Soil electrical resistivity is a key factor when determining the design of the grounding system for new installations and is strongly affected by thecontent of electrolytes in the soil, its moisture content, and its temperature.Appropriate soil surveys and models are the basis of all earthing designs, and they are accomplished from an accurate soil resistivity testing.
The test method involves placing four equally spaced and in-line electrodes into the ground. The two outer electrodes (current electrodes) inject current into the soil. The two inner electrodes(potential electrodes) measure voltage, which is then used to calculate soil resistance.
Soil resistivity influences the plan of an earthing system absolutely and is the major factor that decides the resistance to earth of a grounding system. Thus, before designing and installing a new grounding system, the determined location should be tested to find out the soil’s resistivity.