26 mm 2 (10 AWG) ground wire must be used, and in all other markets a 6 mm 2 must be used. If you've ever found yourself scratching your head over whether that metal door on your distribution cabinet really needs a grounding wire, you're not alone. In factories, construction sites, and even commercial buildings, this question pops up all the time. Each DISTRIBUTION BOX and controller must be grounded. During fault. A distribution box is the heart of any electrical system. The voltage, system arrangement, loads connected, and continuity of. When inspecting the interior of a stainless steel outdoor electrical box distribution box, pay attention to the copper or tin-plated terminals on the base plate or side walls.