Test Meter Recommendation

[Bob Eager]

So how do you propose to test the insulation at 500V?

[Dave Plowman (News)]

Out of interest, I wonder just how often such a high voltage is needed when testing household wiring for poor insulation - especially with new or recent wiring. I'd say a simple resistance test with a decent DVM would be more than ok in the vast majority of cases. Might be different when checking ancient wiring.

I haven't the experience of the likes of Adam, but have yet to come across a fault like this that a DVM doesn't show up. And yes, I do have a high voltage insulation tester.

[Archibald]

Precisely! I too have an insulation tester available. I have never used it at home. Should the need for a high volts test arise, I have an old flashgun somewhere that would function perfectly as the source.

I would hazard a guess that even an old mobile phone could generate the Voltage if there were a few diodes and capacitors to hand. Likewise a car battery along with a suitable limiting load will indicate any earth bond problems. Assuming we know V and a reliable bit of the "R", then our Two for four quid [Yes Maplin were selling DMMS at this price], meter would reliably tell us the current flow, and I'm sure the earth bond resistance wouldn't take a genious to find after that. Although in all fairness this couldn't hope to compete with the 1kV earth bond test Voltage the cretins that used to test our companies tools nominated oneach and every one of our class1 PAT cetificates.

Any domestic leakage would more often than not be due to moisture. Who waits for a downpour before testing?

My main fear would be water across live & neutral or an arcing connection feeding a resistive load. Both these scenarios can generate a lot of heat before the supply fails, whereas leakage to ground or overcurrent events hardly ever need any form of test equipment to locate these day's.

AB

[charles]

I have come across many, both in wiring, extension cables and fittings (PATing). I used to have a lovely hand Megger running off 6x AA cells. Unfortunately, a cell exploded inside and F***ed up the contacts.

[Archibald]

You have to be joking! The only fittings I have had fail a leakage test are those ancient bakelite things that probably started off wet anyway. The stink was almost as effective as a meter.

If you are getting insulation fails on installation, its time to come clean on where you are buying your hardware from. It isn't from a car boot sale on a rainy weekend perchance?

Portable appliances aren't really something a DIY type would normally test BTW, You'r surely not suggesting someone tucks a PAT tester amongst the groceries next time they get a kettle from Asda?

AB

[Dave Plowman (News)]

Quite - but did you also do a test with an ordinary DVM to see if it too showed the fault?

What I'm looking for is an insulation etc fault that only shows up at high voltage.

[charles]

The only time I've had an insulation fault on installation was when installing MICC to my garage (in 1968). You are supposed to use a megger when doing that. It was simply a matter of removing the pot, running a blowlamp over the end of the cable & repotting. On the other hand I have had wiring insulation fail over a hot light fitting. It didn't show up on a multimeter..

no, but I've just been to LIDL who sell a wide range of tools

[charles]

500v will track across a gap which 9v will not pass.

[John Rumm]

No, you don't need HRC fuses and blast protection chambers to protect electronics!

Not sure what kind of fuse you have in mind. Most cheap meters will have a 20mm glass cartridge fuse, inline with the current measurement ranges (although often not the highest range). They may not even have any fuse inline when used on other ranges.

Hence these meters are not suitable for making measurements on high energy locations (e.g. inside a consumer unit)

I think you are missing the point. While you can make many useful tests with a multimeter, even a cheap one, there are a number of places where you can't do so safely.

Also how do you carry out a full RCD test, or Insulation resistance test with a MM? You could produce a PSSC result perhaps, but would also have difficulty measuring the earth loop impedance.

These are fine for go/no go indications, but they don't give you a complete set of test capabilities.

Indeed, and usually you will live to tell the tale, but sometimes you wont.

The purpose of the input protection is to protect you primarily and not the meter. If you are taking a voltage reading close to your consumer unit, and the meter experiences a 10kV transient, its better that it dies in the process of blowing its fuse and popping a few MOVs, tham allowing an arc flash to engulf the user.

[John Rumm]

I had one today in someone's kitchen - old socket on the end of a 2m spur. L to E measurement on a MM read open circuit, and at 500V was showing around 54 M ohms (still in spec - but poor enough to warrant replacement shortly)

[Dave Plowman (News)]

Yes - I know the theory. Just wondering how often it happens in practice.

