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Electrical wiring (UK)
Encyclopedia
There are a number of specific national practices, habits and traditions associated with consumer mains wiring
in the United Kingdom
(and Ireland
) that differ significantly from other countries. These include:
IEC 60364
-1 and equivalent national standards in other countries. Accepted ways for fulfilling this legal requirement include:
In Scotland the Building (Scotland) Regulations 2004 apply.
Installations in commercial and industrial premises must satisfy various safety legislation, such as the Electricity at Work Regulations 1989. Again, recognised standards and practices, such as BS 7671 "Wiring Regulations", are used to help meet the legislative requirements.
. This colour scheme had already been introduced for appliance flexes in the UK in the early 1970s, however the original colour scheme recommended by the IEE for fixed wiring was permitted until 2006. As a result, the international standard blue/brown scheme is as of 2006 found in most appliance flexes. In fixed wiring, the blue/brown scheme is only found in very new (post-2004) installations, and the old IEE black/red scheme is likely to be encountered 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 international 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.
On telecommunications nominal 48V DC supplies, the live is usually -42V (flat batteries) to almost -57V(float charge), the positive power wire is thus red (the wiring providing the earth/ground connection at the power source is conventionally-coloured as often will be earth connections not intended to carry power, i.e. on older installations being green); the same principles were also applied to equipment operating at lower voltages which used non-floating power supplies. It is now unusual to encounter such wiring in a domestic installation due to the absence of power supplies for modern systems involving a separate float-charged battery and the general non-provision of backup power; such wiring in domestic premises in any case was only required for the short distances between the rectifier or power unit, battery (if any) and the device receiving the main power feed.
While confusion in identification of these conductors could be dangerous, the combinations of colours used usually resolves ambiguities. The installation of cables with the 'new' colours in an installation where the 'old' colours exist, could leave the way open for confusion; it is important in such situations that consideration is given to correct identification of the cables – with the use of marker tags if necessary. 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, including the old British phase colours.
mains are now only of historical interest in the UK but they also gave rise to possible confusion because the colours used were red for positive
and black for negative
. 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 opportunity for confusion.
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 practice unknown in other 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 supply so that the whole circuit forms a continuous ring. The original purpose was to save on copper during the post-WWII period of shortage, but the primary advantage is to allow more power to be supplied than could otherwise 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 protective earth to which sleeving is added when exposed. The earthing conductor is supplied uninsulated since it is not intended to have any voltage difference to surrounding earthed articles. 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 mm2 are typically used for 6 or 10 ampere lighting circuits and 2.5 mm2 for socket circuits. The protective 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 uninsulated for a number of reasons, primarily because it may be considered safer that way. If the insulation of the live/neutral wire becomes damaged due to intrusion by a foreign object (such as a nail/screw) or by fire or heat (caused by short circuit or poor installation), then the wire is more likely to earth itself and in doing so either trip the RCD
or burn the fuse out by drawing too much current. Some may argue that insulating the earth conductor would unnecessarily increase the cost, weight, size and rigidity of the cable.
Some of the restrictions introduced with Part P were controversial, especially the rules surrounding work carried out by unregistered people such as DIYers. Under the new regulations, commencement of any work other than simple changes becomes notifiable to the local building control authority; "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 enterprises which meet the minimum agreed criteria for Scheme entry:
(The minimum criteria for Scheme entry is set by the EAS Committee, on which all of the commercial enterprises running Competent Persons Schemes are actively represented).
Scheme membership allows an enterprise to "self-certify" work that they carry out without the requirement to have undergone any formal installation training or to hold relevant qualifications in electrical installation practices - since practical competence can be assessment-based only.
The building control authority must be informed of any notifiable work carried out by someone not registered under this scheme before it is started (unless it is an emergency) and must subsequently be approved by them. Originally, it was widely understood that inspection by a qualified person (leading to authority approval) 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 certification of DIY work (or work completed by someone otherwise unable to self-certify) and to "make enforcement more proportionate to the risk".
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 inspection 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 inspections are at the expense of the building authority, notification of building work is a formal process and a building control fee is payable.
In some cases the installation of 12V downlighters is notifiable where as the installation of 230V mains downlighters is not. This is because 12V downlighters draw high currents, in comparison with a mains voltage lamp with the same power rating, and that combined with the wrong choice of cable could lead to a fire.
