Detecting electrical cables in a wall when all the detectors seem crappy
September 1, 2020 3:47 AM Subscribe
We want to put up shelves at home. We have one of these stud/cable detectors, but it doesn't work reliably. Based on user reviews, neither do the much more expensive ones (like this). We really need the extra storage shelves will bring, but right now I'm nervous about drilling anywhere until I can be confident we're not going to hit a wire. How can we drill with confidence?
The issue with the detector we already have is that a) the interface is hard to read and b) it seems to detect live wires absolutely everywhere within our walls. The more expensive model linked to above has many one-star reviews complaining of exactly the same problem, including users who claim it detected live wires inside sofas, kitchen cupboards and boxes of cereal.
We bought the house three years ago and haven't done much drilling or construction/remodelling work since then, so we have no idea where wires are or ought to be within our walls. Given that we don't know where the wires are, none of the tools available seem to be accurate when it comes to detecting wires, and we badly need more shelves, how can we drill with confidence? Are there other products that actually work (i.e. reliably detect wires we shouldn't drill through without many false positives)? Is there some other way of detecting wires that I haven't thought of?
Advice should be UK-specific as that's where the house is and where we'll be buying any additional tools to help with this if needed.
The issue with the detector we already have is that a) the interface is hard to read and b) it seems to detect live wires absolutely everywhere within our walls. The more expensive model linked to above has many one-star reviews complaining of exactly the same problem, including users who claim it detected live wires inside sofas, kitchen cupboards and boxes of cereal.
We bought the house three years ago and haven't done much drilling or construction/remodelling work since then, so we have no idea where wires are or ought to be within our walls. Given that we don't know where the wires are, none of the tools available seem to be accurate when it comes to detecting wires, and we badly need more shelves, how can we drill with confidence? Are there other products that actually work (i.e. reliably detect wires we shouldn't drill through without many false positives)? Is there some other way of detecting wires that I haven't thought of?
Advice should be UK-specific as that's where the house is and where we'll be buying any additional tools to help with this if needed.
I have one of these old-school ones. It just bleeps, and there's a knob you turn to set the sensitivity - it works like a cheap metal detector. It's very simple to dial down the sensitivity to reduce false positives. They're not perfect, but I haven't found the newer 'digital' ones to be any better.
Once you work out the stud spacing for the wall (assuming it's an internal stud/plasterboard wall), you'll know where to expect the studs, and that's a big help.
Electricians will try to do vertical runs of cable to sockets and switches, but that's by no means a given, as it's all based on 'safe zones'. I would just be wary of drilling anywhere that's vertically in line with a switch or socket, or horizontally in line with a socket, and check it out fully with a detector.
posted by pipeski at 4:13 AM on September 1, 2020 [1 favorite]
Once you work out the stud spacing for the wall (assuming it's an internal stud/plasterboard wall), you'll know where to expect the studs, and that's a big help.
Electricians will try to do vertical runs of cable to sockets and switches, but that's by no means a given, as it's all based on 'safe zones'. I would just be wary of drilling anywhere that's vertically in line with a switch or socket, or horizontally in line with a socket, and check it out fully with a detector.
posted by pipeski at 4:13 AM on September 1, 2020 [1 favorite]
I sense [heh] that no stud finder / wiring detector will instill confidence, so maybe you need to look for solutions that don't use one.
Do you have reason to suspect wiring in the area you want to put up a shelf?
What is the era of construction and what is the wall constructed of?
posted by Glomar response at 4:14 AM on September 1, 2020
Do you have reason to suspect wiring in the area you want to put up a shelf?
What is the era of construction and what is the wall constructed of?
posted by Glomar response at 4:14 AM on September 1, 2020
Response by poster: Do you have reason to suspect wiring in the area you want to put up a shelf?
No, but I also don't have reason not to suspect wiring, or even the background knowledge to know where wiring is/isn't likely (the info above about it mostly coming down from the top of the wall where sockets/switches are is very useful, thanks). I'm generally an anxious person who tends to assume the worst so I have visions of my partner getting electrocuted the moment he tries to drill anywhere.
What is the era of construction and what is the wall constructed of?
It's a late 70s/early 80s council build. The walls are made of...wall (seriously, that's the level of home improvement knowledge I'm working with). All of the interior walls feel a lot more hard/solid than the drywall I grew up with (in a house that was built in the early 90s). Hard enough that it would be challenging to punch through them with a fist, which wasn't a challenge with the drywall in my parents' house (accidents happen). Beyond that I have no idea.
posted by terretu at 4:38 AM on September 1, 2020
No, but I also don't have reason not to suspect wiring, or even the background knowledge to know where wiring is/isn't likely (the info above about it mostly coming down from the top of the wall where sockets/switches are is very useful, thanks). I'm generally an anxious person who tends to assume the worst so I have visions of my partner getting electrocuted the moment he tries to drill anywhere.
