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. That cable running from your main service entrance to your distribution box isn't just another wire – it's the critical link that determines how safely and efficiently power flows through your entire building. Make poor choices here, and you're potentially looking at: Electrical systems are like a. A distribution box is the heart of any electrical system. Whether in a home or an industrial facility, this box keeps your electrical setup organized, functional, and efficient. However, the key to. 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. Identify the dual power switch (if any): Understand the working principle and. This technical article describes single line diagrams of two typical power substations 66/11 kV and 11/0.