CMP, CMR and Low-Voltage Cable Fire Ratings
Read communications and power-limited cable fire ratings, distinguish them from category performance and LSZH claims, and record the required installation basis.
Last updated:
Identify the cable family
A cable's transmission category and its fire-related installation classification are separate specifications. First establish whether the circuit uses a communications, power-limited or another cable family. Then read the complete designation and the requirements for the actual route.
| Family | Plenum designation | Riser designation | Other common designation |
|---|---|---|---|
| Communications cable | CMP | CMR | CM / CMG; other designations have their own scope |
| Class 2 circuit cable | CL2P | CL2R | CL2 |
| Class 3 circuit cable | CL3P | CL3R | CL3 |
This is an identification table, not a universal substitution hierarchy. The P and R variants apply within the stated cable family. Verify the adopted rules, route conditions, product listing and any permitted substitutions from the applicable documentation.
Do not label every ceiling space a plenum or every vertical cable a riser installation solely from its appearance. The space classification and route must be established from the building and project information. The UL guide provides cable categories and substitution guidance; it is not a substitute for the locally adopted requirements.
Separate fire and signal ratings
| Marking or claim | Question it helps answer | What it does not establish |
|---|---|---|
| CMP / CMR and related family designations | What fire-related cable classification is marked? | Category 6A performance or suitability for every possible route. |
| Cat 5e / Cat 6 / Cat 6A | What transmission performance is specified for this cable? | Whether the jacket classification is suitable for an air-handling space. |
| LSZH / LSOH | What low-smoke, halogen-related material or test claim is documented? | A U.S. CMP or CMR classification by itself. |
| Shielding description | How the cable screens are constructed? | A fire rating, installed link certification, or a universal grounding arrangement. |
| Outdoor / wet-location / sunlight claim | What environmental exposure has the manufacturer specified? | Permission for every interior route or a required fire classification. |
These specifications may appear on the same product, but one does not replace the others. Obtain the complete technical sheet rather than selecting a cable from a photograph, a jacket color or an abbreviated purchase title.
Review a proposed substitution
- Record the circuit type and its source/equipment requirements; do not assume all small conductors belong to the same power-limited category.
- Record the route and the required installation classification from approved project and building information.
- Transcribe the original and proposed cable legends, catalog numbers, certifications and data-sheet revisions.
- Compare fire classification, voltage, signal category, shielding, temperature, exposure and termination compatibility separately.
- Check any proposed cable substitution against the applicable rules and project approval process. Preserve the source of that decision.
A higher-sounding marketing term does not settle every field in that comparison. Similarly, matching CMP markings do not prove equal data performance or connector compatibility. Where the circuit, space or acceptance basis is unclear, identify the missing information instead of assuming a substitution is allowed.
Read an example specification
In an illustrative specification reading “Cat 6A, CMP,” Cat 6A describes a transmission-performance target and CMP describes the communications cable's plenum classification. Neither entry establishes the installed link result. Add the exact product, required environmental conditions, compatible connecting hardware and project testing basis to make the purchase and handover record useful.
For contact and pair order use the T568A/T568B reference. The PoE tables address power types and classes; the PoE budget tool compares entered device loads and switch ratings. Record the chosen cable and unresolved approvals in the job card.
For a separate resistance-based calculation, use the low-voltage drop calculator or, for its supported notification-circuit model, the NAC voltage-drop calculator. Use the required electrical inputs; jacket fire classifications do not supply conductor resistance or approve the installed circuit.