Riser vs Plenum Cabling Explained

By Brian Rhodes, Published Apr 18, 2019, 02:05pm EDT

You could be spending twice as much for cable as you need. The difference between 'plenum' rated cable and 'riser' rated cable is subtle, but the cost difference is big.

What is the proper use for each type, and how can you avoid costly mistakes? We look at the differences between 'plenum' and 'riser' types, and why not knowing the difference could be costing you big.

Flammability ********

*** ********** ******* ***** riser ** ****** (***/***) cable *** ****-***** ***** is ***** ** *** jacket ***********. ******, ******* ***-**** ***** jackets *** ********* *** can ******** **** ***** in * ******** ****, providing ** ****** *** flame ** ****** *************** ********. ********** ** ******-**** areas **** ******** ****** or ******** ******, *** velocity ** *** ****** in *** ***** *** turn * ******* **** a *************. *** ***** jacket ****** ******** **** fuel *** ******* *** a ****.

** ********, ***** (***) and ****** (***) ****** are ******** *********** **** fire-resistant materials **** ****-********** *****, or *** *** *********, to **** *** ******** fire ***********. **** ** run ** ****-********** **************** ******** ****** ** in ******, ***** ******** do *** ********** ** a ****'* ******.

Plenum ** *****

** **********, ****** ******* have **** ********* **** rating **** ***** *******. The *** ******** ****** to ******* *** ****** rating ** **** ********* than ******** ** ***** products:

  • ***: *** ****** ******, *** additive '*********** ******** *******' *** * **** high ******* ***** (***° F). ** *******, ** remains ******** ****** ** lower ************ ** **** and ****** **** ***-***** cable, *** *** *********** electrical ********** **********.
  • ****: *** ***** ******, jacket ******** ******** ** *********** ********* ************* * ****** ******* point **** '*******' *** (usually 250 °*), *** ** less ********* **** *** as * *** ********.** **** *** **** insulating ********** ****** *** Datacom *****.

Cost **********

*** ********* **** ********** in ***** ********* *** be ***** *****. ******** the ***** ** ***-***** vs ***** ******* ** almost ****** ****** *%, the **** ******* ***** (CMR) *** ****** (***) can****** ****** ** ****:

When ** *** ****

**** ********** ***** *** security ********, ** *** be ****** *** ******** to ******** ** ********* 'Plenum ***** **********'.  ***** plenum ******* ***** *** most ********* ************ ** cabling ** * ********, many ********** *** ** reduce **** ** ********* inventory ** **** ****** *** rated *****.

** *** ***** ****, some **** ******* ** architects ***** ******* ****** by ******* ** ***** the ******** ** ******** specification ** ** '***** themselves' ** **** **** a ******. 

*******, ** **** *****, cost *** ** ******* by ***** *** ******* cable **** *** *** job.  ** ********* ****** where **** **** *** be **** *****:

***** (***) *****

**** ***** ****** ******* two ******, ** ********* is *** ******* * hole ** * ******** conduit ** * ******** spot. **** **** ** called * '***** *****' and ** ******* ******* in * ******, ** a **** *********** '***** closet' **** ********* ****** also ****** ******* ******. Since *** ***** ******* is ******, *****, *** typically **** *** **** a **** ******** *******, the ***** ******* ******* this ***** **** *** need ** **** ****** 'plenum' **************:

****** (***) *****

**** ***** ******* ******* rooms ** ****** ****** HVAC ********, ** ****** be ****** *****. ******* ducts *** ***** *** shortest ******** ******* *** points, ***** ** ****** inside ** ** *** outside ******* ** *** duct.

*******, ******** ** ******* perception, *** *** ***** above * **** ******* is *** ****** ******. In **** *****, **** is * ****** ********** if **** *** ***** is *** ** ****** part ** *** **** air **** *******. 

***** *** ** ***** more *********** **** ***, it *** ** **** in *** ***** ** riser ******* ** *** expense ** ****** *****.

******** *****

** ***** ******* ******* in * ****** *****, nor ******* ******, ** requires ** ******* ******:  

*******, ***** ************ *** apply, **** ******* ****** protected ** *******, ***** trays, ** **** *****. Running ****** *********** **** ceiling *****, ********** ** high-voltage *******, ** ** areas ******* ** *** are ***** ****** ********, but ** ******* ************ rating *******.

****** **************'*

** * ******* ***, using *** ***** ** is *** ******** ******** take ********, ***** ********* off *** ****** ****.  If * ** **** non-rated ***** *** ***** ~$3.50 ** *****, ********** using *** *** **** than ****** ***** ** ~$7.60.

