Take reasonable measures to ensure that the resistance to ground is 25 ohms or less for typical loads. Power from factory ground must be installed by a qualified electrician. Each DISTRIBUTION BOX and controller must be grounded. Grounding of the units: Attach a ground wire from one of. 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. Preparation: First, you need to prepare some necessary tools, including grounding wire, grounding rod, voltmeter, insulating gloves and insulating tools. During fault conditions, low impedance results in high fault current flow, causing overcurrent protective.