TESTING FOR ABSENCE OF VOLTAGE

To add to my query, they are referring to the typical proximity tester

I couldn't find anything in our EU regs related directly to this device, therefore we would only confirm by carrying out a Live-Death-Live LDL test.

I do not claim to be au fait with every standard but I am not sure you will find anything that stark in any mandatory EU or UK specific document. Non contact devices like that are certainly permitted and in common use, but the normal recommended approach (for any kind of tester actually not just non contact ones ) is to verify the tester is working by making it indicate a live condition first, before using it to show dead - after all not lighting up may just mean a flat battery in the tester.... Such advice is in the guidance for inspection and testing.

Note of course that non contact devices are only OK on AC devices and when there are not other things that might false alarm or blind the detection, such as in the vicinity of high power RF kit - this may or may not affect your application.

Mike

It's a complicated one. The Swiss regulations suggest that after testing for dead you should then earth (ground) the conductors to ensure that they remain dead in case you have used the wrong isolator and someone else can re energise them.

I am happy to work on an earthed circuit. You have to have a good confidence in your test equipment before you make the earth connection.

Can I just point out that the UK is not part of the EU and our government are ditching all EU legislation, so what will be acceptable in the UK may not be acceptable in the EU.

I don't think non-contact voltage testers are mentioned in the wiring regs.

They are mentioned in Electrical test equipment for use by electricians GS38 (hse.gov.uk)

"13 Single-pole or non-contact live-circuit detectors sometimes referred to as ‘voltage sticks’ should only be used for identifying live equipment, not for proving that it is dead. There are particular requirements for the use of non-contact devices in coalmines. Only devices which make contact with the conductor (ie not proximity devices) should be used for proving dead. However, non-contact or proximity detectors can be useful in indicating if something is live, eg when attempting to remove a single cable installed in trunking containing many single cables"

further info about working practices here Electricity at work: Safe working practices HSG85 (hse.gov.uk)

Yes OM, and it is very important to understand that whilst useful they depend on lots of assumptions, the biggest one is that one is testing a phase cable, but the neutral is still potentially dangerous! This may not show on these testers, they simply detect an electric field around a conductor, but essentially this is referred to Earth. This may sound strange, but if not every mains connected piece of Earthed metalwork would show live which is not the desired result! Contact dead measurements are essential for safety.

Aroi Rodriguez said:

NFPA 70E does NOT permit using a noncontact type tester (see image) when testing for the absence of voltage on electrical systems rated 1000 volts or less.

Well, that is interesting ... and I think I disagree with an absolute ban on their use. Better to check with BOTH in a number of cases.

Let me expand on this. Yes, I agree that a non-contact voltage indicator should not be the sole means of indicating absence of voltage (as per HSE Guidance Note GS38) ... BUT ... there are cases where touch current may be present, that a contact voltage instrument may not detect, but a non-contact detector (volt-stick) may detect.

One example is with diverted Neutral currents ... see Appendix D to the 9th Ed (2022) of IET Guidance Note 3 Inspection and Testing, which multiple times recommends the use of a non-contact voltage detector, and gives the reason for this as "Voltage indicators do not detect diverted neutral currents while it is able to flow using an alternative path. A volt-stick should also be used."

I don't believe there is such a thing as actually 'proving dead' (you can only amass evidence that a circuit is not energized, but I don't believe there is ever firm proof, simply because of the possibility of electromagnetic induction or capacitive coupling, and a human being completing the coupled circuit, if the source of inductive or capacitive coupling was inactive at the point of "proving dead" or the instruments used didn't permit the current to flow).

Ignoring regulatory advice for a moment, as I am wont to do, really what we need to show is not ' dead' in the sense of open circuit at some remote point, but rather 'safe to handle' which means the conductor to be worked on, is at more or less the same  voltage as the simultaneously accessible parts in the local envoronment. Any absolute reference to some remote 'zero' is only really of secondary interest and it ought to be possible to show no current available to the local metalwork, certainly by direct connexion, and probably by non-contact probe as well,

Mike.

Mike, whilst I think I agree with your perspective in part, the issue we have to face up to, as well, is that it's not always safe (or wise) to disconnect protective conductors.

Even in TN-S systems, diverted protective conductor currents can exist. We know they are more prevalent in TN-C-S as neutral currents can be shared also.

Even if you test for potential before starting work, the act of disconnecting a protective conductor can leave a latent voltage, as you break the circuit current was travelling through ... but the voltage that remains, even if not 230 V, may be capable of driving a few mA through the human body ... perhaps enough to be lethal.

I think there's a difference, though, on working in a very large installation, to a "basic semi" - agree with you that in the semi, unless you are unlucky enough to have diverted PME neutral currents, removing a cpc is unlikely to expose you to danger (if there's bonding or fortuitous earth connection downstream). But that's not always the case in a larger installation ... as some telecomms engineers know all too well.

In the rule book that I promulgate, I advise those carrying out the so-called safe isolation procedure to be aware of the dxxk head factor! That factor considers that the installation may have been erected by a wally!

Many years ago my friend, an electrician, was severely injured by an electric shock even though he followed the safe isolation procedure to the letter. Switched off and locked off a single phase double pole isolator to remove a central heating control valve  in domestic premises. Some dxxk head had used the cpc as a line. With both line and neutral isolated at the double pole isolator, there was no reference earth. He was in a crouch position, jammed in against copper pipe work and on contact with the live cpc he could not move away and suffered serious injury, including broken jaw and a number of broken teeth. He spent two weeks in hospital.
Hindsight is a wonderful thing and had he checked to the copper pipes the danger would have been obvious. The irony was that he had been persuaded to ditch his phase tester screwdriver in preference for the voltage indicator following a safety course he had attended just a few months earlier.

I completely agree with GK and would advise using a voltage indicator that will also pick up a live part with single probe contact or without contact.