Tools · deterministic engine
Cable sizing — voltage drop
Enter the design current, run length and supply, and get the smallest standard conductor that stays within your volt-drop limit. Deterministic from first-principles resistance; current-carrying capacity is confirmed against BS 7671 by the engineer.
Smallest CSA within 5% volt drop
10 mm² · 3.96% drop
| CSA (mm²) | Volt drop (V) | Volt drop (%) | |
|---|---|---|---|
| 1.5 | 105.61 | 26.4 | |
| 2.5 | 63.37 | 15.84 | |
| 4 | 39.61 | 9.9 | |
| 6 | 26.4 | 6.6 | |
| 10 | 15.84 | 3.96 | ✓ within limit |
| 16 | 9.9 | 2.48 | ✓ within limit |
| 25 | 6.34 | 1.58 | ✓ within limit |
| 35 | 4.53 | 1.13 | ✓ within limit |
| 50 | 3.17 | 0.79 | ✓ within limit |
| 70 | 2.26 | 0.57 | ✓ within limit |
| 95 | 1.67 | 0.42 | ✓ within limit |
| 120 | 1.32 | 0.33 | ✓ within limit |
Volt drop only — preliminary. This sizes the conductor for voltage drop from first-principles resistance. It does not check current-carrying capacity (Iz), installation method, grouping, ambient/soil derating, fault rating or protection — those must be confirmed against BS 7671 by a competent engineer before issue. Copper/aluminium resistance taken at ~70°C operating temperature.