Resistance Measurement of Large Grounding Systems

Difficult problems are encountered when the resistance of a large grounding system is measured by the universally used fall-of-potential method. It is the purpose of this paper to analyse the basic factors involved and examine their effects on the accuracy of the measurement. A typical grounding grid, buried in a two- layer soil, is analysed. The results obtained show that the exact location of the potential probe is influenced considerably by the size and arrangement of the return electrode and by the characteristics of the soil. The paper presents several curves and charts which are useful to evaluate these effects and avoid errors during the interpretation of the measurement results.