Due to the modern design and manufacturing process, the motors currently in use often become hotter during operation than motors used in the past. In practice, the surface temperatures of some modern motors may reach temperatures of up to 90°C (194°F). Nevertheless, the service life of such motors is equal to or even greater than that of the old motors. High surface temperatures are not necessarily a sign that something is wrong. However, if the motor becomes excessively hot during operation, a number of causes may be at work:
Electrical causes: Undervoltage or overvoltage, asymmetrical three-phase current, diminishing insulation resistance.
Environmental impacts: High ambient temperatures, lack of ventilation or poor ventilation, high installation elevation (low air density).
Mechanical causes: Too many switching cycles, flow rate too high or too low, high resistance to rotation due to damaged pump, high viscosity or density of the pumped medium, clogged or blocked pump.