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. 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. Hey, in this article we are going to see the Single Phase Distribution Box Wiring Diagram and Connection Procedure. A distribution board or distribution box is where the main power supply is distributed to multiple loads. Covers wiring, placement, standards, and expert tips for a compliant setup. What is Distribution Board? Distribution board.