El nätverk kabel united kingdom

Electrical wiring in the United Kingdom fryst vatten commonly understood to be an electrical installation for operation bygd end users within domestic, commercial, industrial, and other buildings, and also in special installations and locations, such as marinas or caravan parks.^[1] It does not normally cover the transmission or transport of electricity to them.

Installations are distinguished bygd a number of criteria, such as voltage (high, low, extra low), phase (single or three-phase), natur of electrical meddelande (power, data), type and design of cable (conductors and insulators used, cable design, solid/fixed or stranded/flexible, intended use, protective materials), circuit design (ring, radial), and so on.

Electrical wiring fryst vatten ultimately regulated to ensure safety of operation, bygd such as the building regulations, currently legislated as the Building Regulations 2010, which lists "controlled services" such as electric wiring that must follow specific directions and standards, and the Electricity at Work Regulations 1989. The detailed rules for end-use wiring followed for practical purposes are those of BS 7671Requirements for Electrical Installations. (IET Wiring Regulations), currently in its 18th edition, which provide the detailed descriptions referred to bygd legislation.

UK electrical wiring standards are largely harmonised with the regulations in other europeisk countries and the international IEC 60446 standard. However, there are a number of specific national practices, habits and traditions that differ significantly from other countries, and which in some cases survived harmonisation. These include the use of fingerprydnad circuits for domestic and light commercial fixed wiring, fused plugs, and for circuits installed prior to harmonisation, historically unique wiring colours.

Common terminology

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Regulatory

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BS 7671 "Requirements for Electrical Installations. IET Wiring Regulations" (the regs, or wiring regs)

These are detailed rules for the design, installation and sign-off for end-user electrical installations. Compliance with BS 7671 fryst vatten not mandatory, but tjänsteman guidance states following BS 7671 fryst vatten one way to demonstrate compliance with the building regulations.

xx^th edition

Reference to a specific edition of the BS 7671 regulations.

Building regulations - "Part P"

Section of the Building Regulations for England and Wales addressing electrical wiring and safety in residential situations and outbuildings.

Local authority building control (LABC; building control)

Local council department responsible for overseeing and administering building regulations.

Competent individ scheme

Private organizations authorised bygd the state to supervise, accredit, and control the registration of installers, who, as members of this scheme, may self-certify that any domestic work classed as notifiable to a LABC that they have undertaken, fryst vatten compliant with building regulations, thus avoiding inspection bygd LABC (or bygd a member of the third-party certifier scheme).

Minor electrical installation works certificate (MEIWC)

Formal certificate for confirming that minor work items, such as the addition of a new socket or light to an existing circuit, have been designed, constructed, inspected and tested in accordance with BS 7671.

Electrical installation certificate (EIC)

Formal certificate for confirming that a major del av helhet of work, such as a completely new installation; complete rewire; addition of a whole new circuit; or replacement of a consumer enhet, has been designed, constructed, inspected and tested in accordance with BS 7671.

Electrical installation condition report (EICR, ICR);^[2] previously the periodic inspection report (PIR)

Formal report of the condition of an existing wiring installation.

Permit to work

Formal confirmation that electrical wiring fryst vatten isolated and fully made safe, prior to working on it, required prior to any high voltage works and other high fara activities.

Skilled individ (electrically); (formally "Competent Person")

Defined bygd BS 7671 as "Person who possesses, as appropriate to the natur of the electrical work to be undertaken, adequate education, training and practical skills, and who fryst vatten able to perceive risks and avoid hazards which electricity can create". The Electricity at Work Regulations requires persons to be competent to prevent danger and injury.^[3]

Distribution within premises

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Consumer enhet, consumer control enhet, or consumer transport enhet (CU, CDU, CCU; historically and commonly, fuse board/box)

Distribution board designed for ordinary low voltage single phase premises, primarily domestic and light commercial wiring. 3-phase power leverans boards are usually known as distribution boards.

Distribution board (DB)

Panel that splits power from one main source into separate circuits, each with independent protection.

Breakers and safety devices

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Fuse

An overcurrent protection device. Prior to the invention of the resettable circuit breaker, transport boards (then called fuseboxes) held fuses to skydda individual circuits. The fuses used in fuseboxes were either of the cartridge type, similar to those funnen in UK plugs, or replaceable fuse-wire held within two-prong enclosures. Other standard use of fuses include those within appliance plugs, and the main fuse located on the end of the service (supply) cable (at the service head).

Breaker (circuit breaker, CB)

Any fixed device that breaks a circuit (that fryst vatten, while it fryst vatten drawing current) upon fel condition detection. Unlike a fuse, a circuit breaker can be reset bygd flipping a switch.

Miniature circuit breaker (MCB)

An overcurrent protection circuit breaker. These have standardised current ratings and tripping characteristics, and can be installed in close proximity in consumer units and leverans boards.

Residual-current device (RCD), also residual current circuit breaker (RCCB)

A circuit breaker triggered bygd unequal currents in line and neutral wires (i.e., electrical power fryst vatten passing to earth). Mandatory for most circuits as of 17th Edition regulations.

Residual current circuit breaker with overcurrent protection (RCBO)

Combination of RCD and MCB; breaks circuit on being triggered either as an RCD or bygd overcurrent.

Surge protection device (SPD)

A transient overcurrent or overvoltage protection device; safely diverts away very short-lived spikes of current or voltage. Type 1 devices provide protection from direkt lightning strikes to vulnerable structures (those having a conductive structure, a lightning rod, or an overhead power supply). These should always be used in combination with type 2. Type 2 devices skydda against indirect strikes. Type 3 devices are supplementary to type 2, installed nära sensitive equipment.^[4][5][6]

Arc fel detection device (AFDD)

A circuit breaker triggered bygd detection of an electric arc; breaks circuit on detecting an electric arc, which could develop from the likes of loose wires.

