The outermost layer of wires and cables is typically made of rubber or a rubber composite sheath, such as polyvinyl chloride (PVC) or polyethylene. This layer serves not only as insulation but also as protection from external damage and harm to others.
Cables are categorized as either high-voltage or low-voltage. High-voltage cables also have a layer of resin-like filler inside, which acts as insulation. In high-voltage cables, this layer is the most important insulation component. Low-voltage cables lack this layer. A ribbon-like material is also wrapped around the cable to secure each core, fill the gaps between them, and ensure the cable's roundness.
As for the shielding layer, there are two main functions. The shielding layer in power cables serves the following purposes:
1. Because power cables carry high currents, magnetic fields are generated around them. To prevent them from affecting other components, the shielding layer is added to confine this electromagnetic field within the cable and prevent it from interfering with other components.
2. It provides a certain degree of grounding protection. If a cable core is damaged, the leaking current can flow through the shielding layer to the grounding grid, thereby directing it to the earth, providing safety protection. If it is a control cable, there is no other difference, but in many places, especially the control cable of the computer system, the shielding layer here is used to shield external influences. Because the current itself is very weak, it is very afraid of the influence of external electromagnetic fields, so the control cable is shielded in many cases.
