UL Listings for Network Cable: What CMP, CMR, and CM Mean

Why UL Listings Exist

Every commercial building has hidden spaces filled with cable. Those spaces are interconnected, and they can carry fire and smoke from one part of the building to another faster than the fire itself spreads. UL (Underwriters Laboratories) listings exist to certify that a cable jacket will not propagate flame or release toxic smoke in those conditions, regardless of which manufacturer made it.

A UL listing is not a quality grade for electrical performance. It says nothing about whether the cable will pass Cat6A certification or handle PoE without overheating. The listing is purely about what happens to the jacket and conductors when fire reaches them. A cable can be UL-listed CMP and still be electrical garbage if the copper is undersized.

The Four Ratings You Will See

The NEC defines a hierarchy of communications cable ratings. Each higher rating can substitute for any lower rating. The reverse is never permitted.

CMP — Communications Multipurpose Plenum

The highest commercial rating. CMP cable is required wherever cable is installed in a plenum — an air-handling space used as part of the HVAC return system. The classic case is the space above a suspended ceiling where the ceiling tiles serve as the bottom of an air return. That entire ceiling cavity is a plenum.

CMP cable passes the NFPA 262 Steiner Tunnel Test (also called UL 910). The test runs the cable horizontally through a 25-foot combustion chamber with a 300,000 BTU flame at one end. To pass, the flame must not spread more than 5 feet, smoke optical density must stay under 0.5 average and 0.15 peak, and the smoke temperature rise must remain limited.

CMP jackets are typically made from FEP (fluorinated ethylene propylene), which has excellent flame and smoke characteristics but costs significantly more than PVC. Plenum cable can run two to three times the price of riser cable for the same conductor count.

CMR — Communications Multipurpose Riser

The mid-tier rating. CMR is required for vertical runs between floors in a commercial building. The concern is that fire on a lower floor could climb the cable jacket up through floor penetrations and ignite the next floor. CMR cable resists that vertical flame propagation.

CMR passes UL 1666, the riser flame test. A 24-foot section of cable is mounted vertically in a two-story burn room and exposed to a 155,000 BTU gas burner. To pass, flame must not propagate higher than 12 feet.

CMR jackets typically use a flame-retardant PVC formulation. They are significantly cheaper than CMP and adequate for everything except plenum spaces.

CM and CMG — Communications General Purpose

The base commercial rating. CM-rated cable can be installed anywhere in a commercial building except a plenum or a vertical riser. That covers most horizontal runs above non-plenum ceilings, runs in conduit, and runs through cable trays in non-air-handling spaces.

CM passes UL 1685, a vertical-tray flame test. Cable is loaded into a ladder rack and exposed to a 70,000 BTU gas burner for 20 minutes. The damage height must remain under specific limits.

CMG (Canadian designation) is essentially equivalent. Many cable manufacturers list both on the same jacket so the cable is approved on both sides of the border.

CMX — Limited Use

The lowest commercial communications rating. CMX is allowed only in single-family dwellings and in raceways within one-story non-residential buildings. It cannot be used in any concealed space of a multi-occupancy commercial building.

CMX passes the VW-1 vertical-burn test, which is performed on a single conductor rather than a bundle. The threshold is much lower than CM, which is why CMX is restricted to residential applications.

The Substitution Hierarchy

NEC 800.154 explicitly permits higher-rated cable to substitute for lower-rated cable. The order is:

One direction only. CMP can sit in a riser. CMR cannot sit in a plenum. The substitution only goes from a more-tested rating to a less-tested rating.

How to Identify the Rating on a Cable

Every UL-listed communications cable must be marked with its rating on the jacket print at intervals not exceeding 24 inches. The print typically includes:

• Manufacturer name or trademark
• UL listing mark (UL in a circle)
• Rating designator (CMP, CMR, CM, CMX)
• Performance category (Cat5e, Cat6, Cat6A)
• Construction (4-pair, 24 AWG, etc.)
• Footage marking (sequential length)
• Country of origin

When you receive a box of cable, pull a few feet out and read the print before you start pulling cable. If the print is missing the UL mark or the rating designator, you have a problem. Some grey-market cable will print Cat6 and a fake UL number but lack actual listing. You can verify any UL listing at productiq.ulprospector.com using the file number printed on the jacket.

