Why calculate the phase-neutral loop
The single-phase S/C current (phase-neutral loop) determines whether the MCB will trip within the required time (0.4 s for 220 V, IEC 60364). Insufficient S/C current → MCB won't trip in time → the enclosure stays live.
Formula
Isc(1) = Uph / (Ztr + Zw × L). Where: Uph = 220 V, Ztr — transformer impedance (typically 0.01-0.05 Ω), Zw — loop impedance per km for the cable (phase + neutral), L — line length.
Example
Outlet 30 m from panel, cable 3×2.5 mm² (copper). Zw = 14.8 Ω/km. Zline = 14.8 × 0.03 = 0.444 Ω. Zloop = 0.02 + 0.444 = 0.464 Ω. Isc(1) = 220 / 0.464 = 474 A. C16 MCB: 16 × 10 = 160 A (C upper limit). 474 > 160 — protection works.
Automation in GorkyCAD
GorkyCAD automatically calculates S/C currents for each line, checks compliance with MCB characteristics, and warns on non-compliance. Saves up to 50 manual calculations per project.
Frequently asked questions
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