Cable Sizing Formula May 2026

[ I_req = 84.9 / 0.87 \approx 97.6 \text A ]

Voltage drop (use R=0.87 Ω/km, X=0.08 Ω/km for 25 mm²): [ V_d = \sqrt3 \times 0.1 \times 84.9 \times (0.87\times0.85 + 0.08\times0.526) \approx 11.8 \text V ] % drop = ( 11.8 / 400 \times 100 = 2.95% ) → OK (<5%).

Correction factors: ( k_t ) (40°C PVC) = 0.87 ( k_g ) (single circuit) = 1.0 ( k_s ) (air) = 1.0 cable sizing formula

[ A_min = \fracI_sc \times \sqrttk ]

[ V_d = \sqrt3 \times L \times I \times (R_ac \cos\phi + X \sin\phi) ] [ I_req = 84

From table — 25 mm² Cu/PVC (rated ~110 A in air at 30°C). Acceptable.

Short-circuit thermal check (k for Cu/PVC = 115): [ A_min = \frac10,000 \times \sqrt0.1115 \approx 27.5 \text mm^2 ] 25 mm² is slightly below → upgrade to 35 mm² for fault withstand. Short-circuit thermal check (k for Cu/PVC = 115):

[ I = \fracV_dR_cable ]