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{{Short description|Electrical installation of cabling}}
{{Redirect-distinguish|Wiring|Wiring (software)}}
{{About|building wiring|power distribution|Electric power transmission|and|Electric power distribution}}
{{broader|Electrical cabling}}
{{Use British English|date=June 2016}}
{{Use dmy dates|date=November 2019}}
{{Electrical wiring sidebar}}
[[File:WiringSymbols.png|thumb|Electrical symbols for wiring{{vague|date=December 2022|what standard?}}]]

'''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]] and [[electrical cable|cable]] types and sizes are specified according to the circuit operating [[voltage]] and [[electric current]] 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]] (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==
{{Main|Electrical code}}
{{More citations needed section|date=April 2021}}
[[File:Architectural wiring diagram minihome.svg|thumb|Wiring layout plan for a house]]
Wiring installation codes and regulations are intended to protect people and property from [[electrical shock]] 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 [[International Electrotechnical Commission|IEC]].

===Australia and New Zealand===
{{Anchor|AS3000}}
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 [[International Electrotechnical Commission|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 adopted as a national wiring code. Neither is it designed for field use by electrical tradespeople 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 [[Verband der Elektrotechnik, Elektronik und Informationstechnik|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. In Germany, blue can also mean phase or switched phase.

====United Kingdom====
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 17th edition (issued in January 2008) included new sections for [[microgeneration]] and [[photovoltaic system|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 2 was issued March 2022. 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===
{{Further|Electric power distribution#Secondary distribution|Electrical wiring in North America}}
The first electrical codes in the United States originated in [[New York (state)|New York]] in 1881 to regulate installations of electric lighting. Since 1897 the US [[National Fire Protection Association]], a private non-profit association formed by insurance companies, has published the ''[[National Electrical Code (US)|National Electrical Code]]'' (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]], [[tradesmen]], manufacturer representatives, fire fighters, and other invitees.

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]] (''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]] (NAFTA) program, US and Canadian standards are slowly converging toward each other, in a process known as harmonisation.

==Colour coding of wiring by region==
{{More citations needed section|date=April 2021}}
{{Anchor|Color code}}
[[File:ElectricWireGrounded.jpg|thumb|upright|Colour-coded wires in a flexible plastic [[electrical conduit]] found commonly in modern European houses]]

In a typical [[electrical code]], some colour-coding of wires is mandatory. Many local rules and exceptions exist per country, state, or region.<ref>{{cite web |title=National Electrical Code |url=https://www.nema.org/Technical/FieldReps/Pages/National-Electrical-Code.aspx |publisher=National Electrical Manufacturers Association |access-date=4 January 2016}}</ref> 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 electric power|single-phase]] conductors.<ref>{{cite web |title=New Cable Colour Code for Electrical Installations |url=https://elise.ema.gov.sg/safety/about.html#2 |publisher=Energy Market Authority |access-date=4 January 2016}}</ref>

==== 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.<ref>[https://www.sis.se/produkter/elektroteknik-24c2329a/allmant/ss4364000elektronisktformat/ SS-436 40 000 section 514.3. (Swedish)]</ref><ref>[https://www.elinstallatoren.se/2020/03/far-jag-anvanda-bla-ledare-som-tandtrad/ Cecilia Axelsson (Swedish]</ref>

====United Kingdom====
{{Main|Electrical wiring in the United Kingdom}}
The [[United Kingdom]] requires the use of wire covered with green/yellow striped insulation, for safety earthing (grounding) connections.<ref>{{cite book |title=NEC Q and A: Questions and Answers on the National Electrical Code |author=Noel Williams, Jeffrey S. Sargen |year=2007 |url=https://books.google.com/books?id=fBkUkF2ZRU4C&q=electrical+codes+require+green+with+yellow+stripe&pg=PA117 |page=117 |isbn=9780763744731 |access-date=4 January 2016}}</ref> 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 2004, the UK adopted the European Union standard for phase colours of brown, black, and grey, and for neutral, blue.  However, the old phase colours of red, yellow, and blue with black for neutral are still found in old installations.  Single-phase wiring should strictly be in brown (red in old system), regardless of which phase it originated from, but it is common practice to use three-core cable in the three-phase colours for two-way lighting switches.  The accepted practice is to sleeve the ends of the cores in brown or blue sleeves as appropriate.<ref>Bill Atkinson, Roger Lovegrove, Gary Gundry, ''Electrical Installation Designs'', pp. 111–112, John Wiley & Sons, 2013 {{ISBN|1119992842}}.</ref>

===United States===
{{Main|Electrical wiring in North America}}
The United States [[National Electrical Code]] 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]] 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.<ref>{{Cite book |last=National Fire Protection Association |title=National Electrical Code 1968 a USA Standard |date=January 1, 1968 |publisher=National Fire Protection Association; NFPA No. 70-1968 USAS C1-1968 edition |edition=1968 |pages=34 |language=en}}</ref>

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.<ref>{{cite web |title=Color Coding Chart |url=https://www.conwire.com/about/technical-info/ |publisher=Conwire |access-date=4 January 2016}}</ref> Some local jurisdictions do specify required colour coding in their local building codes, however.

=={{Anchor|Color code|Colour code|Colour codes}}Color codes==
{{More citations needed section|date=September 2022}}
{| class="wikitable" style="font-size:90%; width:auto; margin:0 0 1em;"
|+ Standard{{efn|The colors in this table represent the most common and preferred standard colors for wiring; however others may be in use, especially in older installations.}} wire insulation colours for alternating current
|-
! Standard<br>Region or country
! Phases (L, L1/L2/L3)
! Neutral (N)
! Protective earth/ground (PE)
|-
| [[IEC 60446|IEC&nbsp;60446]] {{awrap|(now part of [[IEC 60445|IEC&nbsp;60445]])}}
* European Union from April 2004
* [[Electrical wiring in the United Kingdom#Wiring colors|United Kingdom]] from April 2004 (BS&nbsp;7671)
* Switzerland from 2005
* Argentina
* Hong Kong from July 2007
* Singapore from March 2009
* Russia from 2009 {{awrap|(GOST R 50462)}}
* Ukraine, Belarus, Kazakhstan
* South Korea from January 2021<ref>{{cite web|url=http://kec.kea.kr/ebook/2021/book1_1/index.html |title=Korea Electro-technical Code |work=Ministry of Trade, Industry and Energy |access-date=17 September 2021}}</ref>
* Australia and New Zealand{{efn|name=iecasnzs|Australian and New Zealand wiring standards allow both Australian and European color codes.}}
* Italy
| '''Prohibited:''' [[File:Color wire green yellow.svg|80px|Green/Yellow]] <br><br>   [[File:Color wire brown.svg|80px|Brown]] [[File:Color wire black.svg|80px|Black]] [[File:Color wire grey.svg|Grey|80px]] <ref>Switzerland before 2005 also red and white for phases.</ref>
| [[File:Color wire light blue.svg|80px|Light Blue]]{{efn|Sweden allow the use of blue for other purposes in circuits without a neutral, for instance two-phase with ground.}}
[[File:Color wire blue.svg|80px|Dark Blue]] <ref>Switzerland blue or light&nbsp;blue for neutral conductors</ref>
| [[File:Color wire green yellow.svg|80px|Green/Yellow]]
|-
| rowspan=5 | [[AS/NZS 3000|AS/NZS&nbsp;3000:2018]]
* Australia and New Zealand{{efn|name=iecasnzs}}
| '''Installation wiring:''' (section 3.8.1)<br> '''Prohibited:''' [[File:Color wire green yellow.svg|80px|Green/Yellow]] [[File:Color wire green.svg|80px|Green]] [[File:Color wire yellow.svg|80px|Yellow]] [[File:Color wire light blue.svg|80px|Light Blue]]{{efn|name=asnzsblue|Australian-standard phase colors conflict with IEC 60446 colors, where IEC-60446 supported ''neutral'' color (blue) is an allowed ''phase'' color in the Australia/New Zealand standard. Care must be taken when determining the system used in any existing wiring.}} [[File:Color wire black.svg|80px|Black]]<br>To designate any phase, the above colours are '''prohibited'''.
[[File:Color wire red.svg|80px|Red]] [[File:Color wire brown.svg|80px|Brown]] ''recommended'' for single phase
<br>[[File:Color wire red.svg|80px|Red]] [[File:Color wire white.svg|80px|White]] [[File:Color wire blue.svg|80px|Dark Blue]]{{efn|name=asnzsblue}} ''recommended'' for multiphase
<br>While light blue is prohibited from use for active function, dark blue is recommended for L3.
<br>[[File:Color wire white.svg|80px|White]] ''usually'' used for "Switched Line" <ref>{{cite book |date=2007 |title=AS/NZS 3000 "Wiring Rules", Table 3.4, CONDUCTOR COLOURS FOR INSTALLATION WIRING, "Function: Active:  Any colour other than green, yellow, green/yellow, black or light blue."|no-pp=y}}</ref>
| [[File:Color wire black.svg|80px|Black]]
[[File:Color wire light blue.svg|80px|Light Blue]]{{efn|name=nzblack|Except that in New Zealand domestic installations, the only permitted color for Neutral is Black.}}
