×
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

VFD controlled wiring question.

VFD controlled wiring question.

VFD controlled wiring question.

(OP)
I've encountered a new situation regarding grounding of VFD controlled motors and need some opinions. I spec'd out the proper size VFD cable from the drive to the motor (125HP), but the customer is requiring a second cable (same size and type, with all conductors and shield connected at the motor and drive on the ground terminals. Can someone offer an explanation? Never seen this before. Thanks, Greg


https://res.cloudinary.com/engineering-com/image/upload/v1553804565/tips/VFD_grounding_sflxfn.pdf

RE: VFD controlled wiring question.

It's lunacy.



However the high frequency currents that leak out of a VFD driven motor can cause a bunch of problems in a complex environment. They need a very low impedance back to the VFD. That is actually pretty hard to come up with using large round cable. If not using flat braid which has much lower high-frequency impedance than multiple big-round-cables multiple round ones will do a better job than a single one. As many as I see there, is overkill, but will certainly assure the highfreq current will go back to the VFD directly instead of thru every other wires in the area.

Keith Cress
kcress - http://www.flaminsystems.com

RE: VFD controlled wiring question.

It’s not lunacy. That is depicting a particular type of VFD shielded cable in which there are 3 ground wires nested in with the power wires for full symmetry of the conductors and ground paths, a recommendation on larger HP applications. They are also using one with both a shield and a drain wire for the shield, and it is recommended that shielded power cables be grounded at both ends. That is actually a best practice all around.

Example:
https://www.servicewire.com/Products/Service-Drive...


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: VFD controlled wiring question.

Yup, it's a specific VFD cable with 3 ground conductors. The customer interpreted the drawing wrong.

A VFD cable with a braided shield using the proper gland connectors which fully connect to the shield is another good alternative.

RE: VFD controlled wiring question.

Thanks Hutzy. I've never seen that special cable. Makes sense in that case.

Keith Cress
kcress - http://www.flaminsystems.com

RE: VFD controlled wiring question.

(OP)
Thanks, everyone. Makes sense now, I've just never seen all the ground conductors and shields connected on a diagram before.

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


Resources


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