Conservative measurements of touch and step voltages by auxiliary electrodes at reduced distance

Abstract

Protection against electric shock requires grounding systems that must be designed primarily to keep touch voltage and step voltage below a safe value. The measurement of the ground resistance in a large grounding network requires to place current electrodes at adequate distances. In urban areas, buildings grow adjacent each other, and the choice of suitable locations for auxiliary electrodes becomes increasingly difficult; rigorous ground resistance measurements may result practically impossible. The measurement of touch voltage and step voltage can be done by a simplified conservative testing method based on using one or more current electrodes at short distances. An error is caused by the leakage current distribution around the ground electrode increasing the gradients in the area influenced by the auxiliary electrodes at short distance. The paper demonstrates how effectively the measurements of surface potentials with the auxiliary electrode at reduced distance are always conservative, because the error is positive. A simulation program has allowed to confirm these effects.