Electrical wiring

Electrical wiring in general refers to insulated conductors used to carry electricity, and associated devices. This article describes general aspects of electrical wiring as used to provide power in buildings and structures, commonly referred to as building wiringSONY VAIO VGN-FW21E Battery .

This article is intended to describe common features of electrical wiring that should apply worldwide.

Wiring safety codes

Wiring safety codes are intended to protect people and buildings from electrical shock and fire hazards SONY VAIO VGN-FW21J Battery .

Regulations may be established by city, county, provincial/state or national legislation, sometimes by adopting in amended form a model code produced by a technical standards-setting organization, or by a national standard electrical code.

Electrical codes arose in the 1880s with the commercial introduction of electrical power SONY VAIO VGN-FW21L Battery .

Many conflicting standards existed for the selection of wire sizes and other design rules for electrical installations.

The first electrical codes in the United States originated in New York in 1881 to regulate installations of electric lighting SONY VAIO VGN-FW21M Battery .

Since 1897 the U.S. National Fire Protection Association, a private nonprofit association formed by insurance companies, has published the National Electrical Code (NEC). States, counties or cities often include the NEC in their local building codes by reference along with local differences SONY VAIO VGN-FW21Z Battery .

The NEC is modified every three years. It is a consensus code considering suggestions from interested parties. The proposals are studied by committees of engineers, tradesmen, manufacturer representatives, fire fighters, and other invitees SONY VAIO VGN-FW25T/B Battery .

Since 1927, the Canadian Standards Association (CSA) has produced the Canadian Safety Standard for Electrical Installations, which is the basis for provincial electrical codes. The CSA also produces the Canadian Electrical Code, the 2006 edition of which references IEC 60364 SONY VAIO VGN-FW26T/B Battery

(Electrical Installations for Buildings) and states that the code addresses the fundamental principles of electrical protection in Section 131. The Canadian code reprints Chapter 13 of IEC 60364, and it is interesting to note that there are no numerical criteria listed in that chapter whereby the adequacy of any electrical installation can be assessed .SONY VAIO VGN-FW27/B Battery .

Although the U.S. and Canadian national standards deal with the same physical phenomena and broadly similar objectives, they differ occasionally in technical detail. As part of the North American Free Trade Agreement (NAFTA) program, U.S. and Canadian standards are slowly converging toward each other, in a process known as harmonization SONY VAIO VGN-FW27/W Battery.

In European countries, an attempt has been made to harmonize national wiring standards in an IEC standard, IEC 60364 Electrical Installations for Buildings. Hence national standards follow an identical system of sections and chapters. However, this standard is not written in such language that it can readily be adapted as a national wiring code .SONY VAIO VGN-FW31ZJ Battery

Neither is it designed for field use by electrical tradesmen and inspectors for testing compliance with national wiring standards. National codes, such as the NEC or CSA C22.1, exemplify the common objectives of IEC 60364, and provide rules in a form that allows for guidance of those installing and inspecting electrical systems SONY VAIO VGN-FW27T/H Battery .

DKE - the German Commission for Electrical, Electronic and Information Technologies of DIN and VDE - is the German organisation responsible for the promulgation of electrical standards and safety specifications. DIN VDE 0100 is the German wiring regulations document harmonised with IEC 60364 SONY VAIO VGN-FW29/B Battery .

In the United Kingdom wiring installations are regulated by the Institution of Engineering and Technology Requirements for Electrical Installations: IEE Wiring Regulations, BS 7671: 2008, which are harmonised with IEC 60364. The previous edition (16th) was replaced by the current 17th Edition in January 2008 SONY VAIO VGN-FW290JRB Battery .

The 17th edition includes new sections for microgeneration and solar photovoltaic systems. The first edition was published in 1882.

AS/NZS 3000 is an Australian/New Zealand standard, commonly known as the "wiring rules," that specifies the requirements for the selection and installation of electrical equipment and the design and testing of such installations SONY VAIO VGN-FW290JTB Battery .

The standard is a mandatory standard in both New Zealand and Australia; therefore, all electrical work covered by the standard must comply.

The international standard wire sizes are given in the IEC 60228 standard of the International Electrotechnical Commission. In North America, the American Wire Gauge is used SONY VAIO VGN-FW290JTH Battery .

Materials for wiring interior electrical systems in buildings vary depending on:

• Intended use and amount of power demand on the circuit
• Type of occupancy and size of the building SONY VAIO VGN-FW32J Battery
• National and local regulations
• Environment in which the wiring must operate.

Wiring systems in a single family home or duplex, for example, are simple, with relatively low power requirements, infrequent changes to the building structure and layout, usually with dry, moderate temperature, and noncorrosive environmental conditionsSONY VAIO VGN-FW33G/E1 Battery .

In a light commercial environment, more frequent wiring changes can be expected, large apparatus may be installed, and special conditions of heat or moisture may apply. Heavy industries have more demanding wiring requirements, such as very large currents and higher voltages, frequent changes of equipment layout, corrosive, or wet or explosive atmospheres SONY VAIO VGN-FW33G/W Battery.

In facilities that handle flammable gases or liquids, special rules may govern the installation and wiring of electrical equipment in hazardous areas.

Wires and cables are rated by the circuit voltage, temperature rating, and environmental conditions (moisture, sunlight, oil, chemicals) in which they can be used SONY VAIO VGN-FW33GW Battery .

A wire or cable has a voltage (to neutral) rating, and a maximum conductor surface temperature rating. The amount of current a cable or wire can safely carry depends on the installation conditions (Dell XPS M1210 Battery) http://www.hdd-shop.co.uk .

Early wiring methods

The very first interior power wiring systems used conductors that were bare or covered with cloth, which were secured by staples to the framing of the building or on running boards. Where conductors went through walls, they were protected with cloth tape Dell Studio XPS 1640 Battery .

