Resistance formulas of grounding systems in two-layer earth

This paper lists, under one umbrella, the resistance formulas of grounding systems, namely : the buried grid, the driven rodbed, and the combination of the buried grid and rodbed. The formulas are synthesized from rigorous asymptotes; as a result, they are accurate (averaged error approximate to 5%) and do not require empirical tables or graphs. The validity of these formulas is verified in this paper, not by their derivations, since they are too lengthy, but by checking numerically, against the results of detailed-numerical methods and analytically, against asymptotes. The formulas are suitable for calculation with a handheld calculator, and therefore they are useful tools for an engineer in the field.