Plenum, Riser, and General Purpose: Where Each One Goes

The hardest part of choosing the right rating is identifying which spaces in a building are which. The NEC and the architect's drawings control this, not the installer's judgment.

What Counts as a Plenum

A plenum is any space used for environmental air movement that is part of the building's HVAC system. The most common plenum is a ceiling cavity above a suspended grid ceiling when air return is drawn from the cavity rather than through dedicated ductwork. Underfloor cavities in raised-floor data centers are also plenums if air conditioning is delivered through the floor.

Spaces that are NOT plenums: ducts (those have their own rules), ceiling cavities with hard ceilings, walls with no air movement, conduit runs. If the space does not handle environmental air, plenum rating is not required by code.

What Counts as a Riser

A riser is a vertical run that passes from floor to floor through a floor penetration in a commercial building. The classic case is a telecom closet (TR/IDF) on each floor stacked vertically with cable rising through a sleeved core hole. Anywhere cable enters one floor's fire-rated assembly and exits another, you have a riser run.

What Counts as General Purpose

Horizontal runs above non-plenum ceilings. Runs through conduit throughout a building (the conduit itself protects against fire spread). Runs in cable trays in mechanical rooms or non-occupied spaces. Drops to outlets within a single room.

Mixed Cable Types and Compatibility

You can install higher-rated cable wherever lower-rated cable is allowed, so a common strategy on small projects is to standardize on CMR for everything that is not plenum. That avoids confusion and keeps the supply chain simple. On a large project where plenum runs are a small percentage of total footage, standardizing on CMR for general purpose and stocking CMP only for plenum runs is more cost-effective.

For terminating either rating, the connector itself does not need a UL plenum listing. RJ45 connectors like the EZ-RJ45 Cat6 work on plenum-jacketed cable just like they work on PVC-jacketed riser cable. The only difference you may notice is that FEP plenum jackets are slightly stiffer and require more care when stripping with a jacket stripper.

Outdoor and Direct-Burial Variants

CMP/CMR/CM/CMX cover indoor cable. For outdoor applications, look for additional designations:

• OSP (Outside Plant) — UV-resistant black jacket, not flame-rated for inside the building.
• Direct Burial — gel-filled or armored construction for in-ground installation without conduit.
• Aerial Messenger — includes a steel support strand for aerial spans between poles.

When OSP cable transitions into a building, NEC requires it to terminate within 50 feet of the entry point in a CM-or-better jacketed cable. You cannot run OSP cable up to a workstation.

UL Listings vs Other Marks You Will See

Cable jackets often carry several listing marks. Knowing what each one means helps you verify the cable is fit for its installation location.

Note the last row. UL Verified is different from UL Listed. Listed covers the fire rating. Verified covers the electrical performance. Cable can be UL Listed (CMR) without being UL Verified Cat6 — meaning the jacket is safe but the electrical category is the manufacturer's claim alone. For high-stakes installs, look for both.

Common Inspection Failures Tied to Cable Rating

Inspectors who pull ceiling tiles and pull a foot of cable down to read the print catch a few standard issues:

• CMR or CM cable in a plenum. Wholesale failure; cable must be ripped out.
• CMX cable in a commercial install. Same outcome.
• OSP cable extending more than 50 feet inside. Requires transition to listed indoor cable.
• Cable pulled through a fire-rated wall without a firestop. The cable rating is fine but the penetration must be sealed with an approved firestop putty or sleeve.
• Cable jacket print illegible. Inspector cannot verify rating, fails the install.

How CrimpShop Catalog Aligns With Each Rating

CrimpShop sells connectors, tools, and testers — not bulk cable — but every termination solution we carry is appropriate across CMP, CMR, CM, and CMX cable. Pass-through connectors handle the slightly stiffer FEP jackets of plenum cable as easily as PVC.

Related Articles

• Plenum vs Riser Cable: What's the Difference? — Deeper comparison of CMP and CMR construction.
• BICSI Cable Installation Standards Every Tech Should Know — Industry installation standards that work alongside NEC.
• PoE Cable Requirements: AWG, Bundling, and Heat — How cable rating interacts with PoE bundling rules.