120/277V Power Connect for Hot Water Tank


Thread Starter


I have a 50 Gallon American Hot Water Tank that is 120V and 277V wired for single phase only. Does the power connect have to be 110 or can it be 220?

Bob Peterson

If you wire it up with 220V to the 277 V teminals you will only get about 60 % of full power but it will probably work. Having said that I can't recall ever seeing an electric water heater rated 120/277.
I think, it is pretty safe to use 110V instead of 120V and 220V instead of 277. Only problem is bad efficiency in ac transformers, but boiler didn't need in transformers.
Watts = Esq./R. A heater element has a fixed resistance. The wattage is based on a specific voltage. So as mentioned, if you apply 220V to the 277V terminals, the wattage output of your heater elements will go down by the square of the voltage difference. So 220/277V = 79% V, so the Watts will be 63% of what it is rated (not 60%, but close). What that means in a water heater is that it will take longer for the water to heat up, and thus longer for it to recover from a long sustained use of hot water. So take shorter showers, or at least always make sure you take yours first!