IEC 61643-331:2020 is available as IEC 61643-331:2020 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.IEC 61643-331:2020 is a test specification for metal oxide varistors (MOV), which are used for applications up to 1 000 V AC or 1 500 V DC in power lines, or telecommunication, or signalling circuits. They are designed to protect apparatus or personnel, or both, from high transient voltages. This document applies to MOVs having two electrodes and hybrid surge protection components. This document also does not apply to mountings and their effect on the MOV’s characteristics. Characteristics given apply solely to the MOV mounted only in the ways described for the tests. This third edition cancels and replaces the second edition published in 2017. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: - a Varistor MCOV rating assurance test; - an energy rating test (2ms); - revised Dielectric strength and insulation resistance tests.