How is an electric water heater wired?

Answer 1

Hot water tanks

Amps = Watts/Voltage. 4500/240 = 18 amps. You would use a #12 copper wire which is rated at 20 amps. On a hot water tank there is only one of the elements on at a time. The incoming cold water is taken to the bottom of the tank through a pipe inside the tank. When the lower thermostat senses the cold water, the lower element turns on. As you draw hot water from the top of the tank the cooler water from the bottom will rise. When the top thermostat senses the cool water it shuts off the bottom element and turns on the top element. When this water is heated to the tank set point it shuts off and the lower element turns on to heat the rest of the water. When the total tank temperature is at the set point all elements turn off. By using this type of procedure there is always hot water at the top of the tank for use.

Actually, not all of this first answer is correct! A 4500 watt heater will draw around 18.75 amps. However, electric water heaters are considered "continuous loads". This means you can't load it's circuit more than 80%. So a 4500 watt heater circuit must be "sized up" to either a 25 amp or 30 amp circuit. This means that #10 copper wire will also be used. Now, a 3800 watt heater will draw around 15.8 amps. In this case, a 20 amp breaker and #12 copper wire can be used. Always check the heater's nameplate to be certain of it's ratings. The calculation used is correct.