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SESK: Stuff Everyone Should Know · sesk.info/elec-motor-overload-125

A motor with a 1.15 or higher service factor can have overload protection sized to what maximum percent of nameplate current?

125% for service factor 1.15 or more, 115% for others.

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  1. 125% ✔
  2. 100%
  3. 150%

Why: Section 430.32 allows up to 125% for motors with a service factor of 1.15 or more or a temperature rise of 40C or less. Other motors are limited to 115%.

Huh, didn't know that: The overload is sized from the nameplate current, not the table full-load current.

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Why did the overload stay cool? It knew when to trip.
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References

Answer: 125%. Section 430.32 allows up to 125% for motors with a service factor of 1.15 or more or a temperature rise of 40C or less. Other motors are limited to 115%.

  1. EC&M: Motor Calculations Part 1 www.ecmweb.com/design/article/20897071/motor-calculations-part-1-motors-and-branch-circuit-conductors
    must have an overload protection device sized no more than 125% of the motor nameplate current rating.
    Checked 2026-10-10.

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