� Routine checks that should be made � Contact numbers

The Radon CouncilThe Radon Council is a non-profit making self-regulatory body formed in 1991 in response tocalls from the Chairman of a Parliamentary Selectcommittee on Indoor Pollution. The organisation runsfull day training courses with an examination, andissues an annual list of contractors who havesuccessfully completed one of its courses and havesigned a Code of Practice.

For further information on radon, contact the Radon Council at PO Box 39, Shepperton, Middlesex,TW17 8AD. Telephone 01932 221212 and website www.radonhotline.org.

Another valuable contact is the Building ResearchEstablishment, Bucknalls Lane, Garston, WatfordWD25 9XX. Telephone 01923 664707, Fax 01923 664711 orwww.bre.co.uk/radon.

The National Radiological Protection Board (NRPB)may be contacted at Chilton, Didcot, Oxon OX11 0RQ,Telephone 01235 831600 and website www.nrpb.org.uk.A free answerphone for householders is available on0800 614529 and a radon report service on 01235 822784.

Radon levels in properties with suspended timber floors can be reduced by increasing the air flow beneath the floor

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THE IEE receives a number of enquiries fromdesigners and installers and others regarding theapplication of Regulation 527-02-01 when installingrecessed luminaries in ceilings in domestic premises.Regulation 527-02-01 is clear enough. It requires thatwhere a wiring system passes through elements ofbuilding construction such as floors, walls, roofs,ceilings, partitions or cavity barriers, the openingsremaining after passage of the wiring system shall besealed according to the degree of fire resistancerequired of the element concerned (if any). The twowords in brackets at the end of the Regulation, (ifany), highlight the problem. Simply stated, thequestion is: if an electrician is installing one or morerecessed downlighters in a location such as a domestickitchen, for example, what degree of fire resistance isrequired? Is any degree of fire resistance required?This question has been highlighted by theintroduction of Part P into the Building Regulations.This article will not deal with protection againstthermal effects, for which reference should be made toChapter 42 of BS 7671: 2001 and IEE Guidance Note 4,Protection Against Fire. Reference should always bemade to Part B of the Building Regulations for firesafety requirements. For sound insulationrequirements, reference should be made to Part E ofthe Building Regulations. It should be emphasised atthe outset that this article is intended to provideguidance, which, it is hoped, will prove helpful; it isrecommended that the local building control beconsulted for advice.

Fire compartmentsLet’s begin with a brief review of some theory aboutfire safety. The spread of fire within a building isrestricted by sub-dividing the building intocompartments separated from one another by wallsand/or floors of fire-resisting construction. There aretwo reasons for this:� To prevent the rapid spread of fire that could trapoccupants of the building; and� To reduce the chance of fires becoming large on thebasis that large fires are more dangerous not only tooccupants and fire service personnel but to people inthe vicinity of the building.

DwellingsWalls that separate semi-detached houses or terracedhouses are constructed as fire compartment wallsand the houses are considered as separate buildings.Where a domestic garage is attached to a house, (orforms an integral part of it), the garage should be

INSTALLINGRECESSEDLUMINAIRESIN CEILINGSby Bill Allan

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separated from the rest of the house. In buildingscontaining flats or maisonettes, every floor isconstructed as a fire compartment floor (unless it iswithin a maisonette, i.e. between one storey andanother within one dwelling) and every wall thatseparates a flat or a maisonette from any other partof the building is constructed as a fire compartmentwall. Otherwise, the walls and ceilings withindetached, semi-detached and terraced houses are notconstructed as fire compartment walls and ceilings.

Installing downlighters in ceilings that are not firecompartmentsDownlighters are commonly installed in locationssuch as kitchen ceilings, which are not firecompartment ceilings. But because they are not firecompartment ceilings does not mean that they don’trequire some degree of fire resistance. The minimumfire resistance of a floor in a two-storey house, forexample, is given in Appendix A of ApprovedDocument B , ‘Fire Safety’, as 30 minutes (See

Table A1). The idea is that, in a fire situation, the floorwill not collapse for at least 30 minutes, enablingbuilding occupants to leave safely.

Downlighters are usually made of steel oraluminium and have a diameter of approximately50mm (the holes themselves being about 60mm).Common sense suggests that cutting a number of holesin the plasterboard ceiling of a timber joisted floor maycompromise its fire resistance capability. One measureto help the situation is to keep the number ofdownlighters in any one area to a minimum and tospace them as far apart as possible. Solutions proposedto restore the integrity of the ceiling’s fire resistanceinclude building a plasterboard box around luminairesor installing commercially available ‘fire hoods’. But is it necessary to restore the fire resistancecapability of ceilings?

