Information Technology Reference
In-Depth Information
manufacturer's name and part number are also normally shown. A typical marking
might be:
4PR—24GA—CMP—Category 5e—XYZ Cable Company—PN 99999
This example of a cable marking would indicate a 4-pair, 24 AWG cable, tested
for fire/smoke/voltage ratings to CMP standards of the
NEC
, certified to Category
5e TIA standards, manufactured by XYZ Cable Company, with a part number of
99999.
Because standards for cable have changed so much over the past few years, you
may encounter older cables with a variety of markings for their transmission char-
acteristics and fire and smoke ratings. Because the TIA standards have been contin-
ually refined, you might find cables that bear markings of the older standard
revisions or the levels program (for example, TSB-40, Level 5, or EIA/TIA-568). The
plenum rating might be marked as “Article 800” or “UL 910,” rather than the CMP
wire use type. This cable is acceptable if already installed in appropriate applications
(such as 10BaseT, for example), but should not be installed for new service. Most of
this early cable will not meet the rigorous standards for today's Category 5e, which
should really be the minimum quality cable for any new installations.
UTP/STP Shielding and Screening
Shielding is sometimes used with twisted-pair cable to provide better noise immu-
nity and lower emissions. Two types of shielding are commonly available for STP
cable: the foil shield and the braided wire shield.
The foil shield usually has a bare stranded wire, called a
drain wire
, that is in
contact with the shield and provides the electrical connection for the foil. Braided
shields may have a drain wire, or the braid may be formed into a wire or clamped
to make electrical contact. Some cables may have combination foil/braid shields or
double shields.
Screening
is another term that is often applied to the type of electromagnetic
shielding used with twisted-pair cables. The term has gained new acceptance with
the latest revisions to the international standards.
Cables that are referred to as screened are generally constructed with an over-
all foil screen, which means that the foil screen wraps completely around all four
pairs (or all 25 pairs in a multi-pair jumper cable).
Screened cables are in much greater use in Europe than in North America,
where their use is found mostly in high-interference locations.
Screened cables require special plugs and jacks to allow for the screen intercon-
nection. In addition, the connection of cable screens to a building ground (earth) can
