Abstract: A method for determining loop impedance active and reactive components of an alternating current network and a device for carrying out the method. The active and reactive components are determined by applying a test load to the loop, by measuring the loop voltage prior to the application of the test load and, when the test load is applied, measuring the voltage time evolution during the application of the test load and determining the active resistance R and reactive inductance L parts of the loop impedance by jointly analysing differential measurements of the loop voltage and the time evolution of the test load voltage.