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

Current Flowing in a star delta motor cables

Current Flowing in a star delta motor cables

Current Flowing in a star delta motor cables

Can someone explain the mathematics behind the current that flows in one of the legs of a motor in star delta configuration.  There are six connections - one from each end of the six coil terminals.

I believe that if the motor full load current is 100%, then the current magnitude in each leg is 58% (=1/sq root of 3).

Much Thanks

RE: Current Flowing in a star delta motor cables

If you connect star then the phase voltage is 0.577 line voltage.  If you connect delta then phase voltage is line voltage.

RE: Current Flowing in a star delta motor cables

Adding to previous post:
There are three circuits in the motor.  Phase A is T1 and T4.  Phase B is T2 and T5.  Phase C is T3 and T6.  The motor you have may have different markings such as U1-U2, V1-V2, W1-W2.  Same thing.  When the motor is connected star, or wye, the voltage that is applied to the winding is 1/1.732 times phase voltage.  When the connection is changed to delta then phase voltage is line voltage.
If you have a nameplate rated 460 volt motor rated star start and delta run then the motor will be connected for 796 volts on start but will only get 460 volts applied; so it starts a little slower.  When the contactors connect it to delta then the motor attains full power. Acceleration time is dependent on the load.  Hope this helps.

RE: Current Flowing in a star delta motor cables

Yes, the current in each of six leads is 0.577 per-unit of nameplate.  Remember to apply (99)NEC310-15(b)(2)(a) ampacity-adjustment factors if the six leads are in a raceway or cable.

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


White Paper - Design for Additive Manufacturing
With a growing number of parts manufactured directly by additive manufacturing techniques, it is important to lay down design principles suitable for such manufacturing processes and to ensure parts are designed for additive manufacturing. There are several factors that are to be considered at the design stage. Few such design issues in additive manufacturing are discussed in this paper. 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