Abstract: The arrester comprises an insulating housing with end terminals and a plurality of varistors inside the housing electrically connected between the terminals. The varistors are provided individually or in groups with a heat transfer and sinking collar which is electrically insulating and thermally conducting. The collar may be in thermally conducting contact with the inside wall of the housing to improve heat dissipation to the housing. The configuration of the collar is such that when it is installed in the housing, there is a passageway through it to provide a longitudinal space in the arrester for accommodating arcing and for the venting of gas in the event of an arrester failure.