From the course: CompTIA Network+ (N10-009) Cert Prep

Fire ratings: Plenum vs. non-plenum

From the course: CompTIA Network+ (N10-009) Cert Prep

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Fire ratings: Plenum vs. non-plenum

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- I love old movies. And there's one thing, if you want to talk about old movies, I am the guy to talk to, well, mainly because, well, I'm old. Anyway, there was a movie done in the early '70s called "Towering Inferno," and it was kind of a dumb movie, but the whole premise behind the movie is that all the electrical wiring in this big skyscraper was done using substandard materials. And they had this little tiny fire that happened to catch on the wiring and the jackets of the wiring made this fire propagate all over the skyscraper and, you know, the firemen saved the day and the whole shebang. Anyway, in this particular episode, what I want to do is talk about fire ratings with network cabling. So to keep things safe, (grunts) we'll keep this fire extinguisher really nearby, just in case. We have fire ratings for different types of cabling. Basically, there are three fire ratings you need to know for the exam. First of all, there's what we call plenum. A plenum is a space between a drop ceiling and the actual ceiling or the space between a raised floor and the actual floor itself. So let's go ahead and take a minute. I'm going to grab this broom and let's go check out a plenum. So here's just a regular old drop ceiling here in my studio. So what I'm going to do is push this drop ceiling up. I'm going to do it neatly so I don't break this drop ceiling. You can actually see a couple of cables up there. This is the plenum area. So the plenum area is a gap, in this particular building, from the bottom of this drop ceiling up to the top of the real ceiling is almost four feet. The plenum area is not there for the convenience of putting cables. It's really there for HVAC systems, for air conditioning and stuff like that. This is where all the return air is sucked in from all over the building and then pulled into the heating/air conditioning system. So it's also a really convenient place though to drop cable. (ceiling panel bangs) Plenum rated cabling is cabling that's designed to be run through the different plenums. It has the highest fire rating of any type of cladding that you can put on cabling, and it has the highest fire resistance. However, there's two others. The second one is called riser. Riser is designed to run between floors in a building. With riser cabling, it actually doesn't have quite the same fire rating as plenum, which always seemed interesting to me, 'cause you would think if something's going between floors that you'd want more resistance. But the answer is, is that when you're properly pulling cable between floors, you use stuff called fire stop, which is designed to prevent the stuff from going very far, so riser-level cable doesn't have to have the same fire resistance of plenum. The last type of cabling is what we call, well, nothing (chuckles), better known as PVC. PVC or non-plenum is basically absolutely no fire protection at all. So to put this to the test, I've got a couple of pieces of cable here in front of me. So one of these is PVC cable. This PVC cable has really no fire protection at all. Now, before you start to worry too much, it's very difficult to actually catch this on fire, but it can make a lot of smoke and noxious fumes. So, here, I'll hold it away from me a little bit. So let's give this a whirl. (lighter clicking) Okay, so you can see it took me almost no time at all and I began to get smoke and burning and charring, and that's what's going to happen with PVC. Now I have a piece of plenum-rated cabling here. Let's try the same thing, see what happens. (lighter clicking) So it does make a little smoke, but you'll notice in this particular case, it's not nearly the amount of smoke that we would generate with PVC. The big thing that separates plenum from PVC is price. Plenum-rated cabling is usually going to be two to three times more expensive than PVC-rated cabling. However, most cities have fire codes that require you to use this. So how do you know what your rating is? Well, it's usually pretty simple. (box rustling) All you got, whoops. All you got to do is take a look in the boxes that the cabling comes in. So this is, this is a thousand foot of cable, and if we take a look here down towards the bottom, you're going to see, with a big American flag around it, I'm not quite sure what that means, it says non-plenum. So this is PVC cabling. We use it here at Total Seminars for training. We would never put this in our walls but it's really great when we're teaching people how to cut and crimp cabling because it's cheap, more than anything else. So for the exam, the big thing I want you to remember is that there's three types of fire rating. The lowest is PVC or non-plenum, which is no fire rating at all, second is riser, and the best is always called plenum.

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