In a three-phase four wire low-voltage distribution network, if the three-phase load is asymmetric, an unbalanced current will flow through the neutral line to the system side. The neutral line can eliminate the potential change at the neutral point and keep the voltage of each phase symmetrical, thereby making the potential of the neutral line to ground zero. However, when the neutral line is disconnected due to overcurrent or other faults, it will inevitably cause the neutral point of the three-phase load to shift, which may cause electrical equipment to burn out or malfunction. In response to the above issues, the harm of neutral wire breakage in low-voltage distribution networks was explained from a theoretical perspective. After comparing and analyzing various neutral wire breakage detection methods, a new detection circuit was designed based on the DC signal injection method. Multiple unit detection devices were used to locate the breakage position. The impact of this method on current transformer-based leakage protection was analyzed, and the results have showed that it could meet the requirements of both breakage detection and leakage protection simultaneously. The scientific and correctness of the above method have been verified through simulation.