Residential National Electrical Code
Category Construction Glossary
For residential wiring, some basic rules given in the NEC are:
Phase wire in a circuit may be black, red, orange (high leg delta) insulated wire,
sometimes other colors, but never green, gray, or white (whether these are solid colors or
Neutral wire is connected to the center tap of the final step-down transformer and is
identified by gray or white insulated wire, perhaps with stripes; most commonly bonded to
earth for a fixed known path to stabilize the voltages only at the main service panel; many
times called the grounded wire. Note that all metallic systems in a building are to be
bonded to the panel; e.g., water, natural gas, HVAC piping, etc.
Grounding wire of circuit may be bare or identified insulated wire of green or having
Larger wires are furnished only in black; these may be properly identified with suitable
paint or tape. The phase wire for a switch "leg" is the white wire of a two insulated wire
cable; the black wire is connected to the light.
All wiring in a circuit except for the leads that are part of a device or fixture must be the
same gauge. Note that different size wires may be used in the same raceway so long as
they are all insulated for the maximum voltage of any of these circuits.
There is no maximum number of receptacles on a circuit, but the Code gives rules for
calculating circuit loading.
Ground-fault circuit interrupter (GFCI) protection is required on receptacles in wet
locations. This includes all small appliance circuits in a kitchen, receptacles in a crawl
space, basements, bathrooms and a receptacle for the laundry room, as well as outdoor
circuits within easy reach of the ground. However, they are not required for refrigerators
because unattended disconnection could cause spoilage of food, nor for garbage
disposals. Instead, for refrigerators and other semi-permanent appliances in basements
and wet areas, use a one-outlet non-GFCI dedicated receptacle. Two-wire outlets having
no grounding conductor may be protected by an upstream gfci and must be labelled "no
grounding". Most GFCI receptacles allow the connection and have GFCI protection for
down-stream connected receptacles. Receptacles protected in this manner should be
labeled "GFCI protected".
Branch circuits with receptacles must have arc-fault circuit interrupter protection, unless
wired with specific types of armored cable.
Most circuits have the metallic components interconnected with a grounding wire
connected to the third, round prong of a plug, and to metal boxes and appliance chassis.
furnaces, water heaters, heat pumps, central air conditioning units, stoves on dedicated
Use exterior components for exterior lighting and outlets
Electrical boxes must be properly sized to prevent heat build-up, especially from joints,
and just having so many items in too small a space.