The Ultimate Guide to Plenum Rated, Riser Rated, and LZSH Cables: Know the Difference

The Ultimate Guide to Plenum Rated, Riser Rated, and LZSH Cables: Know the Difference

Written by Ben Hamlitsch, trueCABLE Technical and Product Innovation Manager RCDD, FOI


Plenum Riser


When it comes to the low-voltage wiring requirements for an office or data center, it is all too simple to greatly underestimate the challenges involved. A lot of individuals aren't familiar with the National Fire Protection Association (NFPA), so they think that any cable will do for their purposes. As a result, they neglect to check whether or not their cables genuinely satisfy the standards of the National Electrical Code (NEC or NFPA 70). This book of codes helps a telecommunication systems designer understand where certain types of cables can or cannot be installed.

When preparing a plan and budget for a new cable installation or selecting a low-voltage cabling contractor, businesses need to be aware of the various cable ratings that are mentioned in the NEC. These ratings may be found in several different places in the NEC. CL/CM cables, CMP cables, and CMR cables are examples of some of these ratings. These cable types are typically referred to as general-purpose/residential cables, communications plenum cables, and communications riser cables, respectively. There are a few more ratings for communications cables that are applicable to outdoor conditions; however, in this article, we will stick to CMP, Plenum, CMR Riser, and LSZH cables. We will also go over Low Smoke Zero Halogen LSZH cable and what the differences are.

Note that the CL/CM, CMP, and CMR designations solely relate to the rating of the cable "jacket" and its fire-resistant features; they have no influence on the data transmission capabilities of the cable at all. This is something that is important to note; these designations only refer to the cable's fiber resistance. In order to comply with fire safety regulations, the vast majority of commercial facilities will be required to employ either plenum or riser-rated cables. LSZH has become kind of an in between cable in the industry. It falls in between the Plenum and Riser ratings in terms of fire resistance. As a result, a lot of people are curious about the distinction between plenum-rated, LZSH, and riser-rated cables.

What exactly is the plenum?

In a building, a "plenum space" is the area used for air circulation in heating, ventilation, and air conditioning (HVAC) systems. This space is often located between the structural ceiling and a drop-down ceiling or under a raised floor. It's basically a big open area that allows air to move around freely, which is necessary for controlling the temperature and airflow in a building.

Now, when it comes to communications cables, like those used for internet or telephone services, these cables often need to be run throughout a building to connect different rooms and areas. Sometimes, the easiest path for these cables is through the plenum space.

But here's the catch: the plenum space is part of the air circulation system. That means if a fire were to start, it could spread quickly through these areas, and any smoke produced by the fire would be distributed throughout the building. That's a big problem because the insulation on standard cables can produce toxic smoke when it burns.

To solve this problem, we use what's called "plenum-rated" cables when we need to run cables through the plenum space. These are special cables that are designed with fire-resistant and low-smoke-producing materials. This makes them safer to use in these spaces, protecting the building and the people inside in case of a fire.

So, to sum up, plenum spaces are areas in a building used for air circulation. Communications cables sometimes need to run through these spaces, and when they do, we use special "plenum-rated" cables to ensure safety in case of a fire.

What exactly is the riser?

In the context of a building, a "riser" is a vertical space that runs between the floors. This space is typically used to accommodate the passage of utility elements such as water pipes, electrical conduits and, most importantly, for our conversation, communication cables.

So when we talk about "riser spaces" in relation to communication cables, we're referring to these vertical pathways that allow the cables to move from one floor to another. For example, if you want internet access on the 10th floor of a building, the communication cables will likely travel through the riser space to reach there from a central server located on a lower floor.

Just like with plenum spaces, we also need to think about safety. In the event of a fire, it can potentially spread quickly from floor to floor through these riser spaces. That's where "riser-rated" cables come in.

Riser-rated cables are designed to prevent the spread of fire between floors. They are made from materials that resist burning, thereby containing any fire to their floor of origin. There is less chance for air flow and rapid fire spread in riser spaces than in plenum spaces, so they are not as fire-resistant as plenum-rated cables. However, using them is still safer than using non-rated cables.

