What the wire colors mean

In US homes the color tells you the job: black and red carry power, white carries it back, bare or green is the ground. The one exception you will meet is a white wire taped black.

Wire colors inside the cable

Color	Job	Where it goes
Black	Hot	Brass screws, LINE and LOAD terminals, the breaker
Red	Hot	A traveler between 3-way switches, a switched leg, the second hot on 240 V circuits
White	Neutral	Silver screws, white fixture leads, the neutral bar
White taped black or red	Hot	A white used to carry power, usually in a switch loop or on a 240 V circuit
Bare copper or green	Ground	Green screws, metal boxes, the ground bar
Gray	Neutral	Used in conduit for a second system's neutral
Blue, yellow, orange	Hot	Mostly in conduit and commercial wiring

Cable jacket colors

NM-B house cable (often called Romex) is color coded by wire size, which tells you the breaker it belongs on.

Jacket	Wire size	Breaker
White	14 AWG	15 A
Yellow	12 AWG	20 A
Orange	10 AWG	30 A
Black	8 or 6 AWG	40 to 55 A, depending on size
Gray	UF cable for underground runs	by size

The print on the jacket says the rest: "14/2 WITH GROUND" is two insulated wires (black and white) plus a bare ground. "14/3" adds a red.

When colors lie

Older homes, previous owners and repairs do not always follow the code. Treat every wire as live until your tester says otherwise. How to test for power.