Jacob
New Luddism. Wake up and resist.
New house means new shelves!
What's a good mains detector and how reliable are they?
What's a good mains detector and how reliable are they?
Mains detector
- Thread starter Jacob
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I assume you mean something to find cables in walls before you drill through them. The first is any cables should run vertical from a socket BUT having seen them laid diagonally and in many other odd configurations then a decent detector is worth having but they do not come cheap. Using a cheaper tester will give an idea but with less certaintity which is less of an issue in your own property providing there is RCD protection.
The one to look at is the Bosch, available in screwfix Bosch Truvo Digital Detector - Screwfix
There is a more expensive version that will detect much deeper but I doubt you are using 4 inch screws.
The Bosch one is available on Amazon at a better price
https://www.amazon.co.uk/Bosch-detector-one-button-handling-Detection/dp/B01J1FN7ZE?th=1
They also do the more advanced version at £90 but I doubt you need all those features, by the way the professional Fluke detectors are around £700 !
If in any doubt then before drilling turn of the local sockets after using the detector just in case someone has done some dodgy work and the cable for some reason has no electrical protection.
The one to look at is the Bosch, available in screwfix Bosch Truvo Digital Detector - Screwfix
There is a more expensive version that will detect much deeper but I doubt you are using 4 inch screws.
The Bosch one is available on Amazon at a better price
https://www.amazon.co.uk/Bosch-detector-one-button-handling-Detection/dp/B01J1FN7ZE?th=1
They also do the more advanced version at £90 but I doubt you need all those features, by the way the professional Fluke detectors are around £700 !
If in any doubt then before drilling turn of the local sockets after using the detector just in case someone has done some dodgy work and the cable for some reason has no electrical protection.
RogerS
Established Member
Just pray that they didn't use that plasterboard with the silver foil on one side as that renders these devices pretty much useless, I've found.
eribaMotters
Established Member
I found my old Bosch was pretty good until I came across a similar problem to above. We have a new build with 100mm foiled insulation in the cavity. Needless to say it went nuts, but not as nuts as me.
Volin
Volin
That is why some are much more expensive like the fluke, it is not expensive if you are working in customers property and could end up not only repairing the cable but also to re decorate a room.
Jacob
New Luddism. Wake up and resist.
Thanks for that. £90 is good value even of if it only saves just one or two hits.
Detectors are tricky.
I have an expensive fluke that will find cables buried upto 2 metres below ground, but at £400 odd used prices this isn't sensible for you.
I have a early bosch cable/pipe/ stud detector that costs still around £100 and it's better than nothing but I don't entirely trust it. These I think are the worst value. It's a lot of money for something unreliable.
For electricity, I think the best value answer is a good (not a cheap) non contact voltage detector or "volt stick".
You can use these around switches and sockets to quickly see which direction the cable is headed up down or across the wall when it leaves the socket.
This is useful to know, and then you trust that the cable won't randomly head off at a diagonal but follows the rules. If not, you are relying on your rcd and will need a sparky and a plasterer !
A volt stick won't read very far into the wall so it will never guarantee that a place where you want to drill is safe. There's always an element of risk, but if you have figured out where all the obvious cables do seem to run, then maybe you accept it.
My favorite volt stick is the latest Megger VF5 model. It has an extra high sensitivity range (down to 12V ac).
If not that one, get the fluke VF2 model. It blinks while turned on so you always know that it is active.
You'll pay 25-35 for one of these but you're getting the best of the breed in terms of sensitive, reliable and useable.
Lastly a trick. Sometimes it seems detectors go off as soon as you bring them anywhere near a wall and there is no selectivity at all. For the most pinpoint reading, place your spare hand flat on the wall a few feet to the side of the area you're interested in. The detector will settle down and work properly. It applies to volt sticks and to the Bosch type detectors both.
The Bosch "radar" type detectors btw are supposed to be v.good, but your into more money than my Fluke transmitter / receiver set.
I have an expensive fluke that will find cables buried upto 2 metres below ground, but at £400 odd used prices this isn't sensible for you.
I have a early bosch cable/pipe/ stud detector that costs still around £100 and it's better than nothing but I don't entirely trust it. These I think are the worst value. It's a lot of money for something unreliable.
For electricity, I think the best value answer is a good (not a cheap) non contact voltage detector or "volt stick".
You can use these around switches and sockets to quickly see which direction the cable is headed up down or across the wall when it leaves the socket.
This is useful to know, and then you trust that the cable won't randomly head off at a diagonal but follows the rules. If not, you are relying on your rcd and will need a sparky and a plasterer !
A volt stick won't read very far into the wall so it will never guarantee that a place where you want to drill is safe. There's always an element of risk, but if you have figured out where all the obvious cables do seem to run, then maybe you accept it.
My favorite volt stick is the latest Megger VF5 model. It has an extra high sensitivity range (down to 12V ac).
If not that one, get the fluke VF2 model. It blinks while turned on so you always know that it is active.
You'll pay 25-35 for one of these but you're getting the best of the breed in terms of sensitive, reliable and useable.
Lastly a trick. Sometimes it seems detectors go off as soon as you bring them anywhere near a wall and there is no selectivity at all. For the most pinpoint reading, place your spare hand flat on the wall a few feet to the side of the area you're interested in. The detector will settle down and work properly. It applies to volt sticks and to the Bosch type detectors both.
The Bosch "radar" type detectors btw are supposed to be v.good, but your into more money than my Fluke transmitter / receiver set.
HamsterJam
Let’s take it apart to see what’s inside….
I have the green Bosch Truvo metal and wire detector and don’t rate it. It is a replacement for a very old Draper detector that gave up the ghost after thirty years or so of pretty heavy use. In comparison the Bosch anppears over sensitive. Could be we have foil backed plasterboard in some places but other areas are lime plaster over cobb. Placing my spare hand on the wall helps but still not 100%. I wonder if the moisture content in the cobb is high enough to trigger it.
Fortunately the Bosch seems better at finding live wires and I have a fair idea where the pipes run.
Fortunately the Bosch seems better at finding live wires and I have a fair idea where the pipes run.
naughtymoose
Established Member
When the Bosch ones came out a lot of us electricians moaned because they "didn't work". The hand trick was in the instructions, if I remember correctly!
Jacob, don't forget our (electrical types) "Safe Zone". It is 150mm from corners and tops of walls. These zones are sometimes used to route cables about from floor to floor. Congratulations on the new home!
Richard_C
Established Member
Brother in law bought a 1970's built house, after a few mishaps we realised the electrician/builder had saved a few yards of cable by running everything by the shortest possible route including diagonally from sockets and switches. I reckon they would have dangled cable diagonallay across the windows if they could have got away with it.
(a year or two in, when he could afford it, he had a complete rewire. That was when we discovered that some wiring ran around the architraves of the pantry and boiler room, held in place by drawing pins ......)
But things are better now - aren't they?
Enjoy your new house, it takes a while to get to know all you want to know, but with easy digital photography on your phone you can take pictures of everything you can - I keep a folder of pictures of undersink pipework, anything I find if I take a bit of floor up, anything new I put in, the inside of the porch roof when I re-clad it ....because in a few years you won't remember it all and an archive is invaluable. On the back of the airing cupboard door I have a schematic of the plumbing and which stop valve works what, by the fuse/MCB box I have an authoritative list of which mcb works which lights and socket. It might seem a bit obsessive, but most of my paint and walls used the Dulux 'mix' colours so I keep a spreadsheet of the colour codes and how much I needed for each room.
(a year or two in, when he could afford it, he had a complete rewire. That was when we discovered that some wiring ran around the architraves of the pantry and boiler room, held in place by drawing pins ......)
But things are better now - aren't they?
Enjoy your new house, it takes a while to get to know all you want to know, but with easy digital photography on your phone you can take pictures of everything you can - I keep a folder of pictures of undersink pipework, anything I find if I take a bit of floor up, anything new I put in, the inside of the porch roof when I re-clad it ....because in a few years you won't remember it all and an archive is invaluable. On the back of the airing cupboard door I have a schematic of the plumbing and which stop valve works what, by the fuse/MCB box I have an authoritative list of which mcb works which lights and socket. It might seem a bit obsessive, but most of my paint and walls used the Dulux 'mix' colours so I keep a spreadsheet of the colour codes and how much I needed for each room.
scholar
Established Member
That is not quite right - cables can be vertically or horizontally in line with fixtures as well as in the corner and top of wall zones as already mentioned (they are now called prescribed zones).
Here is a useful picture
But @Spectric is correct otherwise in saying they can be anywhere if people have not followed the rules.
A detector is useful to confirm other evidence in my experience, but not as the sole basis to rely on.
One thing I encountered recently was cutting into some plasterboard on one side of a wall - there were no fixtures on that side but a wall switch on the other side. Fortunately I was wary of this and indeed the cables were pressed against the far side of plasterboard away from the switch side and held in place by the intra-wall sound insulation batt - an unbelievably stupid installation. (I still nicked the cable so had to sort that out).
Cheers
I was managing a factory refit once.
We needed to remove a large section of the floor slab to install 4 foot deep reinforced concrete foundations for a machine.
The contractors diced the floor into metre squares with a diamond saw, bolted an eye into the centre and plucked them out with the crane.
At one point, they lifted a slab and found a plastic conduit containing 400 ethernet cables running diagonally below, unmarked on any plans. Because they had set the saw to "just" deeper than the thickness of the slab, we got away with cutting through the wall of the round conduit without nicking a single cable. To trace and rejoint that bundle could have been a nightmare .
The experience was v transferrable. It's why I never set my table saw full height for cutting thin material. Theoretically more efficient, things can and do go wrong and you want the minimum blade projection through the stock when that happens. Same goes for plunge routing, cutting floorboards and plasterboard....
