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First, calculate the current assuming no heat loss (the conservative baseline). This formula is derived from IEC 60364-5-54 or IEC 60949 Annex A. iec 949 pdf
$$I_AD = K^2 \cdot A^2 / t$$
Wait, strictly speaking, the formula is usually rearranged to find the minimum cross-section or max current. The direct formula for maximum adiabatic current is:
$$I_AD = A \cdot \sqrt\fracKt$$ (Where K is a material constant based on the temperature limits). IEC standards are protected by copyright and are
If you are using the standard for a calculation, follow this workflow:
If $I_permissible > I_system_fault$, the cable is safe.
You require this specific standard if you are: Do not download or share unauthorized copies; use
Without the IEC 949 PDF, engineers typically fall back on conservative adiabatic calculations, potentially over-sizing cables by 20-30%.
Let's walk through a typical scenario where you would reference the IEC 949 PDF.
Scenario: You have a 240 mm² copper cable, XLPE insulated, carrying a fault current of 25 kA for 0.5 seconds.
This practical guide is detailed fully in the IEC 949 PDF, including worked examples for aluminum and copper cables, PVC and XLPE insulations.
To perform the calculation, you need the following data: