In-building fire emergency voice/alarm communications systems require what secondary power supply capacity?

• A. 24 hours standby plus 15 minutes of all connected load
• B. 8 hours standby plus 30 minutes of load
• C. 12 hours standby
• D. 24 hours standby only

Answer: (A)

The main idea is that emergency voice/alarm systems must stay operable during a power outage. To ensure this, the secondary power supply is sized to provide both long standby and sufficient run time at full load.

24 hours standby keeps the system ready without mains power for a full day, so warnings and monitoring can continue even during extended outages. At the same time, 15 minutes of all connected load guarantees the system can deliver full-power announcements across all connected devices (speakers, amplifiers, control gear) for a sufficient initial evacuation window if an alarm is triggered. This combination ensures the system is both ready and capable during an emergency.

Other options don’t meet both needs: they either shorten standby time, reduce the duration of full-load operation, or both, which could compromise evacuation communications.