voltage on earth

[rwb]

hello all,
Just revieced a call from a colleague asking what maybe causing him to be getting a reading of 97 volt on the main incoming earth? would welcome any ideas sorry its a bit vague but this is about all the information that I have currently.

 

[telectrix]

sounds like his main earth is floating. 97 volts, if he's got it right needs investigation urgently.

 

[telectrix]

what is he using as a reference point? 97volts between the main earth and what?

 

[topquark]

Floating external earth or maybe an internal short. If they can isolate all of the circuits, get them to check it again once isolated and see if it's still present. Then check again once the circuits are back on (if it went and it's now back again it's an internal fault).

 

[rwb]

Not sure where he was getting these readings waiting for him to get back to me with more info

 

[nickblake]

Check your supply if its TNCS the neutral could be down causing backfeed down the earth ,

 

[telectrix]

Check your supply if its TNCS the neutral could be down causing backfeed down the earth ,

and buy a good pair of wellies.

 

[rwb]

Floating external earth or maybe an internal short. If they can isolate all of the circuits, get them to check it again once isolated and see if it's still present. Then check again once the circuits are back on (if it went and it's now back again it's an internal fault).

The voltage was measure between the earth from the board and the suppliers earth block. When all MCB are turned off there is 0 volt but increase up to 97 as each circuit is turned back on.

Checked supply it is TNCS so could be the neutral causing backfeed down the earth.


WELLIES it is then

 

[Octopus]

Is there bonding between the CU and the suppliers earth?

 

[topquark]

Could still be either, but most likely what Nick has said, as you're most unlikely to have affected every circuit in one go.