| [[File:Color wire green yellow.svg|80px|Green/Yellow]]<br>[[File:Color wire green.svg|80px|Green]] (before 1980)<br>[[File:Color wire bare copper.svg|80px|Bare copper]] (before 1966)
|-
| '''Cable identification colours:{{efn|name=asnzsnocombine|Australian and NZ cable identification colours and European cable identification colours should not be combined within the same wiring enclosure.}}''' (section 3.8.3.4)<br>'''Multiphase cables'''<br>[[File:Color wire red.svg|80px|Red]] [[File:Color wire white.svg|80px|White]] [[File:Color wire blue.svg|80px|Dark Blue]]{{efn|name=asnzsblue}} Current AS/NZS cables
| <br><br>[[File:Color wire black.svg|80px|Black]]
| <br><br>[[File:Color wire green yellow.svg|80px|Green/Yellow]]
|-
| [[File:Color wire brown.svg|80px|Brown]] [[File:Color wire black.svg|80px|Black]]  [[File:Color wire grey.svg|80px|Grey]] European cables
| [[File:Color wire light blue.svg|80px|Light Blue]]
| [[File:Color wire green yellow.svg|80px|Green/Yellow]]
|-
| '''Single-phase cables'''<br>[[File:Color wire brown.svg|80px|Brown]] Current AS/NZS flexible cords, flexible cables and equipment wiring, and European cables
| <br>[[File:Color wire light blue.svg|80px|Light Blue]]
| <br>[[File:Color wire green yellow.svg|80px|Green/Yellow]]
|-
| [[File:Color wire red.svg|80px|Red]] Superseded AS/NZS flexible cords
| [[File:Color wire black.svg|80px|Black]]
| [[File:Color wire green.svg|80px|Green]]
|-
| Pre-2004 IEE{{Explain|reason=Standard predating IEC 60446|date=September 2022}}
* [[Electrical wiring in the United Kingdom#Wiring colours|United Kingdom]] until April 2006 (BS&nbsp;7671)
* India, Pakistan
* Hong Kong prior to 2009
* Malaysia and Singapore prior to February 2011
| [[File:Color wire red.svg|80px|Red]] [[File:Color wire yellow.svg|80px|Yellow]] [[File:Color wire blue.svg|80px|Blue]]
| [[File:Color wire black.svg|80px|Black]]
| [[File:Color wire green yellow.svg|80px|Green/Yellow]]<br>[[File:Color wire green.svg|80px|Green]] (before 1977)
|-
| {{awrap|[[Brazilian National Standards Organization|ABNT]] NBR 5410}}
* Brazil
| '''Prohibited:''' [[File:Color wire green yellow.svg|80px|Green/Yellow]] [[File:Color wire green.svg|80px|Green]] [[File:Color wire yellow.svg|80px|Yellow]]{{efn|name=bryellow|For safety reasons, yellow should not be used when green/yellow striped cables are present.}} [[File:Color wire light blue.svg|80px]]<br>To designate any phase, the above colours are '''prohibited'''.
Local rules may specify colours to be used for phases.
| [[File:Color wire light blue.svg|80px|Blue]]
| [[File:Color wire green yellow.svg|80px|Yellow]]<br>[[File:Color wire green.svg|80px|Green]]
|-
| [[South African Bureau of Standards|SABS]] SANS&nbsp;10142-1
* South Africa
| '''Prohibited:''' [[File:Color wire green yellow.svg|80px|Yellow]] [[File:Color wire green.svg|80px|Green]] [[File:Color wire black.svg|80px|Black]]<br>To designate any phase, the above colours are '''prohibited'''.
| [[File:Color wire black.svg|80px|Black]] || [[File:Color wire green yellow.svg|80px|Green/Yellow]]<br>[[File:Color wire bare copper.svg|80px|Bare copper]]
|-
| {{awrap|GB 50303-2015}}
* China (PRC)
| [[File:Color wire yellow.svg|80px|Yellow]] [[File:Color wire green.svg|80px|Green]] [[File:Color wire red.svg|80px|Red]]
| [[File:Color wire light blue.svg|80px|Light Blue]]
| [[File:Color wire green yellow.svg|80px|Yellow]]
|-
| {{awrap|JIS C 0446}}
* Japan
| [[File:Color wire red.svg|80px|Red]] [[File:Color wire black.svg|80px|Black]] [[File:Color wire blue.svg|80px|Blue]]
See [[:ja:識別標識 (電線)]] for details
| [[File:Color wire white.svg|80px|White]]
| [[File:Color wire green.svg|80px|Green]]
|-
| rowspan=2 | [[National Electrical Code|NEC]] (NFPA&nbsp;70)
* United States{{efn|name=noram|Canadian and American wiring practices are very similar, with ongoing harmonisation efforts.}}
* Mexico ([[Norma Oficial Mexicana|NOM]]-001)
* Puerto Rico, Guatemala, Nicaragua,<br>El Salvador, Honduras, Costa Rica,<br>Panama, Dominican Republic, Colombia,<br>Ecuador, Peru, Venezuela<ref>{{cite web|url=https://www.nfpa.org/NEC/NEC-adoption-and-use/NEC-adoption-and-use-in-Latin-America|title=NEC adoption and use in Latin America}}</ref>

