Wiring through joists w/ Hot Air Ducts

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According to Clark W. Griswold, Jr. <73115 dot 1041 at compuserve dot com>:

Of course, the incremental risk of 18" worth of PVC isn't very high.
It's not hard to see that hot air entering the return vent could melt the PVC and produce fumes that are 100% captured and ejected into other rooms, adding quite a bit of toxic fume load to prevent occupants from waking up - toxic fumes directly generated from the fire tend to rise away from the flame point, and not go into a return duct (which is on or near the floor).
I'm sure the rule is primarily focused at using the duct for a raceway, but they decided to simplify it as much as possible - it generally doesn't cause that much of a hardship anyway.
It's more of a hardship in buildings which use dropped ceilings as a air plenum. Here, _any_ wire in a dropped ceiling used as a plenum _must_ be in conduit, tho, I believe they now accept teflon (despite the fact that at higher temperatures teflon produces _really_ nasty fumes).
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Chris Lewis, Una confibula non set est
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|> So what non-metallic can be used?| | Essentially none. Consumer-available non-metallic conduit is pretty well | all PVC. Almost all plastics have a noxious fumes issue anyway.
What about wood?
What I mean is a tube made of wood, with a hole drilled down the middle of sufficient size to hold the cable with sufficient heat dissipation. Maybe it would be the same wood as the joists.
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Yes, there was: nail a 1x4 across the joists below the duct, and staple the NM cable to the 1x4. This *does* comply with the NEC.
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|> |>I had a house like that. The "duct" was the space between the joists with |>sheet metal nailed to the bottom of the joists. I hired an electrician to |>wire from one side to the other. He went all the way around the cellar, said |>there was no other way to cross the duct.| | Yes, there was: nail a 1x4 across the joists below the duct, and staple the | NM cable to the 1x4. This *does* comply with the NEC.
On the side of the 1x4, right?
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On Wed, 18 Aug 2004 21:37:13 GMT, someone wrote:

& abrasion, not heat? (Same reason as not to run it under the joists.) Because a "hot" air duct is just "warm", its not hot enought to melt the cable. I'd think a "hot" thing would be like smoke pipe from a conventional furnace.
But it still doesn't get him under the duct. Can he furr and go between the furring strips? Does he really need flush clear to bottom of joist, or could the future (speculative if ever) finish go on the furring or on tracks anyway? What's more important to him, or will he insist on a combo that can't be done?
-v.
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Correct, that *is* a code violation. However, the code does explicitly permit NM cable to be stapled to running boards that cross the joists. So wherever you need to cross joists, nail a 1x4 to the joists and staple the cable to the 1x4. When the cable runs parallel to a joist, code permits (requires, in fact) that it be fastened to the face of the joist.

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