10 mm² copper multicore PVC cable carries 50 A enclosed in air at 30 °C in New Zealand. That is its corrected rating Iz from AS/NZS 3008.1.2:2017 Table 13. The largest curve C breaker it allows is 50 A, a common sub‑board feed.
The case
The circuit is single‑phase at 230 V and runs 20 m at the full 50 A of the breaker. Table 5.1 gives a 4 mm² earth. The voltage drop is 1.94 % and the earth fault loop impedance is 0.51 Ω, inside the 0.61 Ω that Table 8.1 allows.
The loop impedance margin is small. On a longer run, check Zs before the cable runs out of capacity.
The circuit check reads Passes.
What changes the rating
Clipped direct to a surface, the cable carries 58 A.
At 40 °C ambient it carries 44 A. Bunched with two other circuits, it carries 35 A.
See also: Earth fault loop impedance and disconnection time and Ib, In and Iz.