Arrester with spark gap

In an overvoltage arrester composed of two electrodes each presenting a side wall and an end wall transverse to the side wall and whose perimeter is borderd by the side wall, the electrodes being spaced apart to define a spark gap and with their end walls facing one another, and an insulating member interposed between the end walls of the two electrodes, the improvement wherein said insulating member is dimensioned to protrude laterally beyond the entire perimeter of said end wall of at least one said electrode for causing the initiation of an arc to generate a sliding arc discharge following a curved path around the laterally protruding part of said insulating member, said insulating member is of a material which emits a quenching gas under the influence of heat, each said electrode exhibits an abrupt change in diameter at a location spaced from its associated end wall, said electrodes present at the location of their abrupt change of diameter respective opposing electrode end faces spaced from one another by a distance which is greater than the spacing defined by said insulating member interposed between said end walls of said electrodes, and the perimeter of said end faces protrudes laterally beyond the perimeter of said insulating member.