Residential smokes on GFCI

[tonyi]

Some time ago Roger claimed NFPA 72 prohibited smoke detectors on GFCI protected branches. I just spent an hour pouring through the (apparently) relevant sections of the 99' edition and could find no language to support this claim.

There was some language to the effect that "a fault" (generic wording, not necessarily GF) should not prevent initiating units from signaling an alarm, but this is easily satisfied by battery backups and 72 goes on at length about battery backups, UPS's for computer controlled gear etc. The "a fault" language also occured in the context of "systems" (i.e. having their own fire control panels and such). It seemed to be agreed recently here that ordinary residential smokes are not "systems" in this sense.

So what's the real deal here? Is this claimed prohibition in some obscure section I didn't read?

I see this as a particularly relevant question in regards to old work and protecting existing wiring. Something like the Cutler combo AF/GF breakers are attractive for this purpose when there's a bunch of 2-prongs that would like to be swapped for 3-prong and you'd be taking the new hardwired smokes off one of the existing branches. In a two story building with a all BR's upstairs, grabbing some existing BR branch in the attic for smokes would be a lot more convenient than dragging new up from the basement.

 

[roger]

Re: Residential smokes on GFCI

Tony, why didn't you ask? It's 11.6.3(5) in the 02 edition.

11.6.3 AC Primary Power Source

11.6.3 (5) Operation of a switch (other than a cicuit breaker) or a ground-fault circuit-interupter shall not cause loss of primary (main)power.


Roger

[ November 11, 2003, 10:07 AM: Message edited by: roger ]

 

[pierre]

Re: Residential smokes on GFCI

Tony
protecting three prong receptacles with GFCI protection is acceptable with CLASS A GFCI protection. The GFCI protection provided by Arc fault breaked is CLASS B protection, therefore that method is not permitted.
Class A GFCI protection is 4-6 miliamps, class B GFCI protection is 30-40 miliamps.

Pierre

 

[tom baker]

Re: Residential smokes on GFCI

Pierre, Tonyi is referring to the CH AFCI/GFCI device which is a listed class A GFCI and an AFCI in one unit. I have one in my product samples, seems like it cost me $38.00

 

[pierre]

Re: Residential smokes on GFCI

Tom
Just for clarification: Are you sure that The Cutler AFCI breaker is listed for combo meaning AFCI/GFCI - Where the GFCI is Class A? I have looked in the 2003 UL White Book and cannot find the listing for such a unit. I would like to know if it offers Class A, maybe I will contact Cutler Hammer to see how they are providing this.

Pierre

 

[pierre]

Re: Residential smokes on GFCI

Tom
I just visited the Cutler website and they do have a combo unit. I could not get the listing of the product, or the number of the product, because I had a popup stopper installed and it will not let me access certain pages. I will have my computer guy fix this and then I will see if I can get the product number.

Pierre

 

[roger]

Re: Residential smokes on GFCI

Pierre, part of the confusion is that all AFCI's incorporate GFP or class B protection for gaurding series arcing.

The AFCI/GFCI combo does infact provide class A or people protection.

Roger

 

[Guest]

Re: Residential smokes on GFCI

It's interesting to me that in 680.5 the Handbook implies that both Class A and Class B are GFCI.

See the definition of ground-fault circuit interrupter in Article 100.
A ground-fault circuit interrupter is intended to be used only in a circuit that has a solidly grounded conductor; however, an equipment grounding conductor is not necessary in order for the GFCI to function. A Class A GFCI trips where the current to ground has a value in the range of 4 through 6 mA; it is suitable for use in swimming pool circuits. It should be noted, however, that circuits supplying pool equipment that were installed before local adoption of the 1965 edition of the Code may have sufficient leakage current to cause a Class A GFCI to trip. A Class B GFCI trips if the current to ground exceeds 20 mA ; it is suitable for use only with underwater swimming pool lighting fixtures installed before the local adoption of the 1965 Code

However, the Article 100 definition of a GFCI only mentions Class A protection:

Ground-Fault Circuit Interrupter. A device intended for the protection of personnel that functions to de-energize a circuit or portion thereof within an established period of time when a current to ground exceeds the values established for a Class A device.

 

[tonyi]

Re: Residential smokes on GFCI

Maybe 72 should be updated to disallow class A explicitly since an ordinary AFCI provides some measure of GFP by default that is unavoidably present when an AFCI is mandated for smokes in BR's.

I believe the CH combo units are virtually identical electrically to ordinary AFCI under the covers with the exception of recalibrated GF trip level and the addition of the AF/GF test rocker rather than AF test button.

 

[tonyi]

Re: Residential smokes on GFCI

Originally posted by pierre:
The GFCI protection provided by Arc fault breaked is CLASS B protection

Not the Cutler combos. These are the relevant part numbers:

BR115AFGF
BR215AFGF (2-pole)
BR120AFGF
BR220AFGF (2-pole)
CH115AFGF
CH215AFGF (2-pole)
CH120AFGF
CH220AFGF (2-pole)

 

[tonyi]

Re: Residential smokes on GFCI

Originally posted by roger:
Operation of a switch (other than a cicuit breaker)...

This is pretty restrictive (and probably not well thought out) wording. There's a lot of places with fused pullout mains that aren't "circuit breakers" but OCPD in the generic sense. GE made at least one such panel I've encountered - a 100A/150A/200A with ordinary THQL/TQL type stabs below. You'd just choose main fuses based on service size.

To meet this 72 wording to the letter, it seems you'd have to tap the mains ahead of the fuses since they're not "circuit breakers" (but the pullout does meet the technical definition of a "switch") and then go to a small panel with an AFCI breaker.

 

[roger]

Re: Residential smokes on GFCI

Tony, doesn't every dwelling with a feed thru meter have a "pull out main" technically speaking?

Roger

 

[tonyi]

Re: Residential smokes on GFCI

With the exception and rule using the exact same phrasing for the GF(whatever) in question, its not unreasonable to question this. I don't know of any service type GFP that would provide 5ma personel levels of protection, so they have to be talking about GFP in the generic sense.

The NEC and 72 are obviously out of synch and in disagreement. One is requiring what the other prohibits

 

[iwire]

Re: Residential smokes on GFCI

Originally posted by tonyi:
The NEC and 72 are obviously out of synch and in disagreement. One is requiring what the other prohibits

Looks like that may change for 2005.

2005 NEC Draft copy
II. Non?Power-Limited Fire Alarm (NPLFA) Circuits
760.21 NPLFA Circuit Power Source Requirements.
The power source of non?power-limited fire alarm circuits shall comply with Chapters 1 through 4, and the output voltage shall not be more than 600 volts, nominal. These circuits shall not be supplied through ground-fault circuit interrupters or arc-fault circuit interrupters. [ROP 3?236]

Now if this applies to dwelling unit smokes I am not sure but it is another indication that the NEC is not looking for AFCI or GFCI protection on FA systems.