Earth Cable Sizing Page

If you’re designing or installing an electrical system, you already know the importance of live and neutral conductors. But the earth cable (protective conductor or grounding conductor) is arguably the most critical wire for safety . It’s the silent guardian—the path that clears a fault and saves lives.

But how do you size it correctly? Too small, and it could vaporize under a fault. Too large, and you’re wasting copper. Let’s break down the rules, the math, and the practical steps. When a fault occurs (say, a live wire touches a metal casing), the earth cable must carry the full fault current until the protective device (breaker or fuse) trips. During that short time—milliseconds to a few seconds—the earth wire heats up. earth cable sizing

When in doubt: . The cost of one cable size up is trivial compared to the cost of a failed protection path. If you’re designing or installing an electrical system,

Stay safe, and keep that ground path solid. Disclaimer: This post is for informational purposes. Always consult your local electrical code (NEC, IEC, BS 7671, AS/NZS 3000) and work with a licensed electrician. But how do you size it correctly

| 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 |

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