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Old 10-19-2008, 02:14 PM   #1
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In one room, there is a return air duct inside ceiling joists. It does not take the entire cavity up from end to end, just a few feet into the room and then its capped off inside the joist with that shiny thermal cardboard. About 8ft away, in the same joist span is a light box. From where the return air ends and the light box is, the cavity is fully insulated with R20.

I know that romex can pass through return air joists, but not run parallel or have a box placed inside. Since this light box is not officially inside a return air duct, and has the thermal pan and insulation, is this ok?
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Old 10-19-2008, 03:14 PM   #2
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yup
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Old 10-20-2008, 10:09 AM   #3
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The emoticon makes me wonder......
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Old 10-20-2008, 01:20 PM   #4
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The emoticon makes me wonder......
Its good, but if you want, you could drill through the joist and run the wire in a different joist space, unnecessary, but easier without that duct in the way.
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Old 10-20-2008, 01:23 PM   #5
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It is widely accepted that when an electrical box or lengthwise wire occurs in a duct (which this effectively is), that you can pan off that box or wire to isolate it from the duct airspace.

This can be done with wood, sheet metal, or thermopan (the foil faced cardboard you described). As long as it is done tightly the hazard has been effectively mitigated. In the event of an electrical fire, they don't want the burning wire to immediately introduce toxic by-products into an HVAC system that conveys air.

Wires can pass through the duct, but not along its length. Most inspectors will be reasonable enough to recognize that running a foot or so across a duct is no different that running a foot or so lengthwise in the duct. But, per code, you cannot have romex paralleling the duct inside it.
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Old 10-20-2008, 09:16 PM   #6
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Is there any restrictions on how far or close you can box off from?
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Old 10-20-2008, 10:47 PM   #7
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It would be up to the inspector that is being asked to approve it. Ideally, any panning that takes place in an HVAC run won't block too much of the duct's cross-section.
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Old 10-21-2008, 05:21 PM   #8
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Sorry to sound like a knob, ducts cross section?
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Old 10-21-2008, 05:51 PM   #9
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If I'm understanding correctly you have a ceiling box sharing the same joist cavity but not inside the return air duct. If is isn't inside the duct and the wiring isn't inside you can run parallel to the duct, over it whathever you want. As long as the romex is fastened correctly as per Art. 334 and not inside the duct space I don't see any issue.

Last edited by Stubbie; 10-21-2008 at 05:54 PM. Reason: added nec articles.
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Old 10-21-2008, 07:55 PM   #10
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If I'm understanding correctly you have a ceiling box sharing the same joist cavity but not inside the return air duct. If is isn't inside the duct and the wiring isn't inside you can run parallel to the duct, over it whathever you want. As long as the romex is fastened correctly as per Art. 334 and not inside the duct space I don't see any issue.
Yep, exactly. Just wanted to ensure that wiring could be run anyway you want and if any type of electrical box(light box, junction, receptacle, etc) could also be located in that cavity as long as its not inside the return air duct as this is what I have except there is a distance of about 8 feet between where the return air is capped off with thermal pan and duct tape, and insulation in between.
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