An electric machine includes a stator stack of laminations, pierced with a cylindrical passage for housing a rotatable rotor therein. The stator includes a magnetic circuit of laminations stacked between first and second terminal faces crossed by the passage and by a series of slots housing conductors, which are folded over to form coils. An electrically insulating reinforcing wedge piece is interposed between an internal wall of a first tubular end and a corresponding portion of a block of resin surrounding a region of winding heads of the conductors, which follow a looped path in the block of resin. A wedging unit wedges the insulating reinforcing piece in position to prevent the insulating reinforcing piece from protruding axially internally on the internal wall with respect to the region so as to leave a determined annular sector of the internal wall in direct adhering contact with the block of resin.