David West
Hi Rob It depends on what Wattage the water heater is. If its a standard 3KW heater (Similar to immersion heaters) then it will need a 2.5mm cable. This however needs to be run off its own circuit from the consumer unit using a 16 Amp breaker and connected via a 20 Amp rated switch. If it is a higher Wattage...say 7KW, then you will need something more robust! A 6mm cable will be needed and up to a 32 Amp breaker. Again on its own circuit connected via a 45A Cooker type switch. Kind regards Dave ADW Domestic Electrical
