×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Hooking up a Water Heater
2

Hooking up a Water Heater

Hooking up a Water Heater

(OP)
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

RE: Hooking up a Water Heater

NO.  You will overheat and destroy the heating elements.

RE: Hooking up a Water Heater

2

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.
  

RE: Hooking up a Water Heater

(OP)
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

RE: Hooking up a Water Heater


“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
  

RE: Hooking up a Water Heater

(OP)
Thanks for the info, I appreciate all your help!

RE: Hooking up a Water Heater

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.

RE: Hooking up a Water Heater


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.
  

RE: Hooking up a Water Heater

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

RE: Hooking up a Water Heater

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?

RE: Hooking up a Water Heater


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.
 

RE: Hooking up a Water Heater

Ahhhh.  Thanks.

Red star for you.

RE: Hooking up a Water Heater

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

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources