An overvoltage protection device for protecting electrical low-voltage installations, having a lower device part and at least one upper device part, wherein the lower device part has input and output terminals for the electrical conductors to be connected and contact elements connected to the input and output terminals. The upper device part has at least one overvoltage protection element. An intermediate device part is additionally provided which can be fitted onto the lower device part and onto which the upper device part can be fitted. The intermediate device part has mating contact elements corresponding to the contact elements of the lower device part and also has contact elements connected to the mating contact elements. The intermediate part has at least one longitudinal element connected between two mating contact elements, and the upper device part has mating contact elements corresponding to the contact elements of the intermediate device part.