maybe this is too hard to answer without lots of details, but i'll try anyway, might need an ebngineer even.
i'm looking at a job that replaces a 3-phase 800a main switchboard that has 3 200a panels downstream, one feeds a 200kva transformer that feeds 4 more downstream panels and one of these 4 is downstream of a transfer switch.
the engineers plans puts a 225a 3-phase main breaker ahead of everything. then theres a transfer switch to a 75kva generator one way, and the other way goes to all of the others (the 800a main switchboard with the 3 panels, one of which feeds the 200kva transformer which now feeds 5 downstream panels)
how can a 225a main breaker with four 4/0 thwn coppers feed all of the panels that used to be serviced by a 800a switchboard?
this is what i think. tell me if i'm thinking wrong. the new 225a main breaker is only feeding 3 panels so the load may calculate out to fit within that 225a feeder. the one that feeds the step-up transformer now takes the increased loads downstream so those loads dont need to be calculated with the main service feeder to the first set of 3 panels. you just recalculate the feeder downstream from the transformer for those panels.
ok you can wake up now, i'm done.