Splices were done similarly to telegraph connections, and soldered for security. Underground conductors were insulated with wrappings of cloth tape soaked in pitch, and laid in wooden troughs which were then buried. Such wiring systems were unsatisfactory because of the danger of electrocution and fire and the high labour cost for such installations Dell Vostro 1710 Battery .

The earliest standardized method of wiring in buildings, in common use in North America from about 1880 to the 1930s, was knob and tube (K&T) wiring: single conductors were run through cavities between the structural members in walls and ceilings Dell KM958 battery ,

with ceramic tubes forming protective channels through joists and ceramic knobs attached to the structural members to provide air between the wire and the lumber and to support the wires. Since air was free to circulate over the wires, smaller conductors could be used than required in cables Dell Studio 1555 battery .

By arranging wires on opposite sides of building structural members, some protection was afforded against short-circuits that can be caused by driving a nail into both conductors simultaneously. By the 1940s, the labour cost of installing two conductors rather than one cable resulted in a decline in new knob-and-tube installations Sony VGP-BPS13 battery .

Metal-sheathed wires

In the United Kingdom, an early form of insulated cable, introduced in 1896, consisted of two impregnated-paper-insulated conductors in an overall lead sheath. Joints were soldered, and special fittings were used for lamp holders and switches Sony VGP-BPS13/B battery .

These cables were similar to underground telegraph and telephone cables of the time. Paper-insulated cables proved unsuitable for interior wiring installations because very careful workmanship was required on the lead sheaths to ensure moisture did not affect the insulation Sony VGP-BPS13/S battery .

A system later invented in the UK in 1908 employed vulcanized-rubber insulated wire enclosed in a strip metal sheath. The metal sheath was bonded to each metal wiring device to ensure continuity Sony VGP-BPS13A/B battery .

A system developed in Germany called Kuhlo wire used one, two, or three rubber-insulated wires in a brass or lead-coated iron sheet tube, with a crimped seam. The enclosure could also be used as a return conductor. Kuhlo wire could be run exposed on surfaces and painted, or embedded in plaster Sony VGP-BPS13B/B battery .

Special outlet and junction boxes were made for lamps and switches, made either of porcelain or sheet steel. The crimped seam was not considered as watertight as the Stannos wire used in England, which had a soldered sheath.

A somewhat similar system called "concentric wiring" was introduced in the United States around 1905 Sony VGP-BPL9 battery .

In this system, an insulated copper wire was wrapped with copper tape which was then soldered, forming the grounded (return) conductor of the wiring system. The bare metal sheath, at earth potential, was considered safe to touch Sony VGP-BPS13B/B battery.

While companies such as General Electricmanufactured fittings for the system, and a few buildings were wired with it, it was never adopted into the US National Electrical Code. Drawbacks of the system were that special fittings were required, and that any defect in the connection of the sheath would result in the sheath becoming energized Sony VGP-BPL15 battery .

Other historical wiring methods

Other methods of securing wiring that are now obsolete include:

• Re-use of existing gas pipes for electric lighting. Insulated conductors were pulled into the pipes feeding gas lamps Dell Inspiron E1505 battery .
• Wood mouldings with grooves cut for single conductor wires, covered by a wooden cap strip. These were prohibited in North American electrical codes by 1928. Wooden moulding was also used to some degree in England, but was never permitted by German and Austrian rules Dell Latitude E6400 battery .
• A system of flexible twin cords supported by glass or porcelain buttons was used near the turn of the 20th century in Europe, but was soon replaced by other methods HP Pavilion dv6000 Battery .
• During the first years of the 20th century various patented forms of wiring system such as Bergman and Peschel tubing were used to protect wiring; these used very thin fibre tubes or metal tubes which were also used as return conductors SONY VAIO VGN-FZ Battery .
• In Austria, wires were concealed by embedding a rubber tube in a groove in the wall, plastering over it and then removing the tube and pulling in wires in the cavity SONY VAIO VGN-FZ18 Battery .

Metal moulding systems, with a flattened oval section consisting of a base strip and a snap-on cap channel, were more costly than open wiring or wooden moulding, but could be easily run on wall surfaces. Similar systems are still available today SONY VAIO VGN-FZ21E Battery .

Armoured cables with two rubber-insulated conductors in a flexible metal sheath were used as early as 1906, and were considered at the time a better method than open knob-and-tube wiring, although much more expensive SONY VAIO VGN-FW31J Battery - 5200mAh/7800mAh/10400mAh, 11.10V .

The first polymer-insulated cables for building wiring were introduced in 1922. These were two or more solid copper wires, with rubber insulation, woven cotton cloth over each conductor for protection of the insulation, with an overall woven jacket, usually impregnated with tar as a protection from moisture SONY VAIO VGN-FW31J Battery - 5200mAh/7800mAh/10400mAh, 11.10V .

Waxed paper was used as a filler and separator.

Rubber-insulated cables become brittle over time because of exposure to oxygen, so they must be handled with care, and should be replaced during renovations SONY VAIO VGN-FW21E Battery .

When switches, outlets or light fixtures are replaced, the mere act of tightening connections may cause insulation to flake off the conductors. Rubber was hard to separate from bare copper, so copper was tinned, causing slightly more resistance SONY VAIO VGN-NR11S/S Battery .

About 1950, PVC insulation and jackets were introduced, especially for residential wiring. About the same time, single conductors with a thinner PVC insulation and a thin nylon jacket became common.

The simplest form of cable has two insulated conductors twisted together to form a unit SONY VAIO VGN-NR11M/S Battery ;

such unjacketed cables with two or three conductors are used for low-voltage signal and control applications such as doorbell wiring. In North American practice, an overhead cable from a transformer on a power pole to a residential electrical service consists of three twisted (triplexed) wires SONY VAIO VGN-NR11Z/S Battery ,

often with one being a bare copper wire (protective earth/ground) and the other two being insulated for the line voltage (hot/live wire and neutral wire).

