What are Plenum Cables, and When Should They be Used?


BY: Shane Weaver

what does 'Plenum' actually mean?

What Does "Plenum" Mean, Anyway?

The word “plenum” gets thrown around a lot in cabling circles. But what does it mean? It kind of sounds like some obscure anatomical term. Some kind of a membrane, maybe, or bodily fluid. But thankfully, “plenum” is none of those gross-sounding things. So what is it, then? Let’s look up some definitions, shall we? Let's see here…A plenum is “a full assembly, as a joint legislative assembly.” Wait, what? That can't be right, I don't even know what that means. No, wait, here it is:

Plenum – a space, usually above a ceiling or below a floor, that can serve as a receiving chamber for air that has been heated or cooled to be distributed to inhabited areas.

Ahh, that's better. At its root, plenum refers to “full space,” and most of its varying definitions pertain to a separate enclosed space that is set apart from surrounding areas. To use terminology that our likely readership will understand: it's the space above a building's dropped ceilings, or below a raised flooring system that gets used for heating, ventilation, or air conditioning (oft shortened to “HVAC”).

cable rating:plenum vs riser vs general purpose

What's That Got to Do with Cabling?

So how do cables factor into all of this? Excellent query, my friend. In addition to being utilized for routing air, plenum spaces are often used to house telephone and network communication cables being run from one location to another. These cables, appropriately, are referred to as plenum cables. What sets these wires and cords apart from regular old cables? Another fantastic question. The answer is that they need to adhere to special fire-safety standards.

According to Article 800 of the National Electrical Code (NEC), plenum cables must comply with the specifications for flammability and smoke density outlined in Underwriters Laboratories (UL) and National Fire Protection Association (NFPA) testing methods.

To accomplish this greater resistance to fire, plenum-rated cables use special types of plastics in their jacket coverings. Flame-retardant, low smoke materials such as polyvinyl chloride (PVC), fluorinated ethylene polymer (FEP), or a polyolefin offer good resistance against fire, and in the event that they do begin to burn, they will not emit large quantities of harmful fumes. Which is a win-win!

where Plenum, Riser & General Purpose spaces are located

But WHhhhhhhhhyyyyyy?

Why is this all necessary? Since plenum cables are routed through air circulation spaces which often contain very few fire barriers, they need to be coated in material that won't contribute to the spreading of flames. Also, as network and communications cabling runs typically spread throughout buildings (to make sure everyone is connected to everyone else), having them ignite would be a surefire (no pun intended) way for the flames and smoke to spread that much quicker. So seriously, this is not the place you want to cut corners.

Now, perhaps you've also heard of a thing called riser cables. You might have heard that these are also flame retardant, so maybe you think you can get away with using riser cables in plenum spaces. Well, if I had a ruler I'd rap your knuckles with it for even thinking such an obscenity, because DON'T DO IT.

Riser cables are intended for non-plenum, vertical applications (ie. between floors of a building). They typically incorporate load-bearing strengtheners since they need to stay upright without being stressed too hard, and it's true that they do have to be fire resistant. However, the specifications are much stricter for plenum cables, so they are 100% not interchangeable. While you can use plenum cables in riser applications, the opposite is definitely not true.

Bottom line? If your cabling application requires materials that are flame-retardant or compliant with strict safety standards, always opt for plenum-rated products. As it happens, CableOrganizer.com offers a full line of plenum-grade cable, raceway, wire connectors and more to meet all of your fire safety requirements!


©2016 CableOrganizer.com, LLC. This article may not be reproduced in part or in full without the written permission of CableOrganizer.com.
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(based on 4 reviews)

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(5 of 5 customers found this review helpful)


Well written and cogent article

By Harry

from North Carolina

I work in the security industry, and find that this article touches the high points and gives a very cogent overview of what Plenum Cable actually is, and where it might be used. It also refers to the specific code for those who are actually in the industry, and need complete and exact guidance. I have copied this article to use for my customers who want to know why this wire is twice the price of that wire. Easy for them to understand

(8 of 13 customers found this review helpful)


Confusing for Amature

By SearchingForAnswers

from Atlanta, GA

About Me Enthusiast

Verified Reviewer

After reading the reply to a previous commenter, I'd have to agree with the previous poster that this article is somewhat misleading. An amature would infer from the diagram that all cables running through a drop ceiling need to be plenum rated. This is not the case when seperate ducting is run through the drop ceiling for HVAC, as is the case in the large majority of residential construction. Nowhere is this mentioned in the article, and amature residental installers are the primary audience for this type of article.

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(4 of 4 customers found this review helpful)


On point

By Eric the IT Pro

from Seattle, WA

About Me Enthusiast


  • Very Information


    Best Uses

    • As A Starter Guide

    This is a great starter guide for anyone beginning their journey with rated cabling systems. It is always good to reference your applicable state law on low voltage systems as well as your local permit requirements for installation of wiring systems.

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    • Business

    (9 of 19 customers found this review helpful)



    By ATechGuy

    from Houston, TX

    About Me Power User

    The article diagrams are misleading because not all air spaces above drop ceilings are "plenums". A specific example would be a drop ceiling where air ducts supply air to the space below the ceiling. In this example the HVAC ducts are the plenum, not all the space above the ceiling as the article seems to imply.

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    • Business

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