Metal electrical boxes must be grounded because they are conductive components that enclose energized wires and connections. Each DISTRIBUTION BOX and controller must be grounded. 26 mm 2 (10 AWG) ground wire must be used, and in all other markets a 6 mm 2 must be used. Grounding the box prevents this. Understanding how to ground metal electrical box components is not just about following code—it's about protecting your home and family. Code Change Summary: Clarifications were made regarding the connection of equipment grounding conductors in a box. When conductors are spliced inside a box or terminated to. NEC 250. Skip the grounding, and you're gambling with safety.