Hi guys the wire coming in from the top is 10mm and was already installed from the cupboard to the shower when I moved in, and the shower is a 8.5 kw. I was told 6mm cable would be fine for the rating of the shower and the consumer unit is a shower kit from screwfix with a 63a rcd & 40A mcb. the distribution cable is coming from a 32a mcb which I was thinking of changing and yes the top does have a gland just out of sight.