[ S = \fracI_sc \cdot \sqrttk ]
[ I_rms = \sqrtI_1^2 + I_2^2 + ... + I_h^2 ] And derating factor: cable calc formula
:
(185 mm² Cu, R=0.106 Ω/km, X=0.078 Ω/km): [ V_d = \sqrt3 \cdot 340 \cdot 0.250 \cdot (0.106\cdot0.85 + 0.078\cdot0.527) \approx 12.9V ] Drop % = (12.9/400 = 3.2%) — within typical 5% limit. [ S = \fracI_sc \cdot \sqrttk ] [
[ R_ac = R_dc \left(1 + y_s + y_p\right) ] Where (y_s) (skin) and (y_p) (proximity) depend on frequency and conductor spacing. For longer faults (>0.5s), the heat conducts into insulation. Use IEC 60949’s iterative method, which adds a factor (\epsilon): For longer faults (>0
: [ S_min = \frac25,000 \cdot \sqrt0.2143 \approx \frac25,000 \cdot 0.447143 \approx 78 , mm^2 ] 185 mm² >> 78 mm² — thermal withstand OK.
[ S = \fracI \cdot \sqrtt\kappa \quad \text(adiabatic) ]