Cable Size Calculator

For a 10 kW, 400 V three-phase load at 0.8 PF over 50 m, the calculator recommends ~6 mm² copper (Direct Buried). This sizing ensures voltage drop ≤3% (≈12 V), per IEC 60364-5-52 and IEEE 141 guidelines. Current draw is ~18.1 A (I = P / (√3 × V × PF)). The 6 mm² copper cable has ~3.7 mΩ/m AC resistance (IEC 60228 Class 2), yielding ~1.85 V drop — well within limits. Always verify against local codes: UK’s BS 7671 mandates ≤5% drop for final circuits; NEC Article 215.2(A)(1) suggests ≤3% for feeders. Ambient temperature derating may require upsizing if >30°C.

Aluminum has ~61% higher DC resistivity than copper (28.2 nΩ·m vs. 17.2 nΩ·m at 20°C), per IEC 60228 Annex A. For identical current-carrying capacity and voltage drop, aluminum must be ~56% larger in cross-section — e.g., 16 mm² Al ≈ 10 mm² Cu. Additionally, aluminum’s lower tensile strength and higher thermal expansion demand careful termination (UL 486A/B, IEC 61238-1) to prevent loosening and overheating. IEC 60502-1 specifies tighter bending radii and torque requirements for Al conductors. Always apply 1.25× derating for continuous loads (NEC 210.19(A)(1)) and confirm ampacity tables (e.g., IEC 60364-5-52 Table D1/D2 or NEC Table 310.16).

Installation method directly impacts thermal dissipation and thus ampacity. Direct-buried cables benefit from soil’s high thermal resistivity (~1.2 K·m/W), allowing higher current ratings than conduit-installed cables in air (thermal resistivity ~0.3 K·m/W), per IEC 60287-2-1. Conduit reduces heat transfer, requiring up to 20–30% larger cable for the same load. Tray installations (unenclosed) fall between these extremes. The calculator applies standardized derating factors: IEC 60364-5-52 Table B.52.2 assigns 0.72 for 3-core cables in conduit vs. 0.92 for direct burial. Always validate ambient temperature, grouping, and solar radiation effects — especially for aerial or tray-mounted runs per IEEE Std 835.

Both are critical, but the *governing* factor depends on application context. Current-carrying capacity (ampacity) prevents thermal damage and is primary for safety (IEC 60364-4-43, NEC 310.15). Voltage drop governs performance — typically limited to ≤3% for feeders and ≤5% for final circuits (IEC 60364-5-52, BS 7671 Regulation 525.1). For long runs (>30 m) or sensitive equipment (VFDs, PLCs), voltage drop often dictates larger sizing *before* ampacity limits are reached. Example: A 100 A load over 200 m may require 95 mm² for <3% drop, even though 50 mm² satisfies ampacity. Always perform both checks — undersized cables risk fire; oversized ones waste cost and space.

Yes — but with key adjustments. For DC, omit √3 and power factor; use I = P/V directly. The calculator’s voltage drop formula assumes single-phase AC line-to-neutral or DC, so ensure ‘voltage’ input reflects system voltage (e.g., 48 V DC, 600 V DC string). Resistance calculation uses DC resistivity (IEC 60228), not AC skin/proximity effects — valid for ≤1 kHz. For PV, apply NEC Article 690.7(A) temperature correction (e.g., +25°C above ambient for rooftop mounting) and 125% continuous current rule (690.8(A)(3)). Aluminum PV wire requires UL 4703 listing; copper must meet UL 854. Always verify with manufacturer datasheets — especially for XLPE vs. USE-2 insulation.

The voltage drop calculation uses V_drop = √3 × I × L × R_ac (3-phase) or 2 × I × L × R_dc (DC/single-phase), where R_ac is derived from IEC 60228 resistivity values and standard stranding factors. It assumes sinusoidal steady-state, uniform conductor temperature (70°C for PVC, 90°C for XLPE), and ignores reactance — acceptable for ≤35 mm² cables at 50/60 Hz (<5% error). For larger cables or harmonics, impedance (R + jX) should be used per IEC 60287. Accuracy is ±5% under nominal conditions, but real-world variables — soil thermal resistivity, actual conductor temperature, contact resistance — can add ±10–15% uncertainty. Always measure post-installation.

The calculator implements core principles from IEC 60364-5-52 (selection and erection of cables), IEC 60287 (ampacity), and IEEE 141 (voltage drop limits), with alignment to NEC Article 215.2 (feeder drop), 310.15 (ampacity), and BS 7671 Chapter 52. It applies standardized resistivity (IEC 60228), derating factors (IEC Table B.52.2), and 3% / 5% voltage drop thresholds common across jurisdictions. However, it does *not* replace jurisdiction-specific compliance checks — e.g., NEC requires AWG sizing (not mm²), while IEC mandates metric. Local amendments (e.g., UK’s Amendment 2, Australia’s AS/NZS 3008) may impose additional constraints. Always cross-check with official tables and engage a licensed professional for certification.

Aluminum is preferred for cost-sensitive, high-current, long-distance applications — especially MV distribution, utility feeders, and large PV farms — where weight and material cost dominate. Per IEEE 80 and IEC 61558, Al offers ~50% cost savings and ~30% weight reduction vs. equivalent Cu. Modern AA-8000 series alloys (ASTM B800) resolve historic creep/oxidation issues. Critical requirements: UL 486B-listed lugs, antioxidant paste (MIL-A-81706), and torque verification (per manufacturer specs). Avoid Al for <10 mm² conductors or in vibration-prone locations. Always apply 1.25× continuous load factor (NEC 310.15(A)(1)) and verify fault current withstand per IEC 61439-1.