While not directly related, my compressor is rated for 15 amps at 120v and 7.5 at 220v (switchable), I can run the compressor continously on a 15 amp circuit without tripping the breaker. So maybe breakers are not created equally? Another unrelated example is one of my welders is rated at 20amps. I have plugged it in a 15 amp circuit and tacked 1/4" plate, so that tells me that a 15 amp breaker will exceed the current load for very short times.