In other words, riser spaces are vertical areas in a building used for running utilities, including communication cables, between floors. When cables need to run through these spaces, we use riser-rated cables that are designed to resist fire and help prevent its spread between floors.

What exactly is enclosed plenum cabling?

Plenum cabling is a type of cable that employs materials such as polyvinyl chloride (PVC) or fluorinated ethylene polymer (FEP) for the construction of its jacket. According to the criteria established by the NFPA's NEC, this type of cable is categorized as CMP. When compared to other plastic polymers, these materials offer a greater degree of resistance to fire and produce fewer harmful emissions during combustion.

When running cables in plenum areas, you really need to use plenum cables. The cost of installing plenum cabling is higher than that of installing riser cabling because plenum cables are constructed to a higher grade of fire protection than riser cables. If you are working in a "riser" environment, you have the option of replacing riser cabling with plenum cabling. However, if you are working in a plenum location, you cannot replace riser-rated cables with plenum-rated cables.

We can simply explain it this way. You know how, in your house, you have pipes for water to travel from one place to another, like from the kitchen sink to the bathroom? Well, in big buildings, they have something similar, but instead of water, they have internet and telephone cables to travel from one room to another.

Imagine you have a secret tunnel in your house where you could race toy cars, and this tunnel runs all over the house, including above the ceiling and below the floor. This is similar to what we call a "plenum space" in a big building. It's a special tunnel where air can move around to help heat and cool the building.

But these secret tunnels or plenum spaces can be dangerous if there is a fire because the fire could spread fast through them and the smoke could reach every room in the building. So, for safety, we don't use regular cables in these spaces. We use "plenum-rated" cables, which are like superhero cables. They're stronger and safer because they are designed to not catch fire easily, and even if they do, they don't produce much smoke.

"Enclosed plenum cabling" refers to these special, superhero-like cables that are placed in their own special protective tube or conduit within the plenum space. This is like putting your toy cars in a protective case while racing them in the secret tunnels, to keep them extra safe. These cases or tubes add an extra level of safety because they further contain any potential fire or smoke within the tube and prevent them from spreading in the plenum space.

So, enclosed plenum cabling is just a really safe way of running important cables through the special tunnels in a building.

What exactly is riser cabling, though?

So, you remember the secret tunnels we talked about for the plenum space, right? Well, there are also special vertical tunnels or pathways in a building that help move things like water, electricity, and internet cables from one floor to another. These vertical tunnels are like elevators for these things and are called "riser" spaces.

Imagine you have a multi-story dollhouse, and you want to run a tiny toy string (representing our communication cable) from the bottom floor to the very top. You'd likely run this string up through the middle of the house, just like the cables run up through the riser spaces in a real building.

But what if a tiny toy fire started on one of the floors of the dollhouse? We wouldn't want that fire to use our toy string as a ladder to climb up and reach the other floors, right? This is where "riser-rated" cables come in.

Riser-rated cables are like super-strong toy strings. They are made from special materials that don't burn easily. This means that if a real fire started on one floor of the building, the fire would have a hard time using the riser-rated cables to climb to the other floors.

So, riser-rated cabling is a safe way to run cables from one floor to another in a building. They're like a super-strong toy string that helps keep the whole building safe in case of a fire.

To summarize the distinction between riser-rated cables and plenum-rated cables, cost is a significant element, but the essential question is how fire-resistant the jackets of the cables are and how much smoke is produced if the wires catch fire. Because of their superior resistance to fire, plenum cables represent far less danger in the event of a fire in a structure than riser cables do (and riser cables, in turn, are safer than general-purpose cables).

Terms to know when choosing plenum vs riser cabling:

Here’s a short list of some acronyms and other terms to know when looking for plenum or riser-rated cables:

CL/CM/CMG Cables. The term for residential-grade or general-purpose cabling NOT SUITABLE FOR COMMERCIAL USE IN RISER OR PLENUM ENVIRONMENTS.

CMR Cables. Communications Riser. Approved for use in riser spaces.

