Fire & Life Safety: Pop Quiz for Powering Residential Fire Detection

This article originally appeared in the August 2012 issue of SD&I magazine

Do you think you know all the ins and outs regarding the installation power requirements for residential smoke and fire alarm systems? Did you know that in one- and two-family homes, you should not use a dedicated AC circuit breaker to power interconnected smoke alarms? Are you still confident in your knowledge? Do you often confuse residential rules with the commercial requirements? Let’s try a few more questions to test your residential fire alarm system IQ.

Q. Does NFPA 70 require a “dedicated outlet” for powering the FACP of a combination home fire/burglar alarm systems when the outlet is located in an unfinished basement?

A. The following areas are required by the NEC to have GFCI protected outlets. As you can see, number five requires GFCI protected outlets in unfinished basements. However, the exception allows you to omit this protection providing the outlet only serves the fire/burg FACP.

“210.8 Ground-Fault Circuit-Interrupter Protection for Personnel.

FPN: See 215.9 for ground-fault circuit-interrupter protection for personnel on feeders.

(A) Dwelling Units. All 125-volt, single-phase, 15- and 20-ampere receptacles installed in the locations specified in (1) through (8) shall have ground-fault circuit-interrupter protection for personnel.  

(1) Bathrooms

(2) Garages, and also accessory buildings that have a floor located at or below grade level not intended as habitable rooms and limited to storage areas, work areas, and areas of similar use                      

           (3) Outdoors                      

Exception to (3): Receptacles that are not readily accessible and are supplied by a dedicated branch circuit for electric snow-melting or deicing equipment shall be permitted to be installed in accordance with 426.28.

(4) Crawl spaces — at or below grade level

(5) Unfinished basements — for purposes of this section, unfinished basements are defined as portions or areas of the basement not intended as habitable rooms and limited to storage areas, work areas, and the like.

Exception to (5): A receptacle supplying only a permanently installed fire alarm or burglar alarm system shall not be required to have ground-fault circuit-interrupter protection.”

This exception means the answer is “yes,” the outlet would have to be dedicated to the FACP. (This can be accomplished by the use of a single outlet receptacle, of a duplex receptacle, with one-half disabled by breaking the tabs feeding the second outlet.)

Q. Does NFPA 72 allow the audible trouble signal of a residential fire alarm system to be programmed as “silent” by the alarm company so that the rechargeable battery can be removed for service?

A. Look to Chapter 29 in the 2010 Edition of NFPA 72 to find five rules at, 29.6.2 “Household Fire Alarm Systems.” Rule number (3) contains the answer. Power for household fire alarm systems shall comply with the following requirements:

(1) Household fire alarm systems shall have two independent power sources consisting of a primary source that uses commercial light and power and a secondary source that consists of a rechargeable battery.

(2) The secondary source shall be capable of operating the system for at least 24 hours in the normal condition, followed by four minutes of alarm.

(3) The secondary power source shall be supervised and shall cause a distinctive audible and visible trouble signal upon removal or disconnection of a battery or a low battery condition.”

Since the audible trouble signal is required for the listing of the FACP, your technician cannot re-program this required function out of the system.

 Q. What is the maximum length of 16 AWG or 18 AWG conductor allowed to extend to the input leads of a power transformer powering a fire alarm system?

A. After the manufacturer’s published installation instructions, look to NEC article 760.127 “Wiring Methods on Supply Side of the PLFA Power Source,” which gives us the minimum rules for wiring transformers:

“Conductors and equipment on the supply side of the power source shall be installed in accordance with the appropriate requirements of Part II, and Chapters 1 through 4. Transformers or other devices supplied from power-supply conductors shall be protected by an overcurrent device rated not over 20 amperes. Exception: The input leads of a transformer or other power source supplying power-limited fire alarm circuits shall be permitted to be smaller than 14 AWG, but not smaller than 18 AWG, if they are not over 12 in. long and if they have insulation that complies with 760.49(B).”

