High Ze

[Rich.M]

Doing an EICR earlier and got some wierd readings not experienced before, thankfully property is empty.

I did a Zdb on a TNC-S system and got an earth loop of 0.44 this was with all earths connected at the MET in the DB so I checked the main earthing conductor into the cut out in the outside meter cabinet and all was ok, nice and tight, so I then disconnected the main earthing conductor in the DB and tested the Ze which measured 0.38 still above max.

As I put the main earth back into the MET I got a little bit of arcing , so with test leads I measued between the MET and main earth and got 40V!!!!!!! I also got 39V reading between N & MET.

Going back tomorrow for further investigation, but any ideas out there?

 

[suffolkspark]

Well theres likely a fault to earth (or general leakage from some equipment) and with you having the earth dissconnected with the installation live (???) it's got nowhere to go. Contact dno about high ze though, from experience I doubt they'll do anything though

 

[Strima]

Did you isolate the installation before disconnecting the main earthing conductor?

 

[davesparks]

so I then disconnected the main earthing conductor in the DB and tested the Ze which measured 0.38 still above max.

As I put the main earth back into the MET I got a little bit of arcing , so with test leads I measued between the MET and main earth and got 40V!!!!!!! I also got 39V reading between N & MET.

What maximum is that above? There is a nominal value of 0.35 but this isn't a maximum.

Apologies for the stupid question but did you confirm that the installation was isolated before disconnecting the earthing conductor? There must be a source of voltage connected to cause this, but with the installation isolated that should be impossible.

The neutral and earthing conductor are joined together in the cutout so yes you will get the same voltage on each one.

 

[Lucien Nunes]

[/QUOTE]There must be a source of voltage connected to cause this, but with the installation isolated that should be impossible.[/QUOTE]

The voltage was between the TN-C-S earth (or neutral, same thing) and the DB earth, which may be in contact with local true earth. So the source of voltage might actually be the PEN of the supply sitting rather high, with current flowing back to local earth when connected. 40V is a bit high though so until confirmed by the OP I won't speculate on whether the installation was properly isolated.

Nonetheless, a highish Ze on a TN-C-S would tally with a highish voltage between PEN - local earth under typical distributor load.