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Motor Control Tools

Motor Current Calculator

Estimate motor full-load current and a starting overload relay setting range from motor power, voltage, efficiency, and power factor.

Inputs
Result
14.0A FLC

Estimated motor full-load current is 14.0 A. A 115% reference gives 16.1 A.

Motor output7.50 kW
Estimated FLC14.0 A
Overload reference16.1 A
Efficiency90.0%
Next checks
  • Use motor nameplate current for final overload relay setting.
  • Select contactor by utilization category, voltage, duty, and coordination type.
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Motor current equation

This calculator estimates three-phase motor full-load current from output power, voltage, efficiency, and power factor.

Horsepower conversion
Pout = hp × 0.746
Three-phase motor current
IFLC = Pout × 1000 / (√3 × V × PF × η)
Overload reference
IOL = IFLC × Fol

where:

Pout
Motor output powerkW
hp
Motor horsepower
IFLC
Estimated motor full-load currentA
V
Line-to-line voltageV
PF
Motor power factor
η
Motor efficiency as a decimal
IOL
Overload relay current referenceA
Fol
Selected overload reference factor

Nameplate full-load current should override calculated current for final overload relay, contactor, and motor protection settings.

Assumptions

  • Three-phase motor
  • Nameplate data is not available
  • Overload setting is a starting reference only

Important Warnings

  • Motor protection settings must follow the motor nameplate, starter type, duty, and applicable standard.
  • Starting current, utilization category, and coordination are not selected here.

FAQ

Can this select a contactor size?

It provides a current estimate. Contactor selection also needs utilization category, voltage, duty, and coordination requirements.

Should overload relay setting equal breaker size?

No. Overload protection and short-circuit protection have different jobs and are selected differently.

Next calculators

Continue the selection workflow.