Electrical Wiring
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Electrical wiring is an electrical installation of cabling and associated devices such as switches, distribution boards, sockets, and light fittings in a structure. Wiring is subject to safety standards for design and installation. Allowable
wire Overhead power cabling. The conductor consists of seven strands of steel (centre, high tensile strength), surrounded by four outer layers of aluminium (high conductivity). Sample diameter 40 mm A wire is a flexible strand of metal. Wire is c ...
and
cable Cable may refer to: Mechanical * Nautical cable, an assembly of three or more ropes woven against the weave of the ropes, rendering it virtually waterproof * Wire rope, a type of rope that consists of several strands of metal wire laid into a hel ...
types and sizes are specified according to the circuit operating
voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to m ...
and
electric current An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The moving pa ...
capability, with further restrictions on the environmental conditions, such as ambient temperature range, moisture levels, and exposure to sunlight and chemicals. Associated circuit protection, control, and distribution devices within a building's wiring system are subject to voltage, current, and functional specifications. Wiring safety codes vary by locality, country, or region. The
International Electrotechnical Commission The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an international standards organization that prepares and publishes international standards for all electrical, electronic and r ...
(IEC) is attempting to harmonise wiring standards among member countries, but significant variations in design and installation requirements still exist.


Wiring codes of practice and regulations

Wiring installation codes and regulations are intended to protect people and property from
electrical shock Electrical injury is a physiological reaction caused by electric current passing through the body. The injury depends on the density of the current, tissue resistance and duration of contact. Very small currents may be imperceptible or produce a ...
and fire hazards. They are usually based on a model code (with or without local amendments) produced by a national or international standards organisation, such as the
IEC The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an international standards organization that prepares and publishes international standards for all electrical, electronic and r ...
.


Australia and New Zealand

In Australia and New Zealand, the AS/NZS 3000 standard, commonly known as the "wiring rules", specifies requirements for the selection and installation of electrical equipment, and the design and testing of such installations. The standard is mandatory in both New Zealand and Australia; therefore, all electrical work covered by the standard must comply.


Europe

In European countries, an attempt has been made to harmonise national wiring standards in an
IEC The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an international standards organization that prepares and publishes international standards for all electrical, electronic and r ...
standard,
IEC 60364 IEC 60364 ''Electrical Installations for Buildings'' is the International Electrotechnical Commission (IEC)'s international standard on ''electrical installations of buildings''. This standard is an attempt to harmonize national wiring standards ...
''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 adopted as a national wiring code. Neither is it designed for field use by electrical tradesmen and inspectors for testing compliance with national wiring standards. By contrast, national codes, such as the NEC or CSA C22.1, generally exemplify the common objectives of IEC 60364, but provide specific rules in a form that allows for guidance of those installing and inspecting electrical systems.


Germany

The
German Commission for Electrotechnical, Electronic, and Information Technologies of DIN and VDE The German Commission for Electrotechnical, Electronic & Information Technologies of DIN and VDE (german: Deutsche Kommission Elektrotechnik Elektronik Informationstechnik im DIN und VDE), abbreviated DKE, is the German organisation responsible fo ...
(DKE) (Deutsche Kommission Elektrotechnik Elektronik Informationstechnik in DIN und VDE) is the organisation responsible for the promulgation of electrical standards and safety specifications. DIN VDE 0100 is the German wiring regulations document harmonised with IEC 60364.


United Kingdom

In the United Kingdom, wiring installations are regulated by the
Institution of Engineering and Technology The Institution of Engineering and Technology (IET) is a multidisciplinary professional engineering institution. The IET was formed in 2006 from two separate institutions: the Institution of Electrical Engineers (IEE), dating back to 1871, and ...
''Requirements for Electrical Installations: IEE Wiring Regulations,
BS 7671 British Standard BS 7671 "Requirements for Electrical Installations. IET Wiring Regulations", informally called in the UK electrical community "The Regs", is the national standard in the United Kingdom for electrical installation and the safet ...
: 2008,'' which are harmonised with IEC 60364. The 17th edition (issued in January 2008) included new sections for
microgeneration Microgeneration is the small-scale production of heat or electric power from a "low carbon source," as an alternative or supplement to traditional centralized grid-connected power. Microgeneration technologies include small-scale wind turbin ...
and solar photovoltaic systems. The first edition was published in 1882. In 2018, the 18th edition of the wiring regulations BS7671:2018 was released and came into force in January 2019 and BS7671:2018 Amendment 1 was issued February 2020. BS 7671 is the standard to which the UK electrical industry adheres, and compliance with BS 7671 is now required by law through the Electricity, Safety, Quality and Continuity Regulations 2002.


