Resistivity testing for earthing safety

One of the fundamental building blocks for reviewing, modelling, and predicting the safety of an earthing system is the soil resistivity. To determine the soil resistivity measurements are taken on site. For power system reviews, a number of test methods have been developed, particularly the Wenner and Schlumberger methods. The Wenner and Schlumberger methods use four probes in the ground. Generally the Wenner method is the preferred method, as the set up and understanding of this method is much simpler. We have developed a test method, which only requires one probe to be shifted and gives the same results as the Wenner method. This method takes less time to conduct a traverse, meaning that the testing cost can be reduced, or that twice as many tests can be conducted, giving a wider knowledge of the soil structure across a site. This paper presents the new test methodology. Several case studies are also provided.