When buying a new above ground Spa or Hot Tub, the showroom where it was purchases rarely shows what is involved with the installation. The electrical part is very strict and can get quite complicated, depending on which tub you purchase. Some are quite cheap and use only 120 Volts. They claim you can plug them directly into an existing wall outlet, but that is rarely the case because that wall outlet is shared with other things going on in the home and it will trip the breaker sooner or later. They also perform very poorly and take forever to heat up and stay hot.
The far better tubs are 240 volt units and they come in either 50 amp, 60 amp or 70 amp sizes. For most practical purposes, the 50 amp tub will work very well and is what makes up 85% of installs nationwide. This requires a dedicated, 4 wire circuit ran in copper wire (no aluminum) from the main panel of the home to the tub with GFCI protection. A disconnect must be installed near the tub so the power can be turned off in emergencies or if the tub is being serviced.