The scope of this project is to summarize the general considerations in grounding of generating station auxiliary power systems, the factors to be considered in selecting between the appropriate grounding classes, and specifying equipment ratings. This guide applies to both medium-voltage (1 kV-15 kV) and low-voltage (less than 1 kV) auxiliary power systems. The intent of this guide is to discuss grounding methods which may be used to limit equipment damage. The emphasis is on reliability and availability of auxiliary power system service, achieved through control of ground-fault currents and transient overvoltages.