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NFPA 72 2019 · 2022 · free calculator

Fire alarm battery calculation

Enter each load’s standby and alarm current from the data sheet. The calculator applies the standby and alarm times for the system type and the safety factor for your NFPA 72 edition, shows the working, and prints a PDF for the record.

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Factor 1.20 (10.6.7.2.1.1)
24 unless the AHJ or the design asks for more.
Or type the unit: 250mA, 0.25A, 300µA.

Loads — current per unit from the data sheet

= 0.0000 A standby · 0.0000 A alarm
= 0.0000 A standby · 0.0000 A alarm
= 0.0000 A standby · 0.0000 A alarm

Battery required

0.00 Ah

Standby
0.0000 A × 24 h = 0.000 Ah
Alarm
0.0000 A × 5 min = 0.000 Ah
Subtotal
0.000 Ah
× 1.20
minimum 20 percent safety margin (2019, 10.6.7.2.1.1) = 0.000 Ah

Use a battery rated at or above this. Include every load not automatically disconnected on transfer to battery, and check the panel manufacturer’s own calculation.

Questions

What is the formula?

Required amp-hours = (total standby current × standby hours + total alarm current × alarm hours) × the factor. Standby is normally 24 hours; alarm is 5 minutes for a general fire alarm and 15 minutes at maximum load for in-building voice evacuation or mass notification.

Why 1.20 in one edition and 1.25 in the other?

The 2019 edition asks for a minimum 20 percent safety margin on the calculated capacity (10.6.7.2.1.1). The 2022 edition replaced it with a minimum correction factor of 1.25 for battery aging (10.6.7.2.14), so the battery still covers the load near the end of its life. Pick the edition adopted where the building is.

Which loads count?

Every load that is not automatically disconnected when the system transfers to battery — the panel itself, initiating devices, notification appliances in alarm, modules, annunciators, and the communicator that reports to the supervising station.

Does this replace the manufacturer’s battery calculation?

No. Use the current figures from the panel and device data sheets, and check the result against the manufacturer’s own calculation and what your authority having jurisdiction requires.

Put the result on the record

The calculated standby and alarm capacity goes on the record of completion (system power) and the yearly inspection and testing form. Not sure of the edition? Look up your state.