Wiring safety codes are intended to protect people and property from electrical shock and fire hazards. Regulations may be established by city, county, provincial/state or national legislation, usually by adopting a model code (with or without local amendments) produced by a technical standards-setting organization, or by a national standard electrical code.
Electrical codes arose in the 1880s with the commercial introduction of electrical power. Many conflicting standards existed for the selection of wire sizes and other design rules for electrical installations.
The first electrical codes in the United States originated in New York in 1881 to regulate installations of electric lighting. Since 1897 the US National Fire Protection Association, a private non-profit association formed by insurance companies, has published theNational 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 harmonization.
In European countries, an attempt has been made to harmonize national wiring standards in an IEC standard, IEC 60364 Electrical Installations for Buildings. Hence national standards follow an identical system of sections and chapters. However, this standard is not written in such language that it can readily be 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.
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.
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) includes new sections for microgeneration and solar photovoltaic systems. The first edition was published in 1882.
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.
The international standard wire sizes are given in the IEC 60228 standard of the International Electrotechnical Commission. In North America, the American Wire Gaugestandard for wire sizes is used.
[edit]Color code
To enable wires to be easily and safely identified, all common wiring safety codes mandate a colour scheme for the insulation on power conductors. In a typical electrical code, some colour coding is mandatory, while some may be optional. Many local rules and exceptions exist. Older installations vary in colour codes, and colours may shift with insulation exposure to heat, light, and ageing.
Many electrical codes now recognize (or even require) the use of wire covered with green insulation, additionally marked with a prominent yellow stripe, for safety grounding (earthing) connections. This growing international standard was adopted for its distinctive appearance, to reduce the likelihood of dangerous confusion of safety grounding wires with other electrical functions, especially by persons affected by red-green colour blindness.
| Standard wire colours for FLEXIBLE cable (e.g. Extension cords, power (line) cords and lamp cords) | |||
|---|---|---|---|
| Region or Country | Phases | Neutral | Protective earth/ground |
| European Union (EU), Australia, South Africa (IEC 60446) |  |  |  |
| Australia, New Zealand (AS/NZS 3000:2007 3.8.3) | ,  |  ,  | |
| Brazil |  , | |  |
| United States, Canada | (brass) |  (silver) | (green) |
| Standard wire colours for FIXED cable (e.g. In-, On-, or Behind-the-wall wiring cables) | |||
| Region or Country | Phases | Neutral | Protective earth/ground |
| European Union (EU) (IEC 60446) including UK from 31 March 2004 | , ,  | | |
| UK prior to 31 March 2004 | , , | | (formerly) bare conductor, sleeved at terminations (formerly) |
| Australia, New Zealand (AS/NZS 3000:2007 clause 3.8.1, table 3.4) | Any colour other than , , , , or Recommended: or for single phase; or , or  for multiphase | or | (since about 1980) (since about 1980) bare conductor, sleeved at terminations (formerly) |
| Brazil | , , , | | |
| South Africa | , or , | | bare conductor, sleeved at terminations |
| India, Pakistan | , , | | |
| United States | , , (120/208/240V) (brass) ,  , (277/480V) | (120/208/240V) (silver)(277/480V) | (green) bare conductor (ground or isolated ground) |
| Canada | , (120/208/240V), , (600/347V), (single phase isolated systems), , (three phase isolated systems) | (120/208/240V)(600/347V) | (green) bare conductor (isolated ground) |
| Notes:
Parenthesized colours in italics are used on metallic terminals. "Green/yellow" means green with yellow stripe. See illustrations nearby.
The colours in this table represent the most common and preferred standard colours for wiring; however others may be in use, especially in older installations.
Australian and New Zealand wiring standards allow both European and Australian colour codes. Australian-standard phase colours conflict with IEC 60446 colours, where IEC-60446 supported neutral colour (blue) is an allowed phase colour in the Australia/New Zealand standard. Care must be taken when determining system used in existing wiring.
Canadian and American wiring practices are very similar, with ongoing harmonization efforts.
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[edit]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.
[edit]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. Spliceswere 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.
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