The difference in conductor diameter from 10mm to 16mm is less than a millimetre ie from 3.162mm to 4mm so I'm not expecting it to be difficult to get it in to the terminal.
It will be a problem getting the horse to water but not getting it to drink as it were.
TLC Says:
230v 9K6W 5m run under more than 100mm insulation above plasterboard (even at 25 degrees C)
Required Cable Size 16 mm
Voltage Drop 0.584 Volts.
Percentage Drop 0.25%
Current Load 41.7 Amps
Max Cable Load* 47.4 Amps
Bond to incoming water goes through wall and ceiling void and down to incoming water in kitchen. picture coming soon.
Cu is going to be split load unit like this:
Protective Multiple earth notice - so TN-C-S?
Service Head
Main Cutout detail
CU
Unused way, Fused unused. Downstairs Lighting, Upstairs Lighting, Sockets, Cooker
Incoming Gas bonding
Spoken to EDF who think the main Cutout is 60A because that's what it usually is...