National Electrical Code Explanations

Based on the 2020 NEC

by Mark Lamendola

National Electrical Code Tips: Article 760, Fire Alarm Systems, Part 6

All of the following tips apply to Power Limited Fire Alarm (PLFA) circuits.

  1. 760.139 provides the rules for installing conductors of different PLFA circuits, Class 2, Class 3, and Communications circuits in the same enclosure. It also applies if those are installed in the same cable, cable tray , raceway, or cable routing assembly.
  2. You can install two or more PLFA circuits, communication circuits, or Class 3 circuits in the same enclosure, cable, cable tray , raceway, or cable routing assembly [760.139(A)]. Notice that Class 2 is conspicuously absent from this list..
  3. Just previous to this point, we didn't mention Class 2 circuits. The same rule as 760.139(A) applies to them, but only if the insulation of the Class 2 conductors is at least at the level required by the PLFA circuits. That is, if your PLFA circuits require 600V insulation then so will any Class 2 circuit conductors you run with them [760.139(B].

  4. For low-power network-powered broadband communications cables, 760.139(A) also applies [760.139(C)].
  5. Audio system circuits described in 640.9(C) installed using Class 2 or Class 3 wiring methods cannot be installed with PLFA circuits (that is, 760.139(A) does not apply to them) [760.139(D)].


  6. To use 26AWG conductors, you must ensure they are spliced only with a connector listed as suitable for 26AWG to 24AWG or larger conductors that are terminated on equipment. Or, you can use them where they terminate on equipment is listed as suitable for 26AWG conductors. Single conductors can't be smaller than 18AWG [760.142].

  7. You cannot use the exterior of any raceway as a means of support for PLFA conductors [760.143]. You can't use the exterior of any raceway as a means of support for anything, actually.

  8. You can use listed continuous line-type fire detectors, but you must install them per 760.124 through 760.130 [760.145].
  9. Wanting to substitute fire alarm cable types? See Figure 760.154(A) and Table 760.154(A).
  10. Note that when using Table 760.154(A), it also indicates where no substitution is permitted. Pay attention to whether an N or a Y appears where the cable types intersect (merely intersecting is not telling you the whole story). Also, no substitutions are permitted in plenum cable routing assemblies, so if you have those don't bother looking in the table.