A Graphical Explanation of the Resistance and Surface-Potential Calculations for Grounding Systems in Two-Layer Earth

Comprehensive equations for calculating grounding resistances and surface potentials associated with grounding systems are readily available. However, these are not always readily understood in a physical sense. Easily-constructed image location maps and reflection diagrams are introduced to explain the method of images as it is applied to the calculation of grounding resistances for horizontal and vertical rods in two-layer earth. The relationships between this set of diagrams and the corresponding analytical equations for resistances and surface potentials are explored. The use of generalized equations involving numerical integration is discussed.