| Breaker / Fuse Rating | Minimum Earth Size (Copper) | Minimum Earth Size (Aluminum) | | :--- | :--- | :--- | | | 14 AWG | 12 AWG | | 20 Amps | 12 AWG | 10 AWG | | 30 Amps | 10 AWG | 8 AWG | | 40 Amps | 10 AWG | 8 AWG | | 60 Amps | 10 AWG | 8 AWG | | 100 Amps | 8 AWG | 6 AWG | | 200 Amps | 6 AWG | 4 AWG |
Electrical regulations vary by country and region. Always consult a qualified electrician or your local wiring codes (such as BS 7671, NEC, or AS/NZS 3000) before performing electrical work.
[ S = \frac\sqrtI^2 \times tk ]
| Phase conductor cross-section (S) | Minimum protective conductor (copper) | |-----------------------------------|----------------------------------------| | S ≤ 16 mm² | S (same as phase) | | 16 < S ≤ 35 mm² | 16 mm² | | S > 35 mm² | S/2 |
Where:
Electricians generally use two methods to determine the correct earth cable size: Method A: The Selection Table
The cable connecting the installation's earth bar to the supplier's earth terminal (or earth rod) is sized differently than circuit earth wires. earth cable sizes
Copper is the standard. Aluminum requires a larger cross-section to achieve the same conductivity.
If the live wire is , the earth should be at least half the size of the live wire. Method B: The Adiabatic Equation For precise engineering, the Adiabatic Equation is used: S = Minimum cross-sectional area (mm²) I = Fault current (Amps) t = Disconnection time (Seconds) | Breaker / Fuse Rating | Minimum Earth
The National Electrical Code (NEC) Table 250.122 sets minimum sizes for equipment grounding conductors based on the rating of the overcurrent protection device (the breaker/fuse).
If you have a specific application (solar, motor, sub-panel, or TT/TN earthing system), provide details for a more tailored review. Copper is the standard