2009 30 spring wiring matters protective measures and special installations or locations

Protective Measures & Special Installations | 21

IET Wiring Matters | Spring 09

There are a number ofmeasures to protect againstelectric shock. This article,which is the first part of two,looks at summarising theseprotective measures applied toSpecial Installations orLocations as defined in Part 7of the 17th Edition of the IEEWiring Regulations(BS7671:2008). In particularthis article looks at Sections701 to 711.One of the fundamental

principles for electricalinstallations is protection forsafety (Section 131) in which

Regulation 131.2, Protectionagainst electric shock,requires protection to preventa person or livestock cominginto contact with live parts bythe provision of basicprotection (direct contact) aswell as fault protection(indirect contact) to preventan electric shock when anexposed conductive partbecomes live due to a fault.The technical requirementsof this principle are dealt within Part 4 of the Regulationsby Chapter 41 “Protectionagainst electric shock”.

This chapter highlights fourgeneral protective measuresthat are generally permitted(Regulation 410.3.3):

� Automatic disconnection ofsupply (Section 411)

� Double or reinforcedinsulation (Section 412)

� Electrical separation for thesupply to one item ofcurrent using equipment(Section 413)

� Extra –low voltage SELV andPELV (Section 414)

The application of one or

more of these protectivemeasures in an installationneeds to take into account theexternal influence. Section415 also gives requirements toprovide additional protectionby the provision of a residualcurrent device (RCD) andsupplementary equipotentialbonding for certain conditions,including Special Installationsor Locations. For SpecialInstallations or Locations (Part7) there are particularrequirements for each Sectionthat either supplement ormodify the requirements of

Protective Measures & SpecialInstallations or Locations (Part 1)by Paul Bicheno

22 | Protective Measures & Special Locations


AutomaticDisconnectionof Supply (411)

Double or ReinforcedInsulation(412)

Electrical Separation–supplying single itemof equipment (413)

Extra LowVoltage(414)

General Requirementsand AdditionalProtection (415)

Locationscontaining abath orshower (701)

All circuits of the location requireadditional protection by provisionof one or more 30 mA RCDs withthe characteristics specified inRegulation 415.1.1.

General Regulations of this Sectionapply

Circuits can only supply one itemof current using equipment orthere can only be one singlesocket outlet allowed.

Not permitted for electric floorheating systems.

Irrespective of the nominal voltageused there shall be provision ofbasic protection of live parts inzones 0, 1 and 2 by either;(i) Basic insulation complying withRegulation 416.1.(ii) Barriers or enclosures affordinga degree of protection at leastIPXXB or IP2X in accordance withRegulation 416.2.If SELV is used to supply anelectric floor heating system thenconnection of the metallic grid tothe supply circuit is not required.

Local supplementary bonding isrequired connecting protectiveconductor of each circuitsupplying class I or II equipmentto accessible extraneousconductive parts in the location.

Note: This can be omitted undercertain conditions (See Regulation701.415.2)

Swimmingpools andother basins(702)

All extraneous conductive parts inzones 0, 1 and 2 are to beconnected by supplementarybonding conductors to theprotective conductors of exposedconductive parts of the equipmentsituated in the zones.

If using this measure forequipment for use in the interior ofa basin when not occupied thecircuit is to be protected by a 30mA RCD with the characteristicsspecified in Regulation 415.1.1

If using this measure for zones 0and 1 of a fountain then the circuitis to be protected by a 30 mARCD with the characteristicsspecified in Regulation 415.1.1

If using this measure for zone 2then the circuit is to be protectedby a 30 mA RCD with thecharacteristics specified inRegulation 415.1.

General requirements of thisSection apply except wherespecific zone requirementsdetermine the protective measure

If using this measure forequipment for use in the interior ofa basin when not occupied it shallonly supply one item of equipmentwith the source being installedoutside zones 0, 1 and 2. (Thesource can be installed in zone 2 ifthe supply circuit is protected by a30 mA RCD with thecharacteristics specified inRegulation 415.1.1)

If using this measure for zones 0and 1 of a fountain then only oneitem of equipment can be suppliedwith the source being installedoutside zones 0 and 1.