The TTL testsIn 1996, the DoE and TRADA commissioned TRADATechnology Limited (TTL), a member of the TTLChiltern group of companies, to test the effect ofrecessed downlighters (with no boxing in or firehoods) on the fire resistance of plasterboard ceilingswith conventional rectangular joists. TTL has beeninvolved in fire research and testing for many yearsand is the UK’s leading authority on the fireprotection of timber. During 1994/95, TTL carried outthe tests. The results of the tests were published inthe July 1996 edition of Building Control magazine.These results were, perhaps, surprising in that theyconfirmed that downlighters, even without beingboxed in and with no fire hoods, in plasterboardceilings have little significant effect on fire resistanceratings up to 30 minutes. It must be inferred fromthese tests therefore, that, at least with plasterboardceilings with conventional rectangular joists, it is notnecessary to ‘box in’ luminaries or to use fire hoodsfor the purpose of restoring the fire resistancecapability of ceilings which are not of firecompartment construction.

Downlighters in ceilings under roof spacesHowever, in situations where downlighters areinstalled in ceilings under roof spaces, where debrisor thermal insulation may accumulate on top of theluminaire, a case could be made for building aplasterboard or metal box around the luminaire orinstalling a fire hood. When boxing in a luminaire, inthe absence of any manufacturers’ guidance, a gap ofabout 100mm around the luminaire and 75mm aboveis recommended to allow for heat dissipation.

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Downlighters in flats and maisonettesAs mentioned earlier, in buildings containing flatsor maisonettes, floors are constructed as firecompartment floors. However, suspended ceilings,comprising metal grids and plasterboard with voidsof approximately three inches, are frequentlyinstalled for sound insulation and to hide services.Where suspended ceilings have been installed inflats and maisonettes, they can conveniently beutilised to install downlighters without fireproofing.In Scotland, the Building Regulations don’t allowdownlighters to be installed in fire compartmentceilings if they are timber-based, unless a suspendedceiling has been provided. It is understood that thisrequirement is to reduce noise transmissionbetween dwellings.

Installing downlighters in fire compartment ceilingsFor fire compartments to be effective, there must becontinuity at the junctions of the fire-resistingelements that enclose them, and any openings fromone compartment to another should not present aweakness. Section 9 of Approved Document B, ‘FireSafety’ permits openings to be made incompartment walls and floors for certain purposes,including the passage of pipes, etc, that meet theprovisions in Section 11. Clearly, the requirementsof Approved Document B must be satisfied wheninstalling downlighters in fire compartmentceilings. The advisability of keeping the number ofdownlighters in any one area to a minimum and tospace them as far apart as possible was mentionedearlier but it is especially important wheninstalling downlighters in fire compartmentceilings. As the period of fire resistance for firecompartment ceilings will be at least 60 minutes, itwill be necessary to restore their fire resistancecapability. The use of fire hoods or ‘boxing in’ ofluminaries could be considered as a way ofachieving this. Any openings remaining after theinstallation of downlighters must be sealedaccording to the degree of fire resistance requiredof the ceiling. The fire resistance of a firecompartment floor is typically 60 minutes butreference should be made Table A2 of the abovedocument.

Smoke alarmsIt would seem remiss not to mention that TheBuilding Regulations 2000 and the BuildingStandards (Scotland) Regulations 1990 require all

new and refurbished dwellings to be fitted withmains-operated smoke alarms, which may have asecondary power supply such as a battery (eitherrechargeable or replaceable) or a capacitor. Thesemust be installed in accordance with BS 5839, Part 6:2004. Such alarms, along with the fire resistancecapability of building elements, are an importantpart of the strategy for protecting buildingoccupants in case of fire. They would, after all, bereasonably expected to operate within minutes of asmoke situation developing.

ConclusionIt should be pointed out that manufacturers’instructions must be followed when installingdownlighters. It is hoped that this article will provehelpful in the application of Regulation 527-02-01 tothe installation of downlighters.

For such installations, it is recommended that thelocal authority building control be consulted.

IEE Wiring Matters | Spring 2005 | www.iee.org

Professional Engineering Technicians are involved in applying proven techniques andprocedures to the solution of practical engineering problems. They carry supervisory ortechnical responsibility, and are competent to exercise creative aptitudes and skills withindefined fields of Technology.

The benefits of the EngTech qualification:� sets a professional Engineering Technician apart from a technician who is unregistered;� establishes proven knowledge, understanding and competence;� demonstrates a commitment to professional standards, and to the development and

enhancement of competence;� an increasing number of countries formally recognise the standing of Engineering

Technicians, and in some cases reserve particular work for them. Evidence of registrationcan prove helpful in applying for jobs and tendering for work in those countries;

� adds credentials to your CV that are instantly recognised and respected by employersand colleagues.

