The instructor was actually an employee of a local POCO and the topic of the class was farm wiring.
Those who think they know everything are really obnoxious to those of us who do.
Back when I was a helper and in night school, a POCO employee substituted for class one week. A dimmer was mentioned, and he said it was just a variable resistor.
Of course, I corrected him, and he blasted me. The next night, I showed him a dimmer I opened, pointed out the triac, and told him how big a 600w resistor would be.
He was totally competant on Art. 547. Although I knew he was incorrect on the need for a main breaker, I've been searching for the code reference to prove it but can't seem to find it. I'm sure one of you will chime in............
Ding, dong! Show him the locations where MB's are required, and that within the same building isn't one of them. That it isn't in the NEC is the proof.