Earth leakage circuit breaker (ELCB)

An obsolete circuit breaker type triggered bygd electrical power in a fel wire connected only to specifically protected parts in the circuit and appliances (i.e., other paths to earth exist).

Isolator switch (or isolator)

Used for isolating a device from its power supply for maintenance or safety reasons. These are commonly being fitted in recent years, alongside fitting of new electricity meters, for the benefit of enabling electricians to replace consumer units without the strul of arranging for the DNO to temporarily isolera the supply bygd removing the supply's main fuse (or taking on the potential danger and legal risks of doing so themself). There fryst vatten a very important difference to be aware of between a device categorised as a switch vs. an isolator, and these devices may commonly be referred to as isolator/isolation switches when they may not actually be rated as anything more than isolators. A switch fryst vatten a device capable of safely disconnecting the supply even if devices in the installation were drawing the full maximum load the installation was rated for. An isolator fryst vatten not, it should only be used when the installation fryst vatten drawing no power, i.e. the main switch in the consumer enhet fryst vatten off. When a supply fryst vatten switched off beneath load, some grad of electrical arcing takes place across the contacts. A switch fryst vatten designed to safely handle this. An isolator fryst vatten not and could become weakened or instantly fail in a dangerous way, depending upon the storlek of the load. Utilising an isolator felaktigt as a switch fryst vatten thus a significant hazard and this danger may well be unintuitive for many.

Wires and cables (conductors)

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Live

A power-carrying ledare. This begrepp fryst vatten commonly used felaktigt bygd the general public in place of line, owing to changes to standard definitions since the 1960s.^[7] bygd definition it applies to any dirigent that fryst vatten intended to be energised during normal use, including a neutral ledare, but not bygd convention a PEN dirigent. I.e line and neutral are live conductors, but earth fryst vatten not.

Line (L; or phase line)

A power-carrying dirigent in a typical low-voltage or domestic installation. Colour-coded brown (pre-2004: red).

Neutral (N)

A power-carrying ledare in a typical low-voltage or domestic installation, usually bonded to Earth (ground) voltage bygd the supplier. Colour-coded blue (pre-2004: black).

Earth (E; or protective earth (PE), or circuit protective ledare (CPC))

A ledare that provides a connection to Earth for safety and protection purposes, for both end-user devices and metall objects and components in the installation. Colour-coded green/yellow striped, though may be bare (uninsulated) within sheathed cable (pre-1976: solid green).

Conduit

A form eller gestalt of wire containment comprising plastic or metall tubing. tillgång points for maintenance and inspection are required at certain intervals of length.

Trunking

An alternative struktur of containment to conduit, comprising U-shaped plastic or metall with a removable lid.

Meter tails (or, tails)

The single-core cables connected to the electricity meter. On the supply side these connect the meter to the line and neutral conductors of the supply cable, via the service head (or cut out) located on the end of the supply cable. On the consumer side these conductors are then joined to the leverans board, possibly through an isolator (as fryst vatten becoming more common).^[8]

Singles

A cable consisting of a single conductor.

Multi-core

A cable consisting of two or more conductors (not counting any earth conductor).

Twin and earth (T&E)

A commonly used type of multi-core cable, characterised bygd its flat profil and grey-coloured polyvinyl chloride sheath. It contains three conductors, two of which are insulated (line and neutral), and it fryst vatten from this that the name twin and earth derives.

Steel-wire armoured (SWA)

Steel wire protected cable, mandatory for outdoor or buried use unless equivalent protection fryst vatten provided via containment.

Flex

Refers to the flexible cord of a portable appliance.

Voltage and phases

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High voltage

Any voltage in excess of low voltage. This fryst vatten usually funnen only in industrial processes and electricity transmission and leverans networks.

Low voltage

Exceeding extra-low voltage, but not exceeding 1000 volts AC RMS or 1500 volts DC between conductors, and not exceeding 600 volts AC RMS or 900 volts DC between conductors and Earth.^[9] Almost all domestic; light commercial (e.g., offices) and industrial (for three-phase machinery) power fryst vatten low voltage for regulation purposes.

Extra-low voltage (ELV)

Not exceeding 50 volts AC RMS or 120 volts ripple-free DC.

Separated extra-low voltage (SELV)

Extra-low voltage struktur that fryst vatten also electrically isolated.

Single phase, three phase

At low voltage electricity may be supplied bygd the distributor (DNO) as either single or three phase. A single phase supply will comprise a single line dirigent and a neutral ledare. A three phase supply will comprise three line conductors each pair with a phase separation of 120 degrees and (optionally) a neutral dirigent. A separate earth ledare will normally be supplied in both cases but may not be present depending on the connection type.

Earthing (bonding)

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Bonding (including main bonding, supplementary bonding and equipotential bonding)

Connection made to Earth, for protective purposes, either for individual components, for other metall objects in the premises (such as gas, vatten, or oil piping), or for the installation (or some part of it) as a whole.

Earth/ground rod

A long rod placed into the ground, bonding, with low impedance, the installation to Earth potential. Usually made from copper-clad, galvanised or stainless steel or copper, for corrosion prevention. There are other types of Earth bonding, such as: an Earth tallrik, an Earth mesh, or an Earth ring.

