I need to understand how a GFI works when there is no Nuetral coming from spa to GFI/Shutoff. I have a Cutler-Hammer 50A GFI/Cutoff and it gives explicit instructions that 3-wire spa connections (240v 2 hot/1 GND) obviously will not make use of the Nuetral lug on the GFI. The pigtail is connected to the neutral bus as well the neutral from the service panel also connects to this bus. The breaker neutral lug is left open. Explain how the GFI breaker detects faults in this case.

As soon as there's a 5 millamp difference between the two hots, it trips. The AMP draw between each hot log should be identical- when it isn't the GFCI will detect it, and trip.

Thanks. That was my guess, but have read if there was a diff between a hot and neutral it would trip so wasnt really sure. How trustworthy is the test button to reacting correctly to an actual fault? The test button just tests the mechanics if i am not mistaken. Is there a way to simulate a fault condition. -- safely --