Where does my responsibility start?

[dellboy78]

Hi all,
I changed a consumer unit today in a top floor flat in a converted town house. Down at the intake position is a PME head. There is a 63A switchfuse for the flat then a 16mm T&E going up to the flat where the meter and consumer unit is. By the look of it the meter would have been downstairs at some point but now has been moved upstairs. I have always been of the opinion (correct me if i'm wrong!) that anything before the DNO's meter has nothing to do with me and that this is the 'origin' to which the installation I am working on connects to the supply. If that is the case then would that not mean that the supply to this flat is now effectively TN-S? I need to take the main bonding into consideration too as at the moment they are in 6mm taken from the CCU (which in turn has only got the 6mm cpc in the submain.) Obviously if this is still classed as TN-C-S then I will need to upgrade the bonding. What do you guys think?

 

[jaydee81]

whats the arrangement at the intake where do the tails for 63a sw fuse connect to

 

[dellboy78]

TN-C-S at the intake, the tails from the switchfuse connect straight into the head (via a henley block where the meters original position must have been.

 

[Engineer54]

Hi all,
I changed a consumer unit today in a top floor flat in a converted town house. Down at the intake position is a PME head. There is a 63A switchfuse for the flat then a 16mm T&E going up to the flat where the meter and consumer unit is. By the look of it the meter would have been downstairs at some point but now has been moved upstairs. I have always been of the opinion (correct me if i'm wrong!) that anything before the DNO's meter has nothing to do with me and that this is the 'origin' to which the installation I am working on connects to the supply. If that is the case then would that not mean that the supply to this flat is now effectively TN-S? I need to take the main bonding into consideration too as at the moment they are in 6mm taken from the CCU (which in turn has only got the 6mm cpc in the submain.) Obviously if this is still classed as TN-C-S then I will need to upgrade the bonding. What do you guys think?

If the supply into this building is PME/TNC-S then PME conditions will need to be met THROUGHOUT the whole of the building, (eg ...each individual flats bonding cable size/arrangement). This seems to be a common misconception by many on the forum, thinking that a PME installation can suddenly become a TN-S, because there is no sign of a N-E link on the section of the installation that they are working on...

So YES, you will need to replace/upgrade the present 6mm bonding conductors to 10mm.

 

[ackbarthestar]

If the supply into this building is PME/TNC-S then PME conditions will need to be met THROUGHOUT the whole of the building, (eg ...each individual flats bonding cable size/arrangement). This seems to be a common misconception by many on the forum, thinking that a PME installation can suddenly become a TN-S, because there is no sign of a N-E link on the section of the installation that they are working on...

So YES, you will need to replace/upgrade the present 6mm bonding conductors to 10mm.

The simple answer would be to run an extra 4 or 6mm2 bonding conductor from the MET sub-main DB in the flat.

Assuming that the MPB at the service head to the utilities was the correct size, I would have to ask, in the 'unlikely' situation where there was a PEN fault the only problem I could envisage would be the rise in potential on all the exposed conductive parts in the flat, unless, maybe, there were any extraneous parts. The problem, then would be the risk of fire due to high neutral currents looking for a return path via the earthing system (extraneous conductive parts).

Often, providing supplementary bonding within the flat should be acceptable I would have thought?

 

[Engineer54]

The simple answer would be to run an extra 4 or 6mm2 bonding conductor from the MET sub-main DB in the flat.


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PME installations require 10mm, you can't run a combination of different sizes either!! Apart from that the bonding of extraneous services is to be carried out within in each flat, and connected to the flat's MET which is effectively a building EMT, not taken to the buildings MET!!

There is a possibility that this building has been PME'd, since the original splitting of this building into flats. Personally i would not and never have used T&E cable for sub-mains to flat's/apartments etc, especially on a PME install.

 

[ackbarthestar]

PME installations require 10mm, you can't run a combination of different sizes either!!

If we answering on the basis of 'a test out of context....' then its perfectly acceptable to use parallel conductors of the same size.

So the simple answer would be a 6mm2 bonding conductor.

Wouldn't you agree ?

 

[Engineer54]

If we answering on the basis of 'a test out of context....' then its perfectly acceptable to use parallel conductors of the same size.

So the simple answer would be a 6mm2 bonding conductor.

Wouldn't you agree ?

Yep!! Nothing wrong with running parallel conductors of the same size, length and type etc!!

 

[cobrauk]

I am surprised the the elec board moved the meter up like that ?