However, the rated ampacity ($I_rated$) of a cable depends on several correction factors. The practical formula for selecting a cable based on heating is:
The raw current calculated in Part 1 rarely reflects reality. Cables rarely sit in open air at perfect ambient temperatures. You must apply "Derating Factors" to determine the minimum required capacity. formula for cable size calculation
Then, verify this size against current-carrying capacity tables. However, the rated ampacity ($I_rated$) of a cable
You calculate the size required for the current, then check if that size works for the voltage drop. If the voltage drop is too high, you must pick a larger cable. You must apply "Derating Factors" to determine the
The cable must be able to handle more current than the circuit breaker or fuse. The rule of thumb is:
To size a cable for a 100 A load current, 30 meters long, with a 3% voltage drop allowed on a 230V supply, and assuming copper conductors: