I received the utility contribution and they gave me contribution numbers at the time of the calculation as well as maximum contribution. I ran the analysis on both and the maximum contribution has higher incident energies at 100% and 85% then the "time of calculation" numbers.

My question is which one do I go with? It makes sense to go with the maximum contribution, but I am just questioning the "time of calulation" numbers and if that is more of a realistic snapshot of what is out on site. Any feedback would be greatly appreciated.

I assume that the "time of the calculation" means using the existing system configuration and impedances. The maximum probably allows for replacing the transformer with another one in the future with lower impedance, and maybe allows for more generation on the system.

If this is correct, then by definition, the "time of the calculation" numbers are more realistic for present conditions. You have to take the worst case, however. Otherwise, you or the owner will have to monitor the available fault current and revise the study if it changes.