TIA-568 Cable Length Limits: 90 m Permanent Link vs 100 m Channel

Under TIA-568.2-D, a balanced twisted-pair channel can run up to 100 m (328 ft) total, while the permanent link is capped at 90 m (295 ft). The ~10 m (33 ft) difference is reserved for patch and equipment cords at both ends. Plan your horizontal run to the 90 m number, not the 100 m number, and you stay out of trouble.

Permanent link vs channel, in plain terms

These are two different measurements of the same cabling run, and mixing them up is where a lot of failed runs start.

• Permanent link (90 m / 295 ft max): the fixed, in-wall portion you install and leave alone — from the work-area outlet, through the wall and ceiling, to the patch panel in the closet. This is what your installers actually pull and terminate.
• Channel (100 m / 328 ft max): the whole connection end to end, including the permanent link plus the patch cord at the desk and the equipment/patch cords in the rack.
• The ~10 m cord budget: that extra distance between 90 m and 100 m exists for those flexible cords. Patch cords are lossier per foot than solid horizontal cable, which is why the budget is set aside up front.

If you let the in-wall run creep toward 100 m, there is no room left for cords — and the real-world channel blows past 100 m the moment someone plugs in a 3 m patch cord.

What counts as the horizontal run

The horizontal run is the fixed cable from the outlet to the patch panel. When you estimate length, measure the actual path the cable travels, not the straight-line distance on the floor plan. That means including:

• The vertical drop from the ceiling down to the outlet.
• The rise from the device or tray up into the pathway.
• Every turn, offset, and route around obstructions.
• Service loops and slack left at both ends for termination and future moves.

A run that looks like 70 m on a flat drawing can easily land near 90 m once you add verticals, routing, and slack. That is why the longest drops on a floor deserve a real path measurement before you commit.

Why exceeding it fails

Length limits are not arbitrary. Copper insertion loss (attenuation) climbs with distance, and past the limit the signal-to-noise margin gets too thin for the link to test clean. An over-length run will not pass field testing, and a run that fails testing is one you pull and redo on your own dime. Catching it during estimating is far cheaper than catching it on a ladder.

The Cat6 vs Cat6A 10G nuance

For 1 Gigabit Ethernet and PoE, both Cat6 and Cat6A reach the full 100 m — there is no length penalty. The catch only appears at 10GBASE-T over copper:

• Cat6A supports 10G to the full 100 m.
• Cat6 can carry 10G, but only to roughly 37–55 m depending on the alien-crosstalk environment (per TSB-155-A). In a tight, densely bundled space you are at the low end of that range.

So the shorter Cat6 figure only matters when 10G is on the table. If the design calls for 10G to the desk and you have long runs, that is the case for Cat6A. Keep in mind Cat6A is a fatter cable, so a higher count fills trays and conduit faster — pathway fill scales with the square of cable diameter.

How estimators should plan the longest runs

You do not have to measure every drop, but you do have to know your worst case.

• Identify the drops farthest from each closet and measure those paths in full — verticals, routing, and slack included.
• Hold the fixed horizontal run at or under 90 m so the cord budget survives.
• If long runs need 10G, spec Cat6A rather than gambling on a short Cat6 limit.
• Where runs are genuinely too long, the fix is a closer telecom room or an intermediate distribution point — price that in early, not after a failed test.
• For budgeting, rough rules of thumb: cabling labor runs around 11 hours per 1,000 ft, carry a waste factor of about 10–15%, and add slack at both ends. Treat these as starting points that vary by job, not fixed numbers.

This is general design guidance and an estimating aid, not a substitute for the current published standard or review by a licensed RCDD or PE. Field conditions and the latest revision always govern.

Cable Takeoff's Compliance Pre-Flight flags any run that exceeds the 90 m permanent link before it reaches the field, so over-length drops surface during the takeoff instead of during certification testing. Your plans are processed in your browser and stored encrypted to your account.