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What is the role of the shielding layer required by the wire and cable?

Update:29-09-2020
Summary:

The outermost layer of wire and cable is generally rubb […]

The outermost layer of wire and cable is generally rubber or rubber composite sheath. The function of this layer is firstly to insulate, but also to protect the cable from damage.

The cable is divided into high voltage or low voltage cable. If it is high voltage, there will be a layer of resin-like filler inside, which serves as insulation. In high voltage cables, this layer is the most important part of insulation. The low voltage does not have this layer. Then there will be something like a ribbon wrapped inside, which is to fix each core of the cable and fill the gap in the middle.

As for the shielding layer, there are two cases. The function of the shielding layer of the power cable is as follows:

1. Because the current through the power cable is relatively large, a magnetic field will be generated around the current. In order not to affect other components, the electromagnetic field can be shielded in the cable by adding a shielding layer.

2. It can play a certain role of grounding protection. If the cable core is damaged, the leaked current can flow along the shielding layer like a grounding grid, which plays a role of safety protection.

If it is a control cable, there is no difference. It is just that in many places, especially the control cable of a computer system, the shielding layer here is used to shield external influences, because its own current is very weak, and it is very afraid of external electromagnetic fields.