You shouldn't be connecting a UPS to a circuit or feeder that is of a higher amp rating then the UPS is rated for, 240.21 is about taps from a larger feeder to a smaller feeder with the requirement of OCPD to be provided before any loads are applied to the feeder within a given distance from the tap, the UPS should be after this OCPD, in most cases a fusible disconnect would be installed ahead of the UPS that protects the UPS and or the by-pass contactor or switch's, I would believe that the UPS also has internal fuses on its input as well as protection on its output, smaller units may only have electronic overload protection for the output, buy like was asked is this unit designed to be hard wired or is it the type that has receptacles on the output?, is it single conversion or dual conversion? (does the load always run off the inverter or is it switch in when power fails)???
The way you are stating your question is not one that would be commonly asked for a UPS installation? if you can provide more data on the UPS and how you are feeding it and what it is feeding maybe we can give a more clearer answer?