In wiring diagrams, common colors used include white, black and red. White, represented by WH, denotes a neutral wire that carries current at zero voltage. Black and red colors, represented by BK and RD respectively, denote a wire carrying voltage at full voltage.
Standard color codes are important for the correct configuration of electrical systems and also for safety purposes, as the colors assist in identifying the function of each wire in the circuit. Wiring diagrams make use of color codes to identify the colors of the wires being used to connect the various components in the circuit. Most of the diagrams have a key that explains the color codes used.
Black is always used to denote power-carrying wires, typically the power feed for a switch or an outlet; it is never used for ground or neutral wires. Red is used for the secondary live wires in a circuit. The red wires can be connected to black wires. Blue and yellow, represented by BU and YL respectively, are also used to show wires carrying power, although they are not used to wire outlets for common plug-in devices. Green, often represented by the code GR, is used to denote grounding wires.