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I have to anchor a bookcase to a wall to prevent it from tipping over.

When drilling into the wall, how do I make sure I can avoid drilling into the wires behind the wall?

I have bought a Stud finder which says it can detect wires, but I am not sure if it's that's the only thing I should rely on.

One of the Anchors will be on a stud, and the other will be on just dry wall.

Thanks.

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wires passing through studs should be under 36" and protected by nail plates, while wires between studs should have some freedom to move to mitigate the risk of puncturing. There are no guarantees, of course, especially in older homes or with remodels done incorrectly. Regardless, drilling that high up should lower, but not eliminate, the risk of hitting a wire. – Snowman Feb 17 at 22:29
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@Snowman, there is absolutely NO requirement or convention that says wiring should be under 36", and if the framing is drilled so that the hole is at least 1-1/4" from the edge of the hole to the facing edge of the framing no nail plates are required or typically used. Your assumption of what's correct is incorrect. – Speedy Petey Feb 18 at 12:42
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@SpeedyPetey where did I cite a code requirement or convention? I made a brash generalization and specifically said "there are no guarantees". Houses are like a box of chocolates: you never know what you're going to get. – Snowman Feb 18 at 15:46
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@Snowman, OK, but you did specifically say it "should" be like that, and then very obviously implied if it wasn't it was done "incorrectly". Neither of which is accurate. – Speedy Petey Feb 18 at 16:59
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Make sure to turn on all of the light switches in the room that you are drilling and the room on the other side of the wall, before attempting to use the wire finder! Also, think about if there might be pipes as well... Drill gently. – Bailey S Feb 19 at 0:39
up vote 9 down vote accepted

This is something that you have minimal control over. Most electrical runs going horizontally are about 2 feet off the floor or very close to the ceiling. There are lots of reasons for this but one of the obvious ones is it limits the areas of concerns when drilling.

Also for horizontal runs there should be a little slack where an anchor would just push the wire out of the way. For vertical runs these are stapled to studs on one side or the other. So just hit the middle of the stud.

Really two things that help me investigate walls if I am worried are monkey hooks and my magnetic stud finder. With the monkey hooks you can prick a wall for a good two inches plus while causing almost no damage. You can easily "feel" something if you hit plumbing, electrical, insulation, whatever.

With the magnetic stud finder you can use the drywall screws to find your on center of your framing members. With a spare yardstick or 2x4 and a couple of screw points you can find the center of a stud the drywall is attached to. From there you can assume that there is a 1-2 inch "don't screw" zone on each side. As usually the only issues you will have with anchors is screwing into something tightly stapled. Even screwing into a wire ran through a bored hole would be hard because unless the hole is really small or there are a lot of wires the screw will push the wire out of the way.

Note: For a heavy bookcase I would rely on an L bracket using toggle anchors - pictured below - in the wall. My reasoning for toggle anchors is that other anchors could effectively strip or lose binding but in effect stay in place because the shelf hasn't moved enough. You don't want to find out that your anchor has stripped when you climb up to get something off a top shelf. The toggle anchor won't give you a snug connection but you don't need it to be hardcore snug, you need it to work. (also note that the toggle anchors usually don't have a sharp tip, therefore making it ultra hard to damage wiring)

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+++ This answer was meant for anyone dealing with wood/metal framed walls. This would include most people in USA, Canada, Australia, New Zealand, parts of Mexico, parts of Asia, most dividers in large apartment buildings. The safe zones for drilling are usually the same no matter the country but the depth of the wiring and how it is secured is not. As for safety I would still offer that a prick test is better than any voltage meter I have ever used. If I was afraid of the prick going through the electrical conduit after going through a cinder block I would simply cover the tip (rubber, plastic, chewing gum).

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Thanks. I love that Monkey Hooks tip, I will pick one up today. For the scanner, I have already purchased this for Stud and Electric Scan (Please let me know if you think its not good enough): homedepot.com/p/… – ritK Feb 17 at 22:57
    
Also please let me know what Anchors you would use. For Dry Wall and for Stud. These bookcases are big - around 36 inches wide, 16" deep, and 77" or 84" height. – ritK Feb 17 at 22:58
    
@ritK - IMO they are all crap. To me either it works or it doesn't. A false positive or not seeing something 1 out of 10 times mean it is crap. I know that a series of screws are attached to a stud so I rely on magnets. If I were just doing some quick investigating and needed a wire finder I might use it but using it for your case I don't think it is useful. – DMoore Feb 17 at 22:59
    
I would get a plate or anchor system that allows me to attach 2-3 screws to the bookcases. I am sure someone can point you to the ones that come with IKEA shelves. The wall anchor systems they use are pretty good. – DMoore Feb 17 at 23:01
    
That "magnetic stud finder" looks handy. I'm not sure where to find one, but I do have a stack of neodymium magnets lying around. I should try waving them at my walls and seeing if they react to anything. – Ilmari Karonen Feb 18 at 14:23

I agree with the answer about using a stud finder with a voltage sensor. Also, bear in mind that while the horizontal wire runs are typically close to the floor or the ceiling, there are also cables running up studs, and they aren't necessarily stapled directly to the stud itself, either. Consider the NM cable standoffs (or "stack staples") in the pictures below, as well as the ad-hoc example with the cables tied up with a bit of extra NM. You really can't tell exactly what's in your walls without looking in there, although you can generally tell where this sort of thing might be an issue based on where you find things like light switches. But not always.

