High Voltage Cable Sizing Calculator
Estimate the minimum conductor cross-section for a three-phase high-voltage feeder based on its allowable voltage-drop limit. Enter the load current, line voltage, run length and the percentage drop you can accept, and the tool returns the smallest copper/aluminium area that keeps the drop within budget.
Enter Values
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter the balanced three-phase load current in amps and the nominal line voltage in kilovolts.
- Enter the one-way cable run length in metres and the maximum voltage drop you allow as a percentage of line voltage.
- Optionally override the conductor resistivity (default 0.0225 Ω·mm²/m for aluminium; use about 0.0175 for copper) to read off the required cross-section.
How it works
The allowable drop in volts is the percentage limit applied to the line voltage (Vd = %/100 × kV × 1000). For a balanced three-phase circuit the drop is √3 × ρ × L × I ÷ CSA, so rearranging for area gives CSA = (√3 × ρ × L × I) ÷ Vd. Larger current, longer runs or tighter drop limits all push the required conductor size up.
Worked example
Worked example. A 100 A load on an 11 kV feeder run 500 m with a 2.5% drop limit: Vd = 2.5% × 11,000 = 275 V, so CSA = (√3 × 0.0225 × 500 × 100) ÷ 275 ≈ 7.09 mm². The next standard size up would be selected.
Common mistakes
- Sizing on voltage drop alone — HV cable choice is usually set by continuous thermal rating and short-circuit withstand, which often demand a much larger conductor.
- Entering the phase voltage instead of the line (phase-to-phase) voltage, or forgetting that the input is in kV not V.
- Using copper resistivity for an aluminium cable (or vice-versa); the resistivity default is aluminium.
Frequently asked questions
Is voltage drop the only thing that sizes an HV cable?
No. In practice the continuous current (thermal) rating, short-circuit withstand and screen/earth-fault current usually govern HV cable selection. This tool gives the minimum area for voltage drop; take the largest area from all the checks.
What resistivity should I use?
About 0.0225 Ω·mm²/m for aluminium and 0.0175 Ω·mm²/m for copper at operating temperature. The field defaults to aluminium; override it for copper or for a temperature-corrected value.
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