1.SY-A 2.ISO9001 3.professional lightning ... Principle:Under normal circumstance, the SPD is in a high impedance condition, when the power grid ... into the earth, meanwhile, limits the overvoltage in a protection level. When the instant overvoltage disappear, ... of the power grid line.Model SY-A-50KA4PBSY-A-30KA4PBSY-A-25KA4PBSY-A-15KA4PBRated Working Voltage ACUn385V385V385V385VLightning current impulse ...