The TIA 568-C standard defines the maximum length of the Permanent Link to be 90m and the maximum length of the Channel to be 100m, typically made up of 90m of solid conductor cable and 10m of stranded conductor cable.
It is important to note that the lengths specified in the TIA 568-C standard refer to the physical sheath length, i.e. the actual measured distance between the distribution patch panel and the work area outlet when following the route of the cable. However, when testing the finished installation we measure the electrical length of the cable, which will always be shorter than the physical length due to the twists in the wires. This means that there can be instances when testing links with a physical length of around 85m and longer where the electrical test can fail on length.
One way around this is to test the cabling to the ISO/IEC 11801 or BS EN 50173 standards as neither of these standards specify a maximum length of cabling. Instead the length is limited by the attenuation of the cable so, provided that good quality cable is used, it is extremely unlikely that any cabling with a physical length of less than 90m will fail to pass the relevant standard.
On the topic of attenuation it should be noted that stranded cable is assumed to have an attenuation that is 50% higher than that of solid core cable. This means that, if extended length patch leads are used or if stranded cable is used in the Switch Links and/or the Consolidation Point cords, the maximum length of the channel will be less than 100m. To calculate the maximum channel length for different cabling configurations please refer to the following table and diagrams (see Clause 126.96.36.199 of EN 50173-2:2007+A1:2010).