VALICALC · ENGINEERING WORKFLOW
Three-phase motor power and current check
Separate shaft output, real input power, apparent power and running current for a balanced three-phase motor; carry a checked current into a cable calculation.
Start this workflowWhat do I need to know first?
- Shaft rating, line-to-line voltage, efficiency and power factor
- Measured line current if checking an operating motor
- Whether the load is balanced and which power value was measured
Goal and model boundaries
Reconcile motor kW/HP, efficiency and power factor with a balanced three-phase operating current and power budget.
- The model assumes a balanced sinusoidal system; it does not diagnose phase imbalance or harmonics.
- Current scenarios are conditional estimates, not a regulatory full-load current table.
Keep shaft and input power separate
Convert the nameplate unit and enter the operating η and PF.
Pinput = Pshaft / η; I = Pinput / (√3 × VLL × PF).
- Expected output
- Estimated running current and real input power.
- Next step
- Use the electrical power tool to compare measured current with the estimate.
Reconcile measured electrical power
Use measured voltage/current with the stated PF.
P = √3 × VLL × I × PF; apparent power excludes PF.
- Expected output
- Real power, kVA and reactive-power estimate for the balanced model.
- Next step
- Investigate inconsistent nameplate or measured assumptions before sizing the cable.
Carry the checked current onward
Enter the confirmed operating current, candidate conductor and run.
A resistive steady-state cable model checks drop; motor starting requires separate data.
- Expected output
- A running voltage-drop estimate.
- Next step
- Use the motor cable workflow for conductor lookup and an explicit independent ampacity review.
Units and context
- For three phase, enter VLL, not phase-to-neutral voltage.
- kW measures real power; kVA is apparent power. HP here is mechanical horsepower.
Common mistakes to avoid
- Confusing power factor with efficiency
- Using single-phase equations for a three-phase supply
- Applying a capacitor correction without a harmonic/resonance assessment
Related engineering jobs
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