North America

The first electrical codes in the United States originated in
New York New York most commonly refers to: * New York City, the most populous city in the United States, located in the state of New York * New York (state), a state in the northeastern United States New York may also refer to: Film and television * '' ...
in 1881 to regulate installations of electric lighting. Since 1897 the US
National Fire Protection Association The National Fire Protection Association (NFPA) is an international nonprofit organization devoted to eliminating death, injury, property and economic loss due to fire, electrical and related hazards. As of 2018, the NFPA claims to have 50,000 mem ...
, a private non-profit association formed by insurance companies, has published the ''
National Electrical Code The National Electrical Code (NEC), or NFPA 70, is a regionally adoptable standard for the safe installation of electrical wiring and equipment in the United States. It is part of the National Fire Code series published by the National Fire Prote ...
'' (NEC). States, counties or cities often include the NEC in their local building codes by reference along with local differences. 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 Engineers, as practitioners of engineering, are professionals who invent, design, analyze, build and test machines, complex systems, structures, gadgets and materials to fulfill functional objectives and requirements while considering the limit ...
,
tradesmen A tradesman, tradeswoman, or tradesperson is a skilled worker that specializes in a particular trade (occupation or field of work). Tradesmen usually have work experience, on-the-job training, and often formal vocational education in contrast ...
, manufacturer representatives, fire fighters, and other invitees. Since 1927, the
Canadian Standards Association The CSA Group (formerly the Canadian Standards Association; CSA) is a standards organization which develops standards in 57 areas. CSA publishes standards in print and electronic form, and provides training and advisory services. CSA is composed ...
(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 IEC 60364 ''Electrical Installations for Buildings'' is the International Electrotechnical Commission (IEC)'s international standard on ''electrical installations of buildings''. This standard is an attempt to harmonize national wiring standards ...
(''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, but there are no numerical criteria listed in that chapter to assess the adequacy of any electrical installation. Although the US 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 The North American Free Trade Agreement (NAFTA ; es, Tratado de Libre Comercio de América del Norte, TLCAN; french: Accord de libre-échange nord-américain, ALÉNA) was an agreement signed by Canada, Mexico, and the United States that crea ...
(NAFTA) program, US and Canadian standards are slowly converging toward each other, in a process known as harmonisation.


Colour coding of wiring by region

In a typical
electrical code {{Electrical Wiring Sidebar An electrical code is a set of regulations for the design and installation of electrical wiring in a building. The intention of a code is to provide standards to ensure electrical wiring systems that are safe for peopl ...
, some colour-coding of wires is mandatory. Many local rules and exceptions exist per country, state, or region. Older installations vary in colour codes, and colours may fade with insulation exposure to heat, light, and aging.


Europe

As of March 2011, the European Committee for Electrotechnical Standardization (CENELEC) requires the use of green/yellow colour cables as protective conductors, blue as neutral conductors and brown as
single-phase In electrical engineering, single-phase electric power (abbreviated 1φ) is the distribution of alternating current electric power using a system in which all the voltages of the supply vary in unison. Single-phase distribution is used when load ...
conductors.


Sweden

In Sweden, IEC 60364 is implemented through the national standard SS-436 40 000. Notable is the exception for blue, where while the colour normally is used for neutral may be used as connecting wire between switches and between switch and fixture, as well as phase wire in a two-phase circuit , all under the condition that no neutral wire is used in the particular circuit.


United Kingdom

The
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
requires the use of wire covered with green/yellow striped insulation, for safety earthing (grounding) connections. This growing international standard was adopted for its distinctive appearance, to reduce the likelihood of dangerous confusion of safety earthing (grounding) wires with other electrical functions, especially by persons affected by red-green colour blindness. In the UK, phases could be identified as being live by using coloured indicator lights: red, yellow, and blue. The new cable colours of brown, black, and grey do not lend themselves to coloured indicators. For this reason, three-phase control panels often use indicator lights of the old colours.