To work towards becoming registered as an Engineering Technician through the IEE, you must first apply for IEE membership. You can apply for membership online or request the application form through the IEE website: http://www.iee.org/Membership/index.cfm

Once your application for membership has been approved, you can then submit yourapplication to register as an EngTech, which is available on the IEE website:http://www.iee.org/ProfessionalRegistration/FormsAndGuides/

If you would like further information on EngTech or membership, please email technician@iee.org.uk. Alternatively log on to the IEE website at: http://www.iee.org/professionalregistration/engtech/index.cfm

EngTech – Could you qualify as a professionalengineering technician?

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SWIMMING POOLSNo need to make wavesBy John Ware

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The IEE’s technical helpline continues to receive regular questions

about Section 602 – Swimming Pools, which include queries on the

zonal concept and earthing and bonding. This article is intended to

provide guidance that, it is hoped, will prove helpful.

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A SWIMMING POOL will oftenform part of a sports complex, however,these days, swimming pools arebecoming commonplace and are ofteninstalled for home use.

The increased risk associated withswimming pools is that of electricshock due to a reduction of bodyresistance because a person is wetand, also, the possibility that a personis in contact with Earth potential.Because of this risk, additionalrequirements for safety above andbeyond the general requirementsplaced by BS 7671 apply to basins ofswimming pools and paddling poolsand their surrounding zones. Theadditional requirements are detailedin Section 602 of BS 7671.

Zonal concept The basins of swimming pools and theirsurrounding areas are divided intozones A, B and C for shock protectionpurposes and for the purpose ofselecting suitable equipment.

Protection against electric shockIn zones A and B, protection againstelectric shock must be achieved by oneof the following:

� SELV. The SELV nominal voltagemust not exceed 12V a.c. or 30V d.c.and the safety source must be installedoutside of zones A, B and C.

� If floodlights are required in zones Aor B, each floodlight must be suppliedat an open-circuit voltage notexceeding 18V from its owntransformer or from its own windingof a multi-secondary transformer

� Socket-outlets should not normallybe installed in zone B. For a smallerswimming pool, where it is notpossible to install the socket-outletsoutside of zone B, the socket-outletsmust be protected by an RCD with aresidual operating current notexceeding 30mA or by electricalseparation (Regulation 602-07-01refers).

The following, rather uncommon,measures of protection againstelectric shock must not be used in anyzone of a swimming pool:

� Obstacles and Placing out of reach(for protection against direct contact)

� Non-conducting location and Earth-free equipotential bonding (forprotection against indirect contact)

Supplementary equipotential bondingSupplementary equipotential bonding(or ‘supplementary bonding’ for short)is a complementary measure forprotection against indirect contact thatis required for locations containing aswimming pool. Supplementarybonding involves connecting togetherthe conductive parts (exposed andextraneous) of electrical items and non-electrical items to prevent theoccurrence of a voltage between themunder earth fault conditions. Such avoltage could present a risk. Wheresupplementary bonding is necessary, itmust connect together the exposed-conductive-parts of equipmentin the circuitsconcerned

including the earthing terminal ofsocket-outlets and extraneous-conductive-parts. (Regulation 413-02-27refers).

Local supplementary bonding isrequired in zones A, B and C toconnect together all extraneous-conductive-parts (which could includemetal handrails, pipes, exposedsteelwork, etc) and the protectiveconductor of all exposed-conductive-parts, irrespective of whether theconductive parts are simultaneously-accessible. If a metallic grid isinstalled, it must be connected to thesupplementary bonding – but note thatthere is no requirement to providesuch a grid.

Supplementary equipotentialbonding must not be connected toSELV circuits.

Protective Multiple EarthingProtective Multiple Earthing (PME) isan earthing arrangement commonlyused by electricity distributors fortheir distribution networks where thesupply neutral conductor provides thefunction of both neutral conductorand protective conductor (A TN-C-Ssystem). Where PME is used, thepublic supply neutral conductor isreferred to as the PEN (combinedprotective and neutral) conductor orCNE (combined neutral and earth)conductor and to improve the securityof the earthing arrangements, theneutral conductor is earthed at several

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points (multiple-earthed). TheElectricity Safety, Quality andContinuity Regulations (ESQCR) 2002permit an electricity distributor toprovide a consumer with an earthingterminal which is connected to thesupply neutral conductor.

