I'm currently working a job (I just moved into training for line voltage, still VERY new) where they have 7 or 9 MC cables paralleled to a 5000A 480V delta switchboard from a 35kV xfmr. Very nice work, cable tray and RMC 20' in the air (heavy industrial site). If I read the ampacity tables correctly, not only does wire get too heavy, there just isn't really any wire to handle 5000A.
