An ac generator for a vehicle is constituted so that the thickness in insulation layers of conductors in the slot-in portions located in the slot is smaller than the other to permit a metal portion of conductors to be much larger and to increase a density of conductors in the slots, causing heating from electrical conductors to efficiently conduct to a laminated core and a housing. On the contrary, the thickness in insulating layers of the cross-over portions is larger than the other to assure insulation capability among the coils and to prevent conductors of the cross-over portion axially exposed from the core to air from water immersion to improve an electrolytic corrosion resistibility without disposing unnecessary space among coils.
