For network cable laying, external jackets protect cables against crush, abrasion, and moisture, and they also ensure longevity and compliance with codes. However, various mill environments will need different kinds of jackets. Cables with a wrong type of jacket cause wrong inspections, safety hazards, and additional insurance costs.
Therefore, here is the information about some common types of materials and NEC jacket ratings for Ethernet cables.
How Does a Plenum Space Look Like?
The term plenum describes the air distribution zones in buildings that facilitate the circulation of heated or cooled air through the heating/ventilation/air conditioning (HVAC) system. This is typically found in the area above the dropped ceiling or below the raised floor.
The ceilings of a dropped ceiling and the floors above a raised floor are common plenum spaces that have air move between them and the rest of the building. Smoke from a fire can spread rapidly to different parts of the building via the plenum space, thus creating dangerous situations for anyone in the building, including the workers and the firefighters. And as these spaces disperse air in the whole building, any fire spread in them could in addition spread the smoke and flames. Therefore, communication cables in plenum areas must comply with high standards of fire safety.
If being used in such instances, they should definitely be rated as CMP (Communications Plenum). These cables are manufactured with FEP (fluorinated ethylene propylene), a K-type plastic like Teflon, with low smoke generation and flame-resistant properties. They are classified as low smoke cables and their burning does not present any significant health risks and their visibility is high during an evacuation.
In ceilings, schools, hospitals, and commercial plenum spaces with speed ventilation of airflow
All air spaces that have fire safety control factors.
What About the Riser Space?
Riser spaces, or vertical shafts that bind different floors of buildings, have power lines, telephone wiring, and other means of interconnection of each floor. It is in these spaces that the cables pass from floor to floor.
Despite the fact that the air circulation system is not occupied in the riser spaces, fire can still reach the upper floors within a shorter period of time. To this end, the cables must be made with resistance to of flame spread.
Cables destined for riser installations are classified as CMR (Communications Riser). These cables primarily feature fire-retardant additives weaved into PVC (polyvinyl chloride), strongly allowing them to self-extinguish if a fire breaks out or stopping the flames from moving upward.
In-wall vertical runs between floors
Commercial buildings where cables run up or down inside walls
External environment of plenum zones
Common Jacket Materials
PVC – Polyvinyl Chloride
A prevalent type of insulated outdoor cables
Lightweight, flexible, non-rusting, and low cost
Not processed PVC forms high density and lethality of smoke
Untreated PVC has to be treated chemically to be used in CMR/CMP
Does well for cables other than general-purpose cables, indoor and outdoors (CM or CMG) proportion and riser rated (CMR)
LLDPE – Linear Low-Density Polyethylene
The manufacturer employs it in the making of outdoor Ethernet cables
Highly resistant to UV rays, moisture, and temperature changes
Superior in non-hygroscopic, flexible, and durability to pure polyethylene
Low tensile strength and combustibility—unsafe to carry indoors
Mostly present in CMX-rated cables
Common Cable Jacket Ratings (NEC Standards)
The National Electric Code (NEC) defines specific ratings for communication cables. Each rating tells you where the cable can be safely installed.
Below is a complete list of key NEC jacket ratings and their approved uses:
| Rating | Description | Approved Uses |
|---|---|---|
| CMP | Communications Multipurpose, Plenum | Plenum spaces, risers, general areas. Lowest smoke emission; required for air-handling spaces |
| CMR | Communications Multipurpose, Riser | Vertical runs between floors. Fire-resistant but not for plenum; emits some toxic fumes |
| CM / CMG | Communications General | Single-room use, patch cables. No fire rating; not for in-wall or plenum use |
| CMX | Communications, Outdoor/Residential | Outdoor, direct burial, residential indoor/outdoor. UV and water resistant; not fire-safe for indoor use |
| CATVP | Cable TV Plenum | Plenum spaces for coaxial video. For video systems in commercial plenum areas |
| CATVR | Cable TV Riser | Riser spaces for coaxial video. Vertical runs for TV/cable installations |
| CATV | Cable TV | General indoor video use. Non-fire-rated; limited to non-critical areas |
| CATVX | Cable TV, Residential | Residential video installations. For home TV systems; outdoor entry allowed |
| CL2P / CL3P | Class 2 / 3 Plenum | In-wall plenum spaces with power-limited circuits. For low-voltage wiring (e.g., thermostats, speakers) |
| CL2R / CL3R | Class 2 / 3 Riser | In-wall riser spaces with power-limited circuits. For vertical low-voltage runs |
| CL2 / CL3 | Class 2 / 3 | Non-plenum, non-riser in-wall use. General low-voltage indoor use |
| CL2X / CL3X | Class 2 / 3, Residential | Residential in-wall use. For low-voltage wiring in homes |
• CMP is the highest indoor rating. It can replace CMR or CM in any indoor application.
• CMR cannot be used in plenum spaces.
• CMX is for outdoor or residential use only.
• Always verify local codes—some areas have stricter rules than NEC minimums.
Quick Reference: Where to Use Each Jacket Type
- Above ceiling (plenum) — CMP
- In-wall between floors — CMR
- Inside a single room (patch cable) — CM or CMR
- Outside, exposed to sun — CMX
- Buried underground — CMX (direct burial rated)
- Residential in-wall — CMR or CMX (with indoor transition)
- HVAC air ducts — CMP only
This structured, accurate breakdown helps installers, IT professionals, and DIYers choose the right cable for safety and compliance. By understanding materials and ratings, you avoid code violations and keep buildings safer in the event of a fire.
Contact us for more information
Will is the Copper Cabling Product Manager at Zion Communication,
specializing in the development and marketing of Ethernet cabling solutions.
With extensive industry experience, he is dedicated to delivering high-performance
and reliable cabling products to OEM/ODM clients worldwide.
will@zion-communication.com
+86 -18268007201
