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


Nominal Voltage

Nominal Voltage

Nominal Voltage

A question for our American friends. I'm in the UK and working on a US project.

When working with 4.16kV to 480V transformers.  Is that the open circuit voltage or the full load voltage?

What should the motor nameplate voltage be when connected to the "480V" system?


RE: Nominal Voltage

ANSI Std C84.1 is normally used by the North American utilities and will help with your questions.  This covers voltage ratings (60 Hz) for electric power systems and equipment.

The nominal voltage of a system is near the voltage level at which the system normally operates.  Most of these operate within a window of +/- 5%.

On a 480 V system, the motor nameplate applied most often is 460 V.  The NEMA MG 1 standard for motors specifies a +/- 10 % tolerance for motor operating voltage around the nameplate value.

If you do the math, you'll find that the operating of a 460 V motor on a 480 V system works quite well.

The nominal voltage is not really the open circuit voltage or the full load voltage.  I'd expect the open circuit voltage to be between the nominal and the 1.05 X 480 V value and the full load voltage to be between the nominal and 0.95 X 480 V value.

RE: Nominal Voltage

It is the full load voltage.

Motor are usually rated 460 Volts.   

RE: Nominal Voltage


Nominal voltage is the designated voltage for an electrical  system. Based on the nominal voltage , all the other parameters are defined. (It is like your name. Everything is based on your name) But if you measure the voltage on a system where the nominal voltage is 480 V or 4.16 kV you will not find that value. It may vary +/- (x) percent. Therefore, in ANSI world, that variation is defined in ANSI C84.1. Similarly, Based on above, in ANSI world, the motor "Rated Voltage (Name plate voltage)" is listed for various nominal voltages.

So you have to select the motor name plate voltage accordingly.

Therefore, 460V should be the name plate voltage for motors operating on a nominal system voltage 480V.

In ANSI world. ANSI C57.12.10 lists the standard nominal voltages of the high voltage side of transformers. Accordingly, a 4.16 kV-480 V transformer shall be connected to a network where primary nominal system voltage is 4.16 kV. Then 480V will be the voltage at transformer secondary terminals at full load.

But in IEC world this ratio is different. IEC 60076 doesnot list any secondary voltages.

Hope the above answers your question.


RE: Nominal Voltage

Thanks for the quick and helpful answers.

RE: Nominal Voltage

The secondary nominal voltage on an ANSI design transformer is the open circuit voltage when nominal primary voltage is applied to the primary.  No voltage drop through the transformer is included.  The regulation value indicates what the loaded secondary voltage would be.

RE: Nominal Voltage


Sorry. Made a mistake.

Then 480V will be the voltage at transformer secondary terminals at full load.

Wrong. It should read as "at NO LOAD".


RE: Nominal Voltage

Supply voltages up to 480V in the US and up to 600V in Canada are multiples of 120V.
120V, 240V, 480V, 600V.
Standard motor ratings are multiples of 115V. 115V, 230V, 460V, 600V.
A relatively new motor voltage is 200V for use on 208V systems.
Common star voltages, 120/208V, 277/480V, 347/600V.
In Canada 347V lighting is used in office buildings.

"Why not the best?"
Jimmy Carter

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!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close