The cable’s safe capacity is just 36% of its nominal rating. To carry the desired 350A load, the engineer would need to upsize to ~300mm² or redesign the installation completely (separate trays, improve soil, reduce ambient).
Deeper burial means more soil above the cable, which acts as thermal insulation. The earth’s temperature also increases with depth due to geothermal gradient, though for shallow power cables (<2m), ambient ground temperature dominates. cable derating factors
A 120mm² copper, XLPE cable (90°C rating) has nominal 400A in free air at 30°C. The cable’s safe capacity is just 36% of
The real world, however, is far less forgiving. The earth’s temperature also increases with depth due
The base ampacity of a cable is calculated assuming a specific reference ambient temperature (usually 30°C in the UK/EU/IEC standards and 30°C or 40°C in the NEC).
This standard is organized into installation methods (Reference Methods A, B, C, D, E, F, G).