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I had to install a new wire for my water heater (higher amperage/bigger wire), and was drilling through the wooden top plate to snake the wire down the wall to the pass-through. Everything seemed standard. Put the wire in and heard what sounded like wire scraping something (possibly metallic). Pulled it out, and the cable sheath had little scratches on it; not gouges, or cuts. The hole was at least 3x larger than the wire and was clean.

Now this house in Florida where metal studs are commonplace. Elsewhere in the house there have been metal bottom plates which transition to wood as we exit the exterior wall zone so I suspect under this wooden top plate there was a metal top plate - probably a few mm of metal.

I know that with metal studs anti-short bushings are used, but I am curious how this kind of situation is handled in old-work scenarios such as this where putting in an anti-short bushing isn't possible. Short length of conduit? Don't worry about it? Pulled the wire in and out a few times - more scratches but no cuts or gouges.

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    How good of access do you have to the hole that was drilled through this top plate? For example do you have direct access or was some very long drill bit used to create the hole? – Michael Karas Oct 21 at 11:33
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    I have not run into this problem but when you were drilling you should have seen some metal flakes if it was a plate, usually you feel nails when drilling through them but nails and hurricane straps are all I have ever hit, I would want to get advice from a local pro as this may be something your inspector looks for if it is common there. – Ed Beal Oct 21 at 13:05
  • If you were drilling through metal, you'd know it... – Harper - Reinstate Monica Oct 21 at 14:49
  • @Harper I was using a high powered drill and this is the kind of metal I am talking about: images.homedepot-static.com/productImages/… it is literally a couple mm thick. easy to rip through when going full blast – Alex Oct 21 at 20:25
  • @MichaelKaras not enough to put my finger in to feel the other side, but enough that a spade bit cut through everything – Alex Oct 21 at 20:27
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Easy. Place a thin-yet-protective sheathing around your new wire's existing cable sheath. Then slide the extra-protected wire into the opening without and worries; the little scratches won't even cut into the cable sheath.

Sturdy, but stiff: small-diameter pvc tubing Sturdy yet flexible: thin plastic tubing made for aquariums. Go to your local pet store for the right diameter. Less sturdy, still flexible but cheap and easy : use duct tape!

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    That may work but if metal top plates on wood is common an inspector may be looking for a listed bushing of some type, I would want to check with an inspector or local pro because a 1 or 2 dollar fix now is better than an inspector requiring a bushing that requires another inspection. – Ed Beal Oct 21 at 13:10
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    Hold on. Remember NEC 110.2 equipment must be approved, and 110.3 must be used in accordance with labeling and instructions. Your tubing suggestion is essentially "use flexible conduit, but get something random at the hobby-store instead of using a proper conduit type", I suppose that might be legal if it surrounds cable, but still... – Harper - Reinstate Monica Oct 21 at 14:50
  • i think he is talking about: cabletiesandmore.com/… but yea, definitely not nec approved although I would feel perfectly comfortable using it for a 10in piece but still – Alex Oct 21 at 20:26
  • A short section of smurf tube should be good enough (cheap plastic flex conduit ) I would want to check so you don’t have to rework I have gotten bit on a few really simple things like this in the past , 2 days extra for close / cover inspection over less than a dollar’s worth the plastic and the inspector was new and would not let me take a picture to verify I did the work, most take your word but I still show them photos. – Ed Beal Oct 23 at 14:32

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