No-load Current Basics: Practical Guidelines for Assessment

1 EASA CURRENTS February 2005 Applied Voltage (% Of Rated)ABCurrent25%125%100%75%50%Full load CurrentContinued On Page 2No- load Current basics : Practical Guidelines For AssessmentBy Chuck YungEASA Technical Support SpecialistHow much No-load Current shouldI expect when testing a motor? Wewould like to have a ratio of no-loadamps / full- load amps, for qualitycontrol purposes.**Many of us expect a motor todraw approximately one-third of ratedcurrent, when operating from ratedvoltage on our test panel. That is agood rule of thumb most of thetime. While there are lots of excep-tions, most of them are explain the rule of thumb andthe exceptions, we will use someterms familiar to most readers:FLA = Full- load ampsNLA = No-load amps; this ismagnetizing Current plus somelosses (mostly windage)Flux = Lines of magnetic forceAGD = Airgap density; in lines offlux per unit areaV = Applied voltageHere are some exceptions youprobably recognize: The higher the flux density, thehigher the No-load Current will beas a percentage of FLA.

Practical Guidelines The intent of this article is to explain why those statements are valid and, in the process, to offer practical guidelines for assessing no-load current. Many of us apply these principles daily. Knowledge is power. We should, whenever possible, improve our knowledge by gathering facts: •Use the AC Motor Verification &

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