Shielded Wires and Wiring

Shielded conductors permit the transmission of low level signals, at high impedance levels, through areas where excessive interference voltages would be induced into low impedance conductors by low frequency magnetic fields, or in areas where sensitive information must be sent. Shields on wires act the same as shields on rooms, the continuous enclosure acting as a Faraday cage barrier to radiated fields. Magnetic fields near the surface will set up currents in the conductor which tend to cancel the incident fields. However, the shield is only as good as its ground reference, since shield currents radiate like any other wire. For best results, both the internal wire and the outer cable must be individually shielded.