Fatal Incident - Safe Isolation failure?

Before working on equipment that I judged to be high risk, or in doubtful condition, I would prefer to test to “true earth” and not just to the CPC or frame of a machine.

Test to structural metalwork, or to a metallic pipe, or to the CPC of another circuit. if outdoors test to a metal fence or even to a temporary earth rod.

This being AFTER the usual tests.

Even the much derided neon screwdriver will detect a dangerous voltage between allegedly earthed equipment and true earth upon which the operator is standing.

It's interesting that use of a non-contact, single-pole tester (Voltstick) is only recommended for proving live in GS38, yet from the evidence presented here use for ‘checking dead’ in this case may have been life-saving.

John Peckham: 
 

No such thing as Safe Isolation.

Firstly a lot of 2 pole testers need a potential difference between the poles to detect anything? If you have a live conductor or terminal and no earth or neutral a 2 pole tester will not detect anything. Some 2 pole testers will give you a one pole warning but not all.

Secondly testing only may prove dead at the time of testing micro seconds later a terminal may become live through a borrowed neutral, another supply not known about or someone doing something daft like breaking off your padlock.

At all times treat everything as live including anything coloured green/yellow.

I agree with Zoom get a voltstick. Preferably the Kewtecch Duo with the dual sensitivity. Keep it in the top of your shirt at all times and use it before you poke your digit(s) in to anything electrical. Yes you can get cheaper voltsticks but they are probably crap and what price your life.

If the poor man had used a voltsick then he would still be alive.

 

 

 

 

I use a Schneider Electric Volt stick. It came in a kit called a DIY detector kit. You can buy them separately though. I have found them to be of very good quality and they are reliable. The batteries last for a very long time.

I do at least three testes to prove dead, but even then I normally work assuming that the cables are live in most cases.

a, Two probe Voltage tester.

b, Voltstick.

c, Neon tester screwdriver, as it only needs one probe to work. The make is CK and is German made.  The screwdriver is of very good quality and can be used all day without breaking, unlike the cheap Chinese types.

Z.

Mike's comments remind me of an incident many years ago when wound ballasted fluorescents were popular.

A batten fluorescent fitting in a domestic garage was misbehaving. I was up a metal  step ladder having an initial look and fiddle. I received a mild but unpleasant shock.

The terminal block inside had three terminals. L. E. and N.  E. was connected via a small metal tab to the metal batten body and was designed to be the earth terminal.

A clown had connected the E. terminal to the permanently live loop conductors. Earth (C.P.C.) was not connected at all.

I was saved by the fact that the steps had plastic feet on them.

Z.

A bit difficult to prove dead if it is the enclosure itself which is live!

The fact that the worker in the OP lay unnoticed for an hour sounds bad, but unless somebody was present, it wouldn't have made any difference to the outcome.

It also suggests that that particular part of the premises was not visited often. Like Zoom's garage light, an ECP may have been live for years, but nobody touched it.

slightly embarrassed to admit, but i have had two belts in my life, both of which would have been avoided if I had used my multimeter to test, both because I thought I had isolated the supply but hadn't. 

If I touch copper now, I test, test again and test again, L-N L-E N-E and if there is some steel nearby, usually to that too. 

It wasn't pleasant, I don't want to make the same mistake a third time.

I also have fluke volt sticks, and don't rate them at all, both from activating on dead circuits, and not activating on live. 

The one belt I got was on a 2 gang hallway/landing light switch, which were (as was obvious in hindsight) on separate circuits. Now I always use a wand before unscrewing a supposedly isolated lighting accessory, and then a quick wand around the innards, before sticking probes in for “proper” isolation testing.

I had a close shave before my training.

Plug in a vacuum cleaner and turn it on. Then go to the CU and ensure that the breaker turns it off (and on and off again). My near miss is that I very nearly opened the wrong JB, which would have been live! In fact, I might have opened it, but then thought better of attacking the terminals.

Somebody was looking after me that day.

I suspect that the DIY-minded general public get away with quite a lot, more by luck than judgement.

Chris

A near miss as the second best method of learning to be careful! 

Had you used the  Kewtech dual sensitivity Voltsick waved over the cables and junction box on maximum sensitivity, before opening it, would give you a possible life saving warning. A 2 pole tester would require opening the JB first.

Even better, frankly, in the domestic situation is to turn off the main switch, or as I have mentioned, keep the main fuse in your pocket.

Easy in a new build, but not so easy when the householder wants to keep the wifi and computers running!

Or the other trades want somewhere to plug in.