AC SPD is suitably used in the TT, TN-S, TN-C, IT, TN-C-S and etc power supply system of AC 50/60Hz,<380V, installation om the joint of LPZ1 or LPZ2 and LPZ3, it is designed according to IEC61643-1, GB18802.1, it adopts 35mm standard rail, there is a failure release mounted in the module of surge protection device. When the SPD fails in breakdown for over-hart and over-current, the failure release will help electric equipment separate from the power supply system and give the indication signal, green means normal, red means abnormal, it also could be replaced for the module when has operating voltage.