Contact US

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!

*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

CT Thermal Rating Factor and CT Class

CT Thermal Rating Factor and CT Class

CT Thermal Rating Factor and CT Class

If I can't find the CT Thermal Rating Factor TRF (or Rating Factor RF) on the nameplate, is there a way to find that knowing the CT class? In other words, how can I come up with a TRF if I do have the CT nameplate data and saturation curves.
Station that I am doing settings for has this 1960s breaker which doesn't have this data listed on whatever documentation I can find. And assuming a conservative TRF of 1.0 is not helping me since the max continuous current expected on the CT will be higher than it can take. Now if TRF is 1.5 or 2.0, then I am good.
Attaching the CT curves that has data, incase there is a way I can assume the TRF from it.

RE: CT Thermal Rating Factor and CT Class

You won't be able to get any information on the rating factor from the class, or excitation curves.

These seem to be bushing CTs on breaker, so the rating factor of the CT is based on the secondary winding and specifically the size conductor used on the secondary winding.

The curve does give you the secondary resistance, but one would need to know the size of the core to be able to guess on the wire size used on the secondary.

From an engineering perspective, if you don't know the RF of a CT, you should assume it is 1.0.

I'm surprised the ratings of the CT, including RF, aren't on the breaker nameplate.

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


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. 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