A plastic case surrounds a primary winding of a multicharge ignition system, and has a rib in which the high voltage end is routed back to the low voltage end, so that the low and high voltage ends can be closely juxtaposed with each other while advantageously permitting the primary winding to have one and only one winding layer to reduce resistance and size. The rib of the case extends into the slot of the magnetic shields of the winding.