Abstract: A modular overvoltage protection unit for electrically connecting a first power line and/or a second power line to a protected earth (PE) line in the case of an overvoltage event on the first or second power line includes a unit enclosure defining an enclosure cavity, and first and second surge protection devices (SPDs) each disposed in the enclosure cavity. Each of the first and second SPDs includes: a first electrode in the form of a metal housing defining a housing cavity; a second electrode disposed within the housing cavity; and a varistor member captured between and electrically connected with each of the first and second electrodes, wherein the varistor member is formed of a varistor material.