Are we to assume that the voltage is 480v?
You don't size the feeder to the OCPD. You compute that load first, then size the feeder to carry the load. The feeder must carry the load. As such the feeder ampacity rating will be greater than the load.
Then and only then you will select the OCPD which will be sized to protect the feeder.
240.4 Protection of Conductors. Conductors, other than
flexible cords, flexible cables, and fixture wires, shall be
protected against overcurrent in accordance with their am-
pacities specified in 310.15, unless otherwise permitted or
required in 240.4(A) through (G).
(B) Devices Rated 800 Amperes or Less. The next higher
standard overcurrent device rating (above the ampacity of
the conductors being protected) shall be permitted to
used, provided all of the following conditions are met:
(3) The next higher standard rating selected does not ex-
ceed 800 amperes.
At this point you should have picked up on the fact that the OCPD is based on the feeder's rated ampacity and not the load itelf, that the OCPD's rating will most likely be greater than the feeder's rated ampacity.
(C) Devices Rated Over 800 Amperes. Where the over
current device is rated over 800 amperes, the ampacity
the conductors it protects shall be equal to or greater th
the rating of the overcurrent device defined in 240.6.