Why does shielding cable have such a big effect? ​​But remember that it must be grounded at one end!

Part 1: The role and use of shielding cable

Shielding cable is a transmission line that uses a metal mesh braided layer to wrap the signal line. The braided layer is generally red copper or tinned copper.
Shielding cable is a kind of wire with a metal braided shell specially used to reduce the influence of external electromagnetic fields on power or communication lines. This shielding cable also has the function of preventing the line from radiating electromagnetic energy outward.
The shielding layer needs to be grounded, and external interference signals can be introduced into the earth by this layer.
The shielding layer of the shielded cable is mainly made of non-magnetic materials such as copper and aluminum, and the thickness is very thin, which is much smaller than the skin depth of the metal material at the frequency of use (the so-called skin effect refers to the distribution of current in the conductor cross section tending to the surface of the conductor as the frequency increases. The higher the frequency, the smaller the skin depth; that is, the higher the frequency, the weaker the penetration ability of electromagnetic waves. The effect of the shielding layer is not mainly due to the reflection and absorption of the electric field and magnetic field by the metal body itself, but due to the grounding of the shielding layer. Different grounding forms will directly affect the shielding effect.

Part 2:  Structure

The wrapped conductor is called a shielding layer, which is generally a conductive cloth, a braided copper mesh, or copper (aluminum) platinum.

Ordinary: insulation layer + shielding layer + conductor; advanced: insulation layer + shielding layer + signal conductor + shielding layer grounding conductor

The shielding layer generally needs to be grounded. The function of the shielding wire is to isolate the electromagnetic field noise source from the sensitive equipment and cut off the propagation path of the noise source.

Shielding is divided into active shielding and passive shielding. The purpose of active shielding is to prevent the noise source from radiating outward, which is a shielding of the noise source; the purpose of passive shielding is to prevent sensitive equipment from being interfered with by the noise source, which is a shielding of sensitive equipment.

The shielding layer of the shielded wire is not allowed to be grounded at multiple points, because different grounding points are always different, and there is a potential difference at each point.

If multiple points are grounded, current will be formed in the shielding layer, which will not only fail to play a shielding role, but will also introduce interference. Especially in occasions where frequency converters are used frequently, the interference contains various high-order harmonic components, which will cause greater impact and should be paid special attention to.