×
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

Motor grounding provisions

Motor grounding provisions

Motor grounding provisions

(OP)
We received new AC motor (140 HP). The cast iron terminal box is bolted with 4 bolts (through rubber gasket) to the flange. One of these bolts is marked and designated as a motor ground terminal for connection of equipment grounding conductor. The flange itself is bolted (through another gasket) to the motor frame. It seems the the only path for ground current is through the threaded connection between the flange and the frame. Is this considered as sufficient grounding provision?  Or there is a standard which would define better connectivity to the frame (directly)? BTW, this motor has UL label although its grounding method looks questionable. Any comments, gentlemen?

RE: Motor grounding provisions

The grounding system that you describe is not used by serious manufacturers any more. The reason is that, although it may (or may not, I would say) be sufficient for safety - it is not a good HF ground. And a good HF ground is what you need if you are running the motor from a frequency inverter. A good VFD motor cable is next to meaningless if you cannot terminate the shield in a gland that contacts a terminal box wall that is solidly (around the perimeter) connected to the stator frame.

Gunnar Englund
www.gke.org

RE: Motor grounding provisions

thinker,
 
 As i recall, we provide grounding requirement to our installation to "wound rotor induction machines" less on squirell cage induction machines.
 
 It's better to provide grounding to your machine.

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!


Resources