In response to the demand for the design and measurement of grounding loops in high-voltage substations, Measuring Ground Resistance and Ground Potentials addresses the basic concepts of an electrical grounding loop, measuring ground resistance and ground surface potentials in the loop. The procedures currently used for measurements will be shown, which are based on the IEEE Std. 81-2012 - Guide for Measuring Earth Resistivity, Ground Impedance, and Earth Surface Potentials of a Grounding System and ABNT NBR 15749-2009 - Measurement of grounding resistance and ground surface potentials in grounding systems. Finally, the aim of this work is to validate an existing method by means of a case study for a substation grounding grid with a supply voltage of 69kV, which seeks to provide a safe assessment of a system. The study is presented, containing real data obtained from carrying out the tests that will be mentioned.