Cat8 S/FTP Cable: 2000 MHz Inside a 30 Metre Box
Quick answer / TL;DR: Short answer: Cat8 S/FTP is a 2000 MHz shielded cable supporting 25GBASE-T and 40GBASE-T to 30 m, or 10GBASE-T to 100 m. The 30 m limit suits top-of-rack and adjacent-rack links, not horizontal cabling. It requires Cat8.1 RJ45 or Cat8.2 GG45/TERA connectors, and beyond 30 m at 25G or 40G the correct answer is fibre, not a longer Cat8 run.
Headroom is built: separator, 23 AWG copper, foil and drain.Cat8 is the highest copper category in commercial use: 2000 MHz of bandwidth and 40GBASE-T support, but only across a 30 m channel. That distance limit is not a manufacturing shortfall, it is the standard, and it decides where Cat8 can be used before any other consideration.
S/FTP is the dominant Cat8 construction: each pair individually foil-wrapped, with an overall wire braid. Two layers, because at 2000 MHz a single shield layer cannot keep alien crosstalk under control.
Why 30 Metres
40GBASE-T was designed around the distance that makes sense in a data hall: server to switch within a cabinet row. Pushing 2000 MHz through copper costs insertion loss and crosstalk that grow with length, and beyond 30 m the margin for alien crosstalk between parallel cables disappears.
The consequence for design is immediate. Cat8 is a rack-level and row-level cable. It does not replace Cat6A in horizontal cabling, and a project that specifies Cat8 to the desk has misunderstood the standard and will pay a large premium for a channel it cannot legally test.
| Link speed | Cat6A reach | Cat8 reach | Practical use |
|---|
| 1000BASE-T | 100 m | 100 m | either works; Cat8 wasteful |
| 10GBASE-T | 100 m | 100 m | Cat6A cheaper |
| 25GBASE-T | not supported | 30 m | switch to server in same row |
| 40GBASE-T | not supported | 30 m | top-of-rack and adjacent rack |
| Beyond 30 m at 25G or 40G | n/a | not possible | use fibre, AOC or DAC |
S/FTP at 2000 MHz
At 2000 MHz the pair foils handle internal coupling and the braid handles external fields plus the residual alien crosstalk between cables. Braid coverage is typically 60 to 85 percent, which is enough at these frequencies when combined with the pair foil underneath.
The construction is stiff and heavy. Cat8 S/FTP at 22 or 23 AWG commonly measures 8 to 9 mm in diameter with a minimum bend radius several times the diameter. In a dense rack that bend radius, not the bandwidth, is what constrains the cable route.
- Braid and foil must both bond at the connector shell, not one or the other
- Cat8.1 uses RJ45; Cat8.2 uses GG45 or TERA, and they are not interchangeable
- Bend radius is large; plan cable managers sized for Cat8, not Cat6A
- Weight per metre is high; check vertical cable management load
- Patch cords must be Cat8 rated, or the channel fails regardless of the bulk cable
Real-World Applications
Top-of-rack server connections
The canonical Cat8 use: a switch at the top of the cabinet feeding servers in the same cabinet, runs of 3 to 10 m. Cat8 S/FTP patch cords handle 25G or 40G without optics, which keeps cost and latency low for short links.
Adjacent-rack spine links
Where two cabinets sit side by side and the run stays under 30 m, Cat8 copper is often cheaper than optics plus transceivers. Beyond that distance the economics flip quickly toward DAC, AOC or fibre.
High-density storage arrays
Storage controllers with 25G or 40G copper ports inside a single rack benefit from Cat8 because the cabling stays passive. The constraint is cable management space, since Cat8 patch cords do not bend tightly enough for a standard 1U finger duct.
Test labs and equipment rooms
Development labs that need to move large datasets between machines in one room use Cat8 for short, fast links. It keeps the setup passive and reconfigurable, which matters more in a lab than in production.
Related reading: Where Cat8 deployment actually stops — blogs/news/cat8-deployment-limits
Related reading: Connector options for Cat8 — blogs/news/cat8-rj45-connector
Standards and Verification
Cat8 is defined in ISO/IEC 11801-1 and ANSI/TIA-568.2-D at 2000 MHz with a 30 m channel. Component requirements are in IEC 61156-5. Confirm which version applies: Cat8.1 specifies RJ45 and is backward compatible with lower categories, Cat8.2 specifies GG45 or TERA and is not RJ45-compatible.
Ask for a 30 m channel test report at 2000 MHz covering all pairs, with the connector and cord models named. A bulk cable component report alone does not demonstrate a passing channel, and Cat8 channels fail more often from connector and cord choices than from the cable.
For alien crosstalk, request PSANEXT and PSAACRF from a bundle test. At 2000 MHz this is the parameter most likely to fail in a dense rack, and it is the one most often omitted from supplier documentation.
Cat8 patch cords are frequently the weak point. A Cat8 bulk cable terminated with Cat6A cords is a Cat6A channel. If the project warrants Cat8, budget for Cat8 cords and confirm the supplier tests the assembly as a channel.
Frequently Asked Questions
Is Cat8 worth it over Cat6A?
Only for 25G or 40G links under 30 m. For 10GBASE-T, Cat6A reaches 100 m at a much lower price, so Cat8 adds cost with no benefit. Judge by the link speed and distance, not by the category number.
Why is Cat8 limited to 30 metres?
Because 40GBASE-T was specified for data hall distances, and alien crosstalk between parallel cables beyond 30 m cannot be controlled within practical cable designs. The limit is part of the standard, not a quality issue with any particular product.
What is the difference between Cat8.1 and Cat8.2?
Cat8.1 uses RJ45 connectors and is backward compatible with Cat5e through Cat6A. Cat8.2 uses GG45 or TERA and is not RJ45-compatible. Both reach 2000 MHz and 30 m; the difference is the interface and the compatibility you get.
Can I use Cat8 for PoE?
The conductor gauge supports it, but Cat8 is rarely the right choice for PoE because the runs are long and Cat8 is expensive. PoE lives in horizontal cabling at 100 m, where Cat6A is the practical answer.
Should I use Cat8 instead of fibre?
No. Beyond 30 m at 25G or 40G, fibre, DAC or AOC is the answer. Cat8 is a short-reach copper option that avoids optics, not a replacement for fibre in backbone or long horizontal runs.
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