This is a must know question for any good Electrical Engineer
Black wire: This wire is used for power supply in all circuits. Any circuits with this color is considered hot or live. It is never used for a neutral or ground wire.
Red wire: This color wire is a secondary live wire in a 220 volt circuit and used in some types of interconnection. You can join the red wire to another red wire or to a black wire
Blue and Yellow wire: These wires are also used to carry power but are not wiring the outlets for common plug-in electrical devices. They are used for the live wire pulled through the conduct. You will see yellow wire in the fan, structure lights, and switched outlets.
White and Gray: This color wire is used as a neutral wire. It carries the current (unbalanced load) to the ground. You can join white and gray only to other white and gray wires
Green: It is connected to the grounding terminal in an outlet box and run from the outlet box to the ground bus bar within an electric panel
