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.

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.

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.

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. Plenum cable is expensive, but rewiring everything after the fact is even more expensive.