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. The best distribution system is one that will, cost-effectively and safely, supply adequate electric service to both present and future probable loads—this section is intended to aid in selecting, designing and installing such a system. The function of the electric power distribution system in a. Analyze the incoming line part: Determine the incoming line source of the distribution box and the configuration of the incoming line circuit breaker, and understand the power supply method of the distribution box. Make poor choices here, and you're potentially looking at: Electrical systems are like a. mm (minimum) in length on cable connection side as shown in the drawings. In 63 / 100 / 160 / 315 KVA distribution box, the cross se the Isolator with cross section as mentioned above throughout the length. Porcelain. The Key Diagram of Substation can be explained as under: 1. The calculated rating of copper busbar equals to 1.