An electrical cable consists of a conductor, which channels the electrical flow, and an insulation containing this electrical flow in the conductor. In addition, they can incorporate other auxiliary elements that guarantee their longevity.
What are the parts of a cable?
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1. CABLE CONDUCTOR
This is where the electrical current is actually transmitted, with copper being the most commonly used material.
In some cases, aluminium conductors are also used, despite the fact that this metal is 60% worse conductor than copper (at the same cross-section it has more losses due to the Joule effect). In practice, aluminium is used almost exclusively for power transmission cables in electrical distribution networks (electricity companies).
There are two sizing criteria for copper conductors: the North American criterion and the European criterion. In North American (AWG) sizing, conductors are defined by specifying a number of wires and a diameter of each wire. In European sizing (mm2), the conductors are defined by specifying the maximum resistance of the conductor (Ω/km). Solid or flexible conductors are defined by specifying the minimum number of wires or the maximum diameter of the wires that form them. In addition, the actual geometrical sections are somewhat smaller than those indicated as nominal.
2. CABLE INSULATION
The insulation is the polymer, plastic or elastomer layer that surrounds the conductor and isolates it from external contacts.
There are thermoplastic and thermosetting insulations. The first one are those in which the material applied does not undergo chemical transformations. PVC, the most common thermoplastic insulation, has a maximum service temperature of 70 °C.
Thermosetting insulation is chemically transformed during extrusion, resulting in a more stable compound in the face of increased temperature. This is why they allow for higher operating temperatures.
The most common thermosetting insulation materials (XLPE and EPR) have maximum operating temperatures of 90 °C.
The higher the maximum operating temperature of an insulation, the more current the conductor can carry. And the more current, the more power it will have. This is the main advantage of thermosetting insulation over thermoplastics.
3. CABLE METAL PROTECTION
In some cases the cables may have metal protections. Electrical metal shields (screens) are applied to isolate the signals that pass through the interior of the cable from possible external interference. Mechanical protections (armours) protect the cable from possible external aggressions..
4. CABLE OUTER SHEATH
In almost all cases the cables have an outer sheath. Its function is eminently protective. They are usually made of polymeric material and must be chosen in accordance with the nature of the insulation material.