Multi-function tester discrepancies

[s6stu]

Hi all,

got a bit of a puzzler here;

A mate of mine uses a Megger and i use a Fluke multi function tester. We both had them calibrated recently by the same guy and even when we use the same leads on the same socket outlet, (with accurate zeroing on the fluke), we get different Zs values, 0.94 with the Megger and 0.34 with the Fluke. I am tempted to believe the Fluke due to the close location of the socket to the fuse board, but this does not really solve the issue.

When we used our own calibration device the values were all close to expected. The one thing that was odd with the Megger was that when we checked the volts at the outlet, both testers were very similar, but when the Megger was then selected round to the 'no trip' Zs test, the voltage detected and consequently tested at, dropped by about 6/7 volts. I don't see how this would affect the reading of the Zs value so greatly though.

Any thoughts or suggestions welcome,

thanks in advance,

Stuart

 

[derek]

How do they both compare to R1+R2 plus Ze? I have heard others mention that the no trip Zs on the megger is not very reliable but I don't use one myself.

 

[s6stu]

We didn't try R1+R2, but the proving/calibration unit that we used had various continuity tests to perform and they were both accurate.

 

[pencilpusher]

The Megger 1700 series has problems with a two lead no trip loop test. I recently had a ZS measurement of 0.94 ohms when I knew it should read about 0.54. It seems to be about the firmware on the 1700 series. It seems the latest firmware v2.06 (I think) seems to have solved the problems but anything earlier than that this is pants apparently. I would only use a three wire test on these units or ask Megger to update the firmware. If the unit is under 3 years of age, they may do it under warranty! Mine is away at present having an upgrade. Check the firmware version on your Megger!

 

[smoggy]

This is my megger stu is talking about, just gone through some old records, i have a test socket at home, now getting higher readings than before, going to ask guy who calibrated it and see if firmware was changed for some reason! Any other 1552 users had probs?