Buyers read “class 2” on a datasheet and assume it’s a quality rank, second best to something. It isn’t. IEC 60228 (and IS 8130, the Indian equivalent) sorts conductors by how they’re stranded and therefore how flexible they are. Nothing more.
The four classes
| Class | Construction | Intended for | Where you’ll meet it |
|---|---|---|---|
| 1 | Solid | Fixed installation | Small house wiring sizes, some LV cores |
| 2 | Stranded, circular or shaped | Fixed installation | Most power, control and armoured cables |
| 5 | Flexible, many fine wires | Flexible cables and cords | Solar DC cable, welding cable, appliance flex |
| 6 | Extra flexible, more and finer wires than class 5 | Cables that move repeatedly | Trailing and festoon applications |
Classes 5 and 6 are meant for flexible cables and cords, but the standard permits them in fixed installations too. That’s why you occasionally see class 5 in a panel: someone wanted an easier bend radius at termination.
The rule most people miss
For classes 1 and 2, the number of strands given in the standard is obligatory. For classes 5 and 6 it isn’t. There, the standard sets a maximum strand diameter and a maximum resistance, and a manufacturer may use fewer strands so long as the finished conductor stays under the resistance figure. Resistance is the acceptance test, not the strand count.
Which is the useful takeaway: if you want to know whether a conductor is honest, measure resistance. Counting strands proves nothing on a class 5 or 6 cable.
Verified resistance limits (IS 8130, 20°C)
| Size | Copper, plain, class 2 (Ω/km) | Aluminium, class 2 (Ω/km) |
|---|---|---|
| 1.5 mm² | 12.1 | not offered |
| 16 mm² | 1.15 | 1.91 |
| 25 mm² | 0.727 | 1.20 |
The physics check worth stealing
Any resistance figure has a floor it cannot go below. R = 1000ρ/A ohms per km, where ρ is 0.017241 for copper and 0.028264 for aluminium and A is the cross-section in mm². Run 16 mm² copper: 1000 × 0.017241 / 16 = 1.078 Ω/km, against a standard limit of 1.15. Sensible. Now run 16 mm² aluminium: 1.767 Ω/km floor, against a limit of 1.91.
If a printed table shows an aluminium conductor at or near the copper number, the table is wrong. We’ve caught exactly that error in published brochures more than once. Aluminium’s resistivity sits about 64 per cent above copper’s, and no amount of stranding cleverness changes it.
Which class turns up where at APAR
- Class 2 stranded copper in the LV control cables up to 61 core and in fire alarm cables
- Tinned class 5 copper in solar DC cables, where the tinning fights oxidation on a rooftop
- Flexible constructions in welding cables and trailing and material-handling cables, which are dragged for a living
One last thing. A class number tells you nothing about insulation, temperature rating or fire behaviour. Those are separate lines on the spec, and they’re the ones that usually matter more.