If using this measure for zone 2then only one item of equipmentcan be supplied with the sourcebeing installed outside zone 2.(The source can be installed inzone 2 if the supply circuit isprotected by a 30 mA RCD withthe characteristics specified inRegulation 415.1.1)

Irrespective of the nominal voltageused there shall be provision ofbasic protection of live parts inzones 0, 1 and 2 by either;(i) Basic insulation complying withRegulation 416.1.(ii) Barriers or enclosures affordinga degree of protection at leastIPXXB or IP2X in accordance withRegulation 416.2.

If using this measure forequipment for use in the interior ofa basin when not occupied theSELV source is to be installedoutside zones 0, 1 and 2. (Thesource can be installed in zone 2 ifthe supply circuit is protected by a30 mA RCD with thecharacteristics specified inRegulation 415.1.1)

If using this measure for zones 0and 1 of a fountain then the SELVsource is to be installed outsidezones 0 and 1.

If using this measure for zone 2then the SELV source is to beinstalled outside zones 0, 1 and 2.(The source can be installed inzone 2 if the supply circuit isprotected by a 30 mA RCD withthe characteristics specified inRegulation 415.1.1)

Zones 0 and 1Except for fountains, in zone 0only protection by SELV notexceeding a nominal 12 V ac (30V dc) and in zone 1 not exceeding25 V ac (60 V dc) is allowed. Ineither case the source is to beinstalled outside zones 0, 1 and 2.

Equipment for use in the interior ofbasins that is intended to be usedwhen people are not inside thezone 0 are to be supplied by eitherSELV, automatic disconnection ofsupply or electrical separation(refer to each measure for therequirements). If a socket outlet isused to supply this equipmentthen a notice is to be provided towarn the user that is shall be usedonly when the basin is notoccupied by persons.

Zones 0 and 1 specific tofountainsThese zones shall use one or moreof SELV, automatic disconnectionof supply and electrical separation(refer to each measure for therequirements)

Zone 2This zones shall use one or moreof SELV, automatic disconnectionof supply and electrical separation(refer to each measure for therequirements)

Rooms andcabinscontainingsauna heaters(703)

All circuits for the location requireadditional protection by providingone or more 30 mA RCDs with thecharacteristics specified inRegulation 415.1.1. An exceptionis the sauna heater unlessrecommended by themanufacturer.



Irrespective of the nominal voltageused there shall be provision ofbasic protection of live parts inzones 0, 1 and 2 by either;(i) Basic insulation complying withRegulation 416.1.(ii) Barriers or enclosures affordinga degree of protection at leastIPXXB or IP2X in accordance withRegulation 416.2.

Circuits require additionalprotection by RCDs (refer toautomatic disconnection of supply)

Constructionanddemolitionsiteinstallations(704)

If using this measure for supplyinga socket outlet or hand held pieceof electrical equipment notexceeding 32 A then additionalprotection is required by a 30 mARCD with the characteristicsspecified in Regulation 415.1.1

A circuit supplying one or moresockets outlets with a ratingexceeding 32 A shall have an RCDnot exceeding 500 mA interruptingthe supply to the line conductors.Also Regulations 411.3.2.5 and411.3.2.6 are not applicable

A TN-C-S supply shall not be usedto supply the site, except for thesupply to fixed building(s).

General Regulations of this Sectionapply except where specificmeasures are required

If using this measure for supplyinga socket outlet or hand held pieceof electrical equipment notexceeding 32 A then each socketoutlet and hand held piece ofelectrical equipment is to besupplied by an individualtransformer or by a separatewinding of a transformer.

Special attention to be paid toRegulation 413.3.4 which requiresflexible cables and cords to bevisible throughout their length ifliable to mechanical damage

Irrespective of the nominal voltageused there shall be provision ofbasic protection of live parts byeither;

(i) Basic insulation complying withRegulation 416.1.(ii) Barriers or enclosures inaccordance with Regulation 416.2.

