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Voltage Drop Calculator
This calculator computes voltage drop in a cable line using the formula from IEC 60364 and GOST R 50571. All calculations are performed client-side — your data never leaves the browser.
How the calculation works
• For single-phase (230 V): ΔU = (2 × I × L × ρ × cos φ) / S • For three-phase (400 V): ΔU = (√3 × I × L × ρ × cos φ) / S • ρ (copper) = 0.0175 Ω·mm²/m, ρ (aluminum) = 0.028 Ω·mm²/m • ΔU% = (ΔU / U_nom) × 100% • Limits: < 3% — excellent, 3–5% — acceptable, > 5% — exceeded per IEC.
Frequently asked questions
What is the maximum allowable voltage drop?
5% from the service to the last outlet (NEC 210.19, IEC 60364-5-52), 2.5% for lighting. Increase the cross-section if exceeded.
How to reduce voltage drop?
Increase the cable cross-section (drop is inversely proportional), shorten the run, or move the load to 3-phase.
Why is the drop calculated with double length?
In single-phase, current flows through phase and neutral — the length counts twice: ΔU = 2·I·L·ρ·cosφ/S. For 3-phase, the factor is √3.
What drop does 2.5 mm² have over 50 m?
At 16 A and cosφ = 0.9: ΔU ≈ 10 V ≈ 4.4% — at the limit. Consider 4 mm² for socket circuits.