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I have a new switch that requires a neutral. There is a neutral wire in the box, in the back, but it's continuous -- comes in one side and goes out the other. Is the proper procedure to cut it, then bundle the two ends along with the neutral going to the switch? And then cap the new bundle of course.

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  • Can you post a photo of the inside of the box please? – ThreePhaseEel Feb 2 '19 at 19:25
  • The neutral is just passing through...comes in one side and out the other. – Roger Feb 2 '19 at 21:05
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You are in conduit, which changes everything.

Nope, you can't cut it. You don't have enough length remaining. Both stubs will be illegally short and you would then have to replace both of them.

However, what you can do is replace just one half of the run, left or right, whichever one is easier to fish/pull. Continue using the original wire on the other half of the run.

Identify which one is easier to replace by opening up both connecting boxes, and push and pull on the white wire from here. You will get tactile feeling on which one moves easier. While you're there, see if there is an abundance of slack in those boxes and you can just move wire around. The legal absolute bare minimum is 3" of insulated wire sticking out beyond the surface of the wall at each box.

Then on the "easy end" pull the slack out of the old wire, and lash it to the new wire with electrical tape at least 6-8", as long as you can. Streamline the "nose" so it doesn't hang up on things. Then, from this box, pull the old wire out, dragging the new wire in.

Shove the old wire down the other pipe back to center, because you probably pulled all the slack out of the other box. That box needs that slack. Then unsplice old and new wire, position everything and cut all the wires so they are 8" beyond the surface of the wall.

You could also leave the old wire and double back from the next or previous box on that conduit. I do the "pass thru and double back" trick all the time to reduce practical box crowding, but that won't help you here.

Since you will be making all your joins at a wire nut, you might as well use stranded THHN wire which is more flexible and easier to handle, there's also no stiffness penalty for #12 wire. Must be white or gray.

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    Fantastic! Thank you for taking the time to give this detailed explanation! – Roger Feb 3 '19 at 16:50
  • Is the legality of the length the only issue with the OP's proposal? Just from a pure circuit diagram perspective those wires need to be spliced and then connected to the neutral node on the switch right? – Peter Moore Jan 20 at 21:41
  • Also couldn't something like this be used without violating the code? Then he wouldn't have to cut the wire. 3m.com/3M/en_US/company-us/all-3m-products/~/… – Peter Moore Jan 23 at 21:51
  • FYI, being in the same position as the OP, I wound up using the Scotchlok T-tap connector (from the link above, and with the matching female crimping connector) and it works like a charm. I'm sure running new wire through conduit is a blast but this was much simpler. As for whether it's code compliant, all I can say is it's fundamentally the same as stripping insulation without cutting, which I see throughout my home, except safer because the tap is completely surrounded by hard insulation. – Peter Moore Feb 9 at 13:48
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I am in the same position, Roger. I am not an authority on the NEC, but I have been researching extensively after reading Harper - Reinstate Monica's answer and I have to say there are other sources saying it is perfectly fine to use splicing to extend the wire to sufficient length to satisfy NEC 300.14. See, e.g.: https://www.facebook.com/mikeholtenterprises/videos/2721769841295232.

The code section 300.14 simply says there must be 6" of "free conductor" running from the entry point of the box, and for certain size boxes, at least 3" that extends out past the wall. But, does "free conductor" mean unbroken conductor? Well, I cannot find anyone (other than Harper - Reinstate Monica) suggesting that if a wire winds up being cut too short inside a box that the code requires completely re-running it from its source. That seems like overkill and makes no logical sense from a safety/engineering perspective, assuming the splice is done properly.

And if it doesn't require that, then there is nothing wrong with the OP's idea. He could simply cut the neutral wire as long as he adds sufficient length to both ends to satisfy 300.14.

I welcome anyone to correct me if I'm wrong here, but I think before jumping straight to running new wire that less labor intensive means should be considered, and citing published sources would be great too.

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