Residential Electrical

Electrical Wiring Methods

Residential National Electrical Code
Electrical Wiring Method
 
Residential Electrical Code
 
Category Construction Glossary
Wiring methods

Most circuits in the modern North American home and light commercial construction are
wired with non-metallic sheathed cable designated type (often referred to by the brand
name Romex).  This type of cable is the least expensive for a given size and is
appropriate for dry indoor applications. The designation NM XX-Y indicates, respectively,
the type of sheathing (in this case, non-metallic), the size of the main conductors, and the
total number of circuit conductors (exclusive of the grounding conductor). For example,
NM 14-2 cable contains three conductors (two plus one ground) at 14 gauge, a size
typically used for circuits protected at 15 amperes. Circuits with larger currents (such as
for 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.

In type NM cable, conductor insulation 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 represent the identified or neutral conductor, near ground
potential ; and the bare/green conductor, the safety grounding conductor not normally
used to carry circuit current. In 240 V applications not requiring a neutral conductor, the
white wire may be used as the second hot conductor, but must be recolored with tape or
by some other method. Four-wire flexible equipment connection cords have red as the
fourth color; unlike European practices, color-coding in flexible cords is the same as for
fixed wiring.

Several other types of wiring systems are used for building wiring in the United States;
these include corrugated metal armored cable, mineral-insulated cable, other types of
power cable, and various types of electrical conduit. In industrial applications cables may
be laid in cable trays. Cable type TC is especially intended for use in tray systems.
Special wiring rules apply to wet or corrosive locations , and to locations which present an
explosion hazard.. Wiring materials for use in the United States must 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.