21.5A is in the range of a 5 HP 1Ø motor, the NEC requires that the table in art 430 be used to size the circuit & be 125% of the value which comes out at 35A, so if NM cable is used, 8 AWG is minimum since NM is sized by the 60° column, if THHN/THHW is is used then 10 AWG is permitted, since...