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When is Hot "Too Hot" For Your Electric Motor?

Fire, Heat

It is that time of year again.  Summer is here, and the temperatures are soaring.  But unfortunately for your business it doesn’t stop there.

Did you know?

As the ambient temperature rises, the operating temperatures of your electric motors also increase. 

Inevitably, someone will take note of the increased operating temperature during a maintenance activity or periodic inspection, at which point the question suddenly becomes:

At what point is the motor exceeding its design operating temperature? 

Today’s article is intended to provide some practical information concerning motor operating temperatures.

So, how hot is too hot?

Most electric motors used in industrial settings are Class B or Class F designs.  So, what happens if we operate a motor above its design temperature?

A general rule of thumb to consider is that for every 10°C above design temperature, the life of the insulation system is cut in half. 

Take a Look at Table 1 – Insulation Class

Motors are commonly equipped with protective devices (typically thermal cut-out devices on smaller low voltage motors <600v) or temperature sensors (typically rtd’s on medium and high voltage motors). 

You should utilize these devices to track operating temperatures (rtd’s) and actively employ them as thermal overload protection (rtd’s and thermal cut-out devices). 

Now Let's Look at Table 2 – Recommended Alarm and Trip Temperatures

If you find that you are exceeding one or more of these recommended temperature ranges you might ask yourself…

What are Some Possible Causes of Overheating?

Answers can include but are not limited to:

  • Restricted airflow (blocked fan cover / debris blocking stator cooling ribs TEFC motors)
  • Dirty air filters
  • Motor overloaded
  • Incorrect direction of rotation (for motors with unidirectional fans)
  • Oil leaks (oil drawn into the motor coats the windings and attracts dirt and particulate effectively insulating the coils)
  • Phase voltage imbalance / incorrect voltage
  • Blocked cooling tubes (TEAAC and TEWAC designs)
Where Can I Go to Learn More?

The above information is intended to give you a general idea of motor operating temperatures for comparison purposes.  For information specific to a particular machine, contact the original equipment manufacturer. 

And if you are in need of periodic maintenance, inspection or repair to ensure that your motors are operating at proper temperatures, Contact Us today.

About the author

RSAW

RSAW

RSAW's team of thought-leaders on all things motor repair, sales, storage, and field services contributed this post.