Page 2 of 2 FirstFirst 12
Results 11 to 16 of 16

Thread: Main Vs. MCB

  1. #11
    Join Date
    Jun 2006
    Location
    Ohio
    Posts
    20,617
    Perhaps switchgear/MCC with 1200A horizontal bus and 600A vertical, i.e. each section is 600A max while feedthrough bus is 1200A?
    I'll never get there. No matter where I go, I'm always here.

  2. #12
    Join Date
    Feb 2003
    Location
    Wisconsin
    Posts
    9,764
    Quote Originally Posted by Sahib View Post
    If 600A bus bars are not suitably brazed to withstand the higher fault current of 1200AF, then such MCB not to be used, IMO.
    Actually, the 600A bussing only needs to be capable of handling the maximum available short circuit current, whether the actual or design. The nameplate AIC rating of the 1200AF breaker possibly being larger than a 600AF is immaterial.
    Just because you can, doesn't mean you should.

  3. #13
    Join Date
    Jul 2006
    Location
    San Francisco, CA, USA
    Posts
    6,545
    Quote Originally Posted by jim dungar View Post
    Actually, the 600A bussing only needs to be capable of handling the maximum available short circuit current, whether the actual or design. The nameplate AIC rating of the 1200AF breaker possibly being larger than a 600AF is immaterial.
    In fact the MCCB AIC rating is often higher than the MCC bus bracing when you get into 1000A and above... i.e. the MCCB will have an 85kAIC rating, but the MCC might only require 65kA or even 42kA bracing.

    Back to the other issue, it seems to me that jumping from a 600AF breaker to a 1200AF breaker just to get bigger lugs is an expensive way to solve a minor problem. There are lots of less expensive options to get there and in most MCCs and some switchboard designs, you are looking at a half section of space for a 600AF breaker (maybe even less), compared to a full height section for a 1200AF main breaker. But, to each his own I suppose...

    The coordination issue though, that makes more sense to me. 600AF breaker will have I trips at 400-1000%, so 2400 to 6000A, vs 1200AF will have 4800 to 12,000A I trip settings.
    __________________________________________________ ____________________________
    Many people are shocked when they discover I am not a good electrician...

  4. #14
    Join Date
    Feb 2003
    Location
    Wisconsin
    Posts
    9,764
    Quote Originally Posted by Jraef View Post
    The coordination issue though, that makes more sense to me. 600AF breaker will have I trips at 400-1000%, so 2400 to 6000A, vs 1200AF will have 4800 to 12,000A I trip settings.
    I first ran into this situation when manufacturers created a 600AF breaker, prior to that the sensors were commonly 800 or 1200A. It was easy to have an INST setting of 7000-8000A especially for fire pumps and other larger inrush loads.
    Just because you can, doesn't mean you should.

  5. #15
    Join Date
    Feb 2003
    Location
    Wisconsin
    Posts
    9,764
    Quote Originally Posted by Jraef View Post
    600AF breaker will have I trips at 400-1000%, so 2400 to 6000A, vs 1200AF will have 4800 to 12,000A I trip settings.
    I first ran into this situation, when 600AF breaker became an industry standard, prior to that the 'sensors' were commonly 800 or 1200A so it was easy to get an INST setting of 7000-8000A for fire pumps and other large inrush loads.
    Just because you can, doesn't mean you should.

  6. #16
    Join Date
    Feb 2003
    Location
    New York, 40.7514,-73.9925
    Posts
    4,213
    Quote Originally Posted by petersonra View Post
    maybe it is a typo. or a copy and paste error.
    This is likely the case. This happened to one of my junior EEs recently
    Last edited by ron; 07-18-17 at 08:08 AM.
    Ron

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •