Calculating Connected Load for a Panel with Redundant UPS Feeder.

There may be local code variations that specify the terminology to be used.

Where I am, "connected load" means everything that could be connected to the electrical supply, even if it all isn't actually running. In some cases, even when you can't know everything for sure (such as a bunch of residences in an apartment complex), you may be allowed to use a "diversity factor" to calculate an assumed load thast will be less than every possible item. Moreover, you may be able to identify specific loads that would not run simultaneously; e.g., duty vs. standby pumps where only one would run. In that case, you may be able to establish a "maximum concurrent load" that might be considerably less than the whole lot. And still furthermore, if you must switch to a smaller supply, you can have load-shedding schemes that cut out certain loads so as not to exceed the lesser supply rating.

In your example, combined with my local terms, the total connected load would still be 50 kw, even though the actual running load would be only 25 kw. In any event, you will need to see how your local code defines its terms, and what it will allow.

Loading at the output of UPS is 25 Kw but do consider that at times the batteries of the UPS need a charge so you have to have some additional capacity that would be ascertainable from the equipment data sheets or practically assessing the consumption under performance testing when only the batteries are being charged.

Please do realize that the UPS has a very limited time backup and the standard practice is to provide two distinctly separate (25 Kw) feeders from two distinctly separate sources so that if one feeder is faulty or under routine maintenance the scheme still is reliable and state of emergency is not declared.

It depends somewhat on how the system is configured, but generally each feeder cable is rated to the load expected to be connected (in your case 25kW) plus the inefficiencies of the UPS, anticipated charging of batteries while supplying load. But in general the load on the output of the UPS cannot exceed the nameplate rating anyways, therefore the input feeders should not see more than that.