40-gal240vdual 4500w 1875A connected to the circuit breaker panel Double Pole-40A breaker with a 1220Amp cable. Choose the right tankless electric water heater for you. Color Code For Residential Wire How To Match Wire Size And Circuit Breaker Electrical Circuit Diagram Home Electrical Wiring Residential Wiring Just follow the three simple steps below to choose the right model and size you need. Hot water heater breaker size . The wire supplying power from the breaker panel to your water heater will usually be a 102 Romex cable Blk wire- hot Marked White wire - hot Bare copper wire - ground. To make your final choice we recommend getting a circuit breaker that offers at least twice the amount of amperage that your water heater will need. For a tank-style heater household size is a simple indicator of hot water needs. So if you have a heater using 6000 watts in total in a 240-volt connection the operative ampere total would be 25 Amp. Now in order to choose an electric brea...