Gas filled surge arrester

A gas-filled surge arrester comprising a generally cylindrical tubular insulator member, a pair of electrodes of substantially uniform composition having opposed generally planar end faces, said electrodes being hermetically sealed to opposite ends of said insulator member, said insulator member, serving to isolate electrically said electrodes and to space apart said opposed end faces to define a discharge gap therebetween, said electrodes including at least one pair of opposed cavities formed as recesses in the end faces, the cavity in each face being of a size as to occupy less than the full end face area and the cavities having respective end walls which are spaced apart a distance greater than the width of said gap, said cavities being lined with a substance of high electron emission ability relative to that of the adjacent electrode material at said gap, said substance in each cavity forming a ring substantially coplanar with the associated end face and the depth and width of the cavities being such that the discharge tends to take place between said lined cavities to discourage dispersion of particles from the electrodes during discharge onto the insulator member.