I need to fit a shower pump in my house, the pum needs a 30ma RCD, power via a double switched fuse with a 13Amps. I have a 13A isolator switch which will be in the hot press next to the pump and a cable from this switch going to the distribution board where I already have a 30ma RCD 40Amps. My question is I am doing right by connecting a 13A isolator to a 40Apm 30ma RCD? what section of cable should I use for about 10m lenght.