Calculation Result
Advanced Three Phase Voltage Drop Calculator
Example Data Table
These examples show common three phase feeder cases. Values are for planning only.
| Case | Voltage | Current | Length | Material | Size | Power Factor | Typical Use |
|---|---|---|---|---|---|---|---|
| Small Motor | 415 V | 35 A | 45 m | Copper | 8 AWG | 0.86 | Pump feeder |
| Workshop Feeder | 400 V | 80 A | 75 m | Copper | 2 AWG | 0.85 | Panel supply |
| Long Run | 480 V | 160 A | 130 m | Aluminum | 4/0 AWG | 0.90 | Remote equipment |
Formula Used
For a balanced three phase circuit, this calculator uses:
Voltage Drop = √3 × I × L × (R × cosφ + X × sinφ)
Here, I is load current in amperes. L is one way cable length in kilometers.
R is conductor resistance in ohms per kilometer. X is reactance in ohms per kilometer.
cosφ is the power factor. sinφ is calculated from the power factor.
Resistance is corrected for temperature:
RT = R20 × [1 + α × (T - 20)]
Copper uses an alpha value of 0.00393. Aluminum uses 0.00403.
Parallel runs divide resistance and reactance by the number of conductors per phase.
How to Use This Calculator
- Enter the line to line voltage of the three phase system.
- Add the expected load current in amperes.
- Enter the one way cable distance from source to load.
- Select the conductor material and conductor size.
- Adjust power factor, reactance, temperature, and parallel runs.
- Enter the allowable voltage drop percentage for comparison.
- Press the calculate button to view drop, loss, and recommendations.
- Download the CSV or PDF file for project records.
Three Phase Voltage Drop Guide
Why Voltage Drop Matters
Voltage drop is the reduction of voltage along a cable run. It happens because every conductor has resistance. Long feeders, high current, and small cables increase this drop. In a three phase system, voltage drop can affect motors, panels, pumps, compressors, and lighting circuits. Low voltage may create overheating, poor torque, dim light, or nuisance tripping.
Important Design Inputs
A good calculation needs more than current and distance. Conductor material, power factor, reactance, cable temperature, and parallel runs also matter. Copper normally has lower resistance than aluminum. A higher power factor usually reduces the resistive part of voltage drop. Reactance becomes more important on larger conductors and longer feeders.
Using Results Correctly
The percent drop shows how much voltage is lost compared with the supply voltage. Many designers aim for low values on feeders and branch circuits. Sensitive equipment may need a stricter limit. Motors may need special attention because starting current is much higher than running current. The calculator gives a planning result, not a final code ruling.
Cable Selection Tips
If the drop is too high, increase conductor size first. You can also shorten the route, use parallel conductors, improve power factor, or raise the distribution voltage where allowed. Always check ampacity, insulation rating, termination limits, ambient temperature, conduit fill, and local electrical rules. A safe design needs both voltage drop control and thermal protection.
Professional Review
This calculator helps compare options quickly. It is useful during estimates, maintenance checks, and early design work. Final installations should be reviewed by a qualified electrical professional. Real projects may include harmonics, unbalanced loads, derating, transformer impedance, motor starting, and local inspection requirements.
FAQs
1. What is three phase voltage drop?
It is the voltage lost as current flows through three phase conductors. Resistance and reactance cause the loss. Longer cable runs and higher current usually create greater voltage drop.
2. Why does this calculator use √3?
Three phase line voltage relationships include the square root of three. The formula uses √3 because the calculation is based on line to line voltage in a balanced three phase system.
3. Is cable length one way or round trip?
Use one way distance from the source to the load. The three phase formula already handles the phase relationship. Do not double the distance for this calculator.
4. What is an acceptable voltage drop?
Many designs target about three percent for branch circuits or feeders. Some projects use tighter or wider limits. Always follow the electrical rules and project specifications for your location.
5. Does power factor affect voltage drop?
Yes. Power factor changes the balance between resistance and reactance effects. A lower power factor can increase voltage drop, especially on motor loads and long cable runs.
6. Why is conductor temperature included?
Conductor resistance rises as temperature increases. A hot cable has more resistance than the same cable at room temperature. This can increase voltage drop and power loss.
7. Can this calculator size a cable completely?
No. It estimates voltage drop and related values. Final cable sizing must also check ampacity, protection, installation method, derating, insulation rating, and local electrical requirements.
8. What can reduce voltage drop?
Use a larger conductor, shorten the cable route, use parallel conductors, improve power factor, or select a higher system voltage where suitable. Each option must be checked for safety.