Structured Cabling Channel Length (TIA-568)
Whether a twisted-pair horizontal channel is within the TIA-568 limits: 100 m total = a 90 m permanent link plus up to 10 m of patch and equipment cords, with the permanent-link maximum de-rating above 20 deg C (about 0.4% per deg C for UTP). An 85 m link with 8 m of cords at 20 deg C passes (93 m channel, link within the 90 m max); at 40 deg C the max link de-rates to 82.8 m so the 85 m link fails and must be shortened. A design aid; the cable's published de-rating and the adopted TIA-568 edition govern.
Formula and source
max_pl = 90 x (1 - max(temp - 20, 0) x derate); channel = permanent_link + cords; pl_ok = permanent_link <= max_pl; chan_ok = channel <= 100 m.
ANSI/TIA-568 (Balanced Twisted-Pair Telecommunications Cabling) 100 m channel model and the temperature de-rating of the permanent link, by name.
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