Bonding issue upon upgrading fusebox.

[rattlehead85]

Best Practise Guide No2 - Consumer Unit replacement in domestic and similar premises says the following on Page 5 (note 3)

"A 6mm main protective bonding conductor size could be deemed adequate where the minimum size required by regulation 544.1.1 of BS7671 is 10mm if the bonding conductors have been in place for a significant time and show no signs of thermal damage."

So it looks like you're ok as long as you meet those 2 criteria.

Also worth looking at note 2 on the same page (5) which mentions certain criteria for using a 6mm main earthing conductor.

http://www.esc.org.uk/fileadmin/user_upload/documents/industry/best_practice/BPG6_09.pdf

I had totally overlooked using BPG 2 which clearly points out what is permissible on a board change.
I was correct with regards to checking the bonding for thermal damage and corrosion if less than 10mm for continued use. I had also confirmed the adequacy of the earthing conductor by applying the adiabatic. On existing installations where a board change is needed i will from now on make reference in the 'extent of works' box that the change has been completed in accordance with BPG 2.and will note any departures found in the relevant box on the EIC.

 

[rattlehead85]

As far as the bonding cables go, both water and the gas bonding cables should be connected between the service pipes as they enter each flat, and the flats MET (which is an installation EMT) not to the buildings intake position (MET).


As this is a TNC-S (PME) installation, a minimum 10mm main earthing conductor should be run in with the 16mm T&E. I'd personally, never even think about running/using T&E as a sub-main cable to supply flats, even for TN-S systems, it just smacks of amateurism to me!! ...lol!!

I appreciate your view on this mate. If this was a new installation i also wouldn't consider using a t&e cable for the main supply and would use the sizing tables for the required earthing over the use of the adiabatic, however, this is an existing installation with very limited to no possibility for upgrade.
As a thought, as the flats have separate supplies fed from individual switch fuses at the intake and the service belonging to each flat are bonded to these wouldn't this be classed as satisfactory as the M.E.T within the switch fuse could be classed as part of that installation only?