Running NM cable alongside a heat duct?

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Old 10-19-05, 08:11 AM
Blakeharrison
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Running NM cable alongside a heat duct?

I would like to run nm cable for a new branch circuit from the cellar to the attic, but in my old house the best place to do so is alongside an straight up and down opening up through the center of the house in which the heat duct to the first and second floors runs. There is room in this opening alongside the heat duct for the wire. That is no problem (in fact there is an old cable TV wire in there now, which is dead). But there is no way of knowing whether the nm cable in actually touching the vent down there in the walls in places that I can't see.

Is this a problem? Will the nm insulation be damaged by the heat from the vent? I thought about using schedule 40 pvc conduit and stripping out individual wires from the nm cable to use in the conduit, but is this necessary?
 
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Old 10-19-05, 08:18 AM
I
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You are okay to run the NM parallel to a heating duct. The duct should never get warm enough to damage the wire.

I thought about using schedule 40 pvc conduit and stripping out individual wires from the nm cable to use in the conduit, but is this necessary?
This is technically not allowed anyway, you would need to use THHN in the conduit. Individual conductors of NM cable are not rated for use outside of the factory made NM cable assembly.
 
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Old 10-19-05, 08:24 AM
R
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As ibpooks said, you can run the NM alongside the duct. This is allowed.

If you really wanted to use conduit, then you could simply run the NM inside the conduit for this area of the wall. When used for protection, NM can be run inside conduit.
 
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Old 10-19-05, 08:27 AM
Blakeharrison
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Thanks for the advice. But I had thought that running nm cable in conduit lowered the heat dissipating capacity of the cable, and therefore lowered its load carrying capacity.

Is that not true?
 
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Old 10-19-05, 08:38 AM
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Not the expert here...but I would think if the wire was generating enough heat that a short piece of conduit would effect its performance.....your already in too much trouble.
Any warm wires bother me.
 
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Old 10-19-05, 08:54 AM
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The concern with conduit and heat has to do with the number of wires and the current flowing through them. Using a section or two of conduit for protection of a single NM cable is not a problem.

You do not need conduit for your situation, but you can use it if you want with no adverse effects, except to your wallet.
 
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Old 10-19-05, 09:11 AM
Blakeharrison
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Thanks very much Racraft.

Your response raises a related issue, if I may ask....

We were considering adding a motion light outside. The cable would run 50 ft from the power source to the light, **all of which is under the roof of a screened-in porch.** Can regular indoor 14/2 nm cable be used for this if I run it through the pvc conduit for this length? Or should I use THHN? Or should I use outdoor rated wire inside the conduit, even though the conduit is going to be mounted under the roof of the porch?

Just want to be sure to do the safest thing.

Thanks again for the help.
 
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Old 10-19-05, 10:02 AM
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Do not use indoor wire. You are talking about an OUTSIDE location. For that distance, I would use THWN (individual conductors) in conduit, or just use UF wire and skip the conduit.
 
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