Anyways, Great video- and I must say accurate too I can see this being required watching for apprentices- I wish this was around when I first started to learn about these.
My understanding is the 1p breakers were usually ok, it was the common trip mechanism for the 2p that jammed and would never trip again. I'd like to see that jam occur.
and thanks 480 for uploading the video. I think the geometry of the trip mechanism, how it moves, is more interesting than the the reason(s) of why it trips.