Fire Alarm and Signaling Systems
Code and standard
NEC Article 760 governs fire alarm wiring: non-power-limited fire alarm circuits (NPLFA, 760.41) and power-limited fire alarm circuits (PLFA, 760.121 through 760.130). NFPA 72 governs system performance, initiation, notification, and pathway survivability. In Minnesota, plans are reviewed and the installing company must be properly licensed; the PLT scope often covers the low-voltage field wiring.
Design points
- PLFA cable is listed FPLR, FPLP, or FPL; NPLFA uses NPLF types. Plenum spaces require the P suffix.
- 760.130 separates PLFA conductors from power and Class 1 circuits; 300.22(C) applies in air-handling spaces.
- 760.41 and 760.43 cover NPLFA overcurrent protection and conductor sizing.
- NFPA 72 pathway survivability Levels 0 through 4 set how long circuits must remain operational during a fire; higher levels are common in high-rise and protected-premises designs.
- Notification appliance circuits are supervised and must deliver the appliance-rated voltage at the last device, not just at the panel.
Worked example
A 24 V NAC draws 1.0 A and runs 250 ft on 14 AWG. Table 9 resistance is about 3.07 Ω per 1,000 ft. VD = 2 × 250 × 0.00307 × 1.0 = 1.5 V, so the last device sees about 22.5 V. That is above a 20.4 V listed minimum, so the circuit passes. Doubling the length would drop about 3.1 V and likely fail.
Traps
- Mixing PLFA and NPLFA cable types in one circuit.
- Using riser-rated cable in a plenum.
- Checking voltage only at the panel terminals.
- Treating supervision and pathway survivability as the same requirement.