neutral to earth high voltage

[Simon-0116]

Been to look at a faulty socket on a rcbo and wont hold in, tried to test trip times etc but reading voltage on earth. Supply is tt, 3ph and 1 ph to a domestic property. Shared earth rod. Cant turn house off as belongs to separate person. So tested voltage at 3 ph db, 230, 400 v etc but got 48v n to e.. so i did insulation test on incoming swa, phase to earth, one down to 350 ohms, n to phase, one 459 ohms, n to e grater than 500 ohms. But can work out why 48v n to earth. House looks to have split load rcds, looking through window. My only conclusions is swa supplying house has low insulation. Am i looking in wrong direction. Ive turned power off to barn till i can look at house supply.

 

[PEG]

Hi simon, You need to explain the layout better,as order of installations is important,you must have isolated the 3ph to IR test those conductors,so did you turn off the house supply? ....Also,your IR readings need amending :yes:

 

[Simon-0116]

Dno supply 2 supplys 1 3ph for barn and 1 1ph for house. Ie 1 dno cable coming in with 2 heads / meters, but only one earth rod used.

 

[davesparks]

How much greater than 500 ohms? They are all very very low for IR bearing in mind the minimum permitted is a million ohms!

 

[Pete999]

Been to look at a faulty socket on a rcbo and wont hold in, tried to test trip times etc but reading voltage on earth. Supply is tt, 3ph and 1 ph to a domestic property. Shared earth rod. Cant turn house off as belongs to separate person. So tested voltage at 3 ph db, 230, 400 v etc but got 48v n to e.. so i did insulation test on incoming swa, phase to earth, one down to 350 ohms, n to phase, one 459 ohms, n to e grater than 500 ohms. But can work out why 48v n to earth. House looks to have split load rcds, looking through window. My only conclusions is swa supplying house has low insulation. Am i looking in wrong direction. Ive turned power off to barn till i can look at house supply.

Are you sure those readings are not Mohms?

 

[Simon-0116]

Yes they are M Ohms

 

[Pete999]

Yes they are M Ohms

So not much wrong with that cable then

 

[Lucien Nunes]

What reading did you get for Zs?

 

[PEG]

High dude,as i now understand it,you NEED to be able to start from incomer,for your testing to be conclusive,which means permission to isolate all that is fed from there,house included.

Although peeping through a window is fun,it does not constitute a comprehensive inspection of that properties installation :yes:

 

[Deleted member 72666]

High dude,as i now understand it,you NEED to be able to start from incomer,for your testing to be conclusive,which means permission to isolate all that is fed from there,house included.

Although peeping through a window is fun,it does not constitute a comprehensive inspection of that properties installation :yes:

Is it now!

 

[kevin.bl]

you would expect voltage n to e on a tt

 

[PEG]

you would expect voltage n to e on a tt

That would be very much dependent on where you measured it,what loads were still connected,and what measuring device you were using...:smile5:

 

[kevin.bl]

True but at first glance on a 3p and 1p tee off on a tt i wouldnt be supprised to see a voltage. Yes it is high but probably nothing to do with the rcbo tripping unless the voltage drops when it is isolated. I suppose people are right its hard ro guess without more info but personally id start with the device upstream as appose to the stray voltage between n and e. If the mft wont test because of pd you could isolate all board app from rcbo with a temp n to e link in to peform them but fck sake dont forget to take it out lol.

 

[Simon-0116]

Been back and pulled main fuse to house, n to e voltage drops to 3.8v, still couldn't get live test ze, but got L to n ze 0.4 ohms. Rcbo no tests fine with house disconnected. Owner wont let me do insulation test on there swa house supply. So had to leave fault i presum coming from there cable, as boards a dual rcd set up.

 

[uksparks]

If I'm reading this right, you have disconnected one if the other phases going to another board and now the one you are one which is on a different phase now tests correctly?

would I be right in thinking there's a loose neutral on the house supply which is shoving voltage back down the earth?

to be honest I'm just guessing with a stab in the dark, I would need to be there and have it all fully isolated and test it all to know what the issue is.

 

[Lucien Nunes]

A loose neutral connection would not affect the voltage at the MET with respect to real earth. It would also have caused incorrect voltages L-N and L-L which the OP says were OK at the time when there was excess voltage N-E. So I think that's a red herring.

There was a test result for Zpn (not 'L-N ze' that doesn't make sense!) of 0.4ohms, which is plausible, but the MFT couldn't test Ze. As the installation is TT that suggests the rod is completely hopeless and a small amount of leakage (possibly a perfectly normal amount) from equipment in the house is enough to raise the voltage drastically. Nothing terribly surprising there.

 

[UKMeterman]

We have one of two things going on here;
Either the earth rod is high resistance and thus not working and needs fixing, or there is a L-E fault that is putting AMPS down that earth rod. In both cases there is a fault that needs fixing so the installtion in the first case is properly earthed and in the second case prevent fire and the electricity meter going round like a cathrine wheel!

Go back to the customer and explain that if this leak was gas, would they stop you from fixing it? If the property is rented then they have a duty of care and you may also find suitable phrases in the Electricty at work at.