I'm planning on wiring my house with CAT6 cable. I'm finding a large jump in price between CMR and CMP cabling, and I'm confused by what counts as a 'plenum' and what does not.

As I'm wiring my house, I'm planning on going through interior (hollow) walls, and through the attic and crawlspace to get to the points I wish to wire. I will be going between floors at one point, which leads me to believe I need at least CMR, and obviously CMP wouldn't hurt either.

I don't mind spending the extra money if I need to, but is it overkill going for CMP if the bulk of the wires are either going vertical, or through a crawlspace or attic?

3 Answers 3


If you will never need to run it through air-handling ducts/spaces, just get Riser rated. But, for retrofits, that's often the easiest route from basement to the upper floors... and sometimes a few basement ceiling joist spaces are covered over with tin (or foil-covered cardboard) to use as inexpensive cold air return ducts - if you have to go through those, Plenum rating is required, too. If there's ever a hot enough fire to melt CMR's covering, any toxic fumes it might emit will be among the least of your worries... but the Riser rating means its fire-resistance will keep the flames from following it between floors. DO use firestop caulk to seal the holes in the sill plates or flooring wherever they're penetrated with wiring/cables or pipes. Even if you didn't make the holes, taking care of that detail can mean having many extra minutes to find/reach someone trapped on upper floors while they're still alive.


In most cases, Plenum is a space that acts as part of the HVAC system. A typical suspended ceiling that allows air back into the HVAC system would be a plenum. The Plenum rated cable will produce lees noxious fumes if it burns. This would be critical if a fire in one part of a building pumped deadly fumes into occupied spaces through the HVAC system.

It does not sound like you need plenum rated cable.


Check with your local electrical building code. Some cities require plenum cable to be used regardless if you need it or not.

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