3 phase to 240

[Plumber69]

Is it ok to use 3 phase to a standard 240 hotwater tank and cap the unused wire?

 

[Jadnashua]

Depends...what are the actual supply's voltages? 3-phase tends to be with the phases 120-degrees out of phase, so if the WH doesn't have any electronics in it, it would depend on what voltage you actually develop between the two phases you choose. A heating element just cares about the voltage between the two ends. If that's matched to the supply, doesn't matter.

In a really large situation, that unbalanced load on the supply transformer might be an issue.

 

[Sponsor]

 

[Reach4]

Was that 208 three phase?

Is it ok to use 3 phase to a standard 240 hotwater tank and cap the unused wire?

I presume 208. The Franklin AIM manual specifies to change out the start relay in their 3-wire pump boxes. I did not see that they say what to do for a 2-wire pump.

https://faradynemotors.com/faradyne-products/control-boxes says the same... special relay available.

Oops.. I was somehow thinking well pump.

They sell WH elements intended for 208 if you want faster heating.

 

[Bannerman]

Assuming the voltage is 208 volts between any two phases, the water heater will receive 208 volts so the heating elements output will be roughly 13% lower and so the water will heat slower compared to when 240 volts is supplied.

As you will be using only 2-phases of 3, the remaining wire will need to be capped.

With 3-phase, best if power usage is as equal (balanced) as possible across all 3-phases. Perhaps the phase that remains unused for water heating, can supply another high consumption heating device somewhere else in the home?

 

[wwhitney]

If you run a resistive heating element designed for 240V at only 208V, the current will also be 208/240 as much as designed, so the heat output will be (208/240)^2 = 75% of the design level.

Cheers, Wayne

 

[Plumber69]

he used 3 of the 4 wires. Capped other. Im not an electrician