Additionally, whilst the Building Regulations apply equally to anyone carrying out electrical work in dwellings, without adequate knowledge and test equipment it is not possible to ensure that the work carried out is safe. Registered Scheme members must issue appropriate certification, yet the householder will almost certainly be unable to.
Another element of confusion is that the term "Special Locations" has different meanings in Part P of the Building Regulations and BS7671 (the "Wiring Regulations").
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 4662:2006 - Boxes for flush mounting of electrical accessories – Requirements, test methods and dimensions, 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 horizontal centre line, 60.3 mm apart. Double face plates for BS 4662 boxes measure 147 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 diversity and design sophistication found in other European markets. The UK installation-accessory industry is therefore occasionally criticized for being overly conservative. 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 diameter, 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 connection unit") in the UK because of the lower plug rating.
, commonly rated at 3 A, 5 A, or 13 A.
In the case of permanently connected equipment the fuse is contained in a holder mounted in an accessory known as a Fused Connection Unit, 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 circuit, 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 small 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 disadvantage is that despite warnings to the contrary people often use a fuse rated at too high a current, or even wrap a blown fuse in aluminium foil, meaning that under fault conditions the contacts and flex will be subjected to anything up to the maximum ring circuit current. This is likely to cause a fire.
The appliance itself should have its own protection measures, such as another fuse, if the plug fuse doesn't provide the required overcurrent protection (this is often the case with electronic items).
Most fixed-wiring double socket outlets to BS1363 are rated 20A total, 13A per socket, and don't include a 13A fuse. However double sockets on extension leads are usually rated at 13A, and this rating applies to the total rating of the two sockets together. Some wall mounted multiple sockets are also 13A rated in total, these types have an inbuilt 13A fuse.
or miniature circuit breaker (MCB)
for each final circuit.
Older regulations defined Zone 3 as 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, from BS7671:2008this is replaced by the term 'outside the zones'. This includes any space under the bath or shower that can only be accessed with a tool.{ref bs7671:2008}
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 required in Zone 1–3. Otherwise, in Zone 3 and beyond, an ingress protection rating of IP20 is the minimum required. Equipment in Zones 1 and 2 must be protected by a 30 mA residual current device (RCD).
Shaving sockets (with isolating transformer) are permitted in Zone 2 if direct spray from a shower is unlikely, even if they are only IP20. Before the 2008 regulations, such shaving sockets were the only sockets permitted in a bathroom or shower room. Since BS7671:2008 normal domestic sockets are permitted, at distances greater than 3m from the edge of the zones, providing the circuit is RCD protected. As the new regulations also require all general purpose sockets not for use by skilled or instructed persons to be RCD protected, this effectively permits normal wiring in the larger bathroom.
(Earlier British wiring rules in bathrooms used to be far more restrictive, leading to British peculiarities in bathrooms such as the use of cord switches. The 2001 edition of the Wiring Regulations is more flexible now, placing restrictions on bathroom installations that are now more similar to those in other European countries. )
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. Since 2008, all sockets for general use should be RCD protected, removing the questions that used to arise, such as if a socket by the door might power a lawnmower does it need an RCD?
(RMS
) at 50 Hz. In 1988, a Europe-wide agreement was reached to unify the various national voltages, which ranged at the time from 220 V to 240 V, to a common European standard of 230V (CENELEC Harmonization Document HD 472 S1:1988).
The standard nominal supply voltage
in domestic single-phase
50 Hz installations in the UK is still 240V AC (RMS), but since 1 January 1995 (Electricity Supply Regulations, SI 1994, No. 3021) this has an asymmetric voltage tolerance of 230 V+10%-6% (216.2–253 V), which covers the same voltage range as continental 220v supplies to the new unified 230v standard. This was supposed to be widened to 230 V ±10% (207-253 V), but the time of this change has been put back repeatedly 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 suppliers 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 manufacturers, who require tighter voltage tolerances to optimise the operating temperature
and lifetime of their products, and who currently have to continue producing separate 230 V and 240 V versions.
Consumer mains wiring
Đomestic consumer mains wiring refers to the wiring in the house hold premises and low voltage installations. Even though arbitrary electric wiring demands detailed calculations for selection of conductor sizes, circuit breakers, voltage drops and so on, for domestic wiring some standard methods...
in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
(and Ireland
Republic of Ireland
Ireland , described as the Republic of Ireland , is a sovereign state in Europe occupying approximately five-sixths of the island of the same name. Its capital is Dublin. Ireland, which had a population of 4.58 million in 2011, is a constitutional republic governed as a parliamentary democracy,...
