A shielded cable or screened cable is an electrical cable that has a common conductive layer around its conductors for electromagnetic shielding. This shield is usually covered by an outermost layer of the cable. Common types of cable shielding can most broadly be categorized as foil type (hereunder: metallised film), contraspiralling wire strands (braided or unbraided) or both.
A longitudinal wire may be necessary with dielectric spiral foils to short out each turn.
The shield acts as a Faraday cage – a surface that reflects electromagnetic radiation. This reduces both the interference from outside noise onto the signals and the signals from radiating out and potentially disturbing other devices (see electromagnetic compatibility). To be effective against electric fields (see also capacitive coupling), the shield must be grounded. The shield should be electrically continuous to maximize effectiveness, including any cable splices. For high frequency signals (above a few megahertz), this extends to connectors and enclosures, also circumferentially: The cable shielding needs to be circumferentially connected to the enclosure, if any, through the connector or cable gland.
Some types of shielded cable use the shield as the return path for the signal. As contrasting examples, coaxial cable does, whereas twinax cable does not.
High voltage power cables with solid insulation are shielded to protect the cable insulation, people and equipment.
There are many types of cable shields available commercially, and usage depends on the application.
Combination shields
Foil Shields
Metallic Braid Shields
Spiral Shields
Serve Shields
Tape Shields
Screen Shields
The best way to wire shielded cables for screening is to ground the shield at both ends of the cable. Traditionally there existed a rule of thumb to ground only the source end of the shield to avoid ground loops. Best practice is to ground at both ends, but there is a possibility of ground loops.
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Copper has been used in electrical wiring since the invention of the electromagnet and the telegraph in the 1820s. The invention of the telephone in 1876 created further demand for copper wire as an electrical conductor. Copper is the electrical conductor in many categories of electrical wiring. Copper wire is used in power generation, power transmission, power distribution, telecommunications, electronics circuitry, and countless types of electrical equipment. Copper and its alloys are also used to make electrical contacts.
A shielded cable or screened cable is an electrical cable that has a common conductive layer around its conductors for electromagnetic shielding. This shield is usually covered by an outermost layer of the cable. Common types of cable shielding can most broadly be categorized as foil type (hereunder: metallised film), contraspiralling wire strands (braided or unbraided) or both. A longitudinal wire may be necessary with dielectric spiral foils to short out each turn.
Une cage de Faraday ou bouclier de Faraday est une enceinte utilisée pour bloquer les champs électromagnétiques. Un écran de Faraday peut être constitué d'un revêtement continu de matériau conducteur, ou dans le cas d'une cage de Faraday, d'un maillage de tels matériaux. Les cages de Faraday portent le nom du scientifique Michael Faraday, qui les a inventées en 1836. Une cage de Faraday fonctionne parce qu'un champ électrique externe provoque la répartition des charges électriques dans le matériau conducteur de la cage de sorte qu'elles annulent l'effet du champ à l'intérieur de la cage.
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