Communications Cables Revised: 08/22/99 18:40
Plenum vs. PVC Reason for Revision: Add header


There is no PVC in plenum cables.

Plenum cables have a Teflon* jacket.

There is a difference in signal transmission performance between Plenum and "PVC" cables.

A plenum cable is tested for corrosive or toxic elements in the smoke when it is burned.

Answer to all the above: FALSE

These are all common misconceptions about voice and data premises cables in the US, especially when Category 5 cable is being considered. You may want to review NEC Flame Ratings of Communications Cables and Categories of Cable Transmission Performance before reading further.

Here is some additional clarification of this subject:

In the US, four pair cables in Category 5 and higher usually have PVC jackets whether they are CMR or CMP rated. The PVC composition varies according to the flame and smoke requirements to be met, but it is still all PVC. Depending somewhat on pair count, most cables lower than Category 5 also have PVC jackets.

In US cables Category 5 and higher, a four pair cable is usually insulated with FEP if it is CMP rated, and with a polyolefin (polyethylene, polyproplyene, or either with some flame retardant modifications) for CMR, CM, or CMX.

CMX, CM, CMG, and CMR flame ratings are based on restricting flame spread, i.e, transfer of the fire. They are respectively more stringent as you move from CMX to CMR.

CMP rating requires not only the most strict limitations on flame spread, but tests for the generation of VISIBLE smoke as well.

There is no requirement in the US that checks for either toxicity or corrosivity in the burning of communication cables. NEC article 800 burn requirements are based on providing time and visibility in order to safely evacuate a building.

Both CMP and CMR (or CM, CMG, or CMX) products meet the same signal transmission requirements within a given Category if they are compliant with ANSI/TIA 568-A. Flame ratings and signal transmission performance are independant requirements. They are only related in that you have to choose a material SYSTEM (insulation and jacket combination) that allows you to meet signal transmission performance parameters and still meet the flame/smoke safety requirements.

FEP insulation (marketed by DuPont under the tradename Teflon and by Daikin under the tradename NeoFlon) has very good transmission properties and also is very resistant to burning and generates relatively little visible smoke. It is also very expensive and is only available from the two manufacturers. This pretty much relegates its use to Category 5 and higher CMP rated cables and some specialty types.

Polyolefins also have very good signal transmission properties. Polypropylene approaches FEP in this regard and polyethylene is not far removed. The problem with polyolefins in a premises environment is that they burn very readily (like a candle) and generate smoke. By using a PVC jacket highly loaded with flame retardants, a manufacturer can choose to use polyolefins for Category 5 and higher cables in all but CMP rated produtcs. For Category 3 and lower, the manufacturer may choose to use PVC as an insulating compound as well as a jacketing compound.

Manufacturers account for the differences in signal transmission performance of the insulation raw material with the cable design, so that for a given Category, the installed cable looks basically the same to system electronics regardless of the NEC flame rating.


*TEFLON is a registered trademark of DuPont

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