What is the era of construction and what is the wall constructed of?
It's a late 70s/early 80s council build. The walls are made of...wall (seriously, that's the level of home improvement knowledge I'm working with). All of the interior walls feel a lot more hard/solid than the drywall I grew up with (in a house that was built in the early 90s). Hard enough that it would be challenging to punch through them with a fist, which wasn't a challenge with the drywall in my parents' house (accidents happen). Beyond that I have no idea.
posted by terretu at 4:38 AM on September 1, 2020
So I don’t usually go straight to drilling, mostly because drill holes are much bigger and harder to fill than nail holes. Once I have a reasonable idea of where the stud is (either by using a stud finder or by measuring a standard stud spacing distance from a known/suspected stud), I will bang in a thin nail with a hammer, same as if I were hanging a picture. It’s very easy to tell whether you’ve hit a stud or not - either you go through the drywall/plaster and you're in open space, or you feel it grab into the wood of the stud. I suppose it’s possible you could hit a wire this way, but an insulated wire ought to just shift out of the way if you came at it with a nail - a glancing blow from a nail shouldn’t remove the insulation.
Also you can turn off your power at the panel while you’re doing this.
posted by mskyle at 5:55 AM on September 1, 2020 [4 favorites]
Also you can turn off your power at the panel while you’re doing this.
posted by mskyle at 5:55 AM on September 1, 2020 [4 favorites]
Drywall is 'plasterboard' in the UK. There are a couple of different thicknesses, and newer houses tend to have the thinner stuff. Also, it's no longer that common to add a skim coat of plaster to walls, so your 70s/80s wall might still be plasterboard, just thicker than the new stuff, and with a bit of plaster on top, not to mention decades of paint.
The 70s council house I grew up in had plasterboard over studs, so I'm guessing yours will probably be the same. Earlier buildings sometimes used cinderblock, a sort of lightweight cement block that turns to dust if you look at it funny. If the powder that falls out is a dark grey and it seems solid all the way through, it could be that. It's too new to be lath and plaster, which is what my 1920s house has in the old parts. If you knock and the wall sounds hollow, it's plasterboard on studs.
Drilling a test hole to determine what kind of wall it is might be a good idea. When you drill plasterboard, you're only drilling 1/2" at most, and you just go gently, so that it doesn't punch through the other side with any force. If you do that, you won't damage any wiring that might be in there, as the wiring runs down through the noggings (horizontal pieces of wood between the studs) so it's kept away from the surface of the wall anyway.
posted by pipeski at 5:55 AM on September 1, 2020 [3 favorites]
The 70s council house I grew up in had plasterboard over studs, so I'm guessing yours will probably be the same. Earlier buildings sometimes used cinderblock, a sort of lightweight cement block that turns to dust if you look at it funny. If the powder that falls out is a dark grey and it seems solid all the way through, it could be that. It's too new to be lath and plaster, which is what my 1920s house has in the old parts. If you knock and the wall sounds hollow, it's plasterboard on studs.
Drilling a test hole to determine what kind of wall it is might be a good idea. When you drill plasterboard, you're only drilling 1/2" at most, and you just go gently, so that it doesn't punch through the other side with any force. If you do that, you won't damage any wiring that might be in there, as the wiring runs down through the noggings (horizontal pieces of wood between the studs) so it's kept away from the surface of the wall anyway.
posted by pipeski at 5:55 AM on September 1, 2020 [3 favorites]
Most store-bought wire detectors are way over-sensitive (I suspect it’s for liability reasons, but I don’t actually know).
Put sheets of paper between the detector and the wall. This will decrease the sensitivity of the detector. Keep adding sheets until the detector only beeps occasionally (you may need a magazine-thickness stack). You can do a sanity check by making sure it beeps when vertically above an outlet.
I have used this method with great success.
posted by mekily at 6:17 AM on September 1, 2020 [3 favorites]
Put sheets of paper between the detector and the wall. This will decrease the sensitivity of the detector. Keep adding sheets until the detector only beeps occasionally (you may need a magazine-thickness stack). You can do a sanity check by making sure it beeps when vertically above an outlet.
