Why Plenum?

If you have been on the cable search lately, chances are that you have run into a cable type described as “plenum.” What is plenum cabling, and why is it more expensive than other types of cable? Below we will give you the scoop all about plenum, when it should be used and why.

There is a sad story behind how plenum cable came to be created. Way back in November of 1980, there was a fire that broke out in the MGM Grand Hotel in Las Vegas. The result of this hotel fire was tragic; over 85 people were killed, and more than 700 people were injured. The cause of the fire ended up being an electrical short circuit. The hotel’s network cables were ran through the plenum of the building, which is typically the space above the ceiling or below the floor. These are the areas where air circulates, so they are extra dangerous when there are cables present that may emit toxic smoke when exposed to fire. Because air is circulating to the rest of the building through vents, toxic air can circulate around the building very quickly, and can be fatal, as it was in the MGM fire. There has been much speculation that the toxins inside the cables sparked the fire to become larger and hotter, and all of the toxic smoke spread throughout the hotel very quickly.

Out of this catastrophe came new regulations for the types of cable that were used inside commercial buildings. This is when flame retardant cables, aka plenum, became the norm for use in large industrial buildings. Plenum cables are constructed to be fire retardant, which means that when they are exposed to flame they will burn much slower, and release less toxic smoke into the air. The jackets that coat plenum cables is a special type of PVC, which explains why plenum cables are typically pricier than other cables. Today many government installations require that only plenum cables be installed, whether the cable is installed in the plenum of the building or not. The same goes for large office buildings and hotels. It was a tragedy that pushed plenum cables into the limelight, but now that they are here to stay we can all feel a little safer.

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