To determine the size of wiring for a hot tub, check the owner manual to find the American wire gauge number and use that number to determine the wire thickness needed. For wire length, measure the distance between the ground fault circuit interrupter breaker and the hot tub. Use the shortest wire possible to prevent moisture damage.
The AWG number determines the thickness of the wire because of its ability to facilitate the current and volume of the amps and volts. If the AWG number is high, the wire is thin. It is possible to use a wire with a lower AWG number in a hot tub because it means the wire is thicker and better able to facilitate current and volume. However, a wire with a higher AWG number is too thin to handle the current. If the distance of the interrupter breaker and the hot tub is too great, use a thicker wire with a low AWG number.
Choose a wire made with copper when possible. Avoid aluminum wires, even if they are coated with copper. Use a solid wire over a stranded wire for less resistance. For a four-wire system, use multicolored wires, such as a green ground wire, black and red hot wires, and a white wire for the neutral wire.