*******

** *******, ****** ***** should ** **** ****:

  • ******* **** ** ** on ********:**** **** ***** *** 'if ** ******* ******, it **** ** ****** rated', ** **** ****** run ******* * **** run **** ** *** rated.
  • ******* **** **** ** active ******** ********: **** ** ***** overhead **** *****, ** still *** ** ** exchange ****** ******-********. ** ******** ********** into************* ** ******* *****, it ****** ** *** active. *******, ** ***** furnace ***** ** ****** vents *** *******, *** space ****** ******** *** cable.
  • ******* ******* ******: *** *** ** used ** ***** ** CMR ** ******.

*******, ***** ****** *** used ** *** ******* application:

  • ******* ******* ******: ****** ******* ** or **** ** ******** floors ****** ** *** rated, *** *** ******* designated ******** ** *****.

***** ***** ***** *** be **** ** '******* purpose' *** ***-***** ******, it ****** ** **** in ****** ************, *** tends ** ** ****** higher **** ***** *********.  Utility *** *** ** limited, *** **** ****** in **** ****** *********** for ****** *****.

*** ****** ********** ** both ***** *** ******** for ******* ******* ********, but ** ******* ********** like ********* ** ***** wires *** ********, *** must **** ** *********.

Comments (15)

OK, I'll admit I'm fighting a cold and hopped up on DayQuil, but I don't see any prices in this graphic:

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Ha! It's not the DayQuil!  We edited out specific prices, but didn't update that part of the text.  I will now!  Thanks.

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Good article.  What about a whole home multi floor home network in a typical North American wood frame house.  Does non-rated cable add a fire-risk?  I’m hoping the answer is “no” due to the “wood frame” part?

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Does the house have a plenum? If the house is on fire to the point where the actual frame is burning the cable type is not an issue. Think of all the chemicals in furniture, electronics, plastics...that concoction inhaled is enough to kill you twice. I never seen a residential rated cable for different types of residential constructions new or aged homes but that is because I simply know nothing about it.

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Having installed tens of thousands of feet of coax, CAT3, CAT5, etc. in residential establishments while employed by major service providers, I can tell you (in Canada anyways) that riser rated cable is acceptable in almost every residential circumstance.

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  • Cabling runs in or on Ductwork: Most AHJs adopt the 'if it touches plenum, it must be plenum rated', so even cables run outside a duct run must be CMP rated.

I'm trying to understand this.  If it touches the outside of a duct it must be CMP?  Is there a reference in NEC to this?

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As a 20 year ex HVAC expert, what the hell are you doing installing cable within my ductwork?

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Good article but I would caution against calling consultants and specifiers lazy or covering themselves because they err on the side of caution when it comes to fire safety. A consultant is liable for any specification he puts his name to and generally speaking should put the  safety and the lives of people before profit (one would hope). 

 

Another consideration is that there often local / national / international fire safety regulations that dictate the type of cable used, and it is in many instances now a requirement to use Low Smoke Zero Halogen (LMZH) as part of cable specifications in many of the projects I work on.

This is because the spread of fire is not the only concern when cable specifications are defined  and the  emission of noxious gas poses a significant threat to survival rates in building fires.

In my opinion as a specifier / consultant  ( neither lazy or gutless) I would be happy to discuss the increased cost of using a fire resistant or LMZH cable if it saves even one life.

 

 

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Thanks Warren, I changed the text to eliminate 'lazy', as it just read as a cheap shot and does not convey a professional objection.

The broader point is that CMP specifications can be wasteful when not needed.

Your rebutt makes sense, and to me argues that a consultant/specifier should be involved as early as possible in a project. However, in terms of expanding code specification  requirements so that all cable is CMP or LMZH or non-toxic, which code authorities specify this?  I certainly do no doubt it, but we'd like to revise the report to reflect 'Expanded Requirements' and cite examples.

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Consultants, sales people or whoever can specify the correct type cable for wherever it goes but there is still one detail left out here, the technician. If the technician is on a large project where there are multiple types of cables being installed I guarantee a cable will get ran where it is not supposed to get ran. I am not blaming the technician either.

Depending on the number of cables being ran there is no way to truly keep track of what cable goes where. Even if you mark the boxes or reels well. Plenum has a different feel to it other than straight PVC typically but not always. I worked for a company that had special cable marked for access control, this was right before we started using composite cable, and the idiot PM that placed the $20,000 order didn't specify plenum cable, even though that's what we used 99% of the time. Well they delivered the cable to us over two hours away for a last minute prewire and we installed said cable. Sure I could have read the box labels, and should have, but I also figured if we bought $20K of customized cable that the cable would have been verified before is was delivered 2 hours away, but the cable felt like plenum so I didn't question the cable. Well a couple of weeks later a go getem' inspector came out and actually looked at the cable and noticed it wan't plenum. Guess what we had to rewire the whole damn site. 

We always use plenum cable in our projects regardless unless we know the entire job is going to be in conduit.