I have used this method with great success.
posted by mekily at 6:17 AM on September 1, 2020 [3 favorites]
How about a freestanding bookcase from Ikea / Homebase etc?
posted by Kiwi at 7:16 AM on September 1, 2020
posted by Kiwi at 7:16 AM on September 1, 2020
I never was comfortable with stud detectors, and I switched to a strong magnet taped to a string. Swing that gently along your wall and it will definitely twitch at the nails in framing, but it won't notice copper wiring because that isn't magnetic.
I guess there is some wiring that might be steel? But there's a two-part test to distinguish wiring from framing. 1. Does it go all the way from the ceiling to the floor in a straight line? 2. If it does, is there a similar pattern 16 in away on the horizontal?
If so, that's a stud.
posted by stupidsexyFlanders at 7:50 AM on September 1, 2020 [1 favorite]
I guess there is some wiring that might be steel? But there's a two-part test to distinguish wiring from framing. 1. Does it go all the way from the ceiling to the floor in a straight line? 2. If it does, is there a similar pattern 16 in away on the horizontal?
If so, that's a stud.
posted by stupidsexyFlanders at 7:50 AM on September 1, 2020 [1 favorite]
I second the recommendation to use a magnetic stud finder. Electronic ones are finicky and have a lot of false positives when used on their own, but are really nice when used in conjunction with a magnetic stud finder.
Move the magnetic stud finder over your wall - when the magnet hits a nail, it will stick strongly. Once you get a hit, move the magnet vertically looking for additional nails. If you hit a bunch of nails in a vertical sequence, you've found the stud. You can then use your electronic stud finder to accurately find the edges of the stud, starting in the center and moving left or right until the signal drops off.
I use the one recommended by Wirecutter that uses 2 very strong magnets, and it works in situations where electronic ones are really difficult to trust.
posted by Fidel Cashflow at 8:01 AM on September 1, 2020
Move the magnetic stud finder over your wall - when the magnet hits a nail, it will stick strongly. Once you get a hit, move the magnet vertically looking for additional nails. If you hit a bunch of nails in a vertical sequence, you've found the stud. You can then use your electronic stud finder to accurately find the edges of the stud, starting in the center and moving left or right until the signal drops off.
I use the one recommended by Wirecutter that uses 2 very strong magnets, and it works in situations where electronic ones are really difficult to trust.
posted by Fidel Cashflow at 8:01 AM on September 1, 2020
You won't find non-copper wiring in UK walls, if that's any help. There's a small chance there might be aluminium wiring if it's 40+ years old and they haven't renewed the wiring. Either way, you won't detect wiring with a magnet.
I like the idea of using some paper to reduce the sensitivity of the detector (although I'd be surprised it has no adjustment). Once you can get it to detect known wires (such as those above or below a socket), you should be able to locate unknown wires with more confidence.
posted by pipeski at 8:18 AM on September 1, 2020
I like the idea of using some paper to reduce the sensitivity of the detector (although I'd be surprised it has no adjustment). Once you can get it to detect known wires (such as those above or below a socket), you should be able to locate unknown wires with more confidence.
posted by pipeski at 8:18 AM on September 1, 2020
One way to do this is to use this sort of tone tracer [1] to follow the route of the specific circuits you're worried about (e.g. the ones connected to the lights and the socket ring in the room you're working in).
You'd do this by isolating the power to your consumer unit, then disconnecting the cables coming from the breakers for those circuits. You attach the tone generator to the cables for the circuit you want to trace, which basically turns those cables into an antenna which transmits an audio tone.
Then you can use the probe to follow the route those cables take behind the walls by moving it around and listening to the tone - the volume increases & decreases as it gets nearer or further from the cable.
[1] NB - not a recommendation, just a random cheap one on Amazon to illustrate the type I mean. There are lots of models but they all do the same thing.
posted by automatronic at 8:49 AM on September 1, 2020
You'd do this by isolating the power to your consumer unit, then disconnecting the cables coming from the breakers for those circuits. You attach the tone generator to the cables for the circuit you want to trace, which basically turns those cables into an antenna which transmits an audio tone.
Then you can use the probe to follow the route those cables take behind the walls by moving it around and listening to the tone - the volume increases & decreases as it gets nearer or further from the cable.
[1] NB - not a recommendation, just a random cheap one on Amazon to illustrate the type I mean. There are lots of models but they all do the same thing.
posted by automatronic at 8:49 AM on September 1, 2020
Electricians are not allowed to run electrical wires willy-nilly anywhere in a wall. Here is some guidance useful for the UK. Note that when they say "safe zone" they mean safe for the electrician. In other words, zones where wires might be and you should avoid. This would be similar in the U.S.
So avoid drilling holes within 150 mm (6 inches) of the ceiling. Avoid drilling holes within 150 mm (6 inches) of a inside or outside corner. Avoid drilling holes horizontally or vertically from any switch or socket.
