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The 100 m Ethernet channel limit includes patch cords at both ends, so the permanent link in the wall is typically capped at 90 m. Copper derates further in heat — roughly 0.4 percent per degree above 20 C — and in dense bundles where mutual heating raises the conductor temperature, which is why PoE-heavy installations need shorter runs.
Length limit
derated channel = standard limit x (1 - temperature derating - bundle derating); permanent link = derated - patch cord length
Alien crosstalk between adjacent cables. Cat 6a adds tighter twisting and often shielding to control it, restoring the full 100 m.
Indirectly. Power dissipation heats the conductors, and the resulting temperature rise derates the permitted length, which matters most for high-power PoE in full bundles.