For a fire alarm system that uses an automatic starting engine-driven generator as the secondary power supply for the dedicated branch circuit, how many hours of capacity must the dedicated storage batteries provide?

For a fire alarm system that uses an automatic starting engine-driven generator as the secondary power supply for the dedicated branch circuit, how many hours of capacity must the dedicated storage batteries provide?

• A. 4
• B. 12
• C. 24
• D. 60

Answer: (A)

When a fire alarm system uses an engine-driven generator as the secondary power source for the dedicated branch circuit, the storage batteries are there to bridge power during the short interval between losing normal power and the generator taking over. This bridging time is designated as four hours of capacity. The idea is that the batteries keep the system energized long enough for the automatic generator to start and supply power without the alarms or controls losing power. If there were no generator, the batteries would need to provide power for a much longer period (for example, 24 hours) to cover a extended outage. So the four-hour requirement reflects the need to cover the transfer period to an automatic standby generator.

When a fire alarm system uses an engine-driven generator as the secondary power source for the dedicated branch circuit, the storage batteries are there to bridge power during the short interval between losing normal power and the generator taking over. This bridging time is designated as four hours of capacity. The idea is that the batteries keep the system energized long enough for the automatic generator to start and supply power without the alarms or controls losing power. If there were no generator, the batteries would need to provide power for a much longer period (for example, 24 hours) to cover a extended outage. So the four-hour requirement reflects the need to cover the transfer period to an automatic standby generator.