Aaaargh!!! Electrical current detectors aren't always - Powerfix. Recommendation for new?

[David]

I have a Powerfix IAN30295 KH 3236 multi-function detector with laser.

One function is to detect AC Wire.

I thought I had checked this out properly with a live and dead stretch of wire, but apparently not.

I've been scratching my head over why I wasn't getting any power to my new sockets when I had connected into a 13 Amp ring main.

The detector showed there was current in the wires, but my socket testing plug didn't show anything at the sockets.

I tried probing the Wago connectors (see other thread) and got nothing.

So I uncoupled all the connectors and used the continuity testing function on my new test meter. [Additional buggeration, the black wire pulled out of the probe. Compensating factor, I had just bought a pack of extra probes and crocodile clips so I could carry on testing.]

Continuity on my new wiring was fine (phew). So what the?

I checked continuity on the wires that I had cut into and there was no continuity at all between all the lives. Also nothing between all the neutrals, and all the earths. Also checked against the wiring in the known working socket in the room. [Another tale of buggeration there.] Again no continuity. So how could there be current?

*Further testing showed that the AC Wire test showed a positive as soon as it came in the general area of a live wire - up to about a hand's breadth away. However if the tester was moved right up to the wire then it registered an AC current on un-powered cable.*

So I have spent loads of time and energy trying to fault find a connection into a 13A ring which isn't.

The existing working double socket has wires which go down through the floor into the landing on the wrong side of a joist for me to get at from the office/3rd bedroom.

So I now have to lift the floor in the landing (which is full of stuff out of the office) and try and locate the working ring main.

Meanwhile, is there a recommendation for a tester which will reliably detect live wires?

I know I saw something in the Wiki but I can't find it at the moment.

I was thinking of the pen type, perhaps something from Screwfix in this list?

. Fluke is a good name, but will the LAP one be adequate, for example?

Cheers

Dave R

[David]

On Sun, 07 Jul 2019 16:01:55 +0000, David wrote: <snip>

I've just been reading the details on the Screwfix page above, and the Fluke tester listed has to be pressed against the live wire (on the outside of the T&E sheathing) to detect current.

Other testers are listed as "non-contact" and can apparently detect live cables without needing to touch the wires.

Could someone please explain the advantages and disadvantages of each type?

The first thing that comes to mind is that the Fluke one can be used around a consumer unit where there are loads of live wires and test a specific wire.

The non-contact ones would, presumably, light up anywhere near a consumer unit and not be any good for detailed testing.

This makes the Fluke seem more versatile. What are the downsides?

Cheers

Dave R

[newshound]

In my experience the cheaper volt sticks are OK. I have a Kewtech Duo, but I don't think I paid as much as £20 for it.

With the cheaper ones, I'd use the same method as one does with a neon screwdriver, keep checking for positive on a known live immediately prior to assuming a negative is in fact dead.

At that price the Fluke is going to come from a similar Chinese factory to the others. It won't have the level of QA that goes into the proper Fluke meters and testers.

[Andy Burns]

They're all non-contact (except the kewtech one with dual probes) probably just varying sensitivity, you don't want it going off just because there's something live nearby, you need to discriminate which actual wire it is ...

[David]

Confusing thing (for me) is that the description of the Fluke says that it has to be touching the live wire which implies less sensitivity.

Others are described as not having to touch the wire.

I quite like the idea of a contact detector if you have a mixture of 13A and lighting run close together.

Cheers

Dave R

[Andy Burns]

yes, less sensitivity may be preferred ... none of them need to actually touch the copper, just touch the insulated wire, one that's too sensitive may indicate power whenever it's e.g. within 1/2" of the cable, a less sensitive one may be able to tell which side of the cable is L or N within a T&E cable ...

[Brian Gaff]

Some bright designer should make a device that only responds to those wireless internet over the mans plugs and then if the signal is not on a wire its not connected. Brian

[Brian Gaff]

Oh for the days when neeon screwdrivers were legal.... I of course do not do much wiring since I've yet to find a colour detector that can tell me which wire is which. Brian

[Harry Bloomfield]

It happens that David formulated :

The Fluke has similar sensitivity, I have two or three around here - it does not need to be in contact just near. The don't work on current, they pick up the radiated field.

[Harry Bloomfield]

Andy Burns explained on 07/07/2019 :

You can de-sense/ shield the tip with your fingers, obviously not where there are bare wires.

[Harry Bloomfield]

Brian Gaff formulated the question :

That doesn't sound as if it would be a major problem for someone to solve, using a camera and google image recognition.

[Dave W]

There's voltage, and there's current - they are not the same. Most none-contact testers respond to the electrostatic field from live wires, whether or not they're passing current. I couldn't see anything about pressing against the live wire in the link you gave, but there are real current detectors available from the same firm. A Fluke one was £140, and you have to put the wire into a V-shape gap in the tester, so that it can detect the magnetic field from the current flowing.

[David]

Update:

I bought both the LAP and the Fluke from Screwfix.

The LAP detects a live wire from several inches away.

The Fluke needs to be touching the wire.

This suits me as I can use both for different levels of discrimination.

Cheers

Dave R

[David]

Hmmm....the Fluke seems to be pretty solid, only lighting up when next to the live wire inside the insulation. For example on T&E you have to put the tip against both edges of the wire to confirm the wire is live.

The LAP is more "enthusiastic" but I seem to be getting the occasional "false positive" (subject to double checking the instructions). It gives an intermittent "cheep" when getting close to a live cable (device flex or mains wiring) and a continuous "cheep" when held against the cable. However it also seems to give the "getting close" cheep to unpowered cable (old cable left under floor after the major rewire). It doesn't do this for a completely isolated cable. I can also get this effect by waving it around a light switch in the wall. I suspect it may be picking up some kind of induced current in the wiring, but who knows? Anyway, it is potentially misleading if you aren't careful.

Memo to self, if we have electricians in again, encourage them to remove the old wiring completely as they replace it. Noting that access may have been an issue at the time. I've lifted boards which I don't think came up during the rewire.

Cheers

Dave R

[Cursitor Doom]

My Meggar sits right in the middle between these two in terms of discrimination which is ideal AFAIC.

[Cursitor Doom]

Soz, *Megger*

[Harry Bloomfield]

David explained on 09/07/2019 :

I would say 'close to'. It depends on the surface area of copper and whether there is grounded metal in the immediate area.

You can use them to find breaks inside cable too. You can follow a live in a cable and it will stop indicating where the live breaks. Neutral break can be traced, with the Fluke indicating all the way around the cable after the break. Good live and neutral in a two core will only indicate for around half way around the axis, or one third of a three core with neutral and earth.

A single live can be located in a tight bunch of wires, by shielding the tip between two fingers, to desense the Fluke.

[newshound]

IIRC (but without fishing it out to check) the Kewtech duo has a low sensitivity and a high sensitivity button.

[Andy Burns]

I think you're right, I only have the Uno, it does have a marker to tell you where to hold your thumb which seems to affect the sensitivity

[newshound]

They might be deprecated, but I hadn't heard that they are illegal.