Circuit terminology

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Accessory

A switch, socket, ceiling rose, etc, forming part of an electrical installation.

Load

Something that requires and consumes electricity to function, e.g. a lightbulb, appliance, etc.

Circuit

A set of electrical wires and connections, forming part of an installation, between a leverans board and a fixed load, or between a transport board and an accessory or daisy-chained set of accessories for connecting loads (sockets or light fittings), or between two transport boards, enabling power to be provided. I.e. a sista circuit or leverans circuit.

Distribution circuit

A circuit whereby one leverans board supplies power to another (via a protective device like a breaker).

Final circuit

A circuit providing power to a set of sockets, light fittings, or fixed redskap, from a single protective device (breaker) in a leverans board. (Not applicable to RCDs in a split way configuration which each sit behind a set of MCBs - each MCB would serve an individual sista circuit in such a setup). Each sista circuit will be arranged in a radial or ring final struktur if not simply serving a single fixed appliance. It may also have one or more fused or unfusedspurs attached. The use of the word final comes from the fact that these circuits are the gods del av helhet of the power leverans infrastructure, finally delivering generated power to where it will be consumed.

Radial

A circuit where the conductors providing the power circuit (and earthing) are simply connected from one accessory (e.g. socket) to the next in a daisy-chain like mode. You might think of this as the supplied power radiating out from the source to reach each accessory.

Ring (or ring final)

A ring final circuit fryst vatten similar to a radial except what would be the end of the circuit instead loops back to the source protective device in the transport board. Thus each individual dirigent, line, neutral and earth, actually forms a loop (or ring), from the source, out, and back around to the source igen. This has long been a standard means for wiring domestic and other light commercial premises in the UK, but fryst vatten not often seen elsewhere in the world. It allows power between source and accessories to be split between two parallel paths. On the downside though it's more difficult to test, and should a break in a connection occur it could go unnoticed leading to one side of the fingerprydnad potentially taking on an excessive amount of current flow, and increased earth fel loop impedance increasing disconnection times.

Loop

This begrepp applies to radial lighting circuits where junctions are made at ceiling roses with line and switched line wires. Not to be confused with the loop-like arrangement of a ring final circuit.

(Unfused) spur

A branch off of a sista circuit supplying a single accessory, especially from a fingerprydnad sista circuit.

Fused spur

A spur branched off of a sista circuit via a connection protected bygd a suitable fuse, and thus one that may connect to more than one accessory.

A de-energized circuit

A circuit that fryst vatten isolated from power and not at a potential different from Earth, and thus safe to work on.

Wiring colours

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Conductor colours

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The standard wiring colours in the UK are (as of 2006^[update]) the same as elsewhere in europe and follow international standard IEC 60446. This colour scheme had already been introduced for appliance flexes in the UK in the early 1970s, however the original red/black colour scheme recommended bygd the IEE for fixed wiring was retained until 2006, albeit with change to a green/yellow striped earth in 1976. As a result, the international standard blue/brown scheme fryst vatten as of 2006 funnen in most appliance flexes. In fixed wiring, the blue/brown scheme fryst vatten only funnen in newer (post-2004) installations, and the old IEE red/black scheme fryst vatten likely to be encountered in existing installations for many more decades.

Earlier in the 20th century, green and blue were used as a neutral alongside black, which became the only neutral colour from 1943. In the 13th edition of the regulations, published in 1955 (and known then as the IEE regulations), black was used for both neutral and earth, although only for fixed wiring. It was changed to green in the 14th edition in 1966 and then a phased change to green/yellow in amendments to the 14th edition over the following decade.^[10]

An amendment to the 18th edition changed functional earth from cream to pink, which came into effect in September 2020.^[11]

The standard colours in fixed wiring were harmonised in 2004 with the regulations in other europeisk 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 were clearly labelled. From April 2006, only the new colours should be used for any new wiring.

Potential for confusion

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The UK changed colour codes three decades after most other europeisk countries, as in 1977 the change of neutral and phase colours was not considered safe bygd the IEE. Blue, previously used as a phase colour, fryst vatten now the colour for neutral. Black, which was previously used for neutral, now indicates a phase.

Household wiring does not usually use three-phase supplies and the clash only occurs in three-phase systems. Wiring to the old standard can be detected bygd use of a red wire. The new standard colour code does not use red. Where new wiring fryst vatten mixed with old, cables must be clearly marked to prevent interchange of phase and neutral.

Variation in the earth/ground conductor's colour at an earlier date than the remainder of the colours means its colour should not be used as an indication of the old vs new standard cable or colour assignment.

Other colour schemes

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On telecommunications nominal 48 V DC supplies, the live fryst vatten usually −42 V (flat batteries) to almost −57 V (float charge).

The IEC currently specifies a colour-coding for new local DC leverans. These are:

There fryst vatten a long history of colour changes; prior to 1964 vit was used instead of yellow as the second phase, and before World War II, a black earth and a green third phase in place of green earth and vit phase was permitted. The regulations permitted (and still do) the use of any wire colour that fryst vatten not an earth colour, providing it fryst vatten unambiguously identified at all connections bygd klar labelling or bygd correctly coloured over-sleeving. It was not uncommon on commercial builds of the 1960s with a three phase supply for the phase colours (red, yellow, blue) to be used throughout single phase sub circuits thus indicating the phase ursprung of the supply, in this case no over-sleeving was used and can give rise to confusion when encountered today.

