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Voltage limiting type SPD combined with voltage switching type SPD is formed the Group SPD, which is suiting to A. C 50/60 Hz , 380V and under 380V voltages electric power system and protects all the distribution systems shocked by the thunder or surge over voltage.
Using the combination SPD between phase line and earth line in the distribution system, which not only eliminates the power-frequency continuous current, but also over comes the leakage tripping which results from the bad performance of MOV. So SPD is suitable to all the distribution system which is with the protection of surplus current. Since the voltage switching SPD is connected between zero line and earth line, at the same time with its much higher maximum continuous operating voltage and enough impulse current capacity, it will have its peculiar superiority when used in TT system.