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Conductor Examples

These worked examples apply the conductor resistance formula and related relationships to find resistance from material properties, express it per unit length, and find the maximum resistance allowed by a voltage drop limit.

  1. Step 1

    A copper conductor (resistivity ≈ 0.0172 Ω·mm²/m) is 30 m long with a 2.5 mm² cross-sectional area. Find its resistance.

    R = (ρ × L) ÷ A = (0.0172 × 30) ÷ 2.5 ≈ 0.206 Ω

  2. Step 2

    A 200 ft conductor run has a total resistance of 0.5 Ω. Find the resistance per 1000 ft.

    R/1000ft = (R ÷ L) × 1000 = (0.5 ÷ 200) × 1000 = 2.5 Ω/kft

  3. Step 3

    A circuit allows a 4.5 V drop at 20 A. Find the maximum conductor resistance.

    R = VD ÷ I = 4.5 ÷ 20 = 0.225 Ω

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