Abstract
Erling D. Sunde obtained an equation for the underground vertical electrodes resistance in a groundbed configuration, with the top of the electrode at the earth surface. The Average Potential Method (APM) and the method of images were used to obtain this equation; all the anodes having the same length. W. Von Baeckmann, et al, presented an equation for vertical electrodes, where the distance from the top of the electrode to the ground surface is taken into account; all of the vertical electrodes have the same length. Also the distance from the top of the electrode to the soil is a non-zero constant value for all of the electrodes. There is not a generalized resistance equation where the distance between the anodes, soil surface and the length of the anodes vary.
The APM calculates the electrode potential to remote earth in regards to the current distributed on the electrode axis, averaging the potential value at a point in the electrode surface over the entire electrode length, through an integration process. The influence of parallel electrodes is included with an integral-matrix approximation, as an interference factor that increases the total groundbed resistance as a function of anode length, distance to soil surface and separation between anodes.
