Shielded cable
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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 (often utilizing a 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.…
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 (often utilizing a 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.
Applications
The use of shielded cables in security systems provides some protection from power frequency and radio frequency interference, reducing the number of false alarms being generated. The best practice is to keep data or signal cables physically separated by at least 3 inches (75mm) from 'heavy' power circuits which are in parallel. Analog signal cable used in professional audio applications is usually shielded twisted pair cable terminated in XLR connectors. The twisted pair carries the signal in a balanced audio configuration. The audio multicore cable laid from the stage to the mixing console is also shielded. Consumers use screened copper wire with one central conductor in an unbalanced configuration.
Text derived from https://en.wikipedia.org/w/index.php?oldid=1362410669 under CC BY-SA 4.0; modifications have been made.