I was ask to hook up a single phase water heater. The label on the water heater says: 208v or 240v. The power they had was 480v/277v (Wye). Would it be safe to hook up the 277v to the water heater.
This is a misapplication. Resistive power dissipation increases with the square of voltage ratio. Your proposal is hazardous and the heater will likely fail in a short interval.
Lewish, I'm assuming the voltage is to high! Now with the higher voltage there would have been lower amps, correct. I was also concerned with only one leg of the 277 having a breaker vs the 208/240 with a double pole breaker. I wasn't going to hook it up, I told my boss it wouldn't work, but had these questions in my mind.
“higher voltage there would have been lower amps” won’t work, and will get you into trouble. You have a constant-resistance application, not constant-power. An appropriate size of 277 - 120/240 Volt dry transformer can do the job. An example is page 17 of
busbar: he said the heater was single phase, 208 or 240 volt. I don't understand why he could not take 277 and transform that down to 208 or 240 using a buck transformer. What issue do you have with that? Where's the misapplication?
As a condition of listing and labeling, some ‘2-wire’ 200-230V electrical equipment is labeled "120/240V" or “for operation at not more than 150V-to-ground,” ostensibly to limit voltage from phase-to-ground on the equipment internals. This is not possible with a 277-240 buck transformer. Operation in the suggested manner may void NRTL listing.