Control Units, Power Supplies, and Wiring
Control unit and power
The fire alarm control unit (FACU) receives primary 120 VAC power from a dedicated branch circuit and secondary power from sealed lead-acid batteries. Remote power supplies and NAC extenders add capacity but must be supervised and listed for fire alarm use. The FACU must be grounded and accessible only to authorized personnel.
Wiring methods
NEC Article 760 separates power-limited fire alarm circuits from non-power-limited circuits. Use FPL, FPLR, or FPLP for power-limited wiring; use NPLF, NPLFR, or NPLFP for non-power-limited wiring. Keep fire alarm cable at least 2 in. from power conductors or use a barrier. Support cable at 4.5 ft intervals and within 12 in. of boxes. Firestop penetrations and protect cable in exposed areas.
Supervision
Open and short faults on IDCs, NACs, and SLCs must produce a trouble signal. End-of-line devices, addressing, and isolators are part of supervision. A ground fault on a fire alarm circuit must be detected and annunciated.
Worked example
A contractor installs a remote NAC power supply in a janitor closet and feeds it from a nearby lighting circuit. The installation fails for two reasons: fire alarm equipment needs a dedicated circuit, and the remote supply must be supervised and listed for the purpose. The correction is a dedicated circuit and a supervised connection to the FACU.
Traps
Do not use FPL cable on a non-power-limited circuit. Do not assume a remote power supply is unsupervised. Do not run fire alarm cable in the same raceway as power conductors without a barrier. Do not ignore ground-fault supervision.