The influence of seasonal soil moisture on the design of grounding systems

This paper discusses the influence of the moisture content on the seasonal behavior of soil resistivity and on the ground resistance of protection systems. Laboratory tests show that this influence is very large on the resistivity of several types of soil, although field researches indicate a wide variation in the resistivity and moisture content only in the topmost layers of the soil. However, this variation may significantly change the ground resistance values of systems with small dimensions, thus compromising the performance of protection systems of electrical installations. The strong correlation between the soil moisture, and consequently the soil resistivity, and monthly rainfall values allows extrapolating resistivity measurements for the most critical conditions and thus improving the design of grounding systems.