The product is suitable for the protection of a monitor head, a decode circuit, and entrance guard data line, a visual-speaking system, an intelligent water meter, an intelligent gas meter, and intelligent meter, a wide-used ID system and a fireproof alarm line, and prevents the damage of line induction overvoltage equipment due to earth potential increase, has low output residual voltage, little insertion loss and double overcurrent protection , and is suitable for the protection of the ports such as the RJ11, connection terminals, RS232 and so on. And the protective lines can be divided into the the single circuit type, double circuit type or multiple-circuit type.