Analysis of Current Density in Soil for Resistivity Measurements and Electrical Grounding Designs

The design of electrical grounding systems is crucial to ensure people's safety and equipment integrity. The performance of the grounding system is critically dependent on the characteristics of the local soil surrounding the grounding system. Some wrong concepts and assumptions on soil electrical properties are still prevalent among professionals regarding soil resistivity measurements and grounding designs. The objective of this paper is to examine the current density in the earth surrounding measurement electrodes and electrical grounding systems and discuss the effects of soil structures on measurements and grounding related studies. The analyses described here are based on electromagnetic field theory. First, this paper examines soil resistivity measurements using the Wenner method in three typical, but different soil structure models, by exploring the distribution of earth current density in the soil surrounding the current injection electrodes. The computed results are illustrated using appropriate plots to understand better the influence of soil structure and characteristics on the current penetration across the soil layers. Furthermore, a detailed study on the influence of nearby buried grounding systems on soil resistivity measurements was also carried out. Finally, the performance of grounding systems in the three soil structure models has been studied in order to gain an intuitive understanding of the effects of soil structures on grounding. The results clarify and invalidate some misleading arguments used by a few practicians. All computed results are summarized in appropriate tables and figures which should provide helpful visual clues and useful information when planning soil resistivity measurements and designing electrical grounding systems.