Calculate secondary power supply sizing in compliance with NFPA 72.
Fire alarm designers, low-voltage contractors, and inspectors use a fire alarm battery standby calculation to size secondary power for panels, notification appliances, initiating devices, and auxiliary loads. The worksheet adds standby amp-hours, alarm amp-hours, derating, and installed battery capacity so submittals can be checked against NFPA 72 requirements.
Standby current includes the control unit, initiating devices, modules, power supplies, communicators, and any connected loads that draw current while the system is normal.
Alarm current is usually much higher because notification appliances and control outputs operate. NFPA 72 battery sizing accounts for both standby time and alarm time.
You should follow the adopted code, manufacturer instructions, and project specifications. Many designs include derating or reserve capacity to account for aging, temperature, and discharge characteristics.
No. Required secondary power duration depends on system type, occupancy, monitoring, and adopted code edition. Confirm the applicable NFPA 72 section and local amendments.