Aluminium conductors

Aluminium wire was common in North American residential wiring from the late 1960s to mid 1970s due to the rising cost of copperSONY VAIO VGN-NR11Z/T Battery .

Because of its greaterresistivity, aluminium wiring requires larger conductors than copper. For instance, instead of 14 AWG (American wire gauge) for most lighting circuits, aluminium wiring would be 12 AWG on a typical 15 ampere circuit, though local building codes may vary Sony VAIO VGN-FZ21E Battery .

Aluminium conductors were originally used with wiring devices intended for copper wires. This can cause defective connections unless the aluminium was one of a special alloy, or all devices — breakers, switches, receptacles, splice connectors, i.e., wire nuts, etc Sony VAIO VGN-FW21E Battery .

— were designed to address problems with junctions between dissimilar metals, oxidation on metal surfaces and mechanical effects that occur as different metals expand at different rates with increases in temperature. Unlike copper, aluminium has a tendency to cold-flow under pressure, so screw clamped connections may get loose over time Sony VAIO VGN-NR11S/S Battery .

This can be mitigated by using spring-loaded connectors that apply constant pressure, applying high pressure cold joints in splices and termination fittings, and torquing the bolted connection. Unlike copper, aluminium forms an insulating oxide layer on the surface Sony VAIO VGN-NR11Z/S Battery .

This is sometimes addressed by coating aluminium wires with an antioxidant paste at joints, or applying a mechanical termination designed to break through the oxide layer during installation.

Because of improper design and installation, some junctions to wiring devices overheated under heavy current load and caused firesSony VAIO VGN-NR11M/S Battery .

Revised standards for wiring devices (such as the CO/ALR "copper-aluminium-revised" designation) were developed to reduce these problems. Nonetheless, aluminium wiring for residential use has acquired a poor reputation and has fallen out of favour Sony VAIO VGN-NR11Z/T Battery .

Aluminium conductors are still used for power distribution and large feeder circuits, because they cost less than copper wiring, and weigh less, especially in the large sizes needed for heavy current loads. Aluminium conductors must be installed with compatible connectors SONY VAIO VGN-FZ180E Battery .

Modern wiring materials

Modern nonmetallic sheathed cables (NMC), like (U.S. and Canadian) Type NM, consist of two to four wires covered with thermoplastic insulation and a bare wire for grounding (bonding) surrounded by a flexible plastic jacket SONY VAIO VGN-FZ220E Battery .

Some versions wrap the individual conductors in paper before the plastic jacket is applied. It is often called Romex™ cable, since the first of its type was manufactured by Rome Cable Division of Cyprus Mines, Rome, New York. The trade name has been owned by Southwire since it purchased the electrical building wire assets of General Cable in 2001 SONY VAIO VGN-FZ340E Battery .

Rubber-like synthetic polymer insulation is used in industrial cables and power cables installed underground because of its superior moisture resistance.

Insulated cables are rated by their allowable operating voltage and their maximum operating temperature at the conductor surfaceSONY VAIO VGN-FZ430E Battery .

A cable may carry multiple usage ratings for applications, for example, one rating for dry installations and another when exposed to moisture or oil.

Generally, single conductor building wire in small sizes is solid wire, since the wiring is not required to be very flexible SONY VAIO VGN-FZ460E Battery .

Building wire conductors larger than 10AWG (or about 6 mm²) are stranded for flexibility during installation, but not stranded enough to be flexible enough to use as appliance cord.

Cables for industrial, commercial, and apartment buildings may contain many insulated conductors in an overall jacket SONY VAIO VGN-FZ480E Battery ,

with helical tape steel or aluminium armour, or steel wire armour, and perhaps as well an overall PVC or lead jacket for protection from moisture and physical damage. Cables intended for very flexible service or in marine applications may be protected by woven bronze wires SONY VAIO VGN-FZ4000 Battery .

Power or communications cables (e.g., computer networking) that are routed in or through air-handling spaces (plenums) of office buildings are required under the model code to be either encased in metal conduit or rated for low flame and smoke productionSONY VAIO VGN-FZ31E Battery .

For some industrial uses in steel mills and similar hot environments, no organic material gives satisfactory service. Cables insulated with compressed mica flakes are sometimes used. Another form of high-temperature cable is a mineral insulated cable, with individual conductors placed within a copper tube, and the space filled with magnesium oxide powder SONY VAIO VGN-FZ31B Battery .

The whole assembly is drawn down to smaller sizes, thereby compressing the powder. Such cables have a certified fire resistance rating, are more costly than non-fire rated cable, and have little flexibility and are effectively rigid to the user of the cable SONY VAIO VGN-FZ31J Battery .

Because multiple conductors bundled in a cable cannot dissipate heat as easily as single insulated conductors, those circuits are always rated at a lower "ampacity". Tables in electrical safety codes give the maximum allowable current for a particular size of conductor SONY VAIO VGN-FZ31M Battery ,

for the voltage and temperature rating at the surface of the conductor for a given physical environment, including the insulation type and thickness. The allowable current will be different for wet or dry, for hot (attic) or cool (underground) locations. In a run of cable through several areas, the most severe area will determine the appropriate rating of the overall run SONY VAIO VGN-FZ31Z Battery .

Cables usually are secured by special fittings where they enter electrical apparatus; this may be a simple screw clamp for jacketed cables in a dry location, or a polymer-gasketed cable connector that mechanically engages the armour of an armoured cable and provides a water-resistant connection SONY VAIO VGN-FZ38M Battery .

Special cable fittings may be applied to prevent explosive gases from flowing in the interior of jacketed cables, where the cable passes through areas where inflammable gases are present. To prevent loosening of the connections of individual conductors of a cable, cables must be supported near their entrance to devices and at regular intervals through their length SONY VGP-BPS8 Battery .

In tall buildings special designs are required to support the conductors of vertical runs of cable. Usually, only one cable per fitting is allowed unless the fitting is otherwise rated.

