70 mm² copper is rated about 213 A installed per Method C (clipped direct, 70 °C thermoplastic) and drops 0.6 mV/A/m (single-phase figure, matching BS 7671 Appendix 4 within rounding). The chart shows how far it runs before the drop exceeds the limits.
| Load | 230 V @ 3% | 230 V @ 5% | 400 V 3Ø @ 5% |
|---|---|---|---|
| 6 A | 1789 m | 2981 m | 5987 m |
| 10 A | 1073 m | 1789 m | 3592 m |
| 16 A | 671 m | 1118 m | 2245 m |
| 20 A | 537 m | 894 m | 1796 m |
| 32 A | 335 m | 559 m | 1123 m |
| 40 A | 268 m | 447 m | 898 m |
| 63 A | 170 m | 284 m | 570 m |
Computed with ρ ≈ 0.0225 Ω·mm²/m (copper at operating temperature), matching BS 7671 Appendix 4 mV/A/m values within rounding. Grouping, insulation type and installation method change the amp rating — treat 213 A as the Method C reference figure.
The nearest equal-or-larger AWG size is 3/0 AWG — see the gauge converter for exact areas.
About 213 A for copper clipped direct (Method C). Enclosed in conduit in insulation it derates substantially — always check the installation method column in BS 7671 Appendix 4.