Residential Interconnecting Smoke Alarms Feeder Circuit

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The Great Sarducci

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Detroit, MI. USA
Today I ran into an unusual situation regarding a residential dwelling's interconnecting smoke alarm main power feeder circuit. The interconnecting smoke alarm circuit in itself is wired properly, however rather than having a dedicated branch circuit feeding power to the circuit, the homeowner has dedicated power for the smoke-alarms (and only for the smokes, as I was sure to verify) coming from a separate fused disconnect box, which is then fed from above-disconnect in the main service panel. In other words, the external disconnect box dedicated only to the smoke alarm circuit, is fed from above the main breaker in the main panel. This is the first time that I've ever seen it done this way, and my thought is that this was probably wired this way by some other sparky or DIY with the thought in mind that it would keep the smoke alarm circuit always switched ON even when the main breaker was switched off. It would make perfect sense if the smokes weren't already battery-backup. But since they are, I'm not quite sure what the point was of doing it this way? What I'd like to know is; is this setup even permitted? I tried surfing thru the code to find an answer, but not finding much (assuming as how most everything for smoke alarms is in the NFPA 72 code book; which incidentally I don't have a copy of). From a pure electrical standpoint, it would be safe; as it is properly protected. But coincidentally in my mind, I always understood that when a main CB is present in the service panel, that it must be able to disconnect EVERYTHING in the dwelling when opened. Now that I've witnessed this setup, I now need to be sure that I am not leaving something illegal in place as-is when the job gets wrapped up.
 
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Of course it is not permitted. You have an unprotected circuit running thru the home. Unless you have an rule that says it must be on a separate circuit then it does not need to be done that way. Perhaps Michigan requires it.
 
Dennis Alwon said:
Of course it is not permitted. You have an unprotected circuit running thru the home. Unless you have an rule that says it must be on a separate circuit then it does not need to be done that way. Perhaps Michigan requires it.
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...coming from a separate fused disconnect box, which is then fed from above-disconnect in the main service panel.
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As long as that disconnect box is mounted outside the home, grouped with the main panel, and possibly labelled, there will not be any unprotected wires running through the home. As long as the fuse(s) in the disconnect match the ampacity of the circuit to the smokes, of course.
I agree that in the absence of a local rule it is not necessary to use a separate service disconnect for the alarms.
 
GoldDigger said:
As long as that disconnect box is mounted outside the home, grouped with the main panel, and possibly labelled, there will not be any unprotected wires running through the home. As long as the fuse(s) in the disconnect match the ampacity of the circuit to the smokes, of course.
I agree that in the absence of a local rule it is not necessary to use a separate service disconnect for the alarms.
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He also said this
is fed from above the main breaker in the main panel
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Dennis Alwon said:
He also said this
is fed from above the main breaker in the main panel
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It is fed from above the main breaker in the main panel, yes. And if that main panel is inside that would be against code. If the main panel is outside, what is the problem?
The fused disconnect would have to be rated SUSE and meet any AIC limitations of the service of course.
 
Dennis Alwon said:
Of course it is not permitted. You have an unprotected circuit running thru the home. Unless you have an rule that says it must be on a separate circuit then it does not need to be done that way. Perhaps Michigan requires it.
Click to expand...

Thanks. As far as Michigan is concerned, there is no rule that I know of that if must be on a separate circuit. Although usually when we do a new interconn. smoke alarm system for new work or after a new addition, I've always had the preference of giving it it's own dedicated branch (if there's an available spare of course, which is usually the case at least). Anyway, thanks for the feedback. You confirmed my original hunch, but I still wanted to be sure.
 
GoldDigger said:
It is fed from above the main breaker in the main panel, yes. And if that main panel is inside that would be against code. If the main panel is outside, what is the problem?
The fused disconnect would have to be rated SUSE and meet any AIC limitations of the service.
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Thanks for the input. Being that it is indoors, it makes perfect sense that because it includes an unprotected run between boxes, that it wouldn't be allowed. To this point, I was even more in question because the inter-box wire pull is installed as THHN in EMT. But I know that this still would ultimately not matter. Thanks again.
 
