The utility model provides an over voltage protecting device of the neutral line and the breaking line of a low voltage network. The protecting device is composed of a trigger, a thyristor and an electromagnetic element, wherein, the thyristor is provided with three terminals, namely T1, T2 and G, both terminals of the trigger are respectively connected at the terminal G and the terminal T2 of the thyristor, the terminal T1of the thyristor is connected at one end of the coil of the electromagnetic element, both the terminal T2 of the thyristor and the other end of the coil of the electromagnetic element adopt the wiring terminals of the protecting device; the trigger adopts a varistor or a bidirectional diode; the electromagnetic element adopts a relay or a trip. The over voltage protecting device has the advantages that the structure is simple, the cost is low, the technology is advanced, the over voltage protecting device is easy to realize and is in the passive condition in the normal operation, only when the over voltage protecting device occurs the failure of the neutral line and the breaking line, the protecting device is momentarily charged, no loss exists in the normal operation; the protecting device can be installed at any parts from the secondary side of a transformer to each consumer, to perform the effect of protecting the consumer.