On my fairly new autotransformer 100A, I have experienced the breaker opening a couple of times this week under high load.
The input circuit breaker is being fed by a Quattro 15kVA connected to a Venus monitor. That monitor shows a continuous load of roughly 13kW prior to the trip.
I have additional motorized appliances with nominal loads of 1500W. My suspicion is that one of those motors is drawing additional locked rotor current, and the total is causing the autotransformer's input breaker to trip.
However, even using a conservative 6x for locked rotor current, I would expect only 38A more (1500W * 6A / 240V), and only for a few milliseconds.
I'm wondering if I should be looking at replacing this circuit breaker (perhaps it is not operating to specification), or if this is expected behavior, or even if we know what the trip curve is for this particular model.