Important Intricacies: Fire Alarm System Requirements in the NEC

By Mark C. Ode | Oct 15, 2018
Code Applications October 2018




One of my passions, other than the National Electrical Code (NEC), has been fire alarm systems, as covered by NFPA 72, National Fire Alarm and Signaling Code. When I was a licensed electrical contractor in the Phoenix area in the 1970s and '80s, I specialized in design-build fire alarm systems with about 50 percent of my business devoted to fire alarms. This passion continued when I went to work for NFPA in the 1990s, since I spent between four and five years as the temporary staff liaison for the NFPA 72 committees.

For the past 15 years, I have been a member of NEC Panel 3, which has jurisdiction over Article 725, covering Class 1, Class 2 and Class 3 remote-control, signaling, and power-limited circuits, and Article 760, covering the installation of wiring and equipment of fire alarm systems. I mention Article 725 since many of the Class 1, Class 2 and Class 3 control circuits are associated with fire alarm systems, such as circuits for fire damper controls and fan shutdown, building system safety functions, and other control circuits powered by and controlled by the fire alarm system.

I recently received a question about a fire alarm system installation where I had to provide a detailed explanation on the requirements for splice boxes for smoke detectors and other related fire alarm devices. Many electricians, ECs, and electrical inspectors may have the same problem involving these installations as the person who emailed me, so coverage of these requirements may be worthwhile.

Article 760 covers two different fire alarm circuits. The first is classified as non-power-limited fire alarm (NPLFA) circuits, and the second one is a power-limited fire alarm (PLFA) circuit. Abbreviations can be difficult to understand and not easily remembered, so in this article, I write them out; however, they are worth knowing.

The requirements for circuit wiring of non-power-limited circuits is located in 760.46 and states that these "circuits shall be in accordance with 110.3(B) [install and use in accordance with listing and labeling instructions], 300.7 [exposed to different temperatures], 300.11 [securing and supporting], 300.15 [boxes or fittings-where required], 300.17 [number and size of conductors in raceways], 300.19(B) [supporting fire rated cables and conductors in a vertical raceway] and other appropriate Articles of Chapter 3 [different wiring methods as may be used]."

These requirements in 760.46 are similar to any other non-power-limited source where the output of the power source is not more than 600 volts (V) nominal and, thus, must provide both shock protection and fire initiation protection as would any other normal power circuit. Non-power-limited cables (as opposed to normal 600V conductors in wiring methods based on Article 300) complying with 760.176 shall be permitted to be used on fire alarm circuits operating at 150V or less. Obviously, boxes would be required for any splicing of any non-power-limited fire alarm circuit.

Part III of Article 760 covers power-limited fire alarm circuits with the output of the power-limited source based on the listing requirements in Tables 12(A) and 12(B) in Chapter 9. These two tables provide power limitation for power-limited fire alarm circuits of a maximum power source nameplate rating of 100 volt-amperes for both alternating current and direct current circuits. Wiring methods and materials on the load side of the power-limited power source are covered in 760.130(A) and (B).

Non-power-limited fire alarm wiring can be used for power-limited fire alarm circuits based on 760.130(A) and requires a box as noted in the above paragraph. Section 760.130(A), Exception No. 3 permits power-limited circuits to be reclassified and installed as non-power-limited circuits if the power-limited markings are eliminated and the entire circuit is installed using wiring methods and materials of Part II of Article 760, such as non-power-limited thermostats and similar equipment. Splice boxes would be required for reclassified circuits consistent with non-power-limited circuits.

Where power-limited wiring methods are used, 760.130(B) would apply as follows: "Power-limited fire alarm conductor and cables described in 760.179 shall be installed as detailed in 760.130(B)(1), (B)(2), or (B)(3) of this section and 300.7. Devices shall be installed in accordance with 110.3(B) [install and use in accordance with listing and labeling instructions], 300.11(A) [securing and supporting], and 300.15 [boxes or fittings—where required]."

Can a splice be installed in the power-limited fire alarm circuit without a box? Section 300.15(B) would permit the splice to be in an integral junction box or wiring compartment of approved equipment. Section 300.15(F) permits a fitting to be used in lieu of a box but not for a splice or termination in the fitting, so a box would be required for a splice in a power-limited fire alarm circuit.

About The Author

ODE is a retired lead engineering instructor at Underwriters Laboratories and is owner of Southwest Electrical Training and Consulting. Contact him at 919.949.2576 and [email protected]

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