Cable Size Calculator

Calculate the minimum conductor size from design current and installation method. The app applies NEC 310.16 allowable ampacities for copper and aluminum at 60°C, 75°C, and 90°C, and IEC 60364-5-52 Table B.52.2–B.52.5 base ratings for PVC and XLPE insulation.

Calculate voltage drop using ΔV = (2 × L × I × ρ) ÷ A for single-phase and ΔV = (√3 × L × I × ρ) ÷ A for three-phase, where ρ is 0.0172 Ω·mm²/m for copper and 0.0282 Ω·mm²/m for aluminum. The app flags designs exceeding NEC's 2%/1% split or IEC 62548's 3% total limit.

Apply combined derating factors k = k₁ × k₂ × k₃ from IEC 60364-5-52 Tables B.52.14–B.52.21. Temperature correction at 45°C gives 0.87 for XLPE and 0.79 for PVC; grouping of four circuits in conduit reduces ampacity by 20%; soil thermal resistivity above 2.5 K·m/W further reduces buried cable ratings.

Switch between NEC (AWG/kcmil, Imperial) and IEC (mm², Metric) sizing in one tap. Both calculations follow the same methodology — design current, protective device rating, installation method, derating, and voltage drop — but use the correct tables, reference temperatures, and safety margins for each jurisdiction.

Apply the correct two-step 156% multiplier (1.25 × 1.25) for PV source circuits, as required by NEC 690.8. Size DC conductors for ≤2% voltage drop and AC output conductors for ≤3%, then confirm conductor ampacity after rooftop temperature derating. Common results: 10 AWG residential strings, 8 AWG commercial strings, 4/0 AWG main feeders.

Generate PDF calculation sheets showing design current, selected conductor, derated ampacity, voltage drop, pass/fail status, and the applicable NEC or IEC table references. Export to CSV for project files. All calculations run on-device and work fully offline.