Help please! Cheers guy!!

[Sparky Ninja]

leads are shiney new! tested ze 3 times and zs on all circuits 3 times, no change, tester is however on "no trip" setting, R1+R2 readings are fine and zs reading are fine, just one of those "wonder whats causing that" things!

cheers guys really appreciate it
danny

May I suggest that you test at a location with the high loop reading set (i.e. not on no trip), and then retest at the exact same point on the 'no trip' setting. I did this with my megger to find a it could vary up to 0.5ohms in irregularity..

I created a thread over this subject here

 

[cagedanimal2010]

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its what im getting when trying to access any ideas?

 

[Sparky Ninja]

oh my apologies, I posted it in the electricians arms forum, didn't realise. I'll copy out of it the basic jargon of the discussion...

I posted....

Hi all,

I've always understood that using the anti-trip setting will normally give an inaccurate reading. However I wasn't so aware of level of it's inaccuracy..
My own tester is a KT64.When I've done a comparison test on it the difference between the non-trip and normal reading many times, and the difference in the reading was only ever up to a maximum of 0.1 ohm.
Today I finally received my Megger from one of my employers, and so I had a play with it today and thought I would check for the difference in readings on this kit.

I measured a Ze of 0.16 ohms, and when I turned it to anti-trip it jumped up to 0.63 ohms. I was somewhat amused that this kit could really apply nearly half an ohm in inaccuracy?? I re-tested a couple of times (allowing a bit of time between tests) and it maintained these readings.

I'm not necessarily concened about this, but I thought I would post on here to see if anyone else has checked out their tester and if the readings are similar to this??

to which sintra replied...

Had the same prob with 2 of our megger 1553's. (new at time 2 years ago)
Done the same as yourself and tested a non RCD protected circuit on the high setting and then again on the no trip both meters showed the same inaccuracies of about 0.5 ohms.
Both were sent back to megger and repaired results now are within 0.02 ohms and remain stable as i check them monthly as routine.

then Jason.S said...

I used to have some Megger seperates.

Did exactly the same thing.

Im sure somewhere in the manual it does state this.

then ian added..

I used to have a megger CM500, did exactly the same thing. I spoke to megger and they said it was within there tolerances. I changed to a 1552 and since then everything is fine.

Ian

that's the long and short of it.

 

[cagedanimal2010]

I'll try that today then! Cheers again mate! Danny

 

[cagedanimal2010]

right guys have been playing with my tester and the difference between hi-current and low-current is about .08 ohms, so still not equating to the .70 difference,
so would to rcd main switches cause this? and will the napit assessor pick this up and fail even tho the readings are compliant?
danny

 

[malcolmsanford]

Doubt he would fail you, as if that is your measured reading then that is it. He may ask you to show him how you did it, may even ask you why you think there is a difference.

Have you tried doing the test. Cross connect the LINE/CPC at the end of the circuit. Then at your board with obviously the MCB isolated for the circuit, One croc on the load side of the MCB and then the other on the Line inside of the main switch and test.?

 

[IQ Electrical]

I think he'll be pleased that you spotted the anomaly and have explanations for it!

Do the test as Malcolm has indicated above (on full current test) and see what reading you get.

 

[cagedanimal2010]

Alright guys that great! Cheers!
Danny

 

[Sparky Ninja]

As IQ has pointed out, if you can explain the possibility for the irregularity, along with your observations they'll be more than satisfied.

 

[Richcar]

Have you checked your loop impedance tester with a check box checker to see if it has recently gone on holiday and may need a re-calibration?

 

[cagedanimal2010]

richcar only had it tester a month came with calibration, dating to a week before i brought it.

 

[cagedanimal2010]

guys just thinking would a high resistance say at the meter, loose incomer, whatever cause this?

 

[IQ Electrical]

But that would have shown on your Ze.

 

[cagedanimal2010]

what about in the board flexi tail connections? im just thinking out loud here guys, trying to find a reason! :-D

 

[pevvers]

Are you getting a reading through the rcd main switch (es) or rcbo's when you are measuring the Zs?

This often increases expected results.

I second that thought, found it loads with RCD boards and non-trip instruments.