National Electrical Code ExplanationsBased on the 2014 NEC
National Electrical Code Tips: Article 760, Fire Alarm Systems, Part 6
All of the following tips apply to Power Limited Fire Alarm (PLFA) circuits.
- 760.139 provides the rules for installing conductors of different PLFA circuits, Class 2, Class 3, and Communications circuits in the same enclosure. Also applies if installed in the same cable, cable tray , raceway, or cable routing assembly.
- 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 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].
- For low-power network-powered broadband communications cables, 760.139(A) also applies [760.139(C)].
- Audio system circuits 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)].
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].
You cannot use the exterior of any raceway as a means of support for PLFA conductors [760.143].
- You can use listed continuous line-type fire detectors, but you must install them per 760.124 through 760.130 [760.145].
- Wanting to substitute fire alarm cable types? See Figure 760.154(A) and Table 760.154(A).
- 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.
How the NEC is arranged
- The first four Chapters of the NEC apply to all installations.
- Article 90 precedes Chapter One, and establishes the authority of the NEC.
- Article 80 follows the body of the NEC; it exists as Annex H. It provides the requirements for administration.
- Chapters 5, 6, and 7 are the "special" chapters, covering special: occupancies, equipment, and conditions (in that order).
- Chapter 8 provides the requirements for communications systems.
- Chapter 9 provides tables.
- The appendices provide mostly reference information.
- Appendix D contains examples that every NEC user should study.
Try your NEC moxy:
- Do you know the difference between bonding and grounding? Hint: Look in the NEC, Article 100.
- Does the NEC refer to grounding incorrectly in any of its articles? Yes! So be careful to apply the Article 100 definitions. Don't ground where you should bond.
- When doing motor load calculations, which Article covers hermetic motors? Answer: While Article 440 covers the application of hermetic motors, it does so only by amending Article 430 because hermetic motors are a special case of motors. For motor load calculations, refer to Article 430.
- Does the NEC provide a voltage drop requirement? Yes! It does so in a special case, which is Article 648 Sensitive Electronic Equipment. But for general applications, it does not provide a requirement; it merely provides a recommendation in a couple of FPNs.
- Take our Code Quizzes.
Remember other applicable codes, rules, standards, and references:
- OSHA's electrical worker safety rules.
- IEEE standards.
- NETA standards.
- NFPA standards.
- International Codes (if applicable to the installation).
- State Codes (if the state has them).
- Local ordinances and permit requirements.
- Local fire codes.
- Manufacturer requirements or guidelines.
- Customer security requirements.
- Industry standards.
- Your company's own internal standards, practices, and procedures.
- Engineering drawing notes.
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