Latent potential differences between exposed-conductive-parts under ground-fault conditions in low-voltage systems

In low-voltage systems, ground-faults do not necessarily involve the actual earth, but fault currents may return to the source via conductors; such conductors, which provide a clear path toward the source, are defined in applicable codes and technical standards as equipment grounding conductors or protective conductors. The above situation is for example typical of the North American low-voltage multiple grounded distribution systems, also referred to as TN-C-S, in international standards (IEC). In this paper it is substantiated that under ground-fault conditions even healthy equipment, sharing the same protective conductor with faulty equipment, as well as any metalwork in the building, acquire electrical potentials. Such potentials have a decreasing magnitude toward the electrical source and keep the same constant value on equipment located downstream the ground-fault location. The presence of non-zero potential differences between exposed-conductive-parts is a salient trait of TN systems and may constitute a hazard particularly in special locations, such as bathrooms with showers or bathtubs. In such areas, in fact, the resistance-to-ground of persons may be greatly reduced by moisture, water or the absence of clothing. This paper illustrates the advantages of supplementary equipotential bonding connections in such locations as a possible solution in the reduction of latent potential differences.