Riser vs Plenum Cabling Explained

Author: Brian Rhodes, Published on Oct 07, 2014

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.

*** ***** ** ******** ***** ** **** *** ***** ** you ****. *** ********** ******* '******' ***** ***** *** '*****' rated ***** ** ******, *** *** **** ********** ** ***.

**** ** *** ****** *** *** **** ****, *** *** can *** ***** ****** ********? ** **** ** *** *********** between '******' *** '*****' *****, *** *** *** ******* *** difference ***** ** ******* *** ***.

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Flammability ********

*** ********** ******* ***** ***** ** ****** (***/***) ***** *** none-rated ***** ** ***** ** *** ****** ***********. ******, ******* ***-**** ***** ******* *** ********* *** *** ******** like ***** ** * ******** ****, ********* ** ****** *** flame ** ****** **************** ********. ********** ** ******-**** ***** **** ******** ****** ** ******** spaces, *** ******** ** *** ****** ** *** ***** *** turn * ******* **** * *************. *** ***** ****** ****** provides **** **** *** ******* *** * ****.

** ********, ***** (***) *** ****** (***) ****** *** ******** differently **** ****-********* ********* **** ****-********** *****, ** *** *** *********, to **** *** ******** **** ***********. **** ** *** ** fire-segregated **************** ******** ****** ** ********, ***** ******** ** *** ********** ** * ****'* ******.

Plenum ** *****

** **********, ****** ******* **** **** ********* **** ****** **** Riser *******. *** *** ******** ****** ** ******* *** ****** rating ** **** ********* **** ******** ** ***** ********:

  • ***: *** ****** ******, *** ******** '*********** ******** *******' *** * **** **** ******* ***** (***° *). ** jackets, ** ******* ******** ****** ** ***** ************ ** **** and ****** **** ***-***** *****, *** *** *********** ********** ********** properties.
  • ****: *** ***** ******, ****** ******** ******** ** *********** ********* ************* * ****** ******* ***** **** '*******' *** (******* *** °*), and ** **** ********* **** *** ** * *** ********.** **** *** **** ********** ********** ****** *** ******* *****.

Cost **********

*** ********* **** ********** ** ***** ********* *** ** ***** steep. ******** *** ***** ** ***-***** ** ***** ******* ** almost ****** ****** *%, *** **** ******* ***** (***) *** plenum (***) ********* ****** ** ****. *** ****** ***** *** *** **** foot *****:

When ** *** ****

**** ********** ***** *** ******** ********, ** *** ** ****** and ******** ** ******** ** ********* '****** ***** **********'.  ***** plenum ******* ***** *** **** ********* ************ ** ******* ** a ********, **** ********** *** ** ****** **** ** ********* inventory ** **** ****** *** ***** *****.

** *** ***** ****, **** **** ******* ** ********** ***** specify ****** **** **** ** *** **** **, **** ** avoid *** ******** ** ******** ************* ** ** '***** **********' if **** **** * ******. 

*******, ** **** *****, **** *** ** ******* ** ***** the ******* ***** **** *** *** ***.  ** ********* ****** where **** **** *** ** **** *****:

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

**** ***** ****** ******* *** ******, ** ********* ** *** through * **** ** * ******** ******* ** * ******** spot. **** **** ** ****** * '***** *****' *** ** usually ******* ** * ******, ** * **** *********** '***** closet' **** ********* ****** **** ****** ******* ******. ***** *** riser ******* ** ******, *****, *** ********* **** *** **** a **** ******** *******, *** ***** ******* ******* **** ***** does *** **** ** **** ****** '******' **************:

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

**** ***** ******* ******* ***** ** ****** ****** **** ********, it ****** ** ****** *****. ******* ***** *** ***** *** shortest ******** ******* *** ******, ***** ** ****** ****** ** on *** ******* ******* ** *** ****.

*******, ******** ** ******* **********, *** *** ***** ***** * drop ******* ** *** ****** ******. ** **** *****, **** is * ****** ********** ** **** *** ***** ** *** an ****** **** ** *** **** *** **** *******. 

***** *** ** ***** **** *********** **** ***, ** *** be **** ** *** ***** ** ***** ******* ** *** expense ******** *****.

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

** ***** ******* ******* ** * ****** *****, *** ******* floors, ** ******** ** ******* ******:  

*******, ***** ************ *** *****, **** ******* ****** ********* ** conduit, ***** *****, ** **** *****. ******* ****** *********** **** ceiling *****, ********** ** ****-******* *******, ** ** ***** ******* to *** *** ***** ****** ********, *** ** ******* ************ rating *******.

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

** * ******* ***, ***** *** ***** ** ** *** actually ******** **** ********, ***** ********* *** *** ****** ****.  If * ** **** ***-***** ***** *** ***** ~$*.** ** cable, ********** ***** *** *** **** **** ****** ***** ** ~$7.60.

