Dodgy voltage detector

They use an unsound principle and cannot be relied on. Don't buy

I'd go with a bad batch; what did Screwfix say? You should post feedback on their web site. Never had one with self test (could be a bad instruction leaflet)? The false positive sounds like it might result from inductive coupling with a parallel circuit. You sometimes see this with neon screwdrivers and DVMs, although I've never seen it with a "volt stick".

What I like about volt sticks is that they can often be used to distinguish non-invasively between a plug fuse failure, a line switch failure, or load device failure.

One thing I forgot to mention is that the first one was from a different Sc rewfix branch. doesn't preclude the bad batch theory though. The only rea son I wanted this is to quadruple check I have the correct wire before brea king in to it. The wiring for first floor is a little odd as most sockets are fed from below but for some reason this one seems to be fed from above although it is on the correct circuit. Hence I want to be extra sure I hav e the correct wire before cutting.

The false positive sounds like it might result

Surely more likely with a contactLESS device as is this volts stick

I'd be interested to learn more about that.

they produce false positives and false negatives, relying on one is a hazard

NT

If this type is so unreliable what is the safest way to determine if a cable is safe to cut?

I'm well aware of the possibility of a false negative with them (as with any device I've ever used). But I don't see why that makes the

As for false positives, I take it you mean the way they will detect voltages which are totally safe for human contact. On the whole I prefer to see that not so much a false positive as an indication of the need to check further.

voltmeter

NT

What if there's no neutral, either missing (fault), or unavailable (switch drop)? Possibly no earth either, in the case of a switch drop wired in singles.

it makes the way that principle is always applied unsound.

it isn't, it's just false positives. Come back when you understand them.

NT

use an extension lead

In this case it seems a question of what is positive and what is negative - the presence of mains voltage as a result of the test could be taken either way.

Years ago I was given one of those gadgets. It was dead posh and detected voltage in the walls where I knew there were wires. Then it tried to tell me that there was voltage in the lounge door! I recently bought a volt stick to detect voltage should I have a broken wire in the vac cleaner etc. That is about they are good for.

A volt meter will only be useful once you have cut into the cable. In my situation I want to prove that a cable is part of a particular circuit and is off

One of those things worked out which Christmas tree bulb had failed. Apart from that they're utterly useless.

Detecting voltage without actually touching the wire doesn't work. Even if you take a voltmeter and place the red wire on a live, and the black wire on ground, or your finger, you can get a voltage reading even if no voltage is present, due to induction. These things can't tell the difference between a bit of induced voltage and 240V with current carrying capabilities.

I don't believe you can do that certainly without having a physical connection to the wire involved. I'd certainly not want to rely on something that detects the (weak) radiated field from the wire.

I'd be more impressed by your confidence if you'd bothered to state what you are taking to be the purpose of a volt stick. (Note I never said I approved the use of a volt stick to prove a conductor "dead". I do continue to fail to see why you claim they are "always unsound in principle" to identify a live conductor - eg when there are several conductors in a conduit.)