Cable Resistance Table

DC conductor resistance values for copper and aluminium cables (IEC 60228). Used in voltage drop, power loss, and fault current calculations. Reference temperature: 20°C. Corrected values shown at selected operating temperature.

Material
Conductor
Category
Operating Temp

Showing 19 conductor sizes

Values shown at 20°C. Corrected values shown in grey below each entry.

Copper resistance Aluminium resistance Corrected value differs significantly Not applicable
Size Copper — Solid Copper — Stranded Aluminium — Stranded Derived Values Typical Application
Class 1
Ω/km 		Class 2
Ω/km 		Class 5 Flex
Ω/km 		Class 2
Ω/km 		Class 5
Ω/km 		Cu Resistance
mΩ/m 		Conductivity
% IACS

Temperature Correction Formula

Rt = R20 × [1 + α(t − 20)]

Where R₂₀ = resistance at 20°C (Ω/km) · α = temperature coefficient · t = operating temperature (°C)

Temperature coefficients (per °C):
Copper: α = 0.00393
Aluminium: α = 0.00403

Quick Reference — Resistivity at 20°C

  • Copper resistivity (ρ) 1.724 × 10⁻⁸ Ω·m
  • Aluminium resistivity (ρ) 2.83 × 10⁻⁸ Ω·m
  • Copper conductivity 58.0 × 10⁶ S/m
  • Aluminium conductivity 35.4 × 10⁶ S/m
  • Al vs Cu conductivity ≈ 61% of copper
  • Copper temp coefficient α 0.00393 /°C
IEC 60228 Classes Class 1 = solid round copper conductors. Class 2 = stranded copper or aluminium (most common in power cables). Class 5 = flexible stranded conductors used in trailing cables and flexible cords. Resistance values differ slightly between classes due to packing factor.
Temperature Correction The reference temperature in IEC 60228 is 20°C. At Nigerian ambient conditions (40°C) and under load (90°C for XLPE), copper resistance increases by approximately 3.5% per 10°C above 20°C. Always use operating temperature in voltage drop calculations.
Using in Voltage Drop Calculations Voltage Drop (V) = 2 × L × I × R / 1000 (single-phase) or √3 × L × I × R / 1000 (three-phase), where L = cable length (m), I = current (A), and R = resistance from this table (Ω/km) corrected to operating temperature.
Aluminium Availability Aluminium conductors (Class 2) are typically available from 10 mm² and above. Below 10 mm², copper is the standard choice due to mechanical jointing requirements and the impracticality of terminating small aluminium conductors.