What is a Spa Disconnect?
A spa disconnect, disconnects the spa from the power supply. Not only is a 220v spa is required by the National Electrical code book (680.41) but it provides safety from electrical shock when in or around the spa. The disconnect has a GFCI circuit breaker that will sense unusual fluctuations or issues with the power supply and will trip which will shut the power off to your spa.
Typically a 120v spa does not require a disconnect but requires a GFI and is most of the time still recommended to be on a dedicated circuit.