Plenum and riser are the two fire ratings you will see on bulk Ethernet cable. The rating tells you where the cable may be installed. Plenum cable, marked CMP, is for air-handling spaces. Riser cable, marked CMR, is for vertical runs between floors. The jacket material is the difference, not the data the cable carries.
Plenum vs riser at a glance
| CMP Plenum | CMR Riser | |
|---|---|---|
| Where it goes | Air-handling spaces above ceilings and below raised floors | Vertical runs between floors and inside walls |
| Jacket | Low-smoke, flame-retardant | Flame-retardant |
| Smoke | Low smoke | Standard |
| Cost | Costs more per box | Costs less per box |
| Used for | Office ceilings, schools, hospitals | Floor-to-floor runs, in-wall runs |
What is plenum cable?
Plenum cable is made with a jacket that gives off little smoke and resists burning. Building codes require it in plenum spaces, which are the spaces above a dropped ceiling or below a raised floor where air moves through the building. If your cable runs through those spaces, use CMP plenum cable. Red Cable Technology supplies Cat5e, Cat6, Cat6a and Cat7 in CMP plenum, in shielded and unshielded types and in ETL-listed types.
What is riser cable?
Riser cable is made for vertical runs, such as the cable that runs from one floor to the next through a riser shaft. Its jacket resists burning so a fire cannot travel quickly up the building through the cable. Use CMR riser cable for floor-to-floor runs and for cable inside walls. Our Cat5e, Cat6, Cat6a and Cat7 cables are also available in CMR riser types.
Can you use plenum cable instead of riser?
Yes. Plenum cable meets a stricter fire rating than riser cable, so it may be used in riser spaces too. Riser cable must not be used in plenum spaces. Many buyers order plenum cable for the whole job to keep it simple, but riser cable costs less, so it is the better choice where the code allows it.
What about outdoor and direct burial cable?
Outdoor and direct burial cables use a CMX outdoor-rated jacket and, in the case of direct burial cable, a gel-filled core that blocks water. They are a separate choice from plenum and riser. If the cable runs outside or underground, choose an outdoor or direct burial cable instead. See our guide to how to choose bulk Ethernet cable.
Ordering from Red Cable Technology
Orders are paid in full in advance. Regular delivery takes 2 to 5 business days, and free shipping applies in the continental US. If a cable arrives with a defect, tell us within 7 days and we will replace it. Non-ETL cables carry a 20-year warranty and ETL-listed cables carry a 25-year warranty.
Browse our Cat6 cables in plenum, riser, shielded and unshielded types, or look at Cat5e, Cat6a and Cat7.