IEC TR 63400:2021 is intended to augment that description to enable users of individual IEC SC 45A standards to obtain a more comprehensive understanding of the overall structure of the series and its relationship with other standards bodies and standards. This document outlines the scope of the IEC SC 45A standards series and describes the basic structure of the IEC SC 45A standards series, with particular reference to a hierarchy of levels and subdivision into a set of broad topic areas. it presents the structure of the IEC SC 45A standards series in diagrammatic form.