I have a 250 MCB as the primary protection which supplies a 225KVA, 5.27% Z, the transformer is 480 to 240. There is a secondary fused switch with 250V FRS 200A. I am questioning the incident energy on the secondary side between the bushing and the actual disconnect switch. I am assuming the 250 MCB will determine the incident energy. Any thoughts on calculating this value? Thnaks for reading my post.

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#3@18" 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.

Thanks for the reply

My details which were not many is at a plant I am going to in mid Ocotber. I plan to get more info I will post as I get it.