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 , 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 .To be effective against electric fields , the shield must be grounded. The shield should be electrically continuous to maximize effectiveness, including any cable splices.