[Dave Plowman (News)]

yes - that was one of the possibilities I was thinking of. But was more interested in testing one's own new work, etc, DIY wise. You'd not find any ancient wiring here. ;-)

[charles]

enough to make me cautious - and use the correct measuring kit.

[docholliday93]

The hand-held meter I'm using (which wasn't particularly expensive) uses these:-

It's a real pain when someone 'borrows' your meter and blows the fuse - at that price we don't keep lots of them in stock...

[John Rumm]

On new wiring you would only normally expect to see interesting stuff on IR tests after water ingress or rodent damage IME.

(you may recall my tale of working back through former neighbours cooker, slowly removing more and more bits before eventually tracing the fault to a damp plug - when all I had left of the cooker was its back cover and its mains lead!)

[John Rumm]

Yup, that is a proper HRC fuse... it can interrupt a 10kA fault current. Some of the glass cartridge fuses can't manage more than 20A

[The Natural Philosopher]

when I have seen it it has been down to damaged insulation and usually the spark arcs creating a sort of strange carbon resistor that sputters and arcs.

[Archibald]

Probably as effective as the semiconductor rated devices fitted to the Flukes & similar. Personally I wouln't bother too much about fuses anyway. As you state, the higher current shunts are not fused and at the lower end of the ranges, the components often beat the fuse hands down on the route to destruction.

Bilge! I use a Wickes device, glass fuse, not sure what current because it came out of my bits box last time I tried to check a 110V supply when tweaking a current loop. It has actually lasted aroud five years which is a miracle considering it gets soaked in water, acid, caustic and all the rest of the gunge that ends up in the water treatment system.

I use it for personal domestic wiring and industrial three phase 415V supplies. I could splash out a fortune on test gear, but I know it's going to have a short life whatever its price tag, so I just go for something that is around 1kv max DC & AC, resolves down to a microVolt/ microAmp and will do DC & AC Amps. Most meters have an adequate Ohms range, so that's it.

Whatever meter I have bought, I never did bother trying to find out if it was even fused before purchase, there isn't too much point.

Incidentally, years back I had an AVO eight, the industry standard hyper priced instrument of my youth. I dont even think it was fused. If it was I never changed the thing and it did have an overload or two! That was wat led me to buy cheap incidentally. Very similar specifications at a price range that meant you could buy twenty or so cheapos for the cost of an AVO.

I'm not sure what newsgroup you think you are on but this is uk.d-i-y. No I do not think I would have difficulty measuring earth loop impedance incidentally.

I have never completed an earth loop impedance test on any of my wiring BTW even though we have dedicated testers for the installation personnel, I would doubt that many DIY people have either.

Thank you, I feel most enlightened.

It isn't the test equipment! none of it's perfect and it does not replace common sense. I actually watched a pillock unpack one of those two wire Voltage prodders from RS, fit the batteries and use it to check a three phase socket in the yard after he had isolated it. He was then about to remove the socket, before I stopped him and suggested he try his new tester on something "live" first.

The problem isn't with the equipment! Give me someone with a brain and a bit of experience any day, any idiot can blow his cash

Really? Is this the same mains that all those TV's radios, table lamps and such like are connected to? Perhaps you should go on a crusade to fit better fuses on all this equipment before the users are engulfed in a searing hot plasma, or is there some magical barrier in a consumenr unit that stops transients dead?

Test equipment fuses are not semiconductor rated to protect the user! I suppose people are "semiconductors", but they dont fit semiconductor fuses to toasters do they? If they see fit to put the things in meters and not toasters does it not suggest that they may not after all be trying to protect the user?

AB

[tony sayer]

So your working on those sorts of systems and are that tight to buy a half decent pro meter?. You can get good Fluke meters on e-bay for around 40 to 50 quid sometimes. I managed to get one from a S/H test equipment supplier c/w decent rated leads and fuses etc for that sort of money...

Buggered if I'd use a cheap chinkie one of dubious origin;!...

[Bob Eager]

They have a fuse, and a cut-out.