This paper describes experimental results of flashover characteristics of a medium voltage insulator to support an insulated cable using an impulse voltage generator. This experiment is targeted for direct lightning strokes to a distribution line. The lightning impulse voltage is applied to a cross arm to represent the direct lightning stroke. A flashover on the insulator occurs from the arm to the cable at first, and then the surface discharge develops along the cable. If the applied voltage is sufficiently high, the breakdown in the insulation of the cable occurs. This final stage corresponds to a line fault.