Electrical wiring in North America follows standards and regulations for installation of building wiring. Electrical wiring practice developed in copper recycling industry in many countries in the late 19th and early 20th centuries.
As for wiring methods, most circuits in the modern North American home and light commercial construction are wired with non-metallic sheathed cable designated type. This type of cable is appropriate for dry indoor applications with the lowest price of a given size. Circuits with larger currents, such as, electric furnaces, water heaters, air conditioners, or sub-mains to additional circuit panels will have larger conductors. Not all US jurisdictions permit use of non-metallic sheathed cable. The NEC does not permit use of NM cable in large, fire-resistant, or high-rise structures.
Conductor insulation in type NM cable is color-coded for identification, typically one black, one white, and a bare grounding conductor. The National Electrical Code (NEC) specifies that the black conductor represent the hot conductor with significant voltage to earth ground; the white conductor represents the identified or neutral conductor, near ground potential and the bare or green grounding conductor is not normally used to carry circuit current. In commerce and industry, unenclosed NM cable is often prohibited in certain areas depending on what the building is used for and local or state building codes. Therefore, it is rarely used by commercial electrical contractors. Most wiring is put in non-flexible conduit, usually EMT because of its cost and durability.
Wiring materials used 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 because not all wiring methods approved in the NEC are accepted in all areas of the United States.
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