*******

** *******, ****** ***** ****** ** **** ****:

  • ******* **** ** ** ** ********:**** **** ***** *** '** ** ******* ******, ** **** be ****** *****', ** **** ****** *** ******* * **** run **** ** *** *****.
  • ******* **** **** ** ****** ******** ********: **** ** ***** ******** **** *****, ** ***** *** be ** ******** ****** **************. ** ******** ********** **************** ** ******* *****, ** ****** ** *** ******. *******, if ***** ******* ***** ** ****** ***** *** *******, *** space ****** ******** *** *****.
  • ******* ******* ******: *** *** ** **** ** ***** ** *** ** needed.

*******, ***** ****** *** **** ** *** ******* ***********:

  • ******* ******* ******: ****** ******* ** ** **** ** ******** ****** ****** be *** *****, *** *** ******* ********** ******** ** *****.

***** ***** ***** *** ** **** ** '******* *******' *** non-rated ******, ** ****** ** **** ** ****** ************, *** tends ** ** ****** ****** **** ***** *********.  ******* *** CMR ** *******, *** **** ****** ** **** ****** *********** for ****** *****.

*** ****** ********** ** **** ***** *** ******** *** ******* through ********, *** ** ******* ********** **** ********* ** ***** wires *** ********, *** **** **** ** *********.

Comments (11)

" Nonrated Cable - If cable neither travels in a plenum space, nor between floors, it requires no special rating: "

I believe this is a misleading statement. I know you are mentioning some exceptions afterwards but to my knowledge, the only time (some exceptions) you can run 'Non-rated" cables is when cable is surface mounted. If it goes inside a wall/ceiling, it should still be rated but at a lower standard perhaps like CM or CMG. Perhaps someone else can provide more insight into this

I believe CM or CMG can only be used "within" a single floor. Not in wall or ceiling for a commercial environment.

However, in my opinion, the cable in a commercial building should be rated by UL or the NFPA or both. If in Canada the CSA and or UL. (CM & CMG is rated)

The question is...What is exactly illegal or legal?

We have NEC and local codes. Truthfully the NEC is just a standard for codes. Local codes supersede standards like the NEC. Many local codes are behind-the-times when it comes to the NEC standards. The only thing you can do is to research the heck out of local codes. But as we all know, codes are not always followed. How many times have you been on a commercial job site and looked at the low voltage cabling runs and the AV runs and knew it was not up to code? You really think that last installer was fined or jailed?

The MGM Grand Fire in 1980 changed a lot of things for the better. However, it would be nice if codes were nationally universal...at least in the United States.

"The NFPA has no power, nor does it undertake, to police or enforce compliance with the contents of NFPA Documents."

The MGM Grand Fire in 1980 changed a lot of things for the better.

Some folk might remember it a bit different.

"are flammable and function like fuses". Here fuses functioning better to stop fire before even smoldering start. By a law. else if someone shall use wedge coin, someone shall burn down, someone shall then arrested.

L-Com has a a bunch of videos of different rated/unrated cables burning, which are pretty interesting (as far as burning cables go) if you've never seen the difference. It's especially good for the crowd that insists "Plenum cable doesn't burn!!!" Sure it does.

Learn something new everyday. I was told that reason you run plenum is that when it burn it doesn't produce toxic fumes. So that when one space burns that toxic fumes don't travel to another room. That never made sense to me anyways. I figured there plenty of toxic things burning right along with the wire.

An easy way to identify a plenum air handling ceiling is to look at all the hvac grills in the ceilings, if there is duct work attached to ALL of them, then chances are pretty good your in a non plenum space. However if only some (the air return vents) are simply a grill in the ceiling tile with no duct attached and then your definitely in a plenum space. Further investigation in the ceiling and you'll see the HVAC system has a large open ended duct open to the air to suck the return air in through all open duct grills. While residential is almost always riser rated. And there are additional cable ratings for IN wall, although that is not typically a factor when horizontal cabling is being installed. Another place to watch for is the data center, as raised flooring carrying ventilation is typically a plenum as well. Hospitols, and manufacturing facilities May have both types of ceiling spaces.

In my experience (20+ years in communications cabling/IT/security) about 90% of comercial buildings are plenum rated and require plenum cable. We actually just finished replacing a large amount of fiber that was installed by our competitors. They installed riser rated Non-Plenum throughout the entire campus in which all the space was a plenum air space. very costly mistake!

Also some of those graphs are misleading... I have never seen cables installed in an HVAC duct. pretty sure the HVAC guys would blow a gasket and cut all your cable!

but my experience is based in the Mid West and Texas so maybe ya'all do it different (wrong) ;-p

...But I have seen a sprinkler pipe installed right through an HVAC duct- took a picture but I've since deleted it, should have kept it for the museum of the stupid which is an ongoing project of mine.

I believe that may be OK as long as the sprinkler pipe isn’t supporting the duct work, that’s not allowed.

The sprinkler guy that was on site was pretty amazed- he's the one that pointed it out to me.

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