Electrical wiring (UK) Pre-1977 IEE Pre-2004 IEE Current IEC Protective earth (PE) Green Green/yellow bi-colour Green/yellow bi-colour Neutral (N) Black Black Blue Single phase: Live (L) Three phase: L1 Red Red Brown Three phase: L2 Yellow Yellow Black Three phase: L3 Blue Blue Grey The modern UK standards and regulations for electrical wiring no longer differ sub- stantially from those in other European coun- tries. However, there are a number of note- worthy national peculiarities, habits and tra- ditions associated with domestic electrical wiring in the UK (and Ireland) that differ sig- nificantly from other countries. These, along with their historic background, are the focus of this article. They include: • ring circuits • fused plugs • switched sockets • absence of normal switches and sockets in bathrooms (except for special pull-cord ceiling switches and "shaver sockets" with built-in isolation transformer) • historic wiring colours • asymmetric supply-voltage tolerances Legal basis In England and Wales, the Building Regula- tions (Approved Document: Part P) require that domestic electrical installations are de- signed and installed safely according to the "fundamental principles" given in British Standard BS 7671 Chapter 13. These are very similar to the fundamental principles defined in international standard IEC 60364-1 and equivalent national standards in other countries. Accepted ways for fulfilling this legal requirement include • the rules of the IEE wiring regulations (BS 7671), colloquially referred to as "the regs" (BS 7671: 2008, 17th Edition).; • the rules of an equivalent standard approved by a member of the EEA (e.g., DIN/VDE 0100); • guidance given in installation manuals that are consistent with BS 7671, such as the IEE On-Site Guide and IEE Guidance Notes Nos 1 to 7. Installations in commercial and industrial premises must satisfy various safety legisla- tion, such as the Electricity at Work Regula- tions 1989. Again, recognised standards and practices, such as BS 7671 "Wiring Regula- tions", are used to help meet the legislative requirements. Wiring colours The standard wiring colours in the UK are (as of 2006) the same as elsewhere in Europe, Australia, and New Zealand and follow inter- national standard IEC 60446. This colour scheme had already been introduced for ap- pliance flexes in the UK in the early 1970s, however the IEE recommended a different scheme for fixed wiring until 2006. As a res- ult, the international standard blue/brown scheme is as of 2006 found in all but the old- est appliance flexes. In fixed wiring, the blue/ brown scheme is only found in very new (post-2004) installations, and electricians are likely to encounter the old IEE black/red scheme in existing installations for many more decades. The standard colours in fixed wiring were harmonized in 2004 with the regulations in other European countries and the interna- tional IEC 60446 standard. For a transitional period (April 2004 – March 2006) either set of colours were allowed (but not both), provided that any changes in the colour scheme are clearly labelled. From April 2006, only the new colours should be used for any new wiring. From Wikipedia, the free encyclopedia Electrical wiring (UK) 1 Potential for confusion The colour change has been controversial and was delayed for three decades, because the colour blue which was previously used as a phase colour is now the colour for neutral, and the colour black which was previously used for neutral now indicates a phase. While confusion in identification of these conduct- ors could be dangerous, the combinations of colours used usually resolves ambiguities. The installation of cables with the ’new’ col- ours in an installation where the ’old’ colours exist, could leave the way open for confusion; it is important in such situations that consid- eration is given to correct identification of the cables – with the use of marker tags if ne- cessary. It has also been suggested that the new phase colours are difficult to distinguish in low-light conditions, but the same can be claimed for most colour combinations, includ- ing the old British phase colours. A mnemon- ic advantage of the new colours is that the first two letters of "BLue" and "BRown" match the corresponding positions on the BS 1363 socket face: "bottom left" (neutral) and "bottom right" (live). Direct current systems Direct current mains are now only of historic- al interest in the UK but they also gave rise to possible confusion because the colours used were red for positive and black for neg- ative. With a three-wire distribution system (similar to an AC split-phase electric power system) it was possible for either positive or negative to be live, creating an additional op- portunity for confusion. Ring circuits v. radial circuits UK electrical power circuits are normally de- scribed as either radial or ring. A radial circuit is one where power is transmitted from point to point by a single length of cable linking each point to the next. It starts at the main switch or fuse and simply terminates at the last connected device. It may branch at a connection point. Lighting circuits are normally