I opened an electrical box today to a bit of a surprise - a little bit of exposed conductor on one of the wires! As far as I can tell, there is no damage to the conductor (12 gauge). Note that this is for a 240 volt line voltage thermostat.

Is it acceptable to wrap this wire with electrical tape and call it good? A few notes to help complicate this:

  • This is 12 gauge wire and quite stiff, it looks like it has been twisted and untwisted several times already
  • This is inside a gang box so I don't see any easy way to "add a junction box" which seems to be the normal answer - and I wouldn't want to add a blank cover junction box right below this, it would look awful
  • I'm pretty certain that I wouldn't have enough wire to work with if I trimmed it right behind the knick - this wire connects to a wire nut with 3 total wires when complete
  • I can't easily remove this cable and fish a new one as it is a long run of wire and is stapled behind the dry wall (this is on the cable from the breaker)
  • This is a full junction box already, so I don't really have room to be adding some fancy (read: big) specialty splice piece

All kinds of fun. Seems to me like the only "easy" way to fix it would be with electrical tape. However, having it totally safe and up to code/regulations is most important to me, so if electrical tape won't cut it then I'll probably have to get an electrical to do something (not sure what). If it matters, I'm in WA, USA. Thanks for the help!

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  • 4
    A few turns of black electrical tape and this would be fine. That gauge wire is very stiff. Whoever put in this wire has not looped and folded it neatly and professionally. This blue plastic box is a type called an "old work" box, which to me is a needlessly cryptic term. A more descriptive term would be a "clamp-on" box because it is clamped to the finish wall rather than secured to a stud. These are used to add a box in a closed up wall. What caused you to open up this box? What are you going to do here? Commented Jan 9, 2018 at 8:28
  • Jim, I'm replacing an old mechanical thermostat with a programmable digital one
    – Scott B
    Commented Jan 9, 2018 at 15:36
  • In my HVAC system the thermostat is connected in the 24-V control wiring. These are very small wires in a cable. Are you connecting your thermostat to the 120-V power wiring? Commented Jan 9, 2018 at 17:39
  • 2
    Mine is a line voltage thermostat, quite different that a low voltage one. Yours probably controls a heat pump or furnace, but line voltage is usually used on baseboard heaters.
    – Scott B
    Commented Jan 9, 2018 at 17:51
  • I have to admit that due to a lifetime living in cities in the southern US, I have never had experience with electric resistance baseboard heat. So this is 240 V 60 Hz; what is the amperage rating of the breaker? 20 A? 30 A? I really can't understand how the installer twisted and kinked the wires like that. Does the thermostat intrude into the box or is it mostly outside the box? Is the thermostat simply in series with the heater? Looks like three cables each 12-2+gnd or 10-2+gnd with one cable from the panel on which both the black and the white are always hot. Commented Jan 9, 2018 at 19:39

4 Answers 4


What everyone has said is fine, but here is an optional method I would use. First straighten the wire out as best you can. I usually us a pair of lineman's pliers our a heavy duty needle nose. Then you can purchase some shrink insulation from your local hardware store or electrical supplier and shrink a new piece of insulation around the nicked area. I generally shy away from using tape since you will find it hard to wrap and get a proper application in a small enclosed area. Also, depend on conditions tape has a tendency to come unraveled from time to time.

Good luck and stay safe.

  • Thanks, I may try this route, I'll drop by the hardware store to check out the options. When you straighten the wire, do you just kind of pull it straight or do you actually (un)twist the wire?
    – Scott B
    Commented Jan 9, 2018 at 15:39
  • 1
    @ScottB - Would I sound like a smartelect if I said yes? You might wind up doing both. The idea is to get the wire as straight as possible without damaging the wire anymore than it is. Commented Jan 9, 2018 at 20:49
  • you can put on more than one layer of heat shrink tubing. ... just put one on, shrink it, then put on another ...
    – jsotola
    Commented Jan 10, 2018 at 5:17

Is it acceptable to wrap this wire with electrical tape and call it good?

Jim's comment looks to me good enough to be an answer. So here's a Community-Wiki answer quoting it:

A few turns of black electrical tape and this would be fine. That gauge wire is very stiff. Whoever put in this wire has not looped and folded it neatly and professionally. This blue plastic box is a type called an "old work" box, which to me is a needlessly cryptic term. A more descriptive term would be a "clamp-on" box because it is clamped to the finish wall rather than secured to a stud. These are used to add a box in a closed up wall.

