Home Fire Detection System Design To be in conduit or not is the question! When installing a fire alarm system according to NFPA and NEC 90 articles, any fire alarm cable below 7 feet or in non-accessible areas must be installed in a metallic raceway.
Bare wires can inevitably touch the wrong places: Hot wire to neutral wire means a short circuit that causes sparks to fly; hot wire to grounding wire, or to grounded metal box means ground fault and possible shock.
Fire alarm cables are placed into three broad categories: plenum, non-plenum, and riser. Each of these corresponds to another standardized category, and these terms reflect where the fire alarm cable can be installed safely. Plenum cable, to be used in ducts or other enclosed air spaces, is called FPLP. （Read FPL vs FPLR vs FPLP Fire Alarm Cable)
Either a 15-amp circuit (wired with 14-gauge wire) or a 20-amp circuit (wired with 12-gauge cable) is acceptable for powering hardwired smoke detectors. Then, a 2-wire cable is run from the power source to the first smoke detector.
