I take it that our new friend is Italian?
Well, the good news first:
The difference in frequency is to small to cause a problem. You have to get into special system like 16 2/3Hz or 400 Hz before it seriously affects the breaker. I checked the specs for the Cutler Hammer IEC breakers. They have constant performance from 16 2/3 Hz to 60Hz.
The breaker doesn't know of the respective potential to earth of the wires, so it won't have any problems with a normal fault.
As you knwo, a ground fault on a system where ground an neutral are bonded somewhere (so called TN-C-S or TN-S systems) the fault is sensed by the breaker as a very high over-current. Detecting the fault should work just as fine in Europe as in the US.
The problem comes when it acts on the fault. If the breaker is only rated for 120V, the voltage between the "contacts" in the breaker is twice the usual. This mean that the spark is longer. The effect of this can be seen if you look in the documentation from a manufacturer. Back to Cutler Hammer: Used in a 127/220V system the breaker I picked (a model called WMF) breaks 15 kA, whereas it in a 220V system breaks 10 kA.
I didn't find a 120 to 240 comparison, but from memory I think doubling the voltage reduces the breaking capacity by half.
If you look in the technical documentation from the manufacturer, you will often find that the breaker is tested with a number of systems, including 230/400V 50Hz. I would expect an American 277/480V breaker to work just fine electrically.
If the breaker isn't listed for 230/400V, it is unlikely that it is tested or designed for this system. I don't dare to predict the electrical nor the legal consequences of using it.
[This message has been edited by C-H (edited 05-09-2003).]
