Free Tool · IEC 60287 / NEC 310

Electrical Cable Sizing

Calculate cable ampacity I_z per IEC 60287, voltage drop per NEC 310, short-circuit withstand per IEC 60949, and MV screen sizing. 9 locales, Chart.js, email export.

Cable Parameters
3 Presets
Short-Circuit Withstand (IEC 60949) + MV Screen Sizing — optional
Fold these inputs into the same ampacity + VD calc when a fault-current limit or MV metallic screen is required.
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Enter cable parameters and click Calculate
Related tools
→ Busbar Rating → Grid Connection Study → Voltage Regulation
Standards: IEC 60287, IEC 60364-5-52, IEC 60949, NEC Art. 310
FAQ
IEC 60287 defines the current-carrying capacity of cables in steady state — I_z — based on thermal equilibrium. It accounts for conductor resistance, thermal resistance of insulation, sheath, armour, and surrounding medium (soil or air).
Voltage drop ΔU = √3 × I × (R·cosφ + X·sinφ) × L / V_LL for three-phase, and ΔU = 2 × I × (R·cosφ + X·sinφ) × L / V_LN for single-phase. IEC 60364-5-52 recommends max 3% for lighting, 5% for motors.
The K-factor in IEC 60949 accounts for conductor material (Cu/Al), insulation type (XLPE/PVC/EPR), and maximum允许 temperature. For Cu/XLPE K=143; for Cu/PVC K=108; for Al/XLPE K=94.
Higher ambient reduces the temperature rise available before reaching the cable temperature limit. IEC 60287-2-1 provides correction factors for soil and air temperatures above 30°C.
IEC 60364-5-52 Table C gives grouping factors: 2 cables = 0.85, 3 = 0.78, 4 = 0.73 (direct buried). For cables in air on tray: 2 = 0.80, 3 = 0.70, 4 = 0.65.
For cables above 3.3 kV with metallic screen (Cu tape or wire), the screen must carry earth-fault current for the clearing time. IEC 60287-1-1 §2.3 requires S_screen ≥ I_ef·√t / K_screen.