Plenum vs. Non-Plenum

By Jennifer Leah Stong-Michas | Jun 15, 2004
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A minor decision that can prove costly

Cabling choices are abundant; there are so many options these days that it is almost impossible to list them without leaving a few out. Throughout the years, the variations have continued to grow, and vendors even have their own “lines” of cable depending upon your preference.

There are some things, however, that remain constant when it comes to choosing the right cable for the job. You can usually start by making the decision whether to install plenum or non-plenum cable. This choice is based on the jacket surrounding the cable, not the cable itself, which is a whole separate issue. So after you choose fiber or copper, Category 5 or Category 5e, you still have another decision to make. It may seem like a minor one, but it is important nonetheless since plenum and non-plenum are so different.

In this corner

Plenum-rated cable gets its name from an HVAC term—plenum spaces. The plenum spaces are those that lie between a drop and standard ceiling (or a similar version in the floor space) and it is this section where the air in a building circulates, thus aiding in heating and cooling functions. When no conduit is used, plenum cable is often required since the cable is considered to be freely installed.

Plenum spaces allow fire and smoke to travel quickly. By using plenum-rated cable, the levels of toxicity in the smoke would be lower since plenum cable is coated with a jacket that is typically made of flame-resistant material such as Teflon. This special jacketing makes the cable smoke less than regular PVC cable and the smoke that is emitted is less toxic.

The opponent

Non-plenum cable, which is otherwise known as PVC (polyvinyl chloride) cable, is the less expensive of the two choices. You are likely to see many projects stipulating non-plenum to save on costs, since, more often than not, the decision on the type of cable jacketing is made by the building owner or end user based upon their circumstances. By contrast, most schools stipulate that plenum-rated cable be used, mainly due to insurance requirements.

In projects where plenum is not required, non-plenum is nearly ubiquitous. It is not uncommon for PVC cable to be one-third of the cost of the plenum variety. But, as more and more businesses are becoming burdened with higher insurance premiums, some may choose to go ahead and spend the extra money upfront for plenum in case of fire. By taking such fire safety precautions, companies can lower their liability, since plenum cable causes less overall physical and secondary damage.

Because plenum cable is considered to be less toxic, it is used in locations such as schools and hospitals. Because of the number of people generally contained within these facilities, the potentially toxic smoke emissions from a fire could prove to be deadly. Certain facilities with fewer people about, such as warehouses and distribution centers, seem to lean toward non-plenum, mainly because of the structural setup.

Know the difference

Perhaps the most important thing to remember, from a contractor’s standpoint, is that the biggest difference between the two is cost. Therefore, it is essential to always remember two things.

First, make sure that the project in question truly does require the use of plenum cable. If it is not necessary, then explain that to the customer, since the cost savings of going with the PVC version may make them extremely grateful.

Second, when you initially estimate a project, always check and recheck with your vendor or supplier to make sure whether the pricing you are receiving is for plenum or non-plenum cable. This can save you a lot of trouble and money.

In the end, it is the client’s choice. Some are bound by factors that they cannot control and their cabling choices may not be their own. As a contractor, you need to understand that, as with most things in business, cost is usually a primary deal maker or deal breaker, and the plenum/non-plenum decision is definitely one that falls into this category.

About The Author

Jennifer Leah Stong-Michas is a freelance writer who lives in central Pennsylvania.

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