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 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 specification. Wiring safety codes vary by locality, country or region. The International Electrotechnical Commission (IEC) is attempting to harmonise wiring standards amongst 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 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.
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 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 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
In Germany, DKE (the German Commission for Electrical, Electronic and Information Technologies of DIN and 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.
North America
The first electrical codes in the United States originated in 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 (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.
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 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. Although BS 7671 is the standard to which the UK electrical industry generally adheres, compliance with BS 7671 is not a legal requirement
Colour coding of wiring by region
In a typical electrical code, some colour-coding of wires is mandatory. Many local rules and exceptions exist per country, state or region.[1] Older installations vary in colour codes, and colours may fade with insulation exposure to heat, light and ageing.
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 conductors.
United States
Main article: Electrical wiring in North America
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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.
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, and yellow are used in 277/480-volt systems. 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.[3] Some local jurisdictions do specify required color coding in their local building codes, however.
United Kingdom
Main article: Electrical wiring in the United Kingdom
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The United Kingdom requires the use of wire covered with green/yellow striped insulation, for safety earthing (grounding) connections.[4] 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 will often use indicator lights of the old colours.[5]
Colours, fixed and flexible cable
| Flexible cable (e.g., extension, power, and lamp cords) | |||
|---|---|---|---|
| Region or country | Phases | Neutral | Protective earth/ground |
| Argentina, European Union, South Africa (IEC 60446) | |||
| Australia, New Zealand (AS/NZS 3000:2007 3.8.1, 3.8.3) | |||
| Brazil[6] |
Any color may be used for flexible cable phases, excluding green and green/yellow striped.
| ||
| China (PRC) | |||
| United States, Canada (120 V) | metallic brass | metallic silver | , green/yellow striped |
| United States, Canada (split-phase 240 V)[7] | , green/yellow striped | ||
| Fixed cable (e.g., in-, on-, or behind-the-wall cables) | |||
| Region or country | Phases | Neutral | Protective earth/ground |
| Argentina; China; European Union (IEC 60446) from April 2004; the United Kingdom from 31 March 2004 (BS 7671); Hong Kong from July 2007; Singapore from March 2009; Russia since 2009 (GOST R 50462); Ukraine, Belarus, Kazakhstan | |||
| India, Pakistan; United Kingdom, prior to 31 March 2004 (BS 7671); Hong Kong, prior to 2009; Malaysia and Singapore, prior to February 2011 |
| ||
| Australia, New Zealand (AS/NZS 3000:2018 3.8.1, table 3.4) |
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| Brazil |
Any color may be used for fixed cable phases, excluding blue, green and green/yellow striped.
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In installations where neutral also serves as protective ground, light blue wires with green/yellow striped terminal markings should be used.
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| China (PRC) | |||
| South Africa |
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| United States[e] | metallic brass | metallic silver | |
| Canada[8][e] | |||
Boxes (e.g., translucent purple) denote markings on wiring terminals.
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