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Motor Current

Calculated nominal current and input apparent power.

Calculation inputs

Illustrative example values — replace them before any engineering decision.

Engineering results

Calculated nominal current28.3 A
Estimated electrical input power16.67 kW
Apparent power19.61 kVA

⚠ The starting method is recorded as engineering context; starting current is not estimated without manufacturer data.

Method and traceability

The power equations use motor shaft output, efficiency and power factor. Actual nameplate current remains authoritative.

Visible assumptions: copper ρ₂₀ 0.0175 and aluminium 0.0282 Ω·mm²/m; copper α 0.00393 and aluminium 0.00403/°C. Reactance, density, factors and thresholds remain editable.

Screening lists — sections: 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 150, 185, 240, 300, 400, 500, 630 mm²; breakers: 2, 4, 6, 10, 16, 20, 25, 32, 40, 50, 63, 80, 100, 125, 160, 200, 250, 315, 400, 500, 630, 800, 1000, 1250, 1600 A; transformers: 25, 50, 100, 160, 250, 315, 400, 500, 630, 800, 1000, 1250, 1600, 2000, 2500, 3150 kVA.

Final design must verify applicable IEC 60364 requirements, actual thermal conditions, short circuit, shock protection, selectivity, starting, harmonics and local rules.

IEC 60364-5-52 ↗Guide — voltage drop ↗

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Engineering reference

Three-Phase Motor Current Calculator

Estimate motor nominal current, electrical input power and apparent power from shaft output data.

Calculation method

The entered motor power is treated as output power. The engine divides by efficiency to obtain input kW, then uses voltage and power factor to calculate current and kVA.

Formulas used

  • Three phase: I = Pout × 1,000 / (√3 × V × cosφ × η)
  • Input power: Pin = Pout / η; apparent power S = Pin / cosφ

Worked example

Example: 15 kW, 400 V, 90% efficiency and cosφ 0.85 gives approximately 28.3 A.

How to interpret the result

Use the nominal-current estimate for preliminary feeder checks. Starting method is reported qualitatively because transient current depends on motor and drive data.

Common mistakes

  • Entering electrical input kW as shaft output kW.
  • Ignoring efficiency or power factor.

Scope and limitations

  • Confirm final current and starting duty from the motor nameplate and manufacturer data.

Frequently asked questions

Why is motor current higher at low power factor?

More current is required to deliver the same active power at the same voltage.

Does this calculate starting current?

No. It calculates nominal current and flags starting method for a separate equipment-specific check.

Should I use shaft or input power?

Enter shaft output power; the calculator applies the visible efficiency.