This standard applies to the Class 1E portions of the following systems and equipment in single-unit and multiunit nuclear power generating stations: -- Alternating current (ac) power systems -- Direct current (dc) power systems -- Instrumentation and control (I&C) 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).