Earthing in a flat

[Mashby22]

Hi guys

I'm new to testing. I have installed a lighting circuit and ring final which I am doing an eic for. I noticed in the board it seems like there isn't a main earth. The service cupboard on landing has 3 box with 3 meter for 3 flats on that landing. Those boxes are fed from a box in riser where the bs88 fuses are. There fed from 3 metal tubes fed from below which feeds the fuses, the neutral bar and the earth bar. From the earth bar there are 3 earths which feed the 3 boxes with the meters. From there to the flats are fed by a mineral cable. Each mineral gland is connected together by a bar which is connected to the end box which happens to be the flat I'm working on. So I've established the flat is earthed by the gland. Behind the c/u in the flat there are two metal backboxes in the wall which has the cable for their circuits and the mineral cable to the main switch. Those backboxes have a 6mm earth to the earth bar in board.
To test if those were the main earth I tested between earth in a socket near by and the earth by getting continuity as should, disconnected one of the 6mm from the backbox still getting continuity. Disconnected both together and still get continuity... So how do I disconnect to do ze, or test for the pfc. Hope I'm making a meal out of a mole hill here.
Appriciate the help guys:/)

 

[Leesparkykent]

Ze should be done at the origin.

 

[Simonslimline]

Ze should be done at the origin.

Zdb would be the test being carried out.

 

[Leesparkykent]

Zdb would be the test being carried out.

Exactly so he doesn't have to disconnect anything at the sub board.

 

[Mashby22]

I've never had to test a board in flat of those size just houses. I thought you test for ze by disconnecting main earth and test between earth and live into main switch? I can't do that here as I don't know what is the main earth. Am I doing This correctly?

 

[Simonslimline]

I've never had to test a board in flat of those size just houses. I thought you test for ze by disconnecting main earth and test between earth and live into main switch? I can't do that here as I don't know what is the main earth. Am I doing This correctly?

Ze can only be taken at the origin!

 

[Mashby22]

Ok I can get ze by contacting the supplier but how about pfc?

 

[Leesparkykent]

Ok I can get ze by contacting the supplier but how about pfc?

Ze is taken at the origin so in your case more than likely in the intake room/service cupboard. Zdb will be taken at the board in the flat.

 

[Mashby22]

Ze is taken at the origin so in your case more than likely in the intake room/service cupboard. Zdb will be taken at the board in the flat.

I don't have access to the intake room so i can call supplier for ze. For zdb I still need to know what is the main earth don't I? So how do I do that from my first post.

 

[davesparks]

I've never had to test a board in flat of those size just houses. I thought you test for ze by disconnecting main earth and test between earth and live into main switch? I can't do that here as I don't know what is the main earth. Am I doing This correctly?

The correct term is earthing conductor, not main earth.
The real world rarely reflects the ideal works of the text books. Sometimes it's not possible to disconnect an earth, such as when micc, SWA, conduit or trunking are forming the earthing conductor.
You have to apply knowledge and experience, initially that which is handed down by your mentor during your apprenticeship and latterly through your own experience and continued learning.

In your situation the Ze can only be tested at the intake into the building. Disconnecting the incoming earth to the flat and testing will only serve to give you an incorrect Zs of the circuit feeding the DB (known as Zdb)

 

[Mashby22]

So to get zbd test between earth bar in board and line in main switch witch bonding disconnected. And to get pfc, test between line and neutral to get pssc and line and earth bar ( bonding connected) to get pefc which ever is highest give me my pfc?

 

[davesparks]

So to get zbd test between earth bar in board and line in main switch witch bonding disconnected. And to get pfc, test between line and neutral to get pssc and line and earth bar ( bonding connected) to get pefc which ever is highest give me my pfc?

No, you must not disconnect any bonding in a live installation.

 

[Simonslimline]

So to get zbd test between earth bar in board and line in main switch witch bonding disconnected. And to get pfc, test between line and neutral to get pssc and line and earth bar ( bonding connected) to get pefc which ever is highest give me my pfc?

Zdb is taken with bonding connected. You have inspection and testing quals according to your profile!!!

 

[Mashby22]

So zdb test between line and earth is the same as the test for pefc? But on a different setting

 

[davesparks]

So zdb test between line and earth is the same as the test for pefc? But on a different setting

That depends on the tester being used.
The PEFC isn't actually tested, it's the EFLI which is tested and the tester calculated PEFC from that