Ned Sigmon, amp Inc.
One hundred-ohm screened twisted-pair (sctp) cabling, also called foiled twisted-pair cabling, took another step closer to standardization when the latest draft document was sent out for tia TR-41.8.1 committee ballot in July. Ballots were due back to tia by early August and scheduled for review at the tia TR-41.8.1 meetings later that month.
As of press time, those meetings have not yet taken place, and the outcome of the ballot is not known. However, if this standard follows the path of most, it will require several ballots and draft revisions in order to satisfy all the questions or issues that will be raised, pushing completion into early 1998 at the earliest.
sctp cable uses an overall foil shield around all the cable pairs (there can be 4 or 25 pairs). The connectors for 4-pair cabling typically are 8-position modular plugs and jacks that also have an overall shield terminated to the shield of the cable
The proposed sctp standard is being positioned as a supplement to the ansi/tia/eia-568a standard and the requirements that are already in the 568A standard for 100-ohm unshielded twisted-pair (utp) cabling. Cables and connecting hardware must meet the same transmission-performance specifications for all the same categories as utp. The requirements of the new standard will deal specifically with the differences between sctp and utp, which include:
cable bend radius (because sctp cables typically are stiffer than utp cables),
shielding effectiveness of both the cables and the connecting hardware,
the shield interface between the modular jack and plug,
continuity and grounding of the shield during installation.
The shielding effectiveness requirements, being specified as transfer impedances, will provide a common basis for comparing the shielding performance of components from different manufacturers. The connector shield interface requirements will allow users to mix and match mating connectors from different manufacturers. The grounding requirements should remove the uncertainty of where and how often to ground the shield.
Ned Sigmon is associate director of technical marketing at amp Inc. (Harrisburg, PA). He chairs the tia PN 3193 Task Group, which is drafting the sctp standard.