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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 (UTP) Ethernet?

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 cable.
  • 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.

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