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Tracing motor overload issues

By Barry Paulus

August 2006

At the food packaging plant where I work, one of the batch mixers, which has two 20-hp 460 V 3-phase motors, was activating the motor overload of one of the motor starters. Using a Fluke 336, we observed running current measurements much higher than the motor nameplate rating. Ultimately, we installed a new motor. Even with the new motor, the overload was still tripping (as it should), because we were still seeing high running current values on that motor (up to 40 A on a 27 A rated motor). We were able to determine that the mixer was being loaded with more product than designed for, causing excessive load on the motor. The Fluke 336 allowed us to take quick, accurate current measurements of the motor leads.