I previously ran a 50a circuit for a spa and it had no place for a neutral at the spa end, so I did'nt run one. I put in a 50a GFI breaker (not using a neutral) and tested the GFI hot to ground on both legs at the spa and it worked, the GFI did trip fine. Was I wrong for not running a neutral? Even though it trips ok? I'm not sure why this works since GFI's use the neutral and ground.

I'm not sure of the design of two-pole GFCI breakers, but I believe they are made to measure the difference between the two hots and then any imbalance that may occur with a hot to neutral load is measured as well. As long as the numbers add up, no trip.

Please correct me if I am wrong.