SELV is preferred for portable handlamps in damp or confined spaces

Circuits supplying a socket outletor hand held electrical equipmentnot exceeding 32 A is to beprotected by either;

(i) reduced low voltage (seeSection 411.8 of BS7671)(ii) automatic disconnection ofsupply (refer to protectivemeasure)(iii) Electrical separation (refer toprotective measure)(iv) SELV or PELV (generalrequirements apply)

Reduced low voltage is preferredfor supply to general portable handlamps, portable hand tools andlocal lighting up to 2 kW.

Protective Measures & Special Installations | 23


AutomaticDisconnectionof Supply (411)

Double or ReinforcedInsulation(412)

Electrical Separation–supplying single itemof equipment (413)

Extra LowVoltage(414)

General Requirementsand AdditionalProtection (415)

Agriculturalandhorticulturalpremises(705)

Circuits supplying socket-outletsnot exceeding 32 A are to beprotected by 30 mA RCDs,exceeding 32 A by 100 mA RCDsand all other circuits 300 mARCDs.

A TN-C system shall not be usedin the installation (includingresidences and other premises).



Irrespective of the nominal voltageused there shall be provision ofbasic protection of live parts byeither;(i) Basic insulation complying withRegulation 416.1.(ii) Barriers or enclosures affordinga degree of protection at leastIPXXB or IP2X in accordance withRegulation 416.2.

Supplementary bonding isrequired in locations wherelivestock can touch exposedconductive parts and extraneousconductive parts. This includes ametal grid in the floor if installedand extraneous conductive partsin, or on a floor e.g. reinforcedconcrete. Spaced floorarrangements should also beincluded. (Where no metal grid isinstalled in the floor a TN-C-Ssupply is not recommended).

Conductinglocations withrestrictedmovement(706)

This measure can only be used forsupplying fixed equipment. Alsorequires supplementaryequipotential bonding of allexposed conductive parts of fixedequipment and conductive parts ofthe location

If a functional earth is requiredthen equipotential bonding isrequired between all exposedconductive parts and extraneousconductive parts inside thelocation and the functional earth

This measure can only be used forsupplying fixed class II equipmentor equipment with equivalentinsulation. The supply circuit is tobe protected by a 30 mA RCDwith the characteristics specified inRegulation 415.1.1

This measure can only be used forsupplying a hand held tool or anitem of mobile equipment andfixed equipment as long as onlyone item is connected to asecondary winding of atransformer. The transformer canhave more than one winding.

The unearthed source is to havesimple separation and is to belocated outside the location, unlessit is part of the fixed installationwithin the location.

SELV can be used for supplying ahand held tool or an item ofmobile equipment, hand lampsand fixed equipment.

PELV can be used for supplyingfixed equipment provided there isequipotential bonding of exposedconductive parts, extraneousconductive parts inside thelocation and the connection of thePELV system to earth.

Basic protection is to be providedby basic insulation complying withRegulation 416.1 or barriers orenclosures complying withRegulation 416.2

For this type of location theprotective measures applicable forthe supply to various types ofequipment are limited (refer toeach measure)

Electricalinstallationsin caravan /campingparks (708)

For a TN system only a TN-Sinstallation can be used, howevera TN-C-S system can be used tosupply permanent buildings on thesite.




Each socket outlet is to beprotected by a 30 mA RCD withthe characteristics specified inRegulation 415.1.1

Marinas andsimilarlocations(709)

For a TN system the final circuitsto pleasure craft and houseboatsare not to include a PENconductor.

Socket outlets and final circuitsintended for fixed connections tosupply houseboats are to beprotected by a 30 mA RCD withthe characteristics specified inRegulation 415.1.1





Exhibitions,shows andstands (711)

Structural metallic parts which areaccessible from within the stand,vehicle, wagon, caravan orcontainer shall be connected viamain protective bondingconductors to the main Earthingterminal within the unit.

A system of type TN shall be TN-S(TN-C-S is prohibited for supply toa caravan or similar construction).



Irrespective of the nominal voltageused there shall be provision ofbasic protection of live parts byeither;

(i) Basic insulation complying withRegulation 416.1.(ii) Barriers or enclosures affordinga degree of protection at leastIPXXD or IP4X in accordance withRegulation 416.2

A cable supplying a temporarystructure is to be protected at itsorigin by an RCD not exceeding300 mA. It is to incorporate a timedelay or be of the S-type to providediscrimination where final circuitRCDs are used.

Each socket outlet not exceeding32 A and all final circuits otherthan for emergency lighting shallprotected by a 30 mA RCD withthe characteristics specified inRegulation 415.1.1.

the protective measuresdefined in Chapter 41.Table 1 summarises theapplication of the protectivemeasures for the definedSpecial Installations orLocations, highlighting thespecific supplementary ormodified requirements for aprotective measure. In certain

instances there areadditional generalrequirements as well asadditional protection (Section415) requirements whichenhance the protectivemeasures.As well as the general

protective measures alreadydescribed there is the

protective measure ofobstacles and placing out ofreach (Section 417). It isworth highlighting that this isa protective measure that onlyprovides basic protection andwould only be applicable ininstallations that are restrictedto skilled or instructedpersons under the supervision

of skilled persons. Thereare also other protectivemeasures that are applicablein an installation that iscontrolled or under thesupervision of skilled orinstructed persons(Section 418) to avoidunauthorized changes,these are:

Table 1 – Summary of the general protective measure requirements for Special Installations or Locations (701 to 711)

24 | Protective Measures & Special Locations


Obstacles and placingout of reach(417)

Non-conductingLocation(418.1)

Earth free localequipotential bonding(418.2)

Electrical separation –supplying more than oneitem of equipment(418.3)

Locations containing a bath or shower(701)

Not permitted Not permitted Not permitted See Note 2

Swimming pools and other basins (702) Not permitted Not permitted Not permitted See Note 2

Rooms and cabins containing saunaheaters (703)


Construction and demolition siteinstallations (704)

Not permitted See Note 1 See Note 1 See Note 2

Agricultural and horticultural premises(705)


Conducting locations with restrictedmovement (706)

Not permitted Not applicable as it is a conductinglocation

See Note 3 See Note 2

Electrical installations in Caravan /camping parks (708)


Marinas and similar locations (709) Not permitted Not permitted Not permitted See Note 2

Exhibitions, shows and stands (711) Not permitted Not permitted Not permitted See Note 2

Note 1:

Although the use of this measure is not specifically restricted by a Regulation in Part 7 for this location this method of protection is not recognised for

general application and is only to be applied where the installation is under the supervision of skilled or instructed persons so that unauthorized

changes cannot be made. There are specific requirements for some locations that effectively restrict the use of this measure (refer to Table 1).

Note 2:

Although the use of this measure is not specifically restricted by a Regulation in Part 7 for this location this method of protection is only to be applied

where the installation is under the supervision of skilled or instructed persons so that unauthorized changes cannot be made. There are specific

restrictions in the use of electrical separation supplying only a single piece of equipment for some locations that effectively restricts the use of this

measure (refer to Table 1).

Note 3:

Although the use of this measure is not specifically restricted in Part 7 by a Regulation for this location this measure would not be permitted due to the

requirements for specific equipment types and allowable protective measures (refer to Table 1).

� Non-conducting location(Section 418.1)

� Earth-free equipotentialbonding (Section 418.2)

� Electrical separation for thesupply to more than oneitem of current usingequipment (Section 418.3)

Due the nature of these typesof protective measures thereare a number of restrictions inrelation to Special Installationsor Locations. Table 2summarises the application ofthe above protective measuresfor the defined SpecialInstallations or Locations

(Sections 701 to 711).

The IET Guidance Note 7 –Special Locations deals withSpecial Installations orLocations. This is beingaligned and updated to the17th Edition and will provideadditional guidance to theinformation provided here. �

Table 2 – Specific protective measures applied to Special Installations or Locations (701 to 711)

2009 30 spring wiring matters protective measures and special installations or locations

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