This part of IEC 61557 specifies the requirements applicable to equipment for measuring the loop impedance between a phase conductor and the protective conductor or between a phase conductor and neutral or between two phase conductors by using the voltage drop when the circuit under test is loaded. This second edition cancels and replaces the first edition published in 1997. This edition constitutes a technical revision. The following changes were made with respect to the previous edition: a) definitions complemented; b) revision of some requirements; c) addition of information on operating instructions; d) addition of new influence quantities E9 and E10.