Patent ID: 8217750

Claim:
A 3-electrode surge protective device comprising: a surge protective device body comprising: an earth electrode; a ceramic cylinder bonded to the earth electrode; and a pair of line electrodes bonded to both side faces of the ceramic cylinder, a fail-safe spring with an electrical conductivity that is mounted on an outer face of the surge protective device body, the fail-safe spring comprising: an elastic mount portion provided along an outer peripheral face of the earth electrode to push an outer peripheral face of the surge protective device body, the elastic mount portion including a protrusion projecting from an inner face of the elastic mount portion toward and into contact with the outer peripheral face of the surge protective device body so as to space part of the inner face of the elastic mount portion from the outer peripheral face of the surge protective device body; and a short-circuit portion provided to intersect with the elastic mount portion and electrically connecting the earth electrode to the pair of line electrodes, a conductive material that is sandwiched between an inner face of the fail-safe spring and the outer face of the surge protective device body, the conductive material being provided at an intersecting position of the elastic mount portion and the short-circuit portion; a pair of first lead pins provided on the pair of line electrodes; and a second lead pin provided on the earth electrode, wherein, in a normal state, the conductive material serves as a spacer to support the short-circuit portion at a separation position where the short-circuit portion is separated from the outer peripheral face of the surge protective device body and the first lead pins, and wherein, in case where the surge protective device body is overheated and the conductive material is melted, the short-circuit portion is moved to a contact position where the short-circuit portion comes into contact with the second lead pin and the first lead pins, by a pushing force of the elastic mount portion.