Testing for dead. What does the team think?

[ericmark]

We see the testers, and we, or at least I, have been forced to use them, idea is can't be switched off, so not battery powered, and no switches, and the proving unit will show if it will not detect 50 volts AC or 75 volt DC.

But most of the proving units I have used, were well over 50 volts AC or 75 volt DC, so they did not prove the tester will detect over extra low voltage. About a good as a chocolate fireguard if they will not prove the tester will work on low voltage.

So if the proving unit is no good, is there any point using a tester with can't be switched, has no batteries, etc? Or if the proving unit is useless, may we just as well use our multi-meter?

I have two multi-meters I use on a regular basis, the yellow on will only measure AC current, the red one will do AC and DC current, and has non-contact voltage testing option, so between the two, can do most the testing I need, I have got a martindale tester as shown, and I have a battery pack with 230 volt AC output so could use it as proving unit, but why bother, using a neon screwdriver should an error be made, likely that will highlight error.

If I select wrong range it may damage the meter, but it will not damage me, I can't cause a short circuit with the meters even if on the wrong range.

So in real terms other than to satisfy some jobs worth safety officer, with low voltage supplies, is there really any need for the special proving for dead testers? I am sure, like the doctor's stethoscope around his neck, the volt tester around one's neck is more a badge of office than a tester which is really required.

So what does the team think?

 

[plugwash]

I'm sure I've seen some proving units that step up through a series of voltages.

I also think that while "partial line" voltages are a potential threat, full line voltage is a far more common threat.

What worries me far more about "2 pole" testers is that they can't handle the "everything is live" situation. That is where tools like volt sticks and neon screwdrivers (where are IMO unfairly maligned by H&S types) shine.

and pretty much *NO* tester will tell you that a neutral wire will become live when you disconnect it!

 

[ericmark]

pretty much *NO* tester will tell you that a neutral wire will become live when you disconnect it!

I would have thought, if the clamp on shows no current in the neutral, then unlikely it will become line when disconnected, and using a neon screwdriver to disconnect with is also likely to give one a warning although not 100%.

 

[plugwash]

I suspect that depends on the particular clamp meter. One of the ones suitable for RCD testing will probablly pick up any current that would give you a nasty shock. Some of the more oldschool models may not.

And not all wires can reasonably be clamped.

 

[JohnW2]

I would have thought, if the clamp on shows no current in the neutral, then unlikely it will become line when disconnected ...

Probably true, but since when was use of a clamp meter a part of routine 'testing for dead'? ?

 

[ericmark]

Probably true, but since when was use of a clamp meter a part of routine 'testing for dead'? ?

Since when disconnected, a neutral and was getting sparks from what should have been a dead cable, once bitten twice shy.

 

[JohnW2]

Since when disconnected, a neutral and was getting sparks from what should have been a dead cable, once bitten twice shy.

I understood your point, and the reasoning behind it, BUT, as I asked, since when was use of a clamp meter part of any guidance or teaching about how to #test for dead'?

 

[bernardgreen]

Best practise is to work as if the circuit was Live.

Only if the double pole main switch by the meter was locked off would it safe to assume the circuits ( all of them ) are dead.

And even that may not be 100% safe, I once came across a socket in a house that was connected to the next door supply, The owner of the house was curious as to why it was dead whenever the people next door were away on holiday.

 

[Adam_151]

I would have thought, if the clamp on shows no current in the neutral, then unlikely it will become line when disconnected

While a sensible precution, you need to know what sometimes you might get a false possitive - or rather its showing an issue, but its not the one you are worrying about. In a large installation neutral and earth can sit a few volts apart due to volt drop of the later, you can have a sitiation where a clamp meter shows a small current on the neutral, but the issue isn't that the circuit isn't been made live from another source and returning down that neutral, but rather it has a N->E short and there are circulating currents through the fault. The really nasty situation is where you also have one of the borrowed neutral faults as well, as it will tend to be masked by the cirucit with N->E short until one of them has the neutral disconnected from the (supposedly isolated and proved dead) neutral bar

 

[ebee]

And even that may not be 100% safe, I once came across a socket in a house that was connected to the next door supply, The owner of the house was curious as to why it was dead whenever the people next door were away on holiday.

I came across similar with a lighting circuit.
Indeed, in homes similar to mine I have advocated a sensor on an intruder alarm to detect entry from loft (usually a simple door contact on the loft hatch but sometimes a PIR detector for around the hatch/ceiling area - heat from sunny weather needs mitigating consideration though with a PIR if in loft area and strong drafts too), also similar ground floor floorboards.
I only mention it once the installation is started so as to not give the idea out to the gen population.

They are usually are suspicious of my sanity or honesty thinking am I asking/encouraging extra work, so explain to them via drawings and pics and if it happens that they have been in the loft a few times and usually they take a peek and the exclaim "Oh heck, I would never have considered that", I reply "Sykes does!" .

