No trip Zs tests

[telectrix]

True,but on a TN system with a type C/D mcb it may be that the measured Zs slightly exceeds the max allowed for the mcb....is it worth changing the mcb for a type b when the required disconnection time is met by an RCD?....not for me,there may be reasons why a type b might not be suitable..(high inrush currents etc)....if you refuse to accept that the rcd can provide fault protection ,the alternative is rewiring with a larger cable.....pointless for a circuit which already complies with the regs.

totally agree with you there, but we should endeavour to meet the tabulated values where possible.

 

[Amp David]

Anyways chaps, good to read throuhg the post and hear everyones point, but all I'm concerned with is the readings being different use 'no trip and high tests'.

I think a phone call to the people at megger might be in order. Saying that, isn't a forum member connected to Megger Tech Support?

 

[Deleted member 9648]

Did a series of tests today on a non rcd protected socket with the new megger ELI tester.....on high current setting 5 tests produced 5 identical results..0.13 ohms.
5 tests on no trip setting gave these results,
0.17
0.21
0.14
0.12
0.06
Not an acceptable level of consistancy on no trip setting IMO.....the meter has been returned to megger under warrenty,will keep you posted.

 

[brucelee]

Did a series of tests today on a non rcd protected socket with the new megger ELI tester.....on high current setting 5 tests produced 5 identical results..0.13 ohms.
5 tests on no trip setting gave these results,
0.17
0.21
0.14
0.12
0.06
Not an acceptable level of consistancy on no trip setting IMO.....the meter has been returned to megger under warrenty,will keep you posted.

nice oe maqte lets see what they say if it doest accuratly measure the value then there is no point its innaccurate

 

[Sintra]

I have sent 2 mft 1553's back to megger for this reason. Now both nearly perfect within 0.02.


Sent from my iPhone using Tapatalk

 

[IQ Electrical]

I have sent 2 mft 1553's back to megger for this reason. Now both nearly perfect within 0.02.


Sent from my iPhone using Tapatalk

That's interesting, was any reason given?

 

[Sintra]

No mate just got them back and problems were sorted. I check both of them regularly and they are both very consistent.

Just to add they were sent away separately and sorted under warranty.


Sent from my iPhone using Tapatalk

 

[Amp David]

Warranty ran out on mine in May of this year, bummer

 

[brucelee]

You have got me thinking now need to check mine if its out i am also going to return it still got 18months left of the warranty

 

[Amp David]

Tested a feed to an outhouse this morning and got the following results -

Ze = 0.15
r1+r2 = 0.16

So calculated Zs = 0.31

Measured values high setting

0.37, 0.37, 0.37, 0.37, 0.37

and measured values no trip setting

0.36, 0.36, 0.36, 0.36, 0.34

So looks to me as though the meter is OK as its nice and consistant, but always seems to give higheer values than a calculated Zs, even with any parallell paths included

 

[morph]

thats fine
read the book it came with it gives tolerances , its cool beans man

 

[Deleted member 9648]

Did a series of tests today on a non rcd protected socket with the new megger ELI tester.....on high current setting 5 tests produced 5 identical results..0.13 ohms.
5 tests on no trip setting gave these results,
0.17
0.21
0.14
0.12
0.06
Not an acceptable level of consistancy on no trip setting IMO.....the meter has been returned to megger under warrenty,will keep you posted.

Update.....
Tester came back yesterday and I tried it on the same socket and got very similar results on the no trip setting.
Contacted megger again who pointed out that in Gn3 it states that loop testers cannot be relied on to be accurate where the Zs is under 0.2 ohms. This was not something I was aware of so checked Gn3 and sure enough it is there....(every days a school day).
The obvious next step was to try it out on a socket with a higher Zs which produced much more consistent readings....although still not as consistent as the high current test.....we did a series of test and one thing that was apparent was that on no trip a percentage of the tests produced random results.....
High current tests produced a consistent 0.36 ohms.....no trip produced fairly consistent readings between 0.30 and 0.38.....but one test gave 14.8 ohms(!)....and another 0.78...........I think on no trip I will get into the habit carrying out each test twice,as long as they are ballpark that will be good enough.
Hope this helps others concerned with the accuracy of the no trip function.

 

[IQ Electrical]

Wirepuller, I have a method to lift the tester into it's accurate 'sweet spot' also works on supplies in close proximity to the transformer where accuracy is very important for accurate PFC measurement.

I'm out on-site now but I'll post it up later.