Electrical Wire Color Coding

To the untrained eye, all those wires look like a bowl of spaghetti. What do the red wires do? What are the black wires for? Why are there green, blue and yellow wires? Well, the truth is that there are more than just these colors. Wire colors come in many different combinations. Each has a specific use in general, which is outlined here.

Black wires are ALWAYS used for the primary hot wire in a circuit. They can also be used for a "switch leg" in some applications. Black wires should NEVER be used for grounding the circuit. When you see a black wire, you know that it is carrying live current.

Red wires are also used as hot wires. Red is the secondary hot wire in all 220 volt electrical circuits. When you see a red wire in that circuit, you can be sure it is running live voltage. One other common use for a red wire is as an interconnection between two components that are hard wired in line.

Wires that are yellow or blue are hot wires, too, but where black and red are simply run to the box, blue or yellow wires are normally pulled through electrical conduit. This differentiation is very useful for electricians.

That leaves us with green wires and bare copper wire. These two colors are used only for grounding the circuit. The ground wire is usually bonded to the box or connection for the purpose of safety. That does not mean that you can touch these wires however. They still carry live current and can supply quite a shock.

It should be stated that the color of the casing on the wire has no bearing on the size or gauge of the wire. That information is stamped or written on the outside of the casing. This is usually stated in terms like 8 gauge, 10 gauge etc... An 8 gauge wire and a 10 gauge wire can both be red or black or any color. They can both be used in the same application.

There are exceptions to this color scheme and their uses. In multi-wire cables like 12/24 or 14/36 cable, the black wire and the white wire could be used as the two hot wires for a certain circuit. There may not be a red one available for whatever reason. I have even seen multi-wire cables that have all the wires a single color, but with numbers stamped onto the casings of the internal wires.

In any case, it is suggested that you follow the universal color coding whenever possible:

  • Black wire for primary hot wire.
  • Red for secondary hot wire in 220 circuitry
  • Blue wire for any current carrying line that is run through a conduit.
  • Yellow wire for a secondary line that holds live current in a conduit.
  • Bare copper or green wire for grounding the circuit and closing the circuit.

Comments 1 comment

Lucky Joestar 4 years ago

Those wire colors in the above diagram are European wire colors, yet you’re talking about American colors in the text. Let me clarify something:

Grounds are green and yellow in Europe and just green in America.

Neutrals are blue in Europe and white or grey in America.

Primary hot is brown in Europe and black in America.

Secondary hot is black in Europe and red in America.

Tertiary hot is gray in Europe and blue, and rarely found, in America.

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