It’s a known peculiarity of the Ultrex that if you run it on 10 for some time, it will trip the breaker, even with a 60 amp device which it calls for. On 10, current draw is mid 50 amps. It has been mentioned many times over the years on the electrical forum over on Bass Boat Central. Apparently, somewhere in the manual MK mentions not to do so. You already have discovered that running it on 9 avoids that issue.