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I regularly and purposely overspec cables because

1. The man-hours required to perform the installation are the true cost drivers, not the cable itself

2. Safety first; as Warren stated above, I won't put lives at risk for a few bucks

3. Future proofing; this is a slightly different point but also a cost driver: in addition to the overall shielding of the cable, it also makes sense to screen or shield each twisted pair to reduce interference and support higher bandwidths or future applications. In my own home, I went as far as to exceed Cat 8.2 specs (S/FTP, 2000 Mhz). It's much cheaper to do this than to rewire the place even once (see point 1 above).

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Something worth noting and often overlooked is that if you are running non-plenum cabling and it traverses or enters a plenum space even if for only a minimal distance, say 6 inches, the entire run must be plenum rated cabling.  And honestly, the general statement that consultants are too lazy or too concerned about covering their butts is not only absolutely inaccurate but very unfortunate to see from a company such as IPVM, who is seen and read by so many people in this industry.  To me it simply shows that there is a significant lack of appreciation or true understanding of the impact that consultants have in this industry.  Do consultants sometimes make mistakes?  Absolutely and we have all seen some obvious mistakes on specs that just make you shake your head and wonder how this person gets paid for such work.  But at the same time, we have also seen some detailed specs that baffle you.  The level of detail and thorough understanding of the codes, the technology, the manufacturers, the industry trends and on and on are nothing short of amazing.  

The use of plenum over non-plenum is one that I have seen debated for the past 25 years.  Most companies I have worked for take the position that all projects should be run with plenum cabling period.  Sometimes the added cost to verify that each section the cabling will be installed into is plenum or not makes no sense.  Just run it with Plenum and call it a day.  Save money by not stocking multiple versions of the same type of cable.  Save even more money by not losing a lawsuit for specifying or installing the wrong cable.  Save a ton more by not accidentally contributing to the death of an innocent person in the building who was overcome with noxious gases.  Oh and to those who comment that what difference does it make when you have so many other materials that will release dangerous smoke and gases during a fire, they should really consider whether or not they should remain in an industry that is trying to protect assets and lives.  Just because there are other toxic fumes released by materials that are not as tightly regulated does not mean it is more than okay to go ahead and add even more toxicity especially when doing so is a violation of code and of morals.

Just my two cents.  Plus when you analyze the actual impact of the cost differential to err on the side of caution and choose to use plenum when maybe you could've gotten away with non-plenum, only comes down to just over 1%.  For example let's say you have a project that you sell for $117,000.  The cost of the plenum cabling runs around $3,800 ((6) 1000' spools of plenum rated unshielded CAT6).  The cost of non plenum unshielded CAT6 cabling is about 40% less which for (6) 1000' spools will run you about $1,520 less.  That equates to about 1.3% reduction.  If you are losing your projects based on that differential and the customer does not see the added value of your life safety consideration and understanding of code compliance, then I feel for you.  Maybe it would make sense to reduce your margin by 1.3% to cover the cost of doing it right especially if you know you are competing against the proverbial trunk slammer just to ensure you do not lose squarely due to your cabling selection.  The time spent researching non-plenum cabling alternatives to your most likely already stocked warehouse of plenum cabling and the added legal risks and all other concerns regarding this small decision just make no sense to me.  Use plenum and save yourself from the small risk that a fire marshal or other AHJ will require you to rip it out and start over with plenum-rated only cabling.  That brings up another point... Is everybody out there removing vacated cabling when running new cabling for systems? For example, when you install a new IP video system are you removing all of the existing coaxial cable, which may be tie wrapped or bundled tightly with other system cabling or in pipe with too many cables and a fill ration too close to 100%.  The NEC requires this and has for like 18 years or something.  I'm just curious if that is the standard method of operation being used by most integrators?  I do not want to be blamed for hijacking this forum and this plenum / non-plenum post but I am curious... 

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This is fantastic, I often get told which class of cable to run, but never think to ask why we are using CMP vs CMR and vice versa.

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Another consideration I don't think anyone has mentioned is outdoor/wet enviroments. My background is mostly sales, but we've found that a plenum cable will degrade much more quickly if exposed to moisture, such as in a conduit in a parking deck or on a roof. Yes, most cables do have outdoor jacketing that should be used where moisture is encountered, like if it's underground, but I would think "riser-rated" non-plenum meets codes when run in a conduit if it's on a parking deck, roof or other "unconditioned" areas exposed to moisture. Again, if you're company's standard is "just use plenum" that could create a performance and/or service issue down the road. IPVM, did you address outdoor and wet environments and the proper jacket-rated cable to use?

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I have replaced lots of plenum cable in underground conduit runs. The conduits all eventually get water in them. Plenum cable is even worse as it acts like a sponge. Typically for just a few dollars more you can run the correct cable the first time. Of course if you aren't around when the cable goes bad then perhaps you never know.

I know years ago getting the proper cable for underground use was hard to get and much more expensive than it is now.

Our standard is to just use plenum except when you are dealing with outdoor cable runs either in conduit or direct burial. Then we use the appropriate cable. Too often for indoor cable runs if we use different types then always non plenum cable gets ran in plenum spaces.

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