Calculator Inputs
Example Data Table
| Scenario | System | Voltage | Current | Length | Material | Size | Drop % |
|---|---|---|---|---|---|---|---|
| Temporary tower crane feeder | Three phase | 400 V | 125 A | 85 m | Copper | 70 mm² | 1.32% |
| Portable site office board | Single phase | 230 V | 52 A | 60 m | Copper | 25 mm² | 2.41% |
| Remote dewatering pump | Three phase | 415 V | 94 A | 180 m | Aluminum | 95 mm² | 3.27% |
Formula Used
Temperature-adjusted resistance: RT = R20 × (1 + α × (T - 20))
Base resistance per kilometre: R20 = (ρ × 1000) / A
Single phase AC drop: Vd = 2 × I × L × (R × cosφ + X × sinφ)
Three phase AC drop: Vd = √3 × I × L × (R × cosφ + X × sinφ)
DC two-wire drop: Vd = 2 × I × L × R
Drop percentage: % Drop = (Vd / Vs) × 100
Receiving voltage: Vr = Vs - Vd
In this calculator, L is one-way feeder length expressed through the effective one-way impedance. Parallel runs divide resistance and reactance, lowering the calculated drop.
How to Use This Calculator
- Choose the system type to match the feeder arrangement.
- Pick current mode or power mode for the load entry method.
- Enter supply voltage, feeder length, conductor size, and material.
- Add power factor, reactance, temperature, and parallel run count.
- Set the allowable voltage drop limit for the project requirement.
- Submit the form to show the result above the calculator.
- Review the voltage drop, receiving voltage, loss, and compliance status.
- Use the export buttons to save a CSV summary or PDF report.
Frequently Asked Questions
1. Why is voltage drop important on construction sites?
High voltage drop can reduce equipment performance, increase motor heating, and cause nuisance trips. Temporary and remote site feeders often become long enough for drop to matter.
2. When should I use the power entry mode?
Use power mode when you know the connected kilowatt demand but not the feeder current. The calculator converts power into current using the selected system voltage and power factor.
3. Does conductor temperature really change the result?
Yes. Resistance rises as conductor temperature increases. A hot cable produces more voltage drop than the same cable at 20°C, so temperature adjustment improves design realism.
4. Why does the tool ask for reactance?
AC feeders have both resistance and reactance. Reactance matters more on longer circuits, larger conductors, and lower power factors. For DC systems, the reactance term is ignored.
5. What do parallel runs change?
Parallel runs split current across multiple conductors and reduce effective impedance. That lowers voltage drop and conductor losses when the runs are equal in size and length.
6. What allowable drop should I enter?
Enter the design limit required by your project specification or electrical code practice. Many designers check around 3% for feeders, but local requirements may differ.
7. Is this tool suitable for final code approval?
It is a practical design aid, not a substitute for full engineering review. Final selections should still be checked against local codes, installation conditions, and manufacturer data.
8. Can I use this for aluminum feeders?
Yes. Select aluminum from the material list. The calculator applies a different resistivity and temperature coefficient, which usually produces a larger drop than copper at equal size.