When the Motor Runs Hot, Part 1

Following your repair procedure, you use your handy infrared gun to measure temperatures at various points on the motor. Your repair procedure lists a high limit of 135°C for motors of this insulation class. But you read 152°C. The procedure doesn’t state what to do when the temperature is out of spec.

Should you replace this motor?

Maybe, because internal motor issues could be causing this high heat. But so could external motor issues. Here are two options to consider:

• Voltage imbalance. This is the usual culprit. If the difference between any two phases is more than 2% of the nominal voltage, you have excessive voltage imbalance. The typical cause is improper allocation of single-phase loads. Lighting is a prime suspect, so look there first.
• High ambient temperature. You may be able to solve this by improving air flow around the motor. It might be necessary to add ducting and even an electric fan. If the motor already has ducted cooling, check the air filter. It might just be clogged.

We’ll look at a few more options in Part 2.