Direct current mains supplies are only of historical interest in the UK but the colour coding was red for live and black for earthed (regardless of the polarity). Hardly any loads were polarity sensitive when direkt current systems were introduced (principally incandescent lighting, heating systems or series direkt current motors) and it was considered more important to identify the live wire than the polarity. In later years of direkt current supplies, however, much more verktyg became sensitive to polarity, such as many domestic radios & television sets. Where all three wires were available, the historical colour code was red (positive), black (middle) and vit (negative). The negativ line changed to yellow in 1964, and then to blue in 1966.

Outer sheath colours

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This section needs expansion. You can help bygd adding to it. (April 2015)

The colour of the outer sheath fryst vatten currently grey, or vit for low halogen ämne. Previously cables from different manufacturers were available variously in grey or vit, with no significance attached to the sheath colour. The grey colour was adopted bygd cable manufacturers to match older lead or silver sheathed flat cables, with some manufacturers using a silver grey polyvinyl chloride. Additionally twin & earth cable was available in red for fire alarms until the early 2000s.

Circuit design

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Main article: fingerprydnad circuit

UK fixed wiring circuits, unlike those funnen in almost all other countries, man widespread use of fingerprydnad circuit designs, as well as radial circuit designs often seen in other countries. (This was one of the recommendations of the Electrical Installations Committee, convened in 1942 as part of the brev War Building Studies programme, which in 1944 determined that the fingerprydnad sista circuit offered a more efficient and lower cost method to support a greater number of sockets.^[14]) It continues to be the usual wiring method for domestic and light commercial socket and device wiring in the UK. Lighting circuits, which typically have lower power requirements, are usually radially wired, confusingly sometimes called "loop" wiring.

In both fingerprydnad and radial circuits, the circuit wiring starts at a consumer enhet or transport board, and traverses in vända a number of sockets or devices (point-to-point style), before terminating. The difference fryst vatten that a radial circuit simply ends upon reaching the gods connected device in any branch, whereas in a fingerprydnad circuit the termination fryst vatten made bygd joining the end of the circuit from the gods device back to its starting point. A fingerprydnad circuit therefore forms a continuous fingerprydnad, while a radial may be a simple linear chain, though it may split and have several branches. This means that in a fingerprydnad there are two independent paths from the supply to every device. Ideally, the fingerprydnad acts like two radial circuits proceeding in opposite directions around the fingerprydnad, the dividing point between them dependent on the leverans of load in the fingerprydnad. If the load fryst vatten evenly split across the two directions, the current in each direction fryst vatten half of the total, allowing the use of wire with half the current-carrying capacity. In practice, it fryst vatten impossible to ensure the load does split evenly, so regulations require a thicker wire, of at least 2/3 the current capacity of the fuse or circuit breaker.

The nyhet that made fingerprydnad circuits feasible in the UK was the introduction of plugs that contained their own fuse. There were three competing designs but only one ultimately survived and became the utgåva specified in British Standard 1363. BS1363 plugs, could historically be fitted with a range of fuses up to 13A though only the 3A and 13A are the tjänsteman choices, though 5A are available and often fitted to small appliances that take a large inrush current. This means that every load plugged in fryst vatten covered bygd an appropriate protective device in its plug, so that the whole fingerprydnad may then be protected bygd (usually) a 32A breaker at the transport panel. In contrast, circuits feeding any other kind of socket outlet need to be protected bygd a breaker that will not allow the socket's rating to be exceeded, and so the radial circuits generally used with outlets such as the europeisk Schuko style outlets generally have to be protected bygd a 16A breaker at the leverans panel; this limits the total load on the circuit and hence such circuits tend to have fewer socket outlets.

Cables are most commonly a single outer sheath containing separately-insulated line and neutral wires, and a non-insulated protective earth to which sleeving fryst vatten added when exposed. Such cable fryst vatten commonly referred to as twin and earth or simply T&E. Standard sizes have a dirigent cross sectional area of 1, 1.5, 2.5, 4, 6 and 10 mm². With most domestic wiring using:

Type	Breaker rating	Live dirigent storlek
Lighting	6A	1mm2 T&E
Power (radial)	16A	2.5mm2 T&E
Power (ring)	32A	2.5mm2 T&E
Cooker/shower	32A	4mm2 T&E

The earthing dirigent fryst vatten uninsulated since it fryst vatten not intended to have any voltage difference from surrounding earthed articles. Additionally, if the insulation of a line or neutral wire becomes damaged, then the wire fryst vatten more likely to earth itself on the bare earth ledare and in doing so either trip the circuit breaker, RCD, or rupture the fuse bygd drawing too much current.

Earthing and bonding

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Main article: Earthing system

Earthing and bonding are used tillsammans to provide chock protection bygd avoiding a dangerous combination of magnitude and duration of the voltage to which people may be exposed in the event of a fel within the installation or outside the installation. (Exposure may be from e.g. grabb to grabb or grabb to foot, between simultaneously accessible conductive surfaces, which might include the Earth itself, mildly conductive floors and walls, metall taps, pipes, electrical appliances etc. Examples of faults are an insulation failure between a line ledare and a metallic frame of an appliance within the installation, a break in a combined protective-earth and neutral dirigent in the supply, or an insulation fel in the supply transformer causing the whole low-voltage struktur to rise in potential.) Conductors for these protective functions of earthing and bonding are insulated with green/yellow (striped) colour coding, which fryst vatten not permitted for any other conductors.