Special cable constructions and termination techniques are required for cables installed in ocean-going vessels SONY VGP-BPS13/S Battery ;

in addition to electrical safety and fire safety, such cables may also be required to be pressure-resistant where they penetrate bulkheads of a ship.

Insulated wires may be run in one of several forms of a raceway between electrical devices SONY VGP-BPS13A/B Battery .

This may be a pipe, called a conduit, or in one of several varieties of metal (rigid steel or aluminum) or non-metallic (PVC or HDPE) tubing. Rectangular cross-section metal or PVC wire troughs (North America) or trunking (UK) may be used if many circuits are required SONY VGP-BPS13B/B Battery .

Wires run underground may be run in plastic tubing encased in concrete, but metal elbows may be used in severe pulls. Wiring in exposed areas, for example factory floors, may be run in cable trays or rectangular raceways having lids SONY VGP-BPS13A/S Battery .

Where wiring, or raceways that hold the wiring, must traverse fire-resistance rated walls and floors, the openings are required by local building codes to be firestopped. In cases where the wiring has to be kept operational during an accidental fire SONY VGP-BPS13AS Battery ,

fireproofing must be applied to maintain circuit integrity in a manner to comply with a product's certification listing. The nature and thickness of any passive fire protection materials used in conjunction with wiring and raceways has a quantifiable impact upon the ampacity derating Dell Inspiron 1320n Battery .

Cable trays are used in industrial areas where many insulated cables are run together. Individual cables can exit the tray at any point, simplifying the wiring installation and reducing the labour cost for installing new cables Dell Inspiron 1464 Battery .

Power cables may have fittings in the tray to maintain clearance between the conductors, but small control wiring is often installed without any intentional spacing between cables Dell Inspiron 1564 Battery .

Since wires run in conduits or underground cannot dissipate heat as easily as in open air, and adjacent circuits contribute induced currents, wiring regulations give rules to establish the current capacity (ampacity).

Special fittings are used for wiring in potentially explosive atmospheres Dell Inspiron 1764 Battery .

For very heavy currents in electrical apparatus, and for heavy currents distributed through a building, bus bars can be used. Each live conductor of such a system is a rigid piece of copper or aluminium, usually in flat bars (but sometimes as tubing or other shapes)Dell Studio 1450 Battery .

Open bus bars are never used in publicly accessible areas, although they are used in manufacturing plants and power company switch yards to gain the benefit of air cooling. A variation is to use heavy cables, especially where it is desirable to transpose or "roll" phases Dell Studio 1457 Battery .

In industrial applications, conductor bars are assembled with insulators in grounded enclosures. This assembly, known as bus duct or busway, can be used for connections to large switchgear or for bringing the main power feed into a building. A form of bus duct known as plug-in bus is used to distribute power down the length of a building Dell Latitude D610 Battery ;

it is constructed to allow tap-off switches or motor controllers to be installed at definite places along the bus. The big advantage of this scheme is the ability to remove or add a branch circuit without removing voltage from the whole duct Toshiba NB100 Battery .

Bus ducts may have all phase conductors in the same enclosure (non-isolated bus), or may have each conductor separated by a grounded barrier from the adjacent phases (segregated bus). For conducting large currents between devices, a cable bus is usedToshiba Satellite M65 battery .

For very large currents in generating stations or substations, where it is difficult to provide circuit protection, an isolated-phase bus is used. Each phase of the circuit is run in a separate grounded metal enclosure. The only fault possible is a phase-to-ground fault, since the enclosures are separated Toshiba Satellite M60 battery .

This type of bus can be rated up to 50,000 amperes and up to hundreds of kilovolts (during normal service, not just for faults), but is not used for building wiring in the conventional sense.

In the electrical wiring of buildings, a cable tray system is used to support insulated electric cables used for power distribution and communication Dell Latitude D830 Battery .

Cable trays are used as an alternative to open wiring or electrical conduit systems, and are commonly used for cable management in commercial and industrial construction. They are especially useful in situations where changes to a wiring system are anticipated, since new cables can be installed by laying them in the tray, instead of pulling them through a pipe Dell Latitude D620 Battery .

Types

Several types of tray are used in different applications. A solid-bottom tray provides the maximum protection to cables, but requires cutting the tray or using fittings to enter or exit cables. A deep, solid enclosure for cables is called a cable channel or cable troughDell Inspiron Mini 10 Battery .

A ventilated tray has openings in the bottom of the tray, allowing some air circulation around the cables, water drainage, and allowing some dust to fall through the tray. Small cables may exit the tray through the ventilation openings, which may be either slots or holes punched in the bottom Sony VGN-FW11S Battery .

A ladder tray has the cables supported by a traverse bar, similarly to the rungs of a ladder, at regular intervals on the order of 4 to 12 inches (100 to 300 mm).

Ladder and ventilated trays may have solid covers to protect cables from falling objects, dust, and water Sony VGN-FW11M Battery .

Tray covers for use outdoors or in dusty locations may have a peaked shape to shed debris including dust, ice or snow. Lighter cable trays are more appropriate in situations where a great number of small cables are used, such as for telephone or computer network cables Sony VGN-FW139E/H battery .

These trays may be made of wire mesh, called "cable basket", or be designed in the form of a single central spine (rail) with ribs to support the cable on either side Dell Latitude E5400 Battery .

Large power cables laid in the tray may require support blocks to maintain spacing between conductors, to prevent overheating of the wires. Smaller cables may be laid unsecured in horizontal trays, or secured with cable ties to the bottom of vertically-mounted trays Dell Latitude E4200 Battery .