wired in this way, but it may also be used for low power socket circuits. A British peculiarity unknown in many oth- er national wiring codes is the ring circuit. A cable starts at the supply point and goes to each device in the same way as with a radial. The last device is connected back to the sup- ply so that the whole circuit forms a continu- ous ring. The primary advantage is to allow more power to be supplied than could other- wise be carried with a given size of cable. Cables are most commonly a single outer sheath containing separately insulated live and neutral wires, and a non-insulated pro- tective earth to which sleeving is added when exposed. There is some confusion as to why the third earthing conductor is supplied unin- sulated, however the general consensus is for ease of terminating. Standard sizes have a conductor cross sectional area of 1, 1.5, 2.5, 4, 6 and 10 mm2. Sizes of 1 or 1.5 mm are typically used for 6 or 10 ampere lighting cir- cuits and 2.5 mm for socket circuits. The pro- tective earth conductor in older cables was normally one standard size smaller than the main conductors but is now specified to be the same size. The earthing conductor is supplied uninsu- lated for a number of reasons, primarily be- cause it may be considered safer that way. If the insulation of the live/neutral wire be- comes damaged due to intrusion by a foreign object (such as a nail/screw) or by fire or heat (caused by short circuit or poor installa- tion), then the wire is more likely to earth it- self and in doing so either trip the RCD or burn the fuse out by drawing too much cur- rent. Some may argue that insulating the earth conductor would unnecessarily in- crease the cost, weight, size and rigidity of the cable. Regulations All electrical work within a domestic setting must comply with Part P of the Building Regulations in England and Wales introduced on 1 January 2005., which are legally en- forceable. One way of achieving this is to ap- ply British Standard BS 7671 (the "Wiring Regulations"), including carrying out ad- equate inspection and testing to this stand- ard of the completed works. Some of the restrictions introduced with Part P were controversial, especially the rules surrounding work carried out by non- professional (or, more accurately, unre- gistered) people such as DIYers. Under the new regulations, commencement of any work other than simple changes becomes From Wikipedia, the free encyclopedia Electrical wiring (UK) 2 notifiable to the local building control author- ity; "other than simple" in this context means any work in a kitchen or bathroom other than like-for-like replacement, work in other areas more than just adding extra lights or sockets to an existing circuit or meeting certain other criteria, such as outdoor wiring. To coincide with the new regulations, the Government approved several professional bodies to award "competent persons" status to individuals and this allows them to "self- certify" work they carry out. The building control authority must be informed of any no- tifiable work carried out by someone not qualified under this scheme before it is star- ted (unless it is an emergency) and must sub- sequently be approved by them. Originally, it was widely understood that inspection by a qualified person (leading to authority approv- al) must be organised and paid for by the home-owner or person responsible for the site and this caused some considerable criticism. On 6 April 2006, Part P was amended to clarify the actual requirements around certi- fication of DIY work (or work completed by someone otherwise unable to self-certify) and to "make enforcement more proportionate to the risk".[1] The 2006 amendment makes it clear that it is the responsibility of the building control authority to issue the necessary certificate (a Building Regulations Completion Certificate) once work has been completed. Any inspec- tion required to safely issue that certificate must be determined by, and paid for by, the building control authority. This can be done "in house" or they may contract the work out to specialist body. Note that although any in- spections are at the expense of the building authority, notification of building work is a formal process and a building control fee is payable. One of the quirks of Part P is that in some cases the installation of 12 V downlighters is notifiable where as the installation of 240 V mains downlighters isn’t. This appears strange but it’s because 12 V downlighters draw high currents and that combined with the wrong choice of wire could lead to a fire. Another element of confusion is that the term "Special Locations" has different mean- ings in Part P of the Building Regulations and BS7671 (the "Wiring Regulations"). Installation accessories Many accessories for electrical installations (e.g., wall sockets, switches) sold in the UK are designed to fit into the mounting boxes defined in BS 4662, with an 86 mm×86 mm square face plate that is fixed to the rest of the enclosure by two M3.5 screws (typ. 25 mm or 40 mm long) located on a horizont- al center line, 60.3 mm apart. Double face plates for BS 4662 boxes measure 143 mm×86 mm and have the two screws 120.6 mm apart. Accessories in the BS 4662 format are only available in a comparatively limited range of designs and lack the product di- versity and design sophistication found in other European markets. The UK installation- accessory industry is therefore occasionally criticized for being overly conservative.