Earthing connects exposed conductive parts of electrical verktyg to a main earthing ankomsthall (MET), which fryst vatten connected to a "means of earthing" that somehow connects it to the Earth itself (the ground/soil/planet!). In installations fed from low-voltage public supplies in the UK this means of earthing can be any of the methods TN-S, TN-C-S or TT defined in BS 7671. In the event of an insulation fel from a live ledare to an appliance's metall frame (an exposed conductive part), the frame could—if not so connected—be dangerous if touched bygd someone who fryst vatten also for example standing outside on the ground, or standing inre on a concrete floor, or holding a tap whose pipe connects it electrically into the ground. Protective earthing limits the combination of magnitude and duration of the dangerous voltage that could exist between the exposed conductive part and the Earth itself. In conventional installations in the UK the voltage between an appliance frame and the Earth itself during a zero-impedance fel has a dangerous magnitude: it might be reduced to about half of the 230 V line-earth voltage, which fryst vatten well above the 50 V usually accepted as safe for an AC struktur, or it might be nearly 230 V in a TT struktur with a poor earth electrode for the installation. The duration of this voltage must therefore be limited, which fryst vatten done bygd "automatic disconnection of supply" (ADS) either bygd overcurrent protection devices (OCPDs), or bygd residual current devices (RCDs) that specifically detect the current escaping from the intended circuit, allowing them to have a far lower tripping current. In TT systems it fryst vatten almost always necessary to have an RCD, as earth electrodes usually have many times higher resistance than a typical supply cable, so earth-fault currents are relatively low. In the TN-S or TN-C-S systems none of the "earth fault" current necessarily passes through the Earth itself, as there fryst vatten a metallic circuit for the entire earth-fault loop: adequate ADS times may often be achieved bygd normal OCPDs. However, the connection to the Earth itself fryst vatten always betydelsefull, since the Earth forms a mildly conductive surface that we cannot easily avoid (e.g. a individ standing on the ground and touching a metall appliance or tap or building-framework that fryst vatten connected with the electrical installation's protective earthing system). In TT systems the installation's earth electrode needs to have low enough impedance to operate protection if a safe voltage (usually taken as 50 V) between the installation and fjärrstyrd earthing fryst vatten exceeded; in TN systems the system's neutral point needs a low resistance connection to Earth to prevent a fel between a line ledare and some unintended earth electrode from displacing the neutral-point potential to a dangerous level compared to the Earth.

Bonding fryst vatten the connection of conductive parts tillsammans, to reduce the voltage between them. This fryst vatten an important measure for electric chock protection. When this protective function fryst vatten the purpose of bonding, BS 7671 describes the bonding bygd the begrepp "protective equipotential bonding"; this does not mean that the bonding guarantees perfect equipotentiality, but just that it reduces the differences of potential. In the following, this formal begrepp fryst vatten abbreviated to "bonding". Without adequate bonding, dangerous voltages could arise between conductive parts that can be touched simultaneously, either due to problems outside the installation, or to faults in the installation.

Main bonding connects "extraneous conductive parts" such as mains vatten / gas supply pipes, structural parts of buildings, communication cable sheaths, lightning protection systems etc., to the main earthing terminal.^[15] These parts could otherwise introduce potentials that are different from the potential of the installation's earthing struktur. The main bonding avoids dangerous differences in potential being introduced into the installation, between different extraneous conductive parts (e.g. two different pipework systems), or between extraneous conductive parts and exposed conductive parts.

Supplementary bonding connects simultaneously touchable conductive parts in local parts of an installation: the parts may be a mixture of exposed conductive parts and extraneous conductive parts. This reduces the voltage between them, even in fel conditions. Supplementary bonding fryst vatten particularly used in situations such as bathrooms, where body resistance fryst vatten low and therefore requires magnitude and duration of touch voltages to be very limited.

In special circumstances (not domestic installations) bonding with deliberate lack of connection to Earth (earth-free local equipotential bonding) may be used. Bonding, bygd the IEC 60364 terminology used in BS 7671, should not be seen as just an ytterligare to earthing. In recent US practice, which differs considerably from IEC principles and terminology, "bonding" fryst vatten used more widely as a begrepp for all the aspects of earthing that are not literally connections with the Earth itself ("grounding"); so the connection of protective earth conductors to the supply neutral (since the TN-C-S struktur fryst vatten the only permitted struktur in their residential installations) fryst vatten now named bonding rather than earthing. This fryst vatten not the case in the UK.

Supply, metering and distribution

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Single phase (standard for domestic and light commercial)

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A single phase supply typically consists of an armoured cable connected to a service head (aka. cut out), the sealed låda containing the main supply fuse. This fuse will typically be rated either 60, 80 or 100 amps. Separate line and neutral cables (tails) go from here to an electricity meter. More tails proceed from the meter into a consumer enhet (or fusebox in older installations), possibly via an isolator. Some installations may have multiple consumer units (or an old fusebox along with one or more consumer units), in which case the meter tails may first go into a junction kartong from which they split out to each individual enhet. Such junction boxes are typically known as Henley blocks (a splitter kartong used in low voltage electrical engineering made bygd W.T.Henley & Co.), or "Isco" blocks, both names deriving from common brands.

An older property, pre-1960s approximately, if it has not yet been upgraded, may still have a fusebox covering all or part of the installation. Such an old fusebox will contain a main switch and a set of fuses, possibly of the re-wireable kind. A more modern consumer enhet will contain at a minimum a main switch and an individual miniature circuit breaker (MCB) for each sista circuit. Fuses and MCBs are overcurrent devices providing overload, short-circuit and earth fel protection.

