IEC 61051-2:2021 is a sectional specification and is applicable to metal oxide varistors with symmetrical voltage-current characteristics for use in electronic equipment connected to any AC or DC supply system.
These varistors are designed to protect electronic and other sensitive equipment from high transient surges. Varistors under the scope of this sectional specification are not intended to give primary protection against lightning surges.
These varistors have metallic connections and are intended to be mounted as through hole component or directly on to printed boards.
The object of this document is to prescribe preferred ratings and characteristics and to select from IEC 61051-1 the appropriate quality assessment procedures, tests and measuring methods, and to give general performance requirements for this type of varistors.
This edition includes the following significant technical changes with respect to the previous edition:

1. revision for the structure in accordance with ISO/IEC Directives, Part 2) to the extent practicable, and for harmonizing with IEC 61051-1:2018;
2. Annex X has been added for comparison with the previous edition;
3. two lists of preferred voltage ratings for disk type and SMD type varistors have been added;
4. permissible numbers of non-conforming items have been set to zero (zero fault) in the test schedule in 8.4.3.