Hi Ze reading's got me confused

[Stanstan]

Got a curious one, ran into a Hi Ze reading during some routine checks and wanted to see what others make of it. I know high earth impedance can throw all kinds of issues into the mix, from nuisance RCD trips to serious safety concerns, especially on older installs. This was on a domestic ring Ze came in way above what's expected for a TN-C-S setup. Double checked everything, and the reading held steady. Could be a dodgy main earth, corrosion, or just poor supply connection?
If anyone has come across thus issue or has a similar or even has an idea of what could be wrong.

 

[circleofdown]

Got a curious one, ran into a Hi Ze reading during some routine checks and wanted to see what others make of it. I know high earth impedance can throw all kinds of issues into the mix, from nuisance RCD trips to serious safety concerns, especially on older installs. This was on a domestic ring Ze came in way above what's expected for a TN-C-S setup. Double checked everything, and the reading held steady. Could be a dodgy main earth, corrosion, or just poor supply connection?
If anyone has come across thus issue or has a similar or even has an idea of what could be wrong.

What's the matter? Is this a new thing? You should definitely try to test the Ze at different times of the day because you may end up with different readings and that would mean a supply-side issue. Let's just deal with it via a process of elimination first, what you think?

 

[wisengruber]

Could point to a poor main earth connection or a loose or degraded supply neutral. Since the reading held steady, its less likely to be a fluke and more likely a real issue. Best to inspect all connections and notifying the DNO as needed, as this could surely compromise safety and cause erratic behavior in the system.

 

[Deleted member 119]

What system and what is the reading?

 

[Castello_V]

What's the matter? Is this a new thing? You should definitely try to test the Ze at different times of the day because you may end up with different readings and that would mean a supply-side issue. Let's just deal with it via a process of elimination first, what you think?

He should be seeing a pretty low Ze, but it's unusually high and consistent across checks, its not a new thing for you? but yeah you're right it might be a supply issue. @Stanstan start by confirming the integrity of the main earth connection like @wisengruber said, I've also seen it where the neutral/earth link at the head was compromised

 

[truffle pig]

Hi, What was the ZE? If its a TNC-S system the Ze (live to earth) and the Live to neutral should be substantially the same (earth slightly higher dues to small csa of cable from supply head. if its different the fault would be on the earth from the supply head to where you are taking the reading from (presumably within 3mtrs of the incoming, if they are very similar then it will be a DNO fault. DNO usually very quick to respond

 

[CircuitRick]

Got a curious one, ran into a Hi Ze reading during some routine checks and wanted to see what others make of it. I know high earth impedance can throw all kinds of issues into the mix, from nuisance RCD trips to serious safety concerns, especially on older installs. This was on a domestic ring Ze came in way above what's expected for a TN-C-S setup. Double checked everything, and the reading held steady. Could be a dodgy main earth, corrosion, or just poor supply connection?
If anyone has come across thus issue or has a similar or even has an idea of what could be wrong.

I agree with @wisengruber here. I've seen this before and it's usually a bad connection at the main earth terminal or cut-out, or even corrosion. It could also be an issue with the DNO's PEN conductor, like a break or high resistance joint. Check all your accessible connections first. If they're all good, you need to call the DNO immediately. This is a big safety concern because a high Ze could mean a loss of protective earth, which could make metallic parts live! Better get someone trained to handle it for safety!

 

[yojdee_]

Have you figured out if the problem is with the installation or supply side?