Dc Electricity
Cable Resistance
The resistance of a cable depends on the material, its length and its cross-sectional area. Resistivity is a property of the material, length increases resistance and area reduces it. A longer or thinner cable therefore drops more voltage and dissipates more heat at the same current. Convert practical cross-sections from square millimetres to square metres before substituting into the formula.
Cable Resistance
R = ρ × L ÷ A
Variables and units
| Symbol | Quantity | Unit |
|---|---|---|
| R | Conductor resistance | Ω |
| ρ | Resistivity of the material | Ω·m |
| L | Conductor length | m |
| A | Cross-sectional area | m² |
Conditions of application
Uniform conductor at a stated temperature. Resistivity depends on the material and rises with temperature for metals; convert mm² to m² before calculating.
Worked example
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Resistance of a conductor from resistivity, length and cross-sectional area.