Ultimately, an adequately sized earth conductor ensures that when a fault occurs, the circuit breaker trips, not the conductor itself.
In many Low Voltage (LV) installations, regulations allow earthing conductors (Circuit Protective Conductors or CPC) to be sized relative to the phase conductor ($S_phase$) without calculation, provided mechanical protection is present. earthing cable sizing
Round up to next standard (e.g., 16, 25, 35, 50, 70, 95 mm²). Ultimately, an adequately sized earth conductor ensures that
Based on largest ungrounded service conductor (Copper only): the circuit breaker trips