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I've got a situation where I want to put a wire in a concrete wall (I have a channel), but the one coming in isn't long enough. I cannot replace the incoming cable, so I need to join it with another one inside the channel. Said channel will afterwards be filled with cement, so I won't be able to access the joint anymore without some serious destruction. What is the best way to join the cable so that I can sleep easily knowing that there will be no problems there? If it matters, the cable will not be carrying significant loads (less than 100W max).

Added: Clarification was asked in comments. Location in world: Latvia. We're a 220V country. The incoming cable in question is marked "2x1,0" which (if I understand correctly) means two wires, each 1mm2 cross-section. Copper. It's pretty thin. The cable with which I will join it will be similar.

It will feed one LED lighting fixture (up to 50W, but probably less) and a wifi router. The location makes it unlikely that heavy loads would be attached there, however, of course, I cannot predict the future.

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    Type of cable and location in the world will help. There are some connectors for being hidden in walls that are allowed in some locations. 100w now might turn into 1500w in the future. Cables can always be replaced or replaced and moved.
    – crip659
    Feb 20, 2023 at 15:21
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    It might be helpful to ask yourself, “if my splice failed in 6 months, how would I run power?” Then save yourself the trouble and do that alternative. Feb 20, 2023 at 15:58
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    @FreeMan I'm not quite at the point where I can cast close and reopen votes on diy, but I don't think it is possible to "vote to leave it open". You can "vote to close", or "vote to reopen" once it is closed, but there is no "vote to leave open". Feb 20, 2023 at 16:07
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    @MartinBonnersupportsMonica I think he meant not to vote to close. It takes three votes to close. I have the option to vote to close, but I do not need to take that option.
    – crip659
    Feb 20, 2023 at 16:22
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    Does Latvia use IEC 60364? That seems on-topic to me and falls under, "National building codes (of any country)."
    – watkipet
    Feb 20, 2023 at 17:05

3 Answers 3

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if i interpret your description properly - where your existing incoming wire length ends up ending somewhere within the existing wall, you pull that length of it out and cut it and have the splice on the outside of the wall. Then you get whatever proper wire and lay a single run of wire through the wall (channel) and have any splices happen outside the wall. So you would be wasting the existing length of incoming wire that goes however far into your channel. You want one good continuous length of wire that would be encased within the concrete wall never to be touched again.

in the US there is UF-B wire which has extra thick insulation and is rated for direct burial in the earth as well as being ultraviolet resistant. But it is not approved for being used in poured concrete. You would not want to run that or any other non conduit protected wiring within poured cement (or concrete) because as the cement cures is becomes very alkaline like PH 13 for a period of time, and that can harm the insulation of the wiring.... I mean you could do it and take your chances but to do it properly and have no future problems is why you would use some sort of pvc or metal type conduit that encases the wire and have the concrete/cement poured over that. And then after the wall is cured, you can always simply pull wiring through the conduit... you didn't elaborate but I assume your channel is a straight run; if not then you want it to be unless you have good reason for it not to be.

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  • I think I'll try to go with this option.
    – Vilx-
    Feb 21, 2023 at 8:59
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I doubt anyone here is familiar with code in Latvia.

That being said, the "correct" way to do this in most code-complying areas would be to leave the splice serviceable. One option in your case would be to carve a hole in your wall and install a box to splice the wires in, and leave the box cover accessible (do not cover in cement). If you don't want a box cover there, then another option is to trace you cable back to a place where a box would be acceptable, and run new cable from that point.

Some jurisdictions allow the use of splice kits that are designed to be inaccessible after installation.

If you don't know what is acceptable in your jurisdiction and you can't learn yourself, then you will need to hire a professional to either do it for you or educate you.

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    This, exactly. There's no sense gaining access to make the splice and then deliberately making it not only inaccessible, but un-locateable (because you'll forget the exact spot on the wall.) A suitable box can be placed in the wall and cemented around, with an accessible cover, and then it can be found, and it can be repaired if repair is ever needed. Alternatively, you just cut a whole new channel with the tools that folks in countries that use that method have available and run a whole new cable without joints.
    – Ecnerwal
    Feb 20, 2023 at 16:13
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"cable in a concrete wall" is not a good idea, and this is why. No maintainability. Better to put the wires through conduit. This is one place where steel conduit is not good, and plastic works better.

With conduit, you can pull the wires out readily and at will, and then pull in replacement wires. The conduit must be built "to be able to be pulled" e.g. you can't have a plumbing elbow in there, it needs to be broad "sweeps" of turns. In North America conduit is required to be built empty of wires, and then wires pulled in after completion. This "keeps you honest" lol.

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    You're probably referring to US code. In Europe, embedding cables in concrete is allowable. The focus is on safety, and concrete solves a lot of problems, including fire hazard.
    – vidarlo
    Feb 20, 2023 at 22:27
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    Safety is the same either way though @vidarlo. You also have zero maintainability. So you're forced to bust more concrete. Feb 20, 2023 at 22:44
  • Safety need not be an issue. Reliability to a certain extent yes, but safety can be handled. In general applicable standard in Europe is IEC60364, and local laws generally allow solutions that is comparable to IEC60364 level.
    – vidarlo
    Feb 21, 2023 at 7:35
  • In the post-Soviet world, cable in concrete is pretty much a common occurrence. And don't even get me started me on conduits.
    – fraxinus
    Feb 21, 2023 at 9:19

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