Wire Conductor
- Copper and aluminum are the two most commonly used conductor materials. The specific gravity of aluminum is only 2.703 compared to 8.89 for copper, and the conductivity of aluminum is 62% of that of copper. As a result, the cross-section of an aluminum conductor will be about 61% greater than that of copper in order to carry equivalent current.
- In the case of insulated conductors and cables, the cross-section is to be determined by resistance measurements. The cross-section is to be understood as the electrical rather than the geometric one.
- The value of cable conductor resistance is influenced by:
- The lay in a standard conductor and in the laid-up cores in multi core cables. The wires wound on bobbins are then loaded on the stranding machines for the manufacture of stranded wires. The assembly coefficient is as shown in the table below.
- The diameter tolerance for the individual wires and for solid conductors are extremely under each table of cable specifications.
- The International Electrotechnical Commission Specification IEC –228 cover all the above factors by stipulating the resistance of the cross-section of each cable according to its formation, by classifying the conductor into 6 groups, of which the first three refer to the conductor used in cables for permanent installations and the remaining conductors are used for flexible cables.
- Measured resistance in the following tables at 20°C
- The value of correction factors are based on resistance temp. coefficient of 0.004 per °C at 20 °C, e.g.
* at 21°C coefficient = 0.996
* at 19°C coefficient = 1.004
- Asembly coefficient
To determin the whole conductor diameter
the whole conductor diameter = diameter of strand × Asembly coefficient
Number of cores |
Assembly coefficient (k) |
Number of cores |
Assembly coefficient (k) |
2 |
2.00 |
25 |
6.00 |
3 |
2.16 |
26 |
6.00 |
4 |
2.42 |
27 |
6.15 |
5 |
2.70 |
28 |
6.41 |
6 |
3.00 |
29 |
6.41 |
7 |
3.00 |
30 |
6.41 |
7 * |
3.35 |
31 |
6.70 |
8 |
3.45 |
32 |
6.70 |
8* |
3.66 |
33 |
6.70 |
9 |
3.80 |
34 |
7.00 |
9* |
4.00 |
35 |
7.00 |
10 |
4.00 |
36 |
7.00 |
10* |
4.40 |
37 |
7.00 |
11 |
4.00 |
38 |
7.33 |
12 |
4.16 |
39 |
7.33 |
12* |
5.00 |
40 |
7.33 |
13 |
4.41 |
41 |
7.67 |
14 |
4.41 |
42 |
7.67 |
15 |
4.70 |
43 |
7.67 |
16 |
4.70 |
44 |
8.00 |
17 |
5.00 |
45 |
8.00 |
18 |
5.00 |
46 |
8.00 |
18* |
7.00 |
47 |
8.00 |
19 |
5.00 |
48 |
8.15 |
20 |
5.33 |
52 |
8.41 |
21 |
5.33 |
61 |
9.00 |
22 |
5.67 |
84 |
10.5 |
23 |
5.67 |
91 |
11.00 |
24 |
6.00 |
|
|
For four-core cables with one insulated conductor with reduced cross-section:
| D F = |
| 2.41 (3 D c1 + D c2) |
| ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ |
4 |
|
in millimeters |
Where:
D c1 = fictitious diameter of insulated phase conductor, including metallic layer, if any
D c2 = fictitious diameter of insulated conductor with reduced cross-section
|