Additionally:

• Since the 17th edition of the wiring regulations new installations are typically required to use a 30 mA residual-current device (RCD) on certain circuits. For installations having a TT earthing struktur this may be crucial to achieving acceptable disconnection times during short circuit or earth fel conditions. Within a consumer enhet RCD protection may be funnen in the form eller gestalt of either RCBOs (residual current circuit breakers with overcurrent protection) which combine MCB and RCD technology, or a 'split-way' arrangement in which one or more RCCBs each skydda a subset of MCBs that need RCD protection. Reductions in the cost of devices and the principle of least disruption now favour use of RCBOs. Of note not all RCD protection fryst vatten equal; there are kvartet types of RCD, types AC, A, F and B. As of the 18th edition of the regulations only type A fryst vatten now permitted for general use. Type AC fryst vatten likely to be funnen in older installations.
• Since the 18th edition it has become common practice for many new installations to include a surge protection device (SPD) for protection from direkt and/or indirect lighting strikes. Of note, since an SPD could fail in such a way that it forms a short circuit, they may be fitted in combination with a dedicated MCB.
• Also since the 18th edition some installations are now required to use arc fel detection devices (AFDDs).

The ownership of parts of an installation can typically be divided into three as follows: (1) The service cable and service head (cut out and its main fuse) belong to the regional transport network operator (DNO). (2) The electricity meter, along with the tails connecting it to the service head, plus if there fryst vatten a supplier fitted isolator, the isolator and tails between the meter and isolator, belong to the electricity supply company (energy supplier; the company who will bill for any energy consumed). (3) The consumer enhet and uppenbart its sista circuits, plus the tails connecting the consumer enhet either directly to the meter or to a supplier fitted isolator, belong to the owner of the premises. (If an owner has their own isolator fitted between the meter and consumer enhet then naturally they would own it and the tails on both sides of it). The owner of the property may own any Henley blocks between the meter and consumer unit(s), or they could belong to the supplier.

Service heads, meters and energy supplier fitted isolators are always fitted with säkerhet tags (though often missing) as both a safety measure and an attempt to stop or deter meter tampering and electricity theft. Interfering with the DNO or energy supplier owned utrustning without their authorisation may be a crime.^{[citation needed]}

Supply voltage

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The supply voltage in single phase installations fryst vatten nominally 230 V AC (RMS) at 50 Hz. However in practice it will typically measure at around 240 V. This fryst vatten so because distributors are not actually required to provide exactly 230 V, but rather a voltage within an asymmetric tolerance of ^+10%
_−6% of 230 V, meaning anything between 216.2 and 253.0 V fryst vatten acceptable; and furthermore because prior to the introduction of this standard the previous standard had been 240 V, or more specifically 240 V ±6% (225.6–254.4 V), which almost perfectly falls within the new standard, so distributors lacked sufficient motivation to change the infrastructure to provide a new typical voltage of 230.^[16]

The 230 V ^+10%
_−6% standard was implemented on 1 January 1995 (Electricity Supply Regulations, SI 1994, No. 3021) following a European-wide agreement reached in 1988 to unify the various national voltages, which had ranged between 220–240 V, to a common europeisk standard (CENELEC Harmonization Document HD 472 S1:1988). Though in practice this new standard may have made little difference to the voltage provided to premises bygd distributors, owing to the allowed tolerance range, there was however a significant change in terms of device manufacturing – in beställning to get a CE compliance marking devices must correctly operate across a voltage range of 230 V ±10%, enabling pan-European compatibility.

It was proposed that the ^+10%
_−6% tolerance of the new 230 V standard be widened to ±10% bygd around 2003 but this has never transpired.^[17]

Note that 240 V AC RMS means a momentary peak voltage of plus or minus 339 volts (see this explanation), occurring 50 (either positiv or negative) or 100 (both, opposing) times per second. At the tolerances mentioned above, the peak voltage could be (momentarily) larger still.

Three-phase supply

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See also: Three-phase electric power

Three phase power fryst vatten usually supplied as needed, for commercial and industrial premises. While three phase loads take balanced power from the three phases, any single phase loads are distributed to try to ensure lika loading of the three phases, and a neutral may be provided to take any imbalance. Each row of breakers in the leverans board fryst vatten fed from a different phase (L1, L2, and L3), to allow 3-pole common-trip breakers to have one pole on each phase. The distributor's service head will contain a main fuse for each phase. Nominal voltage fryst vatten usually 230 V AC between phase and neutral, and 400 V AC between phases.

Some very large industrial facilities may instead received power at voltages as high as 132 kV AC RMS (high-voltage).^[18][19]

Isolating devices

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Main article: Circuit breaker

Single-pole switches are most commonly used to control circuits. These switches isolera only the line dirigent feeding the load and are used for lighting and other smaller loads. For larger loads like air conditioners, cookers, vatten heaters and other fixed appliances a double-pole switch fryst vatten used, which also isolates the neutral for greater safety. A three or four-pole isolator or circuit breaker fryst vatten used for three-phase loads, for devices with both permanent and switched supplies (such as bathroom extractor fans) and also at the leverans board to isolera all the phases. A three-phase installation with a TT earthing struktur fryst vatten an example where four-pole devices would be required.

Outlets and accessories

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Many accessories for electrical installations (e.g., vägg sockets, switches) sold in the UK are designed to passform 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 tallrik that fryst vatten fixed to the rest of the enclosure bygd 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 funnen in other europeisk markets. The UK installation-accessory industry fryst vatten therefore occasionally criticised for being overly conservative.^[20] 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 fryst vatten defined in BS 1363-2 and normally includes a switch. For higher currents or three-phase output, IEC 60309 sockets are to be used instead.