United States

The United States
National Electrical Code The National Electrical Code (NEC), or NFPA 70, is a regionally adoptable standard for the safe installation of electrical wiring and equipment in the United States. It is part of the National Fire Code series published by the National Fire Prote ...
requires a bare copper, or green or green/yellow insulated protective conductor, a white or grey neutral, with any other colour used for single phase. The NEC also requires the high-leg conductor of a
high-leg delta High-leg delta (also known as wild-leg, stinger leg, bastard leg, high-leg, orange-leg, red-leg, dog-leg delta) is a type of electrical service connection for three-phase electric power installations. It is used when both single and three-phase po ...
system to have orange insulation, or to be identified by other suitable means such as tagging. Prior to the adoption of orange as the suggested colour for the high-leg in the 1971 NEC, it was common practice in some areas to use red for this purpose. The introduction of the NEC clearly states that it is not intended to be a design manual, and therefore creating a colour code for ungrounded or "hot" conductors falls outside the scope and purpose of the NEC. However, it is a common misconception that "hot" conductor colour-coding is required by the Code. In the United States, colour-coding of three-phase system conductors follows a de facto standard, wherein black, red, and blue are used for three-phase 120/208-volt systems, and brown, orange or violet, and yellow are used in 277/480-volt systems. (Violet avoids conflict with the NEC's high-leg delta rule.) In buildings with multiple voltage systems, the grounded conductors (neutrals) of both systems are required to be separately identified and made distinguishable to avoid cross-system connections. Most often, 120/208-volt systems use white insulation, while 277/480-volt systems use grey insulation, although this particular colour code is not currently an explicit requirement of the NEC. Some local jurisdictions do specify required color coding in their local building codes, however.


Color codes


Wiring methods

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 * 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 non-corrosive environmental conditions. 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. 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. 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. The
international standard international standard is a technical standard developed by one or more international standards organizations. International standards are available for consideration and use worldwide. The most prominent such organization is the International Or ...
wire sizes are given in the
IEC 60228 IEC 60228 is the International Electrotechnical Commission (IEC)'s international standard on ''conductors of insulated cables''. the current version is Third Edition 2004-11 Among other things, it defines a set of standard wire cross-sectional a ...
standard of the
International Electrotechnical Commission The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an international standards organization that prepares and publishes international standards for all electrical, electronic and r ...
. In North America, the American Wire Gauge standard for wire sizes is used.


