And don't take any notice of this trash. So many inaccurate statements. If you need to ask why be concerned about voltage drop you should find something else to do. DC needing higher voltages to travel longer distances than AC etc? 40 amp RCD? I would love to see him try and get a 300mm SWA down a conduit. No rules in the home? Part P may be a clue let alone BS7671 Yes, armoured cable is armoured for a reason like paint is coloured for a reason - plonker! Heaters use more than motors? You must have some big heaters. What a shame Lucia isn't around to comment on the piffle Logic has turned out, she would have a field day. Kind regards BS
Swa submain does not normally need RCD protection. RCD and earth rod at point of use to form TT earthing system