Electricity detector

[LittleEars]

I have a Bosch detector (Bosch Truvo Multi detector | DIY at B&Q) and I use it to detect studs and electrical cables.

When I was boarding the attic I came across a cable with a bare unconnected end. I passed the detector over it and it flashed telling me it was live. I quickly departed the attic and called an electrician to come and work out where it was connected to.

Turns out it wasn't, and it was just an old cable not connected to anything. He said my cheap tool was not quality enough to establish it wasn't connected, whereas his was. Nice guy didn't even want to charge me for the call out as nothing needed to be done (obviously I wouldn't accept that).

I need to put up a mirror directly below my consumer unit, and I need to check I'm drilling in a safe spot. I have zero faith in the Bosch tool and would like to know if anyone can please recommend something more professional that will help me stay alive.

Thanks

 

[dzj]

I also have this detector. It does give false positives sometimes.
Mine usually flashes and beeps if the wire is live.
I mostly use it for detecting nails in recycled wood.

 

[LittleEars]

That's what it did for the dead cable.

 

[Sideways]

Try this.
When you use your detector, hold it in one hand but place your other hand flat on the wall just to the side of the area you're scanning.
My £80+ Bosch detector from years ago was an annoying waste of money until I did this by accident one time. It seems to ground whatever weak interference causes false positives and the behaviour is more reliable.

Also, if in doubt and if you can, turn off any circuits that are likely to be wired in that area before drilling. No detector is totally trustworthy.

 

[MikeK]

Since you asked for something more professional, hang on to your wallet.

I have the Bosch D-tect 150 SV because all of the walls and slabs in my current and previous houses are cast in place reinforced concrete, with the utilities embedded in the concrete.

https://www.amazon.co.uk/dp/B00714AN2S
Prior to buying the D-tect 150, the fastest way for me to find a live cable or water line was with the SDS rotary hammer. I had a detector similar to yours and thought I had accurately identified the electrical and water paths in the living room wall. Unfortunately, on the third of four holes for a set of shelves, I hit a cold water pipe and thought I was in a U-boat that had been hit.

Bosch replaced the 150 with the D-tect 200, but I don't have any reason to upgrade.

https://www.amazon.co.uk/dp/B093PZTX17
Makita also makes the DWD181ZJ scanner at significantly more cost than the Bosch. I don't have any experience with the Makita and have never seen one.

https://www.amazon.co.uk/dp/B08HN4M6WH

 

[deema]

@MikeK wow, I have to say wow!

 

[graham88]

Why not just get a non-contact detector pen? Make sure to check it on a known live source before testing anything in case the battery has failed, such as a light switch. They're useless with armoured cable but it's doubtful you have any of that in your home. You can pick them up for less than a tenner in some places. Saves dropping a wad of cash on a proper tool and will still get the job done, keep the bosch to find it and then test with the pen.

 

[MikeK]

@MikeK wow, I have to say wow!

The cost of repair to my wall was over three times the cost of the D-tect 150. The guy who did the repair used his 150 to map out the water line and rebar before he cut into the wall to splice the pipe.

 

[Bingy man]

I have a Bosch pro detector ( can’t recall the model but I use it as a guide only ,, put a live cable under a piece of plywood and mark its position- use your scanner and you’ll probably find it detects the cable 30 or 40 mm either side of your marked live wire position. While fitting the wall cupboards of a kitchen install recently i marked the bracket positions and carefully removed a small section of plaster under each one . The detector had completely missed a double cable in the corner of the wall .

 

[John Brown]

I would only trust a positive result from a non-contact pen type detector. Although some might disagree, I'd rather trust a neon screwdriver tester, provided that I'd just tested it on a live wire.
If your house is fairly modern, then electrical cables are supposed to run either horizontally or vertically. So a visual check is a good starting point.
However, I'm not an electrician. No doubt one or two qualified electricians will be along shortly with comprehensive and reliable advice.

 

[Bingy man]

Why not just get a non-contact detector pen? Make sure to check it on a known live source before testing anything in case the battery has failed, such as a light switch. They're useless with armoured cable but it's doubtful you have any of that in your home. You can pick them up for less than a tenner in some places. Saves dropping a wad of cash on a proper tool and will still get the job done, keep the bosch to find it and then test with the pen.

These are ideal for direct contact with a cable but won’t pick up a cable buried deep in a wall . They also only detect from around 50 vac . They are however invaluable for testing the surfaces prior to you touching them but again should only be used as a guide .

