1) Generally, the incoming line of power distribution box adopts five wire system, that is, a, B and C three-way phase line (the general color is yellow, green and red), one way zero line (the color is light blue) and one way ground line (the color is yellow with green. 1) Generally, the incoming line of power distribution box adopts five wire system, that is, a, B and C three-way phase line (the general color is yellow, green and red), one way zero line (the color is light blue) and one way ground line (the color is yellow with green. Electrical power enters a distribution box through the incoming lines using what we call a five-wire system. Each of these wires has a specific, non-negotiable purpose: The Phase Lines : You've got three of these bad boys – A, B, and C phases. Outgoing line. Live (L) Wire Connection: In a distribution box setup, the incoming live wire (also known as phase or hot wire, denoted as L or Line) connects to the line terminal of the circuit breaker. This serves as the primary source of electrical energy from the mains supply. Whether in a home or an industrial facility, this box keeps your electrical setup organized, functional, and efficient.