Indeed, Not my job but I assisted in maintaining it a few years later, eventually a shop (traditional end terraced house shop scenario) I advised to consider a PIR at the landing area around the head of the stairway. As the shop was always unoccupied after closing time.
Un til one day I was asked to do so but, unfortunately "after the horse had bolted" indeed an innocent employee had been sacked too, later re-employed after it all came to light and giving a whopping great big sorry and treats too, indeed the shop owner greatly appreciated that this employee could have really gone to town in a legal aftermath.

It also sort of "proved" my long held disagreements with customers and installers alike - do not leave PIR detector LEDs active in anything except test mode.

Anyway, Back toi the plot.
Yes Eric, I think most of us Electricians are guilty of not bothering about testing at 50V , probably if we had a reliable source of say 49.5V as a crosscheck, would be a bit safer, I must admit I have used a 50V setting on an ins res setting of 50V periodically to overcheck the tester every few weeks of use but knowing that all of the ins res ranges on my MFT are a little over the stated voltages. I have never bothered to use Zenners to clamp the voltages though.

 

[ericmark]

Your loft PIR would be going off at random times, mostly in the evenings when the intruders leave, but it seems illegal to stop them, they are protected, we started fitting them into BT building, but had to remove most of them. And it was in BT buildings where, testing for 50 volt DC became important.

I started using a neon screwdriver in the 70s after finding a socket live with the main switch off, it was feed from next door, and I have proved dead, only for the cable to become live, when a contactor pulled in, unless one spikes it, one can never be 100%. In the main, proving dead is done when one has no idea where the cable is fed from. In my case, removing the cables from an old batching plant, encrusted with concrete so no way to trace where fed from. After the incident, only done when new plant not running. All the testers and proving units in the world would not have identified that cable as live.

But most of us, I am sure, walk around with a multi-meter of some sort, in one's pocket, and most installations have more than one circuit, so easy enough to test the multi-meter. We start with the neon Martindale, but it gets damaged, so we replace it, we get a new LED version

but never even think about what happens if the batteries fail, so we get one with 0–400,000Ω Continuity and Continuity Test with Audible Results. And we have moved from the tester for testing dead, to a multi-meter. The rot has set in, next upgrade is

which came up with a search for "volt tester" and the problem is carrying all these testers. I remember selecting a tool bag which was large enough to carry a hack saw, and had straps so it could be carried hands free when going up/down the scaffold, and we each job it was a debate, what tools will I likely need? All very well travelling around in a van, or Land Rover, but most of my jobs was, have bag will travel. Including jumping out of hovering helicopters. Today it is trains, hoping on/off as they stop at my red flag. Yet something else to carry, a red and yellow flag.

So I tend to use one meter for all, OK next job I will need my VSWR meter, but we will always need the specials from time to time. But is using my clamp on really that much less safe as using the old testers? They were not that good anyway as it would not detect borrowed neutrals, and neons may not light with lower voltages, and it only delivers AC.

 

[ebee]

Your loft PIR would be going off at random times, mostly in the evenings when the intruders leave

How so?
Yes if they break in downstairs then travel up to make the get away.

I have seen intruders break in thru the loft = as per the example I mentioned.
And yes to protect the loft area itself rather than just the hatch itself has real potential problems unless active infra red beams are used , more expense though.

Hence the area below the loft hatch = on the landing as per that one job I mentioned (after the event - which I warned of prior to it happening)

 

[JohnW2]

Best practise is to work as if the circuit was Live.

True, but that is often not possible/practical, One cannot do a lot 'one-handed' and it can be difficult (or essentially impossible) to do a lot of things whilst wearing ;adequate' gloves. The risk (when using two hands and no gloves is, of course, increased by the wretched metal enclosures which are now being forced on us!

Only if the double pole main switch by the meter was locked off would it safe to assume the circuits ( all of them ) are dead. .... And even that may not be 100% safe, I once came across a socket in a house that was connected to the next door supply,

Very little in life is totally 'foolproof', which is why we do 'testing for dead'.

 

[ericmark]

I have seen intruders break in thru the loft = as per the example I mentioned.

So have I, like a bat out of hell, and you're not permitted to scare them off. One has to wait for them to leave of their own accord.

At least the droppings are only digested insects, but still a pain cleaning them off all the Christmas decorations. How did they get in? We think through the bell box of the disused alarm system. So the whole reason for having bats was due to fitting an alarm.

One cannot do a lot 'one-handed' and it can be difficult (or essentially impossible) to do a lot of things whilst wearing ;adequate' gloves. The risk (when using two hands and no gloves is, of course, increased by the wretched metal enclosures which are now being forced on us!

The reason for my injuries being so bad after my accident, was the gloves were too small, and they restricted the blood flow to my hand, had no option to wear them or not, sackable offence not to wear gloves outside.

 

[ebee]

Must admit.
The intruders I was considering were Human Intruders