The effective loop impedance measuring device MZC-306 from Sonel is designed for loop measurements of ZL-PE, ZL-N, and ZL-L in networks ranging from 110 V to 715 V with frequencies of 45 to 65 Hz. The measurements are conducted after verifying the correct PE connection with a test current, depending on the network voltage, of up to 30 A. After the automatic calculation of the short-circuit current, the correct functioning of the overcurrent protection device can be determined. Additional measurement parameters such as AC voltage and frequency can then be transferred to a PC via USB cable and analyzed using the Sonel Reader software.