tnx petere,
when we begin to discuss cat5e utp (unshielded twisted pair designed for use with in-building lan applications) in this context we're talking about a whole different realm of commercial building wiring than the outside plant grades that would extend to the referenced footage (i forget, was it 1500 ft?). i know that you know that, but others may not, so allow me to muse here for a few moments, which will serve as a refresher exercise for me, if not for you and some others here ;) ...
where inside wiring is concerned, unshielded tp (utp) won out a long time ago in the usa, but in europe there is still quite an affinity for shielded twisted pair (stp). several variations of shielding are used, some of them called sctp, for shielded screened. see:
anixter.com
an excerpt:
"Some STP cables use a thick braided shield. These cables are heavier, thicker, and harder to install than their UTP counterparts. Some STP cables only use a relatively thin overall outer foil shield. These cables, called screened twisted pair (ScTP) cables or foil twisted pair (FTP) cables, are thinner and less expensive than braided STP cable. However, they are not any easier to install the minimum bending radius and maximum pulling tension force must be rigidly observed when these cables are installed; otherwise, the shield may experience a tear."
during the early nineties there was a bakeoff that took place in switzerland to put this issue to rest, with at&t (lu) and several others supporting their utp product lines, and a number of euro players putting up their stp. it was quite an elaborate test bed arrangement that was used, complete with very-high voltage arc-generation, oven testing, etc. when all was said and done the utp held up to the test, and for some parameters surpassed the stp in performance. despite these results stp continues to be favored in euro standards, but utp has made inroads nonetheless due to lower cost and less complexity (grounding of the shield in stp is often done incorrectly, and is cumbersome, at best). i've seen more than one installation where grounding caused more problems than it was intended to prevent, and consequently the shields on both ends of the cabling were 'turned back' [disconnected from ground and left hanging] in order to remedy the problem. in other words, the shields were ungrounded altogether, in violation of the standards, as a means of reducing the overall noise to ground [and ingress] component from the received signal.
i'll see if i can find a document that discusses the bakeoff i discussed above and post it here. actually, the link that i provided above touches on this bakeoff in the section titled:
UTP Cabling Systems and High-Speed Data Transmission
some domestic mfgrs produce outside plant that they claim is rated cat5 utp, or cat5e (enhanced cat5 utp), but these do not receive recognition from eia/tia standards folks for the 'category' classification (how's that for a redundant statement?). this is because once you depart from the 100 meter parameter associated with the catagoried cables the classification no longer applies. i can see where such a classification might apply in campus or enterprise settings, e.g., between adjacent buildings [although, now we're talking about potential lightning problems and the need for properly grounding and bonding, not to mention the need to provide either gas- or carbon-block protection at each end at the entrance points] but not for common carrier pole attachments or longer runs in the local loop.
what i stated above applies to commercial building inside wiring for ieee 'lan' cabling applications.
for inside cabling that is used for t-1 extension from the carrier demarc, on the other hand, shielded cabling is still specified, but in those instances the desired combination is two individually foil-shielded pairs within an outer foil wrapping.
this construction is commonly referred to as "t-spec" [pronounced: teespeck] cabling, for t-1 lines inside of buildings, and it is specified for distances up to 622 feet (as opposed to cat-5 for 328 ft <100m> for the overall channel parameter).
but even here, within buildings, the cat-5 utp cabling has become the defacto winner by enterprise telecom engineering staff in most newer installations, despite its non-support by carriers, oddly enough. cat-5 is used due to its high degree of inter-conductor, inter-pair 'balance' and balance to ground, and the counter-emf effect between transmit and receive pairs that effectively nullifies any mutual inductance between pairs. translation, there is very low longitudinally-induced cross-talk between pairs, as a result.
cross-talk, incidentally, on cat'x' pairs is attributed to inductive and capacitive coupling (jump over) between pins on modular 8-pin connectors, commonly but erroneously referred to as rj-xx jacks, and not from longitudinal imbalance that would otherwise cause crosstalk. again, this is due to the superior balance that has been achieved in the cabling, as i just mentioned above, itself.
another misclassification occurs when associating cat-x cabling in the outside plant, even if distances are within the prescribed 100 meters, where hardware that is connected to outside plant wiring is seldom manufactured to the parameters associated with cat'x' cabling.
fac |