So, personally, if you're worried about it, I'd use a voltage sensor.

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Thanks. Nice tip. I am thinking I will turn of the power and then use the Money Hook to poke around behind the dry wall. I am hoping I can find something like this with hook. – ritK Feb 18 at 15:56

Unfortunately you can't be 100% certain but you can dramatically reduce your risk.

Checking local rules and practices for installing cables should be your first line of defense. For example in the UK we have "safe zones" where wires are normally run http://wiki.diyfaq.org.uk/index.php?title=Safe_zones_for_electric_cables . However it is not a guarantee, there may be exceptions to the rules (for example the UK rules allow running cables outside of the safe zones provided additional protective measures are taken) and there is no guarantee that the person who wired your house actually followed the rules.

Metal detectors and voltage detectors can be useful but again are not 100% certain and can suffer from both false positives and false negatives. Voltage detectors will not detect wires that are hidden behind/inside earthed metal.

P.S. Note that many posters on this site will post information on USA-specific rules and regulations without clearly indiciating them as such.

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Wiring should be roughly centered in the stud. Keep your anchor penetration to an inch or so and you should be safe. It's not common practice to actually locate wiring for this type of thing, though you're wise to be mindful of it. Also consider whether you have plumbing in the wall. Obviously pipes are larger than wires and can be closer to the surface.

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When you say centered - I think you mean it is roughly in the center front-to-back. Wires will most likely be attached to the side of a stud (i.e. at the left or right end). But the point stands that you will know by the feel of the drill when you've made it through drywall, and whether you've hit the open stud bay or hit a stud. – Shimon Rura Feb 17 at 21:18
    
I don't follow. Whether they're drilled through the stud or stapled along its length, they'll be roughly centered. – isherwood Feb 17 at 21:46
    
I agree with you - just thought it might be useful to clarify to clarify within what dimension the wiring would be centered. On first read I interpreted this as "centered within the stud bay" which isn't what you meant, so I wrote down what I thought you meant. – Shimon Rura Feb 17 at 21:57
    
@isherwood thanks. Did you mean inch long anchor is to be used? Or did you mean that the anchor should go into Stud about an inch long. I bought some 2 1/2 inch anchors, but now I am wondering if they are too long. – ritK Feb 17 at 22:15
    
1" to 1-1/4" into the stud should be fine. – isherwood Feb 18 at 0:47

By code, when a hole is drilled to run a wire or pipe through a wood member (stud, plate, etc.), if there is less than 1.5" of wood between the face of stud and edge of hole, a nail plate (made of steel) must be used to protect the wire/pipe from unnecessarily long fasteners. Use a screw that will not penetrate into the wall more than two inches (1.5" of wood plus 1/2" drywall). As far as between the studs, drill as small hole only the depth of the drywall, then use a piece of wire or tip of a screwdriver to 'feel' for a wire or pipe directly behind the hole.

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I've never seen such a plate. Wouldn't it make the drywall not-flush against the studs? – JDługosz Feb 18 at 5:55
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Google "nail plate stud" and you'll see a lot of different types. I think they're thin enough so that the depth doesn't really matter to the drywall's flatness. – Daniel Griscom Feb 18 at 11:02
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It's 1-1/4" from the edge of the framing, not 1-1/2". – Speedy Petey Feb 18 at 12:47
    
This is fine if the wiring is recent and up to code. Many installations fail at least one of these tests. – Ross Millikan Feb 19 at 6:01

Although you can't just trust a voltage sensor you can improve your chances significantly: Find and follow the wires leaving a socket. This will tell you the range over which it can detect voltage and will allow you to adjust the sensitivity if that's an option. If you can't follow the wires away from a socket, it's no use for what you're doing this time.

By following the wires from all nearby sockets, you can get an idea of how they run, and whwther they get near your target area.

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Many stud finders now have a voltage sensor home depot has several. Some are cheaper this is the first one that came up. Use this to find your stud then check for power. No power No worries. This is the safest route.

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Varies depending on your location and building codes there, but as a rule of thumb wires will go vertically or horizontally. Wires should not go diagonally through a wall. So don't drill in the column or row of a power point or switch.

Do remember walls have two sides, check the other side for switches and plugs and fuse boards.

Another option is to push through your gib/drywall with something non-conductive, in the spot where you want the fastener to be anyway. It doesn't take a lot of force to put a hole in drywall linings. An old insulated electricians screwdriver works well.

Once there's a small hole you can use a stiff wire through to sweep around and find anything by contact, although by this stage your hole is probably fine to use for the fastener.

If you want to spend money, a borescope can tell you what's inside the wall, but they need a hole of at least a centimetre to get the camera through, which is probably too big for your fastener.

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