The arc resistant design influences cable/conduit area in the following ways:·

(1) The conduit area (top and bottom) is slightly reduced with the arc resistant design.

(2) If conduit or busway is incoming top and it travels over the top vent stack or top pressure relief flap, it must be above the 118” minimum ceiling height dimension where it travels over the vent stack or vent flap areas.

(3) If conduit or busway is incoming bottom, an opening to a cable or busway vault below the switchgear isn't allowed. You can have a cable or busway vault but it can't be totally open below the switchgear. A rigid (preferably metal) plate would need to be installed covering the vault opening and the conduit/busway would need to run through the plate into the cable vault.