| '''{{awrap|120, 208, or 240&nbsp;V}}'''<br>[[File:Color wire black.svg|80px|Black]] [[File:Color wire red.svg|80px|Red]] [[File:Color wire blue.svg|80px|Blue]]
'''{{awrap|277, or 480&nbsp;V}}'''<br>[[File:Color wire brown.svg|80px|Brown]] [[File:Color wire orange.svg|80px|Orange]] [[File:Color wire yellow.svg|80px|Yellow]]
<br>{{color box|#B5A642}} metallic brass
| '''{{awrap|120, 208, or 240&nbsp;V}}'''<br>[[File:Color wire white.svg|80px|White]]
'''{{awrap|277, or 480&nbsp;V}}'''<br>[[File:Color wire grey.svg|80px|Grey]]<br>{{color box|silver}} metallic silver
| [[File:Color wire green.svg|80px|Green]] {{color box|green}}<br>[[File:Color wire bare copper.svg|80px|Bare copper]] no insulation<br>[[File:Color wire green yellow.svg|80px|Green/Yellow]] for isolated systems
|-
| '''Flexible cable {{awrap|(e.g., [[extension cord|extension]], power, and [[lamp cord|lamp]] cords)}}'''
'''120 V'''<br>[[File:Color wire black.svg|80px|Black]] {{color box|#B5A642}} metallic brass

