I have just installed a John Wood 5500 watt water heater. It runs non-simultaneous operation, only one heater at any time. The owner manual for this electric water heater recommended a 35 amp fuses or circuit breaker for 208 or 240volts. Now the question? #8 wire with a 35amp breaker. If you calulate the load a 30amp breaker with #10 wire should work but the manufacturer recommeded 35amps.
