The tables below indicate the electrical and physical properties of metals commonly used in the manufacture of electric cables in the electrical industry. Familiarity with these properties is required to fully grasp the key advantages and disadvantages of the various materials used and to understand from a practical standpoint why they are applied in the area they are used.
Electrical Properties
The table below indicates the electrical properties of the common metals used in cables. Taking price into consideration the below listed properties, Copper and Aluminium are clearly the best choice for conductors the manufacture of all manner of electric cables although there has been experimentation with other metals for example Sodium in certain applications:
Metals
|
Relative Conductivity (Copper = 100)
|
Electrical Resistivity at 20°C (Ωm, 10-8)
|
Temperature Coefficient of Resistance (per °C)
|
| Silver | 106 | 1.626 | 0.0041 |
| Copper (HC, anealed) | 100 | 1.724 | 0.0039 |
| Copper (HC, Hard drawn) | 97 | 1.777 | 0.0039 |
| Tinned Copper | 95 - 99 | 1.741 - 1.814 | 0.0039 |
| Aluminium (EC grade, Soft) | 61 | 2.803 | 0.0040 |
| Aluminium (EC grade, 1/2H - H) | 61 | 2.826 | 0.0040 |
| Sodium | 35 | 4.926 | 0.0054 |
| Mild Steel | 12 | 13.80 | 0.0045 |
| Lead | 8 | 21.4 | 0.0040 |
Physical Properties of Metals Used in Electric Cables
The physical properties of metals used for conductors and sheaths are given in the table below:
Property
|
Unit
|
Aluminium
|
Copper
|
Lead
|
Density at 20°C
|
Kg/m3
|
8890 | 2703 | 11370 |
| Coefficient of thermal expansion per °C |
x 10-6
|
17 | 23 | 29 |
| Melting point | oC | 1083 | 659 | 327 |
| Thermal Conductivity |
W/cm
oC
|
3.8 | 2.4 | 0.34 |
| Ultimate Tensile Stress | ||||
| Soft temper | MN/m2 | 225 | 70 - 90 | - |
| 3/4H to H | MN/m2 | 385 | 125 - 205 | - |
| Elastic Modulus | MN/m2 | 26 | 14 | - |
| Hardness | ||||
| Soft | DPHN | 50 | 20 - 25 | 5 |
| 3/4H to H | DPHN | 115 | 30 - 40 | - |
| Stress Fatigue Endurance Limit (Approximate) | MN/m2 |
±65
|
±40 | ±2.8 |
Except for conductors of self-supporting overhead cables, Copper is invariably used in the annealed condition. Solid Aluminium conductors are also mainly used in a soft condition but stranded Aluminium conductors are 3H (hard) to H. Aluminium sheaths are now extruded directly onto cables and hence of soft temper but a small amount of work hardening occurs during corrugation.