Our clients frequently ask whether they need plenum or non-plenum copper cable for a particular project. The answer is not always as simple as it may seem, and the easy answer is to defer to the architect of the building and what was specified. However, in many cases we are called in to provide a solution in an existing building. So how do we know which to choose?

In most cases, it comes down to how the ceiling is ventilated.

If you look in the office and see an air vent (return grate) that is pulling the air from the office into the ceiling, and it is using ducting in the ceiling to do this, then you can use non-plenum cable barring any specific code requirements for that facility. Here's a non-plenum example:

If the return air vent is just emptying into the open space above the ceiling with no ducting, then the open space is considered to be a plenum area and will require plenum cable. A plenum area like this reacts to a fire differently. Plenum-rated cable has been manufactured to withstand higher temperatures in the event of a fire and does not cause the same level of smoke or toxicity when burning. Non-plenum does not have these characteristics, and as a result costs much less (usually half as much).

Some building owners choose to use plenum cable because it will lower their insurance premiums, even though it is not required. Usually hospitals and schools will also use plenum cable.

However, most of our clients meet the requirements for non-plenum cable, and that is what is used 90% of the time. It’s important to know the difference and what to be looking for in your building. An experienced structured cabling contractor will consider this when providing an estimate, and will clearly state in the bill of materials that plenum cable is needed.