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ElectroBoard/Tools/Voltage drop calculator
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Calculator voltage drop

Cable voltage drop calculation per IEC 60364 and IEC 60364. Visualization and cross-section comparison for optimal cable selection.

⚙️ Line parameters

Residential: 0.95 · Motors: 0.7–0.85

📊 Result

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Load current
23.9 A
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Voltage drop
4.57 %
10.05 V · End voltage: 210.0 V
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Max. length (≤5%)
33 m
For ≤3%: 20 m
Voltage drop visualization
220 V
−10.0V
210.0 V
● ≤ 3% — normal● 3–5% — acceptable● > 5% — exceeded

Cross-section comparison (length 30 m, current 23.9 A, copper)

Cross-section, mm²Drop, VDrop, %Status
1.5 16.757.61%✕ Exceeded
2.5 ←10.054.57%⚠ Acceptable
4 6.282.85%✓ Normal
6 4.191.90%✓ Normal
10 2.511.14%✓ Normal
16 1.570.71%✓ Normal
25 1.000.46%✓ Normal
35 0.720.33%✓ Normal
50 0.500.23%✓ Normal

Conductor resistivity — reference table

MaterialResistivity ρ, Ω·mm²/mApplicationNote
Copper (Cu)0.0175NYM, H05VV-F, YMYStandard for residential
Aluminium (Al)0.028NAYY, aluminium PVCLegacy networks, overhead SPC
Steel (Fe)0.13Grounding, overhead spansNot for power lines

What is voltage drop and why is it important?

Voltage drop is the reduction of voltage at the end of a cable compared to the beginning. The longer the cable and the higher the current, the more voltage is lost due to the conductor's resistance.

According to IEC 60364, the total voltage drop from the transformer to the consumer must not exceed 5%. For lighting circuits — no more than 3%, as LED drivers are more sensitive to voltage sag.

On long lines (over 30–50 m), it is the voltage drop, not the permissible current, that determines the minimum cable cross-section — this is critical for garages, workshops, and country houses.

Voltage drop calculation formula in cable

ΔU = ρ × k × L × I / S

where: ρ — conductor resistivity (copper: 0.0175 Ω·mm²/m, aluminium: 0.028), k — circuit coefficient (2 for single-phase, √3 ≈ 1.732 for three-phase), L — line length in meters, I — current in amperes, S — cable cross-section in mm².

Example: copper cable 2.5 mm², single-phase, length 25 m, current 16 A.
ΔU = 0.0175 × 2 × 25 × 16 / 2.5 = 5.6 V → 5.6 / 220 × 100 = 2.5% — within limits ✓

For DC, the formula is similar, but k = 2 always (there and back), and the resistivity for copper is the same — 0.0175 Ω·mm²/m. The percentage is calculated from the source operating voltage (12 V, 24 V, 48 V, etc.).

Frequently asked questions about voltage drop

What is the permissible voltage drop according to IEC 60364?
Total drop from transformer to consumer — not more than 5%. For lighting circuits — not more than 3%, since LED drivers are more sensitive to voltage sag. In practice, from the distribution board to socket-outlet, it is advisable to keep within 3%.
How to reduce voltage drop on a long line?
There are three ways: increase cable cross-section (most reliable), shorten line length (move the board closer to the load), or reduce current (switch to three-phase connection for high-power consumers). For lines over 50 m, a cross-section 1–2 steps larger than required by current rating is often needed.
At what distance does voltage drop become critical?
For a 2.5 mm² Cu cable at 16 A load, problems start from 25–30 m (drop exceeds 3%). For 4 mm² cable — from 40–45 m. If the distance from board to consumer is more than 30 m, always check voltage drop by calculation.
Why does three-phase connection reduce voltage drop?
At the same power, current in a three-phase network is √3 (≈1.73) times less than in single-phase. Lower current means lower drop across cable resistance. Therefore, for powerful remote consumers, three-phase connection significantly reduces cable cross-section.
Does the calculator account for the return (neutral) conductor?
Yes. For single-phase lines, the formula uses a factor of 2 (current flows through phase and neutral conductors); for three-phase, √3 (under balanced load). The calculator automatically applies the correct factor.
How to calculate voltage drop for DC (12 V, 24 V, 48 V)?
The same formula: ΔU = ρ × 2 × L × I / S. The factor is always 2 because current flows through phase and return conductors. Resistivity of copper is 0.0175 Ω·mm²/m. Percentage is calculated from source voltage: for a 12 V system, permissible drop 3% = 0.36 V. For battery systems (solar panels, marine electrical), ≤2–3% is recommended. Enter current and length in the calculator — it will compute for any voltage.

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