I'm sure this is going to be lambasted by the code gods, but is it SAFE to solder the wires in a Romex cable to extend it? Obviously I would ground the circuit as normal, just trying to avoid another junction box. Would I heat shrink each individual wire and then the outer sheathing as well? Thanks for any advice

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    Possible duplicate of Can cable splice devices be concealed?
    – JPhi1618
    Commented Mar 6, 2019 at 16:59
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    Solder, whether leaded or ROHS, introduces amalgam material into the joint. This material is subject to electromigration under current and ion diffusion without current, the different ion species will diffuse/migrate at different rates and directions to create distinct layers of homogenous material, the joints between these layers are brittle, resistive, and a source of mechanical weakness. This process takes 10+ Years to happen. Welding does not have this downside.
    – crasic
    Commented Mar 6, 2019 at 19:38
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    Why not pull a longer cable through?
    – LShaver
    Commented Mar 7, 2019 at 3:32
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    Can you cheat, by installing a wall power socket where the cable gets to, and loop off that to the next piece?
    – Criggie
    Commented Mar 7, 2019 at 8:43
  • I actually did that on the wall, unfortunately this section is on the ceiling right near the exhaust fan over the shower. Don't want to put a recepticle there but otherwise yes.
    – BigLake
    Commented Mar 7, 2019 at 12:10

3 Answers 3


They do make Romex Splice Kits that claim to be legal for rework inside of a finished wall without junction boxes. Soldering is absolutely the wrong way, and regular wire nuts are not going to cut it. You need a mechanical fastener rated and tested for the job.

enter image description here

  • Here is another question/answer discussing these devices: diy.stackexchange.com/q/89945/43874
    – JPhi1618
    Commented Mar 6, 2019 at 17:00
  • Excellent, I hadn't seen one of these. Thank you for the suggestion. I'll probably go with that.
    – BigLake
    Commented Mar 6, 2019 at 17:08
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    @JoeDunigan, Just keep in mind that it should be a last resort. If there's any possibility of replacing the whole run of cable, you really should do that. These splices are only meant for "repair" where running new wire would be very difficult.
    – JPhi1618
    Commented Mar 6, 2019 at 17:10
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    There are crimped-and-soldered knob & tube splices that are over 100 years old and as good as the day they were made. The main problem with the old K&T wiring is that the bare wires overheat when they get buried in insulation, and the rubber insulation dries out and falls apart. The problems with solder are, first, that it isn't legal, and also that the skill level of the home installer isn't remotely guaranteed, plus the vinyl insulation on today's wires is more likely to melt than the rubber insulation used in the old days was when the wire is heated with the soldering iron or torch, etc. Commented Mar 6, 2019 at 18:39

Well, they actually make an approved device to splice Romex outside a junction box.

enter image description here

That said, soldering has very specific requirements for splicing it "dry" in advance before solder is even applied (this is a much bigger PitA than you think, because it makes tinning hard!) The splice connection must be both mechanically and electrically complete before you even start soldering. This is called out in NEC 110.14b.

Then you have to wrap and layer insulation in a particular way. I could see where shrink tube could be an option, but any sharp points on the resulting splice will tend to pierce the shrink tube, so I would do 2-3 layers of it over friction tape honestly. Friction tape does something electrical tape does not, and that's protect the insulation from physical damage from corners in the splice.

It is an artisanal craft, exactly the kind of reason why electricians are apprenticeships. Last time I did one, it took a half hour (per wire) and I'm still not confident it's right.

This is not kid stuff. Aside from the fact that you're supposed to pull permits and have inspections... fires get investigated. If it's found to be your negligence, fire insurance won't pay. Then the mortgage lender will call the note.

Every bit of Code I've ever seen, I have ultimately found had very good reasons for being that way. Code is written in blood and ash, it is the collective knowledge of how not to have problems unnecessarily.

With rare exception I have never seen a code violation that also managed to be safe. Those exceptions can be negotiated with your AHJ.

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    Not at all, I'm quite aware and respectful of codes. In fact I oversized everything I did with my plumbing. I am new to wiring and have spent hours on sites like these and talking to friends with experience and electricians about how to do the job safely and effectively. Which is why I asked this question rather than just doing something that I know I COULD do but not knowing the full implications and possible effects. The only reason was I was looking for a way around a jbox for aesthetics, knowing that mechanical connections require them. Just wondering if there was another way.
    – BigLake
    Commented Mar 6, 2019 at 17:05
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    But thank you for your assumption that I'm snubbing codes and people that create them. That's why I used this site to ask, isn't that what it's for?
    – BigLake
    Commented Mar 6, 2019 at 17:07
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    @JoeDunigan I've toned it down. But we get a lot of people come in here going "Code seems stupid to me and I don't plan to follow it". Sorry if I mistook you for that, but you kinda sounded like that coming in. Commented Mar 6, 2019 at 17:13
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    @Harper I for one appreciate you making the point about the electrical code. Sure, it's conservative, but it is meant to be. The point is to prevent people from dying in avoidable fires caused by faulty installations (and also from electrocution). Besides, the code actually the law. Commented Mar 6, 2019 at 18:42
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    @Medievalist NEC is a model law like UPMIFA. Model laws are created by nonprofits to aid states and localities in setting their law. In NEC's case, it is designed to be *incorporated by reference", that is,the Legislature passes a law that says "NEC 2014 is part of our law". And blam! It is. So yes,as a matter of fact, it is law. Commented Mar 7, 2019 at 2:56

Take a step back and consider. The right way to do it would have three distinct components: (a) wirenuts, (b) a box, and (c) accessibility behind a removable faceplate. The last of these is presumably what's causing trouble in this case. Why change the other two components too? Once you've decided you'll compromise code compliance, why not make the minimum possible deviation?

If I were reno'ing a house and found a box buried behind drywall, but it was a code-legal covered box and the connections were properly wire nutted, I'd say, Someone was lazy, and I would not have done it, but I understand, and I really could not say that a functional risk was created. If I found heatshrink-wrapped solder joints, I'd say someone went out of their way to show contempt for code, all current practices, and safety.

And it's not just that the code writers didn't know about solder. It turns out that in short-circuit high-current conditions, solder can melt or even evaporate very quickly, leaving you with no path to ground, or a high-resistance connection. Both very bad.

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