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How to Select the Correct Earthing Cable Size (Step-by-Step Guide)

Selecting the wrong earthing cable size can lead to equipment damage, fire, or fatal electric shock. The earthing conductor must be sized to safely carry fault current long enough for the overcurrent device (breaker or fuse) to trip. how to select earthing cable size

[ S = \frac\sqrtI^2 \times tk ]

[ S = \frac\sqrt5000^2 \times 0.2115 = \frac\sqrt25,000,000 \times 0.2115 = \frac\sqrt5,000,000115 = \frac2236115 \approx 19.4 \text mm^2 ] → Select copper cable. Step 3: Follow Simplified Table (BS 7671 / IEC) If you don’t want to calculate, use this simplified copper earthing conductor size relative to the phase conductor: How to Select the Correct Earthing Cable Size

| Phase conductor area (mm²) | Min. copper earthing conductor (mm²) | |----------------------------|---------------------------------------| | ≤ 16 | Same as phase conductor | | 25 – 35 | 16 mm² | | 50 – 95 | 25 mm² | | 120 – 150 | 35 mm² | | 185 – 240 | 50 mm² | | ≥ 300 | 70 mm² | Step 3: Follow Simplified Table (BS 7671 /

| Conductor material | PVC insulation (70°C) | XLPE (90°C) | Bare copper | |-------------------|----------------------|-------------|-------------| | Copper (Cu) | 115 | 143 | 226 | | Aluminum (Al) | 76 | 94 | 148 |