How is a compressor's rated load amp rating, RLA, determined?

How is a compressor's rated load amp rating, RLA, determined?

• A. It is the compressor's maximum continuous current rating divided by 1.56.
• B. It is the maximum starting current divided by 2.
• C. It is the running current multiplied by 1.2.
• D. It is the sum of current across all windings.

Answer: (A)

At full load, the compressor’s current draw under normal operation is the Rated Load Amps (RLA). This value is used to size protection and controls so the motor isn’t tripped during normal running but will trip if overheating or overload occurs. The method shown—taking the maximum continuous current rating and dividing by 1.56—provides a conservative way to derive the RLA, reflecting heat limits and design tolerances of the motor. It translates the motor’s continuous-current capability into a practical running-current value for routine operation and protection. Starting current is much higher than running current, so using the starting current (or a simple division of it) isn’t the right way to determine RLA. The running current isn’t simply a fixed multiple of the current (dividing by 2 or multiplying by 1.2), and RLA isn’t the sum of currents in all windings, since the motor’s line current is a single value during operation.

At full load, the compressor’s current draw under normal operation is the Rated Load Amps (RLA). This value is used to size protection and controls so the motor isn’t tripped during normal running but will trip if overheating or overload occurs. The method shown—taking the maximum continuous current rating and dividing by 1.56—provides a conservative way to derive the RLA, reflecting heat limits and design tolerances of the motor. It translates the motor’s continuous-current capability into a practical running-current value for routine operation and protection.

Starting current is much higher than running current, so using the starting current (or a simple division of it) isn’t the right way to determine RLA. The running current isn’t simply a fixed multiple of the current (dividing by 2 or multiplying by 1.2), and RLA isn’t the sum of currents in all windings, since the motor’s line current is a single value during operation.