Pulling the wrong jacket rating into the wrong space is one of the easiest ways to fail an inspection, get a job red-tagged, and eat the cost of a re-pull on your own dime. Here is the short version of what jacket ratings mean, where each one belongs, and how to keep your jobs code-compliant.
The National Electrical Code (NEC) classifies low-voltage cable jackets by how they behave in a fire. The three ratings you will see most often on residential and commercial jobs are CMP, CMR, and CM. CMP is plenum-rated, the strictest. CMR is riser-rated, the middle tier. CM is general-purpose, the lowest tier. Each higher rating can substitute for any lower rating, but never the other way around.
Plenum (CMP) is required in any space used for environmental air return. That means above drop ceilings that double as return-air plenums, under raised computer-room floors that move air, and inside HVAC ducts. The jacket is typically a fluoropolymer like FEP that produces less smoke and stops flame spread faster. CMP is the most expensive cable on the shelf, sometimes 2-3x the cost of CM, and it is stiffer and harder to terminate. Use it only where code requires it, but use it every single time code requires it.
Riser (CMR) is required in vertical shafts that pass between floors. The classic example is a multi-story telecom riser closet stack. CMR is rated to prevent fire from traveling floor to floor through the cable jacket. It is fine for general in-wall and in-conduit runs on the same floor too. Most commercial bulk cable in 1000-foot pull boxes is CMR by default because it covers the most use cases.
General-purpose (CM) is the residential and small-office workhorse. It is fine for single-story horizontal runs that do not pass through plenums or risers. CM is the cheapest option and the easiest to terminate, but it cannot be substituted for CMR or CMP under any circumstances. If you are not sure whether a space is a plenum, ask the GC or the mechanical engineer before you pull. Assume plenum if a drop ceiling has return grilles and no ductwork.
A few field rules to live by. Always check local code, because some jurisdictions are stricter than the NEC baseline. Stage your cable boxes by space type before you start pulling, with CMP boxes labeled and separated. Match faceplate, jack, and cable assembly ratings — a CMP cable in a CM jack assembly fails inspection. Document the cable type and lot on every drop, especially in commercial work where as-builts get audited.
Rack IT carries Cat5e, Cat6, and Cat6a in CM, CMR, and CMP jackets, plus matching jacks and patch cords with the right ratings. Trade accounts get tiered pricing on bulk and full-pallet orders. If you are not sure which jacket fits the application, send your spec sheet to support and we will help you size the order.