# Motor ratings



## AK_sparky (Aug 13, 2013)

I thought I had seen all types of motor rating schemes, but the motor calc check thread had me scratching my head.

What is RLA and LRA? I don't think I've ever seen these and can only guess at what they are.

Running load amps?

Also in that thread it was implied that FLA and FLC are different things. I always though they were the same.


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## AK_sparky (Aug 13, 2013)

Just after posting that I got thinking LRA probably means Locked Rotors Amps.

But the FLC and FLA thing still has me curious.


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## glen1971 (Oct 10, 2012)

AK_sparky said:


> Just after posting that I got thinking LRA probably means Locked Rotors Amps.
> 
> But the FLC and FLA thing still has me curious.


FLC = Full Load Current

FLA = Full Load Amps (Pre-1976 terminology for RLA, still used by NEMA (National Equipment Manufacturers Association) to determine current drawn by a motor of a specific horsepower and used as a guide to size the supply wiring, starters and overloads. There is one other term used for electric motors that is important, that being service factor. A motor with a service factor of 1 the name plate amperage is used to calculate overloads. A service factor of 1.15 or other is used as a multiplier of nameplate amperage for temporary conditions to select overload values.)

RLA = Rated Load Amps or Running Load Amps (The maximum current a motor should draw under any operating conditions. Often mistakenly called running load amps which leads people to believe, incorrectly, that the motor should always pull these amps.)

LRA = Locked Rotor Amps (The current you can expect under starting conditions when you apply full voltage. It occurs instantly during start up.)


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## AK_sparky (Aug 13, 2013)

You copy and pasted that!

And it still doesn't tell me the difference between FLC and FLA, unless we stopped using Amps to measure current. I might have missed that memo....


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## JRaef (Mar 23, 2009)

AK_sparky said:


> You copy and pasted that!
> 
> And it still doesn't tell me the difference between FLC and FLA, unless we stopped using Amps to measure current. I might have missed that memo....


FLC if the motor nameplate Full Load Current stamped in by the manufacturer based on testing the motor at full rated torque and speed.

FLA is a published estimate of what the motor current might be, kind of a worst case scenario for 90% of motors of a given HP rating. So the charts in the NEC that you use for sizing conductors based on motor HP are giving you an FLA value. If the motor nameplate FLC is less, you still must use the FLA value for conductor sizing, just in case someone later puts in a motor of the same HP size but has a higher nameplate FLC.

You were right about RLA and LRA definitions.

But RLA is not exactly the same as FLC. For some motors, the FLC would be irrelevant because the nature of the machine design is such that the motor would NEVER get there, plus the motor is not designed to be removed and used anywhere else. Such is the case with a hermetically sealed refrigeration compressor motor; you can't use it if not in the compressor and the running load is supposed to always be the same. So even IF the motor were technically capable of more (as in FLC), that could only happen if something else was wrong and should be shut down anyway. For those motors then, we use RLA since that represents what the motor SHOULD be running at normally, not the amps it COULD be running at.


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## AK_sparky (Aug 13, 2013)

Ok, makes sense. In the great white north we can use nameplate ratings. Typical code wording looks like this:

_Where the full load current rating is not marked, an equivalent full load current rating shall be determined from the horsepower rating by referring to Table 44 or 45, as applicable._


So I guess the distinction never really was an issue.


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## don_resqcapt19 (Jul 18, 2010)

There are a number of people who use FLA=code current (from the tables in Article 430) and FLC = nameplate current.
The short circuit and ground fault protection device sizing and the conductor sizing is based on the "code current" while the overload protection is based on the nameplate current.


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