IEC 61753-061-2:2020 is available as IEC 61753-061-2:2020 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.IEC 61753-061-2:2020 contains the minimum test and measurement requirements and severities which a fibre optic isolator as specified by IEC 61202-1 satisfies in order to be categorized as meeting the requirements of isolators used in controlled environments as specified in IEC 61753-1. The requirements cover single-mode pigtailed style polarization independent isolators for category C used in controlled environments. This second edition cancels and replaces the first edition published in 2012 and constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: - addition of the detail high optical power test procedures and the condition in Annex B; - change of test conditions harmonizing with IEC 61753-1:2018; - addition of category CHD; - addition of the detailed measurements conditions in Annex C; - change of clause structure accordance with the latest ISO/IEC Directives, Part 2.