Suppose the grounding conductor is interrupted. If a fault occurs, no current will flow in the grounding conductor since the circuit is interrupted. This opened grounding conductor could be caused by a grounding prong illegally cut off a plug, a loose connection, a conduit which is not connected properly or many other causes. This fault leaves the frame of the appliance energized. When someone comes by and touches the appliance and also touches the building steel , another piping system, and possible even a wet concrete floor, the circuit will then be completed in current flow through the persons body, injuring or killing them.
Many codes allow the use of metallic conduits to be used as grounding conductors.
Many designers today do not believe that using steel conduits is adequate for this use. Conduit has connections every ten feet and often low grade, cast metal couplings and connectors are used. For this reason we believe that copper grounding conductors should be specified in every power circuit. The secondary benefit of this copper grounding conductor is it will provide an equipotential plane for all equipment connected to it. This often makes the so-called isolated grounding conductors specified by computer and other manufacturers unnecessary.