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. 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. Think of the incoming line as the main artery bringing lifeblood to the entire system. Just like you wouldn't want a weak or clogged artery in your body, you don't want subpar incoming lines feeding your distribution box. We'll walk through everything you need to consider, from choosing the right. A distribution board, also known as a DB box, is like the central hub of an electrical system. It contains multiple circuit breakers and connects various electrical circuits to ensure the safe flow of electricity throughout the building. Whether in a home or an industrial facility, this box keeps your electrical setup organized, functional, and efficient.