I would stay away from used FPE Stab-Lock 2p breakers. Those were the ones that could jam when they tripped, resulting in them never tripping again. I would treat any such FPE 2p breakers like a fuse; dont reset it, replace it with a new one.
eta: there is a video online somewhere of a news team reporting on FPE breakers. They visited a lab where it tested a 60A 2p FPE Stab-Lock breaker. It held a 120A load for 4 minutes and was smoking and still did not trip. Ill see if I can find it.
ETA: here you go:
http://www.nbcbayarea.com/news/loca...gation-Finds-Decades-of-Danger-171406921.html
"NBC Bay Area had FPE Stab-Lok circuit breakers tested at the Berkeley Research Company. Bernard Cuzzillo has a Ph. D. in electrical engineering, is a fire specialist and owns BRC.
Cuzzillo tested a dual pole 60 amp breaker, similar to the ones tested by Underwriter Laboratories and to the ones found in homes in the Bay Area.
To test the circuit breaker, he forced double the electrical current it’s capable of handling and timed it. Cuzzillo says if working properly the Federal Pacific circuit breaker should have tripped in less than two minutes. At one minute ten seconds, Kovaleski noted smoke coming out of the breaker.
Kovaleski and Cuzzillo watched the
circuit breaker smoke for more than four minutes. “It’s smoking and it hasn’t tripped. Why not?” asked Kovaleski. “Because the mechanical mechanism that is supposed to be tripping the mechanism is stuck,” replied Cuzzillo. The expert says, therein lies the problem with FPE Stab-Loks."
If you look at the ammeter in the video, there is over 140A going thru that breaker.