Contributions to the Calculation of Reduction Factor of Contact Resistance of the Foot on Grounding Projects

This paper is concerned about the calculation of reduction factor (C_s) of the ground resistance of the foot in contact with the gravel that covers the soil in substations yards, which is an essential parameter to determining the permissible touch and step voltages. It is proposed a new solution method for the equation published in ANSI/IEEE Std 80-2000 [2], from the points of view of numerical and analytical. In addition to proposing alternative procedures for calculation, this article gives a comparative analysis of different expressions of C_s found in the literature focusing on the accuracy of results and the level of complexity that each expression offers in relation to mathematical operations. Numerical results of the proposed solutions are presented.