Surge Protective Device(Surge Protector,Arrestor) It protects the electric network shocked by ... the thunder or over voltage . Surge Protective Device(Surge Protector,Arrestor)Usage and application scopeBY40 type surge protective device ( ... for AC 50/60 Hz,380V and the following electric power systems,such as TT, IT, TN-S, TN- ... metal or damage insulation. Surge Protective Device(Surge Protector,Arrestor)