Fire Alarm NAC Calculator

Notification appliance circuit load and voltage drop.

Horn/strobes

Strobes only

Horns only

Circuit length (ft)

Wire gauge

Supply voltage (VDC)

Tab to move between fields

Total circuit current (A)

2.46

Voltage drop (V)

6.35

End-of-line voltage (V)17.65

Voltage acceptableYes

Current within ratingYes

NAC circuits needed1

Devices per circuit15

Total devices15

Total power (W)59

Battery for alarm (Ah)0.25

Wire Gauge Label14

How to Use This Calculator

How the result changes with Horn/strobes

Horn/strobes: Number of combination horn/strobe devices (typical draw ~0.177A each).
Strobes only: Number of strobe-only devices (typical draw ~0.138A each).
Horns only: Number of horn-only devices (typical draw ~0.060A each).
Circuit length (ft): One-way wire run from panel/booster to the last device on the circuit.
Wire gauge: 1=14 AWG (2.58 Ω/kft), 2=12 AWG (1.62 Ω/kft), 3=10 AWG (1.02 Ω/kft).
Supply voltage (VDC): NAC panel output voltage (typically 24 VDC nominal).

Total circuit current (A): Sum of all device current draws on the circuit.
Voltage drop (V): Voltage lost in wire resistance (I × R × 2 for round trip).
End-of-line voltage (V): Voltage available at the last device. Must be ≥16V for most devices.
Voltage acceptable: Whether end-of-line voltage is >=16V. If No, use heavier wire or split circuit.
Current within rating: Whether circuit is under 2.5A NAC limit. If No, split into multiple circuits.
NAC circuits needed: Number of circuits required to keep each under the 2.5A limit.
Devices per circuit: Recommended device count per circuit if splitting.
Total devices: Total notification appliances on the circuit.
Total power (W): Total power consumption of the NAC.
Battery for alarm (Ah): Battery capacity for 5-minute alarm duration with 20% safety factor.

Identify Input Parameters
4 parameters
Horn/strobes = 10, Strobes only = 5, Horns only = 0, Circuit length (ft) = 500 = 6 input(s) provided
Calculate Total circuit current
Total circuit current = numHornStrobes * currentHornStrobe +
2.46 = 2.46
Calculate Voltage drop
Voltage drop = totalCurrent * roundTripResistance
6.35 = 6.35
Calculate End-of-line voltage
End-of-line voltage = supplyVoltage - voltageDrop
17.65 = 17.65
Calculate Voltage acceptable
Voltage acceptable
Yes = Yes