Neutral potential on TT system

[Normanw]

Whilst troubleshooting a PV system fault (maybe more of that later but it’s not the issue here) my electrician found 235v L-N 202v L-G and 30v N-G. He disconnected everything including all N  and G tails, same result. Fitted a new Earth rod, same result. Called supplier who disconnected the house completely (which incidentally includes the complete PV system) and found 235v L-N and said “earth problem - we don’t supply it, your problem mate”.

I asked them to check L-G and N-G (my earth rod)whilst house was completely disconnected , they found 202 & 30 but still said your problem mate. I have checked next door who are on same supply, also TT system, they have 235/0/0. 

Supplier checked his supply cable between transfo and me, don’t know how, says it’s ok. So supplier says supply ok, it’s a house problem, my electrician says house is ok, I’m going to try to get them both here together. 

Anybody ever seen this before? Neither electrician nor supplier has apparently 

 

[Andy™]

if you have a fault with some power going to earth through the rod then you will get odd voltages. its also possible that the earth voltage is coming from an external fault (possibly in a different property), which is more likely if you still have the voltages with everything turned off

 

[Normanw]

Thanks Andy, I am not aware of anything but will check with neighbouring properties

 

[Andy™]

you could also (under controller conditions) disconnect bonding from services and measure voltages. see if its coming in from one of them

few years ago called to a job. earth was very live L-E was about 10-15v. N-E was about 220. fault was a dead short L-E in another property upstairs making neighbouring houses earths live through shared metalic gas pipe

 

[Normanw]

As I said above, the Supplier (electric board as they used to be called) checked incoming service cables with house disconnected when he was here, found 235 L-N and concluded it was my problem. Or did I misunderstand what you said, I’m a nuts and bolts engineer, not a sparky?

This is a rural location, we have no shared pipes or whatever with the neighbours. 

Thanks

 

[Andy™]

think you ned a better electrician to check the wiring and find out where the voltage is coming from

 

[Murdoch]

Did the "electrician" actually check the Ze?

The first and most important test.

 

[Normanw]

How do you do a Ze test on a TT system? The issue appears to be that the supplier says he has a good earth at the supply transformer (500yds away) by his test (<0.7ohms) but I don’t understand how I prove that I have a good earth on my earth rod compared to the supply transformer earth. 

 

[Andy™]

any decent electrician would be able to test it

 

[Murdoch]

How do you do a Ze test on a TT system? The issue appears to be that the supplier says he has a good earth at the supply transformer (500yds away) by his test (<0.7ohms) but I don’t understand how I prove that I have a good earth on my earth rod compared to the supply transformer earth. 

You can’t

a Decent spark can .....

 

[Warwick]

The Ze test is testing the external earth fault loop impedance of the installation. A Ze test cannot be carried out when there is voltage showing on the neutral, the tester will pick up the problem and not let the test go ahead.

 

[Normanw]

As I said above, the Supplier (electric board as they used to be called) checked incoming service cables with house disconnected when he was here, found 235 L-N and concluded it was my problem. Or did I misunderstand what you said, I’m a nuts and bolts engineer, not a sparky?

This is a rural location, we have no shared pipes or whatever with the neighbours. 

Thanks

I am being told the Ze cannot be measured because ther

I am being told the Ze cannot be measured because there is a live neutral???

 

[Normanw]

Thanks Warwick, that confirms what my electrician is saying. So now what can I do?

 

[Murdoch]

Thanks Warwick, that confirms what my electrician is saying. So now what can I do?

Did your "electrician" actually check the continuity of the earth conductor?

If the main switch is off and a tester registers voltage on the neutral something VERY odd is going on 

Are you sure you had a proper spark on site with proper test equipment?

 

[Warwick]

Yes, his electrician did check the continuity of the earthing conductor.

The main switch was off and we still got voltage on the neutral and this is why we called in the DNO.

He did have a "proper spark" with a 2391 test and inspect qualification and he was using a Kewtech KT64 tester that had been recently calibrated.

Yes, it is VERY odd

 

[Murdoch]

Who is the person you refer to as "his"?

 

[Sharpend]

Who is the person you refer to as "his"?

I’m reading as Warwick is Normanw sparks? 

 

[binky]

out of interest did your sparky isolate the PV inverter before testing, and what is the fault with the inverter?

 

[Warwick]

His being Norman, Warwick being his electrician

The PV was totally isolated for testing, the inverter initially detected the fault and gave it as a missing earth connection.

 

[Murdoch]

^^ as I previously said, did anyone test the earth ?

I’m reading as Warwick is Normanw sparks? 

Not sure I agree with that.

Maybe they are the same person ....