Checking for motor overload

Motor overload occurs when a motor is under excessive load. The primary symptoms accompanying motor overload are excessive current draw, insufficient torque and overheating. Indeed, excessive motor heat is a major cause of premature wear on electrical and mechanical components that ultimately leads to motor failure.

In the case of an overloaded motor, individual motor components including bearings, motor windings, and other components may be working fine, but the motor will continue to run hot.

For that reason alone, it makes sense to begin your troubleshooting, for an issue such as conveyor malfunction for example, by checking for motor overload. Because 30 % of motor failures are caused by overloading, it is important to understand how to measure for and identify motor overloading.

An ideal instrument to measure and diagnose overload is a Fluke 289 True-RMS Industrial Logging Multimeter with a clamp accessory, or a Fluke clampmeter. You can measure and log current to individual motor phases while the motor is still running under full load. With the 289, you can also communicate wirelessly with your iOS and Android smart devices with the Fluke Connect® mobile app and an ir3000 FC wireless connector (sold separately.)

Clip on a clamp and take an amp reading. Compare that reading to the "Full Load Amps" * Service Factor ratings from the motor’s nameplate.

Check the current to each of the three legs of a three-phase motor to determine if there is single-phasing, a problem that occurs when there is a failure in one of the phases.

Diagnosing motor overload can extend motor life, reducing failure, downtime and economic loss.