Calculator
Example Data Table
| Scenario | Voltage (V) | Current (A) | Length (m) | Area (mm²) | Material | PF | Temperature (°C) |
|---|---|---|---|---|---|---|---|
| Lighting Circuit | 230 | 12 | 22 | 2.5 | Copper | 0.95 | 30 |
| Small Motor Feed | 230 | 18 | 35 | 4 | Copper | 0.85 | 40 |
| Long Run Outlet Feed | 230 | 20 | 55 | 6 | Aluminum | 0.90 | 35 |
| Workshop Heater | 230 | 25 | 28 | 6 | Copper | 1.00 | 45 |
Formula Used
For a single phase circuit, the loop includes both outgoing and return conductors. The calculator uses conductor resistance, reactance, current, power factor, and temperature to estimate drop.
Temperature-adjusted resistivity:
ρT = ρ20 × (1 + α × (T − 20))
Loop resistance:
Rloop = (2 × ρT × L) / A
Loop reactance:
Xloop = 2 × x × L
Voltage drop:
Vdrop = I × (Rloop × cosφ + Xloop × sinφ)
Percentage drop:
Drop % = (Vdrop / Vs) × 100
Receiving voltage:
Vr = Vs − Vdrop
Power loss in conductors:
Ploss = I² × Rloop
Where ρ is resistivity, α is temperature coefficient, T is conductor temperature, L is one-way length, A is conductor area, x is reactance per meter, and φ is the load angle.
How to Use This Calculator
- Enter the source voltage of the circuit.
- Input the expected load current in amperes.
- Provide the one-way cable length, not the full loop length.
- Select copper, aluminum, or enter custom material values.
- Enter conductor area, operating temperature, and power factor.
- Adjust reactance when inductive loads or cable spacing matter.
- Set your allowable drop percentage target.
- Add yearly hours, load factor, and energy cost for loss estimates.
- Click the calculate button to display results above the form.
- Use the export buttons to save the results as CSV or PDF.
FAQs
1. Why does single phase voltage drop use twice the one-way length?
Current travels to the load and returns to the source. Both conductors add impedance, so the electrical loop length is twice the one-way cable distance.
2. Does conductor temperature really matter?
Yes. Higher conductor temperature raises resistance. That increases voltage drop and energy loss, especially on long runs or heavily loaded circuits.
3. When is reactance important in voltage drop?
Reactance matters more on long cable runs, larger conductors, grouped cables, and inductive loads with lower power factor. Resistive loads are affected less.
4. What drop percentage is usually acceptable?
Common design targets are around 3% for branch circuits and about 5% total feeder plus branch, depending on local code and equipment sensitivity.
5. Why does power factor change the result?
Power factor shifts how much of the cable impedance acts through resistance and reactance. Lower power factor can increase reactive voltage drop significantly.
6. Can I use this for aluminum wiring?
Yes. Select aluminum and the calculator applies a higher resistivity and temperature coefficient, which typically produces more voltage drop than copper.
7. What is the recommended minimum area value?
It estimates the conductor cross-section needed to meet your selected drop limit. Final cable sizing still needs ampacity, insulation, installation, and code checks.
8. Does this calculator replace code compliance checks?
No. It is a design aid. Always verify conductor ampacity, fault performance, temperature rating, derating factors, and local electrical code requirements.