The house was built in the 50's, and am in Ontario. The house has all copper wiring, but it is older, and has no ground. I am quite competent when it comes to following code, but I have not found a ton of information on the internet about crossing cold air return ducts with wire. I was just hoping to get an electrician's opinion on the best way to do it.

From what I have found in the CEC and internet, you are allowed to cross cold air return ducts as long as you don't run wire along the inside length wise. I am looking to cross the cold air return duct because it spans almost the entire width of the house. These are the kind of ducts where there is just floor joists covered with sheet metal.

Im not looking to use them as a raceway, i just want to run a wire across them so i don't have to go around

I have read one method would be to drill holes on each side of the joist, use EMT conduit to pass the wires through and caulk the outsides to close the duct off to outside air. Back when the house was built, they just drilled holes and ran NM cable across. How would an electrician approach this problem?

Also, this is the way they ran NM cable across the actual air ducts. What do you guys think of this? Seems hackish to me.


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1 Answer 1


You are correct. You cannot run NM cable through an air duct. EMT is approved to run through a plenum, but I can't speak to the specific method you described. Someone with more experience may edit this answer.

The way they ran the NM looks fine. Some of the holes they drilled might be a little too close to the bottom of the joist, but no big deal. The wood does look a little messy. Looks like something I would have done to keep my wife from hanging clothes from the cables. So long as the radius of the bends in the cable is not too severe and there is no friction wear, no problem.

  • Better to make these rounds, rather than cause a place inside the ducts to gather dust, or worse yet, sharp sheet metal cut through your insulation due to years of vibration in your system from the furnace/AC Oct 23, 2015 at 12:19
  • Make the rounds as in go around the return ducts? I would have to go an extra 50 feet around and I would rather go through the duct. As far as I'm aware it's not against code. I wouldnt think that there would be any risk of sheet metal cutting the wire. It would be the same as going through the side of any other joist no?
    – element11
    Oct 23, 2015 at 19:04
  • @element11, I think he's saying to go under the joists. If you have the time and money, It wouldn't be a bad idea to use all EMT and fasten it to the underside of the joists, instead of going through with NM cable. This is what I did in my basement.
    – Edwin
    Oct 24, 2015 at 0:47

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