... SPD,alias:surge protector,surge arrester)is suitable for TN-S,TN-C-S,TT,IT etc.power supply system ... a failure release mounted on the module of surge protective device,When the SPD fails in breakdown ... release will help electric device separate from the power system and give the indication signal,green means ... by the thunder.TO6-80,TO6-60 series surge protective devices are usually installed in low voltage ...