A cable bent more tightly than its rated radius suffers damage that does not show on inspection. The insulation thins on the outside of the bend and the metallic screen wrinkles on the inside; the cable still passes its tests and energises normally, then breaks down at that point after running warm for a season. Every drum carries a minimum bending radius, and it should be treated as a hard limit.
The radius is quoted as a multiple of the cable’s overall diameter, written as a number times D. A cable 50 mm across with a 12D limit must not bend tighter than 600 mm radius. The figures below reflect common Indian and international practice, broadly in line with IEC 60502-1, and serve as a cross-check against the manufacturer’s own value.
| Cable | Typical minimum bend radius |
|---|---|
| LV multicore, unarmoured | 12 × D |
| LV multicore, armoured | 12 × D |
| LV single-core | 15 × D |
| MV / HV multicore (screened) | 15 × D |
| MV / HV single-core (screened) | 15–20 × D |
| Flexible / trailing cable | Per datasheet (much tighter with rollers) |
Two points are easily overlooked. These limits apply to a fixed, finished bend; during pulling, with the cable cold and under tension, the radius maintained should be wider still, and the cable should run over a roller or shoe rather than a bare edge. The diameter is that of the complete cable, not the conductor, so a 300 mm² cable with heavy armour bends far wider than the copper alone would suggest.
Screened MV and HV cables are the least forgiving, because the metallic screen and the XLPE core do not move together readily. For LV XLPE power cables and MV and HV XLPE cables, the approved drawing states the exact minimum radius for that construction, and that value takes precedence over any general rule, including this chart. Routes should be planned so that the drum position, the pull and the final dressing all remain within the radius, and single-core cables should be cleated as soon as they are positioned.