We are all aware of the T classes.

Question: what happens if my equipment goes up to 84°C? Still T6?

The IEC 60079-0 defines the following points:

26.5 Thermal tests

26.5.1 Temperature measurement

The thermal tests shall be made at the rating of the electrical apparatus, with the exception of the thermal test to determine the maximum surface temperature. The latter test is performed with the most adverse conditions at the most unfavourable voltage between 90 % to 110 % of the rated voltage of the electrical apparatus, unless the manufacturer can demonstrate that other standards prescribe other tolerances for equivalent industrial electrical apparatus.

The measured maximum surface temperature shall not exceed

– for Group I apparatus, those values as given in 5.3.2.1,

– for Group II apparatus subjected to routine testing for maximum surface temperature, the temperature or temperature class marked on the electrical apparatus,

– for Group II apparatus subjected to type testing for maximum surface temperature, the marked temperature or temperature class, less 5 K for temperature classes T6, T5, T4 and T3 (or marked temperatures ≤200 °C), and less 10 K for temperature classes T2 and T1 (or marked temperatures >200 °C).

The result shall be corrected for the maximum ambient temperature specified in the rating. The measurement of temperatures as prescribed in this standard and in the specific standards for the types of protection concerned, shall be made in still ambient air, with the electrical apparatus mounted in its normal service position. For electrical apparatus which can normally be used in different positions, the temperature in each position shall be determined and the highest temperature shall be considered. When the temperature is determined for certain positions only, the electrical apparatus shall be marked with the symbol "X" to indicate this special condition of use according to item i) of 29.2.

Answer: No, it is already T5.

Note: have you ever been aware of the fact? 85°C is only 80°C in reality and so on... very important to know. It is a kind of magic :)