Thus, an must specify which standard it follows. 3. Typical Earth Cable Sizing Chart – IEC / BS 7671 Style Using the adiabatic equation ( S = \frac\sqrtI^2 tk ), or simpler lookup tables derived from it. Below is an abridged table for copper conductors (PVC insulation, ( k = 143 ), fault clearing time ≤ 0.4 s):

The earth cable (protective conductor, grounding conductor, or earth continuity conductor) provides a low-impedance path for fault currents to return to the source (transformer or generator). This allows overcurrent protective devices (breakers/fuses) to trip quickly.

| Rating of OCPD (A) | Minimum copper earth csa (AWG / kcmil) | mm² approx. | |--------------------|------------------------------------------|--------------| | 15 | 14 AWG | 2.1 | | 20 | 12 AWG | 3.3 | | 30 | 10 AWG | 5.3 | | 40-60 | 10 AWG | 5.3 | | 100 | 8 AWG | 8.4 | | 200 | 6 AWG | 13.3 | | 400 | 3 AWG | 26.7 | | 600 | 1 AWG | 42.4 | | 800 | 1/0 AWG | 53.5 | | 1200 | 3/0 AWG | 85.0 | | 1600 | 250 kcmil | 126.7 | | 2000 | 350 kcmil | 177.3 | Earth conductor size may need to be increased if the circuit length is long (to reduce impedance for fault clearing), but Table 250.122 provides the minimum. 5. AS/NZS 3000 Approach (Australian/New Zealand) Similar to IEC, but with local tables. Abbreviated Table (copper, V-90 insulated):