Cables


Modern wiring materials

Modern non-metallic sheathed cables, such as (US and Canadian) Types NMB and NMC, consist of two to four wires covered with
thermoplastic A thermoplastic, or thermosoft plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling. Most thermoplastics have a high molecular weight. The polymer chains associate ...
insulation, plus a wire for Protective Earthing/Grounding (bonding), surrounded by a flexible plastic jacket. In North America and the UK this conductor is usually bare wire but in the UK it is required that this bare Protective Earth (PE) conductor be sheathed in Green/Yellow insulating tubing where the Cable Sheathing has been removed. Most other jurisdictions now require the Protective Earth conductor to be insulated to the same standard as the current carrying conductors with Green/Yellow insulation. With some cables the individual conductors are wrapped in paper before the plastic jacket is applied. Special versions of non-metallic sheathed cables, such as US Type UF, are designed for direct underground burial (often with separate mechanical protection) or exterior use where exposure to
ultraviolet radiation Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30  PHz) to 400 nm (750  THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...
(UV) is a possibility. These cables differ in having a moisture-resistant construction, lacking paper or other absorbent fillers, and being formulated for UV resistance. 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 An operating temperature is the allowable temperature range of the local ambient environment at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the de ...
at the conductor surface. 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. Building wire conductors larger than 10 AWG (or about 5 mm2) are stranded for flexibility during installation, but are not sufficiently pliable to use as appliance cord. Cables for industrial, commercial and apartment buildings may contain many insulated conductors in an overall jacket, 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. 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 building code to be either encased in metal conduit, or rated for low flame and smoke production. For some industrial uses in steel mills and similar hot environments, no organic material gives satisfactory service. Cables insulated with compressed
mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into extremely thin elastic plates. This characteristic is described as perfect basal cleavage. Mica is ...
flakes are sometimes used. Another form of high-temperature cable is mineral-insulated cable, with individual conductors placed within a copper tube and the space filled with
magnesium oxide Magnesium oxide ( Mg O), or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium (see also oxide). It has an empirical formula of MgO and consists of a lattice of Mg2+ ions and O2− ions ...
powder. The whole assembly is drawn down to smaller sizes, thereby compressing the powder. Such cables have a
certified Certification is the provision by an independent body of written assurance (a certificate) that the product, service or system in question meets specific requirements. It is the formal attestation or confirmation of certain characteristics of a ...
fire resistance rating and are more costly than non-fire rated cable. They have little flexibility and behave more like rigid conduit rather than flexible cables. The environment of the installed wires determine how much current a cable is permitted to carry. 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 based on size of conductor, voltage potential, insulation type and thickness, and the temperature rating of the cable itself. The allowable current will also be different for wet or dry locations, for hot (attic) or cool (underground) locations. In a run of cable through several areas, the part with the lowest rating becomes the rating of the overall run. Cables usually are secured with 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. 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 flammable 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 along their runs. In tall buildings, special designs are required to support the conductors of vertical runs of cable. Generally, only one cable per fitting is permitted, unless the fitting is rated or listed for multiple cables. Special cable constructions and termination techniques are required for cables installed in ships. Such assemblies are subjected to environmental and mechanical extremes. Therefore, in addition to electrical and fire safety concerns, such cables may also be required to be pressure-resistant where they penetrate a vessel's bulkheads. They must also resist
corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...
caused by
salt water Saline water (more commonly known as salt water) is water that contains a high concentration of dissolved salts (mainly sodium chloride). On the United States Geological Survey (USGS) salinity scale, saline water is saltier than brackish water, ...
or
salt spray Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantiti ...
, which is accomplished through the use of thicker, specially constructed jackets, and by tinning the individual wire stands. In North American practice, an overhead cable from a transformer on a power pole to a residential electrical service usually consists of three twisted (triplexed) conductors, with one being a bare neutral conductor, with the other two being the insulated conductors for both of the two 180-degree out of phase 120 V line voltages normally supplied. The neutral conductor is often a supporting "messenger" steel wire, which is used to support the insulated line conductors.


Copper conductors

Electrical devices often use copper conductors because of their properties, including their high
electrical conductivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allow ...
,
tensile strength Ultimate tensile strength (UTS), often shortened to tensile strength (TS), ultimate strength, or F_\text within equations, is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials t ...
,
ductility Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stres ...
, creep resistance,
corrosion resistance Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...
,
thermal conductivity The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal ...
,
coefficient of thermal expansion Thermal expansion is the tendency of matter to change its shape A shape or figure is a graphics, graphical representation of an object or its external boundary, outline, or external Surface (mathematics), surface, as opposed to other pro ...
,
solderability The solderability of a substrate is a measure of the ease with which a soldered joint can be made to that material. Good solderability requires wetting (low contact angle) of the substrate by the solder. __TOC__ Of metals Solderability varies depe ...
, resistance to
electrical overload In an electric power system, overcurrent or excess current is a situation where a larger than intended electric current exists through a conductor, leading to excessive generation of heat, and the risk of fire or damage to equipment. Possible cau ...
s, compatibility with
electrical insulator An electrical insulator is a material in which electric current does not flow freely. The atoms of the insulator have tightly bound electrons which cannot readily move. Other materials—semiconductors and conductors—conduct electric current ...
s, and ease of installation. Copper is used in many types of electrical wiring.


