Dave if you take a look at the trip curves for breakers it can be surprising.

A 20 amp breaker (or fuse) may carry 24-25 amps forever and still meet all UL requirements.

Thermal trips are just not that accurate and the ambient temp has an influence on the breaker.

Don't worry about the wire, it can take it, 12 AWG is rated 25 to 30 amps anyway and the tables do not run on the edge of safety.

Bob

Bob Badger
Construction & Maintenance Electrician
Massachusetts