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Keeping it simple: Steps to determine motor’s actual load

Plant Engineering
Publication date: 
October 2014
Chuck Yung, EASA Senior Technical Support Specialist

Contrary to popular opinion, bigger isn’t always better—especially when it comes to electric motors. Plant maintenance and engineering departments like having a little extra power available “just in case,” so they sometimes specify larger motors than applications require. But oversized motors cost more to operate—sometimes a lot more. Fortunately, there’s a simple procedure for determining the actual hp required by a load, without expensive equipment or engineering. Bear in mind that loads should be determined when the motor is operating at its maximum load. Loads that vary widely are good candidates for variable-frequency drives (VFDs), which offer the added benefit of controlling rate of production.

Topics covered include:

  • Estimating actual load
  • Cost of "safety margin"
  • Real life example
  • Power factor and efficiency