Calculator Inputs
Enter circuit details, conductor data, and operating assumptions. The calculator estimates voltage drop, percent drop, resistance, power loss, and delivery efficiency.
Example data table
Use this sample to understand how the inputs relate to the calculated output.
| System | Voltage (V) | Current (A) | Length (m) | Material | Area (mm²) | PF | Estimated Drop (%) |
|---|---|---|---|---|---|---|---|
| Three Phase AC | 415 | 85 | 65 | Copper | 25 | 0.90 | 1.64 |
| Single Phase AC | 230 | 42 | 45 | Aluminum | 16 | 0.88 | 2.91 |
| DC | 48 | 30 | 20 | Copper | 10 | 1.00 | 1.02 |
Formula used
The calculator models conductor resistance at the selected temperature, then applies the correct circuit multiplier for DC, single phase AC, or three phase AC.
1. Temperature adjusted resistance
Rper km = [ρ20 × (1 + α × (T − 20)) × 1000] ÷ [A × n]
Where ρ20 is resistivity at 20°C, α is the temperature coefficient, T is conductor temperature, A is area, and n is parallel runs.
2. Total resistance and reactance
R = Rper km × Lkm
X = Xper km × Lkm ÷ n
3. Voltage drop
DC: Vdrop = 2 × I × R
Single phase AC: Vdrop = 2 × I × (R × pf + X × sinφ)
Three phase AC: Vdrop = √3 × I × (R × pf + X × sinφ)
4. Supporting outputs
Percent drop = (Vdrop ÷ Vsupply) × 100
Power loss = circuit factor × I² × R
Efficiency = (Delivered power ÷ Input power) × 100
How to use this calculator
- Choose the electrical system type for the circuit.
- Enter the sending voltage and expected load current.
- Provide one-way route length, conductor material, and conductor area.
- Adjust power factor, reactance, temperature, and parallel runs.
- Set your allowable voltage drop percentage target.
- Press Submit to show results above the form.
- Review percent drop, terminal voltage, loss, and sizing status.
- Use the CSV or PDF buttons to save the report.
Frequently asked questions
1. Why does cable length strongly affect voltage drop?
Longer conductors have higher resistance and reactance. That increases the voltage lost along the route, especially at higher current levels.
2. Why is the one-way length used?
The calculator uses one-way length because the circuit factor already handles the return path for DC and single phase systems.
3. Does temperature change the result?
Yes. Higher conductor temperature raises resistance. That increases voltage drop and power loss, so hot cables usually perform worse.
4. What is a good voltage drop limit?
Many designs target around 3% for branch circuits and about 5% overall. Actual limits depend on local codes and equipment sensitivity.
5. Why does power factor matter in AC circuits?
Power factor changes the relationship between resistive and reactive components. Poorer power factor can increase calculated AC voltage drop.
6. What do parallel runs do?
Parallel runs share current across multiple conductors. That lowers effective resistance and reactance, reducing drop and thermal stress.
7. Can I use this for aluminum cables?
Yes. Select aluminum in the material field. The calculator applies higher resistivity than copper, which usually gives more drop.
8. Does this replace electrical code verification?
No. It is a design aid. Final conductor selection should still be checked against code, insulation rating, ampacity, and installation conditions.