How To Size A Cable File

If length exceeds Lmax, add an earth conductor or RCD.

Example : Isc = 3 kA, t = 0.1 s (breaker trip), Cu/XLPE, k=143. $S_min = \sqrt(3000^2 × 0.1) / 143 = \sqrt900,000 / 143 = 948 / 143 = 6.6 mm²$. Minimum = 6.6 → choose 10 mm² (next standard size). how to size a cable

The cable must be protected by a circuit breaker or fuse. The rating of the protective device ($I_n$) must be selected such that: $$I_n \geq I_b$$ The chosen cable must be capable of carrying this current continuously without exceeding its temperature limits. If length exceeds Lmax, add an earth conductor or RCD

Result: This is slightly high (limit usually 5%). We should go up one size to . If length exceeds Lmax