# Confused about FLA and LRA



## JRaef (Mar 23, 2009)

Full Load Amps (FLA) = the current the motor will draw wen loaded to it's full capacity where it is exerting it's rated torque at rated slip speed.

Locked Rotor Amps (LRA) = the current the motor will pull when power is applied, but the rotor is not turning, it is either "locked", or has not _yet _begun to move because you just applied power and will continue to draw until the motor gets to about 80% of slip speed. The is usually determined by the type of motor "torque-speed curve" design, which is defined under NEMA rules to be one of 4 different basic curves: A, B, C or D. In 99% of the motors we use every day they are Design B, in which the LRA will be approximately 500-600% of the FLA.

You size conductors based on the FLA, but not* the FLA of the nameplate, the FLA of the charts in article 430 of the NEC that tell you what the FLA might be expected to be, worst case normal. Using that chart, you take the value for the nameplate HP, then add 25% (x 1.25) and pick the next size closest conductor, up, never down. You also use that chart to select the OCPD for the motor branch circuit. The only time* you use the nameplate FLA is for setting / selecting the motor starter thermal overloads. Using those values covers you for the LRA.

* If the actual nameplate FLA is somehow higher than the NEC chart, then you do use the nameplate FLA, but that is rare.


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## gotshokd666 (Oct 17, 2012)

JRaef said:


> Full Load Amps (FLA) = the current the motor will draw wen loaded to it's full capacity where it is exerting it's rated torque at rated slip speed.
> 
> Locked Rotor Amps (LRA) = the current the motor will pull when power is applied, but the rotor is not turning, it is either "locked", or has not yet begun to move because you just applied power and will continue to draw until the motor gets to about 80% of slip speed. The is usually determined by the type of motor "torque-speed curve" design, which is defined under NEMA rules to be one of 4 different basic curves: A, B, C or D. In 99% of the motors we use every day they are Design B, in which the LRA will be approximately 500-600% of the FLA.
> 
> ...


Thank you, thats very informative. The situation I have right now is just a 1/2 HP sump pump, which the spec sheet lists FLA 8.5A and LRA 23A at 115V. Would you size that to Art 430, or just put it on a 20A circuit and be done with it? I know I've always just run a dedicated circuit for sump pumps, but that's how I was taught - doesn't mean it's the correct way...


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## JRaef (Mar 23, 2009)

A 15A circuit / 14ga wire would be fine actually.


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## Meadow (Jan 14, 2011)

What J-raef said :thumbup:


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