Step Potentials and Body Currents Near Grounds in Two-Layer Earth

The equations customarily used in safety calculations for grounding electrodes assume that soil conductivity does not vary with depth. A more realistic model assumes that the soil consists of two horizontal layers of different conductivity. This may occur, for example, if a thin surface layer consists of wet soil, thawed soil, or concrete, and a thick layer of underlying soil is frozen, or consists of rock or dry soil. Such conditions markedly change the step voltage, contact resistance, and body current a creature on the surface will experience in the vicinity of a buried ground electrode. Equations are presented for voltage, voltage gradient (step voltage), contact resistance, body current, and electrode resistance in the vicinity of a ground electrode in the shape of a long buried wire in a two-layered earth. Graphs are also presented to give a quantitative and qualitative understanding of the effect of such layering on step voltage and body current.