Section 10.6.1/Fire Alarm System Power Supply
NFPA 72 Section 10.6 covers fire alarm system power supply requirements including primary and secondary power sources, battery calculations, and transfer time.
Fire alarm systems must have two independent power sources: a primary supply and a secondary (standby) supply. The primary supply must be a dedicated branch circuit from a commercial power source, connected ahead of any disconnect serving the building (or, if connected downstream, provided with a mechanical lock in the on position). The secondary supply must be either storage batteries or an automatic-starting engine- driven generator with 4 hours of battery bridge power. For battery-only secondary supply, the batteries must support the system in supervisory (standby) mode for 24 hours followed by 5 minutes of alarm operation at full load. Systems with an approved generator may reduce the battery standby to 4 hours. Transfer from primary to secondary power must occur within 30 seconds and must not cause loss of signals or system functions. Battery calculations must account for all connected loads during standby (panel quiescent current, detector supervisory current, LED indicators) and during alarm (notification appliance current at maximum connected load).
Why this section exists
Fire alarm systems must be operational during power outages, which frequently coincide with emergency events (storms that cause both power failures and fires). The 24-hour standby plus 5-minute alarm requirement ensures the system can detect and announce a fire even after a full day without primary power. The dedicated circuit requirement prevents the fire alarm from being inadvertently de-energized during maintenance on other building systems. The NEC Article 760 establishes the electrical wiring requirements for these circuits, while NFPA 72 establishes the functional requirements for the power supply system as a whole.
What plan reviewers look for
Plan reviewers check the fire alarm riser diagram for the primary power source (dedicated circuit, breaker identification, lock-on provisions). They verify the secondary power source (battery or generator-with-battery-bridge) and check the battery calculation for 24 hours standby plus 5 minutes alarm. They verify the battery calculation includes all connected loads: panel standby current, initiating device supervisory current, and notification appliance alarm current. They check that the battery type and capacity are specified on the drawings. For systems with a generator backup, they verify the 4-hour battery bridge and automatic transfer switch arrangement.