Sorry Gonk but I just can't agree with that statement. If anything the breaker will trip at a slightly higher level. Since breakers are designed and rated at a temp of 40C (104F) and usually are not in an environment of such high temps, the tripping amperage would be slightly higher. According to a typical manufacturers Trip Chart a breaker will carry the full current rating indefinitely and will carry additional current for proportionally less time. The chart shows how a typical 15 amp breaker will carry 2 times the rated current (30 amps or 3600 watts) for 10 seconds and even carry 5 times the rated current (75 amps or 9000 watts) for 1 second.