To maintain support of cables at changes of elevation or direction of a tray, a large number of specialized cable tray fittings are made compatible with each style and manufacturer. Horizontal elbows change direction of a tray in the same plane as the bottom of the tray and are made in 30, 45 and 90 degree forms Dell Inspiron 300M Battery ;

inside and outside elbows are for changes perpendicular to the tray bottom. These can be in various shapes including tees and crosses. Some manufacturers and types provide adjustable elbows, useful for field-fitting a tray around obstacles or around irregular shapes Dell Vostro A840 Battery .

Various clamping, supporting and splicing accessories are used with the cable tray to provide a complete functional tray system. For example, different sizes of cable tray used within one run can be connected with reducers Dell Studio 1737 battery .

Materials used

Common cable trays are made of galvanized steel, stainless steel, aluminum, or glass-fiber reinforced plastic. The material for a given application is chosen based on the corrosion resistance required for the location Dell Inspiron E1505 battery .

Fire safety concerns and solutions

Combustible cable jackets may catch on fire and cable fires can thus spread along a cable tray within a structure. This is easily prevented through the use of fire-retardant cable jackets, or fireproofing coatings applied to installed cables Dell RM791 battery .

Heavy coatings or long fire-stops may require adjustment of the cable current ratings, since such fireproofing measures may reduce the heat dissipation of installed cables.

Regular housecleaning is important for safety, as cable trays are often installed in hard to reach places Dell XPS M1530 battery .

Combustible dust and clutter may accumulate if the trays are not routinely checked and kept clean.

Plastic and fibreglass reinforced plastic cable trays are combustible; the effect is mitigated through the use of fire retardants or fireproofing Dell XPS M2010 battery .

Ferrous cable trays expand with the increasing heat from accidental fire. This has been proven by the German Otto-Graf-Institut Test Report III.1-80999/Tei/tei "Supplementary Test On The Topic Of Mechanical Force Acting On Cable Penetration Firestop Systems During The Fire Test" Acer Aspire One battery ,

dated 23 October 1984, to dislodge "soft" firestops, such as those made of fibrous insulations with rubber coatings. This also applies to any silicone foam seals, but is easily remedied through the use of firestop mortars of sufficient compression strength and thickness, as shown above Toshiba Satellite P10 Battery .

Also, some building codesmandate that penetrants such as cable trays are installed in such ways so as to avoid their contribution to the collapse of a firewall.

The modern UK standards and regulations for electrical wiring no longer differ substantially from those in Europe SONY VGN-FZ210CE Battery .

However, there are a number of noteworthy national peculiarities, habits and traditions associated with domestic electrical wiring in the UK (and Ireland) that differ significantly from other countries. These, along with their historic background, are the focus of this article Dell Precision M70 Battery .

They include:

• ring circuits
• fused plugs
• switched sockets Toshiba Satellite L305 Battery
• 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 Toshiba Satellite T4900 Battery

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 Toshiba PA3399U-2BRS battery .

These are very similar to the fundamental principles defined in international standard IEC 60364-1 and equivalent national standards in other countries. Accepted ways for fulfilling this legal requirement include Toshiba Satellite A200 Battery

• the rules of the IEE wiring regulations (BS 7671), colloquially referred to as "the regs" (BS 7671: 2008, 17th Edition).;
• the rules of an equivalent standard approved by a member of the EEA (e.g., DIN/VDE 0100) Toshiba Satellite 1200 Battery ;
• 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 Toshiba Satellite M300 Battery .

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 SONY VGP-BPS13A/Q Battery .

Wiring colours

The standard wiring colours in the UK are (as of 2006) the same as elsewhere in Europe, Australia, and New Zealand and follow international standard IEC 60446 SONY VGP-BPS13A/Q Battery .

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 SONY VGP-BPS13B/Q Battery .

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 SONY VGP-BPS13B/Q Battery .

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 SONY VGP-BPS13/Q Battery .

From April 2006, only the new colours should be used for any new wiring.

Potential for confusion

The colour change has been controversial and was delayed for three decades SONY VGP-BPS13/Q Battery ,

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 SONY VGP-BPS21A/B Battery .

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 SONY VGP-BPS21/S Battery .

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 SONY VGP-BPS21B Battery .

Direct current systems

Direct current 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 SONY VGP-BPS21A Battery .

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.

UK electrical socket circuits are normally described as either radial or ring SONY VGP-BPS21 Battery .

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 Sony VGP-BPS21A/B Battery .

A British peculiarity unknown in many 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 Sony VGP-BPS21/S Battery .

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 Sony VGP-BPS21A Battery .

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 Sony VGP-BPS21 Battery .

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 Sony Vaio PCG-5G2L Battery .

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) Sony Vaio PCG-5G3L Battery ,

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 Sony Vaio PCG-5J1L Battery .

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 Sony Vaio PCG-5K2L Battery .

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. Although it must be stated that the British Standard BS 7671 (the "Wiring Regulations") Sony Vaio PCG-5J2L Battery

are 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 Sony Vaio PCG-5K1L Battery .

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 Sony Vaio PCG-6S2L Battery ;

"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 Sony Vaio PCG-6S3L Battery .

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 Sony Vaio PCG-6V1L Battery :

(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) Sony Vaio PCG-6W1L Battery .

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 Sony Vaio PCG-6W2L Battery .

The fact that registration for the purposes of self-certification does not automatically ensure that work will be carried out by a trained and qualified electrician is not widely understood Sony Vaio PCG-6W3L Battery .

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 Sony Vaio PCG-7111L Battery .

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 Sony Vaio PCG-7112L Battery .

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" Sony Vaio PCG-7113L Battery .

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 Sony Vaio PCG-7133L Battery .

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 Sony Vaio PCG-7Z2L Battery . .

One of the many quirks of Part P is that in some cases the installation of 12V downlighters is notifiable where as the installation of 240V mains downlighters isn't. This appears strange but it's because 12V downlighters draw high currents and that combined with the wrong choice of wire could lead to a fire Sony Vaio PCG-8Y1L Battery .

A further quirk of Part P is that 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 Sony Vaio PCG-8Y2L Battery .

