Plenum vs Non Plenum

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Old 03-30-13, 09:08 PM
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Plenum vs Non Plenum

If you are in the process of building your house or constructing a building, which do you prefer the most, Plenum cable or non plenum? Plenum cable acquired its name from HVAC which means plenum spaces. These spaces refer to areas where air can circulate within a building. Plenum cables aid in heating and cooling air. The spaces in plenum help fire and smoke to travel fast. With this, toxicity rate seems to be lower than normal especially that plenum cables are made of materials which are heat resistant. This material is called Teflon which allow cables to emit less smoke compared to regular PVC cables. On the other hand, non plenum cable which is commonly called PVC (polyvinyl chloride) cable, is not so costly between the two choices. The choice of using plenum and non plenum cables should be on the contractors point of view. The main factor that directly affects his decision is the cost. It is best to identify honestly if the project requires plenum based cable of if PVC cable will do. After all, it is the quality and longevity of the project that we are looking forward.
 
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Old 03-30-13, 09:16 PM
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Yeah, I'm well-acquainted with CMP, CMR, CM, and OSP cabling... At work we found a significant code violation and had to have a contractor come in to strip some free-aired OSP fiber out of a plenum airspace and fusion-splice it to where the fiber transitions outside.
 
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Old 03-31-13, 06:11 AM
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In commercial buildings in my area plenum is required for any cabling that isn't in conduit.

Residences almost never use plenum. Either the cabling is required to be in pipe or it's allowed to be free-aired. Cabling is not allowed to be installed in air ducts or returns, so it's a moot point.
 
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Old 03-31-13, 09:26 AM
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Probably more importantly, residential buildings generally don't use plenum air spaces as air returns. That's generally only a commercial building thing with drop-ceilings, as it's easier to reconfigure the building without having to worry about hard-ducted returns.

I would think that it's simply best to assume one needs Plenum cable in commercial buildings because most use drop ceilings, and unless the trusses are wood then there's always the possibility of the space being a plenum airspace, or being turned into one later during an HVAC retrofit. Though if the trusses are wood, then it's not capable of being a plenum airspace.

One thing I'm still trying to find out is if multistory residential buildings require Riser-rated cable, normally specified for crossing floors in non-Plenum environments, or if lesser cable than that can be used. Riser-rated is designed to self-extinguish so that if the cable is in a fire, the jacket and insulation doesn't burn its way up the cable to light the next floor on fire. It's definitely called for in commercial buildings, but there's a possibility that the cable could be transitioning multiple floors, as opposed to a residential building where one could be supplying one floor from the ceiling of the floor below with stub-ups.
 
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Old 03-31-13, 10:31 AM
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In a single family dwelling, riser is not required when penetrating a floor. Only in multifamily dwellings where the cable penetrates a rated firestop (regardless if it is single or multiple floors). So for example, cable going from the utility closet, through the structure of unit 1A, through the firestop to unit 1B (same if it is going through 1A to 2A) would need to be riser. If it is going from the first floor of unit 1 to the second floor of unit 1, and does not pass through a firestop, then riser is not required.
 
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Old 03-31-13, 11:47 AM
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Good to know. I have yet to cable my own home, and while I didn't think it would be a big deal, good to know it won't be a code violation either.
 
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Old 04-02-13, 05:15 AM
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... residential buildings generally don't use plenum air spaces as air returns.
Plenums, no. However, my house has one section of one 2x6 wall where the void is used as the main cold air return.
 
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Old 04-03-13, 07:52 AM
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True, and if you were to run cable up that specific stud cavity, it would be required to be plenum. However if the cable simply CROSSES that kind of airspace at a right angle, then plenum cable is NOT required.

It has to do with the total area of jacketing that is exposed to the airflow. A Cat5 cable crossing a 16" stud cavity only has about 4 square inches of surface area, and there is a minimal amount of toxin that can be released if it burns. If the cable is running a ways inside the duct/return, then it can potentially burn the entire length.
 
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Old 01-02-14, 02:44 PM
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How do codes vary from place to place?

I'm glad to have found this thread!

I'm looking into precisely this question. A salesman from a supplier where I live (San Francisco) suggested I needed Plenum in case an inspector gets in the way.

I've got a single-family home, and based upon what I read here, I wouldn't even need to use CMR, let alone CMP. But I haven't been having any luck in looking up my local building codes. You'd think that sort of thing would be easy to find!
 
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