That part I get; given a 40A continuous load you select conductors and overcurrent protection rated at 50A (in general, ignoring the special cases, etc. etc.) Thanks for confirming that standard circuit breakers are tested to this 80% load requirement.
My question is, given the above, what happens when the breaker is utilized at 100% of its continuous load. This is utilization which is in violation of the listing, and I understand this. What I don't understand is what sort of failure should be expected.
One possibility is that the 'rating' of the breaker is really just a point on its time/temperature curve which will cause the breaker to trip after some number of hours (given standard ambient conditions and air flow, etc.) In this case, if I attempt to _use_ a 20A breaker at 20A, I would expect it to trip after some amount of time, with no damage to the wire or to the breaker itself. In other words, the 'failure' is simply the circuit safely opening.
I guess another way to ask the question: Given the testing on standard molded case circuit breakers, such as those used in residential applications. If a 100% load is applied for an extended period of time, will the molded case circuit breaker protect _itself_ as well as the conductors which it is supposed to be protecting?
-Jon
