Voltage Drop Calculator | Copper & Aluminum Conductors
Calculate the voltage drop along a wire based on material (copper/aluminum), cross-sectional area, length, and current. Shows drop in volts and percentage.
How to Use
- Select the conductor material: copper or aluminum.
- Select the wire cross-sectional area from standard values (e.g. 1.5 mm², 2.5 mm²).
- Enter the one-way wire length in meters.
- Enter the load current in amperes.
- Enter the supply voltage for percentage drop calculation.
- Click 'Calculate' to see the voltage drop, percentage, load voltage, and power lost.
About Voltage Drop
Voltage Drop Formula
Voltage drop ΔV = I × R_wire, where R_wire = ρ × 2L / A. Here, ρ is resistivity (copper: 1.72×10⁻⁸ Ω·m, aluminum: 2.82×10⁻⁸ Ω·m), L is the one-way length (m), and A is the cross-section (m²). The factor of 2 accounts for both conductors (outgoing + return). Power lost in the wire: P_loss = I² × R_wire.
Effect of Wire Material
Copper has about 40% lower resistivity than aluminum, making copper wires carry the same current with less voltage drop and heat generation. However, aluminum is lighter and cheaper for large conductors. Aluminum conductors are common in utility power distribution, overhead lines, and large building feeders. For identical cross-sections, aluminum will drop about 1.64× more voltage than copper.
Temperature Effects
Resistivity increases with temperature: R(T) = R₀ × (1 + α × ΔT), where α ≈ 0.00393/°C for copper. At 75°C (typical operating temperature), copper resistivity is about 22% higher than at 20°C. Electrical codes often use corrected resistivity values for cables operating at their rated temperature. Higher temperature also reduces ampacity due to insulation limitations.
Acceptable Voltage Drop Limits
Standards vary by application and region. NEC (USA) recommends max 3% for branch circuits and 5% total (feeder + branch). IEC 60364 suggests 4% for installations. For 12V automotive systems, even 0.5V (4%) can noticeably affect performance. For motor starting, voltage drop can cause reduced torque and motor heating. Sensitive electronic equipment may malfunction at drops above 5–10%.
Key Features
- Supports copper and aluminum conductors
- Calculates voltage drop, load voltage, and power loss
- Shows drop as both absolute (V) and percentage
- Standard cross-section values from 0.5 to 120 mm²
Common Applications
- Verifying electrical installation compliance with codes
- Evaluating long cable runs in industrial plants
- Solar PV cable sizing for DC circuits
- Motor feeder cable design
- Automotive and marine wiring verification