Aluminium conductors

Aluminium wire Aluminum building wiring is a type of electrical wiring for residential construction or houses that uses Aluminum conductor, aluminum electrical conductors. Aluminum provides a better conductivity to weight ratio than copper, and therefore is als ...
was common in North American residential wiring from the late 1960s to mid-1970s due to the rising cost of copper. Because of its greater
resistivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows ...
, aluminium wiring requires larger conductors than copper. For instance, instead of 14 AWG ( American wire gauge) copper wire, aluminium wiring would need to be 12 AWG on a typical 15 ampere lighting circuit, though local building codes vary. Solid aluminium conductors were originally made in the 1960s from a utility-grade aluminium alloy that had undesirable properties for a building wire, and were used with wiring devices intended for copper conductors. These practices were found to cause defective connections and potential fire hazards. In the early 1970s new aluminium wire made from one of several special alloys was introduced, and all devices – breakers, switches, receptacles,
splice connector In telecommunications, a line splice is a method of connecting electrical cables (electrical splice) or optical fibers (optical splice). Splices are often housed in sleeves to protect against external influences. Splicing of copper wires T ...
s,
wire nut Twist-on wire connectors are a type of electrical connector used to fasten two or more low-voltage (or extra-low-voltage) electrical conductors. They are widely used in North America and several European countries in residential, commercial ...
s, etc. — were specially designed for the purpose. These newer aluminium wires and special designs 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 creep or cold-flow under pressure, so older plain steel screw clamped connections could become loose over time. Newer electrical devices designed for aluminium conductors have features intended to compensate for this effect. Unlike copper, aluminium forms an insulating oxide layer on the surface. This is sometimes addressed by coating aluminium conductors with an antioxidant paste (containing
zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
dust in a low-residue
polybutene Polybutene is an organic polymer made from a mixture of 1-butene, 2-butene, and isobutylene. Ethylene steam cracker C4s are also used as supplemental feed for polybutene. It is similar to polyisobutylene (PIB), which is produced from essentially ...
base) at joints, or by applying a mechanical termination designed to break through the oxide layer during installation. Some terminations on wiring devices designed only for copper wire would overheat under heavy current load and cause fires when used with aluminium conductors. Revised standards for wire materials and wiring devices (such as the CO/ALR "copper-aluminium-revised" designation) were developed to reduce these problems. While larger sizes are still used to feed power to electrical panels and large devices, aluminium wiring for residential use has acquired a poor reputation and has fallen out of favour. Aluminium conductors are still heavily used for bulk
power transmission Power transmission is the movement of energy from its place of generation to a location where it is applied to perform useful work. Power is defined formally as units of energy per unit time. In SI units: :\text = \frac = \frac Since the develo ...
,
power distribution Electric power distribution is the final stage in the delivery of electric power; it carries electricity from the transmission system to individual consumers. Distribution substations connect to the transmission system and lower the transmissio ...
, and large feeder circuits with heavy current loads, due to the various advantages they offer over copper wiring. Aluminium conductors both cost and weigh less than copper conductors, so a much larger cross sectional area can be used for the same weight and price. This can compensate for the higher resistance and lower mechanical strength of aluminium, meaning the larger cross sectional area is needed to achieve comparable current capacity and other features. Aluminium conductors must be installed with compatible connectors and special care must be taken to ensure the contact surface does not oxidise.


