Input
Results
Required ampacity (after derate)—
Min size for ampacity—
Min size for VD ≤ target—
Final size (governs)—
VD at final size—
Method
Required ampacity I_req = I_load × 1.25 (continuous) / derate. Lookup ampacity for THWN/THHN copper at chosen temp. Voltage drop: VD = K · I · L_eff / cmils; here we use SI: VD ≈ (2 · I · L · ρ · cosφ) / A (single-phase) or (√3 · I · L · ρ · cosφ) / A (three-phase). ρ_Cu ≈ 0.0172 Ω·mm²/m. Pick smallest A with VD ≤ target.