THE USE OF SCREENED CABLING - Guide to Separation of Network Cabling from EMI Sources

Guide to Separation of Network Cabling from EMI Sources


Although well-balanced UTP systems provide good EMI performance for typical home, office and industrial (including airports) environments, it is recognized that properly designed and installed twisted-pair cabling with an overall shield (screened twisted-pair cabling, ScTP) may reduce the EMI effects on network performance.

A common problem is that just installing shielded cabling in a building does not bring successful results in terms of network EMI immunity unless several important conditions are met.

Those conditions are stated in the TIA/EIA Interim Standard titled IS-729 "Technical Specifications for 100 Ohm Screened Twisted-Pair Cabling" (March 1999).

Some of the most important conditions are the following:

  • A telecommunications grounding system shall be installed according to the ANSI/EIA/TIA-607 standard.
  • The shield shall be bonded to the telecommunications grounding busbar (TGB) in the telecommunications closet.
  • Grounding at the work area is implemented through the connected equipment.
  • At the work station end of the horizontal cabling, the voltage measured between the shield and the ground wire of the electrical outlet used to supply power to the workstation shall not exceed 1.0 Volt RMS. The cause of any higher voltage should be rectified before using the cable.
  • The shield of a backbone cabling run shall be electrically continuous from end to end. The shield shall be bonded at both ends to a TGB meeting the requirements of ANSI/TIA/EIA-607.
  • The potential difference between the two grounds shall be no more than 1.0 Volts RMS.
  • Connecting hardware shall be terminated according to manufacturer-provided guidelines and
  • manufacturer-recommended installation methods.
For other important mechanical and electrical requirements to screened horizontal and backbone cables, screened connecting hardware, screened patch cords and cross-connect jumpers, please refer to the TIA/EIA Interim Standard IS-729.


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Residential Cabling Guide

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