100+ volts down earth ????

JD6400 · Feb 6, 2014

Just had a call from two of our men who are testing an agricultural dealership , they have found 100 + volts on one of the lighting cpc's .
To cut a long story short , they have cut around 2 and a half meters out of the 10 meter the circuit ( 1.5 T+E ) and have it laid on the floor . They say that they are getting +500 between all conductors ( Two different Fluke MFT's ) , but when they put power on it ( without connecting the cpc either end , they are still getting 100 + volts on it !

Any thoughts !????

Specialist · Feb 6, 2014

Marvo said:
Apologies, I wasn't sure if you were joking or not. Every electrician should carry one, they aren't prone to the confusing readings you get with the MFT's and they have several other advantages as well.

Like some nice quick & dirty tests on electrolytic capacitors Lil.

Marvo · Feb 6, 2014

The analogue insulation testers used to have a winding handle on them to generate the 500v or thousand volt test voltage although there were also some IR testers that used large batteries. Analogue voltmeters and ammeters don't usually need any batteries at all. Only an analogue continuity tester or a multimeter that measures resistance/continuity would need batteries and they used to last months even in the days before Duracells.

When I was an apprentice I had an insulation tester that took two of these batteries. They lasted a long time, in fact usually they started leaking before they were flat.

[ElectriciansForums.net] 100+ volts down earth ????

Specialist · Feb 6, 2014

Hi corpy: a good set of batteries will last for ages in them, my avo 8 is on it's second set of batteries in 5 years & gets used regularly . I find the Alkaline batteries from Lidl the best.

Corpy76 · Feb 6, 2014

Happy days I'm getting one the kids are going to go elsewhere for there xbox controller batteries.

Silly Sausage · Feb 6, 2014

Out of interest, does anybody know how reactive the input impedance of a typical DMM or MFT is?
Or is it purely resistive?

Marvo · Feb 6, 2014

Most DMM's used to have fairly constant impedance on any given test range at a constant test voltage frequency. The input impedance usually got higher as you went more sensitive up the test ranges.

I was looking for a specific instrument a while ago and I skimmed through a Chauvin Arnoux technical document which said that on some testers they're using adaptive impedance and burden control and it's managed intelligently by a built-in logic controller. To be honest it was way over my head but I suspect it's going to be more and more common in the higher end instruments that the input impedance will be highly adaptive. I'm not sure if this is a good thing or not, if it's not seamless and reliable it could easily add to the confusion or the user. Guess time will tell but I'll carry on using my trusty analogue for many tests for the foreseeable future.

Specialist · Feb 6, 2014

Corpy76 said:
Happy days I'm getting one the kids are going to go elsewhere for there xbox controller batteries.

If you mean an analogue, don't buy something like an avo 8. They're too bulky for site work & too good to lose, there are some good analogues from metrel & kewtech for reasonable prices. Try to get a case as well for added protection.

Apparently Kewtech meters are made by Kyoritsu.

Marvo · Feb 6, 2014

I've got acouple of old Kyoritsu analogue testers and I can't fault them. Keep an eye on ebay, they're often available quite cheaply nowadays because they're not very fashionable. It might be worth checking that you can get it calibrated before you buy one.

Specialist · Feb 6, 2014

Still keep my Metrix in my kit & also a cheapie for testing things like microwave capacitors, the metric is too expensive to risk blowing it up.

Specialist · Feb 6, 2014

Couple of places on the bay selling Caltek & Extech analogue meters for under £20 new.

Marvo · Feb 6, 2014

I don't have experience of either of those makes but at price you can't go too far wrong. The Caltek & Extech brands both look promising. I'd suggest just a smallish basic voltmeter or multimeter would suffice for most, something solid and well made and calibratable. I'd avoid the no-name cheap ones you might find in a supermarket or even on ebay, rather a second-hand recognised brand name even if it is a few years old.

DPG · Feb 6, 2014

Agree. Don't buy an ebay £3.99 special !! Get something decent. Daz

Specialist · Feb 6, 2014

Never used Ex tech but heard good reports about them, bought a caltek for my old apprentice & it seemed quite tidy.

PEG · Feb 6, 2014

I have a growing collection of old meters,an AVO 8 is amongst them... i remember the first time i got my hands on a digital meter,and my mates dad,an expert in electron microscopes,saw my excitement and made me re-test a voltage of 230 volts,but via a damp hair he plucked out of his head. If i remember rightly,it was about 180 volts,and he said "do you think you could power a lamp with that?"...lesson learnt...

Specialist · Feb 7, 2014

Bet it's not something they teach you about in college nowadays, a friend had a problem with his car horn but his digital said there was 12v there. Had him tearing his hair out, a quick check with the Avo proved there was no 12v. Turned out there was a dirty earth to the body that went down under any loading.