Smokes on AFI circuits

Need some info from you electricians out there…

I understand that as of Jan 2005 smoke detectors are not allowed on AFI circuits. What I don’t understand is why I see so many of them on AFI circtuits prior to the new NEC. I’m aware that they were not addressed in the NEC prior to 2005, so is it because there was nothing saying you could “not” do it and a bedroom circuit was the most accessible? Why would anyone even consider wiring a smoke detector to a circuit that’s designed to trip if a fire condition is possible? Any enlightenment would be greatly appreciated.

**210.12 Arc-Fault Circuit-Interrupter Protection.

(A) De.nition: Arc-Fault Circuit Interrupter.
**An arc-fault circuit interrupter is 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.

**(B) Dwelling Unit Bedrooms. **
All 120-volt, single phase,

15- and 20-ampere branch circuits supplying outlets installed
in dwelling unit bedrooms shall be protected by a
listed arc-fault circuit interrupter, combination type installed
to provide protection of the branch circuit.
Branch/feeder AFCIs shall be permitted to be used to
meet the requirements of 210.12(B) until January 1, 2008.

FPN: For information on types of arc-fault circuit interrupters,
**see UL 1699-1999, **

Standard for Arc-Fault Circuit

*Exception: The location of the arc-fault circuit interrupter

shall be permitted to be at other than the origination of the
branch circuit in compliance with (a) and (b):
(a) The arc-fault circuit interrupter installed within
1.8 m (6 ft) of the branch circuit overcurrent device as
measured along the branch circuit conductors.
(b) The circuit conductors between the branch circuit
overcurrent device and the arc-fault circuit interrupter
shall be installed in a metal raceway or a cable with a
metallic sheath.

Ok…I am not aware of anything pending with the 2005 regarding this…

Revised text to require, after January 1, 2008 that all dwelling unit bedroom branch-circuit AFCI protection devices must be listed as a “Combination Type AFCI.” And new exception permits AFCI protection by a device that isn’t a circuit breaker (such as a receptacle), but only if it meets stringent requirements.

(B) Dwelling Unit Bedroom Circuits. All 15 or 20A, 120V branch circuits that supply outlets in dwelling unit bedrooms must be AFCI protected by a listed arc-fault circuit interrupter. Figure 210-10
Author’s Comment: Smoke detectors connected to a 15 or 20A circuit must be AFCI protected if the smoke detector is located in the bedroom of a dwelling unit. The exemption of AFCI protection for the fire alarm circuit [760.21 and 760.41] doesn’t apply to the smoke detector’s circuit, because a smoke detector circuit isn’t
defined as a fire alarm circuit; it’s an “alarm circuit” [See NFPA 72, National Fire Alarm Code].

After January 1, 2008 (basically a 2008 NEC requirement), AFCI protection shall be provided by a combination type AFCI protection device.

Author’s Comment: Combination Type AFCI protection devices provide improved safety performance over existing AFCI protection devices, because the combination type is designed to detect arcs as low as 5A peak. Existing branch-circuit AFCI circuit breakers are designed to operate when the arcs exceeds 75A peak. See UL 1699, Standard for Arc-Fault Circuit Interrupters ( for information on differences between a branch-circuit type AFCI and a combination type AFCI.
Ex: The location of the AFCI can be at other than the origination of the branch circuit if in compliance with (a) and (b). (a) The AFCI is installed within 6 ft of the branch-circuit overcurrent device as measured along the branch- circuit conductors. (b) The circuit conductors between the branch-circuit overcurrent device and the AFCI must be installed in a metal raceway or a cable with a metallic sheath.
Author’s Comment: The 120V circuit limitation means that AFCI protectionisn’t required for equipment rated 230V, such as baseboard heater or room air conditioner.

Hope this helps…Courtesy of Mike Holt. Figured this would explain it better .

Paul, thanks for the info… great stuff. I guess where I was getting confused was in 760.21/760.41 exception. Since the smoke detector will be “off” if the circtuit is tripped, it would be wise to make certain back-up batteries are fresh. It still doesn’t make sense to put the detectors on the same circuit. I have seen some that are in fact on their own separate circuit.


The problem has been talked about and discussed by electricians ever since the AFCI first surfaced in the 1999 NEC giving way to much debate. I think the concept is the AFCI would go off ONLY in the event of an AFCI issue…thus would not effect the Smoke Detector Circuit per-say unless their was a AFCI issue. In that case the entire circuit would be off to the room and probably notify the person anyway.

Since we know all Smokes need to be interconnected in modern installations and do have a battery back up that SHOULD notify the person when to change the battery via a “CHIRP” or similar method it should not pose much of a problem to be honest with you.

I will have to say in MY electrical firm we do a individual circuit just for the smokes and end the circuit in the attic to the pull chain or access light…remember the AFCI is for outlets in the bedroom but nothing says if can’t extend OUT of the bedroom…hope this explains it.

Thanks Paul, it helped greatly!!

Great…Glad I could explain it for ya…Remember I am here always if ya need me…:slight_smile:

I think the problem is when you take the battery out they stop chirping. I know some work that way. If you are in a place where homes are only occupied a few months a year the battery could die slowly, chirping all the way and be stone cold dead (effectively taken out) by the time the homeowner gets home.
BTW if nothing changes you will have AFCI on every 15 & 20a 120v outlet in 2008


I can hear the OLD TIMERS causing waves doing so I hope it brings down their price accordingly.

If the price of copper keeps going up like it has you will also see aluminum being used in more places.
Roy Cooke sr

lol…Roy I just had someone call me today and tell me that now Aluminum is going sky rocket in price as well…go figure…lol