Raceways and cable runs

Insulated wires may be run in one of several forms between electrical devices. This may be a specialised bendable pipe, called a
conduit Conduit may refer to: Engineering systems * Conduit (fluid conveyance), a pipe suitable for carrying either open-channel or pressurized liquids * Electrical conduit, a protective cover, tube or piping system for electric cables * Conduit curre ...
, or one of several varieties of metal (rigid steel or aluminium) or non-metallic ( PVC or
HDPE High-density polyethylene (HDPE) or polyethylene high-density (PEHD) is a thermoplastic polymer produced from the monomer ethylene. It is sometimes called "alkathene" or "polythene" when used for HDPE pipes. With a high strength-to-density ratio, ...
) tubing. Rectangular cross-section metal or PVC wire troughs (North America) or trunking (UK) may be used if many circuits are required. 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. Where wiring, or raceways that hold the wiring, must traverse fire-resistance rated walls and floors, the openings are required by local
building code A building code (also building control or building regulations) is a set of rules that specify the standards for constructed objects such as buildings and non-building structures. Buildings must conform to the code to obtain planning permission ...
s to be
firestop A firestop or fire-stopping is a form of passive fire protection that is used to seal around openings and between joints in a fire-resistance-rated wall or floor assembly. Firestops are designed to maintain the fire-resistance rating of a wall ...
ped. In cases where safety-critical wiring must be kept operational during an accidental fire,
fireproofing Fireproofing is rendering something (structures, materials, etc.) resistant to fire, or incombustible; or material for use in making anything fire-proof. It is a passive fire protection measure. "Fireproof" or "fireproofing" can be used as a n ...
must be applied to maintain
circuit integrity Circuit integrity is how little can a fire affect an electrical circuit's operation. It is a form of fire-resistance rating. Circuit integrity is achieved via passive fire protection means, which are subject to listing and approval use and co ...
in a manner to comply with a product's certification listing. The nature and thickness of any
passive fire protection Passive fire protection (PFP) is components or systems of a building or structure that slows or impedes the spread of the effects of fire or smoke without system activation, and usually without movement. Examples of passive systems include floor- ...
materials used in conjunction with wiring and raceways has a quantifiable impact upon the ampacity derating, because the thermal insulation properties needed for fire resistance also inhibit air cooling of power conductors.
Cable tray In the electrical wiring of buildings, a cable tray system is used to support insulated electrical cables used for power distribution, control, and communication. Cable trays are used as an alternative to open wiring or electrical conduit syst ...
s 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. 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. Local electrical regulations may restrict or place special requirements on mixing of voltage levels within one cable tray. Good design practices may segregate, for example, low level measurement or signal cables from trays carrying high power branch circuits, to prevent induction of noise into sensitive circuits. Since wires run in conduits or underground cannot dissipate heat as easily as in open air, and since adjacent circuits contribute induced currents, wiring regulations give rules to establish the current capacity (ampacity). Special sealed fittings are used for wiring routed through potentially explosive atmospheres.


Bus bars, bus duct, cable bus

For very high currents in electrical apparatus, and for high currents distributed through a building, bus bars can be used. (The term "bus" is a contraction of the Latin ''omnibus'' – meaning "for all".) 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). 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. In industrial applications, conductor bars are often pre-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; it is constructed to allow tap-off switches or motor controllers to be installed at designated 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. 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 used. For very large currents in generating stations or substations, where it is difficult to provide circuit protection, an
isolated-phase bus In electrical engineering, isolated-phase bus (IPB), also known as phase-isolated bus (PIB) in some countries, is a method of construction for circuits carrying very large currents, typically between a Electrical generator, generator and its step-up ...
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. 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.


Electrical panels

Electrical panels are easily accessible
junction box An electrical junction box (also known as a "jbox") is an enclosure housing electrical connections. Junction boxes protect the electrical connections from the weather, as well as protecting people from accidental electric shocks. Construction ...
es used to reroute and switch
electrical service Electric power distribution is the final stage in the Power delivery, delivery of electric power; it carries electricity from the Electric power transmission, transmission system to individual consumers. Distribution Electrical substation, substa ...
s. The term is often used to refer to circuit breaker panels or fuseboxes. Local codes can specify physical clearance around the panels.


Degradation by pests

Squirrels Squirrels are members of the family (biology), family Sciuridae, a family that includes small or medium-size rodents. The squirrel family includes tree squirrels, ground squirrels (including chipmunks and prairie dogs, among others), and flyi ...
, rats, and other rodents may gnaw on unprotected wiring, causing fire and shock hazards. This is especially true of PVC-insulated telephone and computer network cables. Several techniques have been developed to deter these pests, including insulation loaded with pepper dust.


Early wiring methods

The 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. 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, plus the high labour cost for such installations. The first
electrical code {{Electrical Wiring Sidebar An electrical code is a set of regulations for the design and installation of electrical wiring in a building. The intention of a code is to provide standards to ensure electrical wiring systems that are safe for peopl ...
s arose in the 1880s with the commercial introduction of electrical power; however, many conflicting standards existed for the selection of wire sizes and other design rules for electrical installations, and a need was seen to introduce uniformity on the grounds of safety.


Knob and tube (US)

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, 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. 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 labor cost of installing two conductors rather than one cable resulted in a decline in new knob-and-tube installations. However, the US code still allows new K&T wiring installations in special situations (some rural and industrial applications).


