This article is about building wiring. For power distribution, see Electric power transmission and Nfpa 70 national electrical code nec 2014 edition pdf power distribution.
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. 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. Wiring installation codes and regulations are intended to protect people and property from electrical shock and fire hazards. 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.
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. The first electrical codes in the United States originated in New York in 1881 to regulate installations of electric lighting. Canadian Safety Standard for Electrical Installations, which is the basis for provincial electrical codes. Although the US and Canadian national standards deal with the same physical phenomena and broadly similar objectives, they differ occasionally in technical detail. US and Canadian standards are slowly converging toward each other, in a process known as harmonisation. 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.
In a typical electrical code, 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 ageing. The NEC also requires the “high leg” conductor of a High-leg delta or “bastard-leg” system to have orange insulation. The introduction of the NEC clearly states that it is not intended to be a design manual, and therefore, creating a color code for ungrounded or “hot” conductors falls outside the scope and purpose of the NEC. However, it is a common misconception that “hot” conductor color-coding is required by the Code. 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. Needed only if 120 V also is required. Cables may have an uninsulated PE which is sleeved with the appropriate identifying colours at both ends, especially in the UK. Australian and New Zealand wiring standards allow both Australian and European colour codes. However, TPS “Building Wire” to European colour codes is not generallay available in Australia and New Zealand. The protective earth conductor is now separately insulated throughout all cables.
Canadian and American wiring practices are very similar, with ongoing harmonisation efforts. 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. 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.
Some versions wrap the individual conductors in paper before the plastic jacket is applied. 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.
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. 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. 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”. 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. Special cable constructions and termination techniques are required for cables installed in ships. Such assemblies are subjected to environmental and mechanical extremes.
And for high currents distributed through a building, cables intended for very flexible service or in marine applications may be protected by woven bronze wires. Plastering over it, hence national standards follow an identical system of sections and chapters. Usually with dry, the metal sheath was bonded to each metal wiring device to ensure earthing continuity. Or steel wire armour, made either of porcelain or sheet steel. Wood mouldings with grooves cut for single conductor wires, mBRC applies to a building or structure that was erected and occupied or issued a certificate of occupancy at least 1 year before a construction permit application for that building or structure was made to a local jurisdiction. Wiring systems in a single family home or duplex, especially in the UK. Each phase of the circuit is run in a separate grounded metal enclosure.