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I've heard conflicting advice whether smoke detectors should be on a simple over-current breaker or a AFCI/GFCI breaker. On one hand you want the circuit to be as reliable as possible and since there will be nothing additional plugged into the circuit a simple over-current breaker makes sense. On the other hand the 2017 code requires just about all 120 volt circuits to be protected at the panel (new construction) with at least AFCI. 2020 code seems to require everything from the doorbell on up to the range to be GFCI protected and most 120 v circuits to be AFCI protected as well.

I'm really curious because I just installed the smokes for my sons new house and the instructions said they should not be on a GFCI/AFCI protected circuit. It passed final electrical inspection today and the smokes were on an AFCI breaker.

Thoughts from others here?

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    Are you talking about smoke alarms powered directly from 120V, or an alarm system with a central panel and system smoke detectors powered from the panel? – ThreePhaseEel Aug 5 at 23:36
  • Just normal smoke detectors connected by 14/3 throughout the house. No main panel or anything like that. Thanks for the clarifying question. – George Anderson Aug 6 at 0:09
  • I’m sure you heard my story about the doofus who puts a low oil level trip on the fire pump engine... warehouse burned down, buy the important part is it saved the engine! – Harper - Reinstate Monica Aug 6 at 2:54
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AFCI is required, but not GFCI, modulo local amendments

Assuming that your jurisdiction doesn't amend this, the requirements for smoke detectors/alarms in bedrooms (NFPA 72, NFPA 101, IRC/IBC) overlap with the AFCI requirement for bedroom outlets (both receptacles and lighting outlets) to force the smoke alarms onto an AFCI protected circuit under all recent NEC editions.

There are two ways I've seen to deal with this: either you can put in a residential alarm system with system smoke/CO detectors (and get the brains of a burglar alarm from the deal), which means you get to take advantage of the 760.41(B) requirement that fire alarm panels not be on AFCI or GFCI, or you put the smokes on the same circuit as frequently used lighting loads, so that breaker trips are troubleshot promptly.

As an aside, NFPA 72 29.9.4 point 5 requires smoke alarms that are AFCI or GFCI protected to have battery backup power. If the 7 days of standby + 4 minutes of alarm backup power requirement given for dual-powered smoke alarms is insufficient, such as if you're dealing with a "snowbird" situation in Florida, then it's best to go to an alarm panel. (You'd probably want the alarm panel anyway, as local smoke alarms are going to do you no good when it's July and the house is vacant and neighborless to begin with!)

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