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The most common method for selecting earth cable size is relating it to the Phase Conductor (Line) size. Below is the standard selection table derived from and BS 7671 .
If the earth wire is "naked" (not inside a conduit or sheath), it usually needs to be at least 4mm² just to ensure it doesn't physically snap or break over time. Summary Checklist Identify your Phase wire size. earth cable size selection chart
Undersizing the earth wire can lead to dangerous overheating before the breaker trips. Oversizing it leads to unnecessary costs. The most common method for selecting earth cable
If you want to save money on copper or are working on industrial projects, you use a specific formula to see if a smaller wire is safe. S: Minimum cross-sectional area ( mm2m m squared I: Fault current (Amps). t: Operating time of the protection device (Seconds). Summary Checklist Identify your Phase wire size