So, the answer is, one foot.

Q. When may a circuit serving a residential fire alarm system in a home be allowed to omit protection by an AFCI? (NOTE: An AFCI is defined in the NEC as “A device intended to provide protection from the effects of arc faults by recognizing characteristics unique to arcing and by functioning to de-energize the circuit when an arc fault is detected.”)

A. You will find this answer in NEC article 210.12, “Arc-Fault Circuit-Interrupter Protection,” after the requirement for installing AFCI protection in dwellings:

“(B) Dwelling Units. All 120-volt, single phase, 15- and 20-ampere branch circuits supplying outlets installed in dwelling unit family rooms, dining rooms, living rooms, parlors, libraries, dens, bedrooms, sunrooms, recreation rooms, closets, hallways, or similar rooms or areas shall be protected by a listed arc-fault circuit interrupter, combination-type, installed to provide protection of the branch circuit.”

Exception. “Where a branch circuit to a fire alarm system installed in accordance with 760.41(B) [NPLFA] and 760.121(B) [PLFA] is installed in RMC, IMC, EMT, or steel armored cable, Type AC, meeting the requirements of 250.118, with metal outlet and junction boxes, AFCI protection shall be permitted to be omitted.”

Q. Does NFPA 72 permit residential smoke alarms to be on regular house wiring/circuits (also used for power and lighting) and also fed through arc-fault circuit interrupters?

 A. This answer can also be found at 29.6.3 “AC Primary Power Source.” Here in the 2010 edition of NFPA 72 it states the following with our answer found in (5).

The ac power source shall comply with the following conditions:

(5) Operation of a switch (other than a circuit breaker) or a ground-fault circuit-interrupter shall not cause loss of primary (main) power. Smoke alarms powered by AFCI protected circuits shall have a secondary power source.”

Yes, and since an AFCI will cause the loss of AC power while detecting a potential for a fire ignition, smoke alarms on AFCI circuits must have battery back-up provided.

Q. Does NFPA 70 allow commercial fire alarm systems to be fed through ground-fault circuit interrupters or arc-fault circuit interrupters?

A. In NPFA 70, 2008, under “760.121 Power Sources for PLFA Circuits” you will find the well-known requirement for ‘dedicated branch circuit,’ that agrees with the same requirement found in NFPA 72. However, NFPA 70 adds an additional stipulation for GFCI and AFCI protection when it states “(B) Branch Circuit. An individual branch circuit shall be required for the supply of the power source. This branch circuit shall not be supplied through ground-fault circuit interrupters or arc-fault circuit interrupters.”  So, the answer to this is “no”.

Q. Does NFPA 72 require either residential fire alarm systems or 110VAC smoke alarms to be wired on a dedicated (AC primary power) circuit?

A. As mentioned in the first paragraph of this article, you are not required to place your fire alarm control unit or interconnected smoke alarms on a dedicated circuit. According to NFPA 72, 2010, 29.6.3, AC Primary Power Source. The AC power source shall comply with the following conditions:   (4) AC primary (main) power shall be supplied either from a dedicated branch circuit or the un-switched portion of a branch circuit also used for power and lighting.”

This means that it isn’t required to be dedicated. So, it may be dedicated, but should it be dedicated? Many say, and some codes now require, that this circuit not be wired on a dedicated circuit. The reason is, that the resident will not notice (or care) if the dedicated circuit breaker has tripped and will not investigate. However, if the same circuit was also used to operate the refrigerator, or living room lights or television, the homeowner would notice right away and be more inclined to get it fixed.

[NOTE: The above code sections have been edited to remove sections not directly related to residential fire alarm and detection. Please take into consideration all applicable sections when determining compliance.]

Quizzes are a good way to occasionally test the strength of your fire alarm knowledge without having to test the strength of your “limitation of liability” clause. Did you miss one or two of these questions? Don’t despair. I would expect maybe only one or two techs out of 100 would be able to answer all of the above questions correctly.

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