CMP Cables. Communications Plenum. Approved for use in riser and plenum spaces.

NFPA, The National Fire Protection Association, This is the organization that created the National Electrical Code.

NEC: The National Electrical Code (NFPA 70) This document is designed to create a baseline for electrical safety in residential, commercial, and industrial buildings.

What are Low Smoke Zero Halogen (LSZH) cables?

Now let’s talk about LZSH cables, what they are, and what the difference is between Plenum and Riser cables.

The term "low-smoke zero-halogen" (LSZH) refers to a material used for the jacket of cables that is both flame retardant and does not contain any halogen. This kind of jacket fabric offers great fire safety properties, including minimal smoke production, low toxicity, and low corrosion rates. Because very little smoke is produced when LSZH fiber optic cables come into contact with a flame, these cables are ideal for applications in which a large number of people are confined in a specific location, such as office buildings, train stations, airports, and other similar locations. People who are trying to find an exit from the structure and inhaling smoke or fumes while doing so are putting themselves in much more danger than they were before the fire started. A fire can be extremely dangerous in a building. LSZH fiber optic cables do not contain any halogenated materials such as fluorine (F), chlorine (Cl), bromine (Br), iodine (I), or astatine (At). It is believed that certain halogenated materials, such as these, have the potential to be transformed into toxic and corrosive matter when they are subjected to combustion. Because they produce very little smoke, LSZH fiber optic cables are not only safe but also quite useful. Smoke inhalation is the leading cause of death among victims of fires. In these kinds of settings, the use of LSZH fiber optic cables, which produce little to no smoke and no halogenated byproducts, would be of critical significance to the protection of people.

LSZH fiber optic cables' various possible applications

As the use of data transmission becomes more widespread, there is no question that the number of fiber optic cables that are being installed in buildings is growing at an increasing rate. Because of the significant relative fuel load that is represented by wire and cable, LSZH fiber optic cables have become increasingly prevalent in the central office areas of telecommunications facilities.

  • Public spaces such as train stations, hospitals, schools, high buildings, and commercial centers where the protection of people and equipment from toxic and corrosive gases is critical
  • Data centers contain large amounts of cable and are usually enclosed spaces with cooling systems that have the potential to disperse combustion byproducts throughout a large area.

It is possible that the burning of other materials will contribute a larger quantity of hazardous gases, which will have an effect that is greater than that of the wires. There have been major incidents in which the burning of cables contributed to corrosion; however, in some cases, improved tactics for responding to flames may have prevented this damage from occurring.

Considerations to make when selecting LSZH fiber optic cables

When selecting LSZH fiber optic cables, it is important to think about things like the price and the surrounding environment. It's possible that a component of the surrounding environment, like the temperature of the installation, could make the cable less flexible. Will it be a restricted area or a public one for the application? Will there be anything else that could catch fire? It is necessary to consider a great deal of information. LSZH fiber optic cables typically come with a bit higher price tag as well, compared to general and riser-rated cables.

When selecting a fiber optic cable or fiber optic jumper cable for any application, the operational environments where the fiber optic cable will be utilized, regardless of whether they are extreme or not, must be considered along with availability, performance, and price. In addition, if you are looking for a solution that offers great performance in addition to capabilities, as well as protection for both humans and the environment, LSZH fiber optic cables could be a fantastic option for you.

In the image below, we can see the differences between the PVC cable jacket, the low-smoke zero-halogen jacket, and the highest-rated plenum. Both LZSH and plenum are designed to eliminate the toxicity of the cable in the event of a fire. In the case of plenum, there is a self-extinguishing feature in which the cable jacket will not generate any toxic fumes.

When there is an enhanced potential for heat and fire hazards, the use of LSZH cables and wire is recommended. There are a lot of positive aspects associated with utilizing LSZH cables, such as the benefits for the environment and toxicity levels. Cables used in communication applications are not immune to catching fire and can emit toxic smoke and gas; consequently, preventative steps have been implemented to ensure that cables are also safe, which is why LSZH cables are becoming more extensively utilized in these applications.

Come check out our Plenum and LSZH cables at trueCABLE.




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