OK lets go a little farther. What if you had a dual lug breaker and maybe even another tap to another transformer? Is that then the feeder?
Now if you just step back a little and see what we are accomplishing you see the stub of 3/0 and the Polaris is unnecessary. The "feeder" is just the lug on the breaker.
At the end of the day the important thing is that the conductor is adequately protected from overload and we have done that with the load side fuses. Short circuit protection is adequately provided from the line side O/C device and we have the conductor in a raceway to deal with the momentary heating until the line side breaker opens.
