The wires that are used in AC power cords typically range from 10 to 18 AWG for residential applications and are selected based on the desired ampere rating and voltage drop. This chart shown here from the NEC (table 400.5(A)) shows allowable ampacity for both two and three conductor power cords based on an ambient temperature of 86° F. As one can see, the larger the wire diameter, the higher the amperes it can handle. Concurrently, because heat is generated when electricity flows through a conductor, both surrounding temperature and the insulating material will regulate the maximum allowable amps.