Exercise EE1-04.R4

Prof. Dr. Thorsten Jungmann (last updated 2025-12-30)

Relates to EE1-04 Resistance

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Task

During earthworks in summer ($T=20°C$), a two-core copper telephone line laid underground has been damaged. It connects the house connection box with the main distributor at the roadside.

At one end of the electric line (at the main distributor), a resistance of $6.1\Omega$ is measured between the two core ends; at the other end (in the house connection box), a resistance of $11\Omega$ is measured. You measure the diameter of each of the copper cores as $0.7\mathrm{mm}$.

You suspect a short circuit between the two cores and now want to locate the point of damage by calculation.

a) Sketch the arrangement with the short circuit and explain which current paths are traversed in the two measurements.

b) Calculate the distance $l_1$ between the main distributor and the point of damage.

c) Calculate the distance $l_{\mathrm{tot}}$ between the house connection box and the main distributor (single cable length).

For the calculation, assume a conductivity of $56\frac{\mathrm{S}\cdot \mathrm{m}}{{\mathrm{mm}}^2}$ for copper at $20°C$.

Solution

$l_1\approx 66\mathrm{m}$
$l_{\mathrm{tot}}\approx 184\mathrm{m}$

Complete solution