The performance of conduits in grounding circuits

Rigid steel, thin-walled steel and aluminium conduits are investigated for their effectiveness in minimizing shock hazard under fault conditions. This analysis considers two extreme cases of internal and external current return paths which exhibit markedly different characteristics. Current distribution in, and potential difference along, the conduit wall also depend on its thickness and permeability. The longitudinal potential difference in rigid steel conduit is considerably larger for external current return paths than for aluminium or thin walled steel conduit. The use of rigid steel conduit grounded before entry to the area may reduce the hazard in installations where even a low potential difference can be hazardous, such as in patient care areas and operating theatres of hospitals. A multiple-bonded conduit may increase the hazard through an increased surface potential gradient.