Unlike regular cables, where a wire is covered by a plastic or insulating material, shielded cable has an extra layer of metal shield surrounding the conductive wire (or wires) inside. This is normally either a metal braid or foil, and often has an insulated conductor core running alongside it for easy connection. As the name implies, it helps to shield the cable from interference and reduces the sensitivity of the cables.
PVC shield wire 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. The shield minimizes capacitively coupled noise from other electrical sources. The shield must be applied across cable splices.
In shielded signal cables the shield may act as the return path for the signal, or may act as screening only.
The best way to pvc shield wire for screening is to ground the shield at both ends of the cable. Traditionally there existed a rule of thumb to ground the shield at one end only to avoid ground loops. Best practice is to ground at both ends, but there is a possibility of ground loops.
The use of pvc shield wire 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.