Top Reasons Why Your Electric Motor is Overheating

September 15, 2023

Overheating is one of the leading causes of winding and bearing failure within an electric motor. But what’s the cause of this excess heat? Understanding the causes of electric motor overheating can help you to either avoid the problem in the first place or more easily find and fix the problem once it arises, allowing your equipment to last longer, saving you on downtime and extra costs.

Research conducted by EASA shows that when the operating temperature increasesjust 10°C, the motor’s lifespan is cut in half. Alternatively, when the operating temperature is decreased by 10°C, the lifespan is doubled.

Below are the factors related to the overheating of your electric motor:


Overload is when the driving force of the equipment is faced with a resistance higher than the manufacturer’s acceptable rating and may not be a constant issue as it’s directly related to load variations in the equipment being driven by the motor. As noted by EASA, most motors run at their highest efficiency when subject to only 75% of the manufacturer’s load rating. This allows the motor to operate at a lower temperature and consume less power.


Motors are designed with a system to allow the offloading of heat that’s produced during operation. This cooling system can consist of air ducts, air deflectors, cooling fans, and other design components such as cooling fins. Many factors can interrupt the cooling system’s ability to do what it was made for, such as clogged air ducts, a buildup of contaminants or ice, running slower than the rated speed, etc.

External factors like ambient temperature, altitude, and sunshine can all affect a motor’s ability to cool itself. Operating in an environment with a higher ambient temperature than the motor’s rating will cause overheating. Higher altitudes equal thinner air, making it harder to carry away heat. And bright sunshine can cause the motor casing to heat up. Some end users have even painted the casing white and provided additional shade to reduce heat absorption.


Motors will run most optimally when the voltage applied is equal to the manufacturer’s nameplate rating. Running a motor at a voltage deficit requires a higher amperage to produce the power needed, and this additional current equals more heat due to the resistance. Running the motor with a voltage above the saturation point will also cause an additional current and, therefore, excess heat. An unbalanced voltage in a 3-phase motor will also result in overheating due to the voltage spikes.

Electrical Steel

An AC motor’s core is made of many pieces of laminated steel, and the windings are wound through this core. The changing magnetic fields due to the spinning rotor can cause a phenomenon called Eddy Currents within the steel core. These Eddy Currents are small and are just energy losses that create heat.

Current Density

As the motor winding wire diameter size is decreased, electrical resistance increases. This increase in resistance will result in an energy loss in the form of heat.

Circulating Currents

When parallel coil groups don’t have the same number of coils, a circulating current will occur in the circuit with fewer coils. These circulating currents don’t add to the work being done by the motor but instead are energy losses in the form of heat.


Harmonics are the distortion of the sinusoidal wave (frequency of the total circuit) by waveforms of other frequencies. These disruptions can be caused by the addition of rectifiers, fans, and pumps, etc. The odd harmonics produced will create a negative torque that’s in opposition to the torque created by the motor. This negative torque increases the load on the motor, causing the motor to have to work harder and in turn producing more heat.


An electric motor operating at a high temperature will cause a low life expectancy. Lowering the operating temperature by improving ventilation, optimizing design, or choosing a motor that’s up to the task in the first place will lead to a more reliable piece of equipment.

Here at eMotors Direct, we want to help you make sure you get the right motor and accessories the first time around. Utilize features on our website like our smart search and related filters or our cross-reference matches to choose the correct motor for your application. And if all else fails, our experts are standing by.

Read more in this linked EASA article.

This article is posted with permission by EASA.

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