Calculator Input
Example Data Table
| Case | Voltage (V) | Current (A) | Length (m) | R (Ω/km) | X (Ω/km) | PF | Drop (Approx. V) |
|---|---|---|---|---|---|---|---|
| Workshop Feeder | 400 | 80 | 50 | 0.20 | 0.08 | 0.90 | 1.63 |
| Pump Motor | 415 | 120 | 120 | 0.15 | 0.07 | 0.85 | 4.22 |
| HVAC Branch | 400 | 60 | 90 | 0.32 | 0.09 | 0.95 | 3.20 |
| Panel Extension | 380 | 45 | 150 | 0.38 | 0.10 | 0.88 | 4.97 |
Formula Used
For a balanced three phase circuit, the line voltage drop is estimated with:
Voltage Drop = √3 × I × L × (R × cosφ ± X × sinφ)
Use the plus sign for lagging power factor loads and the minus sign for leading power factor loads. In this calculator, cable length is converted to kilometers before applying the formula when needed.
Where:
- I = line current
- L = one way route length
- R = conductor resistance per kilometer
- X = conductor reactance per kilometer
- cosφ = power factor
- sinφ = √(1 − power factor²)
The percentage drop is:
Percentage Drop = (Voltage Drop ÷ System Voltage) × 100
How to Use This Calculator
- Enter a load name for reporting and exports.
- Type the system line voltage in volts.
- Enter the expected line current in amperes.
- Provide the one way cable length and choose meters or kilometers.
- Enter conductor resistance and reactance values.
- Select whether those impedance values are per meter or per kilometer.
- Enter the load power factor and choose lagging or leading.
- Press calculate to show voltage drop above the form.
- Use the export buttons to save the calculation summary.
About This 3 Phase Voltage Drop Calculator
This calculator helps engineers estimate voltage reduction along a balanced three phase feeder. It combines load current, cable route length, conductor resistance, conductor reactance, and power factor to produce a practical design estimate.
Voltage drop matters because excessive loss can reduce motor torque, dim lighting, upset control circuits, and lower equipment efficiency. Many design checks compare calculated percentage drop against project limits before finalizing conductor size and feeder length.
The tool supports lagging and leading power factor conditions. That is useful when working with motors, drives, capacitor supported systems, or mixed plant loads. It also converts impedance values entered per meter into per kilometer values automatically.
Results include voltage drop in volts, percentage drop, receiving end voltage, estimated line loss, and real power. The graph shows how voltage drop rises with loading, which makes quick design reviews easier.
Use this as an engineering estimation tool during planning, troubleshooting, and feeder comparisons. Final designs should still be checked against local standards, cable data sheets, installation conditions, temperature correction factors, and harmonic or starting current requirements.
FAQs
1. What does this calculator estimate?
It estimates line voltage drop for a balanced three phase circuit using current, one way length, resistance, reactance, and power factor. It also shows percentage drop, receiving voltage, line loss, and a load trend graph.
2. Why is one way cable length used?
Three phase voltage drop formulas commonly use one way route length because the impedance term already represents the line path correctly for the balanced circuit model. Enter the physical feeder route, not a doubled return length.
3. When should I use lagging or leading power factor?
Choose lagging for most motor and inductive loads. Choose leading when capacitor support or overcorrection makes current lead voltage. The sign before the reactance term changes and affects the final drop estimate.
4. Can I enter impedance values per meter?
Yes. The calculator accepts resistance and reactance per meter or per kilometer. It converts per meter values internally so the main engineering formula stays consistent and the result remains easy to verify.
5. Is this result suitable for final construction approval?
It is best used for design estimation and comparison. Final approval should also consider code limits, installation method, conductor temperature, harmonics, starting conditions, grouping factors, and manufacturer cable data.
6. Why does power factor change voltage drop?
Power factor changes the relationship between the resistance and reactance parts of line impedance. Lower power factor increases the reactive component effect, which often raises the calculated voltage drop in practical feeders.
7. What is an acceptable percentage drop?
Acceptable limits depend on your design standard, utility rules, and equipment sensitivity. Many projects aim to keep feeder and branch circuit voltage drop within defined planning limits to protect performance and reliability.
8. Does the graph use different cable lengths?
No. The graph keeps the same entered feeder data and changes load from ten percent to full load. It helps visualize how voltage drop increases as current rises for the selected circuit conditions.