Overview

The primary objective of all emergency and standby electric power systems is the safety of building occupants following a power outage. The danger to occupants during an outage is increased in the presence of smoke, chemical fumes, fire, or earthquake, adding urgency to any required evacuation of the building.

At the very least, emergency and standby power systems should provide lighting to assure the safe, panic-free exit of people from the building. If an outage occurs during a severe storm, emergency power systems will provide minimal lighting for people taking refuge in or remaining in the building until normal power is restored or the storm abates.

The secondary objective of these systems is the protection of property during loss of normal power. By picking up at least part of the load following an outage, minimal lighting will be restored, security systems will remain active, and critical building services such as heating in the winter or ventilation in the summer will be maintained.

Emergency or standby power will also permit orderly shutdown of computer systems or their continued operation to preserve vital data. In stores, active security systems can prevent theft; in large restaurants and cold storage warehouses, loss of perishable food can be prevented; and in factories, loss of materials in process can be avoided.

This chapter covers National Electrical Code (NEC) requirements for emergency systems and explains the differences between legally required and optional standby systems. Uninterruptible power supplies (UPS) and standby systems are discussed, and...