Cable shielding runs beneath the plastic jacket of a cable and encapsulates the wire or series of wires inside.
This shielding can be made from braided strands of copper, other metals like aluminum, a spiral of copper tape or a layer of conductive polymer. The purpose of cable shielding is to reduce the noise affecting the cable’s signal and to dampen any electromagnetic radiation that might interfere with other devices. In order to work, the shield must cover all splices in the cable.
Electromagnetic interference (EMI), also known as radio frequency interference (RFI) can be extremely disruptive to many electronic devices. EMI can degrade or stop the performance of a circuit, rendering an instrument completely useless.
These EMI currents are generated by both natural and man-made sources, like car ignition systems, cell phones, thunder storms, the Sun, and the northern lights.
There are two distinct types of electromagnetic interference that produce two different effects. The first type is known as “narrowband” EMI or RFI. Narrowband interference comes from transmissions like radio and TV stations or cell phone signals.
The other type of interference is called “broadband”. Broadband interference is caused from unintentional radiation created from things like electric power transmission lines. Cable shielding helps to protect against both types of interference.
Shielded cables are often used in security system applications because they provide protection from power and radio frequency interference. This can drastically reduce the number of false alarms that are triggered.
Microphone cables in PA and recording studios are usually fitted with shielding to prevent interference during recording. Medium and high voltage cables also use copper or aluminum tape shielding to stop any power cable that is touching the ground from discharging electricity upon contact. The cable is grounded in at least two places to prevent shock even when the current is flowing through the shield.
Most cable shielding functions in the same way as a Faraday cage which can be found in electronic devices like mobile phones. A Faraday cage is a metallic cage that encases electrical components to protect from electromagnetic interference.
Cable shielding is essentially doing the exact same thing, only in a different shape because of the various cable sizes and lengths that are manufactured.
Cable Shielding Informational Video