Why is the fuse only rated for 350A on the Maxim+?
The controller current rating is for the phase current and the input current will always be lower than the phase current. You can read about that in our article here:
However, if you are driving a low inductance motor close to full duty cycle it is possible that the input current will exceed the rating of the fuse and blow it, especially if you are using liquid cooling. In that case you have to use an external fuse and bypass the fuse on the controller with a bus bar. Unfortunately we have not found fuses in this size rated for more than 350A.