My colleague was asking about my experiences of having a new electric shower. He has a 60A main cutout and has tried to Google the realistic load that this would take, assuming the shower is on for 5-10 minutes at any one time with few other things switched on. I have been using a 9.8KW shower on a 60A main fuse for months with no trouble, making sure that ovens/kettles etc. are off when showering. I seem to remember reading 75A somewhere.