Yet many old-timers still call it "IEC 949" — a quiet tribute to the first edition that brought order to a wild frontier of power electronics.
Using standard values of θ_i = 90°C and θ_f = 250°C, the expression simplifies to a current density (J₀):
| | Resistivity (ρ) at 20°C (Ω·m) | Specific Heat Capacity (c) (J/(kg·K)) | Melting Point (°C) | | :--- | :--- | :--- | :--- | | Copper | ( 1.72 \times 10^-8 ) | 385 | 1083 | | Aluminum | ( 2.65 \times 10^-8 ) | 900 | 660 | iec 949 pdf
Understanding IEC 949: Calculation of Thermally Permissible Short-Circuit Currents
= Thermally permissible short-circuit current (RMS value in Amperes). Yet many old-timers still call it "IEC 949"
: Material constant (e.g., 226 for copper, 148 for aluminium). : Cross-sectional area of the conductor ( mm2m m squared θftheta sub f : Final permissible temperature ( ∘Craised to the composed with power cap C θitheta sub i : Initial temperature before the fault ( ∘Craised to the composed with power cap C
$$I_SC = I_AD \times \epsilon$$
: Initial and final (maximum permissible) temperatures of the conductor.