NEC (NFPA 70) Requirements for Fire Alarm Circuits
Domain 1 - NEC (NFPA 70) Requirements for Fire Alarm Circuits
Article 760 is the spine of this domain. The exam tests whether you can classify a fire alarm circuit, choose the correct wiring method, and keep fire alarm conductors separated from everything else.
Power-limited vs. nonpower-limited
- NPLFA (Part II) - nonpower-limited fire alarm circuits: typically 120 V control circuits, or 24 V circuits that are not supplied from a listed power-limited source.
- PLFA (Part III) - power-limited fire alarm circuits: supplied from a listed power-limited source and wired with listed fire alarm cable. A circuit stays power-limited only when the source is listed as such and the wiring method matches Article 760.
Cable and separation
PLFA cable is marked FPL (general use), FPLR (riser - vertical runs between floors, in shafts), or FPLP (plenum - installed in environmental air spaces). Conductors are copper. Fire alarm conductors must be separated from electric light, power, and Class 1 circuits by a raceway, barrier, or listed assembly; you cannot pull FPL through the same conduit as 120 V branch circuits.
Installation
Article 300 applies except as modified: secure and support the cable, protect it from physical damage where exposed, and use boxes and fittings listed for the purpose. The fire alarm branch circuit is dedicated to the fire alarm system and must have a means to prevent accidental disconnection.
Worked example
A circuit leaves a panel in an electrical closet, crosses a corridor above a lay-in ceiling that is a return-air plenum, then rises two floors. Above the ceiling use FPLP. In the vertical shaft use FPLR. In the closet, FPL is acceptable. It may not share the 120 V EMT at any point.
Traps
Using FPL in a plenum; ignoring riser ratings; assuming "power-limited" allows mixing with power conductors; forgetting physical protection where cable is exposed.