'''split-phase 240 V'''<br>[[File:Color wire black.svg|80px|Black]] [[File:Color wire red.svg|80px|Red]]
| [[File:Color wire white.svg|80px|White]]<br>{{color box|silver}} metallic silver
| [[File:Color wire green.svg|80px|Green]]{{color box|green}}<br>[[File:Color wire green yellow.svg|80px|Green/Yellow]]{{color box striped|green|yellow|stripe=3}}
|-
| rowspan=2 | [[Canadian Electrical Code|CE Code]] (CSA&nbsp;C22.1)
* Canada<ref>{{cite book |date=2015 |title=C22.1-15—Canadian Electrical Code, Part I: Safety Standard for Electrical Installations |publisher=Canadian Standards Association|edition=23rd |isbn=978-1-77139-718-6 |page=Rules 4-038, 24-208(c) |no-pp=y}}</ref>{{efn|name=noram}}
| [[File:Color wire red.svg|80px|Red]] [[File:Color wire black.svg|80px|Black]] for single-phase systems
[[File:Color wire red.svg|80px|Red]] [[File:Color wire black.svg|80px|Black]] [[File:Color wire blue.svg|80px|Blue]] for three-phase systems
| rowspan=2 | [[File:Color wire white.svg|80px|White]]<br>[[File:Color wire grey.svg|80px|Grey]]
| [[File:Color wire green.svg|80px|Green]]{{color box|green}}<br>[[File:Color wire green yellow.svg|80px|Green/Yellow]]<br>[[File:Color wire bare copper.svg|80px|Bare copper]] no insulation
|-
| [[File:Color wire orange.svg|80px|Orange]] [[File:Color wire brown.svg|80px|Brown]] for isolated single-phase systems
[[File:Color wire orange.svg|80px|Orange]] [[File:Color wire brown.svg|80px|Brown]] [[File:Color wire yellow.svg|80px|Yellow]] for isolated three-phase systems
| [[File:Color wire green.svg|80px|Green]]<br>[[File:Color wire green yellow.svg|80px|Yellow]] for isolated systems
|-
| colspan=4 | Boxes (e.g., {{color box|purple}} translucent purple) denote markings on wiring terminals.
{{Notelist}}
|}

==Wiring methods==
{{Unreferenced section|date=April 2021}}
[[File:Installing electrical wiring.jpg|thumb|upright|Installing electrical wiring by "chasing" grooves into the masonry structure of the walls of a building]]
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]] wire sizes are given in the [[IEC 60228]] standard of the [[International Electrotechnical Commission]]. In North America, the [[American Wire Gauge]] standard for wire sizes is used.

==Cables==
{{Main|Power cable}}
{{More citations needed section|date=April 2021}}

===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-sheathed cable|thermoplastic]] 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]] (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]] 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 [[American wire gauge|AWG]] (or about 5&nbsp;mm<sup>2</sup>) 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.

[[File:Miccable.jpg|thumb|Copper sheathed mineral insulated cables at a panel board]]
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 [[mineral-insulated copper-clad cable|mineral-insulated cable]], with individual conductors placed within a copper tube and the space filled with [[magnesium oxide]] powder. The whole assembly is drawn down to smaller sizes, thereby compressing the powder. Such cables have a [[certification listing|certified]] 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]] caused by [[seawater|salt water]] or [[salt spray]], which is accomplished through the use of thicker, specially constructed jackets, and by tinning the individual wire stands.

