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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 ...
Wiring materials for use in the United States must generally be made and tested to product standards set by NEMA and Underwriters Laboratories (UL) and must bear approval marks such as those set by UL. Approved wiring types can vary by jurisdiction. Not all wiring methods approved in the NEC are accepted in all areas of the United States.
Modern wiring methods assume that two or more load-carrying conductors will lie very near each other, as for instance in standard NM-2 cable. When installed correctly, the K&T wires are held away from the structural materials by ceramic insulators. Over the K&T era multiple wire types evolved.
Those wiring methods acceptable by the NEC are found in chapter 3, thus all approved wiring method code articles are in the 300s. Efforts have been underway for some time to make the code easier to use. Some of those efforts include using the same extension for both code articles and for the support of wiring methods.
Wiring systems in buildings may be subject to frequent alterations. Frequent wiring changes are made simpler and safer through the use of electrical conduit, as existing conductors can be withdrawn and new conductors installed, with little disruption along the path of the conduit. A conduit system can be made waterproof or submersible.
Homes typically have several kinds of home wiring, including electrical wiring for lighting and power distribution, permanently installed and portable appliances, telephone systems, heating or ventilation system control, and increasingly for home theatre and computer networks.
The Carter system, also known as the Chicago system, was a method of wiring three-way switches in the era of early knob-and-tube wiring. This now-obsolete wiring method has been prohibited by the USA National Electrical Code since 1923, [2] even in new knob-and-tube installations which are still permitted under certain circumstances. This ...
The Code uses a prescriptive model, outlining in detail the wiring methods that are acceptable. In the current edition, the Code recognizes that other methods can be used to assure safe installations, but these methods must be acceptable to the authority enforcing the Code in a particular jurisdiction.