 

[Sideways]

The pens don't have a very big range, but they can be handy. Fluke make one for about £20 that blinks every second or two to show you that it's alive and working. It lights solid red when it sniffs a cable. I don't cheap out on electrical test tools so I think this is worth the extra compared to the no name versions. It's far better than the original "volt stick" that introduced these to the market.

 

[Spectric]

Although some might disagree, I'd rather trust a neon screwdriver tester, provided that I'd just tested it on a live wire.

Those are a total no no if you value your pulse. To confirm if a conductor is dead you need the correct tester which will come with a self test module to confirm it is working before you use it. The one I used was by Fluke and this is something similar Safe Isolation and Voltage detection kits from Master Lock and Martindale

I should have added that your prove dead tester should be single function, if you use a DMM or such then there is the risk you can have it set wrong and what you believe to be dead is very much live.

 

[okeydokey]

Hi
Have you considered simply gluing the mirror to the wall?
Search for how to glue a mirror to a wall and there are several brands, pick a well-known maker such as Loctite

https://www.loctiteproducts.com/en/...all-without-nails-a-guide-for-all-diyers.html
If the mirror is small there is a double-sided tape for this purpose as well.

 

[Jester129]

Many moons ago, when we could do our own electrical work, I was going to fit another socket in a bedroom.
Main isolator turned off, I lifted some floorboards in said bedroom and found a cable that went nowhere. Picked it up and got a belt from it!
Trust me to find a live cable that bypassed the isolator! I could only guess it was left there by the sparky when the house was being built.
Note I didn't call him an electrician!

 

[MikeH]

In my experience these devices are an indicator at best, they can give both false positive and miss cables as well giving a false negative. Case in point being the non contact pens, they can give a false positive on a dead cable especially if it runs close to a live cable at some point, a "ghost" signal. I had exactly this earlier this week and have seen it before. I had a sparks in wiring up my new workshop. I had laid in the sockets and cables etc. and he was installing the CU to the armoured and connecting in all the circuits, testing etc. He asked about two lighting T&E cables I had going outside the door. I told him they were two short runs waiting for external lights and showed him the other unconnnected ends, aim is to wire them via a wifi socket so I can control the lights from the house and he didn't need to worry about them. He put his pen detector against one of them and it registered live. I assured him that they could not be live and he was was adamant they must be as the pen detector said they were. I explained I have seen this "ghost" signal before and I was sure they were not but that he should ensure that himself, possible there was a squished cable or something somewhere making the dead cable now live I supposed.

Long story short, he did some more testing and concluded the cables were not live and the detector was giving a false positive. My similar detector did the same when I tried it after he was gone.

So moral of the story is regardless of what any detector says, if you can power everything down before working then do so. However I suppose that if you are then fitting a metal shelf bracket or something then you COULD end up with a live metal bracket after switching the power back on. So this is where RCDs and RCBOs would be your best friend that day!

 

[Spectric]

So moral of the story is regardless of what any detector says, if you can power everything down before working then do so.

Not always an option, most people want minimal disruption, so they don't want to stop production which means you have to just isolate the circuit being worked on. An important point here is that with large industrial installations you don't want to just prove dead, what you need to prove is that it is live and becomes dead through your actions. The reason for this is that it may be dead for a reason not under your control, you start work and then it becomes live because there was no isolation procedure in place.

 

[John Brown]

Those are a total no no if you value your pulse. To confirm if a conductor is dead you need the correct tester which will come with a self test module to confirm it is working before you use it. The one I used was by Fluke and this is something similar Safe Isolation and Voltage detection kits from Master Lock and Martindale

I should have added that your prove dead tester should be single function, if you use a DMM or such then there is the risk you can have it set wrong and what you believe to be dead is very much live.

Got it. I was merely saying that I'd trust a just-tested-on-known-live neon screwdriver over a non-contact pen detector.

 

[Sideways]

With neon testers, you the user are part of the circuit to earth. Not the best of designs.
I was surprised to find one of these included in a brand new maintenance toolkit by Wera. It went straight in the bin ...

 

[John Brown]

With neon testers, you the user are part of the circuit to earth. Not the best of designs.
I was surprised to find one of these included in a brand new maintenance toolkit by Wera. It went straight in the bin ...

Yes. I believe the same is true of the non-contact pen type detectors as well.