Which copper cable categories support which speeds, and what is the distance limit?
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Say this first
Twisted-pair Ethernet is limited to 100 meters per channel: 90 m of fixed horizontal cable plus up to 10 m of patch cords. Cat5e runs 1000BASE-T and also 2.5GBASE-T. Cat6 runs 1 Gbps at 100 m and 10GBASE-T only to about 55 m. Cat6A runs 10GBASE-T at the full 100 m and is the normal choice for new cabling, especially for multigigabit Wi-Fi APs and higher PoE. Cat8 is a short-reach data center cable for 25G and 40GBASE-T up to 30 m.
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Categories
| Category | Bandwidth | Common use |
|---|---|---|
| Cat5e | 100 MHz | 1000BASE-T at 100 m, 2.5GBASE-T |
| Cat6 | 250 MHz | 1000BASE-T, 5GBASE-T, 10GBASE-T to about 55 m |
| Cat6A | 500 MHz | 10GBASE-T at 100 m |
| Cat8 | 2000 MHz | 25GBASE-T and 40GBASE-T to 30 m, rack and row only |
Choices that matter on a real job
- Multigigabit (802.3bz): 2.5GBASE-T and 5GBASE-T were designed to run on installed Cat5e and Cat6 so Wi-Fi 6 and 7 APs can exceed 1 Gbps without recabling.
- Jacket rating: plenum (CMP) for air-handling spaces, riser (CMR) between floors. Local fire code decides.
- Solid versus stranded: solid core for permanent runs, stranded for patch cords.
- Shielding: shielded cable (F/UTP, S/FTP) helps in high-noise areas but must be grounded correctly.
- Between buildings: use fiber. Copper between buildings invites ground potential differences and lightning damage.
They will ask next
Why is the limit 100 meters?
Signal attenuation and crosstalk grow with length. The standards specify performance for a 100 m channel. Longer runs may link up but show errors, especially at higher speeds.
How do you extend beyond 100 meters?
Put a switch in the middle, or use fiber with media converters or optics. For a single device at distance, some PoE extenders exist, but fiber is the clean answer.
Traps
- Saying Cat6 does 10G at 100 m. It is about 55 m; Cat6A is needed for 100 m.