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 nuetral and ground.
The Golden Rule - "The man with the gold makes the rule"
If the spa did not require a neutral then there are no line to neutral loads. The GFCI breaker is seeing equal balance between the phases and thinks life is rosy. When you connect a phase to ground current flows outside the ground fault circuitry, it sees an imbalance, and trips. No you do not need the neutral. Where would you terminate it?