Calculation For Cable Size [patched] Jun 2026

If your load is 20A, but the cable is in a hot roof space with other cables, the derating factor might be 0.7. $$I_adjusted = \frac200.7 = 28.5 , Amps$$ You must calculate cable size based on 28.5A, not 20A.

$$A = \frac20.646.9 \approx 2.99 , mm^2$$ calculation for cable size

If the cable run is short (e.g., inside a house panel), voltage drop is negligible. You select the cable based purely on its . If your load is 20A, but the cable