In industrial facilities generally characterized by grounding grids, the
earth resistance measurement can be facilitated in the presence of
metal bodies embedded in the earth (e.g., EXCPs such as underground
cold water pipes). If such metalwork extends well beyond the facility’s
area and has an estimated negligible resistance-to-ground (i.e.,
REXCP
RG), it can be used at the same time both as a current and as
a potential electrode (Fig. 14.7).