): The maximum allowable short-circuit temperature limit (e.g., 250°C for XLPE).
: Inversed temperature coefficient factor for conductor resistance at 0°C Standard Material Coefficients
This non-adiabatic approach is particularly valuable when evaluating cable screens, where significant heat can be transferred to surrounding materials. It can justify reducing a screen's cross-section by 10-20% compared to the simple, conservative adiabatic formula, leading to lighter, less expensive, and more efficient cables. iec 949 pdf
: Initial and final (maximum permissible) temperatures of the conductor.
The standard uses a factor, often denoted as $\epsilon$ (epsilon), to adjust the adiabatic current to account for heat loss. ): The maximum allowable short-circuit temperature limit (e
You have a 240 mm² copper cable, XLPE insulated, carrying a fault current of 25 kA for 0.5 seconds.
: Maximum final permissible boundary temperature after the fault (°C). : Material-specific thermal constant ( : Initial and final (maximum permissible) temperatures of
While the first edition has remained valid for decades, it is being updated. China's national plan, established in 2021 to create a new standard "Calculation of permissible short-circuit current considering non-adiabatic effects," adopts IEC 60949:1988+AMD1:2008. However, the second edition (IEC 60949 ED2) is currently in development. As of February 2025, its Working Draft (WD) has been approved to move to the Committee Draft (CD) stage, with a forecasted publication date around . This update ensures its continued relevance with modern materials, safety standards, and global energy goals, though the core methodology will remain unchanged. The current version and its 2008 amendment have a stability date of 2030, guaranteeing their validity for several more years.
The IEC 949 PDF document provides recommendations on: