Abstract: A surge arrester of the gas tube type for protecting telephone lines has a primary arc gap and a secondary arc gap electrically coupled in parallel. The primary arc gap is wider than the secondary arc gap and both arc gap are exposed to the inert gaseous medium of the arrester. The gas pressure and the width of the gaps are such that the breakdown voltage of the primary arc gap is less than the breakdown voltage of the secondary arc gap so that in normal operation the arrester discharges through the primary arc gap. However, if the inert gas leaks from the tube and becomes replaced with air at atmospheric pressure, the arrester will discharge through the secondary arc gap to provide a backup protection for the line.

Abstract: A line protector for communications circuits comprises a gas tube having external contact surfaces for connections to communication lines and to ground. A conductive member is proximate to the contact surfaces that are associated with the communication lines. A dielectric substance interposed between the conductive member and the last-mentioned contact surfaces melts upon overheating of the protector resulting from the excessive line current. The conductive member, due to its resiliency, engages the subjacent contact surface or surfaces thereby resulting in a direct short circuit between the protected line and ground. A shield over at least part of the gas tube in the region of the conductive member prevents potting compound or foreign matter from obstructing the function of the conductive member.