100BASE-TX Ethernet Unshielded
Twisted-Pair (UTP) Cable Maximum and Minimum Length Requirements
Last updated: 6/17/2001
Q. What are the maximum
and minimum cable lengths allowed for a 100BASE-TX unshielded, twisted-pair
A. Here are some basic 100BASE-TX horizontal
distance requirements (the are called guidelines in the specification):
- Total distance between an Ethernet Transmitter and Receiver
at the absolute end points of the network (maximum diameter from origin
to final destination, if the wires were stretched out to form a straight
line): 100 Meters (328 ft., 109 yds., or about the length of a football
field). This limitation results from the timing of the Ethernet signals
on the cable and not necessarily the cable characteristics, and is, therefore,
a "hard" number.
- Excluding patch cables, cross connects, etc., the maximum
horizontal cable distance shall be 90 meters (295 ft.). They are
referring to the run from the patch panel to the wall jack with solid core
- Cross-connect jumpers and patch cords in the cross connect
should not exceed 6 meters (20 ft.).
- 3 meters (9.8 ft.) has been allowed for patch cords
from the wall jack to the work area/PC. One could probably make these
cables longer if the total length between Ethernet devices does not exceed
100 Meters. I would not make patch cables with stranded cable longer
than 20 feet.
- 10 meters (33 ft.) is allowed for the total length of
patch cords and cross connect jumpers in a horizontal channel. Cross
connect cables are patch panel cables.
- I can find no minimum length in the chunk of the specifications
I have for 100BASE-TX cable. I read one Internet source that said
it was .5 meters (1.6 ft.). I have read others that said there was
no limit. I have a 2-foot crossover cable that works fine. There
are loopback plugs that have almost no length. I would tend to make
such a cable at least two feet long to permit some noise attenuation by
the twisted pairs. However, RJ-45 plugs are cheap and one could experiment
for a modest cost.