Three-Phase Electrical Power Calculator
Translate measured average line-to-line voltage and line current into balanced three-phase apparent power, real input power, and an efficiency-adjusted output estimate.
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View all saved project estimatesWhat does the three phase electrical power calculation calculate?
Enter average line-to-line voltage, average line current, measured power factor, and equipment efficiency. The calculator estimates balanced three-phase apparent power in kVA, real electrical input in kW, efficiency-adjusted output kW, and horsepower. It does not evaluate phase unbalance, harmonics, motor starting, conductor size, protection, or equipment suitability.
Balanced three-phase apparent and real power
The square-root-of-three factor relates line quantities in a balanced three-phase system. Power factor converts apparent power to real electrical input, while efficiency estimates useful output. The formula is a steady-state balanced model and cannot diagnose unbalance, harmonics, transients, wiring, protection, or motor performance.
How to measure for an accurate estimate
- Use a qualified person and appropriately rated instruments to obtain line-to-line voltage, current, power factor, and operating condition data safely.
- Average all three phase-to-phase voltages and all three line currents only after recording the individual values and checking whether unbalance is acceptable.
- Use measured power factor and efficiency when possible; nameplate or generic assumptions can materially change output estimates.
- Record whether measurements represent steady load, startup, unloaded operation, full load, or a changing process before interpreting the result.
Balanced 480-volt motor input estimate
A balanced planning measurement averages 480 volts line to line and 20 amperes. Measured power factor is 85%, and the motor's operating efficiency is estimated at 90% for the observed condition.
The model gives about 16.63 kVA and 14.13 kW real electrical input. After the efficiency assumption, estimated output is about 12.72 kW or 17.1 horsepower.Before you purchase material
- Do not select motors, conductors, breakers, starters, drives, transformers, capacitors, or generators from this power conversion alone.
- Check equipment nameplates, manufacturer curves, duty, service factor, temperature, altitude, enclosure, starting method, harmonics, and load profile.
- Have a qualified professional evaluate phase unbalance, protection, available fault current, coordination, grounding, and the adopted electrical requirements.
- Measure and trend real equipment under representative conditions before relying on an efficiency or power-factor improvement estimate.
Common questions
Why does three-phase power use the square root of three?
In a balanced three-phase system, the relationship between line and phase quantities introduces a square-root-of-three multiplier when power is expressed using line-to-line voltage and line current. Different voltage/current definitions or unbalanced systems require the appropriate phase-by-phase method.
What is the difference between kVA and kW?
kVA is apparent power based on voltage and current, while kW is real power doing useful electrical work. Multiplying balanced three-phase kVA by power factor estimates real input kW. Reactive power and distortion can make apparent power larger than real power.
Can the calculator determine motor horsepower from the nameplate?
It estimates output horsepower only when the entered voltage, current, power factor, and efficiency represent the operating condition. Nameplate values describe ratings, not necessarily current shaft output. Direct testing and manufacturer performance information provide better evidence for changing loads.
Does averaging the three phases hide electrical problems?
It can. The balanced formula is useful only after individual phase voltages and currents have been recorded and unbalance, harmonics, and waveform quality have been evaluated. Large differences should be investigated with qualified personnel and appropriate power-quality instruments.
Sources and reference standards
- Eaton — Power factor correction guideManufacturer engineering guide documenting real power, apparent power, power factor, and balanced three-phase kW and kVA equations.
- Fluke — Determining three-phase load horsepowerTest-equipment manufacturer guidance relating measured line voltage, current, efficiency, power factor, three-phase power, and horsepower.
- NFPA 70 — National Electrical Code developmentOfficial NFPA information for the model electrical code used by adopting jurisdictions; the locally adopted edition and amendments control an installation.
See every citation and the calculators that use it in the calculator source index.
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