FOLLOW UP:
After the final conclusion, I picked up a pair of brand new circuit breakers for both ZW’s I’m using… at this time I’m happy to report that they are now operating at the powerhouses I always heard they were reputed to be…
These original bi metallic disc breakers do not look that substantial, so it’s not really a surprise they failed. One of the breakers showed evidence of heat cracking on the plastic/phenolic mounting plate.
Thanks for all the conversation and input!