How to correctly specify preferred ratings for MCC, SWG and SWB (short-circuit current, frame, etc)

[Dvhez]

Hi everyone,

When designing a system, I used to draw specs from Eaton's catalogue but then I was requested to justify those values with IEEE standards.
Example of the steps I take to specify these equipment:

1)At design stage I needed a 600 V Motor Control Center that can withstand 12 kA sym fault (from ETAP) and can carry 280 A.
2)Then I go to Eaton's catalogue and see a 600 Frame Size (Amperes) Molded-Case Circuit Breaker for this MCC that has a 35 kA Interrupting Capacity (kAIC)at 575 V... PERFECT.

However, when I tried to search for those values at IEEE Standards, I found the table 5.7.2 for Fused Circuit Breakers (low voltage) in ANSI C037.13 and the short-circuit current rating for this exact frame (600 A) was 22 KA up to a rated maximum voltage of 730V and there's no 35 kA as the catalogue. Also, this table don't have a 1200 frame while Eaton's Catalogue has it...

Any recommendation that could be useful to determine and justify equipment ratings (Switchboard, Motor Control Center and Switchgear) would be really usefull. Thanks!

(C037.13 - Standard for Low-Voltage AC Power Circuit Breakers Used in Enclosures)

 

[jraef]

Are you using a Power Circuit Breaker (PCB) in an MCC? Most of the time they will be Molded Case Circuit Breakers (MCCB). Different beasts, different standards.


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

 

[Dvhez]

And where can I find the preferred ratings for Molded Case Circuit Breakers?