Computers Nationwide - When is Plenum Cable Required?

When is Plenum Cable Required?

Comparing Cable Options

The options available for different cable products these days are very abundant. Everyday new options are being introduced into the electrical market. Whether it be from the specifications changing to the different variations, the choices are becoming more and more plentiful as time goes on. One option; however, which is usually the first thing a person takes into consideration when purchasing cable remains pretty constant. This is whether or not the cable to be used will need to be plenum rated or Non-Plenum rated. When we refer to cable as plenum or non-plenum we are not talking about the cable itself. The plenum rating that we are talking about actually refers to the jacket that surrounds the cable.

This is an important issue related to the chemical composition of the cable and your building‘s construction, especially when it comes to your small business phone system and low voltage data/audio cabling.

There are two basic types of building construction as it regards the movement of heating, air conditioning and ventilation through office buildings. In newer construction and in most high-rise construction the architects save space and the cost of expensive sheet metal return air ducts by simply drawing the air back to the heating/air condition unit through the open spaces above the ceiling and between the walls.

Plenum Cable

Plenum-rated cable actually received this name from an old HVAC term referring to “Plenum spaces”. A “plenum space” is the part of a building that enables air circulation by providing pathways for heated/conditioned and return airflows at a higher pressure than normal. Typically, spaces between the structural floor or a dropped ceiling are considered plenum. Some drop ceilings are actually designed tight enough to where air circulation is restricted and may be considered a non-plenum area. A lot of times when conduit is not installed, plenum cable is required because the cable is “freely installed”

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Non-Plenum Cable

Non-plenum cable or “polyvinyl chloride” cable is often less much less expensive than plenum cable. As far as cost savings, non-plenum cable is usually close to half the price, if not more, than PVC jacketed cable. Many projects will use non-plenum cabling to save on costs; however, it is ultimately up to the building owner or the goverment codes and regulations on whether or not to use plenum vs. non-plenum cabling. Insurance issues may also have an impact on the chose of plenum vs. non-plenum. Companies may choose plenum cable as a way to lower liabilities associated with fires because plenum cable will be the safer option in the case of a fire. Larger building like warehouses and distribution centers with less people tend to lean toward non-plenum rated cable, whereas hospitals and schools will tend to lean towards the safer chose with plenum cable.

Computers Nationwide - Non-plenum cable

The Problem

Now, let‘s discuss the basis of the problem. Standard cable is jacketed in PVC (Polyvinyl Chloride), with the Chloride element causing the trouble. When PVC burns or smolders it releases toxic fumes into the air (Hydrocloric Acid and Dioxin). A plenum air return would unknowingly circulate toxic air throughout an office.

Since both you and the Fire Department don‘t want you to die from breathing in toxic fumes from your cabling, code requires Plenum Rated cable installed through any plenum air return space. Our Installation Team is required run Plenum Rated cable if they determine the air space in not ducted.

How do I determine if my building uses Plenum Air Return?

  1. If you have a large wall or ceiling return air grate; remove and see if there the air is channeled through sheet metal ducting. If there is no sheet metal duct; just the open ceiling or wall space, then you are required by law to use Plenum Rated cable.
  2. If there is no wall or ceiling return air grate; look closely at your fluorescent lighting fixtures to see if there is a gap around the edge of the fixtures and put your hand over the gap and you can feel air movement. Obviously your air conditioner should be running at the time! The lack of wall or ceiling return air grates is usually a sure sign that you require Plenum Rated Cable.
  3. Computer Rooms typically use a raised flooring system for the server racks. This allows intensive cooling to be pumped through the space under the floor to cool the servers, switches, routers, etc. Cabling between the many devices and to the users runs through this open floor space. This by definition is a Plenum Air space and requires Plenum Rated Cable.


Based on the price differences, it is understandable that installers/project estimators want to lean towards using PVC rated cable, but it is important to keep in mind the requirements of the job at hand. As the contractor, one must check and double check with the customer and/or building owner whether or not plenum cable is needed in their space. Remember, if it is not required, explain the difference to the customer and they will must likely be very pleased to see their cost-savings if PVC cable will be used. Also, as a contractor/installer be sure to always ask the supplier/vendor whether the material being quoted out is for the Plenum or Non-Plenum rating to ensure you will not be overcharged for a Plenum rated cable that is not required on the job.

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