What is plenum rated cable?

If you’re a building manager, you probably already know about plenum rated cable. You probably curse under your breath every time you hear it mentioned, because it’s much more expensive than regular cable. For example, our plenum-rated RG6 is almost six times the price of regular cable. That can be a really big expense if you’re talking about wiring a large facility, high-rise office building, or apartment complex.

Never heard of plenum cable?

The good news is that unless you’ve moved recently, if you don’t know about plenum cable you probably don’t need to. Some areas require it by law, and some don’t. It’s more common for large buildings than homes, and that’s a good thing too. There are cases where safety has to come before anything else, and in cases like that you have to take special care.

The key with wiring a large facility is often figuring out where to put the cables. Sometimes there is a dedicated trunk between the walls where you can put as much as you want. Such a space is usually specially fireproofed and there is no ventilation between it and the common spaces where people are. In a case like that, you don’t need to worry about cables giving off harmful gases.

And, harmful gases are an issue when things made of plastic or artificial rubber burn. The chemicals used to make the outer jacket and the foam dielectric can be really bad for you if they burn. Now you probably have a lot more to worry about if there’s a fire than the cables in the walls. I get that. But some governments do try to make fires more survivable whenever possible.

So this is where the plenum comes in.

The “plenum” space of a building is that area where the air conditioning ductwork is, generally above the ceiling. This tends to be a big, open space with very few firewalls, so that the HVAC ducting can travel easily. That also means it’s the most dangerous space in a large building — small and confined, but easy for flames to spread.

If you plan on running cables through that plenum space, local building codes may require plenum rated cable. Plenum rated cable (or plenum cable as it is also known) is specially coated with fire-retardant chemicals and designed to give off no dangerous fumes if it does work. Regular cable is “a little” fireproof but the rubber and plastic inside regular cables will melt and give off dangerous gases. If temperatures are high enough, fire can travel across the cables from room to room. Plenum cable stops this from happening.

LSZH cable – another thing you might need to know about

Plenum-rated cable is pretty darn safe. But it may not be safe enough for some facilities. In a case like that you may be asked to provide cable with an LSZH jacket. LSZH stands for “Low smoke, zero-hydrogen” and that’s pretty much what it is. It’s a material that burns with as little gas emission as possible and has no free hydrogen at all. This is important for areas where oxygen is in use or other really critical applications.

Like plenum-rated cable, if this term is new to you then it’s not something you’re likely to need. But if you’re moving into a new area of expertise, it’s something you might need to be aware of.

The bottom line here is, if you don’t know if you need plenum cable, check with your local building inspector before buying and installing regular cables. And, when you’re ready to buy the cable for your next project, you’ll find all the cables you need when you shop the great selection at Solid Signal!

About the Author

Stuart Sweet
Stuart Sweet is the editor-in-chief of The Solid Signal Blog and a "master plumber" at Signal Group, LLC. He is the author of over 8,000 articles and longform tutorials including many posted here. Reach him by clicking on "Contact the Editor" at the bottom of this page.