Self-recovery type current limiting element

Abstract

A self-recovery type current limiting element for suppressing overcurrent conditions and capable of recovering so as to be operated under normal current conditions including two identical element cylinders coupled therebetween by a coupler. A series of annular insulating members are provided within the element cylinders and include through holes for current limiting material providing a current limiting path extending longitudinally of each cylinder from an entrance opening at one end connected to the coupler to a buffer at the other end. The through holes in certain members nearer the coupler have a cross-sectional area smaller than the other annular members in the respective cylinders, providing a constricted region of the path. The current limiting material vaporizes when heated by current overload so as to increase resistance to suppress the current passing through. Current overload causes vaporization to start near the coupler at the constricted region of the path and to proceed axially such that heat dissipates the full length of each cylinder. The limiting material returns to its normal state to ensure normal operation.