Cable sizing form
Example data table
| Case | System | Voltage | Load / Current | Length | Material | Limit | Suggested Size |
|---|---|---|---|---|---|---|---|
| Workshop feeder | Three phase | 400 V | 25 kW | 45 m | Copper XLPE | 3% | 16 mm² |
| Small pump | Single phase | 230 V | 28 A | 32 m | Copper PVC | 4% | 10 mm² |
| Solar DC run | DC | 120 V | 38 A | 22 m | Copper XLPE | 2% | 16 mm² |
| Aluminum submain | Three phase | 400 V | 72 A | 65 m | Aluminum XLPE | 3% | 35 mm² |
Formula used
1) Current from power
Single phase AC: I = (P × 1000) / (V × PF × η)
Three phase AC: I = (P × 1000) / (√3 × V × PF × η)
DC: I = (P × 1000) / (V × η)
2) Design current with margin
Idesign = Iload × (1 + margin%)
3) Adjusted ampacity
Ampacityadj = Base ampacity × Ambient factor × Grouping factor
4) Operating conductor resistance
R = (ρ × 1000 / Area) × [1 + α × (T - 20)]
5) Voltage drop
Single phase / DC: ΔV = 2 × I × L × R
Three phase AC: ΔV = √3 × I × L × R
The recommended conductor is the smallest listed standard size that satisfies both adjusted ampacity and the chosen voltage-drop limit. Use this as a preliminary engineering estimate and confirm against applicable local standards, installation rules, protection settings, fault level, and manufacturer data.
How to use this calculator
- Select whether you want to size from load power or from known design current.
- Choose the system type, then enter the operating voltage.
- Enter power, or directly enter current, depending on the selected mode.
- Provide power factor and efficiency for AC systems when sizing from load.
- Enter one-way cable length, conductor material, insulation, and installation method.
- Set ambient temperature, grouped loaded circuits, voltage-drop limit, and design margin.
- Press Calculate cable size to display the result above the form.
- Review the summary and full size evaluation table, then export the result as CSV or PDF if needed.
FAQs
1) What does this calculator actually size?
It estimates a practical low-voltage conductor size using current demand, cable length, voltage-drop limit, conductor material, temperature, grouping, and installation assumptions.
2) Why is voltage drop important?
Excessive voltage drop can reduce equipment performance, increase heating, and cause poor motor starting or unreliable operation at the load end.
3) Why does the result change with installation method?
Different installation methods remove heat differently. Better cooling usually allows higher ampacity, which can reduce the conductor size needed.
4) Why does ambient temperature matter?
Higher surrounding temperature reduces a cable’s ability to shed heat. That lowers usable ampacity and may require a larger conductor.
5) What is the grouping factor?
When several loaded circuits are installed together, mutual heating occurs. The grouping factor derates current capacity to reflect that condition.
6) Can I use aluminum instead of copper?
Yes. Aluminum is lighter and often cheaper, but it usually needs a larger cross-sectional area than copper for similar performance.
7) Does this replace local code checks?
No. Final design should still verify code tables, protection coordination, short-circuit withstand, correction factors, and manufacturer guidance.
8) Why might the largest size still fail?
The entered route may be too long, the load too high, or the allowable voltage drop too strict. Parallel cables or revised criteria may be needed.