Hooking up a Water Heater 2

[nod]

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.

Thanks Nod

 

[Lewish]

NO. You will overheat and destroy the heating elements.

 

[busbar]

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.

 

[nod]

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.

Thanks Don

 

[busbar]

“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

http://www.federalpacific.com/literature/drytrans/FPTS-RTB-0701.pdf

 

[nod]

Thanks for the info, I appreciate all your help!

 

[peebee]

To underscore what busbar said, a direct connection of 277v (vs. 240) would:

1. Increase current by 277/240 = 15%
2. Increase electric & heat power by (15%)**2 = 33%

33% is a big increase.

Can't say for sure if what you're proposing is safe, you'd need to check with the manufacturer or UL.

But we can say for sure that if it works, it won't last long.

As was mentioned, buck/boost transformers (small 1-phase autotransformers) are commonly available from all the usual transformer suppliers.

 

[busbar]

peebee, the heater may not be intended to operate on other than a 120/240 or 120Y/208 system, making the buck-boost transformer a misapplication.

 

[BJC]

You could check for a replacement heating element rated for 277 volts and the same wattage.

 

[peebee]

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?

 

[busbar]

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.

 

[peebee]

Ahhhh. Thanks.

Red star for you.

 

[nod]

Thanks guys, I really appreciate all the help, everyone getting involved answers even more questions.