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I have a light switch I want to tap into to add another power outlet a few feet away. I believe this switch's junction box is already too full to accommodate adding new wires. I think I would have to re-wire things so my new outlet goes to this switch instead of an existing wire, and then have that splice with the new wire in the outlet's junction box. The only problem is, the existing wires won't reach to the location of the new outlet. Is there any way to splice a wire behind the wall without using an exposed junction box (with blank wall plate) or is that my only option to be within code? Is there some other option I haven't considered?

  • Is this switch box a 1-gang, a 2-gang . . . etc? – Jim Stewart Nov 28 '18 at 18:42
  • @JimStewart 1-gang. It's on an externior, insulated wall so not sure how much space I have behind it. I haven't cut open the drywall yet, but I will eventually to get a better look. – KyleL Nov 28 '18 at 20:35
  • Is the box made of plastic or metal? – ThreePhaseEel Nov 28 '18 at 23:45
  • @ThreePhaseEel It's plastic – KyleL Nov 29 '18 at 13:43
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What is the size of the box holding this switch? Is it 1-gang, 2-gang, 3-gang, etc?

Would a deeper box allow the new cable and connections? There are 3-7/8" deep 1-gang boxes with a 23 cu in capacity which is higher capacity than standard.

Alternatively you could replace a 1-gang box with a 2-gang old work box. Of course, this might be aesthetically unpleasing.

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    Is there such thing as a 2-gang box that only looks like 1-gang (with the other half behind hidden behind the drywall)? – KyleL Nov 28 '18 at 20:35
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    @KyleL yes, in the metal box world. You use a 4x4 or even 120mm square box, and put a 1-gang mud ring on it. You won't know it's not a 1-gang until you open it up, and cubic inches can be as high as 46 with a 120. – Harper Nov 28 '18 at 22:10
  • There is something like that in plastic, but it does not have any more room (and probably less) than a deep 1-gang, but I don't think it would help with your situation. I think the purpose of this special box is not to provide more fill volume, but to project less inside the wall. It's used for thin or obstructed walls where the inside wall space is little more than 2 inches. The volume is given as 17 cu in which I don't think would be enough. amazon.com/Carlon-B117RSW-Outlet-3-64-Inch-4-07-Inch/dp/… – Jim Stewart Nov 28 '18 at 22:11
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    Another option is to use an extension ring on the existing box -- there is nothing in the NEC that prohibits a box from protruding from a finished wall. – ThreePhaseEel Nov 28 '18 at 23:46
  • @JimStewart I found this one at HomeDepot that I might use if I have no other options. I counted the circuits and the current box is definitely full. homedepot.com/p/Carlon-1-Gang-30-cu-in-New-Work-Box-RD30-6R/… – KyleL Dec 11 '18 at 17:58
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That switch is getting its power from somewhere. Trace that hot line back somewhere to see if it's in another box that you can tap into.

Otherwise, no, you cannot have a junction buried behind a wall - that's not to code and it's dangerous.

  • What about these fittings? diy.stackexchange.com/a/4535/32572 – KyleL Nov 28 '18 at 17:59
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    @KyleL Good find. I guess those are approved. Before jumping on it, I'd wait until one of the many licensed electricians 'round here chimes in. I'm just a handyman 'round my own house and would exercise even more extreme caution when giving advice to others than I might for myself. – FreeMan Nov 28 '18 at 18:06
  • I appreciate the sentiment. The reason I'm here is to make sure its done right! – KyleL Nov 28 '18 at 18:32
  • There are 3-7/8" deep 1-gang boxes with a higher capacity than standard. – Jim Stewart Nov 28 '18 at 19:06
  • Excellent point, @JimStewart - write up an answer of your own. – FreeMan Nov 28 '18 at 19:09
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Yes, Tyco makes a splice for Romex which is meant to be concealed in-wall.

However, are you sure you are counting your cubic inches correctly? Remember

  • all grounds together count as a single wire
  • pigtails do not count at all
  • a yoke (i.e. The switch) only counts as 2 of the largest wire attached to them

And of course, try to use the cubic inches stamped or molded onto the box itself, rather than the codebook values. That gives you credit for larger-than-stock boxes.

  • Also note that if this circuit is on a 15-A breaker, you can use #14 copper wire which is significantly easier than #12 to fold and pack (at least for the less experienced). – Jim Stewart Nov 28 '18 at 22:34
  • Thanks, I will double-check the cu.in. and re-count the wires. Regarding the tyco splice, is this valid for adding new outlets or only for "repair" (is there an important difference)? I have seen some wording changes in different versions of the NEC about this. – KyleL Nov 29 '18 at 15:15

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