(My emphasis)


Minority report here.

Fixing it with electrical tape or shrinkwrap is not Code legal.

I see signs of similar deterioration on the rightmost black, which could be a matter of the insulation aging -- electrical wire does have a working lifetime, and since metallic copper is stable, that refers to the insulation.

I also see 2 complete twists (just in-photo) of the left blacks, and that doesn't make sense as twisting multiple wires together only makes them stiffer still. And given the angles of the wires, this looks like more than a random insulation rub-off -- it looks like the wire was kinked from overtwisting and this action also sheared off the insulation.

Copper is ductile. It's not that ductile. The kink will also have internal cracking and tears of the copper wire itself, which will make a hotspot under the high loads of a heater. Trying to straighten the kink to fit shrinkwrap will only tear it further.

It looks to me like this wire was roughly handled, and is damaged beyond trust. I'm sorry to say I think it needs to be replaced. I know that's an inconvenience for all the reasons you cite.

Is there not a potential junction box location in a basement or crawlspace below? Inside of closet? Etc.

You need good wire sticking at least 3" outside the box.

  • I felt someone would comment on replacement of the wire. What I can tell you is that the municipality of Fort Worth will not allow tape but they say the shrink tubing is their preferred method. I also inquired about liquid insulation but I have never been comfortable with its result. What I can also tell you that I do not know if any other AHJ allows it, even in the DFW area. It probably is a good idea to run it buy your municipality before you proceed. Commented Jan 9, 2018 at 21:03
  • Since this is an old work box it can be released just by loosening the two clamping screws enough to fold in the clamping tabs (bottom left and top right). Then the box could be pulled out of the wall to check for slack in the cables. If there is sufficient slack, then more of the cables could be pushed into the box and the bad wire cut off. homedepot.com/p/1-Gang-14-cu-in-Old-Work-Box-B114RB/100404027 Commented Jan 9, 2018 at 22:13
  • Harper - Reinstate Monica, can you please specify what "Code" you are referring to when you say "Code legal"? Also, can you please provide a citation to the place in the "Code" that justifies your statement? The heat shrink tubing at McMaster-Carr says that it has a dielectric strength of 500V/mil: mcmaster.com/heat-shrink-tubing.
    – cpuga001
    Commented Feb 20, 2020 at 20:41
  • @cpuga001 NEC 110.2, 110.3(B) and Chapter 3. Note the component is UL Recognized (aka ЯU) not UL Listed, so that's not looking good. Note however Retired Master Electrician above, the local AHJ seems to have approved it in Fort Worth. So that is that. Commented Feb 20, 2020 at 21:04
  • So I guess you'd ask "If the AHJ can just approve it anyway, then what does Code even mean?" It means if the AHJ is saying "nope", you can show where Code in fact allows it, and the AHJ should yield. Commented Feb 20, 2020 at 21:25

Using electrical tape or heat shrink tubing to repair compromised insulation on a conductor may be permitted by the NEC. The local inspector has a lot of discretion under 110.2 and 110.3 and, as far as I could tell, there is no section of Chapter 3 in the NEC expressly addressing repair of minor damage to the insulation of conductors. I was pretty bearish on using electrical tape to repair it until I started reading the specs from Gardner Bender regarding their electrical tape, which can be found here: https://www.gardnerbender.com/en/p/GTPC-550/Electrical-Tape#tabOverview. They say its UL listed (UL 510) and for applications up to 600 volts. That being said, I think the workmanlike way to go about fixing compromised conductor insulation is heat shrink tubing. Here's Gardner Bender's heat shrink tubing (https://www.gardnerbender.com/en/p/HST-375/3-8-in-He-Shrink-Tubing-3-Pack#), which they say meets UL 224 and has a dielectric strength of 600 volts/mil. 110.3 of the NEC (no local amendments) specifically says "In itself, 110.3 does not require listing or labeling of equipment. It does, however, require considerable evaluation of equipment." So, I suspect that both using electrical tape and/or heat shrink tubing might meet the requirements of the NEC if approved by the local inspector. Step 1, of course, is pulling permits and calling the local inspector. If you're a DIY'er, some jurisdictions have an exception to the electrician's licensing requirement if you're the homeowner. If you're not, call an electrician and you can use this website as a way to check what they're saying. If they don't want to pull permits, get another electrician. What I think bears repeating, is everyone should pull permits and use their local inspector. In my experience, I find inspectors to be knowledgeable and reasonable people despite what some electricians I've met might say.

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