As technology of inverter-fed motors progresses in recent years, means of protection against inverter surge for the motor windings have been developed. It is strongly required for windings used in electric vehicles and hybrid electric vehicles to have excellent insulations properties together with high heat resistance, especially high partial discharge inception voltage (PDIV). This paper deals with PDIV of ribbon-type enameled wire which is fabricated to increase space factor in the motor windings compared with the conventional enamel wire.