A large portion of 240V spas manufactured today require a 50 amp 4-wire electrical service. Some hot tubs have load requirements of 30A or 40A, and a few even 60A, which should correspond to the size of the new feed circuit breaker installed in the house service panel. The Disconnect GFCI panel's amp rating can be equal to, or larger than the feed breaker in the main panel.
Hot tubs with mixed voltage components (such as 120V ozonator and 240V heater) require 4-wire systems, which means they require an electrical circuit providing (2) hot wires, (1) neutral, and (1) ground wire.
Some 240V spas (and many older ones) use three wire systems with (2) hot wires and (1) ground wire, without a neutral wire. Both 3-wire and 4-wire spas must be GFCI protected. A 4-wire hot tub must not be connected to a 3-wire service. Proper grounding is also essential. In either case, the disconnect panel must be supplied with a 4-wire service in order for the GFCI to function as required.
Because of the reactive loads that spa motors present along with the resistance load of heaters, and the fact that parts of the spa including ozonators may run on 120V, common GFCI breakers sometimes react to a normal spa condition as if it were a ground fault. They can be very unreliable.
The most common wiring mistake occurs with 4-wire systems which leads to GFCI Tripping. It is important that these systems be wired correctly to ensure safety in an environment with water.