This standard applies to the Class 1E portions of the following systems and equipment in single-unit and multiunit nuclear power generating stations: AC power systems DC power systems Instrumentation and control (IC) power systems This standard does not apply to the preferred power supply; the unit generators and their buses; generator breaker; step-up@ auxiliary@ and start-up transformers; connections to the station switchyard; switchyard; transmission lines; and the transmission network (see Figure 2 and Figure 3). Purpose The purpose of this standard is to provide the following: The principal design criteria and the design features of Class 1E power systems that enable the systems to meet their functional requirements under the conditions produced by the applicable design basis events The requirement for tests and surveillance of Class 1E power systems The criteria for sharing Class 1E power systems in multiunit stations The requirement for documentation of Class 1E power systems