What is an acceptable voltage drop per NEC?

NEC recommends: feeder voltage drop ≤2%, branch circuit ≤3%, total ≤5%. IEC typically recommends ≤3-5%. This tool color-codes: green ( 5% - needs thicker wire).

What is the resistivity of copper vs aluminum?

Copper resistivity is ~0.0172 Ω·mm²/m at 20°C. Aluminum is ~0.0282 Ω·mm²/m. Aluminum needs ~1.6× cross-section for equivalent voltage drop. Copper conducts better but costs more.

Voltage Drop Calculator - Wire & Circuit

🔧 Circuit Parameters

Circuit Type

System Voltage (V)

Current (A)

Wire Length (m)

Wire Cross-Section (mm²)

Conductor Material

Power Factor (cos φ) - AC only

Temperature (°C)

📊 Results

Enter parameters to calculate

Wire Resistance

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Voltage at Load

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Power Loss

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📖 Wire Size Reference

Cross-Section (mm²)	AWG	Cu Ampacity (A)	Max Length (120V/10A/<3%)
1.5	16 AWG	~15A	~9m / 30ft
2.5	14 AWG	~20A	~15m / 50ft
4.0	12 AWG	~25A	~25m / 80ft
6.0	10 AWG	~32A	~37m / 120ft
10.0	8 AWG	~45A	~62m / 200ft

How to Use Voltage Drop Calculator

Select Circuit Type
Choose DC, AC single-phase, or AC three-phase. Different types use different formulas.
Enter Parameters
Input system voltage, current, wire length, and cross-section from the dropdown.
Select Material
Copper has lower resistivity; aluminum is lighter and cheaper but needs larger cross-section.
Check Recommendation
Green (<3%) meets NEC. Yellow (3-5%) is acceptable. Red (>5%) needs thicker wire.

❓ FAQ

What is voltage drop and how is it calculated?

Voltage drop is voltage loss due to wire resistance. DC formula: Vd = 2×I×R×L. R = ρ/A, copper ρ=0.0172. Example: 2.5mm² copper, 30m, 10A: Vd=2×10×(0.0172/2.5)×30=4.13V.

What is acceptable voltage drop per NEC?

NEC: feeder ≤2%, branch ≤3%, total ≤5%. This tool: green (<3%), yellow (3-5%), red (>5% - upgrade wire size).

Copper vs aluminum wire?

Copper resistivity: 0.0172, aluminum: 0.0282. Aluminum needs ~1.6× cross-section. Copper conducts better; aluminum is lighter and cheaper but needs special anti-oxidation connections.

⚡ Voltage Drop Calculator