This paper presents a procedure of choosing an appropriate surge protective device for low-voltage systems connected to an overhead line. For a typical surge protection application, an appropriate Electromagnetic Transients Program model is devised. The energy overload is calculated for a surge protective device following a simulation of the lightning effect. This way, it is possible to determine the required class for the surge protective device in question. The procedure has been tested on some typical overhead low-voltage networks. The results of these calculations, as well as very good service experiences, demonstrate that the use of Class II surge protective devices seems to be appropriate for service entrances in buildings that have no lightning protection systems.