That is why I was wondering if manufacturers are still making the 3-pole plug-in style breakers, since I think I still have some older ones left in stock.
This quote is from page 89 of the "07 White Book [DIVQ]. It is the sentence just above the one in my other post.
"3-pole circuit breakers are suitable for use only on 3-phase systems unless marked to indicate otherwise".
It seems that if the manufacturer says its okay, then no problem. Not that I can actually recall ever running into the device situation described in the posts, but would be good to know just in case. They are probably worried about someone using 3-hots on one neutral conductor on single phase. Seems that the NEC assumes that we are all idiots that must be protected from ourselves.
