A really rough estimate on the secondary and the load side of the fused switch could be as high as 85 inch AFB, 12 cal/sm2 @ 18inch CAT#
[email protected]" assuming a SC of 8.6ka.
With my generic data the secondary SC could last a long time before tripping the breaker on a HI trip setting.
However, if you have a low trip level the game changes. I get a 6" AFB .03 cal/cm2 @18" CAT0 @18".
The breaker type and trip data is very important in determining your actual energy levels. The other problem is your transformer inrush which I suspect will probably be the problem to overcome.
I am guessing your trip level is going to be high because of that.