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.

  • How bad is the damage to the cable? Can you see any of the individual wires in the cable, or is it just surface damage?
    – Steven
    Commented Dec 9, 2013 at 0:04
  • Outer jacket is ripped, can see the hot/neutral insulation (black/white). Rip is situated right as it comes out of a joist, so I can't wrap it with electrical tape.
    – Alex Moore
    Commented Dec 9, 2013 at 4:22
  • Considering the effort and expense involved in replacing it, and what sounds like a relatively safe condition of the wires, I'd sure try to figure out a way to repair it in place rather than going the route of replacing it. How deep is the rip behind the exit hole? How about just separating the white and black that are exposed and slipping a piece of slitted rubber hose filled with liquid tape over them?
    – getterdun
    Commented Dec 9, 2013 at 6:12
  • For reference what's the age of the house and jurisdiction. Guessing USA, and 50's based on the duct, wire and subfloor.
    – Bryce
    Commented Dec 9, 2013 at 9:14
  • @Bryce You hit the nail on the head there, 1951 Ranch in Central Ohio.
    – Alex Moore
    Commented Dec 9, 2013 at 20:53

1 Answer 1


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.

  • Is there any downside to getting basement air in the system? Does it affect the life of the blower at all?
    – Alex Moore
    Commented Dec 9, 2013 at 20:52
  • Basement air could have mold, radon, and almost certainly is dusty. It is energy inefficient as the warm return air conducts directly to the cold ground. Depending on filter location, that dust may bypass the filter and hit the motor. Is it the worst thing in the world? No. Is it good? Definitely not. The Ohio Geological Survey has radon maps for your area.
    – Bryce
    Commented Dec 10, 2013 at 0:26

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