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. 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 stripes). Outgoing line. A distribution box is the heart of any electrical system. It contains multiple circuit breakers and connects various electrical circuits to ensure the safe flow of electricity throughout the building. Most of the time, each of these secondary circuits will be protected with a fuse or breaker.