ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades Will an American 2-pole brkr function properly if wired to a European 220v 50h sys ?

Are you talking about GFI or simple breaker? A double pole breaker won't detect ground faults if the current doesn't exceed the breaker's rating. However, the breaker should detect overloads and shorts just like on a US 240V system. A GFI breaker should work as well. In Vienna many old installations have individual fuses for both line and neutral, so I can't see any technical reason why a DP breaker shouldn't work. I don't know whether the Italian codes prohibit the fusing of the neutral though.
But why don't you take a European 1+N breaker (fuses only the phase but always breaks the neutral on tripping, basically a breaker and a switch tied together) or a European double pole breaker or a simple Italian sigle pole breaker? Then you're definitely on the safe side.