The selection of induction motors designed to match the load requirements of any particular application need to ensure that the temperature inside the motor windings does not rise to a level that exceeds the critical temperature.
The critical temperature is the temperature in which the stator and rotor winding insulation can withstand without permanent damage. Insulation damage can shorten the useful life of the motor and eventually results in electrical faults.
IEC 60034-1 classifies the temperature rise limits of insulation materials and specifies the maximum permissible temperatures that the various classes of insulation materials could withstand. The temperature rise of the induction machine is the permissible increase in temperature, above this maximum ambient, to allow for the losses in the motor when running at full load.
A safe temperature is the sum of the maximum specified ambient temperature and the permitted temperature rise due to the mechanical load. This IEc standard specifies a maximum ambient temperature of 40oC.
References:
1. IEC 60038-1 Rotating electrical machines – Part 1: Rating and performance
2. Practical Variable Speed Drives and Power Electronics – Malcolm Barnes
Electrical equipment like circuit breaker have maximum power dissipation (MPD) ratings. If the sum of the individual MPDs of the equipment inside the enclosure does not exceed the MDP of tje enclosure for that temperature rating then you can be sure that even without derating, your enclosure will be fine.
The enclosure MDP need to be provided and certified by the manufacturer.
Another thing to consider is the enclosure protection technique (Exd, exi, exp, etc)
what is affect of enclosure protection, e.g. of MCCBs of enclosure protection IP55, on the equipment temperature rise limit. i.e. if MCCbs of IP 55 to be installaed inside outdoor panel aslo of IP55, Do we need to derate its rating load inorder to not to exeed its temperature rise limit because it is installed inside enclosure.