Earth Live

[Derby Dave]

Hi I have an issue on a large student accommodation block. On any circuit in any part of the building if a earth becomes disconnected then when tested I get 230v live to neutral, 110v live to earth and 120v earth to neutral. As I have said this is on any circuit from any fuse board in any part of the building. Any advice would be appreciated? 

 

[Andy™]

because its floating?

and more importantly, why are you disconnecting an earth on a live circuit!?

 

[ProDave]

As above, what other result would you expect? unless it's a bathroom circuit with the earth cross bonded to another earth.

 

[Derby Dave]

I was originally called out to a electric shock and when investigated found the earth had become disconnected and was now live. I then carried out a test on a number of other circuits and found the same. There shouldn't be 130volts flowing down the earth. 

 

[Sidewinder]

SMPSU's, LED lighting, and various other electronic devices will generate a current in the earthing conductors, so it could be that, or it could be induced voltage.

Measure it with a low impedance volt meter, maybe an AVO8 or 9, or a Fluke DMM with a low impedance input range, or using a phantom voltage eliminator.

Another thing you could do, is measure the earth leakage current, and try to identify where it originates from.

Welcome to the forum btw.

 

[Doc Hudson]

I doubt very much that you have 130v flowing down anywhere, it would be current that flows. A voltage is a potential difference between two points. It sounds more like you are using the wrong meter to do the wrong tests. What are the earthing arrangements, have you verified Ze, Zdb and/or Ra at the distribution boards. With the installation dead what is the resistance between the CPC's to N  and CPC's to L.

Doc H. 

 

[apprentice87]

Going off at a tangent here. Computers and stuff have a very high earth leakage, high enough that often special earthing arrangements are required, but why is this permitted?? Why are the makers not just told to produce decent stuff with proper insulation....

A car maker would not be permitted to produce cars that let out clouds of dense smoke and sparks, and then say. "but that is just how they are.." and expect it would be permitted..

john..

 

[Evans Electric]

Derby , if you are disconnecting various earths to try them , they will have an "induced " voltage on them , collected from adjacent circuits .    Is the wiring twin/earth  ?    Or does EVERY circuit show this even when connected.?

When you say  you were called out because of a shock , it may be just that circuit with a disconnected earth , touching a metal plate or similar would give a shock experience from the induced voltage.

If ALL the earths are showing this I think you need to be checking the main earth connections , Zs, Ze, etc

If you solve this , it would be good to see some feedback , which members would appreciate.

Was it lighting , power  etc? 

 Welcome to the Forum by the way.