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Is there a way without using junction boxes to simply splice in additional length of 12/2 NM-B cable? Can I use twist caps?

I'm putting in a dog door and as it so happens, there is some 12/2 right in the way of the location I've chosen. There's no additional slack in the cable, and I don't want to rip up more drywall than I have to. I'm tempted to just cut it and splice in an additional foot or two with twist caps to get it out of the way. I don't know if this is safe or legal. Do I need to get junction boxes? Attached some pictures for fun.

Also, there is a 1-gang electrical outlet box that is going to the outside. I'm moving that up a bit.

View of the hole with the NM-B in the upper left Close up of the cable

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Since this is an inside view, and the blue box faces the opposite, and the project is a doggy door, I assume that blue box is an outside outlet. Will you be moving that, too? Maybe to above the new door? So where does the existing NM run? To that inside outlet? Could it be rerouted without splicing? –  Skaperen Dec 29 '11 at 23:29
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4 Answers

up vote 21 down vote accepted

Tyco makes NM splices which are concealable and acceptable under NEC for use for rewiring in an existing building.

NM Cable Splices

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NEC 2008

334.40 Boxes and Fittings.

(B) Devices of Insulating Material. Switch, outlet, and tap devices of insulating material shall be permitted to be used without boxes in exposed cable wiring and for rewiring in existing buildings where the cable is concealed and fished. Openings in such devices shall form a close fit around the outer covering of the cable, and the device shall fully enclose the part of the cable from which any part of the covering has been removed. Where connections to conductors are by binding-screw terminals, there shall be available as many terminals as conductors.

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Oh wow, where can I pick these up? –  snicker Feb 8 '11 at 6:58
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In the US - Home Depot carries these for sure. –  kkeilman Feb 8 '11 at 17:53
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Awesome, this will come in handy! Link to the product at Home Depot: homedepot.com/h_d1/N-5yc1v/R-202204326/h_d2/… –  Shimon Rura Feb 8 '11 at 22:07
    
What NEC article allows these to be used? If you are going to say they are acceptable under NEC, please quote the article from NEC. –  Tester101 Dec 28 '11 at 15:47
    
The provided link states: Meets requirements of National Electrical Code, Articles 545, 550, 551, if that's what you're looking for. –  JoeFish Dec 28 '11 at 21:21
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The NEC says that all electrical junctions have to be accessible (and your profile indicates that you're either in Nevada or New Mexico, both of which have adopted the NEC), so you can't legally hide a junction behind the wall.

Probably the easiest route for you would be to install a retrofit gang box to the left of the stud with the other gang box (if there's room, it's hard to tell from the photographs), run the existing wire into it, then run a new, longer, wire from the gang box to the receptacle. Connect the two wires with electrical nuts, and finally, cover the gang box with a blank cover plate.

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absolutely correct!!! UMM what is in the blue J-box on back side of the wall??? possible junction location for an extension wire??? –  shirlock homes Feb 7 '11 at 4:24
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@shirlock: Can you have two unrelated circuits in a single gang box? I thought you had to have a double box, with the wiring for each circuit separated by an insulating divider: am I mistaken? –  Niall C. Feb 7 '11 at 5:01
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I know in commercial settings you have to clearly indicate on the outside of a box "Caution: This equipment is supplied by more than one power source". I'm not sure if this is needed in residential settings or not. Some quick searches don't come up with anything saying you can't do it though (I haven't checked NEC/CEC myself though). –  gregmac Feb 7 '11 at 6:32
    
@shirlock @niall: i'm curious about the answer to that question too because that was the route i was leaning toward. Change the outdoor gang box to a double box and run a new length of NM-B to the indoor outlet.. –  snicker Feb 7 '11 at 18:24
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I don't know about the legality of not using them where you are, but I'd always use junction boxes for this sort of thing if only for the safety aspect.

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Splices have to be in a box, and there must be access to the box. Niall C., above, has it right. While you are at it, buy some plastic staples made for NM-B cable. The metal staple shown in your picture is asking for trouble.

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