We needed to remove a large section of the floor slab to install 4 foot deep reinforced concrete foundations for a machine.
The contractors diced the floor into metre squares with a diamond saw, bolted an eye into the centre and plucked them out with the crane.
At one point, they lifted a slab and found a plastic conduit containing 400 ethernet cables running diagonally below, unmarked on any plans. Because they had set the saw to "just" deeper than the thickness of the slab, we got away with cutting through the wall of the round conduit without nicking a single cable. To trace and rejoint that bundle could have been a nightmare .
The experience was v transferrable. It's why I never set my table saw full height for cutting thin material. Theoretically more efficient, things can and do go wrong and you want the minimum blade projection through the stock when that happens. Same goes for plunge routing, cutting floorboards and plasterboard....
HappyHacker
Established Member
Have a look at Buy The Best Live Cable Detectors For DIY In Wall Detection but all score 9/10.
I have use the Zircon for years and it is reasonable for finding live cables. I tried another expensive make recently but it didn't find cables when I knew there were there and indicated whole walls were live when there were no cables in them. It went back.
I also use professional signal injection/finder equipment and they are usually very good but expensive for occasional DIY use. Cable Tracers & Fuse Finders | RS
But don't do what I did: traced the cables in a wall and marked them then ran a wall chaser straight through them.
I have use the Zircon for years and it is reasonable for finding live cables. I tried another expensive make recently but it didn't find cables when I knew there were there and indicated whole walls were live when there were no cables in them. It went back.
I also use professional signal injection/finder equipment and they are usually very good but expensive for occasional DIY use. Cable Tracers & Fuse Finders | RS
But don't do what I did: traced the cables in a wall and marked them then ran a wall chaser straight through them.
I’m really surprised at so many people rating the Bosch one, I bought a different model at a similar price and honestly it’s no more accurate than rolling a dice. Land on a 3 or a 6 and there’s a cable there all the other number = no cable.
Usually I just apply common sense. Assess both sides of the wall, and ask myself if there’s any chance the bodging silly person who had my house before me could have done anything stupid with any of the sockets that would cause a cable to be there. Even then, if you drill carefully you can feel the second you penetrate through the back side of the plasterboard, so stop drilling and shine a light in to check if you can see anything you shouldn’t (this obviously only works on hollow dot and dab or stud walls)
This is the one I have, just googled and it’s more expensive than I remember. I honestly don’t even use it anymore. I tried again recently when wall mounting a tv in my office. It told me there was a live cable where I wanted to drill, I thought about it for a moment and realised there wasn’t, and sure enough when I drilled, no live cable in sight.
Usually I just apply common sense. Assess both sides of the wall, and ask myself if there’s any chance the bodging silly person who had my house before me could have done anything stupid with any of the sockets that would cause a cable to be there. Even then, if you drill carefully you can feel the second you penetrate through the back side of the plasterboard, so stop drilling and shine a light in to check if you can see anything you shouldn’t (this obviously only works on hollow dot and dab or stud walls)
This is the one I have, just googled and it’s more expensive than I remember. I honestly don’t even use it anymore. I tried again recently when wall mounting a tv in my office. It told me there was a live cable where I wanted to drill, I thought about it for a moment and realised there wasn’t, and sure enough when I drilled, no live cable in sight.
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What you are paying for is certainty, in a working enviroment as an electrician you must have a device that gives a very high level of certainty but for domestic use then it is not viable and you have to buy devices like the Bosch that work but with much lower levels of certainty and accept that you may just damage a wire even if you take all the possible precautions but you can isolate the supply to make the drilling operation safer and worst case the 30mA protective device will trip and you end up with a repair.
If you want a decent detector that also has signal injection then this is what you want
https://www.test-meter.co.uk/fluke-2042-cable-locator
If you want a decent detector that also has signal injection then this is what you want
https://www.test-meter.co.uk/fluke-2042-cable-locator
Were you using the device on cables that were dead ? The advantage of the Fluke is that it does work on dead circuits by injecting a signal which allows you to trace particular cable runs.
No, live. It seems to thing EVERYTHING is live though. It’s just massively over sensitive for live electricity, and it also is wildly inconsistent on finding studs.
When I just used it last I just used my knowledge of the wall (it’s a loft room and I had rewired the lights in the ceiling a few months before, and re-laid the subfloor back in January) as there was one live double gang socket about hip height that came up from the floor, the detector told me the whole wall was live about 700mm above it.
I was actually using it to find the metal studs though as I already knew it to be a chocolate teapot for electricity, and in the end I just had to drill a series of small holes along a horizontal line to find where the centre of the stud was
With this I was able to inject a signal at the consumer unit and trace the incoming mains service 100 metres up and down the street under the pavement before I lost signal ....
It also works for showing cable runs in partition walls.
But £££
Don't forget the value of some neodymium magnets to find drywall screws or flat head nails under the surface and hence the position of studs. Also works on galvanised capping over electricity cable under the plaster but not plastic capping.
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