I need to drill a hole through from my living room to my garage to put an ethernet run between them. I can only drill through from the living room in one spot due to the positioning of the electrical box that I want the ethernet cable to emerge at. I have measured where the hole will come out and found it is directly behind my boiler (the boiler is around 2cm from the wall and the wall is brick and plaster). Is just drilling slowly the trick here or is there another method someone can recommend to stop the drill bit from punching a hole in the boiler once it clears the wall? I was thinking of maybe placing something in the gap betweeen the boiler and the wall as a precaution to slow the drill bit down and give me time to stop drilling?

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    Absolutely protect the boiler. A sheet of scrap plywood and somebody on that side watching would be my suggestion. Commented Nov 7, 2021 at 13:08
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    Plywood is a good idea. You will know when you hit it and have plenty of time to stop drilling because a masonry bit won't quickly cut through it.
    – jay613
    Commented Nov 7, 2021 at 13:56
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    Can you run the cable elsewhere? Ceiling cavity, or perhaps just above the boiler ? Future serviceability is important.
    – Criggie
    Commented Nov 7, 2021 at 22:04
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    I'd use plate metal and an alert assistant.
    – Kyle B
    Commented Nov 7, 2021 at 23:20
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    Cat5s have a bend radius of 1 inch. You'll want to install something so you don't end up with a tighter bend that untwists all your twisted pair right next to a boiler (high energy device).
    – Nelson
    Commented Nov 8, 2021 at 3:30

3 Answers 3


Buy a drill stop to screw onto your bit, and set it to the thickness of the wall. Some drills also have a built-in stop that can be adjusted. If you don't know the thickness of the wall, then just increase the depth each pass.

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    This. But first set it a bit under the expected thickness of the wall. You don't want to find out wall was actually thinner at this point by hitting the boiler.
    – Mołot
    Commented Nov 8, 2021 at 10:34
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    You can also make a single-use stop by wrapping tape around the drill bit, with the edge of the tape at the depth you want to stop drilling. When the tape reaches the wall, stop. I wouldn't use tape by itself to stop me from drilling into a boiler though.
    – Dan C
    Commented Nov 8, 2021 at 18:51
  • Definitely a good tip but I'd still put something on the other-side of the wall as a safety net. Last thing you want is to find your measurements were a little off and your boiler is suffering for it. Commented Nov 10, 2021 at 16:29

Don't. You'll ruin the cable.

As Nelson points out in the comments, CAT5 cables have a turning radius of 1 inch to avoid damage to the cable. In a scenario where the boiler is only 2cm from the wall, achieving this bending radius will be difficult, if not outright impossible. Additionally, the heat from the boiler is also likely to damage the cable if it's held at such close confines to it.

As such, it's highly likely that going through with this wiring scheme will damage the cable, so you should reconsider your plans and possibly drill the hole through the wall somewhere else.

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    The easiest fix is to drill at an angle, and then perhaps chisel out a bit of a ramp leading into the hole to accomodate a nice smooth turn. With some luck, drilling at an angle can also let you avoid the boiler altoghether. You'll need a long bit, but those are readily available.
    – TooTea
    Commented Nov 8, 2021 at 8:11
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    Heat from the boiler? Every boiler I have touched in my life was so well isolated that I could barely tell a difference from the environment.
    – MaxD
    Commented Nov 8, 2021 at 9:09
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    @MaxD Sounds like you spent your life around modern high-efficiency condensing gas units. Traditional non-condensing boilers (gas, oil, wood, coal, …) emit a whole lot of waste heat in my experience.
    – TooTea
    Commented Nov 8, 2021 at 9:40
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    Bending it just once (not flexing back and forth) and running at 100Mbit, CAT5 will handle far tighter bends unless you're very unlucky, i.e. it's highly unlikely that going through with this wiring scheme will damage the cable. An old, badly-insulated boiler is more likely to have an effect, but even my previous one (from 1996) would have been fine with CAT5 touching the outside for long periods.
    – Chris H
    Commented Nov 8, 2021 at 11:02
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    In my experience, that "1 inch turning radius" sounds highly conservative. CAT5 isn't fiber, and in practice you could probably tie an overhand knot in an average CAT5 cable and yank it tight and it wouldn't be any worse for it. (Well, except for having an annoying knot in the cable, that is.) As for heat, +60 °C (which any CAT5 cable must tolerate) is a decent temperature for a sauna. If the exterior of your boiler gets that hot, you'll know it when you stand next to it (and should probably consider getting a better insulated one to save on heating costs, at least during summer). Commented Nov 8, 2021 at 20:51

Get a drill with a depth limiting adjusterenter image description here

  • Note there where it says "Images may be subject to copyright"? Please post the source for your image, but don't use it if it's copyrighted - that violates SE policy. Also, this adds nothing to the highly up voted, already accepted answer.
    – FreeMan
    Commented Nov 18, 2021 at 13:27

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