Enter System Details
Select one source method. Use line-to-line voltage for the three-phase supply.
Example Data Table
| Input or Output | Example Value | Explanation |
|---|---|---|
| Source voltage | 400 V line-to-line | Balanced three-phase supply voltage. |
| Source line current | 12 A | Measured or rated current on each line. |
| Source power factor | 0.86 | Used to calculate real source power. |
| Efficiency and usable share | 90% and 80% | Allows for losses and shared capacity. |
| Estimated source power | 7.15 kW | √3 × 400 × 12 × 0.86 ÷ 1000. |
| Planned single-phase equivalent | 5.15 kW | 7.15 × 0.90 × 0.80. |
| 230 V load current at 0.90 factor | 24.9 A | 5.15 kW ÷ (230 V × 0.90). |
Formula Used
The tool uses balanced three-phase relationships. Enter source voltage as line-to-line voltage.
When a known three-phase power value is entered, the calculator estimates line current with this relationship.
It applies efficiency and planned source allocation to estimate usable single-phase real power.
Finally, it finds expected single-phase current from target voltage and target power factor.
Efficiency and utilization are converted from percentages to decimal factors. The breaker suggestion is the next listed standard size above the design current.
How to Use This Calculator
- Select the source data you have available.
- Enter the three-phase line-to-line voltage.
- Enter line current or known three-phase real power.
- Add realistic source and output power factors.
- Set efficiency for expected conversion and wiring losses.
- Set usable source share for the intended load.
- Choose target single-phase voltage and load type.
- Calculate, then compare capacity, current, and protection guidance.
Important Electrical Safety Note
A capacity estimate does not replace a proper phase converter, transformer, variable-speed drive, or redesigned distribution system. Follow local electrical rules and have a qualified professional verify final equipment, conductor, and protection choices.
Planning Three-Phase Capacity for a Single-Phase Load
Three-phase systems move power efficiently across motors, pumps, and heaters. They use three voltage waveforms that are spaced evenly through the cycle. This arrangement gives smoother power delivery than a comparable single-phase supply. However, a three-phase rating does not become single-phase power through a wiring change. The result is an equivalent capacity estimate. A rated converter, transformer, drive, or redesigned circuit may still be required.
The calculator begins with the three-phase source power. For current-based entries, it uses line-to-line voltage, line current, and source power factor. The square root of three connects those values in a balanced three-phase system. For a known power entry, the calculator can estimate the required line current instead. Both paths produce a source real-power figure in kilowatts. Real power represents useful electrical work. Apparent power, shown in kVA, includes the effect of power factor.
Next, the tool applies efficiency and utilization. Efficiency accounts for losses in conversion equipment, wiring, or associated devices. Utilization limits the share of source capacity intended for the target load. A lower utilization value creates a conservative result. This is often useful when the source also serves other equipment. The remaining figure is the estimated single-phase power that can be planned. It is not an approval for connecting a three-phase circuit directly to a single-phase appliance.
The selected single-phase voltage and power factor determine current. A lower voltage requires more current for the same kilowatt load. A lower power factor also increases current. Higher current affects cable size, breaker ratings, switchgear, and voltage drop. The calculator applies a continuous-load allowance when selected. It then suggests the next common protective-device size. That size is only a planning reference. Local codes, conductor ratings, ambient temperature, installation method, and equipment instructions can change the final selection.
Use measured values whenever possible. Nameplate figures can be useful, but they may describe maximum rather than normal operation. Check whether voltage is line-to-line or line-to-neutral before entering it. The source-voltage field expects line-to-line voltage. Enter a realistic power factor. Resistive heaters often operate near one. Motors and inductive devices can operate lower, especially at light load. Use the single-phase power factor for the intended output load, not automatically the source value.
Balanced loading is an important assumption. Large differences between phases can cause overheating, poor regulation, or unexpected protection trips. This calculator uses a balanced three-phase relationship. It cannot diagnose imbalance, harmonic distortion, starting current, or transient conditions. Motors may require much higher current during starting. Variable-speed drives and electronic converters may add harmonic current. Consider those effects before purchasing components.
Review the result as a capacity-planning number. Compare the available single-phase kilowatts with the actual equipment demand. Leave margin for future expansion and startup conditions. Consult a qualified electrician or electrical engineer before modifying distribution equipment. Verify grounding, earthing, overcurrent protection, isolation, and local regulations. Good calculations support safer decisions. Design and installation complete the job.
Frequently Asked Questions
1. Can three-phase power become single-phase power directly?
No. This calculator estimates comparable usable capacity. Direct conversion usually needs suitable equipment, such as a transformer, converter, or drive. A qualified professional should confirm the method and protection requirements.
2. Why does the formula use the square root of three?
Balanced three-phase systems have phase voltages separated by 120 degrees. The square-root-of-three factor links line-to-line voltage, line current, and real power in that arrangement.
3. What voltage should I enter for the three-phase supply?
Enter line-to-line voltage. Common examples include 400 V, 415 V, and 480 V. Do not enter line-to-neutral voltage in this source-voltage field.
4. What does utilization mean here?
Utilization is the portion of available source capacity planned for the target load. Lowering it preserves capacity for other loads, uncertainty, or future expansion.
5. Why are efficiency losses included?
Transformers, converters, conductors, and related equipment can lose power as heat. Efficiency reduces the source power to a more realistic usable planning figure.
6. Is the breaker suggestion a final electrical design?
No. It is a planning reference based on calculated current and an optional continuous-load allowance. Final protection depends on local rules, conductor ratings, equipment instructions, and installation conditions.
7. What is the difference between kW and kVA?
kW measures real power that performs work. kVA measures apparent power. Power factor connects them. Lower power factor means more kVA and current for the same kW.
8. Can I use the same power factor for both sides?
You can when the intended load behaves similarly. However, source and target loads may differ. Use separate values when better information is available.
9. Does this calculator account for motor starting current?
No. Motor starting current can be much higher than running current. Review starting method, drive settings, voltage drop, and protection coordination separately.
10. Can I calculate from a known three-phase kW value?
Yes. Select the known-power method. The calculator uses the kW value as source real power and estimates line current from voltage and source power factor.
11. What assumptions can make the result less accurate?
Unbalanced phases, harmonics, inaccurate power factor, overload conditions, starting currents, voltage drop, and uncertain efficiency can all affect actual performance. Use measured values where possible.