Information Technology Reference
In-Depth Information
TABLE 15.3
Cable Performance Requirements for Resistance, Capacitance, and Balance
Parameter
Applies to
Conditions
For category
Requirement
Mandatory?
DC resistance
Any conductor
All
9.38 ohms
Yes
per 100 ohms
DC resistance
unbalance
Any pair
All
5%
Yes
Mutual
capacitance
Any pair
1 kHz
Cat 3
6.6 nF
No
per 100 ohms
Any pair
1 kHz
Cat 5 & 5e
5.6 nF
No
Capacitance
unbalance,
Any pair
1 kHz
All
330 pf
Yes
pair to ground per 100 ohms
NOTE: All measurements are to be measured at or corrected to 20°C. The table applies to both horizontal and
backbone cables.
Source: TIA-568-C.
stranded wire for increased flexibility. Stranded wire pairs are expected to have
slightly greater attenuation than solid copper, so an increase of 20% in attenuation
is allowed over that for horizontal cable. The attenuation value is prorated for
length, since patch cords are generally far shorter than horizontal cable runs. These
wires need not be tested at elevated temperatures. In addition, the stranded wires
must have a twist pitch (lay length) of 15 mm (0.6 in) or less.
The standard specifies a clear system of category marking for cable and con-
necting hardware. The category should be marked either with the words Category
N
(where
N
is the category number 5, 5e, or 6) or with a large letter “C” with the
category number in the center. These markings are shown in Fig. 15.1. The category
of some wiring components can be very difficult to determine once they are
installed. A sticker on a plastic bag, label on the package, or note in the data sheet
is not of much use.
The standard requires marking, and it should be easy for most manufacturers
to stamp, emboss, or label each jack, plug, or cable with the rated category number.
After all, you are paying extra for the performance. The best rule is, if it doesn't say
Category 5e (or whatever), don't assume it is Category 5e. Try to use marked com-
ponents wherever possible.
Pitfalls and Specsmanship
The greatest danger in evaluating cable and connector hardware specifications is
that the certifications may not be based on the most current standards. The category
