Cat6 Riser Cable: CMR and the Shaft
Quick answer / TL;DR: Short answer: use CMR (riser-rated) Cat6 for vertical runs in a shaft between floors. It is not plenum-rated – if the shaft is also an air-handling space, CMP is required. Support the cable at the code spacing, firestop the penetration, and test each floor's runs after termination.
Cat6 riser cable is Cat6 with a CMR jacket: the rating that permits a vertical run between floors in a shaft, and prohibits the air-handling spaces where CMP is required. The cable is the same copper; the jacket is what the inspector checks.
This is the riser guide: what CMR permits, where it stops, and the details of a vertical pull that decide whether the installation passes.
What CMR Permits
| The rating | The permitted route | The limit |
|---|---|---|
| CM | General-purpose spaces | Not risers or plenums |
| CMR | Vertical shafts between floors | Not air-handling plenums |
| CMP | Plenum and air-handling spaces | Higher cost, stiffer jacket |
The ratings form a ladder, and the route decides which rung applies – not the cable's performance.
The Vertical Pull
- Support: at the spacing the code requires for vertical cable, not hanging free
- Firestop: at every floor penetration, with an approved system
- Bend radius: larger cable needs more, especially at the top
- Weight: a full-height bundle is heavy – plan the support before the pull
The vertical details are where riser jobs fail inspection: support spacing and firestopping are checked, not assumed.
Where It Stops
| The space | The requirement |
|---|---|
| Sealed shaft | CMR |
| Shaft used as return air | CMP |
| Floor void | Check the rating required |
| Exterior | Outdoor-rated jacket |
Standards and Verification
| The reference | The relevance |
|---|---|
| UL 444 / NEC | Jacket ratings and permitted routes |
| TIA-568.2-D | Installation practice |
| Local code | Support spacing and firestopping |
| Field test | Channel test per floor |
Per-market code details are not provided in the knowledge base. The rating ladder is standard; confirm the local requirement for the specific shaft.
Real-World Applications
The six-floor riser
A sealed shaft serving six floors: CMR Cat6 on supports at code spacing, firestopped at each slab – the inspection passed first time.
The return-air shaft
A shaft doubling as a return-air path: CMR already installed. The inspector required CMP – the run replaced, the rating checked against the space rather than the habit.
Related reading: The jacket ratings compared? Read the jacket ratings guide — blogs/news/cable-jacket-ratings
Related reading: Riser against outdoor rating? Read the CMR outdoor question — blogs/news/cmr-outdoor-rating
Frequently Asked Questions
What is Cat6 riser cable?
Cat6 with a CMR jacket, rated for vertical runs in a shaft between floors.
Can CMR be used in a plenum?
No – plenum and air-handling spaces require CMP.
Does the riser jacket change performance?
No – the copper and category are the same. The jacket governs where the cable may run.
What do inspectors check on a riser?
Support spacing and firestopping at penetrations, plus the jacket rating for the space.
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