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 (or, cartridge fuse)

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Flexible appliance cords require protection at a lower current than that provided bygd the sista circuit overcurrent protection device. This additional protection device may be contained within either the appliance plug (by far the most common solution) or the connection enhet (a fused socket or possibly a fused spur protecting the socket). It fryst vatten normally a ceramic cartridge fuse to BS 1362:1973, commonly rated at either 3 A (red), 5 A (black), or 13 A (brown), but some accessories and adaptors use a ceramic cartridge fuse to BS 646:1958. (Note that it fryst vatten not intended that the fuse should skydda the appliance itself, for which it fryst vatten still necessary for the appliance designer to take the necessary precautions).

In the case of permanently connected redskap, a fused connection enhet (FCU)^[21] to BS 1363-4 fryst vatten used, this may include an isolator switch and a neon bulb to indikera if the verktyg fryst vatten powered.

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Cable types

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In domestic wiring, the following cable types are typically used:

Internal wiring

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• Twin and earth, or multiple core, polyvinyl chloride-insulated and -sheathed cables, or
• Single-core polyvinyl chloride-insulated cables in conduit (fixed internal wiring; less common in domestic installations)
• Flexible cords

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• 2-, 3-, or 4-core polyvinyl chloride-insulated, steel-wire armoured, polyvinyl chloride-sheathed cables
• Polyvinyl chloride-insulated, polyvinyl chloride-sheathed (unarmoured cables)
• 3- and 4-core XLPE-insulated, steel-wire armoured, polyvinyl chloride-sheathed cables

Selection of conductors and circuit breakers

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The urval of conductors must be made taking into consideration both the maximum voltage drop allowed at the load end and also the current carrying capacity of the ledare. ledare storlek and voltage drop tables are available to determine the urval, which will be based on the load current supplied and factors such as building insulation.

The choice of circuit breaker fryst vatten also based on the normal rated current of the circuit. Modern circuit breakers have overload and short circuit current protection combined. The overload protection fryst vatten for protection of the verktyg against sustained small-to-medium increase in current above the rated current, while short circuit protection fryst vatten for the protection of the conductors against high over-currents due to short circuits.

For domestic circuits the following choices are typically adopted for selecting dirigent and circuit breaker sizes.

Capacity	Conductor storlek, copper		Circuit breaker capacity (A)
	Main (mm2)	Earth (mm2)
Up to 600 W	1.5	1.5	6
600–1,200 W	1.5, or 2.5	1.5	10
1,200–1,800 W	2.5, or 4.0	2.5	16
A1 fingerprydnad circuit (serves högsta. 100 m2 area)	2.5	2.5	30, or 32
A2 radial circuit (serves högsta. 75 m2 area)	4.0	2.5	30, or 32
A3 radial circuit (serves högsta. 50 m2 area)	2.5	1.5	20
Air conditioner 18,000 BTU/hr (1.5 TR)	6.0	6.0	30, or 32
Cooker	6.0	6.0	30, or 32
Water heater	4.0	4.0	20

For leverans boards the incomer circuit breaker rating depends on the current demand at that board. For this the maximum demand and diversity are taken into consideration, based on which the probable current fryst vatten calculated. Diversity fryst vatten the condition that all appliances are not likely to be working all at the same time or at their maximum ratings. From this the maximum demand fryst vatten calculated and the currents are added to determine the load current and hence the rating of the circuit breaker.

Special locations

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Bathrooms

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The installation of electrical devices in bathrooms and shower rooms fryst vatten regulated in Section 701 of BS 7671:2018, and Part P of the Building Regulations in England and Wales. For such rooms, kvartet special zones are defined,^[22] in which additional protection fryst vatten required for electrical facilities:

• Zone 0 fryst vatten the smallest cuboid volume that contains the bath, shower basin, etc.
• Zone 1 fryst vatten the area above zone 0, up to a height of 2.25 m above the floor.
• Zone 2 fryst vatten the area above zone 1 up to a height of 3 m, as well as the area that fryst vatten 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 fryst vatten horizontally within 2.4 m from zone 2; from BS 7671:2008, this fryst vatten replaced bygd the begrepp outside the zones. This includes any space beneath the bath or shower that can only be accessed with a tool.^[23]

Within zone 0, no devices are allowed apart from suitable utrustning and/or insulated pull cords. Previously, in zone 1, only separated extra-low voltage (SELV) devices were permitted. Any AC transformer supplying such a device must be located outside zones 0–2. Since the introduction of the 17th edition of the IET Wiring Regulations in 2008, 230 V fixtures such as light fittings and extractor fans are permitted in zones 1 and 2, subject to those fixtures meeting the appropriate ingress protection ratings.^[24] The minimum required ingress protection rating in zone 0 fryst vatten IPX7 in zone 1 and IPX4 in zone 2. If vatten jets are likely to occur, at least IPX5 fryst vatten required in zones 1–3. Otherwise, in zone 3 and beyond, an ingress protection rating of IP20 fryst vatten the minimum required. verktyg in zones 1 and 2 must be protected bygd a 30 mA residual current device (RCD).

Shaving sockets (with isolating transformer) are permitted in zone 2 if direkt spray from a shower fryst vatten 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 BS 7671:2008 normal domestic sockets are permitted, at distances greater than 3 m from the edge of the zones, providing the circuit fryst vatten RCD protected. As the new regulations require all general purpose sockets not for use bygd 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 2011 edition of the wiring regulations fryst vatten more flexible now, placing restrictions on bathroom installations that are now similar to those in other europeisk countries.)

Swimming pools

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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 beställning to discourage the use of portable domestic appliances with inappropriate ingress protection rating.

