Zs reading with main earth disconnected

[dtec dave]

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??

 

[APE37]

Parallel earth path with bonding still in place?

 

[telectrix]

pics. would help. is you 2.2.ohms a reading from the bonding?

 

[dtec dave]

Bonding not connected, it goes direct into Henley block. Main earth comes from henley block but is disconnected.

 

[static zap]

Outside lights (parallel path)?

 

[Strima]

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?

 

[APE37]

Good point. Regarding the installation energised with main earth disconnected.

 

[buzzlightyear]

Also why is the installation energised with the main earth disconnected

stupid thing any body can do ,op where you going to rely on the bonding .

 

[westward10]

I don't understand what you are doing. Zs at board with earthing conductor disconnected?

 

[Lucien Nunes]

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.

 

[7029 dave]

If you have main earth disconnected , surely it would be ZE not ZS.? (at source)

 

[DPG]

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.

 

[dtec dave]

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?

 

[dtec dave]

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.

 

[dtec dave]

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?
[/QUOTE

 

[Charlie_]

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...

 

[westward10]

Disconnecting the earthing conductor for an energised system isn't the wisest thing to do. You are better to try dead tests by way of a continuity tester.

 

[buzzlightyear]

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...

working on the HIGGS BOSON PROJECT.

 

[Baddegg]

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.....

 

[davesparks]

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!