Most hot tubs are powered using 240 volts with alternating current, according to Spa Depot. Standard 240 volt wires in the United States are red for hot, black for hot, white for neutral and green for ground. Some hot tubs use 120 volts which do not use the red wire.
Hot tub wire sizes depend on the current consumption of the hot tub, but typically range from 10 gauge to 6 gauge. Ensure the wire sizes and circuit breaker are properly sized for the hot tub. The specific wiring details for the selected hot tub are found in the installation manual.