This part of IEC 61557 specifies the general requirements for measuring and monitoring equipment for testing the electrical safety in low voltage distribution systems with nominal voltages up to 1 000 V a.c. and 1 500 V d.c. When measuring equipment or measuring installations involve measurement tasks of various measuring equipment covered by this series of standards, then the part of this series of standards relevant to each of the measurement tasks is applicable. This second edition replaces and cancels the first edition published in 1997. It constitutes a technical revision. The following changes were made with respect to the previous edition: a) revision of the definitions; b) addition of influence quantities E9 and E10; c) the subclause on Electromagnetic compatibility was complemented; d) inclusion of performance monitoring devices in the introduction; e) addition of new requirements for operating instructions.