To solve the problem that multi-level residual current (RC) leakage protection cannot be used in LV TN-C-S distribution systems because of the large inherent RC, a current separation leakage protection method based on RC and unbalanced current mutation vectors is constructed. First, the RC in TN-C-S systems is analyzed. It is proposed that load switching without faults does not affect M, the ratio of the RC vector to the unbalanced current vector, and single-phase grounding faults will lead to sudden changes of M. Then, M is continuously updated using the characteristics of frequent load switching in the LV systems, and the leakage current mutation amplitude of the system is calculated in real time. The ‘amplitude exceeding limit’ is used as the fault criterion. Simulations and field tests show that the proposed method has a correct recognition ratio of over 99% for leakage faults above 50 mA, and the reliable action threshold at the outlet of the transformers can be as low as 70mA. This meets the sensitivity requirements for the multi-level leakage protection of TN-C-S systems. This work is supported by the National Natural Science Foundation of China (No. 52077221).