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 - Sony Vaio PCG-8Z1L Battery

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 Sony Vaio PCG-8Z2L Battery .

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 SONY VAIO VGN-FW31J Battery

. 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 formatSONY VAIO VGN-FW31E Battery ,

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 SONY VAIO VGN-FW31B Battery .

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 60309sockets are to be used instead SONY VAIO VGN-FW31M Battery .

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 SONY VAIO VGN-FW31Z Battery .

Plug and accessory fuses

Some accessories require protection at a lower current than that provided by the ring main protection device. The protection device used in such accessories is a 1" (25.4mm) ceramic cartridge to the requirements of BS 1362:1973 fuse, rated at 3 A, 5 A, or 13 A SONY VAIO VGN-FW38M Battery .

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 SONY VAIO VGN-AW41JF Battery .

In the case of non-permanently connected domestic equipment, a socket rated at 13 A is attached to the ring main, into which a fused plug may be inserted. The fuse protects the contacts (including any switch contacts) and the equipment flex. There are two benefits to this arrangement SONY VAIO VGN-AW41JF/H Battery .

Firstly with low power equipment a flex with a low current rating (and therefore minimal diameter) can be used. Secondly, if the equipment is moved to a different socket, it will remain protected by the same (hopefully correct) fuse. The disadvantage is that despite warnings to the contrary people often use a fuse rated at too high a current SONY VAIO VGN-AW41MF Battery ,

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 main current. This is likely to cause a fire SONY VAIO VGN-AW41MF/H Battery .

Note that the equipment itself should have its own protection measures, such as another fuse, unless the plug or accessory fuse affords all required protection (as is the case with most table lamps, for example). It is also important to be aware that when a double socket is rated at 13 A this applies to the total rating of the two sockets together SONY VAIO VGN-FW30B Battery ,

and in this case the use of a 13 A-rated double socket (e.g., a "free double socket" on an extension lead) for powering more than one highly rated appliance, such as an electric fire, is dangerous. (This is not the case for most fixed-wiring outlets to BS1363, which states that the standard rating of a double socket for use as part of the fixed wiring is 20 A SONY VAIO VGN-FW50B Battery .

Other "high-current" appliances such as washing machine and clothes dryer should ideally be fed from separate sockets for various reasons, but note that they do not use their full rated current at all times (in the cases of the Washing Machine and Dishwasher, for example, only when heating water which is a small percentage of the cycle) SONY VAIO VGN-FW51B/W Battery .

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 60–100 A SONY VAIO VGN-FW51MF Battery .

Separate live and neutral cables go from here to a meter, and from there proceed to one or more consumer units. This contains a main switch and individual fuses or miniature circuit breakers (MCBs) for each circuit SONY VAIO VGN-FW51MF/H Battery .

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 SONY VAIO VGN-FW51ZF Battery :

• Zone 0 is the smallest cuboid volume that contains the bathtub, shower basin, etc..
• Zone 1 is the area above Zone 0, up to a height of 2.25 m above the floor SONY VAIO VGN-FW51ZF/H Battery .
• 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' SONY VAIO VGN-FW52JB Battery .

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 SONY VAIO VGN-FW54FB Battery .

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 SONY VAIO VGN-FW70DB Battery .

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 SONY VAIO VGN-FW71DB/W Battery .

Before the 2008 regulations, such shaving sockets were the only sockets permitted 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 SONY VAIO VGN-FW72JGB Battery .

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 SONY VAIO VGN-FW73JGB Battery .

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 SONY VAIO VGN-FW74FB Battery .

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 SONY VAIO VGN-FW81HS Battery .

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 SONY VAIO VGN-FW81NS Battery

(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 equipment outside the equipotential zone" SONY VAIO VGN-FW81S Battery

(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 SONY VAIO VGN-FW82DS Battery ,

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 AC (RMS) at 50 Hz SONY VAIO VGN-FW82JS Battery .

In 1988, a Europe-wide agreement was reached to change the various national voltages, which ranged at the time from 220 V to 240 V, to a common European standard of 230 V (CENELEC Harmonization Document HD 472 S1:1988) SONY VAIO VGN-FW82XS Battery .

As a result, the standard nominal supply voltage in domestic single-phase 50 Hz installations in the UK has been 230 V AC (RMS) since 1 January 1995 (Electricity Supply Regulations, SI 1994, No. 3021). However, as an interim measure, electricity suppliers can work with an asymmetric voltage tolerance of 230 V+10%-6% (216.2–253 V) SONY VAIO VGN-FW83DS Battery .

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 SONY VAIO VGN-FW83JS Battery .

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 SONY VAIO VGN-FW83XS Battery .

Electrical wiring in North America follows regulations and standards for installation of building wiring. Electrical wiring in the United States is generally in compliance with the National Electrical Code, a standard sponsored by the National Fire Protection Association which has been periodically revised since 1897 SONY VAIO VGN-FW90NS Battery .

Local amendments or supplements to this model code are common in American cities or states. For electrical wiring in Canada, the Canadian Electrical Code is a very similar standard published in Canada by the Canadian Standards Association since 1927. Other countries neighboring the U.S. also usually use the same standards, including much of Mexico SONY VAIO VGN-FW90S Battery .

Terminology

Although much of the electrician's field terminology matches that of the electrical codes, usages can vary.

