Wire Resistance Calculator
About Wire Resistance Calculation
This calculator determines the electrical resistance of a wire or cable based on its material, length, and cross-sectional size. It can work either from a known cross-section (mm2) or from the conductor diameter (mm), automatically converting between them. The results are commonly used for evaluating line losses, voltage drop, and general circuit behavior in low-voltage electrical installations.
Tips and Tricks
Electrical resistivity as a base. The calculation starts from the material resistivity at 20 °C, expressed in Ω·mm2/m. Typical reference values are widely used in practice: copper ≈ 0.0175 and aluminum ≈ 0.0283. These values form the baseline for all further resistance calculations.
Cross-section and diameter relationship. If the diameter d (mm) is provided instead of cross-section, the calculator converts it using the geometric relation S = π × d2 / 4. This ensures that resistance is always computed from the actual conductive area S in mm2, regardless of the input mode.
Resistance of one conductor. The resistance of a single straight conductor is calculated as R = ρ × L / S, where ρ is resistivity (Ω·mm2/m), L is length (m), and S is cross-section (mm2). This formula reflects that resistance increases linearly with length and decreases with larger cross-sectional area.
Temperature correction. If a conductor temperature other than 20 °C is specified, resistivity is adjusted using a linear temperature coefficient α: ρT = ρ20 × (1 + α × (T − 20)). Higher temperature always increases resistance, which is important for long runs and heavily loaded circuits.
Loop resistance concept. For most single-phase circuits, current flows through two conductors (for example, phase and neutral). The calculator therefore also provides loop resistance, calculated simply as Rloop = 2 × R. This value is used in voltage drop and power loss evaluations.
Voltage drop and power losses. When load current I (A) is known, voltage drop is obtained from ΔU = I × Rloop, and resistive power losses from P = I2 × Rloop. These results help assess compliance with common installation practices described in IEC 60364, where excessive voltage drop and heating are limited.
FAQs
Why does a longer cable always have higher resistance?
Resistance is directly proportional to conductor length according to R = ρ × L / S. Doubling the length doubles the resistance, assuming the same material and cross-section.
Is diameter input as accurate as cross-section?
Yes, if the diameter is known accurately. The calculator converts diameter to cross-section using a standard geometric formula, so the electrical result is equivalent to entering the cross-section directly.
Why is loop resistance twice the single-conductor resistance?
In typical circuits, current travels to the load and back through another conductor of the same length and size. This doubles the effective length of the current path and therefore doubles the resistance.
How important is temperature in resistance calculations?
Temperature can noticeably affect resistance, especially for long cables or high currents. As conductors heat up, resistance increases, leading to greater voltage drop and higher power losses.
Are the calculated values suitable for final design?
The results are well suited for estimation and comparison. Final electrical design should also consider installation method, grouping of cables, permissible voltage drop limits, and national rules based on IEC 60364.