IEC 61300-3-21:2019 is available as IEC 61300-3-21:2019 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.

IEC 61300-3-21:2019 describes a method to measure the switching time and related performance parameters of a fibre optic spatial switch when the actuation energy is applied or removed to change the state of the switch. This third edition cancels and replaces the second edition published in 2014. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
- changes to remove redundant overlap with IEC 60876-1;
- clarifications to definitions and diagrams;
- generalization of the detection apparatus beyond an oscilloscope.
Keywords: switching time, performance parameters of a fibre optic spatial switch, actuation energy