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NM-8 feeding smoke detectors on hard-wired 15A circuit -- why?

NM-8 feeding smoke detectors on hard-wired 15A circuit -- why?


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Old 03-09-14, 08:28 AM
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NM-8 feeding smoke detectors on hard-wired 15A circuit -- why?

I'm looking to add a new smoke detector to my existing hard-wired circuit. The circuit is 15A and shared with some light fixtures. When inspecting the existing smoke detectors, I saw that they are fed with NM-8 cable.

Why would they have used such a heavy gauge? Any reason I can't just tie in with 14/3 and run to my new detector?
 
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Old 03-09-14, 09:31 AM
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Is the "NM-8" the number you saw on the outside of the cable? Are you sure it is #8 cable/wire? It would be quite a bit larger, and in most cases, a black cable.

If it is #8 wire, you could connect the #14 to it if the breaker protecting that circuit was no larger than 15 amps. However, if the #8 runs to the panel, it might not be good practice as someone later in life could change it to a larger breaker and over fuse the #14 wire.
 
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Old 03-09-14, 09:48 AM
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Are you sure that's not NM-B. Maybe 14/3 w/G
 
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Old 03-09-14, 09:48 AM
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Are sure that the 8 isn't a B as in NM B Romex.
 
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Old 03-09-14, 09:56 AM
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Thanks everyone. It is definitely #8 (heavy black cable, more round than flat). I checked another detector box upstairs and there is #8 going in and #14 going out to some fixtures. Odd. But I will move ahead by tying my new detector in with 14/3.
 
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Old 03-09-14, 10:13 AM
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It would be just about impossible to get 8-3 cable into a 1/2" knock out..... or did they not use connectors.
 
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Old 03-09-14, 11:10 AM
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The normal labeling for a cable says "NM-B 14-2 w grd. Something certainly sounds unusual. It would be a pain to fit that in a box.
 
 

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