The international standard for conductors is IEC 60287. The standard classifies conductors according to four classes:
- Class 1: solid conductors
- Class 2: stranded conductors
- Class 5: flexible conductors
- Class 6: flexible conductors (more flexible than class 5)
For each class of conductor, the standard defines the maximum allowable resistance at 20 oC:
| Maximum Resistance of Conductors in mΩ/m |
| CSA mm² |
Copper (plain) |
Copper (tinned) |
Aluminium |
| class 1 & 2 |
class 5 & 6 |
class 5 & 6 |
class 1 & 2 |
| 0.5 |
36.0 |
39.0 |
40.1 |
- |
| 0.75 |
24.5 |
26.0 |
26.7 |
- |
| 1 |
18.1 |
19.5 |
20.0 |
- |
| 1.5 |
12.1 |
13.3 |
13.7 |
- |
| 2.5 |
7.41 |
7.98 |
8.21 |
- |
| 4 |
4.61 |
4.95 |
5.09 |
- |
| 6 |
3.08 |
3.30 |
3.39 |
- |
| 10 |
1.83 |
1.91 |
1.95 |
3.08 |
| 16 |
1.15 |
1.21 |
1.24 |
1.91 |
| 25 |
0.727 |
0.78 |
0.795 |
1.20 |
| 35 |
0.524 |
0.554 |
0.565 |
0.868 |
| 50 |
0.387 |
0.386 |
0.393 |
0.641 |
| 70 |
0.268 |
0.272 |
0.277 |
0.443 |
| 95 |
0.193 |
0.206 |
0.210 |
0.320 |
| 120 |
0.153 |
0.161 |
0.164 |
0.253 |
| 150 |
0.124 |
0.129 |
0.132 |
0.206 |
| 185 |
0.0991 |
0.106 |
0.108 |
0.164 |
| 240 |
0.0754 |
0.0801 |
0.0817 |
0.125 |
| 300 |
0.0601 |
0.0641 |
0.0654 |
0.100 |
| 400 |
0.0470 |
0.0486 |
0.0495 |
0.0778 |
| 500 |
0.0366 |
0.0384 |
0.0391 |
0.0605 |
| 630 |
0.0283 |
0.0287 |
0.0292 |
0.0469 |
| 800 |
- |
- |
- |
0.0367 |
| 1000 |
- |
- |
- |
0.0291 |
| 1200 |
- |
- |
- |
0.0247 |