Why do we provide surge suppression on fire alarm circuits? The simple answer is to protect the fire alarm system from power surges caused by nearby lightning or a power surge originating from within the protected premises. The detailed answer is a bit more complicated.
First, we looked into NFPA 72, the National Fire Alarm and Signaling Code (2022 edition) Section 12.2.3.3 which states, “Fire alarm system wiring and equipment, including all circuits controlled by and powered by the fire alarm system, shall be installed in accordance with the requirements of this code and NFPA 70 Article 760.”
Next, we reviewed the reference to the National Electric Code, NFPA 70 (2023 edition) Article 760.32 which says, “Non-power-limited fire alarm circuits and 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 805 and shall meet the requirements of Part I of Article 300.”
The relevant portion here is the reference to Article 805. Article 805.90(A) Application states, “… where there exists a lightning exposure, each interbuilding circuit on premises shall be protected by a listed primary protector at each end of the interbuilding circuit.” This applies to the fire alarm conductors running from a building to a fire pump house as well as a fire alarm circuit running from a building to an indicator post valve tamper switch and the valve tamper switches in a backflow preventer vault/Hot-Box.
Additionally, NFPA 70 Article 760.33 states, “A listed surge protective device shall be installed on the supply side of a fire alarm control panel in accordance with Part II of Article 242.” NFPA 70, Article 100 defines a Surge Protective Device (SPD) as, “a protective device for limiting surge voltages by discharging or bypassing surge current; it also prevents continued flow of follow current while remaining capable of repeating these functions…” This applies to the AC power circuit for fire alarm panels (FACU, DACT, NAC, RSFACU, etc.). Even if there is surge suppression on the main AC power supply, a transient can be developed within the protected premises.
Other locations that benefit from surge protection include any incoming POTS lines (if still in use) or cellular dialer’s exterior antenna.
Keep in mind, all surge protective devices need a suitable ground to be effective. Simply attaching a ground wire to the junction box may not offer a suitable ground. Utilize terminal strips rather than wire nuts on the ground to ensure a proper connection.
Have you experienced a loss that could have been prevented by an SPD?
We would like to thank our friends at @Ditek for their research assistance with this edition of HGI’s Think Upstream.