Fault Loop Impedance Measurement in Low Voltage Network with Residual Current Devices

摘要

According to the standard [1] every low voltage electrical installation shall be verified before being put into service by the user and verified periodically in order to check whether the installation and all its equipment are in satisfactory condition for use. The scope of the initial and periodic verification covers fault loop impedance measurement. Value of loop impedance and selected protective devices influence electric shock and overvoltage hazard [2-4]. The fault loop impedance is measured in circuits with residual current devices (Fig. 1) which are obligatory in selected circuits [4, 5]. Residual current devices cause the problem in fault loop impedance measurement. They trip out during the measurement because the measurement current I_M is the residual current for residual current devices. Proper verification of the installation is then impossible.