SPD for AC Power Supply is mainly applicable to the power distribution systems for Class I / II / III( Type1, type 2, type3) protection. Surge arresters for AC line units can protect electrical equipment from the impact of lightning electromagnetic pulse, induced over-voltage, transient operation, and resonance(<100μs) overvoltage. Common AC surge protection devices (SPD) are single-phase or three-phase, 4 poles or multi-pole, with slightly different ac spd prices.