I want to install fiber optic in my house. It shouldn't be an issue except at some point my phone cable goes through a 5cm-thick concrete slab that was cast around it. This happens in a weird corner which makes using heavy machinery difficult. My plan right now is to break the slab around the cable with a hammer and a chisel.

Is there a big risk to damage the phone wire? Is there an other way to proceed you recommend?

  • You want to install fiber optic, doesn't that mean the utility provider needs to bring a new fiber cable into your house? Oct 27, 2020 at 14:59
  • @PlatinumGoose Not into your house but to a point on an outside wall if buried or inside to a junction box if conduit is installed by builder.
    – JACK
    Oct 27, 2020 at 15:48
  • 3
    It isn't clear why adding fiber inside or outside the house should have anything to do with the existing phone cable. If the fiber service replaces the phone service, the phone cable can be abandoned in place. In any case, there isn't a clear need for the fiber to follow the same path as the phone cable.
    – Greg Hill
    Oct 27, 2020 at 15:54
  • Basically there is a point outside my house where is fiber is connected, and from this point there is a tube that goes to my house, and the phone wire goes through this tube. The tube goes underground for around 10 meters and the phone wire comes out of the ground inside my cave except the concrete was casted on top of the tube. (I hope that's clear) Oct 31, 2020 at 23:02

4 Answers 4


If you need to maintain the existing phone cable, leave it alone. Actually, even if you're not planning on using the existing phone cable, just leave it alone.

If you want/need to run the fiber close to the existing cable, drill a new hole. That will give you a neat, tidy opening you can run the fiber through and shouldn't cause any damage to the existing cable, so long as you're not trying to get too close to it.

Optionally, run the fiber in a totally different location. Bring it to the slab, then run it up, in EMT or Schedule 80 PVC (for protection on the outside of the house), until you hit wood, then go in through the wood instead of through concrete. This will make all your work much easier as any work to get through wood is much easier than any method of getting through concrete.


I understand the desire to do it properly and fix the issue, but cutting concrete is a lot of work and is probably going to rip your wire apart in any case, no matter how carefully you try to break it. So isn't it easier to lay new wire behind/above/around the concrete slab, or if available, using a different tube for electric wires that is also already cast in there? Tidy up the old wire and cut it off at both sides of the slab, but otherwise don't touch the concrete?

  • 1
    Cutting concrete with a saw is almost no work compared to a chisel.
    – Ed Beal
    Oct 27, 2020 at 16:10

I would probably want to cut the slab, using a masonry blade on a skill saw and leave that small chunk intact it is really hard to keep from damaging wires through concrete the vibrations tear up the insulation. Once you get the slab removed you could try to break the small piece up but be ready to splice in a new piece using a wet location communications crimps. The ones I have use a dielectric jell you slip the 2 wires in and smash with pliers.

  • I agree. Make a bunch of shallow cuts. those communication splices work great.+1
    – JACK
    Oct 27, 2020 at 14:11

The other answers are good. If you do decide to go ahead with hand tools, I recommend using a digging bar (it has many names).

Use it vertically, hitting the concrete with the blunt end, causing the concrete to break at its weakest places. Fewer chips flying around, and safer.


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