@mikey Since he replaced 12-2 with 10-2, he had to replace the 20 amp breaker with a 30 amp breaker. Seems like overkill to me, but I obviously don't have the whole picture...
@mikey
A 50 amp breaker feeding a 10ga or 12 ga circuit is definitely not right at all; most people would go so far as to say dangerous.
Almost always, it's a 30 amp breaker for 10 ga, and a 20 amp breaker for 12 ga.
50 amp is generally seen feeding an electric stove/oven combo.