Enter Load Details
Use measured values whenever available. All current fields are line-current readings.
Formula Used
Iavg = (IA + IB + IC) / 3
S = √3 × VLL × Iavg
Pinput = S × PF
Q = √(S² − Pinput²)
Poutput = Pinput × Efficiency
Pdemand = Pinput × Demand Factor
S is apparent power in volt-amperes. P is real power in watts. Q is reactive power in vars. Efficiency and demand factor are entered as percentages.
How to Use This Calculator
- Select the wiring description that matches the installation.
- Confirm the line-to-line voltage. Use 208 volts for a nominal 208 volt supply.
- Enter the measured current from each phase conductor.
- Enter the documented power factor for the connected load.
- Use 100 percent efficiency for simple resistance loads.
- Enter a demand factor only when estimating coincident operating load.
- Add operating hours and the energy rate for energy estimates.
- Review imbalance before relying on the balanced-load estimate.
- Use the CSV or PDF button after calculating the result.
Example Data
| Input | Example value | Purpose |
|---|---|---|
| Line-to-line voltage | 208 V | Nominal three phase supply voltage |
| Line currents | 10 A, 10 A, 10 A | Balanced measured current readings |
| Power factor | 0.90 | Converts apparent power into real input watts |
| Efficiency | 92% | Estimates useful output power |
| Demand factor | 100% | Uses the full calculated input demand |
Understanding 208 Volt Three Phase Power
A 208 volt three phase supply is common in commercial buildings. It powers motors, pumps, compressors, heaters, panels, and production equipment. The system uses three voltage waveforms separated by 120 electrical degrees. This arrangement delivers power more smoothly than a comparable single phase supply. It also supports compact motors and efficient distribution equipment.
Current Readings and Balance
Power calculations begin with the line to line voltage. For this calculator, the default voltage is 208 volts. Enter the current on each line when readings are available. The calculator finds the average line current. It then applies the three phase relationship. This produces an equivalent balanced-load estimate. Large current differences indicate imbalance. Investigate imbalance before selecting conductors or protective devices.
Power Factor and Efficiency
Power factor matters because current and voltage may not align. Resistive heaters often have a power factor near one. Motors, transformers, and electronic drives can have lower values. A lower power factor raises current for the same real output. It also increases apparent power. Therefore, enter a measured or documented power factor whenever possible. Guessing can produce an incorrect watt result.
Efficiency is useful for motors and driven equipment. Electrical input watts represent power delivered from the supply. Useful output watts represent mechanical or process power after losses. The efficiency setting converts input power to estimated useful output. Do not apply efficiency to a simple resistance heater. In that case, use 100 percent unless measured losses are relevant.
Demand, Energy, and Cost
Demand factor estimates expected operating demand. It is not a replacement for code-based load calculations. Use it to compare operating scenarios or diversified equipment groups. Set it to 100 percent for continuously operating equipment. A smaller factor can estimate coincident demand. Keep documentation for every assumption used during planning.
Operating hours and energy price extend the calculation. Daily energy uses demand watts and scheduled hours. Monthly energy uses thirty days as an estimate. Monthly cost multiplies energy by the selected electricity rate. Actual bills may differ because of tariffs, peak charges, and operating changes. Use measured interval data for procurement decisions.
Reading the Result Panel
The result panel lists apparent power, input watts, reactive power, useful output, and estimated demand watts. Apparent power is measured in volt-amperes. Real power is measured in watts. Reactive power is measured in vars. These values help compare breaker loading, transformer capacity, and equipment requirements. Always use the correct unit for the design decision.
Practical Limits
The calculation assumes a three phase system with a usable 208 volt line voltage. It estimates an equivalent balanced condition from the average measured line current. Nonlinear loads, severe imbalance, harmonics, and unusual wiring require more detailed analysis. Qualified electrical professionals should verify final designs. Follow local rules, equipment instructions, and safe measurement practices.
For best results, measure all three currents under normal load. Record the instrument range, date, and loading condition. Repeat readings after major equipment changes. Compare calculated watts against meter readings. That comparison improves confidence and reveals unexpected operating behavior.
Frequently Asked Questions
1. What is the basic three phase watt formula?
For a balanced load, real power equals √3 × line-to-line voltage × line current × power factor. This calculator uses the average of the three entered currents as the line current.
2. Why does the calculator use average current?
Average current creates an equivalent balanced-load estimate. It is useful when three measured line currents are close. Large differences should be investigated separately because the standard balanced formula becomes less representative.
3. Does 208 volts mean line-to-line voltage?
Usually, yes. In a 208Y/120 volt system, 208 volts is measured between phase conductors. The line-to-neutral voltage is normally 120 volts.
4. What power factor should I enter?
Use a measured value or the equipment nameplate value. Resistance heaters are often near 1.00. Motors and electronic loads can be lower, especially at light loading.
5. Should efficiency be 100 percent for a heater?
For simple electric resistance heating, 100 percent is often reasonable at the point of use. Use a lower value only when you need to represent documented equipment or process losses.
6. What does demand factor change?
Demand factor reduces the calculated real input watts to estimate expected coincident demand. It does not change the actual connected load and should not replace required electrical design methods.
7. How is reactive power calculated?
Reactive power is calculated from apparent power and real power. The calculator uses Q = √(S² − P²). The result is shown in vars.
8. Is this suitable for unbalanced loads?
It gives an equivalent balanced estimate from the average current. For strongly unbalanced, nonlinear, or harmonic-rich loads, use phase-by-phase metering and a detailed engineering review.
9. Can I use this for motor sizing?
Use it as a planning check. Final motor and conductor selection also needs starting current, duty cycle, protection settings, ambient conditions, voltage drop, and applicable requirements.
10. Why is my bill different from the estimated cost?
Actual bills can include time-based prices, demand charges, taxes, meter intervals, and changing schedules. The cost result uses a steady daily schedule and one energy rate.
11. Can the result be exported?
Yes. After entering valid values, select Download CSV or Download PDF. Each export contains the calculated voltage, current, power, energy, and cost values.