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

Breakdown Torque

Breakdown Torque

Breakdown Torque

Is there a rule of thumb for the ratio of breakdown torque to full load running torque for NEMA B 3 phase motors?  I've been told it is aroung 3.0 +/-.  

RE: Breakdown Torque

Breakdown torques for motors are given in NEMA MG 1, Part 12.  The value varies with speed and motor size.  The breakdown torque is given in percent of full-load torque.  For NEMA B motors 250 - 500 hp, minimum breakdown torque is 175% of full-load torque.  For the vast majority of NEMA B motors 5 - 200 hp, the minimum breakdown torque is 200% of full-load torque.  For motors smaller than 5 hp, minimum breakdown torque ranges from 200 - 300%.

Of course, there is nothing to stop a manufacturer from designing a motor with more than the minimum breakdown torque.

RE: Breakdown Torque

Addition to my previous post - looking at performance data published by Toshiba for their 575 V EQP III+ premium efficiency TEFC motor, their breakdown torques handily beat the NEMA minimums, ranging from a smoking 400% for 1.5 and 2 hp, 3600 rpm motors to 225% for a 100 hp, 1200 rpm motor.

I don't know if you could derive a rule of thumb that the ratio is 300% (breakdown to full-load torque).  In general, the smaller motors have higher breakdown torque than the big ones.

RE: Breakdown Torque

Thanks for the info.  For the preliminary work, I'll use 200%-400%, as most motors I deal with are below 100 HP.  For final work, I'll get the data sheet from the manufacturer.

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! Already a Member? Login


eBook - Integrating the Engineering Ecosystem
Aras Innovator provides multiple options for integrating data between systems, depending on the scenario. Utilizing the right approach to meet specific business requirements is vital. These needs range from authoring tools, federating data from various and dissimilar databases, and triggering processes and workflows. Download Now
Research Report - Simulation-Driven Design for SOLIDWORKS Users
In this engineering.com research report, we discuss the rising role of simulation and the paradigm shift commonly called the democratization of simulation. In particular, we focus on how SOLIDWORKS users can take advantage of simulation-driven design through two analysis tools: SOLIDWORKS Simulation and 3DEXPERIENCE WORKS. Download Now
White Paper - Industry 4.0 and the Future of Engineering Education
With industries becoming more automated, more tech-driven and more complex, engineers need to keep their skills and knowledge up to date in order to stay on top of this wave—and to be prepared for the Industry 4.0 future. The University of Cincinnati offers two online Master of Engineering degree programs designed specifically for practicing engineers. Download Now
eBook - The Design Gridlock Manifesto
In this eBook, you’ll learn 6 ways old CAD technology slows your company down and hear how design teams have put those problems to rest. “The Design Gridlock Manifesto” shares first-hand modern CAD experiences from 15 companies around the world. Download Now

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