×
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

MCC Bus Current Question

MCC Bus Current Question

MCC Bus Current Question

(OP)
I have a 480V MCC with a 3000A bus rating.

Normal load on MCC is between 900A and 1000A.

I have a 350HP (Class G) motor with FLA of 389A.

I was wondering if it would be ok to run this motor from the MCC...if the bus can handle it with regard to starting current. Will the starting amperage (something like 2600A if I calculated correctly) be an issue for the bus?

Any thoughts would be appreciated.

Thanks!

RE: MCC Bus Current Question

It will be fine. The busbars have a much longer themral time constant than the cable to the motor and the motor windings, so if you don't damage those then that bus will be ok. It's good that you are questioning if you are not sure though. smile

Don't forget that the bus is braced and able to thermally withstand a massive fault current, typically a value like 50kA for 1s or 100kA for 1s, or in the Middle East it seems like 100kA for 3s is becoming common.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: MCC Bus Current Question

Spark-O-Matix,

Bus rating is for continuous current.  Transients such as starting currents are accommodated.

Double-check the coordination of your motor circuit protection with the MCC mains protection, you should be good to go.

Good on ya,

Goober Dave

RE: MCC Bus Current Question

(OP)
I thank you both for your quick and informed response.  I am pleased to find a forum with such knowledgable people who are willing to share their knowledge.  Again, thank you.

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