Neutral and ground wiring errors on the user side are common in low-voltage transformer districts, which can cause user load currents to be converted into residual currents, resulting in frequent tripping of residual current circuit protection devices in the transformer district and their forced deactivation, thereby posing a threat to electrical safety. Since such wiring errors are present on the user side and are difficult to locate and troubleshoot, they have become a major obstacle to the deployment of residual current protection in transformer districts. This paper proposes a method for locating the user-side leakage due to wiring errors based on the significant correlation between user load currents and the residual current in the transformer districts, using correlation analysis and a gradient boosting decision tree (GBDT). The method starts with a qualitative and quantitative analysis conducted on the correlation between the residual current in the transformer district and the load current of users, with the Pearson correlation coefficient used to determine whether a causal relationship exists. A GBDT model is then constructed for the load current of each user in relation to the abnormal residual current in the transformer district, and importance scores are calculated to measure each user’s contribution to the fluctuations in residual current. This allows for the precise identification of user-side abnormalities. Experimental results demonstrate that the proposed method can accurately identify user-side abnormalities even in complex fault scenarios.