When shopping for Ethernet or communication cables, you’ll often see fire ratings like CM and CMR. They may sound similar, but they serve very different purposes in building safety.
CM vs CMR Cable
What Is CM Cable?
CM (Communication Multipurpose): General-purpose communication cable.
Application: Used for simple, in-wall wiring in homes and offices.
Fire Test: Must pass a basic flame test (horizontal burn).
What Is CMR Cable?
CMR (Communication Riser): Riser-rated communication cable.
Application: Designed for vertical cable runs between floors in a building.
Fire Test: Must pass a vertical flame test (riser test), preventing flames from spreading upward.
Key Differences: CM vs. CMR
| Feature | CM Cable | CMR Cable |
|---|---|---|
| Fire Rating | Basic, horizontal flame | Riser-rated, vertical flame |
| Use Case | Residential, in-wall runs | Vertical shafts between floors |
| Cost | Cheaper | Slightly more expensive |
👉 Rule: CMR can replace CM, but CM cannot replace CMR in riser spaces.
Conclusion
If you’re wiring a single floor home or office, CM cable works fine. For multi-floor installations, always choose CMR for safety and NEC compliance.
“For a complete overview of CM, CMR, and CMP ratings, see our ultimate fire rating guide.”
