If you’re taking on an installation or electrical wiring project - such as installing a new fire alarm system or maintaining an old one - there are numerous factors you need to weigh.

For instance, you need to make sure you get the proper AWG fire alarm cable to ensure it’s safe to use with your intended system.

You also need to make sure you’re using a shielded fire alarm cable if there is a lot of electromagnetic interference in the area which could adversely affect signal transfer - or even cripple it entirely.

Then again, you need also to make sure that you’re using the right type of cable for the job - either plenum-rated or riser-rated AWG fire alarm cable.

But understanding why these two different classes of alarm cable are so categorized begins with a thorough understanding of what exactly plenum and riser space are in the first place.

Let’s put it this way: they don’t exist for the purpose of wiring buildings! (Although that is one of their purposes, but who’s counting?)

So let’s take a close look at these two different features of buildings and why different cables must be used in each.

What Is Plenum Space?
When you think about it, it might seem like all of the utilities - such as HVAC ductwork, plumbing lines, gas lines, and electrical wires are “in the walls,” away from hidden view.

This is partially correct but doesn’t paint an architecturally sound picture. Some of these are literally in the walls. Others are under or above the floors and ceilings, respectively, in an area known as plenum space.

Many buildings - not so many homes, but facilities and places of public gathering - have what are known as drop ceilings. Some have raised floors.

In a drop-ceiling configuration, the actual ceiling of the room is concealed beneath ceiling tiles. In a raised floor configuration, the situation is the opposite. The actual floor is concealed beneath a “false” raised floor. Often you can tell from how hollow the floor sounds when you walk on it.

Drop ceilings utilize this spare space to run a variety of utilities, distributing them across the floor, away from public view but still easily accessible. Typically, HVAC ductwork is run under raised floors and above drop ceilings, but electrical wiring resides in that space as well.

Since it is the case that plenum space can often communicate physically with the interior, occupied spaces through airflow, different wires must be used in plenum space as compared to riser space (see below).

What Is Riser Space?
Riser space is slightly different from plenum space, although it is used for somewhat similar purposes. If you think of plenum space as the space above a drop ceiling or beneath a raised floor, think of riser space sort of like the space behind the walls.

More properly, riser space is the vertical space within a building that communicates between the different floors. So it is “behind” the walls, but it also traverses the floors in a manner that walls don’t.

This space is vital for allowing utilities to reach between the upper and lower levels within a building. Naturally, there is some HVAC ductwork present, but riser space is primarily used to distribute water, gas, and electrical lines between the different floors of a building.

One of the main differences between plenum and riser space is that riser space is not typically open to any occupied rooms within the building. It is more or less shut off from them.

Plenum vs. Riser-Rated AWG Fire Alarm Cable: What You Need to Know

Given that riser space typically does not communicate with a building’s interior and that plenum space does, it’s generally the case that the NEC requirements for plenum-rated AWG fire alarm cable and riser-rated cable are different.

The plenum-rated cable typically contains fire-retardant insulation that produces low levels of non-toxic smoke, even when it is subjected to flame or high heat. Often these plenum-rated cables are insulated with PVC or FEP (fluorinated ethylene polymer) plastic insulation.

Riser-rated cables are typically held to slightly lower standards than their plenum-rated counterparts, although they must still meet the requirements of the NEC and any other applicable codes to be used in such spaces.

Because the standards for plenum-rated cables are more stringent than those for riser-rated cables, it’s sometimes considered acceptable to use plenum-rated cables in riser space, but not the other way around - consult an electrical engineer for details.

Typically, AWG fire alarm cable will also be self-extinguishing and will resist burning, regardless of its rating. It wouldn’t be much use as a fire alarm cable otherwise.

Plenum and Riser-Rated AWG Fire Alarm Cables Are Here
Looking for high-quality, plenum, and riser-rated AWG fire alarm cables with a wide range of unique specifications? Get them here at EWCS WIre! We guarantee satisfaction and that your order will be delivered as specified.

If you have any questions about plenum space, riser space, fire protective notifications circuits or signaling circuits, or instrumentation and alarm cable in general, get in touch with us at Sales@EWCSWire.com or at 800-262-1598.