• A neutral wire is the return leg of a circuit; in building wiring systems the neutral wire is connected to earth ground at least at one point SONY VAIO VGN-FW91NS Battery .
• North American standards state that the neutral is neither switched nor fused. The neutral is connected to the center tap of the power company transformer of a split-phase system, or the center of the wye connection of a polyphase power system SONY VAIO VGN-FW91S Battery .
• American electrical codes require that the neutral be connected to earth at the "service panel" only and at no other point within the building wiring system. Formally the neutral is called the "grounded conductor" SONY VAIO VGN-FW92DS Battery ;
• as of the 2008 NEC, the terms "neutral conductor" and "neutral point" have been defined in the Code to record what had been common usage.
• Hot is any conductor (wire or otherwise) connected with an electrical system that has electric potential relative to electrical ground or neutral SONY VAIO VGN-FW92JS Battery .
• Grounded is a conductor with continuity to earth.
• Leg as in 'hot leg' refers to one of multiple hot conductors in an electrical system. The most common service in the U.S., single split-phase, 240 V, features a neutral and two hot legs, 240 V to each other, and 120 V each to the neutral. A three-phase system will have three "hot" legs SONY VAIO VGN-FW93DS Battery .
• An outlet is called a receptacle in the NEC. In the NEC an outlet is "a point in the wiring system at which current is taken to utilization equipment SONY VAIO VGN-FW93JS Battery ."

Electrical codes and standards

The National Electrical Code (NEC) specifies acceptable wiring methods and materials.Local jurisdictions usually adopt the NEC or another published code and then distribute documents describing how local codes vary from the published codes SONY VAIO VGN-FW139E/H Battery .

They cannot distribute the NEC itself for copyright reasons.

The purpose of the NEC is to protect persons and property from hazards arising from the use of electricity SONY VAIO VGN-FW145E/W Battery .

The NEC is not any jurisdiction's electrical code per se; rather, it is an influential work of standards that local legislators (e.g., city council members, state legislators, etc. as appropriate) tend to use as a guide when enacting local electrical codes SONY VAIO VGN-FW190EBH Battery .

The NFPA states that excerpts quoted from the National Electrical Code must have a disclaimer indicating that the excerpt is not the complete and authoritative position of the NFPA and that the original NEC document must be consulted as the definitive referenceSONY VAIO VGN-FW190EDH Battery .

New construction, additions or major modifications must follow the relevant code for that jurisdiction, which is not necessarily the latest version of the NEC. Regulations in each jurisdiction will indicate when a change to an existing installation is so great that it must then be rebuilt to comply with the current electrical code SONY VAIO VGN-FW21E Battery .

Generally existing installations are not required to be changed to meet new codes.

Enforcement of code requirements varies by jurisdiction in the United States. In many areas, a homeowner, for example, can perform household wiring for a building which the owner occupies;this may even be complete wiring of a home SONY VAIO VGN-FW21J Battery .

A few cities have more restrictive rules and require electrical installations to be done by licensed electricians. The work will be inspected by a designated authority at several stages before permission is obtained to energize the wiring from the local electric utility SONY VAIO VGN-FW21L Battery ;

the inspector may be an employee of the state or city, or an employee of an electrical supply utility.

Design and installation conventions

For residential wiring, some basic rules given in the NEC are SONY VAIO VGN-FW21M Battery :

• Phase wire in a circuit may be black, red, orange (high leg delta) insulated wire, sometimes other colors, but never green, gray, or white (whether these are solid colors or stripes). Specific exceptions apply, such as a cable running to a switch and back (known as a traveler) where the white wire will be the hot wire feeding that switch SONY VAIO VGN-FW21Z Battery .
• Another is for a cable used to feed an outlet for 250VAC 15 or 20 amp appliances that do not need a neutral, there the white is hot (but should be identified as being hot, usually with black tape inside junction boxes).
• The neutral wire is identified by gray or white insulated wire, perhaps with stripes SONY VAIO VGN-FW25T/B Battery .
• Grounding wire of circuit may be bare or identified insulated wire of green or having green stripes. Note that all metallic systems in a building are to be bonded to the building grounding system, such as water, natural gas, HVAC piping, and othersSONY VAIO VGN-FW26T/B Battery .
• Larger wires are furnished only in black; these may be properly identified with suitable paint or tape.
• All wiring in a circuit except for the leads that are part of a device or fixture must be the same gauge SONY VAIO VGN-FW27/B Battery .
• Note that different size wires may be used in the same raceway so long as they are all insulated for the maximum voltage of any of these circuits.
• The Code gives rules for calculating circuit loading SONY VAIO VGN-FW27/W Battery .
• Ground-fault circuit interrupter (GFCI) protection is required on receptacles in wet locations. This includes all small appliance circuits in a kitchen, receptacles in a crawl space, basements, bathrooms and a receptacle for the laundry room, as well as outdoor circuits within easy reach of the ground SONY VAIO VGN-FW27T/H Battery .
• However, they are not required for refrigerators because unattended disconnection could cause spoilage of food, nor for garbage disposals. Instead, for refrigerators and other semi-permanent appliances in basements and wet areas, use a one-outlet non-GFCI dedicated receptacle SONY VAIO VGN-FW29/B Battery .
• Two-wire outlets having no grounding conductor may be protected by an upstream gfci and must be labelled "no grounding". Most GFCI receptacles allow the connection and have GFCI protection for down-stream connected receptacles. Receptacles protected in this manner should be labeled "GFCI protected" SONY VAIO VGN-FW290JRB Battery .
• Most circuits have the metallic components interconnected with a grounding wire connected to the third, round prong of a plug, and to metal boxes and appliance chassis SONY VAIO VGN-FW290JTB Battery .
• Furnaces, water heaters, heat pumps, central air conditioning units and stoves must be on dedicated circuits
• The code provides rules for sizing electrical boxes for the number of wires and wiring devices in the box.

The foregoing is just a brief overview and must not be used as a substitute for the actual National Electrical Code SONY VAIO VGN-FW290JTH Battery .

Comparison of US practices with other countries

Electrical wiring practices developed in parallel in many countries in the late 19th and early 20th centuries. As a result, national and regional variations developed and remain in effect SONY VAIO VGN-FW52JB Battery .

(see National Electrical Code, electrical wiring, electrical wiring in the United Kingdom). Some of these are retained for technical reasons, since the safety of wiring systems depends not only on the wiring code but also on the technical standards for wiring devices, materials, and equipment SONY VAIO VGN-FW51B/W Battery .

