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Lots of home projects involve cutting or drilling through walls (everything from nails, screws, or hooks to mount things to cutting through drywall and drilling through studs to run wire).

In general, how do you know what's safe to break through and what isn't? In other words, when can you just start drilling through a wall and when do you need to be worried about hitting electrical lines, plumbing, etc.

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My friend went to hang a picture and drilled through a water pipe. The stream went quite far. –  Jay Bazuzi Jul 10 '11 at 5:23
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4 Answers 4

up vote 8 down vote accepted

Electrical wires typically run either vertically, up and down the side of a stud (with staples), in order to reach receptacles, ceiling lights/fans, etc., and horizontally in order to get across the room(s). The vertical wires are typically pretty easy to avoid: avoid drilling/nailing above a receptacle or light switch, or, if you have to, avoid missing on the side that the receptacle is nailed to. The horizontal runs should have enough play in them to avoid most damage, unless you drill/nail into the hole in the stud (called a nipple) that they pass through.

I don't think that it's required that you put any metal plate on the stud in order to protect the Romex/cable/conduit, but rather that it is only required if you drill the nipple too close to one side of the stud, at which point a metal brace is needed in order to ensure structural strength. Outside of drilling/nailing into an unprotected nipple, or very near it, there is little to worry about when it comes to the electrical.

When it comes to pipe, you should be able to tell if you hit copper pipe. Even though it might be one of the softer metals, it's still going to offer a substantial amount of resistance, and unless you hit it where it passes through a stud, your nail/drillbit will probably deflect off of the curved surface of the copper pipe. With PVC or ABS, however, yeah, you're most likely going to have a leak if you hit it squarely with a drillbit, maybe even a nail.

When it comes to cutting large holes in drywall, cut horizontally first -- if there's a stud or vertical pipe, it's better for you to find it immediately, at which point you might decide it's better to make a new hole on the other side of the stud, rather than later, after you've already made a long vertical cut in the drywall.

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These things don't provide any structural support, though there are other plates used for those purposes: homedepot.com/h_d1/N-5yc1v/R-100345566/h_d2/… –  BMitch Jul 11 '11 at 11:27
    
@BMitch I like the idea, but they're not required by code, as far as I know... and if they're not required by code, it's unlikely that they would have been installed. –  Michael Jul 11 '11 at 15:34
    
looks like it becomes a requirement at 1 1/4" from the finished surface, so if they drill their hole within 3/4" of the face of the stud (assuming 1/2" drywall) it becomes a requirement. This is from a 2008 internet posting on the NEC, so actual codes may have changed, and localities may be stricter. –  BMitch Jul 11 '11 at 21:16
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Aim for a stud or well away from the stud. If a line goes through a stud, there should be a metal safety plate on the stud that will keep you from going any further.

Lines that go up and down the wall will frequently be attached to the stud with staples (any electrical line running vertically will be attached) so you want to avoid just missing the stud to one side or the other. If you don't need the support of a stud, then just poking a hole in the drywall should be well short of any line that is running between studs, however, it doesn't hurt to exercise a bit of extra caution if your near the height of nearby outlets.

To help, get a stud finder that also includes detection for metal wiring and pipes. They aren't fool proof, but when they do find something, they can be a life saver.

stud finder

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I'll add my experience here for future googlers... don't count on anything being done to code. When I wall mounted my monitor I squarely hit a hot line in a nipple that was protected by a plate on one side only (the OTHER side of course). I had used a stud finder that had a power line detector which registered power all over where I was drilling, but I figured I was using it wrong and proceeded anyways. When I opened up the wall I found diagonal runs, horizontal runs, vertical runs ... just a mess of lazy wiring. Err on the side of caution and pay attention to your detector. –  Stephen Sep 10 '11 at 12:46
    
@Stephen, how did you find out that you had hit the hot line? –  ArgentoSapiens May 30 '12 at 17:41
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In our first house, I was drilling a hole in the kitchen wall to run a cable for a garbage disposal switch. I met some resistance, leaned into the drill, and thought better of it. I dug out photos I'd taken during construction, and found I was about to drill through the waste pipe from the upstairs bathroom. Luckily the metal plate warned me! The moral of this story is to pay attention to what your drill or knife is telling you if you meet unexpected resistance. –  TomG May 31 '12 at 2:53
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@ArgentoSapiens The dull red glow of melting drill bit spinning against live wire left clear gouges along the drill bit. –  Stephen May 31 '12 at 19:12
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Old question, but just my 2 cents for the record.

Code varies but some things are pretty consistent. Here in Ontario, Canada, metal plates to protect wires are required if the wire is witnin 1 1/4" of the outside of the stud. In other words, if you drill a hole for wire through the middle of a 3 1/2" stud, you should try and stay in the middle 1" area. If you go closer to the edges, you need to protect the area with a metal plate. Following that rule, you could easily require a plate on one side and not the other, depending on the size and position of the hole (or holes.)

That rule tells me that, with 1/2" drywall and 3 1/2" stud walls, I should be OK if I don't drill more than 1 3/4" into the wall. Unfortunately, I've seen many cases where metal plates should have been used but weren't but at list limit your drilling to 1 3/4" (or 1 1/2 for a little more safety.)

Oh - and, of course, if you hit something hard, don't just keep pushing and eventually drill through it or you may get a nasty shock.

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Plumbing is the greatest concern. You can probe with a punch or a tool like an ice-pick. Generally check both sides of the wall for clues. Plumbing generally is up/down or straight right/left. Copper tubing is something to be wary of. In walls they lie directly above where the stubout or angle valve is (supply). Remember if you have to drill you really don't need to go deep usually. I never really need to drill. The punch is usually my drill. Wires will move out of the way and short the circuit if compromised so don't sweat it. Plumbing can be troublesome.

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