The design of an emergency power design extends beyond just the electrical aspects of the electrical generation and load transfer equipment. In the event a generator fails to start or enter an overload condition, steps must be taken to selectively reduce the emergency load to a level allowing the generator plant to support higher-priority loads. A brief description is given for some general emergency system design considerations followed by a discussion of selective load shed through the facility’s building automation system (BAS).
The essential electrical system (EES) provides three separate branches for distribution of generator standby power. Each branch is provided with at least one automatic transfer switch (ATS) as required by National Fire Protection Association (NFPA) 70 National Electrical Code (NEC) Article 517 for an EES greater than 150 kVA.