Grounding (earthing) of distribution circuits is a notable difference in practice between United States wiring systems and those elsewhere in the world. Since the early 1960s, wiring in new construction has required a separate grounding conductor used to bond (electrically connect) all normally non-current carrying parts of an electrical installation SONY VAIO VGN-FW50B Battery .

Portable appliances with metal cases also have a bonding conductor in the flexible cable and plug connecting them to the distribution system. The circuit return conductor (neutral) is also connected to ground at the service entrance panel only; no other connections from neutral to ground are allowed, unlike regulations in other parts of the world SONY VAIO VGN-FW47GYH Battery .

Lighting and power receptacle circuits in North American systems are typically radial from a distribution panel containing circuit breakers to protect each branch circuit.The smallest branch circuit rating is 15 amperes, used for general purpose receptacles and lighting. In residential construction SONY VAIO VGN-FW465GJB Battery ,

branch circuits for higher ratings are usually dedicated to one appliance, for example, fixed cooking appliances, electric clothes dryers, and air conditioners. Lighting and general purpose receptacles are at 120 volts AC, with larger devices fed by three wire single-phase circuits at 240 volts SONY VAIO VGN-FW465GJ/BE1 Battery .

In commercial construction, three-phase circuits are used. Generally, receptacles are fed by 120 V or 208 V (in place of 240 V in a house), and can include special current rated outlets for industrial equipment. Lighting is usually fed by 277 V (with exception for special-use lights that use 120 V) SONY VAIO VGN-FW465J/B Battery .

Equipment can be hard-wired into the building using either 120/208 V or 277/480 V.

Countries such as Mexico may adopt the NFPA standard as their national electrical code, with local amendments similar to those in United States jurisdictions SONY VAIO VGN-FW45TJB Battery .

The Canadian Electrical Code, while developed independently from the NFPA code, is similar in scope and intent to the US NEC, with only minor variations in technical requirement details; harmonization of the CSA and NEC codes is intended to facilitate free trade between the two countries SONY VAIO VGN-FW45GJB Battery .

Wiring methods

Most circuits in the modern North American home and light commercial construction are wired with non-metallic sheathed cable designated type (often referred to by the brand name Romex) SONY VAIO VGN-FWZJ/H Battery .

This type of cable is the least expensive for a given size and is appropriate for dry indoor applications. The designation NM XX-Y indicates, respectively, the type of sheathing (in this case, non-metallic), thesize of the main conductors, and the total number of circuit conductors (exclusive of the grounding conductor) SONY VAIO VGN-FW41M/H Battery .

For example, NM 14-2 cable contains three conductors (two plus one ground) at 14 gauge, a size typically used for circuits protected at 15 amperes. Circuits with larger currents (such as for electric furnaces, water heaters, air conditioners, or sub-mains to additional circuit panels) will have larger conductors SONY VAIO VGN-FW41J/H Battery .

Not all US jurisdictions permit use of non-metallic sheathed cable. The NEC does not permit use of NM cable in large, fire-resistant, or high-rise structures.

In type NM cable, conductor insulation is color-coded for identification, typically one black, one white, and a bare grounding conductor SONY VAIO VGN-FW41E/H Battery .

The National Electrical Code (NEC) specifies that the black conductor represent the hot conductor, with significant voltage to earth ground; the white conductor represent the identified or neutral conductor, near ground potential; and the bare/green conductor, the safety grounding conductor not normally used to carry circuit current SONY VAIO VGN-FW37J Battery .

Wires may be re-coloured, so these rules are commonly excepted. In 240-volt applications not requiring a neutral conductor, the white wire may be used as the second hot conductor, but must be recolored with tape or by some other method SONY VAIO VGN-FW378J/B Battery .

Four-wire flexible equipment connection cords have red as the fourth color; unlike European practices, color-coding in flexible cords is the same as for fixed wiring.

In commercial and industrial, NM cable is often prohibited in certain areas or altogether (depending on what the building is used for and local/state building codes) SONY VAIO VGN-FW378DH Battery .

Therefore, it is almost never used by commercial electrical contractors. Most wiring is put in non-flexible conduit, usually EMT because of its cost and durability. Rigid may be required for certain areas and additionally, vapor-lock fittings may be required in areas where a fire or explosion hazard is present (such as gas stations, chemical factories, grain silos, etc.) SONY VAIO VGN-FW373DW Battery

PVC can be used where wire is run underground or where concrete will be poured. A duct bank is usually made of multiple PVC conduits encased in concrete. MC or Flex is used where EMT or other non-flexible conduit is impractical or for short runs, known as "whips", to lights or other devices SONY VAIO VGN-FW36TJ/B Battery .

For power circuits, the color coding uses the same colors as residential construction, and adds the additional wires used for three-phase systems. Black, Red and Blue are used for hot wires and White is used as the neutral wire in a 120/208V circuit. Brown, Orange and Yellow are used as hot wires and Grey is used as the neutral wire in a 277/480V SONY VAIO VGN-FW35TJ/B Battery .

For grounding, regardless of the voltage, Green is used.

Several other types of wiring systems are used for building wiring in the United States; these include corrugated metal armored cable, mineral-insulated cable, other types of power cable, and various types of electrical conduit SONY VAIO VGN-FW35F/W Battery .

In industrial applications cables may be laid in cable trays. Cable type TC is especially intended for use in tray systems. Special wiring rules apply to wet or corrosive locations, and to locations which present an explosion hazard SONY VAIO VGN-FW35F/B Battery .

Wiring materials for use in the United States must be made and tested to product standards set by NEMA and Underwriters Laboratories (UL) and must bear approval marks such as those set by UL SONY VAIO VGN-FW35F Battery .

Approved wiring types can vary by jurisdiction. Not all wiring methods approved in the NEC are accepted in all areas of the United States SONY VAIO VGN-FW355J/H Battery .