The condition:
[ Z_loop \times I_a \leq U_0 ]
[ A_min = \sqrt\frac10000^2 \times 0.4115 \approx \sqrt\frac40 \times 10^6115 \approx \sqrt347826 \approx 590 \text mm^2 ] cable selection calculation
We often treat cable sizing as a simple lookup: "10 amps? Use 1.5mm²." But in the real world—where ambient temperatures hit 50°C in a rooftop conduit, where harmonic currents distort neutrals, and where voltage drop starves a motor 400 meters away—that naive approach fails. The condition: [ Z_loop \times I_a \leq U_0
[ V_d = 2 \times L \times I \times (R_ac \cos\phi + X \sin\phi) ] The answer is rarely just "too much current
Next time you see a burnt cable in a panel, ask: was it undersized, or was it sized for 30°C free air and installed in a 50°C bundled tray? The answer is rarely just "too much current."