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Morning, just checking a lighting circuit on a house, I have the main earth disconnected and still get a zs reading of 2.2 ohms. No evidence of an earth spike and bonding goes direct to henley block.

Any suggestions why this could happen??
 
pics. would help. is you 2.2.ohms a reading from the bonding?
 
Parallel path via CPC to boiler circuit CPC to boiler manifold to pipework within the fabric of the building?

Also why is the installation energised with the main earth disconnected?
 
I don't understand either. And why would you expect the CPC to be insulated from earth throughout the installation? It could take any value from infinity to zero without indicating anything abnormal. I can see why it might be useful to know for forensic analysis but not for normal testing.
 
If you have main earth disconnected , surely it would be ZE not ZS.? (at source)

He says he's checking a lighting circuit though, not at the source.
 
So to answer why I had the circuit energised with the main earthing disconnected..

The lighting circuit connected in board had no CPC so I checked the Zs at a ceiling rose.

I had a reading of 2.2 ohms so I then tried to find out where the earth was coming from.

I disconnected all the CPC's from the other circuit in the board, checked Zs again and still had 2.2 ohms.

Just try and eliminate things and to see if I was picking up earth from elsewhere I then disconnected the main earth and still had a reading of 2.2 ohms.
 
Many years ago I used to disconnect the main earth and carry out various tests to help me understand parallel earths in electrical installations.
Done lots of other experimental testing in a controlled environment...
 
Many years ago I used to disconnect the main earth and carry out various tests to help me understand parallel earths in electrical installations.
Done lots of other experimental testing in a controlled environment...
You can’t make an omelette without breaking a few eggs.....
 
Just try and eliminate things and to see if I was picking up earth from elsewhere I then disconnected the main earth and still had a reading of 2.2 ohms.

Why do this as a live test when that means doing something as stupid as energising the installation with the earthing conductor disconnected?

Electricians are supposed to understand the fundamental principles of electrical safety!
 

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