This section of IEC 721‑3 defines classes of microclimatic conditions, to which components (basic parts, assemblies, built-in units) may be subjected inside products, which are used under the climatic conditions as classified in sections IEC 721‑3‑3 and IEC 721‑3‑4.

Characteristic parameters for the microclimates are high air temperature and high relative air humidity. Further parameters of the climatic classes e.g. low temperature may affect the components additionally, but have not been considered here.

A limited number of microclimatic classes is specified taking into consideration typical limiting high air temperatures of components.

The user of this standard should select the lowest class necessary for covering the intended use.