Insulation Temperature Class

Operating temperature and service life.

If temp class is not specified, you take what the supplier sends you.

....and assume that it is the lowest (cheapest) temperature class unless they can prove otherwise.

NEMA Insulation Classes

You first estimate what maximum temperature will rise in the equipment when it operates at full load. Then tell to your supplier to provide type of Temperature class insulation level is required.

After estimation of maximum temperature rise in equipment, then decide the insulation class as given by above post Guru lyn " NEMA Insulation class"

Design of electrical equipment depends on many factors. The purchaser has to specify various operating conditions, load cycle, any limitation of size and weight, expected life of the equipment etc. Based on these factors, the manufacture designs most cost effective design which meets customers specifications. He may choose amount active material, type of cooling etc. and arrive at final operating temperature. This temperature will decide the temperature class of the material ro be used.