After a circuit breaker has popped a bunch of times, it is weaker. Therefore a 20 Amp breaker might go off at 10 A if it is old and has tripped numerous times. That can be attributed to a weaking of the spring tension and the fact that the contacts have become pitted and have more resistance. This makes the contacts heat up more than normal under load and heat is what trips the breaker. High ambient temperatures can also make a breaker trip below its rating.
Breakers wear out, replace the ones that have tripped a lot. Chris closer with 99674's restoration. ‘--o-O-o--’
