What is the three-phase current formula from kW?
For a balanced load using line-to-line voltage, I = kW × 1000 / (√3 × V × PF). Include efficiency as an additional divisor when converting motor shaft output into estimated electrical input current.
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Three-phase current, motor estimates, and power-factor formulas
A controls-engineering reference for three-phase current at 208, 240, and 480 V, motor estimates, power factor, and common formula errors.
Fully public referenceReviewed 2026-07-163 official sources
Technical orientation
For a balanced three-phase load using line-to-line voltage, real power is P = √3 × V × I × PF. Rearranging gives I = P / (√3 × V × PF). Power must be in watts, voltage must match the formula basis, and power factor must be a decimal rather than a percentage.
Motor-current calculations add another assumption because shaft power is mechanical output. Estimated electrical input is output power divided by efficiency, and current then depends on voltage and power factor. Nameplate current and applicable electrical requirements remain authoritative for equipment selection.
The formula is useful as a reasonableness check: for the same real power and power factor, current falls as voltage rises. If a 480 V result is approximately double the 240 V result, the voltage or formula direction is probably wrong.
Original public reference
Diagram and comparison table
Use this as a screening reference. Confirm the installed equipment, configuration, and site requirements before making a field change.
Real power
P in watts
÷
Three-phase divisor
√3 × V × PF
=
Line current
I in amperes
| Example load | Voltage | Power factor | Estimated current |
|---|---|---|---|
| 30 kW balanced load | 208 V | 0.90 | 92.5 A |
| 30 kW balanced load | 240 V | 0.90 | 80.2 A |
| 30 kW balanced load | 480 V | 0.90 | 40.1 A |
Use line-to-line voltage with the complete balanced three-phase formula.
Convert kW to W and percentages such as 90% to decimals such as 0.90 before calculating.
For motor estimates, divide mechanical output by efficiency before applying voltage and power factor.
Treat calculated current as an estimate; use nameplate and applicable code or engineering requirements for design decisions.
Supporting guides
Continue into the detailed procedures
Electrical
Three-phase current examples at 208, 240, and 480 volts
Use line-to-line voltage, real power, efficiency, and power factor consistently when comparing three-phase current at common industrial system voltages.
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Electrical
Three-phase motor current estimation
Estimate motor input current from horsepower or kilowatts while keeping efficiency, power factor, rated voltage, nameplate current, and code sizing tables in their proper roles.
Open public example and Pro guide
Electrical
Three-phase power-factor cautions
Keep real power, reactive power, apparent power, displacement power factor, and nonlinear-load distortion distinct when estimating three-phase current or correction needs.
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Electrical
Common three-phase formula mistakes
Catch phase-count, voltage-basis, unit, power-factor, efficiency, and load-model mistakes before a three-phase calculator result reaches a design or troubleshooting decision.
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Common questions
Why is current lower at 480 V than at 208 V?
For the same real power and power factor, current is inversely proportional to voltage. A higher line-to-line voltage delivers the same power with less line current.
Can calculated motor current replace the nameplate value?
No. The estimate is useful for screening and troubleshooting. Final conductor, protection, starter, transformer, and generator decisions require the actual nameplate and applicable electrical requirements.