1) Generally, the incoming line of power distribution box adopts five wire system, i. three phase lines a, B and C (generally yellow, green and red), one zero line (light blue) and one ground line (yellow with green stripes). We'll walk through everything you need to consider, from choosing the right wiring approach to avoiding those costly installation mistakes that so many people make. Before we dive into technical details, let's establish why this matters so much. Choose the right box based on environment (indoor/outdoor), load capacity, and durability. ① 220V load generally takes one phase line. Integrating Site Conditions with Design Requirements to Standardize Installation Height.