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The length of wire can be a issue over 75 feet. I would run my wire in conduit and not use romex. It is cheaper than underground approved wire and honestly, You could get buy with 8 gauge wire with no issues unless it is a long run in conduit.Wire amperage is always underrated. I have used 12 gauge romex(rated for 20 amps) many times for a 25 amp continuance service.Your local code will probably dictate your size wire.Yes I am a 26+ year Electrician. I do not know Hot Tubs in and out but I feel I know Electrical well since I am also licensed by my state for 23 years.