That's what I thought but, I keep second guessing myself. I also found this response on Mike Holt's Forum which helped clarify my issue.
Question: Do 2 & 3 pole breakers protect each phase at it's rated ampacity? For example, on a single phase panel with a 200amp main breaker, can you load each phase to 200amps for a total of 400, or 600amps on a 3 phase panel? Or does the breaker trip when it senses a combined load of 200amps? Not sure why this is difficult for me to wrap my head around, maybe you can help.
Response: The part you need to wrap your head around (and this is not an easy thing to get at first), is that if you load each phase to 200 amps, the total is 200, not 400. On a 3 phase panel with 200 amps on each phase, the total is still 200, not 600.
Let�s stick with the single phase panel, and let�s load it to 200 amps on each phase. The current that leaves the panel on Phase A will return to the panel on Phase B. It is the same current. That is why you don�t add the 200 to the 200 to get 400.
Once you get this concept, the answer to your question becomes obvious.
Oh, and by the way, we don't use the word "ampacity" in connection with breakers. That term only applies to wires, and indicates how much current they can handle without overheating their insulation systems.
