Overvoltage Protection A surge protector protects electrical and electronic devices from excessive electrical voltages. Surges can have various causes. Lightning strikes (lightning electromagnetic pulse) Sudden drop in load / increase in load Switching operations (switching electromagnetic pulse) Electrostatic discharges (electrostatic discharge) There is a three-stage concept for protection against overvoltages. Stage 1 A coarse protection (SPD type 1, Surge Protection Device) protects against high-energy disturbances. For example, it prevents lightning from entering the line to be protected. It is designed to limit the residual voltage to 1300 to 6000 V. Stage 2 A medium protection (SPD type 2) is usually located in floor distributors. It is designed to limit the overvoltages to 600 to 2000 V. Stage 3 Fine protection (SPD type 3) is the protection of sockets and connectors. All terms in Expert Know-how