Official IEC standards are generally not provided for free by the International Electrotechnical Commission. However, you can find the standard and its amendments through authorized channels:
standard (officially titled "Calculation of thermally permissible short-circuit currents, taking into account non-adiabatic heating effects" iec 60949 pdf free top download
The standard follows a three-step process to determine the final permissible current: Calculate Adiabatic Current ( IADcap I sub cap A cap D end-sub Official IEC standards are generally not provided for
Direct full-text "free" downloads of active standards are often restricted due to copyright. However, the following sources provide substantial technical depth for study and application: iec 60949 pdf free top download