This standard applies to the Class 1E portions of the following systems and equipment in single unit and multi-unit nuclear power generating stations: alternating current power systems; direct current power systems; and vital instrumentation and control systems. This standard also contains requirements for non-Class 1E interfaces such as the preferred power supply. The purpose of this standard is to provide: the principal design criteria and the design features of the Class 1E power systems that enable the systems to meet their functional requirement under the conditions produced by the applicable design basis events; and the requirements for surveillance of the class 1E power systems.<