I purchased a used spa from a friend. I am ready to run my electrical connections but I noticed the pig-tail that is on the spa has three 6 or 8 Gage wires for hot and common but the wire that I assume is the ground is only 12 Gage or so.

Is this because the ground wire serves only to trip the GFCI breaker (I plan to use a pre-assembled unit purchased a Lowe's or Home Depot)?

My service panel has two 50 amp breakers installed (previous spa) that I plan to use and I plan to run my wire (I will match the size on the pig-tail) through my attic and then down the side of the house, using conduit only on the side of the house.

Any thoughts on the ground wire or problems with my other plans?

Appliances are not built to the building electric code, and manufactures may use smaller wire for certain reasons. This cord should be part of the unit and was UL listed as such.

The equipment ground acts as a safety return for any fault currents, but is not necessary to trip a GFI, because ground fault currents can flow anywhere besides the ground wire.

For a circuit installed in a building, the equipment ground for a 40, 50 or 60 amp circuit is #10 copper green insulated wire, or bare if part of a cable like Romex.

For the other circuit wires, need to check the nameplate of the unit for amperage or wattage/volts=amps, to be sure the manufacturer did not undersize those wires also.

A disconnect needs to be near the tub, no closer than 5 feet no farther than 50 feet and within site of the tub. A conveinence outlet needs to be between 5-10 feet away from the tub. Ground all metal within 5 feet of the tub to the ground lug on the motor with #8 wire.