If the maximum continuous current rating is 20 A, what is the approximate RLA?

• A. 12.8 A
• B. 20 A
• C. 16 A
• D. 9.5 A

Answer: (A)

RLA, or Running Load Amperage, is the actual current the motor draws while running under normal load. It depends on how much electrical power goes into useful output, which in turn depends on the motor’s efficiency and its power factor. A useful way to estimate RLA is to relate it to the maximum continuous current rating (MCCR) by the factors that convert electrical input to useful work: efficiency and power factor. Roughly, I ≈ P_out/(V × pf) and P_out ≈ η × P_in, so I ≈ (η × P_in)/(V × pf) and, when comparing to a given rating, RLA ≈ MCCR × η × pf.

Using typical values (efficiency around 0.8 and power factor around 0.8) gives η × pf ≈ 0.64. Therefore, with a maximum continuous current rating of 20 A, the approximate running current is about 20 × 0.64 ≈ 12.8 A.

So the expected RLA is roughly 12.8 A. If the motor’s actual efficiency or power factor differ, the RLA will scale accordingly.