General-purpose circuit breakers are most often thermal/magnetic types that are suitable for continuous loading (3 hours or more) to only 80% of their rating. This is because ambient temperature affects the trip-point of a thermal/magnetic breaker--the hotter they get, the lower the trip current.
Fully magnetic circuit breakers have a trip-point that is affected very little by ambient temperature. Many entertainment lighting industry dimming systems use fully magnetic breakers and are Listed by an NRTL for 100% loading, 100% duty cycle.
For more on 100% loading of dimmers and their circuit breakers and how it is possible, see attached article.
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