Theo wrote:

For a 32A single phase radial the TLC
calculator indicates it needs 6mm2. What cable do you use for three phase?

There are "lighter" 3-ph cables than SWA, where armour protection isn't
needed (e.g. server rooms) e.g SY flex, or tuff sheathed

https://www.doncastercables.com/cables/5/10/Control-Cable/SY-Steel-Wire-Braid-Flexible-PVC-Control-Cable/

https://www.doncastercables.com/cables/6/24/SWA-and-Mains-Distribution/XLPE-Insulated--PVC-Bedded-and-Tuf-Sheathed-Non-Armoured-Cables/