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Old 01-08-2009, 12:17 AM   #1
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Electric wire in cold air return


Electric wire in a cold air return is clearly not allowed according to code, as pointed out in several other threads on this board.

Here is my situation. I needed to move a light switch and thermostat. I cut a hole in what I thought was an empty wall away from ducts, other utility, etc, and ran my wires. Running the thermostat wire showed me that the entire wall (it is a small wall) is open and being used as a cold air return - even though the vent grates are well to the right of where I am working. Apparently the house was built with central heat and no air, and someone cut the headers above the vents and possibly a vertical wall framing with a drill to make the entire wall act as a vent.

I really didn't want to repaint this room (has a 270 gallon fish tank against the wall), but that is not an option if I cannot keep my switch where I put it. I am thinking of opening the entire wall, installing some sort of barrier to make the vent less wide (shouldn't matter, since the openings are less than 1/2 the width of the vent), and running my wires on the other side of the barrier. Alternatively, running the wires through the vent somehow would make this an easy project. Several others have pointed out the code refers to areas designed for use as vents or phlegms, and I question if this applies to an entire way chewed up by an overzealous air conditioning installer cutting 2x4s with a power drill. Alternatively, I can patch the opening for the switch, and put things mostly back the way I found them.

I know phlegm rated wires in the vent is probably safe and probably not to code. I want everything in my house done right, or at least the part I do. I also question whether leaving this cold air return the way it was is a smart idea, or if I should fix it.

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Old 01-08-2009, 11:09 AM   #2
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Electric wire in cold air return


A similar subject was raised here several months ago. I was wrong on a post when I discouraged someone from running conduit through an air duct. Apparently conduit can pass through a duct, so we must be certain the NM cable cannot. Do you have NM cable? Anyone care to discuss this further. Thanks John

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Old 01-08-2009, 11:41 AM   #3
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Electric wire in cold air return


I already ran regular cable without conduit, but anything I don't have, I don't mind buying and installing. I do need to run parallel to the duct however. I cannot run perpendicular to go around the duct - there is no "around" inside this wall.

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Old 01-08-2009, 01:08 PM   #4
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Electric wire in cold air return


You can't run nm in that wall cavity (return air) as you did. You can however use MC or other metallic armored cable with conductors inside to a metal switch box. You simply need to use some sort of armored cable with enclosed conductors to plenum rated metal boxes. Almost all raco, steel city etc metal boxes are plenum rated.
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Old 01-08-2009, 02:46 PM   #5
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Electric wire in cold air return


Thanks, if anyone could reference the appropriate NEC section, it would be much appreciated. Otherwise, I will try to find it myself. Using metal makes the job much easier.
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Old 01-08-2009, 02:55 PM   #6
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Sure...NEC 2008 art. 300 specifically 300.22(C) and (C)(1) "Other Spaces"
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Old 01-08-2009, 03:20 PM   #7
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Electric wire in cold air return


I would want to close up that wall space; nothing to do with electrical, but if the whole wall is acting as an air duct, what do you think would happen in case of fire?
It would act like a chimney!
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Old 01-08-2009, 05:18 PM   #8
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Electric wire in cold air return


Stubbie, thanks! Looks like metal conduit is the solution.

Now, any ideas on the thermostat? It just has a wire going into the back, and is meant to go into drywall. There is no good way to connect conduit.

KE2KB, I am not worried about that. The openings in the vents and the bottom of the wall are narrow.
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Old 01-08-2009, 06:01 PM   #9
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Electric wire in cold air return


I guess I should use CLP2/CLP3

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