Mixing ac & dc in a cable

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mic

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I have a 120v ac powered smoke detector which uses a 6v dc signal to control a relay located in a different area. There is a 12c/12awg cable running between the two areas that carries the power for the detector, lighting, and receptacle power.

Is it a code violation to run the 6v dc signal through this cable? Which code sections apply?

Article 300-3(c)(1) seems to say that it is acceptable.

In Article 725-8(a) the 6v signal would fall into class 1 since it is a safety control device. But I am unclear as to wheather it can be run with a lighting circuit.
 
Re: Mixing ac & dc in a cable

The 6v dc wire is "functionally associated" with 1 of the 120v ac power lines, but not with the other two. Does it pass because is is associated with 1 line, or does it fail because it is not associated with the other two lines?
 
Re: Mixing ac & dc in a cable

"Article 300-3(c)(1) seems to say that it is acceptable."
See section 90.3
Also see the FPN at the bottom of 300.3(C)(1).
 
Re: Mixing ac & dc in a cable

My technical evaluation would say you have no problem since I think most(not all)of the Article 725 requirements for circuit separation are grossly excessive.

Since my technical evaluation is irrelevant, I would say you would have to make the case that the circuits were associated by virtue of being part of the overall "system."
 
Re: Mixing ac & dc in a cable

Tom,

I'm not sure what I am looking for in section 90.3, this is the code arrangement. Also, the FPN at the bottom of 300.3(C)(1) refers to class 2 and class 3 circuits. Are you saying that the detector signal is not class 1?

At this point I will assume it is a code violation unless someone can show me otherwise. Thanks for all the help.
 
Re: Mixing ac & dc in a cable

90.3 States the rules in article 725 can modify the rules in chapters 1-4, hence 300.3(C)(1) does not apply to class 2 and 3 power limited circuits.
 
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