[[File:Power Transformer.jpg|thumb|upright|US single-phase residential power distribution transformer, showing the two insulated ''line'' conductors and the bare ''neutral'' conductor (derived from the earthed center-tap of the transformer). The distribution supporting cantenaries are also shown.]]
In North American practice, for residential and light commercial buildings fed with a single-phase [[Split-phase electric power|split 120/240 service]], an overhead cable from a transformer on a [[Utility pole|power pole]] is run to the service entrance point. The cable is a three conductor twisted "triplex" cable with a bare neutral and two insulated conductors, with no overall cable jacket. <ref>{{cite web |url=https://science.howstuffworks.com/environmental/energy/power7.htm |title=Generating Power to Your House - How Power Grids Work - HowStuffWorks |work=HowStuffWorks |date=April 2000 |access-date=21 February 2016}}</ref> The neutral conductor is often a supporting "messenger" steel wire, which is used to support the insulated line conductors.

===Copper conductors===
{{Main|Copper conductor}}
Electrical devices often use copper conductors because of their properties, including their high [[electrical conductivity]], [[tensile strength]], [[ductility]], [[creep (deformation)|creep]] resistance, [[corrosion resistance]], [[thermal conductivity]], [[coefficient of thermal expansion]], [[solderability]], resistance to [[electrical overload]]s, compatibility with [[electrical insulator]]s, and ease of installation. Copper is used in many types of electrical wiring.<ref>{{cite journal |author=Pops, Horace |date=June 2008 |title=Processing of wire from antiquity to the future |journal=Wire Journal International |pages=58–66}}</ref><ref>[http://www.litz-wire.com/pdf%20files/Metallurgy_Copper_Wire.pdf The Metallurgy of Copper Wire] {{Webarchive|url=https://web.archive.org/web/20130901142501/http://www.litz-wire.com/pdf%20files/Metallurgy_Copper_Wire.pdf |date=1 September 2013}}. litz-wire.com</ref>

===Aluminium conductors===
[[File:Transistive terminals for AL-CU junction.JPG|thumb|Terminal blocks for joining aluminium and copper conductors. The terminal blocks may be mounted on a [[DIN rail]].]]
[[Aluminum building wiring|Aluminium wire]] 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]], 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.<ref name=NEMA>{{cite web |url=http://www.stabiloy.com/NR/rdonlyres/2AFAE0AC-850A-44C9-A3C2-C54128AE1415/0/NEMAWhitepaperEvolutionofAluminiumConductors.pdf |title=The Evolution of Aluminum Conductors Used for Building Wire and Cable |work=NEMA |date=2012 |access-date=12 October 2016 |archive-date=10 October 2016 |archive-url=https://web.archive.org/web/20161010044452/http://www.stabiloy.com/NR/rdonlyres/2AFAE0AC-850A-44C9-A3C2-C54128AE1415/0/NEMAWhitepaperEvolutionofAluminiumConductors.pdf |url-status=dead }}</ref><ref name=IAEI-Article>{{cite web |url=http://www.aluminum.org/sites/default/files/Aluminum%20Building%20Wire%20Installation%20%26%20Terminations.pdf |title=Aluminum Building Wire Installation & Terminations |work=IAEI News (January/February 2006) |access-date=12 October 2016 |archive-date=27 January 2021 |archive-url=https://web.archive.org/web/20210127230846/https://www.aluminum.org/sites/default/files/Aluminum%20Building%20Wire%20Installation%20%26%20Terminations.pdf |url-status=dead }}</ref> These practices were found to cause defective connections and 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]]s, [[wire nut]]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.{{citation needed|date=January 2017}}

Unlike copper, aluminium has a tendency to [[creep (deformation)|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]] dust in a low-residue [[polybutene]] base<ref>{{cite web |url=http://www.aoc.nrao.edu/engineering/ElChemInventory/Merged%20Files%20BC/Ideal%20Noalox%20anti-oxidant%20joint%20compoind.pdf |title=Ideal Noalox Antioxidant Material Safety Data Sheet}}</ref>) 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 distribution]], 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==
{{See also|Electrical conduit}}
{{More citations needed section|date=April 2021}}
[[File:Conduit firestop us.jpg|thumb|[[Conduit (electrical)|Electrical conduit]] risers, seen inside [[fire-resistance rating|fire-resistance–rated]] shaft, as seen entering bottom of a [[firestop]]. The firestop is made of firestop [[Mortar (masonry)|mortar]] on top, [[mineral wool|rockwool]] on the bottom. Raceways are used to protect cables from damage.]]

