Cable Jacket Fire Ratings — CMP, CMR, CM & CMX
The communications cable fire ratings from NEC Article 800 (2023 edition): the flame test behind each listing (800.179), where each may be installed (800.113), and who substitutes for whom (Table 805.154). This chart is code, not guidance — these listings are law where the NEC is adopted, and the inspector reads the jacket legend.
Communications cable ratings, strictest first
| Rating | Listing | Flame test | Where permitted | CL2/CL3 equivalent | Substitutes for |
|---|---|---|---|---|---|
| CMP | Communications plenum | NFPA 262 (Steiner tunnel) | Ducts, plenums, and other spaces used for environmental air | CL2P / CL3P | CMR, CM, CMG, CMX |
| CMR | Communications riser | UL 1666 (riser shaft) | Vertical runs between floors (shafts, risers) | CL2R / CL3R | CM, CMG, CMX |
| CM / CMG | Communications general-purpose | UL 1685 (vertical tray) | General in-building use on one floor; cable tray | CL2 / CL3 | CMX |
| CMX | Communications limited-use | UL VW-1 (vertical wire) | Dwellings and limited use — in raceway, or exposed runs under 10 ft | CL2X / CL3X | — |
Section numbers moved — cite the cycle
Article 800 is the most renumbered corner of the low-voltage NEC: the 2020 edition split the old Article 800 into 800 (general) plus 805 (communications circuits), and the 2023 edition moved all cable listings back into 800.179 while leaving the substitution table at Table 805.154. Class 2/3 cable listings likewise moved from Article 725 into the new Article 722 (722.179) in 2023. The ratings and hierarchy are stable across all of this — only the section numbers travel — but when a spec or an inspector cites a number, confirm which cycle their jurisdiction has adopted.
One more thing the ratings don't do
A jacket rating says nothing about conduit fill: NEC 800.110(B) exempts communications cable from the Chapter 9 fill rules entirely, which is why the 40% figure on the Cat6 conduit fill chart is TIA guidance rather than code. The parallel fire-alarm cable family (FPL/FPLR/FPLP, NEC 760) follows the same suffix logic — see the fire alarm cable types chart.
Common questions
What is the difference between CMP and CMR cable?
The space each may occupy. CMP (plenum) passes the NFPA 262 Steiner-tunnel test for low flame spread and low smoke, and is the only communications rating permitted in ducts, plenums, and other spaces used for environmental air — like above a drop ceiling used for return air. CMR (riser) passes the UL 1666 shaft test, which proves flame won't climb floor to floor, and is required for vertical runs between floors. CMP may substitute for CMR anywhere; CMR may never go where CMP is required.
What is the cable substitution hierarchy?
Down only: CMP substitutes for CMR, CM/CMG, and CMX; CMR for CM/CMG and CMX; CM/CMG for CMX. A communications cable may also substitute for a Class 2/3 cable of the same or lower fire tier (CMP for CL3P/CL2P, CMR for CL3R/CL2R, and so on) — but never the reverse: a CL3P cable is not a permitted substitute for CMP. Running plenum everywhere as a single SKU is compliant and common; the only cost is the cable.
Where is CMX cable allowed?
The limited-use tier: dwellings, cable in raceway, and short exposed runs (under 10 ft) — the rating on much outdoor and direct-burial cable. In one- and two-family dwellings, CMX under 0.25 inch diameter may run exposed. It passes only the VW-1 vertical-wire flame test, the lightest in the family, which is why its use is boxed in.
Do these ratings apply to Cat6 cable?
Yes — the category and the jacket rating are independent axes. Any Cat5e/Cat6/Cat6A cable carries a communications listing (per NEC 800.179): the same Cat6 construction sells as CMP, CMR, or CM, and the jacket, not the category, decides where it may be installed. A plenum ceiling needs Cat6 CMP; the category only decides how fast it certifies.
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