What size wire is needed for electric water heater?
Similarly, it is asked, what wire do I use for an electric water heater?
Electric hot water heaters typically require a dedicated 30-amp, 240-volt breaker. The wire supplying power from the breaker panel to your water heater will usually be a 10/2 Romex cable (Blk wire- hot, Marked White wire - hot, Bare copper wire - ground).
Also to know is, what size wire do I need for a 50 gallon water heater?
The standard for water heater circuits is #10, two conductors with ground (10/2) and a 30 amp circuit breaker for a water heater. If you are running cable anyway, just run #10 and replace the breaker so it's done right, once and for all.
Most 50 amp water heater will come with 4500 watt elements. On a 240 volt circuit that is 4500 / 240 = 18.75 amps, so, no, that will not trip a 20 amp breakers, however, it will be operating the breaker nearly 95% of its 20 ampacity rating and most breakers are not rated for that.