Insulated wires may be run in one of several forms between electrical devices. This may be a specialised bendable pipe, called a [[conduit (electrical)|conduit]], or one of several varieties of metal (rigid steel or aluminium) 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. 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 rating|fire-resistance rated]] walls and floors, the openings are required by local [[building code]]s to be [[firestop]]ped. In cases where safety-critical wiring must be kept operational during an accidental fire, [[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, because the [[thermal insulation]] properties needed for fire resistance also inhibit air cooling of power conductors.

[[File:OrganizedElectricalWiring.jpg|thumb|A [[cable tray]] can be used in stores and dwellings.]]
[[Cable tray]]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==
{{Main|Busbar|Bus duct}}
{{Unreferenced section|date=April 2021}}
[[File:Conduit busduct.jpg|thumb|Topside of [[firestop]] with [[penetrant (mechanical, electrical, or structural)|penetrant]]s consisting of electrical conduit on the left and a [[bus duct]] on the right. The firestop consists of firestop [[Mortar (masonry)|mortar]] on top and [[mineral wool|rockwool]] on the bottom, for a two-hour [[fire-resistance rating]].]]
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.

[[File:Busbars for earthing.JPG|thumb|Busbars for distributing [[protective earth]] (ground)]]
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.{{Explain|date=June 2011}}

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. 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==
[[File:Electrical panels st marys.jpg|thumb|upright|Electrical panels, cables and [[firestop]]s in an [[electrical room|electrical service room]] at a paper mill in [[Ontario]], Canada]]
'''Electrical panels''' are easily accessible [[junction box]]es used to reroute and switch [[electrical service]]s.  The term is often used to refer to [[distribution board|circuit breaker panel]]s or fuseboxes.  Local codes can specify physical clearance around the panels.{{Citation needed|date=May 2021}}

==Degradation by pests==

[[Tree squirrel|Squirrels]], rats, and other rodents may gnaw on unprotected wiring, causing fire and shock hazards.<ref name=SqAttic>{{cite web |title=Guide to Safe Removal |url=http://www.squirrel-attic.com/ |work=Squirrels in the Attic |access-date=19 April 2012}}</ref><ref name=UIExt>{{cite web |last=University of Illinois Extension |title=Tree Squirrels > Damage Prevention and Control Measures |url=http://web.extension.illinois.edu/wildlife/directory_show.cfm?species=treesquirrels |work=Living with Wildlife in Illinois |publisher=University of Illinois Board of Trustees |access-date=12 March 2013}}</ref> 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.{{Citation needed|date=May 2021}}

==Early wiring methods==
{{More citations needed section|date=April 2021}}
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. [[Line splice|Splice]]s 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]]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)===
{{Main|Knob-and-tube wiring}}
[[File:Splice-knob-corner.jpg|thumb|Knob-and-tube wiring (The orange cable is an unrelated extension cord.)]]
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===
[[File:Lead cased electrical wire from a circa 1912 house on Southern England.jpg|thumb|upright|Lead-cased electrical cable from a circa 1912 house in southern England. Two conductors are sheathed in red and black rubber, and the central earth wire is bare. These cables are dangerous because the sheath is prone to split if repeatedly flexed.]]
In the United Kingdom, an early form of insulated cable,<ref>Robert M. Black, ''The History of Electric Wires and Cable'', Peter Pergrinus Ltd. London, 1983 {{ISBN|0-86341-001-4}}, pp. 155–158</ref> 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.<ref>Croft</ref>

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]] 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.<ref>Schneider, Norman H., '' [https://archive.org/details/wiringhousesfore00schn Wiring houses for the electric light; together with special references to low voltage battery systems]'', Spon and Chamberlain, New York 1916, pp. 93–98</ref>

===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 [[power cable|cables]] for US building wiring were introduced in 1922 with {{cite patent
| country=US
| number=1458803
| status=patent
| title=Insulated electric wire
| gdate=1923-06-12
| fdate=1922-02-06
| pridate=1922-02-06
| invent1=Burley, Harry
| invent2=Rooney, Henry
| assign1=Boston Insulated Wire and Cable
}}. 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.

