Wiring for AC and DC power distribution branch circuits are colour-coded for identification of individual wires. In some jurisdictions, all wire colours are specified in legal documents. In other jurisdictions, only a few conductor colours are so codified. In that case, local custom dictates the “optional” wire colours. IEC, AC: Most of Europe abides by IEC (International Electrotechnical Commission) wiring colour codes for AC branch circuits. Just remember, all electrical wires could carry a current at some point, so treat each colour with equal caution. If you have any hesitations at all, it’s best to leave electrical work to a qualified professional.
Black Electrical Wires
This colour of wire is used to transfer power to switches and outlets in all types of circuits. Black wires are also often used as switch legs in circuits, which is the connection linking a switch to the electrical load. Consider all black wires to be live at all times.
Red Electrical Wires
In 220-volt circuits, red wires are the secondary live wires. Like black wires, they can be used in some types of switch legs. They are also used to connect hardwired smoke detectors to the home’s power system. It’s possible to link two red wires together or a red wire to a black wire.
Blue and Yellow Electrical Wires
While wires in these colours carry power, they are not used in typical outlet wiring. Instead, blue and yellow wires are used as the live wires pulled through a conduit. For example, you might see yellow wires as switch legs to ceiling fans, structural lights and outlets paired with light switches. Then, blue wires are most often used as travellers for three- or four-way switches.
White and Gray Electrical Wires
If you find wires in either of these colours, you’ve located the neutral wires. White is most commonly used, but gray wires serve the same function. The purpose of a neutral wire is to connect to the neutral bus bar, a conductive piece of metal within an electrical panel that attracts the electric current for distribution throughout the house. White and gray electrical wires can only be connected to one another. While they’re called “neutral” wires, they may still carry a current, especially if the load is unbalanced, so handle them cautiously.
Green Electrical Wires
The purpose of green wires is to ground an electrical circuit. They connect to the grounding terminal in an outlet box and run to the ground bus bar in an electrical panel. In this way, green wires act as a failsafe, giving electricity a place to escape into the ground if a live wire within the circuit touches metal or something else conductive. Green wires can only connect to other green wires. Remember, if there’s a fault somewhere in your circuit, green wires could be live, so treat them with caution.