A surge protective device module comprising: a module housing; first and second module electrical terminals (166A, 168A) mounted on the module housing; an overvoltage clamping element electrically connected between the first and second module electrical terminals; a thermal disconnector mechanism positioned in a ready configuration, wherein the overvoltage clamping element is electrically connected with the second module electrical terminal, the thermal disconnector mechanism being repositionable to electrically disconnect the overvoltage clamping element from the second module electrical terminal, the thermal disconnector mechanism including: an electrode electrically connected to the overvoltage clamping element; a disconnect spring elastically deflected and electrically connected to the electrode in the ready configuration; a first fail-safe mechanism including a solder securing the disconnect spring in electrical connection with the electrode in the ready configuration, wherein: the solder is meltable in response to overheating of the overvoltage clamping element; and the disconnect spring is configured to electrically disconnect the overvoltage clamping element from the second module electrical terminal when the solder is melted; and a second fail-safe mechanism including a weak region in the disconnect spring, wherein the disconnect spring is configured to break at the weak region in response to a current through the disconnect spring to electrically disconnect the overvoltage clamping element from the second module electrical terminal and characterised in that the SPD module includes a supplemental spring, wherein, in the ready configuration, the supplemental spring: is electrically connected to the electrode; applies a spring load to the disconnect spring; and provides thermal capacity to cool the disconnect spring. a module housing; first and second module electrical terminals (166A, 168A) mounted on the module housing; an overvoltage clamping element electrically connected between the first and second module electrical terminals; a thermal disconnector mechanism positioned in a ready configuration, wherein the overvoltage clamping element is electrically connected with the second module electrical terminal, the thermal disconnector mechanism being repositionable to electrically disconnect the overvoltage clamping element from the second module electrical terminal, the thermal disconnector mechanism including: an electrode electrically connected to the overvoltage clamping element; a disconnect spring elastically deflected and electrically connected to the electrode in the ready configuration; a first fail-safe mechanism including a solder securing the disconnect spring in electrical connection with the electrode in the ready configuration, wherein: the solder is meltable in response to overheating of the overvoltage clamping element; and the disconnect spring is configured to electrically disconnect the overvoltage clamping element from the second module electrical terminal when the solder is melted; and a second fail-safe mechanism including a weak region in the disconnect spring, wherein the disconnect spring is configured to break at the weak region in response to a current through the disconnect spring to electrically disconnect the overvoltage clamping element from the second module electrical terminal an electrode electrically connected to the overvoltage clamping element; a disconnect spring elastically deflected and electrically connected to the electrode in the ready configuration; a first fail-safe mechanism including a solder securing the disconnect spring in electrical connection with the electrode in the ready configuration, wherein: the solder is meltable in response to overheating of the overvoltage clamping element; and the disconnect spring is configured to electrically disconnect the overvoltage clamping element from the second module electrical terminal when the solder is melted; and the solder is meltable in response to overheating of the overvoltage clamping element; and the disconnect spring is configured to electrically disconnect the overvoltage clamping element from the second module electrical terminal when the solder is melted; and a second fail-safe mechanism including a weak region in the disconnect spring, wherein the disconnect spring is configured to break at the weak region in response to a current through the disconnect spring to electrically disconnect the overvoltage clamping element from the second module electrical terminal and characterised in that the SPD module includes a supplemental spring, wherein, in the ready configuration, the supplemental spring: is electrically connected to the electrode; applies a spring load to the disconnect spring; and is electrically connected to the electrode; applies a spring load to the disconnect spring; and provides thermal capacity to cool the disconnect spring.