Live pipework problem

[Chocolate]

Evening all
Anyone any ideas on a voltage being present on pipework in a flat?
All bonding done and satisfactory Ze at board.
It’s a block of 3 which I’ve isolated all Power to two of the flats the third is a holiday home which I can’t access. I was thinking there is an issue either in the inaccessible flat or an external problem. Any ideas would be appreciated. The incomer to the two I can access is a tn-s 3 phase.
Cheers

 

[Baker1988]

What is the voltage present? Have you measured it to see what voltage is there. Also have you checked the continuty of the said pipework to the met/ earth teminal to be sure it is actually bonded as it could not be

 

[Gavin John Hyde]

possible fault current flowing to earth through the pipe?. could be that the fault current is not sufficient to trip any protective device fitted?
If the pipe runs through the building then the fault could as you said be in any of the flats??
Are you able to access the cutouts for other flats? came across a similar on a TT once where the rod was disconnected as somebody stole the cable! and system was using water pipe as the main earth.
have you fully checked all the bonding and that the necessary clamps are all secured properly?

 

[Wilko]

If Ze and bonding are ok then there can't be much voltage on the pipes, surely? Need a lot of current to generate a potential across 10m of 10mm (say) and that should trip any RCD and probably the circuit breakers too?

 

[Octopus]

How have you measured this “voltage” ?

 

[Wilko]

Next thought is DNO neutral lost.

 

[Andy-1960]

Neutral - earth link missing?

 

[Octopus]

The Ze you have done ..... is it at the incomer or the flat?

 

[Davisonp]

I have had a siuation where after investigation, 0.74 volts was coming in to an installation from outside and finding its round the earhting to return to the substation.

 

[Chocolate]

Was measuring 48 volts using mft. I have measured ze at cut out in flat. The cut out in flat is tapped off the 3 phase tns at entrance stairwell to two of the flats. Im heading back tomorrow to make sure I’ve not missed anything stupid, cheers for replies so far.

 

[Octopus]

^^ that would suggest its not bonded... check this first

 

[PEG]

Where did you measure this voltage between?

 

[Nigel]

I would suggest you check the Ze at the DNO head with all paths removed.

I had this once and it was a dodgy TN-S and a R1+R2 link left in on another flat.

The funny thing is because I reported the poor Ze to the DNO when they put a PME link and everything was sorted I thought no more of it.

It was two years later when I went to test a different flat and spotted the R1+R2 link left in that I put 2 and 2 together. Clearly when the DNO sorted their earth out it tripped the MCB in the flat with the fault as it should have.

 

[dmxtothemax]

pull the breakers one by one, see which circuit is using the ground as a neutral return path.
Bear in mind that it may not be your installation causing this,
it could be the neighbors installation.

 

[PEG]

None of the previous,helpful posts,mean anything,until we know that second test probe was not applied to a recently,vigorously brushed Angora goat

 

[Chocolate]

It is looking like a neighbouring property that is a holiday home so this could drag on. The dno isolated as many properties as possible and the fault was still there. Dno engineer said he would phone me back which will probably be tomorrow.

 

[Fish6328]

Evening,
I have just found a problem that I had with taps giving us a little buzz every now and then, but not enough to trip the RCD's in the CU. I found we had an intermittent 22v coming through the main earth on a TN-S system. I found the 22v by checking the bonding and then measuring between the MET and the main earth. To cut a long story short, it was a fault in the street lights outside that was sending voltage to the earth at the transformer down the road.

 

[Deleted member 26818]

Evening,
I have just found a problem that I had with taps giving us a little buzz every now and then, but not enough to trip the RCD's in the CU. I found we had an intermittent 22v coming through the main earth on a TN-S system. I found the 22v by checking the bonding and then measuring between the MET and the main earth. To cut a long story short, it was a fault in the street lights outside that was sending voltage to the earth at the transformer down the road.

Earth fault voltage from outside the installation will not trip RCDs inside the installation.

 

[stevels4]

Was measuring 48 volts using mft. I have measured ze at cut out in flat. The cut out in flat is tapped off the 3 phase tns at entrance stairwell to two of the flats. Im heading back tomorrow to make sure I’ve not missed anything stupid, cheers for replies so far.

And the Ze at the cut out was?

 

[Squid]

Did hear a story a few years ago about the gas engineers that go a shock when cutting a gas pipe as the home owner bypassed the meter and stuck the neural able to the gas pipe, may be an "Urban Myth"