Cable Resistance Calculator
Calculate electrical resistance of cables based on material, length, area, and temperature
Cable Resistance Calculator
Compliant with IEC 60228 Standards
Calculation Results
Resistance at Operating Temperature
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How to Use the Calculator
Select Material
- Choose "Copper" or "Aluminum"
- This determines the base resistivity
Enter Cable Dimensions
- Input the cable length in meters (m)
- Provide the cross-sectional area in square millimeters (mm²)
Specify Temperature
- Enter the operating temperature in Celsius (°C)
- Default is 20°C, which is the reference temperature for resistivity
How to Calculate Cable Resistance
1. Basic Formula
The resistance of a conductor is primarily determined by its physical dimensions and material properties.
R = ρ × L / A
Where:
- ρ (Rho): Resistivity
- L: Length in meters
- A: Area in mm²
2. Temperature Correction
Resistance changes with temperature. We use a correction factor to adjust for operating conditions.
Rt = R₂₀ × [1 + α(T - 20)]
α (Alpha) is the temperature coefficient of resistance (approx 0.004 for Copper).
3. Material Properties
Different materials conduct electricity differently. Copper is the standard for most wiring.
Copper ρ ≈ 0.01724 Ω·mm²/m
Aluminum ρ ≈ 0.02826 Ω·mm²/m
Aluminum has higher resistance but is lighter and cheaper.
Cable Resistance Chart (at 20°C)
| Size (mm²) | Copper Resistance (Ω/km) | Aluminum Resistance (Ω/km) |
|---|---|---|
| 1.5 | 12.10 | - |
| 2.5 | 7.41 | 12.10 |
| 4 | 4.61 | 7.41 |
| 6 | 3.08 | 4.61 |
| 10 | 1.83 | 3.08 |
| 16 | 1.15 | 1.91 |
| 25 | 0.727 | 1.20 |
| 35 | 0.524 | 0.868 |
| 50 | 0.387 | 0.641 |
Cable Resistance FAQs
How to calculate the resistance of A cable?
To calculate cable resistance, use the formula R = (ρ × L) / A. Multiply the material's resistivity (ρ) by the total length (L), then divide by the cross-sectional area (A). For accuracy, apply temperature correction if the operating temperature differs from 20°C.
What is the resistance of 2.5 mm wire?
For a standard Copper conductor at 20°C, a 2.5 mm² wire has a resistance of approximately 7.41 Ω/km (or 0.00741 Ω/m). This value increases as the cable gets hotter.
What is the resistance of 25mm2 cable?
A 25 mm² Copper cable has a resistance of about 0.727 Ω/km at 20°C. An Aluminum cable of the same size would have a higher resistance, approximately 1.20 Ω/km.
What is the resistance of A 20 cm long wire?
Resistance depends on the area. For example, a 0.5 mm² copper wire that is 20 cm (0.2 m) long: R = (0.01724 × 0.2) / 0.5 = 0.0069 Ω. Always ensure units match (convert cm to meters).
What is a formula for resistance?
The standard DC resistance formula is R = ρL/A. R is resistance in Ohms, ρ (rho) is resistivity in Ω·m or Ω·mm²/m, L is length in meters, and A is cross-sectional area in square meters or mm².
What is the resistance per meter of 1.5 mm cable?
A 1.5 mm² solid copper wire has a resistance of roughly 0.0121 Ω per meter (12.1 Ω/km) at 20°C.
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