"Worried by the review of 'Anonymous - Wirral'. The MCB should be rated to protect the cable and accessories which form the circuit. If too high a capacity MCB is installed without verifying that the circuit can handle it there is a real risk of the cable overheating under load and catching fire. At a 40 amp load (9-10kw shower would get you there) you should be looking at 6mm sq T&E minimum and that assumes the cable is installed in free air.. If in a wall or conduit it would have to be 10mm sq minimum. If in doubt ask a qualified electrician to take a look."