House Wiring Color Code
What Color Wires and Gauges Are For What
When wiring a house, there are many types wire to choose from, some copper, others aluminum, some rated for outdoors, others indoors. In general however, there are only a couple varieties used for wiring a residential home
How Wires Are Sized
Wire is sized by the American Wire Gauge (AWG) system. Wire gauge refers the physical size of the wire, rated with a numerical designation that runs opposite to the diameter of the conductors—in words, the smaller the wire gauge number, the larger the wire diameter. Common sizes include 14-, 12-, 10-, 8-, 6-, and 2-gauge wire. The size of the wire dictates how much current can safely pass through the wire.
Electrical current is measured in ampacity, and each wire gauge has a maximum safe carrying capacity. For standard non-metallic (NM) cable, these amperage capacities are:
Amperage Capacities for Standard Non-Metallic (NM) Cable
These ratings are for standard copper NM sheathed cable, but there are instances where these amperage ratings vary. For example, there is aluminum wiring in some homes, and aluminum wires have their own ampacity-carrying capacity. Aluminum wiring was once widely used, but because it was found that aluminum had a greater expansion profile under load, it often loosened wire connections and sometimes caused electrical fires. That is not to say you are necessarily at risk just because you have aluminum wiring, because those connections may work forever if not overloaded. But an evaluation and replacement with copper wiring may be a good idea.
Shown to the right - [Fig. 1] is your standard 12g - 20A house wire. Note: the color is white. This is the old color, although you might find some places still carrying it. The new color for 12g is yellow.
Types Of Wire
Although THHN is primarily used for commercial or industrial this can also be used for residential. The letters below are substituted for the last letter above. This describes the type of wire:
Outer Sheath Color Coding - [Fig. 5]
The color of the outer sheath tells you the gauge of the wire inside as well as the current rating for the circuit.
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