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. 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. A system later invented in the UK in 1908 employed vulcanised-rubber insulated wire enclosed in a strip metal sheath. The metal sheath was bonded to each metal wiring device to ensure earthing continuity. 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. 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. In this system, an insulated electrical 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. While companies such as
General Electric General Electric Company (GE) is an American multinational conglomerate founded in 1892, and incorporated in New York state and headquartered in Boston. The company operated in sectors including healthcare, aviation, power, renewable energ ...
manufactured 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 energised.


Other historical wiring methods

Armored 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. The first rubber-insulated cables for US building wiring were introduced in 1922 with . These were two or more solid copper electrical wires with rubber insulation, plus 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. Waxed paper was used as a filler and separator. Over time, rubber-insulated cables become brittle because of exposure to atmospheric oxygen, so they must be handled with care and are usually replaced during renovations. When switches, socket outlets or light fixtures are replaced, the mere act of tightening connections may cause hardened insulation to flake off the conductors. Rubber insulation further inside the cable often is in better condition than the insulation exposed at connections, due to reduced exposure to oxygen. The sulfur in vulcanized rubber insulation attacked bare copper wire so the conductors were tinned to prevent this. The conductors reverted to being bare when rubber ceased to be used. 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 (e.g. US Type THN, THHN, etc.) became common. The simplest form of cable has two insulated conductors twisted together to form a unit. Such non-jacketed cables with two (or more) conductors are used only for
extra-low voltage Extra-low voltage (ELV) is an electricity supply voltage and is a part of the Low voltage bandIEC 61140:2016 Chapter 4.2 in a range which carries a low risk of dangerous electrical shock. There are various standards that define extra-low voltage. ...
signal and control applications such as doorbell wiring. Other methods of securing wiring that are now obsolete include: * Re-use of existing
gas pipe Pipeline transport is the long-distance transportation of a liquid or gas through a system of pipes—a pipeline—typically to a market area for consumption. The latest data from 2014 gives a total of slightly less than of pipeline in 120 countr ...
s when converting
gas lighting Gas lighting is the production of artificial light from combustion of a gaseous fuel, such as hydrogen, methane, carbon monoxide, propane, butane, acetylene, ethylene, coal gas (town gas) or natural gas. The light is produced either directl ...
installations to electric lighting. Insulated conductors were pulled through the pipes that had formerly supplied the gas lamps. Although used occasionally, this method risked insulation damage from sharp edges inside the pipe at each joint. * 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 the UK, but was never permitted by German and Austrian rules. * 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. * 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. * In Austria, wires were concealed by embedding a rubber tube in a groove in the wall,
plastering Plasterwork is construction or ornamentation done with plaster, such as a layer of plaster on an interior or exterior wall structure, or plaster decorative moldings on ceilings or walls. This is also sometimes called pargeting. The process of ...
over it, then removing the tube and pulling wires through the cavity.Croft, p. 137 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 surface mounted raceway wiring systems are still available today.


