Define standby power duration and its importance in NFPA 72 compliance.

• A. Standby power duration is the time a fire alarm system must operate on battery/backup power without mains power; typically 24 hours.
• B. Standby power duration is the time to test the system.
• C. Standby power duration is the time to install the system.
• D. Standby power duration is the time to recharge the battery after a discharge.

Answer: (A)

Standby power duration is the length of time the fire alarm system must run on backup power when the main power is lost. This matters for NFPA 72 because life-safety signaling, monitoring, and annunciation need to stay functional during an outage, at least for the specified duration, until power returns or another arrangement is in place. Backup power sources—typically batteries or other independent power supplies—must be sized to support the full load for that period. In many cases this duration is specified as about 24 hours, which drives how batteries are sized, how the system is designed to manage power, and how it’s tested for reliability. If standby duration were shorter, critical alarms and monitoring might fail during longer outages, compromising safety. Standby duration is not about testing time, installation time, or recharge time after a discharge.