[2] As many modern types of electrical accessories (e.g., home automation control elements from non-UK manufacturers) are not available in BS 4662 format, other standard mounting boxes are increasingly used as well, such as those defined in DIN 49073-1 (60 mm dia- meter, 45 mm deep, fixing screws 60 mm apart) or, less commonly in the UK, ANSI/NEMA OS-1. The commonly used domestic wall-mount socket used in the UK for currents up to 13 A is defined in BS 1363-2 and normally includes a switch. For higher currents or three-phase supplies, IEC 60309 sockets are to be used instead. Note that many high load non-UK-sourced appliances need IEC 60309 connectors (or wiring via a British Standard "20 A connec- tion unit") in the UK because of the lower plug rating. Plug and accessory fuses Some accessories require protection at a lower current than that provided by the ring main protection device. The protection device used in such accessories is a 25 mm ceramic cartridge fuse, rated at 3 A, 5 A, or 13 A. In the case of permanently connected equipment the fuse is contained in a holder From Wikipedia, the free encyclopedia Electrical wiring (UK) 3 mounted in an accessory known as a fused spur box, which usually includes an isolator switch and often a neon bulb to indicate if the equipment is powered. In this case the fuse protects the spur (equipment supply) cable and any switch contacts. In the case of non-permanently connected domestic equipment, a socket rated at 13 A is attached to the ring main, into which a fused plug may be inserted. The fuse protects the contacts (including any switch contacts) and the equipment flex. There are two benefits to this arrangement. Firstly with low power equipment a flex with a low current rating (and therefore minimal diameter) can be used. Secondly, if the equipment is moved to a different socket, it will remain protected by the same (hopefully correct) fuse. The disad- vantage is that despite warnings to the con- trary people often use a fuse rated at too high a current, or even wrap a blown fuse in aluminium foil, meaning that under fault con- ditions the contacts and flex will be subjected to anything up to the maximum ring main current. This is likely to cause a fire. Note that the equipment itself should have its own protection measures, such as another fuse, unless the plug or accessory fuse af- fords all required protection (as is the case with most table lamps, for example). It is also important to be aware that when a double socket is rated at 13 A this applies to the total rating of the two sockets together, and in this case the use of a 13 A-rated double socket (e.g., a "free double socket" on an ex- tension lead) for powering more than one highly rated appliance, such as an electric fire, is dangerous. (This is not the case for most fixed-wiring outlets to BS1363, which states that the standard rating of a double socket for use as part of the fixed wiring is 20 A.) Other "high-current" appliances such as washing machine and clothes dryer should ideally be fed from separate sockets for vari- ous reasons, but note that they do not use their full rated current at all times (in the cases of the Washing Machine and Dishwash- er, for example, only when heating water which is a small percentage of the cycle). Consumer unit A domestic supply typically consists of a large cable entering the house which is con- nected to a sealed box containing the main supply fuse. This will typically have a value from 60–100 A. Separate live and neutral cables go from here to a meter, and from there proceed to one or more consumer units. This contains a main switch and indi- vidual fuses or miniature circuit breakers (MCBs) for each circuit. Special locations Bathrooms The installation of electrical devices in bath- rooms and shower rooms is regulated in Sec- tion 701 of BS 7671:2008, and Part P of the Building Regulations. For such rooms, four special zones are defined,[3] in which addi- tional protection is required for electrical facilities: • Zone 0 is the smallest cuboid volume that contains the bathtub, shower basin, etc.. • Zone 1 is the area above Zone 0, up to a height of 2.25 m above the floor. • Zone 2 is the area above Zone 1 up to a height of 3 m, as well as the area that is horizontally within 0.6 m from Zone 1. • Zone 3 is the area above Zone 2 up to a height of 3 m, as well as the area that is horizontally within 2.4 m from Zone 2. Within Zone 0, no devices are allowed apart from suitable equipment and or insulated pull cords. In Zone 1, only separated extra low voltage (SELV) devices are permitted. Any AC transformer supplying such a device must be located outside Zones 0–2. The minimum required ingress protection rating in Zone 0 is IPX7 and IPX4 in Zone 1 and 2. If water jets are likely to occur, at least IPX5 is re- quired in Zone 1–3. Otherwise, in