1.5 mm² copper is rated about 20 A installed per Method C (clipped direct, 70 °C thermoplastic) and drops 30.0 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 | 38 m | 64 m | 128 m |
| 10 A | 23 m | 38 m | 77 m |
| 16 A | 14 m | 24 m | 48 m |
| 20 A | 12 m | 19 m | 38 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 20 A as the Method C reference figure.
The nearest equal-or-larger AWG size is 14 AWG — see the gauge converter for exact areas.
About 20 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.