Residual Current Devices

Chapter 9: Earth fault loop impedance measurement in circuits with residual current devices

Abstract

In low-voltage electrical installations, protection against electric shock in case of fault is performed mainly by the use of the automatic disconnection of supply. To verify the effectiveness of this means of protection in TN systems, the earth fault loop impedance measurement is performed. During this measurement, a testing current flows through the protective conductor of the tested circuit. From the point of view of the measurement accuracy, the testing current should be relatively high. In common solutions of the loop impedance testers, it is around 5–20 A. It is many times higher than the rated residual operating current of the residual ...