PURPOSE: To simplify the shape of an insulating spacer and, at the same time, to improve its reliability by providing a base for forming a recessed part and projecting sections formed at the conductor passing sections of the flat plate section of the spacer, with the leading ends of the projecting sections being made narrower toward the recessed section.

CONSTITUTION: Three conductors 1 are passed through the discoid flat plate section 11 of this insulating spacer 2 formed by molding an epoxy resin at pitches of central angles of 90° on concentric circumferences. A flange section 4 formed as an extension of the flat plate section 11 is constituted of an annular flat plate parallel with the section 11 and the sections 11 and 4 form a recessed section 13 and base 3 together with a conical surface 4. The thickness of the section 4 is made thinner than that of the section 11. The first projecting sections 14 having the shape of a truncated cone are provided on the recessed section side at the parts of the flat plate section 11 where the conductors 1 are passed through the section 11 and the second projecting sections 15 are symmetrically provided against the sections 14. Since the sections 11 and 12 form a truncated cone, the strength of this spacer is increased and, in addition, the mechanical strength of the spacer is further increased by the second projecting section 15.