99NEC250-2(d) …The earth shall not be used as the sole equipment grounding
conductor or fault current path.
A fault in the service-entrance equipment or downstream within the premises may easily cause hazardous touch/step voltage gradients, and non-operation of overcurrent devices to limit the shock hazard. {It’s quite distracting to be jolted touching an electrical enclosure standing on dry soil—with ~277V between two pieces of electrical gear thirty feet apart.}