But even within these wire zones, the wire must be at least 50 mm (2 inches) below the surface. So if you use screws shorter than this length you should be okay.
posted by JackFlash at 10:12 AM on September 1, 2020 [5 favorites]
So avoid drilling holes within 150 mm (6 inches) of the ceiling. Avoid drilling holes within 150 mm (6 inches) of a inside or outside corner. Avoid drilling holes horizontally or vertically from any switch or socket.
But even within these wire zones, the wire must be at least 50 mm (2 inches) below the surface. So if you use screws shorter than this length you should be okay.
posted by JackFlash at 10:12 AM on September 1, 2020 [5 favorites]
So if you use screws shorter than this length you should be okay.
I should clarify that I mean screws that penetrate the wall less than 2 inches. The screw may be long than that if you include the thickness of the object you are attaching to the wall. And this applies only to the wire areas. In non-wire areas it is safe to use bigger/longer screws.
posted by JackFlash at 10:19 AM on September 1, 2020
I should clarify that I mean screws that penetrate the wall less than 2 inches. The screw may be long than that if you include the thickness of the object you are attaching to the wall. And this applies only to the wire areas. In non-wire areas it is safe to use bigger/longer screws.
posted by JackFlash at 10:19 AM on September 1, 2020
USB Borescopes are cheap on Amazon, like $20 cheap, and small. I've got one that's 5.5mm (7/32", so a quarter-inch hole will be just right) and has LED illumination built in. I can plug it into my laptop, fire up the free VLC player, and view what the camera can see. If you can afford the bore-hole into the wall to inspect things, then it's a good solution. (I also see a lot of options in 8mm borescopes, which is 5/16", so a 3/8" hole would be roomy.)
It looks like they make them for USB-C and Micro-USB connectors, so directly viewing on your phone may be a possibility as well.
posted by Sunburnt at 3:31 PM on September 1, 2020 [1 favorite]
It looks like they make them for USB-C and Micro-USB connectors, so directly viewing on your phone may be a possibility as well.
posted by Sunburnt at 3:31 PM on September 1, 2020 [1 favorite]
In the past, I've used the probe from one of the (Ideal brand) tone/probe wire finder kits intended for use with telecom cable to easily locate electrical wires in wall cavities. You don't need the tone generator, just the probe.
An energized electrical wire always has 50/60Hz AC applied to it, the distinctive hum of which you should be able to hear from the activated probe's speaker when you have the probe pointed at the wall if there is an electrical wire present. The only "hard" part is adjusting the volume control such that you can get a reasonably good idea of where the wire actually is rather than the "yep, there's a wire around here somewhere" that you'll get from an excessively high volume setting.
You can point the probe at a wall switch or other known source to get an idea of both the sound that you are looking for and the detection range of the probe and adjust the volume accordingly.
Finding studs can be a harder problem depending on the construction of the wall. Most of the electronic units you'll find at the home center only work well on standard (thin) wallboard. Walls with a double layer for fire protection or walls made of plaster and lath give them fits.
posted by wierdo at 7:37 PM on September 1, 2020
An energized electrical wire always has 50/60Hz AC applied to it, the distinctive hum of which you should be able to hear from the activated probe's speaker when you have the probe pointed at the wall if there is an electrical wire present. The only "hard" part is adjusting the volume control such that you can get a reasonably good idea of where the wire actually is rather than the "yep, there's a wire around here somewhere" that you'll get from an excessively high volume setting.
You can point the probe at a wall switch or other known source to get an idea of both the sound that you are looking for and the detection range of the probe and adjust the volume accordingly.
Finding studs can be a harder problem depending on the construction of the wall. Most of the electronic units you'll find at the home center only work well on standard (thin) wallboard. Walls with a double layer for fire protection or walls made of plaster and lath give them fits.
posted by wierdo at 7:37 PM on September 1, 2020
How old is the house? Older homes in the US have steel jacketed cable, not plastic jacketed. Our house was built in 1970, and has BX cable, which is steel jacketed.
If your home has steel jacketed cable that may help allay your concerns about putting a nail or screw through it.
posted by ZenMasterThis at 4:54 AM on September 2, 2020
If your home has steel jacketed cable that may help allay your concerns about putting a nail or screw through it.
posted by ZenMasterThis at 4:54 AM on September 2, 2020
Steel jacketed cable is also known as armored cable.
posted by ZenMasterThis at 7:34 AM on September 2, 2020
posted by ZenMasterThis at 7:34 AM on September 2, 2020
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posted by stillnocturnal at 3:59 AM on September 1, 2020 [1 favorite]