If it’s undersized:
When the fault current magnitude ($I_fault$) and the operating time of the protective device ($t$) are known, or when the simplified table does not suffice, engineers use the . This formula assumes that all heat generated during the fault remains in the conductor (no heat dissipation to the surroundings) because the fault duration is very short.
| Phase Conductor (mm²) | Min. Copper Earth (mm²) – if same material | |-----------------------|---------------------------------------------| | 1.5 | 1.5 | | 2.5 | 2.5 | | 4 | 4 | | 6 | 6 | | 10 | 10 | | 16 | 16 | | 25 | 16 | | 35 | 16 | | 50 | 25 | | 70 | 35 | | 95 | 50 | | 120 | 70 |
The earthing arrangement of the building impacts the minimum requirements for the :
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