Zone 3 and beyond, an ingress protection rating of IP20 is the minimum required. Equipment in Zone 1–3 must be protected by a 30 mA residual current device (RCD), except for shower pumps and shower heaters, where the use of an RCD is so far only recommended. Shaving sockets (with isolating trans- former) are permitted in Zone 2 if direct spray from a shower is unlikely, even if they are only IP20. In a bathroom or shower room, such shaving sockets are the only sockets permitted in the entire room. In any other room with a bathtub or shower, normal sock- ets are permitted as long as they are outside Zone 3. (Earlier British wiring rules in bathrooms used to be far more restrictive, leading to British peculiarities in bathrooms such as the From Wikipedia, the free encyclopedia Electrical wiring (UK) 4 use of cord switches. The 2001 edition of the Wiring Regulations is more flexible now, pla- cing restrictions on bathroom installations that are now more similar to those in other European countries. The forthcoming 17th Edition of the Regulations is likely to allow 13 A sockets in bathrooms, subject to zoning and protection by a 30 mA RCD.) Swimming pools For swimming pools, Section 603 of BS 7671 defines similar zones. In some of these zones, only industrial sockets according to IEC 60309 are permitted, in order to discour- age the use of portable domestic appliances with inappropriate ingress protection rating. Portable outdoor equipment For use outdoors or in other wet locations (but not bathrooms) special sockets are made. These can be divided into three main groups, industrial sockets which are totally different from the standard sockets, sockets with the same pinout as normal sockets but that will only seal properly when the correct plug and socket are used together (e.g., the 5 A, 13 A, and 15 A variants of Lewden sock- ets) and sockets that completely enclose a normal plug with a seal around the flex (e.g., MK masterseal). Sockets that are outside or can "feasibly supply equipment outside the equipotential zone" (a wording that is fairly ambiguous and the exact interpretation of which is subject to some controversy) should be protected by a 30 mA, or lower, RCD to provide additional safety. Supply voltage Since 1960, the supply voltage in UK domest- ic premises has been 240 V AC (RMS) at 50 Hz. In 1988, a Europe-wide agreement was reached to change the various national voltages, which ranged at the time from 220 V to 240 V, to a common European standard of 230 V (CENELEC Harmonization Docu- ment HD 472 S1:1988). As a result, the standard nominal supply voltage in domestic single-phase 50 Hz in- stallations in the UK has been 230 V AC (RMS) since 1 January 1995 (Electricity Sup- ply Regulations, SI 1994, No. 3021). However, as an interim measure, electricity suppliers can work with an asymmetric voltage tolerance of 230 V+10%-6% (216.2-253 V). This was supposed to be widened to 230 V ±10% (207-253 V), but the time of this change has been put back re- peatedly and currently sits in 2008 (BS 7697). The old standard was 240 V ±6% (225.6-254.4 V), which is mostly contained within the new range, and so in practice sup- pliers have had no reason to actually change voltages. The continued deviation in the UK from the harmonised European voltage has been criticised in particular by light bulb manufac- turers, who require tighter voltage toler- ances to optimise the operating temperature and lifetime of their products, and who cur- rently have to continue producing separate 230 V and 240 V versions. See also • Electric power • Technical standards in colonial Hong Kong References [1] "Note on Part P to the Building Regulations". IET. http://www.theiet.org/ publishing/wiring-regulations/part-p/ index.cfm. Retrieved on 2007-10-28. [2] Pat Delaney: True grid. EMC, February 2003. [3] [1] • Part P of Approved Documents, The Building Regulations 2000: Electrical safety. • The Electricity at Work Regulations 1989 • BS 4662: Specification for boxes for the enclosure of electrical accessories. British Standards Institute, 1970. External links • IEE Wiring Regulations • The Electrician’s Guide to the 16th Edition IEE Regulations (n.b., this guide refers to a deprecated version of the regulations) • Electrician’s Course notes for the 17th Edition IEE Regulations • Electrical Safety at Work, Health & Safety Executive • Electrical standards and approved codes of practice, Health & Safety Executive • The Electrical Equipment (Safety) Regulations 1994 From Wikipedia, the free encyclopedia Electrical wiring (UK) 5 • The Plugs and Sockets, etc. (Safety) Regulations 1994 • The Electricity Safety, Quality and Continuity Regulations 2002 • General Cable - Imperial / Metric Conductor Size Comparison Chart • Meeting the requirements of EaWR 1989 • Wiring a standard UK plug • Approved Document P for guidance on Part P of the Building Regulations • Local Authority Building Control Part P Competent Persons Register Retrieved from "http://en.wikipedia.org/wiki/Electrical_wiring_(UK)" Categories: Electrical wiring This page was last modified on 10 May 2009, at 01:24 (UTC). 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