A shielded cable is a type of electrical cable with one or more cables inside, enclosed by a conducting layer that shields the cables from external electrical noise and interference. When reed switches are tested, shielded cables should be used to connect the device up to the test equipment to ensure accurate measurements.
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A shielded cable or screened cable is an electrical cable of one or more insulated conductors enclosed by a common conductive layer. The shield may be composed of braided strands of copper (or other metal, such as aluminium), a non-braided spiral winding of copper tape, or a layer of conducting polymer. Usually this shield is covered with a jacket.
The shield acts as a Faraday cage to reduce electrical noise from affecting the signals, and to reduce electromagnetic radiation that may interfere with other devices (see electromagnetic interference). The shield minimizes capacitively coupled noise from other electrical sources. The shield must be grounded to be effective. The shield should be electrically continuous to maximize effectiveness, which includes cables splices.
In shielded signal cables the shield may act as the return path for the signal, or may act as screening only.
High voltage power cables with solid insulation are shielded to protect the cable insulation, people and equipment.