Power Struggle

Q. I have a powerful fire alarm control unit that has built-in capability to attach security and access control devices, when it’s desired, to provide a comprehensive (and economical) life-safety protection system. In order to provide an enhanced degree of safety, I’d like to power all motion detectors and access control readers from a separate power supply instead of the FACP’s auxiliary output. The local AHJ says this new auxiliary power supply cannot be powered from the same breaker as the FACP since they are non-fire alarm components. What gives?


A. In the end, probably you will give in. But before you do, let’s look at this dilemma from another point of view. I can feel your frustration because this would be a non-issue with the local inspector if you were to simply power all of the motion detectors and card readers from the FACP’s auxiliary power terminals, as allowed by the FACP’s manufacturer. I see the problem you are addressing in this project; by having a lot of power-hungry detectors and access control devices it makes sense to add a dedicated power supply just for all the “non-fire alarm” auxiliary devices and functions. However, because you have decided to add to your costs of the job by removing a lot of drain on the main FACP power resources and adding a separate power supply, you are now being told by the building official that this voluntary improvement to the reliability of the fire alarm system will now require you to add another AC power circuit since you cannot share the FACP primary power source with the “non-fire equipment.” (Most of you veteran installers know that existing commercial buildings can have all of the available circuit breaker slots already used; and adding an additional AC circuit to some areas of the building can be very expensive).

These three Sections of NFPA 72, 2010 make no mention of any possibility for other than fire alarm devices: “ The location of the dedicated branch circuit disconnecting means shall be permanently identified at the control unit. For fire alarm systems the circuit disconnecting means shall be identified as “FIRE ALARM CIRCUIT. For fire alarm systems the circuit disconnecting means shall have a red marking.” So, it is clear in his mind that a “dedicated branch circuit” means it cannot be used to power non-fire alarm equipment. But is this really “non-fire” equipment? According to Section Building Fire Alarm Systems: “Protected premises fire alarm systems that serve the general fire alarm needs of a building or buildings shall include one or more of the following systems or functions:,” and condition number 11 is “Combination Systems.” This statement is very clear that NFPA 72 considers the entire system to be a “fire alarm system” even when it performs other life-safety or property protection functions: “23.8.4 Combination Systems.* Fire alarm systems shall be permitted to share components, equipment, circuitry and installation wiring with non–fire alarm systems.”

In the end, the inspector’s interpretation is the only one that matters. If the code was more clear, and had specific language for every system configuration, you would certainly win this argument that today’s fire alarm systems can be made of many components with many functions but the “dedicated branch circuit” language is too narrow to support your view, and Section 23.8.4 “Combination Systems” is too far from the “dedicated branch circuit” language to be strong enough to persuade the inspector that “it’s all good.”

If your inspector just won’t budge, and you cannot reasonably get another AC circuit installed for the on-time completion of the alarm system, then consider adding a single fire alarm device to the auxiliary power supply, say a four-wire smoke detector to be used over the FACP(s). Adding a single fire alarm device would officially transform (no pun intended) the entire aux power supply into a fire alarm power supply and allow it to then be connected to the same dedicated circuit as the FACP.



Greg Kessinger is SD&I’s longtime resident fire alarm and codes expert and a regular contributor to the magazine. Reach him at greg@firealarm.org.