OK - but I still don't see what that has to do with the size of the cable, or how he supplies it, or where he runs them, or any of the other things that have been mentioned. I still don't see why you mentioned it as if it somehow made a difference to how we should interpret what you'd been saying, or the answers we'd been giving.jbonding said:
I've said a great deal that is positive and helpful - even my "wake-up" call, as it got you thinking. Replies which to you may have seemed like sarcasm were not - again their aim was to get you thinking. I wanted you to think what the load of two showers was, I wanted you to realise how much of a bite it took out of a 100A supply, or how it exceeded an 80A one. I wanted you to go and read up on the rules for concealing cables rather than being spoonfed answers.
When I asked for clarification of the "25mm", I wasn't jumping on a mistake - this is important.
When I pointed out the Part P issues I wasn't jumping on a mistake - if this is a loft conversion, LABC will be involved, so the electrical work will have to be done by the book.
Returning to your question, I really don't think you should have an installation with two showers in it, but looked at in isolation, I would supply the loft CU like this:
Split the meter tails with a henley block, take the new pair and a 10mm² earth cable from the MET to a 63A switchfuse, then 3-core 10mm² SWA up the outside wall of the house, cores used for L/N/E, and with the armour also earthed, to a metalclad CU in the loft, 20A MCB for a 2.5mm socket radial, 6A Type C or 10A Type B MCB or 6A fuse for the lighting circuit, and a 45A RCBO for the shower.
