# MCCB KA Rating



## Zog (Apr 15, 2009)

alfred751112 said:


> Hi guys!
> 
> We have a 3-phase transformer 2600kVA, with % impedance at 6.15, and secondary voltage of 415V. It feeds to a few DC drives.
> 
> ...


Close, but you are missing one part of the equation. Also your method assumes infinite fault current on the utility side so you will need to know that value from the utility. In short, hire an engineer.


----------



## alfred751112 (Jun 21, 2013)

Thanks Zog for the reply!

Anyway, what is missing in the equation?

And I need clarification that installing a MCCB with 100kA rating is safe, right?


----------



## Big John (May 23, 2010)

Looks like you forgot to divide by 1.732 because it's a three phase circuit, correct? I get 59,009A. But like Zog said that also assumes an infinite primary bus and zero service conductor impedance, so an engineered number will actually be different.


----------



## alfred751112 (Jun 21, 2013)

I believe replacing the mccb with the 100kA will be enough (or more than enough) for our application.

Thanks Zog & Big John! It's a big help to me.


----------

