THE USE OF SCREENED CABLING
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:
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.
- 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.