See also

* 10603 – a frequently used
MIL-SPEC A United States defense standard, often called a military standard, "MIL-STD", "MIL-SPEC", or (informally) "MilSpecs", is used to help achieve standardization objectives by the U.S. Department of Defense. Standardization is beneficial in achievin ...
compliant wire *
Bus duct A bus (contracted from omnibus, with variants multibus, motorbus, autobus, etc.) is a road vehicle that carries significantly more passengers than an average car or van. It is most commonly used in public transport, but is also in use for cha ...
* Cable entry system *
Cable gland A cable gland (more often known in the U.S. as a cord grip, cable strain relief, cable connector or cable fitting) is a device designed to attach and secure the end of an electrical cable to the equipment. A cable gland provides strain-relief a ...
*
Cable management Cable management refers to management of electrical or optical cable in a cabinet or an installation. The term is used for products, workmanship or planning. Cables can easily become tangled, making them difficult to work with, sometimes res ...
*
Cable tray In the electrical wiring of buildings, a cable tray system is used to support insulated electrical cables used for power distribution, control, and communication. Cable trays are used as an alternative to open wiring or electrical conduit syst ...
*
Domestic AC power plugs and sockets AC power plugs and sockets connect electric equipment to the alternating current (AC) mains electricity power supply in buildings and at other sites. Electrical plugs and sockets differ from one another in voltage and current rating, shape, ...
*
Electric power distribution Electric power distribution is the final stage in the delivery of electric power; it carries electricity from the transmission system to individual consumers. Distribution substations connect to the transmission system and lower the transmissi ...
*
Electrical conduit An electrical conduit is a tube used to protect and route electrical wiring in a building or structure. Electrical conduit may be made of metal, plastic, fiber, or fired clay. Most conduit is rigid, but flexible conduit is used for some purpos ...
*
Electrical room An electrical room is a room or space in a building dedicated to electrical equipment. Its size is usually proportional to the size of the building; large buildings may have a main electrical room and subsidiary electrical rooms. Electrical equip ...
*
Electrical wiring in North America Electrical wiring in North America follows the regulations and standards applicable at the installation location. It is also designed to provide proper function, and is also influenced by history and traditions of the location installation. The ...
*
Electrical wiring in the United Kingdom Electrical wiring in the United Kingdom is commonly understood to be an electrical installation for operation by end users within domestic, commercial, industrial, and other buildings, and also in special installations and locations, such as mar ...
* Grounding *
Ground and neutral Ground and neutral are circuit conductors used in alternating current electrical systems. The ground circuit is connected to earth, and neutral circuit is usually connected to ground. As the neutral point of an electrical supply system is often ...
*
Home wiring Homes typically have several kinds of home wiring, including electrical wiring for lighting and power distribution, permanently installed and portable appliances, telephone, heating or ventilation system control, and increasingly for home theatre ...
*
Industrial and multiphase power plugs and sockets Industrial and multiphase plugs and sockets provide a connection to the electrical mains rated at higher voltages and currents than household plugs and sockets. They are generally used in polyphase systems, with high currents, or when protection f ...
*
Oxygen-free copper Oxygen-free copper (OFC) or oxygen-free high thermal conductivity (OFHC) copper is a group of wrought high-conductivity copper alloys that have been electrolytically refined to reduce the level of oxygen to 0.001% or below. Specification Ox ...
*
Portable cord A portable cord (also known as portable cordage, flexible cord, or extension cord) is a cable with multiple conductors used for temporary electrical power connections requiring flexibility. The cord can be employed in a range of applications, su ...
*
Power cord A power cord, line cord, or mains cable is an electrical cable that temporarily connects an appliance to the mains electricity supply via a wall socket or extension cord. The terms are generally used for cables using a power plug to connect t ...
*
Restriction of Hazardous Substances Directive The Restriction of Hazardous Substances Directive 2002/95/EC (RoHS 1), short for Directive on the restriction of the use of certain hazardous substances in electrical and electronic equipment, was adopted in February 2003 by the European Unio ...
(RoHS) *
Single-phase electric power In electrical engineering, single-phase electric power (abbreviated 1φ) is the distribution of alternating current electric power using a system in which all the voltages of the supply vary in unison. Single-phase distribution is used when load ...
*
Structured cabling In telecommunications, structured cabling is building or campus cabling infrastructure that consists of a number of standardized smaller elements (hence structured) called subsystems. Structured cabling components include twisted pair and opti ...
*
Three-phase electric power Three-phase electric power (abbreviated 3φ) is a common type of alternating current used in electricity generation, transmission, and distribution. It is a type of polyphase system employing three wires (or four including an optional neutral ...


References


Bibliography

*Croft, Terrel (1915
''Wiring of Finished Buildings''
McGraw Hill, New York.


Further reading


National Electrical Code
— Basis of most US electrical codes. Choose NFPA 70 (general purpose) or NFPA 70A (one and two family dwellings). Free registration required. * National Electrical Code 2011 (2011 ed.), Quincy, Massachusetts: National Fire Protection Association, 2010. — periodically re-issued every 3 years
NEMA comparison of IEC 60364 with the US NEC
* * Hirst, E

*


External links


Electrical wiring FAQ
(oriented to US and Canadian practice) {{Authority control Building codes Electrical engineering Power cables