10mm².I'm not sure what the requirements for bonding were back in the day, 15th edition was as i recall when it all started getting mad (people bonding metal window frames ffs).
On my own house I used 16mm² as that's what I had. The inspector tried to fail it (prior to resealing head and meter) as the tick box was to verify 10mm².
Also I'd used singles in tube (as most of the house was tubed) and he didn't know how to tick 'earthwires sleeves'.
Last edited: