I read four similar questions, but I am sure I didn't make any of the mistakes mentioned in their answers.

I wired a new service for a used hot tub I recently purchased. I put a paired 50 amp breaker in my main panel and connected them to a 50 amp Cutler Hammer Hot Tub Panel with about two feet of #6 wire. I used two load wires, a neutral and a ground as instructed.

The tub uses only 3 wires, so I hooked the two loads to the breaker and the ground to the ground bar - again like I think I am reading in the instructions. The wires to the tub are about 25 feet long. I did not put anything into the neutral lug on the breaker and only the pigtail and the neutral from the main panel are attached to the neutral bar. Incidentally, I only have one ground bar in my 1970 GE mail panel, so that is where I hooked up both the neutral and ground for the Hot tub panel.

Like the four other questioners, my tub works fine for a while (2 to 6 hours) and then it flips the GFI breaker. It dosen't seem to matter what the tub is doing - full time heating from a cold fill or just maintaining temp.

Can anyone help?

The tub only needed two hots and a equipment ground? No neutral? That is odd, since most pumps are 120 volt, which needs a neutral, and the heater is 240 volts, and does not use the neutral.

Either the pump or the heater must have a ground fault that the breaker is detecting. Try disconnecting one or the other to see which one is tripping the CB to narrow down the search. Consult with the tub's dealer for replacement parts.