) that differ significantly from other countries. These include:
- Ring circuitRing circuitIn electricity supply, a ring final circuit or ring circuit is an electrical wiring technique developed and primarily used in the United Kingdom. This design enables the use of smaller-diameter wire than would be used in a radial circuit of equivalent total current...
s - 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 Regulations (Approved Document: Part P) require that domestic electrical installations are designed 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 standardInternational standard
International standards are standards developed by international standards organizations. International standards are available for consideration and use, worldwide...
IEC 60364
IEC 60364
IEC 60364 Electrical Installations for Buildings is the International Electrotechnical Commission's international standard on electrical installations of buildings. This standard is an attempt to harmonize national wiring standards in an IEC standard...
-1 and equivalent national standards in other countries. Accepted ways for fulfilling this legal requirement include:
- the rules of the IEEInstitution of Electrical EngineersThe Institution of Electrical Engineers was a British professional organisation of electronics, electrical, manufacturing, and Information Technology professionals, especially electrical engineers. The I.E.E...
wiring regulations (BS 7671BS 7671British Standard BS 7671 "Requirements for electrical installations" is the national standard in the United Kingdom for low voltage electrical installations....
), colloquially referred to as "the regs" (BS 7671: 2008, 17th Edition).; - the rules of an equivalent standard approved by a member of the EEAEuropean Economic AreaThe European Economic Area was established on 1 January 1994 following an agreement between the member states of the European Free Trade Association and the European Community, later the European Union . Specifically, it allows Iceland, Liechtenstein and Norway to participate in the EU's Internal...
(e.g., DINDinDIN or Din or din can have several meanings:* A din is a loud noise.* Dīn, an Arabic term meaning "religion" or "way of life".* Din is one of the ten aspects of the Ein Sof in Kabbalah ....
/VDEVerband der Elektrotechnik, Elektronik und InformationstechnikThe VDE Association for Electrical, Electronic and Information Technologies e.V. is one of Europe’s largest technical-scientific associations with 35,000 members, including 1,300 corporate and institutional members and 8,000 students.- Organization :...
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.
In Scotland the Building (Scotland) Regulations 2004 apply.
Installations in commercial and industrial premises must satisfy various safety legislation, such as the Electricity at Work Regulations 1989. Again, recognised standards and practices, such as BS 7671 "Wiring Regulations", are used to help meet the legislative requirements.
Wiring colours
The standard wiring colours in the UK are the same as elsewhere in Europe, Australia, and New Zealand and follow international standard IEC 60446IEC 60446
International standard IEC 60446 defines basic safety principles for identifying electrical conductors by colours or numerals, for example in electricity distribution wiring.-Permitted colours:...
. This colour scheme had already been introduced for appliance flexes in the UK in the early 1970s, however the original colour scheme recommended by the IEE for fixed wiring was permitted until 2006. As a result, the international standard blue/brown scheme is as of 2006 found in most appliance flexes. In fixed wiring, the blue/brown scheme is only found in very new (post-2004) installations, and the old IEE black/red scheme is likely to be encountered in existing installations for many more decades.
| Pre-1977 IEE | Pre-2004 IEE | Current IEC | |
|---|---|---|---|
| Protective earth (PE) Ground and neutral Since the neutral point of an electrical supply system is often connected to earth ground, ground and neutral are closely related. Under certain conditions, a conductor used to connect to a system neutral is also used for grounding of equipment and structures... |
Green | Green/yellow bi-colour | Green/yellow bi-colour |
| Neutral (N) | Black | Black | Blue |
| Single phase: Line (L) Three phase: L1 |
Red | Red | Brown |
| Three phase: L2 | Yellow | Yellow | Black |
| Three phase: L3 | Blue | Blue | Grey |
The standard colours in fixed wiring were harmonized in 2004 with the regulations in other European countries and the international 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.
Other colour schemes
Cables of USA origin will have White as Neutral and Black as live. This can occur on IEC mains leads and dual 220V/110V imported equipment.On telecommunications nominal 48V DC supplies, the live is usually -42V (flat batteries) to almost -57V(float charge), the positive power wire is thus red (the wiring providing the earth/ground connection at the power source is conventionally-coloured as often will be earth connections not intended to carry power, i.e. on older installations being green); the same principles were also applied to equipment operating at lower voltages which used non-floating power supplies. It is now unusual to encounter such wiring in a domestic installation due to the absence of power supplies for modern systems involving a separate float-charged battery and the general non-provision of backup power; such wiring in domestic premises in any case was only required for the short distances between the rectifier or power unit, battery (if any) and the device receiving the main power feed.
