In order to solve the inaccuracy problem in calculating the actual voltage drop and the degree of three-phase load unbalanced of low voltage electrical load when takes no consideration of three-phase unbalanced load and non-ignorable neutral line impedance, a new safety monitoring method is presented by real-time monitoring of real voltage drop across the load. The new method establishes a high order equation model matching the equivalent impedance gird of real load of low voltage distribution network, based on the relationship between equation parameters and equivalent impendance parameters, uses transient signal to identify the model parameters, and calculates load fluctuations in real-time, neutral line impedance and load virtual point voltage. Simulation results demonstrate the effectiveness and accuracy of the proposed method.