The cable in the wall outlives three generations of switches. It is the most expensive thing to change and the least likely to be documented, which is why "we have Cat6" is a claim worth verifying.
The categories that matter
| Category | Rated to | Typical use | Notes |
|---|---|---|---|
| Cat5e | 1 Gbps, 100 m | Legacy access | Still fine for phones and APs |
| Cat6 | 1 Gbps 100 m; 10 Gbps to 55 m | General access | The practical default |
| Cat6A | 10 Gbps, 100 m | Backbone, AP uplinks | Thicker, harder to bend |
| Cat8 | 25/40 Gbps, 30 m | Data center | Not for horizontal cabling |
The distance caveat is the one that bites: Cat6 supports 10GBASE-T only to about 55 meters. A 70-meter run labeled Cat6 will negotiate 10 Gbps on a cool day and drop to 1 Gbps under load, or fail to link.
What "Cat6" does not guarantee
- Installation quality. A crushed, kinked, or stapled cable fails its category.
- Connector quality. A cheap jack can degrade the whole channel.
- Patch cords. Cat5e patch cords on Cat6 permanent links limit the channel.
- Bundle heating. PoE bundles run warmer, which changes insertion loss.
- Alien crosstalk. Adjacent cables in a tight bundle can interfere; Cat6A is specified for it.
The channel is the whole path
Permanent link (wall to patch panel) plus two patch cords equals the channel. Testing only the permanent link is the most common way a "certified" installation still fails at 10 Gbps.
Shielding and grounding
| Type | Shield | Use |
|---|---|---|
| U/UTP | None | Most buildings |
| F/UTP | Overall foil | Electrically noisy areas |
| S/FTP | Braid + foil pairs | Industrial, high EMI |
Shielded cable only helps if it is grounded at both ends through proper hardware. An ungrounded shield is an antenna.
Worked example: an AP that negotiates 100 Mbps
A Wi-Fi 6 AP uplinked at 100 Mbps, with millions of dropped frames. Three candidates:
- Cable damage — a staple through a pair, or a bend radius violation.
- Wrong category or length — Cat5e at 95 m with a cheap patch cord.
- Duplex/speed mismatch — one side hard-set to 100 Mbps.
Check in order: switch port speed/duplex, cable test, then replace the patch cords before re-terminating.
What breaks in production
- Cat6 to 10GBASE-T beyond 55 m, which links at 1 Gbps or flaps.
- Cheap patch cords limiting a certified link.
- Bend radius violations during installation, invisible until 10G.
- Cable shared with fluorescent ballasts or motors, producing intermittent errors.
- Untested cabling, where the certification report was never produced.
Checklist
- Every horizontal run is documented with category and length.
- 10GBASE-T runs are under 55 m on Cat6, or Cat6A.
- Patch cords match or exceed the permanent link category.
- Certification test results exist for new cabling.
- PoE bundles are sized for the heat load.
- Shielded cable is properly grounded, or not used.
Next
Copper has limits. Continue with Fiber Types and Connectors.