meggar 1552 zs test

[kevinjstanley]

Hi all
having just purchased my meggar [i'm broke now] i tested a 30 ma rcd protected circuit and pluged into socket with 3pin plug,
it tripped RCD ON hI of loop,
so tested on no trip of the meggar with same 3 pin and got a reading of 1.1 ohm.

this is higher than my ze of 0.15 and { R1 +R2 OF 0.1 OF MY 6 METER RADIAL CIRCUIT }

I REALISE THAT WITHIN A TOLERANCE ZS SHOULD BE R1 + R2 + ZE = ZS
however zs is 1.1
and R1 + R2 + ze = 0.1 + 0.15 = 0.25

this is no where near a zs reading od 1.1 ??

what am i doing wrong, is it because i am testing on no trip of the meggar
kev

 

[Sparky Ninja]

Applying a loop test on the no trip setting can give inaccurate readings as it is applying a much lower current under test. My current 1552 is regularly checked to make sure its within a tolerance of 0.05 inacurracy that megger suggested to me. It has on occasion peaked much higher though.

I would suggest carrying out a loop test on a non RCD protected source on both Hi and non-trip settings, so you can assess it for yourself. Do remember to allow a little time between carrying out the tests as the tester will become inaccurate if you don't give it time between tests.




Oh, and welcome along.

 

[james king]

what mcb have u got the socket on?

if its a 32A mcb i think i remeber the max Zs being 1.44ohms

so if it was on a 16A mch ur readinging are fine

 

[telectrix]

you will find that the 1552, as most MFts will give you a higher reading for Zs on " no trip". this is normal and as long as your reading is below the max. allowed Zs , then fine.

 

[acvc]

..... and just to clarify, the max (temp adjusted) Zs for a 32A Type B is 1.15ohms.

Thanks for these useful pieces of info about the 1552. I've used it for a couple of years and didn't know about the Zs and NoTrip/Hi variation.

 

[kevinjstanley]

hi all
thanks for replies so far,
i did wonder about the the no trip testing at a different rate. but what do i do about my test sheet
if i put a zs of 1.1 but my R1 +R2 ARE 0.1 and my ze is 0.15
does this not make a mockery of zs = R1 + R2 +ze ?
it was plugged into 32 amp breaker circuit
cheers boys

 

[Sparky Ninja]

You can put down the reading obtained by either calculation or measurement. If the measured value is within the maximum permmited Zs according to BS7671 then just jot it down.
If it is above the maximum, assuming you are testing on the non-trip, then use the calculation. You need to be confident in your R1&R2 of course.

If you do find the tester giving off some inaccurate readings of a higher magnitude that the Zs is too high then it may be worth taking it back where you got it from if its still within warranty. If not, wait to get it callibrated and re-check it then..

 

[Deleted member 9648]

you will find that the 1552, as most MFts will give you a higher reading for Zs on " no trip". this is normal and as long as your reading is below the max. allowed Zs , then fine.

Cant accept this.....my new megger has gone back due to the considerable variation in readings...on the high current setting 5 tests on the same point will give 5 identical results,on no trip 5 tests produce 5 wildly different readings....unacceptable IMO...we are supposed to regularly check our meters accuracy and yet on one setting it's 'normal' to be inaccurate???. It's due back from megger next week.....will let you all know the outcome of the outcome.

 

[kevinjstanley]

Many thanks
widdler

 

[malcolmsanford]

what mcb have u got the socket on?

if its a 32A mcb i think i remeber the max Zs being 1.44ohms

so if it was on a 16A mch ur readinging are fine

As the circuit is RCD protected the maximum Zs would be 1667.

 

[kevinjstanley]

further to this subject and the meggar, i have had a responce from meggar concerning the tripping of the rcd on standard setting and the subsiquent need to test on non trip and then getting a higher reading than ze + R1 +R2 = zs
there take on it is and i quote "
Some RCDs have been found to add impedance. To see if this is the case here, perform a non-trip loop test either side of the RCD. If there is a difference in reading, then the RCD is adding impedance, which will account for the higher loop reading you are getting.

Regards,
Kerry Burdett
Dover Technical Support
Megger Limited Archcliffe Road Dover
Kent CT17 9EN England.

what do you think to that boys ?

 

[Sparky Ninja]

That response doesn't seem to apply to your initial enquiry?

 

[kevinjstanley]

hi m8ty

yea they seem to have answered the question with a question, and from what they appear to say is that a problem you will have to deal with.
my initial question was why the zs does not match ze + R1 +R2 and what can be done about it.
this was not answered.
i assume they would would want me to do this test and subtract the difference in reading ???

 

[Sparky Ninja]

I think they've got confused. We all understand that any device will create some impedance. This is one of the reasons why calculating Zs alone can sometimes trip you up as a deffective MCB can give a really high impedance.

They're just suggesting you test pre and post RCD to assess the impedance that device may be giving off.. nothing to do with this topic.

 

[kevinjstanley]

Hi Wilder

i am totaly buggered, my initial question to meggar was, why my new tester is giving a higher reading than the ze + R1 +R2 an non trip test of zs.
they suggest it is due to the rcd.
further to this i then ask, is it a case that zs does not allways equal ze +R1 +R2 within reason.
but also the result i put on the cert for zs is not the one i get from the tester but rather the calculation of R1 + R2 + my ze reading.

god help me