IEC/TR 60890 Ed. 3.0 b:2022 PDF

This document specifies a method of air temperature-rise calculation inside enclosures for low-voltage switchgear and control-gear assemblies or similar products in accordance with their
respective standard.

The method is primarily applicable to enclosed assemblies or partitioned sections of assemblies without forced ventilation. However, some technical guidance to adapt it for the use of forced ventilation is given in this document. The results obtained by using this method are directly influenced by the accuracy of the evaluation of power losses used as inputs to perform the thermal calculations.

NOTE The air temperature within the enclosure is equal to the ambient air temperature outside the enclosure plus the temperature-rise of the air inside the enclosure caused by the power losses of the installed equipment.

For the method to be applied, the maximum daily average ambient air temperature outside the assembly at the place of installation is specified between 10 °C and 50 °C. The maximum daily temperature does not exceed the maximum daily average temperature by more than 5 K.

Several annexes in this document provide guidance on how temperature-rise within assemblies can be affected by influences which are not considered in the calculation method included in this document, for example, when the assembly is subject to solar radiation. In such cases, different means of verification to that given in this document can be applied to ensure a definitive result and verification of the design.