26 mm 2 (10 AWG) ground wire must be used, and in all other markets a 6 mm 2 must be used. Today, we're diving deep into the world of distribution box grounding, breaking down the standards, and shining a light on those sneaky mistakes that even experienced electricians sometimes make. Grounding of the units: Attach a ground wire from one of. There is a 200amp main service in the basement, which then feeds up to a 100amp sub-panel for the main floor. This 100amp sub feeds a kitchen (fridge, microwave, dishwasher, gas range), a bathroom, 3 bedrooms, and a living room. The 200amp main feeds the 100amp sub, 2 bedrooms, a living room, a. This discussion addresses the safe connection of the bare ground wire to a metal box for 240V machinery.