This paper describes the auxiliary electric power system for the Diablo Canyon Nuclear Plant of the Pacific Gas and Electric Company. The power systems covered are the medium and low voltage distribution systems, the standby and startup systems, and the emergency and engineered safety features systems. Also covered are the selection of voltages, methods of neutral grounding, and automatic transfer to standby power. A discussion is also included for the systems with the largest loads: the main condenser cooling water system and the reactor coolant system.