NFPA 72 work procedure

NFPA 72 Battery Sizing Workflow

A practical calculation sequence for standby load, alarm load, aging margin, and standard battery size selection.

Page role

Use this page for a defined task before moving to the next project record.

Audience: Engineers, designers, contractors, technicians, and reviewers following a tool-backed workflow.
Job: A practical calculation sequence for standby load, alarm load, aging margin, and standard battery size selection.
Evidence: Listed standby current and alarm current source for each panel, device group, or power supply.; Standby duration, alarm duration, aging margin, and selected standard battery size.; NAC load, source voltage, one-way circuit length, AWG resistance, and end-of-line voltage record.
Output: Device currents come from listed data or a current device schedule, not averages.; Battery calculation uses the required standby/alarm durations and margin for the project basis.; Voltage drop uses one-way circuit length and AWG resistance before end-of-line voltage review.
Next: Start with the related worksheet, run the linked calculators, then retain reviewed values before project use.

1Open the worksheet first when the guide spans multiple calculations or review gates.
2Use each linked calculator only after the input source for that step is known.
3Keep warning states, assumptions, and review notes with the project record.
4Move to the handoff panel after the guide sequence is complete.

Follow the sequence as an engineering workflow: each phase lists the action, tools, and evidence to retain before moving forward.

Phase	Action	Tools	Evidence to keep
Step 1	Collect total standby current for all connected equipment.	Fire Alarm Battery Capacity Calculator	Document the source used to start the NFPA 72 workflow.
Step 2	Collect total alarm current for notification and control loads.	Fire Alarm Battery Capacity Calculator, Fire Alarm NAC Voltage Drop Calculator	Keep calculation notes showing how this step supports: collect total alarm current for notification and control loads.
Step 3	Apply the required standby and alarm durations.	Fire Alarm Battery Capacity Calculator, Fire Alarm NAC Voltage Drop Calculator	Keep calculation notes showing how this step supports: apply the required standby and alarm durations.
Step 4	Apply the aging margin when required by the project basis.	Fire Alarm Battery Capacity Calculator, Fire Alarm NAC Voltage Drop Calculator	Keep calculation notes showing how this step supports: apply the aging margin when required by the project basis.
Step 5	Select the next standard battery size and verify cabinet constraints.	Fire Alarm Battery Capacity Calculator, Fire Alarm NAC Voltage Drop Calculator	Record the reviewed output, warning state, and next review decision.

1Listed standby current and alarm current source for each panel, device group, or power supply.
2Standby duration, alarm duration, aging margin, and selected standard battery size.
3NAC load, source voltage, one-way circuit length, AWG resistance, and end-of-line voltage record.
4Cabinet, power supply, product data, and submittal-review notes tied to the battery/NAC worksheet.

1Device currents come from listed data or a current device schedule, not averages.
2Battery calculation uses the required standby/alarm durations and margin for the project basis.
3Voltage drop uses one-way circuit length and AWG resistance before end-of-line voltage review.
4Battery, NAC, voltage-drop, and product data records match the same circuit and revision.

1Open the fire alarm battery/NAC worksheet before treating the battery result as a circuit record.
2Use the voltage-drop and wire-resistance tools when circuit length or conductor size affects acceptance.
3Carry listed device current, standby duration, alarm duration, and margin into the project record.
4Route unresolved product data or submittal questions to the authority/submittal workflow.

NFPA 72 Battery Sizing Workflow

1Open the fire alarm battery/NAC worksheet before treating the battery result as a circuit record.
2Use the voltage-drop and wire-resistance tools when circuit length or conductor size affects acceptance.
3Carry listed device current, standby duration, alarm duration, and margin into the project record.
4Route unresolved product data or submittal questions to the authority/submittal workflow.