Using my loop tester (Metrel MI 2122) to do low current tests on rcd protected circuits, the Zs readings I get are always higher than if I measure Ze, R1 and R2 and add together. If I and keep repeating the test I get a big variation in results, e.g 0.7,1.4,1.1,0.9,0.7,1.1.

Is it time for me to get a new tester or is this the best to be expected wit a 15mA test?

Its a matter of propotion, the lower the test current, the lower the accuracy, that said; the high current ranges are not tha accurate either.
Field tolerance +/- 30%; if you want an accurate value you must calculate it.

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http://www.niceic.biz

Andrew

That sort of variation is common to all low current non-trip loop testers. They have a tough job to do and carry out numerous (100ish) measurements and then display the most common result. The more complex the instrument the more prone it will be to noise and harmonics on the circuit under test. Anyway it does not really matter as you are testing RCD protected circuits and the permitted max. Zs allows for a wide band of tolerance. Plus or minus 1 ohm is said to be acceptable by a well known club.

The most consistant loop tester I have is my old Robin 4120DL. It gives a fast no trip readings on RCD protected circuits which are reasonably consistant. The tests are done at high current with a DC injection (Dlok) to prevent RCDs tripping. The downside is they will trip nearly all RCBOs and some electronic RCDs. Also a good dose of current, 25A ish around the circuit. Nice big arc flash if you don't press hard on the test probes.

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John Peckham

http://www.astutetechnicalservices.co.uk/

I've always used Megger(LRCD220)and found that on the 'no trip' function the results were always lower,so calculation was the order of the day.

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Regards

Dave(not Cockburn)

To get a more accurate reading with my meter. I dont put it on "No Trip" but simply test L to N. Then I calculate the L to E based on what type of earthing is in place. e.g. If it is a Twin and earth cable, I calculate the earth to be L to N x 2.5 / 1.5.

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keithredpath

This is what you need to get an accurate test of the strength and capability of the earth-fault-loop-path under fault conditions.

True Zs Tester

Just place it across the line and earth.



Regards

Geoff Blackwell

Does the spanner come with PPE, GS38 finger guards and a calibration certificate.

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James

It doesn't need calibration as it is a use once device .

Regards

Geoff Blackwell

But its not gold plated

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Regards

Dave(not Cockburn)

I was chatting to our local Megger rep recently about the new MFT1730 and hearing the virtues of this, that, and the other... He went on to mention the two wire no trip loop tests the machine can perform. When I quizzed him on accuracy, he suggested if a result seems wild, try reversing the probes.... Quite what that will achieve I don't know, but that's what he said...

I'm off to the tool sale in the Guild Hall now to buy some spanners!

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Regard
Richard (Dick)

www.rllewellyn.co.uk

From my experience with megger testers they are the worst culprits when it comes to throwing out wild low current Zs test results. I sent two testers back to them as they were hopeless. My old Robin as someone stated above in this thread was superb. I have a Fluke multi jobby now and although not as good as the robin, it does give consistent reults.

One was allegedly dropped across the 50v busbars in the old York telephone exchange - most of the spanner was vapourised I am told (this may be an urban myth)

I saw a spanner dropped across 50v busbars in Dartford - there was nothing left that could be described as a spanner - a better description would be "a lump of metal"!

Regards,

Alan.

I despair, I really do ....

I despair, I really do ....
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So do I napit, how on earth can that give a true (or even meaningful) result?

Dave.

Good grief! You would be just as accurate thinking of a number at random and writing it down, leaving your tester in its case! I hope you are joking here!

Regards,

Alan.

Geoff,

I feel you may have been mislead, the picture clearly shows battery discharge tester not a Zs one

As to Keith's calculations, well I might as well ask my 5 year old for a number between 1 and 10, then divide it by 3 and multiply it by the number of times I've fed the cat today

Stu

How I hope he`s registered and his assessor views this forum ....

"As to Keith's calculations, well I might as well ask my 5 year old for a number between 1 and 10, then divide it by 3 and multiply it by the number of times I've fed the cat today"

The Schrodinger method?

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Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik

Are you using fused test leads?

Regards