What is acceptable voltage drop?

Most electrical codes recommend maximum 3% voltage drop for branch circuits and 5% total (feeder + branch). IEC 60364 and NEC both suggest these limits. For motor circuits, excessive voltage drop reduces starting torque proportionally to V².

How is voltage drop calculated?

For single-phase: ΔV = 2 × ρ × I × L / A. For three-phase: ΔV = √3 × ρ × I × L / A. Where ρ is resistivity (Ω·mm²/m), I is current (A), L is one-way cable length (m), and A is conductor cross-section (mm²).

What is the resistivity of copper vs aluminum?

Copper resistivity at 20°C: 0.0175 Ω·mm²/m (1.72×10⁻⁸ Ω·m). Aluminum: 0.0283 Ω·mm²/m (2.83×10⁻⁸ Ω·m). Aluminum is about 61% the conductivity of copper, so larger cross-section is needed.

Does cable temperature affect voltage drop?

Yes. Conductor resistance increases with temperature. At 75°C operating temperature, copper resistivity is about 0.0216 Ω·mm²/m (vs 0.0175 at 20°C). This calculator uses room temperature values; for hot cables, increase by ~20%.

How do I reduce voltage drop?

Options: (1) Increase cable cross-section, (2) Reduce cable length (relocate distribution panel), (3) Increase supply voltage (e.g. 690V instead of 400V), (4) Use copper instead of aluminum, (5) Apply power factor correction to reduce current.

Free Engineering Tool

Voltage Drop Calculator

Calculate cable voltage drop for single-phase and three-phase circuits. ΔV = k × ρ × I × L / A. Shows absolute drop and percentage.

1-Phase / 3-Phase Cu / Al IEC 60364

System Type

Supply Voltage (V)

Load Current (A)

Cable Length (one way) (m)

Conductor Cross-Section (mm²)

Conductor Material

Quick presets

Results

Voltage Drop

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Percentage Drop

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Voltage at Load

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Cable Resistance

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Power Loss in Cable

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Voltage Drop Formulas

k = 2 for single-phase/DC, √3 for three-phase
ρ = resistivity (Ω·mm²/m) — Cu: 0.0175, Al: 0.0283
I = current (A), L = one-way length (m), A = cross-section (mm²)

💡 Tip: Keep voltage drop below 3% for branch circuits and 5% total (feeder + branch) per IEC 60364 and NEC recommendations.

Voltage Drop Calculator | Free Cable Sizing Tool | Vibromera

Published by Nikolai Shelkovenko on February 15, 2026 March 5, 2026

Results

Voltage Drop Formulas