help with Zs.

[Deleted member 9648]

As already stated...are you measuring at the cooker on the no trip setting?.....this is notoriously inaccurate/random....although the meter manufacturers wont admit it.

 

[topquark]

Is it possible that this is an older PME installation with an MET on top of the service head that has bonding connected and someone has added another MET (EMT) elsewhere? A photo of the service head might help if you had one.

 

[GaryM]

As already stated...are you measuring at the cooker on the no trip setting?.....this is notoriously inaccurate/random....although the meter manufacturers wont admit it.

And one reason why I prefer to calculate Zs values, especially on RCD protected circuits.

 

[GaryM]

Is it possible that this is an older PME installation

OP said it's a new build.

 

[topquark]

OP said it's a new build.

Which could mean it's a very large extension on an old building. New build means different things to different folk. Not always entirely new.

 

[SPARTYKUS]

Had Ze values lower - looked outside and saw the sub station a few feet away mg_smile:

 

[tgtworsley]

it the same for all circuits measured Zs all way to high. my tester has only got none trip its the di log, installed a 17th edition board
it a new installation so new meter

 

[topquark]

What make RCD's are in the board? I'd be tempted to bypass them whilst doing your Zs readings. See what difference that makes. Some makes of RCD have been known to cause problems when trying to use no trip settings on MFTs.

 

[tgtworsley]

using a contactum board

 

[topquark]

Yep, they've been known to have issues. Try linking out one of the RCD's and doing a Zs for one of the circuits then and see if it matches expectations more closely.

 

[tgtworsley]

ok i'll try that tomorrow and let you know thanks

 

[diditrain]

I have had this happen quite a few times recently aswell.
As some of the others have said try bypassing the rcd. I measured the zs on the supply side of the rcd and on the load side and there was a 1.35 ohms difference

 

[tgtworsley]

ok thanks can you think of anything else to try

 

[timo1]

Hello mate, you mentioned that you had a di-log MFT. I read that they can throw up some odd readings sometimes, in fact it put me off of buying one. Worth googling to see if its the tester? There is a way round it apparently. long shot but you never know.

 

[diditrain]

There were other similar posts with similar issues and they appeared to come to the same conclusion.
Your were happy with your other results, quality of workmanship and you are using a calibrated tester. You will see the problem when you go back and retest as the others suggested