To reduce the breakdown potential magnitude between the output tip surface of an ignition distributor rotor output segment and each of the output terminals of the distributor cap, the rotor output segment is made of a low thermally conductive material 0.1 mm to 1.00 mm thick, and a layer of a silicone dielectric material such as a silicone plate, viz., a plate including at least a sheet of silicone varnish-containing glass cloth, is secured to at least a portion of at least one of the top and bottom surface areas of the rotor output segment.