MOTORS · CALCULATOR

Motor service factor calculator

Free motor service factor calculator: get service factor current from current, rated output, nameplate service factor and verified overload multiplier.

Written by Chameera Sampath · Not yet reviewed by a licensed electrician. See the methodology.

US (NEC) only · NFPA 70 / NEC — locally adopted editionDefaults are US values. Verify the locally adopted NEC edition and project data.Official reference ↗

Project inputs

Measurements

Current

Rated output

Nameplate service factor

Verified overload multiplier

Updates as inputs change. Unit changes preserve the same physical values.

THE MATH BEHIND THE ANSWER

Method & assumptions

ISF = I × SF; hpSF = hp × SF

SF is a nameplate operating allowance, not a universal overload setting. Verify motor temperature rise, code and manufacturer.

Results do not check every aspect of an electrical installation. The calculators follow US (NEC) practice only; a regional preset changes defaults such as voltage and units, and no result certifies NEC compliance.

Sources and validation →

Worked example

Current: 20 A · Rated output: 10 hp · Nameplate service factor: 1.15 · Verified overload multiplier: 1.25

Service factor current: 23 A · Service factor output: 11.5 hp · Overload arithmetic: 25 A

This example uses the stated inputs; results for the entered values appear above.

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