What is the function of the secondary power supply in a fire alarm system?

• A. To power only notification appliances during normal operation
• B. To provide backup power during scheduled maintenance
• C. To automatically provide power whenever the primary fails to provide minimum voltage
• D. To recharge the primary power source during a power outage

Answer: (C)

The key idea is that the backup power keeps the fire alarm running when the main power isn’t able to meet the load. In a fire alarm system, the primary power comes from the building’s electrical supply, while the secondary power supply (a rechargeable battery or similar source) is kept charged and ready. If the primary source drops below the minimum voltage or fails, the system automatically switches to the secondary supply, so the alarm controller and all notification devices continue to operate without interruption. The secondary is recharged when normal power is available, but its job is to supply power during outages or voltage drops, not to power everything only during maintenance or to recharge the primary during a blackout.