So what I want to do next is I want to show you a picture of something. Now, this picture is a little bit scary but bear with me here. So this is a picture of a ceiling. You might be thinking, "Well, what so scary about a ceiling?" But this is not an ordinary ceiling, this is what's called a drop ceiling. So sometimes when we build buildings there is a ceiling, but we need to run a bunch of stuff next to it. We need to run wires, and pipes, and things like that, HVAC ventilation and stuff like that. It's stuff people don't want to look at. So what a lot of buildings do is they have these struts hanging down and they have the ability to put pieces of styrofoam up. So you don't have to see all that.That's called a drop ceiling. The real ceiling is higher than this. So if you took the ceiling and you pushed up one of these tiles, You'd see stuff above it. You'd see stuff like this: you'd see wires and HVAC, pipes, insulation, and so on. As you everything you well, what's the big deal about that? But the problem is there's no air flow between this space above, these tiles and the space below. So if there's a fire that starts, it'll just spread, and it'll spread, and it'll spread everywhere and you won't notice it. If there's a gas leak up there, the gas leak you're not going to smell it. The gas will leak and it'll spread everywhere. It'll get everywhere up there and you won't even notice it. Smoke will get everywhere. So the space above a drop ceiling is called the plenum. The plenum is actually a very dangerous area in buildings. If you read about fires like the famous Triangle Shirtwaist factory fire and all these big fires, they all seem to happen in these enclosed areas. It is actually a very common scenario for fires is that you have an enclosed area that no one's watching, fire gets up there, a whole bunch of smoke it's up, and and there's an explosion everything gets out. So plenum areas are very dangerous and people know this. So when we design systems that get deployed in buildings, we need to pay a lot of attention to how they burn, how resistant they are to fire, how we can protect them, and things like that. So because of this there's a lot of ratings that are applied to devices, and cables, and things like that where people have studied and come up with regulations for how these things are constructed and rules to construct them in a way that they're resistant to burning. So in particular, I'm showing you a set of ratings for cable. If you go out and you buy Ethernet cable, or electrical cable, and so on used in your devices or to connect things to wires and so on, you're going to see ratings like this a lot. So these are some very common ones. So I wanted to run through these real quick and give you a sense of what they are. Let's start with the first one. So plenum rating is the toughest rating for cable. It has to be because you're deploying these wires up in your plenum you're not going to see them if they catch fire and they burn you're not going to notice. Wires are a great way for fires to spread because the fire goes around it catches on a cable, is just like a run for the fire. The fire will just track along the cable and spread all over the place. So if you deploy wires in your plenum, you want plenum rated cable because they're jacketed with fire-retardant plastic. They're made with plastic that doesn't smoke when it burns it resists burning. These cables are also resistant to pulling as well. Because if you deploy cable you, throw it up there, and you pull on it pull on it. It might stretch out the copper inside the cable. That's really bad because when copper gets small, it gets thin it can't carry as much electricity. We have a lot of electricity going over a small conductor it heats up. Bigger conductors don't heat as much. So you pull your wire more and more, it'll heat up more and more that could lead to fire. So because of this plenum cables also include a rope or a polymer filament inside of the wire with a high tensile strength and that can help support pulling, people pulling on it. Also dangling cables you have a cable that pulls down, it'll support that. Plenum wires are also solid cable instead of stranded. So you want a nice big thick piece of cable so it can carry a lot of electricity so it's not going to heat up cause fires. It's not stranded so it's not meant to be bin, but you're running it up in your plenum its not like you're going to go up there every day and move it around, it's meant to be deployed once a solid cable is fine for there. There's also a lot of restrictions on the type of chemicals that can be used to manufacture the sheath. These chemicals prevent fire and reuse smoke. So that's good. But there are also more expensive, it reduces flexibility. If you take a plenum cable and you bend it, the outer sheath will turn white a little bit that doesn't happen with regular Ethernet cables. Plenum cables also have higher bend radius. You got to think about where you're running them and you're not going to make sharp corners or sharp turns you have to gradually run them. Because of this they have a higher cost of manufacturer, and higher-cost to deploy as well. Requires more training to deploy. So this is plenum rated. There's some other rating levels as well. So plenum is the most expensive. There's also other levels like riser cable. So riser cable is cable that rises between your floors. It's what connects your first floor to your second floor and your second floor to your third floor in your home. These ratings apply the electrical cable, network cable, and so on. So riser cable needs to be fire-resistant as well because if your first floor catches on fire you don't want that fire getting up to your second floor you want to contain the fire. So riser cable is resistant fire as well. There's also general-purpose cable, residential cable, and so on. These are lower ratings. There's also low smoke zero halogen cable as well. So this is cable where it's manufactured to eliminate toxic gases when it burns. Is designed for enclosed environments where you have people who might be hard to evacuate because if your building catches fire, you don't want everybody getting smoke in their eyes and they can't see breathing toxic gases and they pass out because they can't get out of the building. You want to use low smoke zero halogen cable because when it burns, it'll burn nicely it won't eliminate all these toxic gases. Is good for enclosed areas where you have poor ventilation, or if you run sensitive equipment which can be damaged by chemicals. So what I've done here is I've talked about these different ratings for cables. These ratings apply to network cables, electrical cables. They apply to device construction as well. So when you construct your devices and your cabling, it's important to pay attention to these ratings, to think about your device and how it will act in normal operation, and how it will also act in emergency scenarios when it burns.