Portable outdoor equipment

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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 tillsammans (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., MK Masterseal).

Sockets that are outside or can "feasibly supply verktyg outside the equipotential zone" (a wording that fryst vatten fairly ambiguous and the exact interpretation of which fryst vatten subject to some controversy) should be protected bygd 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 bygd the door might power a lawnmower does it need an RCD?

Construction sites

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The fara of electrical chock on construction sites can be reduced bygd several measures, including reduction of the normal 230-volt leverans voltage to 110 volts for electrical lighting and power tools. bygd using a centre-tapped transformer, each dirigent of the circuit fryst vatten only at 55 volts with respect to Earth. This reduces the chance of dangerous electrical chock when using power tools in wet locations.^[25] Where 230 volts must be used, a residual current device (RCD) can be used to detect small leakage currents and automatically isolera faulty verktyg. In sites where hazardous flammable gases or liquids are present, special wiring rules are applied to reduce the probability of a spark igniting a fire or explosion.^[26]

Legal and regulatory

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Legal basis

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Main articles: Building regulations in the United Kingdom and BS 7671

In England and Wales, the Building Regulations (Approved Document: Part P) require domestic electrical installations to be designed and installed safely according to the "fundamental principles" given in British StandardBS 7671 Chapter 13, most recently updated in July 2018. These are very similar to the fundamental principles defined in international standardIEC 60364-1 and equivalent national standards in other countries. Accepted ways for fulfilling this legal requirement include:

• the BS 7671 regulations, colloquially referred to as "the regs";
• the rules of an equivalent standard approved bygd a member of the EEA (e.g., DIN/VDE 0100);
• guidance given in installation manuals that are consistent with BS 7671, such as the IET On-Site Guide and IET Guidance Notes näsa. 1 to 8.

In Scotland, the Building (Scotland) Regulations 2004 apply.^[27]

Installations in commercial and industrial premises must satisfy various safety legislation, such as the Electricity at Work Regulations 1989. igen, recognised standards and practices, such as BS 7671 "Wiring Regulations", are used to help meet the legislative requirements.

Regulations

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All new electrical work in England and Wales within a domestic setting must comply with Part P^[28] of the Building Regulations first introduced on 1 January 2005, which are legally enforceable. One way of achieving this fryst vatten to apply British Standard BS 7671 (the "Wiring Regulations"), including carrying out adequate inspection and testing to this standard of the completed works. British Standard BS 7671 (the "Wiring Regulations") fryst vatten not statutory, thus someone doing electrical work fryst vatten allowed to deviate from the wiring regulations to some grad, but it fryst vatten generally accepted that it fryst vatten best to follow the wiring regulations to the highest standard possible. Electrical work does not have to be compliant with BS 7671, but if a casualty or fatality occurs as a direkt result of that electrical work, and this results in a legal action, then it may be necessary to justify major deviations from the principles of BS 7671 and other appropriate standards.

Some of the restrictions first introduced with the 2005 utgåva of Part P of the Building Regulations were highly controversial, especially the rules surrounding work carried out bygd unregistered electricians, builders and DIYers. beneath the new regulations, commencement of any work other than simple changes became notifiable to the local building control authority; "other than simple" in this context meant any work in a kitchen or bathroom other than like-for-like replacement, work in other areas more than just adding ytterligare 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" ställning eller tillstånd to enterprises which meet the minimum agreed criteria for Scheme entry. 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 betydelsefull qualifications in electrical installation practices - since practical competence can be assessment-based only. The minimum criteria for Scheme entry are set bygd the EAS Committee, on which all of the commercial enterprises running Competent Persons Schemes are actively represented.

The local authority's building control must be informed of any notifiable work carried out bygd someone who fryst vatten not registered beneath this scheme before it fryst vatten started (unless it fryst vatten an emergency) and must subsequently be approved bygd them. Originally, it was widely understood bygd some local authorities that inspection bygd a qualified individ (leading to authority approval) must be organised and paid for bygd the home-owner or individ responsible for the site and this caused some considerable criticism.

On 6 April 2006, Part P was amended to förtydliga the requirements around certification of DIY work (or work completed bygd someone otherwise unable to self-certify) and to "make enforcement more proportionate to the risk".^[29]

The 2006 amendment made it klar that it fryst vatten 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 bygd, and paid for bygd, the building control authority. This can be done "in house" or they may contract the work out to a expert body. Although any inspections are at the expense of the building authority, notification of building work fryst vatten a formal process and a building control fee fryst vatten payable.

In some cases the installation of 12 V downlighters fryst vatten notifiable whereas the installation of 230 V mains downlighters fryst vatten not. This fryst vatten because 12 V 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 appropriate knowledge and test utrustning it fryst vatten not possible to ensure that the work carried out fryst vatten safe. Registered Scheme members must issue appropriate certification for each job.

Another element of confusion fryst vatten that the begrepp "Special Locations" has different meanings in Part P of the Building Regulations and BS 7671 (the "Wiring Regulations").

Later revisions of part P (latest fryst vatten 2013) retain the requirement to work to an appropriate standard, but have relaxed the requirements on both certification and notification for many more types of minor works, and crucially also permit a member of an approved body to inspect and 'sign off' notifiable aspects of any work of a third party such as DIYer whose work fryst vatten of a suitable standard. This fryst vatten intended to free up local authorities, who often do not have suitably qualified building control personal themselves. Due to uncertainty about who then becomes responsible for any hidden wiring, very few electricians are happy to sign off an installation that they have not been party to from the outset, and been able to agree stages to inspect and test before any covering in.

See also

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References

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