Electrical – How to reroute a circuit that goes through a return air plenum

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Old house, need to replace a wire where the insulation has been stripped off from when the original installer pulled it through a joist. Normally I'd just follow the original path of the old wire, but in this case it runs through a return air duct:

Old work

I believe it's NEC 300.22 (B) that states that I could do this exact thing with MC cable, EMT, IMC, and rigid conduits, but there are supply ducts are on the other side (so no conduit) and I'd like to not mess with MC unless I need to. I think this leaves me with the option of either:

  1. Routing the cable around the duct (would have to take circuit to the center of the basement, and then back to get around the plenum) EDIT: Plenum runs the whole length of the basement, have to go under or through

  2. Putting up a running board across the bottom of the joists / tack wire to running board (NEC 334.15(C))

Am I missing any other options? I also thought about running a conduit along the joists, but I think the running board would be cheaper.

Best Answer

Is that acceptable for new construction? No. Does anything compel you to fix it now? No.

I'd check very carefully that the insulation on the black & white wires is unaffected (sounds like it is). Then slip something over to mechanically protect those wires. A stiff bit of plastic sheet rolled up and slipped through the joist should do it.

Then caulk the hole for airflow purposes, and consider replacing the entire return plenum: there is no caulk and it leaks air. At best you're getting basement air into the plenum because the pressure is lower.

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