Wiring Outside the Box

Normally, the fire alarm initiating device, notification appliance and signaling line circuits are not run outside the building. When we have no choice but to run them overhead or underground, locating the applicable rules in NFPA 72 can be tough...


Normally, the fire alarm initiating device, notification appliance and signaling line circuits are not run outside the building. When we have no choice but to run them overhead or underground, locating the applicable rules in NFPA 72 can be tough. It’s especially tough when 72 refers you to an entire code section in another standard to find the information you’re looking for. In the “Fundamentals” chapter of the National Fire Alarm Code, we find the following:

“4.4.4.3 Transient Protection. To reduce the possibility of damage by induced transients, circuits and equipment shall be properly protected in accordance with the requirements of NFPA 70, National Electrical Code, Article 800.”

In the next section, 4.4.4.4, NFPA 72 requires compliance with the NEC, and adds “specifically” with Article 760. Only two parts of Article 760 apply to our power limited wiring methods. And it says “See Parts I and III” for the power-limited wiring rules. Part I of 760 contains a single sentence declaration of the “Scope” of Article 760, a few definitions, followed by a list of 11 other NEC Articles that also apply to 760.
As it turns out, Article 760 gives more precise directions for locating the transient protection rules we’re looking for:

“760.32 Fire Alarm Circuits Extending Beyond One Building. Power-limited fire alarm circuits that extend beyond one building and run outdoors… shall meet the installation requirements of Parts II, III, and IV of Article 800…”

Article 800 looks to only be about telephone wiring, and in fact, is named “Communication Systems.” Upon closer scrutiny, the “Scope” of Article 800 states that it covers “communications circuits and equipment.” Article 800 then defines a communication circuits as:

“The circuit that extends voice, audio, video, data, interactive services, telegraph (except radio), outside wiring for fire alarm and burglar alarm from the communications utility to the customer’s communications equipment up to and including terminal equipment such as a telephone, fax machine, or answering machine.”

Finally, we’ve found the outdoor wiring rules that cover fire alarm (and burglar alarm) wiring that’s run outside a building or structure. Reading further we find that transient protectors are required by Article 800 to be installed at both ends of these outdoor building-to-building circuits and, of course, “listed for the purpose”:

“III. Protection, 800.90 Protective Devices. (A) Application. A listed primary protector shall be provided on each circuit run partly or entirely in aerial wire or aerial cable not confined within a block. Also, a listed primary protector shall be provided on each circuit, aerial or underground, located within the block containing the building served so as to be exposed to accidental contact with electric light or power conductors operating at over 300 volts to ground. In addition, where there exists a lightning exposure, each inter-building circuit on a premises shall be protected by a listed primary protector at each end of the inter-building circuit.”

Communication circuit surge suppressors are listed as UL 497, UL 497A and/or UL 497B.

UL 497B applies to data communication and fire alarm circuit protectors (communication alarm-initiating or alarm-indicating loop circuits). The title for UL’s standard 497B is “Protectors for Data Communications and Fire-Alarm Circuits.” The scope of this standard is provided by UL:

“1.2 As covered by these requirements, data communications circuit protectors and fire-alarm circuit protectors consist of single- and multiple-pair air-gap arresters, gas-tube arresters, or solid-state arresters, with or without fuses or other voltage-limiting devices. Data communications circuit protectors and fire-alarm circuit protectors are intended to protect equipment, wiring and personnel.”
Remember, you cannot meet NFPA 72 requirements and install wiring in violation of any manufacturer’s installation instructions, even if the NEC allows it. In all cases, the manufacturer’s installation instructions must be followed and supersede the minimum standards printed by NFPA.