The Great Sarducci said:
Today I ran into an unusual situation regarding a residential dwelling's interconnecting smoke alarm main power feeder circuit. The interconnecting smoke alarm circuit in itself is wired properly, however rather than having a dedicated branch circuit feeding power to the circuit, the homeowner has dedicated power for the smoke-alarms (and only for the smokes, as I was sure to verify) coming from a separate fused disconnect box, which is then fed from above-disconnect in the main service panel. In other words, the external disconnect box dedicated only to the smoke alarm circuit, is fed from above the main breaker in the main panel. This is the first time that I've ever seen it done this way, and my thought is that this was probably wired this way by some other sparky or DIY with the thought in mind that it would keep the smoke alarm circuit always switched ON even when the main breaker was switched off. It would make perfect sense if the smokes weren't already battery-backup. But since they are, I'm not quite sure what the point was of doing it this way? What I'd like to know is; is this setup even permitted? I tried surfing thru the code to find an answer, but not finding much (assuming as how most everything for smoke alarms is in the NFPA 72 code book; which incidentally I don't have a copy of). From a pure electrical standpoint, it would be safe; as it is properly protected. But coincidentally in my mind, I always understood that when a main CB is present in the service panel, that it must be able to disconnect EVERYTHING in the dwelling when opened. Now that I've witnessed this setup, I now need to be sure that I am not leaving something illegal in place as-is when the job gets wrapped up.
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By "above" I'm guessing you mean ahead of or before the main breaker. How is this accomplished, a #12/14 jammed in with the feeder from the meter into the mains lugs?

I dont know of any code that would mandate, allow or permit such an install, tho a proper feeder to a fused disco doesnt seem to be a violation to me.
 
It sounds like either the sparky or the homeowner is a New York City transplant, or some other jurisdiction that requires fire alarm systems to be powered ahead of the meter. However, that requirement doesn't apply to residential smoke alarms AFAIK. Although I know of this requirement I've never seen how it's physically executed, so can't comment on the details.
 
JFletcher said:
By "above" I'm guessing you mean ahead of or before the main breaker. How is this accomplished, a #12/14 jammed in with the feeder from the meter into the mains lugs?

I dont know of any code that would mandate, allow or permit such an install, tho a proper feeder to a fused disco doesnt seem to be a violation to me.
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If stuck in same lug with the service conductor then the issue is improper termination, you are still allowed up to six service disconnecting means if all grouped together. Funny thing is for a single 200 amp service disconnecting means you need a 200 amp service conductor, for multiple disconnecting means you still need 200 amps to the 200 amp breaker, but the common supply conductor only needs sized to calculated load.

Why a separate disconnect for the smoke alarms? I have seen many schools, nursing homes or other buildings with fire alarm systems that had electric service installed or upgraded in 1960's or 1970's. I don't know if it was code then or maybe it was fire marshal more then NEC wanting it, but they always had a separate 30 amp fused disconnect tied to the supply side of the main service disconnect (and usually just doubled up in the main lugs of the main service disconnecting means:blink:) They often had all the emergency lighting and exit signs on another 30 amp disconnect installed in same way. Whoever installed this for OP had maybe been involved in some of those type of projects and that is how they though it needed to be.
 
The Great Sarducci said:
Thanks. As far as Michigan is concerned, there is no rule that I know of that if must be on a separate circuit. Although usually when we do a new interconn. smoke alarm system for new work or after a new addition, I've always had the preference of giving it it's own dedicated branch (if there's an available spare of course, which is usually the case at least). Anyway, thanks for the feedback. You confirmed my original hunch, but I still wanted to be sure.
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Smokes are not required to be on dedicated circuits here. In fact, some inspectors prefer they are on a lighting circuit where a tripped breaker would be quickly noticed.

I don't understand what benefit would be gained by putting smokes on a dedicated circuit.
 
K8MHZ said:
I don't understand what benefit would be gained by putting smokes on a dedicated circuit.
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I don't either, but I think there are many that don't realize from a fire codes perspective they are not in the same classification as a true fire alarm system.
 
K8MHZ said:
Technically, aren't 'smokes' actually smoke detectors and not smoke alarms for that very reason?
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I think they are "listed smoke alarms"
What they are not is "fire alarms".

Add: in fact I believe a "smoke detector" is a component of a "fire alarm system".
 
Additional info:

If your AHJ has adopted the IBC and referenced appendix K in the adopting ordinance, those are the administrative provisions for NFPA-70 (NEC).
Section K111.6 Smoke alarm circuits. states that they shall not be connected as the only load on a branch circuit. The branch circuit shall have lighting loads consisting of lighting outlets in habitable spaces.
 
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