Fire Alarm Wire Size Chart
Maximum one-way run length for a 24 V notification circuit by wire gauge and alarm load, before the end-of-line voltage falls below the 16 V appliance minimum. Lengths are the conservative case with the full load at the far end. This is the voltage-drop physics read as "how far can I go" instead of "how much voltage is left."
Maximum run length by gauge & load
| Alarm load | 18 AWG | 16 AWG | 14 AWG | 12 AWG |
|---|---|---|---|---|
| 0.5 A | 1020 ft | 1630 ft | 2600 ft | 4140 ft |
| 1.0 A | 510 ft | 810 ft | 1300 ft | 2070 ft |
| 1.5 A | 340 ft | 540 ft | 860 ft | 1380 ft |
| 2.0 A | 250 ft | 400 ft | 650 ft | 1030 ft |
How to use it
Total up the alarm current on the circuit, pick the row at or above it, and read across to the gauge you plan to pull — the number is the farthest the last appliance can sit from the panel. If your run is longer, move down a gauge (18 → 16 → 14 → 12 AWG), split the appliances onto another circuit to cut the per-circuit load, or add a NAC booster power supply closer to the load. The underlying formula and the voltage-remaining view are on the NAC voltage drop chart, and typical appliance currents by candela are on the NAC current draw chart.
Common questions
What wire gauge for a fire alarm NAC circuit?
It depends on the alarm load and how far the circuit runs. Heavier wire carries lower resistance, so it reaches farther before the end-of-line voltage drops below the 16 V appliance minimum on a 24 V system. At a 1.0 A load, 18 AWG reaches about 510 ft while 12 AWG reaches about 2070 ft. Contractors commonly run 18, 16, 14, or 12 AWG fire alarm cable.
How far can a fire alarm circuit run?
As far as the voltage budget allows: the run length where the end-of-line voltage would fall to the appliance minimum. That distance shrinks as the load rises and grows as the wire gets heavier. The chart gives the maximum one-way length for each gauge and load combination; beyond it, you drop to a heavier gauge, split the load across more circuits, or add a booster power supply.
Does this chart assume the whole load is at the end?
These lengths use the total circuit load as if concentrated at the far end, the standard conservative simplification. When appliances are spread along the run, the true drop is smaller, so the real reach is a bit farther — but designing to the concentrated-load figure keeps a safety margin. The exact answer comes from a point-by-point voltage-drop calculation.
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