[[File:Leitungsende Abisoliert en.svg|thumb|Diagram of a simple electrical cable with three insulated conductors, with IEC colour scheme]]
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.{{citation needed|date=March 2016}}

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]] signal and control applications such as doorbell wiring.

Other methods of securing wiring that are now obsolete include:
* Re-use of existing [[gas pipe]]s when converting [[gas lighting]] 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 [[molding (decorative)|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.<ref>Croft, p. 142</ref>
* 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.<ref>Croft, p. 143</ref>
* 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.<ref>Croft, p. 136</ref>
* In Austria, wires were concealed by embedding a rubber tube in a groove in the wall, [[plasterwork|plastering]] over it, then removing the tube and pulling wires through the cavity.<ref>Croft, p. 137</ref>

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 [[electrical conduit|surface mounted raceway]] wiring systems are still available today.

==See also==
*[[10603]] – a frequently used [[MIL-SPEC]] compliant wire
*[[Bus duct]]
*[[Cable entry system]]
*[[Cable gland]]
*[[Cable management]]
*[[Cable tray]]
*[[Domestic AC power plugs and sockets]]
*[[Electric power distribution]]
*[[Electrical conduit]]
*[[Electrical room]]
*[[Electrical wiring in North America]]
*[[Electrical wiring in the United Kingdom]]
*[[Ground (electricity)|Grounding]]
*[[Ground and neutral]]
*[[Home wiring]]
*[[Industrial and multiphase power plugs and sockets]]
*[[Oxygen-free copper]]
*[[Portable cord]]
*[[Power cord]]
*[[Restriction of Hazardous Substances Directive]] (RoHS)
*[[Single-phase electric power]]
*[[Structured cabling]]
*[[Three-phase electric power]]

==References==
{{Reflist|30em}}

==Bibliography==
*Croft, Terrel (1915) [https://archive.org/details/wiringfinishedb01crofgoog ''Wiring of Finished Buildings''], McGraw Hill, New York.

==Further reading==
* [http://www.nfpa.org/aboutthecodes/list_of_codes_and_standards.asp National Electrical Code] {{Webarchive|url=https://web.archive.org/web/20110728013724/http://www.nfpa.org/aboutthecodes/list_of_codes_and_standards.asp |date=28 July 2011 }} — 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
*[https://web.archive.org/web/20051126103456/http://www.nema.org/stds/electricalinstall.cfm NEMA comparison of IEC 60364 with the US NEC]
* {{cite book |last=Cauldwell |first=Rex |title=Wiring a House (For Pros By Pros) |publisher=Taunton Press |location=Newtown, Connecticut, US |year=2002 |isbn=1-56158-527-0 |url-access=registration |url=https://archive.org/details/isbn_9781561585274}}
* Hirst, E. [https://web.archive.org/web/20120925042240/http://www.ornl.gov/info/ornlreview/rev28_2/text/uti.htm Electric Utilities and Energy]
* {{cite book |last1=Litchfield |first1=Michael |last2=McAlister |first2=Michael |title=Taunton's wiring complete : expert advice from start to finish |year=2008 |publisher=Taunton Press |location=Newtown, Connecticut, US |isbn=978-1-60085-256-5 |edition=Revised}}

==External links==
{{Commons category|Electrical wiring}}
* [http://www.faqs.org/faqs/electrical-wiring/part1/ Electrical wiring FAQ] (oriented to US and Canadian practice)

{{Authority control}}

[[Category:Electrical wiring| ]]
[[Category:Building codes]]
[[Category:Electrical engineering]]
[[Category:Power cables]]