The cable must survive a short-circuit fault long enough for the breaker to trip. The fault current heats the cable almost instantly (adiabatic heating).
If the cable you selected in Step 6 has an area smaller than the calculated $S$ above, you must upsize the cable. calculation of cable size formula
Let's assume we need to calculate the cable size for a circuit with the following parameters: The cable must survive a short-circuit fault long
The cable size calculation formula is based on the following steps: calculation of cable size formula