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 conductors could be dangerous, the combinations of colours used usually resolves ambiguities. The installation of cables with the 'new' colours in an installation where the 'old' colours exist, could leave the way open for confusion; it is important in such situations that consideration is given to correct identification of the cables – with the use of marker tags if necessary. 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, including the old British phase colours.
Direct current systems
Direct currentDirect current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
mains are now only of historical interest in the UK but they also gave rise to possible confusion because the colours used were red for positive
Electric charge
Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...
and black for negative
Electric charge
Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...
. 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
Live wire (electricity)
The live wire in an AC electrical circuit refers to the wire which carries an oscillating voltage with respect to the earth...
, creating an additional opportunity for confusion.
Circuit design
UK electrical socket circuits are normally described as either radial or ring. Socket circuits are usually connected as a ring, with radially connected sockets being the exception.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 practice unknown in other 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 supply so that the whole circuit forms a continuous ring. The original purpose was to save on copper during the post-WWII period of shortage, but the primary advantage is to allow more power to be supplied than could otherwise 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 protective earth to which sleeving is added when exposed. The earthing conductor is supplied uninsulated since it is not intended to have any voltage difference to surrounding earthed articles. 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 mm2 are typically used for 6 or 10 ampere lighting circuits and 2.5 mm2 for socket circuits. The protective 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 uninsulated for a number of reasons, primarily because it may be considered safer that way. If the insulation of the live/neutral wire becomes damaged due to intrusion by a foreign object (such as a nail/screw) or by fire or heat (caused by short circuit or poor installation), then the wire is more likely to earth itself and in doing so either trip the RCD
Residual-current device
A Residual Current Device is a generic term covering both RCCBs and RCBOs.A Residual-Current Circuit Breaker is an electrical wiring device that disconnects a circuit whenever it detects that the electric current is not balanced between the energized conductor and the return neutral conductor...
or burn the fuse out by drawing too much current. Some may argue that insulating the earth conductor would unnecessarily increase the cost, weight, size and rigidity of the cable.
Regulations
All new 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 enforceable. One way of achieving this is to apply British Standard BS7671 (the "Wiring Regulations"), including carrying out adequate inspection and testing to this standard of the completed works. British Standard BS 7671 (the "Wiring Regulations") is not statutory, thus someone doing electrical work is allowed to deviate from the wiring regulations to some degree, but it is generally accepted that it is best to follow the wiring regulations to the highest standard possible.Some of the restrictions introduced with Part P were controversial, especially the rules surrounding work carried out by unregistered people such as DIYers. Under the new regulations, commencement of any work other than simple changes becomes notifiable to the local building control authority; "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 enterprises which meet the minimum agreed criteria for Scheme entry:
(The minimum criteria for Scheme entry is set by the EAS Committee, on which all of the commercial enterprises running Competent Persons Schemes are actively represented).
Scheme membership allows an enterprise to "self-certify" work that they carry out without the requirement to have undergone any formal installation training or to hold relevant qualifications in electrical installation practices - since practical competence can be assessment-based only.
The building control authority must be informed of any notifiable work carried out by someone not registered under this scheme before it is started (unless it is an emergency) and must subsequently be approved by them. Originally, it was widely understood that inspection by a qualified person (leading to authority approval) 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 certification of DIY work (or work completed by someone otherwise unable to self-certify) and to "make enforcement more proportionate to the risk".
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 inspection 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 inspections are at the expense of the building authority, notification of building work is a formal process and a building control fee is payable.
In some cases the installation of 12V downlighters is notifiable where as the installation of 230V mains downlighters is not. This is because 12V downlighters draw high currents, in comparison with a mains voltage lamp with the same power rating, and that combined with the wrong choice of cable could lead to a fire.
Additionally, whilst the Building Regulations apply equally to anyone carrying out electrical work in dwellings, without adequate knowledge and test equipment it is not possible to ensure that the work carried out is safe. Registered Scheme members must issue appropriate certification, yet the householder will almost certainly be unable to.
Another element of confusion is that the term "Special Locations" has different meanings in Part P of the Building Regulations and BS7671 (the "Wiring Regulations").
Installation accessories
ISO metric screw thread
The ISO metric screw threads are the world-wide most commonly used type of general-purpose screw thread. They were one of the first international standards agreed when the International Organization for Standardization was set up in 1947.-Basic profile:...
screws (typ. 25 mm or 40 mm long) located on a horizontal centre line, 60.3 mm apart. Double face plates for BS 4662 boxes measure 147 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 diversity and design sophistication found in other European markets. The UK installation-accessory industry is therefore occasionally criticized for being overly conservative. As many modern types of electrical accessories (e.g., home automation
Home automation
Home automation is the residential extension of "building automation". It is automation of the home, housework or household activity. Home automation may include centralized control of lighting, HVAC , appliances, and other systems, to provide improved convenience, comfort, energy efficiency and...
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 diameter, 45 mm deep, fixing screws 60 mm apart) or, less commonly in the UK, ANSI/NEMA
National Electrical Manufacturers Association
is the association of electrical and medical imaging equipment manufacturers. Founded in 1926 and headquartered near Washington, D.C., its approximately manufacture products used in the generation, transmission, distribution, control, and end use of electricity. These products are used in utility,...
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
IEC 60309
IEC 60309 is an international standard from the International Electrotechnical Commission for "plugs, socket-outlets and couplers for industrial purposes". The highest voltage allowed by the standard is DC or AC; the highest current, ; and the highest frequency,...
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 connection 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 circuit overcurrent protection device. The protection device used in such accessories is a 1" (25.4mm) ceramic cartridge to the requirements of BS 1362:1973 fuseFuse (electrical)
In electronics and electrical engineering, a fuse is a type of low resistance resistor that acts as a sacrificial device to provide overcurrent protection, of either the load or source circuit...
, commonly rated at 3 A, 5 A, or 13 A.
In the case of permanently connected equipment the fuse is contained in a holder mounted in an accessory known as a Fused Connection Unit, 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 circuit, 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 small 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 disadvantage is that despite warnings to the contrary people often use a fuse rated at too high a current, or even wrap a blown fuse in aluminium foil, meaning that under fault conditions the contacts and flex will be subjected to anything up to the maximum ring circuit current. This is likely to cause a fire.
The appliance itself should have its own protection measures, such as another fuse, if the plug fuse doesn't provide the required overcurrent protection (this is often the case with electronic items).
Most fixed-wiring double socket outlets to BS1363 are rated 20A total, 13A per socket, and don't include a 13A fuse. However double sockets on extension leads are usually rated at 13A, and this rating applies to the total rating of the two sockets together. Some wall mounted multiple sockets are also 13A rated in total, these types have an inbuilt 13A fuse.
Consumer unit
A domestic supply typically consists of a large cable entering the house which is connected to a sealed box containing the main supply fuse. This will typically have a value from 40–100A. Separate live and neutral cables ('tails') go from here to a meter, and often an earth conductor too. More tails proceed from the meter to a consumer unit, or in some cases to a Henley type connector block and thence to more than one consumer unit. The consumer unit (aka fusebox) contains one or more main switches and an individual fuseFuse (electrical)
In electronics and electrical engineering, a fuse is a type of low resistance resistor that acts as a sacrificial device to provide overcurrent protection, of either the load or source circuit...
or miniature circuit breaker (MCB)
Circuit breaker
A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow...
for each final circuit.
Bathrooms
The installation of electrical devices in bathrooms and shower rooms is regulated in Section 701 of BS 7671:2008, and Part P of the Building Regulations. For such rooms, four special zones are defined, in which additional protection is required for electrical facilities:- Zone 0 is the smallest cuboid volume that contains the bathtubBathtubA bath , bathtub , or tub is a large container for holding water in which a person may bathe . Most modern bathtubs are made of acrylic or fiberglass, but alternatives are available in enamel over steel or cast iron, and occasionally waterproof finished wood...
, showerShowerA shower is an area in which one bathes underneath a spray of water.- History :...
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.
Older regulations defined Zone 3 as 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, from BS7671:2008this is replaced by the term 'outside the zones'. This includes any space under the bath or shower that can only be accessed with a tool.{ref bs7671:2008}
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 required in Zone 1–3. Otherwise, in Zone 3 and beyond, an ingress protection rating of IP20 is the minimum required. Equipment in Zones 1 and 2 must be protected by a 30 mA residual current device (RCD).
Shaving sockets (with isolating transformer) are permitted in Zone 2 if direct spray from a shower is unlikely, even if they are only IP20. Before the 2008 regulations, such shaving sockets were the only sockets permitted in a bathroom or shower room. Since BS7671:2008 normal domestic sockets are permitted, at distances greater than 3m from the edge of the zones, providing the circuit is RCD protected. As the new regulations also require all general purpose sockets not for use by skilled or instructed persons to be RCD protected, this effectively permits normal wiring in the larger bathroom.
(Earlier British wiring rules in bathrooms used to be far more restrictive, leading to British peculiarities in bathrooms such as the use of cord switches. The 2001 edition of the Wiring Regulations is more flexible now, placing restrictions on bathroom installations that are now more similar to those in other European countries. )
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 discourage 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 sockets) and sockets that completely enclose a normal plug with a seal around the flex (e.g., MKMK electric
MK Electric is a company that makes electrical accessories. The company's headquarters are in Basildon, Essex, England, from where it makes and sells goods worldwide.-History:...
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. Since 2008, all sockets for general use should be RCD protected, removing the questions that used to arise, such as if a socket by the door might power a lawnmower does it need an RCD?
Supply voltage
Since 1960, the supply voltage in UK domestic premises has been 240 V ACAlternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
(RMS
Root mean square
In mathematics, the root mean square , also known as the quadratic mean, is a statistical measure of the magnitude of a varying quantity. It is especially useful when variates are positive and negative, e.g., sinusoids...
) at 50 Hz. In 1988, a Europe-wide agreement was reached to unify the various national voltages, which ranged at the time from 220 V to 240 V, to a common European standard of 230V (CENELEC Harmonization Document HD 472 S1:1988).
The standard nominal supply voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
in domestic single-phase
Single-phase electric power
In electrical engineering, single-phase electric power refers to the distribution of alternating current electric power using a system in which all the voltages of the supply vary in unison. Single-phase distribution is used when loads are mostly lighting and heating, with few large electric motors...
50 Hz installations in the UK is still 240V AC (RMS), but since 1 January 1995 (Electricity Supply Regulations, SI 1994, No. 3021) this has an asymmetric voltage tolerance of 230 V+10%-6% (216.2–253 V), which covers the same voltage range as continental 220v supplies to the new unified 230v standard. This was supposed to be widened to 230 V ±10% (207-253 V), but the time of this change has been put back repeatedly 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 suppliers 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 manufacturers, who require tighter voltage tolerances to optimise the operating temperature
Operating temperature
An operating temperature is the temperature at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the device function and application context, and ranges from the minimum operating temperature to the...
and lifetime of their products, and who currently have to continue producing separate 230 V and 240 V versions.
See also
- Consumer mains wiringConsumer mains wiringĐomestic consumer mains wiring refers to the wiring in the house hold premises and low voltage installations. Even though arbitrary electric wiring demands detailed calculations for selection of conductor sizes, circuit breakers, voltage drops and so on, for domestic wiring some standard methods...
- BS 1363BS 1363BS 1363 is a British Standard which specifies the most common type of single-phase AC power plugs and sockets that are used in the United Kingdom. Distinctive characteristics of the system are shutters on the line and neutral socket holes, and a fuse in the plug...
- BS 546BS 546BS 546 is a pre-Second World War British Standard for domestic AC power plugs and sockets that is also the precursor of current Indian and South African plug standards. This plug is also used in Singapore to a limited extent...
- PattressPattressA pattress or pattress box is the container for the space behind electrical fittings such as power outlet sockets and light switches.A pattress may be made of plastic , or metal...
- Technical standards in colonial Hong KongTechnical standards in colonial Hong KongBritish colonial rule affected the technical standards in Hong Kong. However, not all technical standards in Hong Kong are identical with their counterparts in the United Kingdom due to practical or some other reasons.-Electrical plugs and adaptors:...
Further reading
- BS 4662:2006 Boxes for flush mounting of electrical accessories – Requirements, test methods and dimensions. British Standards Institution.
External links
- IEE Wiring 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
- General Cable - Imperial / Metric Conductor Size Comparison Chart
- Meeting the requirements of EaWR 1989
- Approved Document P for guidance on Part P of the Building Regulations
- Local Authority Building Control Part P Competent Persons Register