What causes overheating in electric motors?

Overheating in electric motors is primarily caused by excessive load or mechanical failure. When a motor is subjected to a load that exceeds its design capacity, it must work harder to operate, which generates additional heat. This increased thermal activity can lead to overheating if the motor's cooling mechanisms, such as airflow or coolant, are insufficient to dissipate this heat.

Additionally, mechanical failures, such as bearing issues, misalignment, or friction, can increase the resistance against which the motor has to work. This extra resistance requires more electrical input, thus generating even more heat. If the heat isn't managed effectively, it can damage the motor winding insulation, degrade lubrication, and ultimately lead to motor failure.

The other choices do not directly contribute to overheating effectively. A lack of electrical supply results in insufficient power for the motor to operate, not heat generation. Low ambient temperatures would generally help in cooling the motor rather than causing overheating. Lastly, while high-efficiency components typically reduce wasted energy and heat production, their overuse does not inherently result in motor overheating.