A distributor may decide not toprovide a PME earthing terminal foran installation such as that of aswimming pool. Where, however, aPME earthing terminal is provided,BS 7671 does not preclude its use foran installation that includes aswimming pool, but the installationdesigner may decide not to employ itbecause of the possibility of perceivedelectric shock within the installationor the possible danger from a brokenPEN conductor.

Perceived electric shockA small voltage difference may exist,under normal operating conditions,between the PME earthing terminalat the origin of an installation and‘true’ Earth potential. The potentialdifference is due to the voltage drop

A IPX8B IPX5

IPX4 where water jets are not likely to be used for cleaningC IPX2 for indoor pools

IPX4 for outdoor poolsIPX5 where water jets are likely to be used for cleaning

Zone Minimum degree of protection

The zonal concept for a particular swimming pool

in the PEN conductor caused by loadcurrent returning to the source of thesupply through the PEN conductorwhich has a certain impedance. Thesmall voltage, above Earth potentialcould, under certain conditions suchas reduced body resistance due to thepresence of water, create thepossibility of a perceived electricshock for a person simultaneously incontact with a conductive part (forexample, a handrail that is connectedto the supplementary bonding) and‘Earth potential’ (for example, anuninsulated, wet, solid floor).Electricity distributors have in thepast received complaints of perceivedelectric shock by persons in suchlocations.

In order to avoid the risk ofperceived electric shock, the

installation within the locationcontaining a swimming pool may bemade part of a TT system. In such asystem, the exposed-conductive-partsand the extraneous-conductive-partswithin the location are separated fromthe PME earthing terminal and theinstallation in the location isconfigured to meet all the associatedrequirements of BS 7671 applicable toa TT system including being connectedto earth by a suitable installationearth electrode.

Broken PEN conductorUnder very exceptional circumstances,the supply PEN conductor connectionto an installation could be lost due to afailed joint. Where the phase conductorremains unbroken, a risk of electricshock from exposed-conductive-parts

and extraneous-conductive-parts couldforseeably arise. In most installations,the main equipotential bonding playsan important role in protecting againstthe danger from the loss of a PENconductor.

External influences and accessibilityEach item of electrical equipment inthe electrical installation must beselected and erected to take account ofthe external influences at theparticular place where it is installed(Section 522 refers). In a swimmingpool environment the presence ofwater (Regulation 522-03) andcorrosive or polluting substances(Regulation 522-06) are of particularconcern. The general requirements ofSection 522 are supplemented by theadditional requirements placed in

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Section 602, which require that theminimum degrees of protection are asindicated in the table in this article.

All electrical equipment must beaccessible, for example, luminariesshould not be mounted over waterunless suitable access is available.

Types of socket-outletA socket-outlet must be either:� An industrial type complying with

BS EN 60309-2; or

� A shaver socket-outlet complying withBS EN 60742(1) Chapter 2 Section 1.

Zones A and BSwitchgear, controlgear andaccessories are not to be installed.Only current-using equipmentspecifically designed for a swimmingpool application may be installed.Socket-outlets may be installed inzone B providing they are more than1.25m from the border of zone A, atleast 0.3m above the floor, protectedby a 30mA RCD or by electricalseparation with the safety isolatingtransformer installed outside of thezones.

The only wiring permitted in zonesA and B is that necessary to supplyequipment in those zones. Wiringsystems using metal conduit, trunkingor exposed metallic sheaths is not

permitted. Exposed earthing orbonding conductors must not be used;neither must metal enclosures ormetal junction boxes.

Zone CExcept for instantaneous waterheaters, equipment in zone C must beprotected by a 30 ma RCD, SELV, orelectrical separation.

A socket-outlet, switch, accessory ispermitted in zone C but must beprotected by electrical separation,SELV, a 30 mA RCD. Shaver socket-outlet complying with BS EN 60742(1)Chapter 2 Section 1 are permitted.Cords of cord-operated switches arepermitted in zone C.

Electric heating embedded in the floorElectric heating embedded in thefloor is permitted in zones B or Cand must either incorporate ametallic sheath or be covered by anearthed metallic grid. In either case,the sheath or the grid must beconnected to the local supplementarybonding.

(1)BS EN 60742 has been superseded by

BS EN 61558-2-5.

Earthed metal grid

IEE Wiring Matters | Spring 2005 | www.iee.org

Volumezone C

Volumezone B

Volumezone A

Volumezone A

Volumezone B

Volumezone A

Volumezone C

NOTE: The dimensions are measured taking account of walls and fixed partitions

1.5m 1.5m

2.5m

2.5m

1.5m 2.0m 1.5m2.0m

Extract from BS 7671, Fig 602A- zone dimensions for swimming pools and paddling pools

SWIM

MIN

GP

OO

LS

19

maintenance engineers,