Div 28 · NFPA 72

Battery & NAC Calc

NFPA 72 secondary-power (battery) sizing and notification-circuit loading. Spec/estimating support — verify against the Simplex battery calculator and the AHJ-adopted NFPA 72 edition.

Secondary Power (Battery)

Total standby current (A)Total alarm current (A)

Standby (hours)Alarm (minutes)

Standby capacity20.4 Ah

Alarm capacity0.267 Ah

Subtotal × 1.2 derate20.667 Ah

Required battery24.8 Ah

NAC / IDNAC Loading

Connected alarm current (A)Circuit rating (A)

Usable3 A

Load2.4 A

Utilization80%

Capacity = (standby 0.850A × 24h + alarm 3.200A × 0.083h) × 1.2 derate.
Standby duration: 24h is typical for protected-premises systems; some occupancies/ECS require 60h. Alarm: 5 min typical; voice/ECS often 15 min. Confirm per the AHJ-adopted NFPA 72 edition.
Verify final battery against the Simplex panel battery calculator and the FACP charger capacity (e.g. 4010ES charges to 110 Ah).
Sum per-appliance ALARM current at the field-set candela (each candela tap draws a different current — see the appliance datasheet current table).
Conventional 24 VDC NAC: also verify end-of-line voltage ≥ the appliance minimum (16–17 VDC typical) given wire gauge + run length. IDNAC (constant 29 VDC) supports T-tapped Class B and longer runs — size with the Simplex IDNAC P2P designer.