Unsafe electrical appliances pose a significant threat to life and properties. Monitoring of electrical appliances has been recognized as an important approach to improve electrical utilization safety. The purpose of this work is to detect leakage current and attribute it to an individual residential appliance in a non-intrusive way, i.e., using measurement at the electrical entry point of a home. Therefore, appliances with fault or at risk can be discovered timely without dedicated sensor installation behind the entry point. The idea is to determine whether the change of residual current is caused by a specific appliance using aggregated data. Cloud-based non-intrusive load monitoring (NILM) with load profiling is implemented to deduce detailed appliance activities and household appliance composition. Appliance leakage current can be determined by analyzing the relationship between residual current change and appliance status. The proposed approach has been verified in the lab and then deployed in a real-world residential property with all measurements integrated in the cloud. The results confirm the effectiveness of the proposed approach to detect leakage current and establish an in-depth understanding of household electrical safety.