The utility model relates to a neutral conductor broken string indicator is equipped with voltmeter, overvoltage protector, undervoltage protection ware, switch, audible -visual annunciator and GSM antenna on the casing, be equipped with AD converter, signal collector and controller in the casing, and signal collector, AD converter and controller connect gradually, and the voltmeter links to eachother with the AD converter, and the controller is connected with overvoltage protector, undervoltage protection ware, switch, audible -visual annunciator and GSM antenna. Exceeding excessive pressuredefault 235V or a phase voltage value when a phase voltage value, to be less than under -voltage default be 198V, explain the neutral conductor fracture of system, and at this moment, the scintillation of audible -visual annunciator red light pipes, and the signal transmission that can break the neutral conductor simultaneously is for in the personnel's of patrolling and examining the cell -phone, and which place the personnel of patrolling and examining can fast, accurately learn through the cell -phone has taken place neutral conductor wire break off fault to the personnel of patrolling andexamining handle as early as possible. Device sensitivity is high, the accuracy is reliable, reduce the user and the power supply enterprise damages the dispute that produces because of equipment.