What they are, what is required by code and how long they need to supply power
Article By Dennis Bergbauer
A fire alarm system must be able to operate during an emergency condition. If, the incoming power to the fire panel fails, the system must still operate. This is why we need backup, or secondary power feed. This can be accomplished with either batteries or a generator.
Primary power to the fire alarm system can be provided by the electric utility, an engine-driven generator, and Stored-Energy Emergency Power Supply System (SEPSS).
Batteries are a common way to provide a secondary power supply, the most common type of battery is a Lead-Acid battery, and they are typically located within the fire alarm control unit enclosure. If they are not found here they may be in a separate battery box located near the fire alarm control unit. Batteries need to be sized so that they can provide power to the entire fire alarm system for 24 hours in standby and 5 minutes in alarm, if the system is an emergency voice alarm communication system (EVACS), then the batteries need to provide capacity for 24 hours in standby and 15 minutes in alarm. The additional time is required to allow for a longer evacuation time as buildings with an EVACS typically utilize a partial evacuation that would require constant communication with the occupants during the evacuation.
Another common way of providing a secondary power supply for a fire alarm system is the use of an emergency generator designed, installed, and maintained in accordance with NFPA 110. These Emergency generators provides power to the fire alarm system through an automatic transfer switch. If you do choose to utilize an emergency generator, you are still required to provide batteries as well just in case there is an issue with getting the emergency generator started. The batteries in this instance however, only need to provide a capacity for 4 hours in standby.
Instead of providing two separate power supplies, you are permitted to provide power via a Stored-Energy Emergency Power Supply System (SEPSS) otherwise known as an Energy Storage System (ESS) or an Uninterruptible Power Supply (UPS). The SEPSS must be configured in accordance with NFPA 111 and provide 24 hours of backup battery. The SEPSS is also fed via a compliant primary power supply such as utility power or an on-site generator.