To cut a long story short, my ethos 7920 failed its last calibration for reading to low on the EFLI (something I wasn't aware of) , I was given a brand new machine through a warranty deal the calibration company has with ethos. Now the new machine is regualry giving me EFL readings of 0.00 ohms and kA's of >30. I rang the calibration company and they assured me the new machine was tested and was working perfect and even offered to send out a representative to show me how to use it!! (Very kind of them.. I did wonder where to put the leads? ) He also said if you are very close to a main sub it would give these low readings but its happening to often and even getting them on sub boards within buildings.

Does any one else own one of these and experienced similar problems? I can take Zs on individual circuits and get reliable readings most of the time but Ze & Zdb is hit & miss.

Cheers

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If you think you're too small to have an impact, try going to bed with a mosquito in the room.

If you have a local 11kv to 400v transformer is on site you would get low Zs. Because the earth loop is very short.

yours do seem very low though.

On my site the Ze is 0.01 i got this from the transformer boys who service it not from measuring it.

And I have measure less than 0.1 on submains. only way to know for sure is try a different meter.

the other thing to check , what it the resolution of your test instrument. it may not go down low enough to give you a reading.

Also make sure you're not inadvertently measuring L-N instead of L-E! I've done that on my Fluke a time or two,

Dave.

Temperature of the tester can be a problem make sure your tester is not left in a cold van over night.

Hope this helps

Why don't you add a known resistance - common practice on extremely low Ze.

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Regards

Martyn.

Only a mediocre person is always at their best



www.electrical contractors uk.com

Yes , I'd agree with that.
A couple of 0.2 Ohm 200W resistors in series with the leads.
Stick them in a box and use them to check the instrument from time to time. and against known supplies.

I remember a few years ago having problems with a brand new Ethos MFT, although this was on the low reading Ohmmeter range .

Legh

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Why do we need Vernier Calipers when we have container ships?

http://www.leghrichardson.co.uk

"Science has overcome time and space. Well, Harvey has overcome not only time and space - but any objections."

i have had the same problem cold weather as a bad effect on testers

Hi, thanks for the replies. Sorry for the mate reply had to check a few things. Not sure on the resolution, how would I check this? I'm not testing between L-N. I am aware of cold meters giving funny readings but this doesn't appear to be the case as most times it well warmed up. I'll have to have a look into the resistor.

So when I get a reading of 0.0 ohms for Ze. Would it be acceptable to record Ze as the enquiry reading (i.e. 0.35 ohms for a TNC-S) as my meter has proved there is a good earth path there but I can't write down a recorded reading of 0.0 ohms.

Cheers

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If you think you're too small to have an impact, try going to bed with a mosquito in the room.

I once had an NICEIC inspector show me a trick with a fluke tester which I was suprised at. He said that I should calibrate the leads on the low reading ohmeter setting before performing an earth fault loop impedance test. I did what he said and it made a considerable difference to the earth fault loop reading. Maybe worth a try