Cable Screen, Screened Cable

The Purpose of this construction is to minimise the effects of electromagnetic interference from both internally or externally generated sources thus allowing the cable to operate effectively. Office equipment and ancillary components are now covered by EMC Legislation with respect to this subject. The simplest way is to use twisted pairs where field cancellation between successive twists of the pairs considerably reduces the internally generated pick-up or transmission.

For even greater protection the twisted pairs can be shielded by the addition of a further foil or wire mesh using the Faraday Cage Principal to reduce electrical noise and electromagnet radiation either to or from other components in the cable or external sources. Finally the addition of a collective shielding over a group of wires or twisted pairs is referred to as Cable screening and Cable Screen. In all cases for the Shield or Cable Screen/Cable Screening to work they must be physically grounded or by the addition of grounding wire called a drain-wire into the lay of the cable. It is also possible to use a Semi conducting Elastomer in combination with any of the wire based constructions.

As is usual the choice as to which form of Cable Sheilding, Cable Screening or Cable Screen to use will depend on the cables application, operational environment and importance of the data or signals being transmitted through the cable. It is also still a cost/benefit decision particularly when specifying a wire construction were you need to decide on a lap (generally used when coiling the cable) or braid style of construction and on the level of coverage deemed necessary to give the level of protection required. CDC Ltd can advise on all these aspects of Design, performance and cost as part of their Custom Cable service, for more detailed information on this subject go to our sections on Cable Knowledge.