Has anyone heard of or experienced a "dead zone" in a circuit breaker? For example, a 20A breaker failing to open at 60A. I know circuit breakers can fail like any other device, but this is supposed to happen with an otherwise functional device. Almost like a resonance where the breaker doesn't see the over current condition because of the changing AC power.
The 60A would be applied indefinitely if the breaker doesn't open. I know the time delay curves of the breakers are shown on the data sheet. 60A through a 20A breaker should trip in less than 1 second, but the supposition is that breaker wouldn't trip at all.
Circuit breakers use Time vs Current to operate, if a high amp spike hits the breaker it can enter a "deadzone" where the appliance will cook before the breaker trips out. However this can only happen for a short time, the breaker would eventually trip out. I would not think that you could hold 60A on a 20A breaker indefinatly.
Good preventive maintenance for circuit breakers should include periodic exercise of the operating mechanism. A better practice is to exercise the trip latch mechanism since it can seize due to lack of use.
I always exercise my breakers at least one a year.