See page 10 of the UL
Circuit Breaker Marking Guide that is on the UL website as well as in the back of the
UL WHite Book in Appendix A.
The excerpt reads:
60/75?C Wire ? All circuit breakers rated 125 A or less are marked for use with 60? C,
60/75?C or 75?C only wire. This marking indicates the proper wire size for termination in
accordance with Table 310.16 of the NEC . It is acceptable to use wire with a higher
insulation rating if the ampacity is based on the wire temperature rating marked on the
breaker. For breakers rated more than 125 A, the proper wire temperature rating is 75?C and
it is optional for the breaker to bear this marking.