A few weeks ago explored the world of plenum cables; this week will be going over the plenum cable’s distant cousin, the riser cable. What is the difference between plenum and riser? Let’s find out.

So far we know that plenum cables are built for the plenum area of a building, but where do riser cables go? The name riser leads us to believe that these cables should be installed up high, but in actuality, riser cables are designed to be placed in between the floors of a building. To differentiate the two, plenum cabling is referred to as CMP, while riser cables are referred to as CMR. A good rule of thumb to remember is that while plenum cables can be used in place of riser cables, but riser cables cannot replace plenum. Riser cable is often referred to by installers as the “backbone” cable, as these cables are typically out of sight and out of mind once that are in place.

While plenum cables have strict specifications they must meet, the rules for riser cables are a little more lax. This is because air does not flow through the floors of a building the same way it does the plenum of a building, so there is no chance of toxic air being pushed through an air vent. But because regular cables can expel harmful toxins in the heat of a fire, it’s important that these cables still be fire resistant. This means their jackets should be self-extinguishing and have a low-smoke rating.

Riser cable can also be used in elevator shafts. In order to be used in that environment, riser cables must be compliant with UL 1666, otherwise known as the “standard test for flame propagation height of electrical and fiber optic cables installed vertically in shafts.”

If you are ever in question Always remember to look for the “CMR” marking on your, to make sure it is the correct cable to use in riser areas. You can also check out our selection here!