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I'm looking into buying a few rolls of bulk Cat6 cable to wire up a few cubicles to a test rack we have. One of the choices is PVC cable versus Plenum cable.

What is the difference? Will this make any difference with crimping or crosstalk/interference?

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up vote 28 down vote accepted

There's no telecommunication difference (e.g. noise, crimping, termination), just the sheathing. The difference is an electrical code safety issue.

Regular network cable (i.e. non-plenum) is flammable, can catch fire, can spread fire, and emit toxic fumes when burning.

Plenum quality cable is required for use if you run your cable in air handling spaces (i.e. air ducts), or if you're running them between floors. Plenum cable is fire-resistant (it will melt, but not support combustion or carry a flame). It also emits less toxic fumes when it does burn.

If you look at some network cable, you can see which type it is:

  • CMP: Plenum rated cable (plenum means "air handling space")
  • CMR: Riser rated cable (riser means "between floors")
  • LSZH: Low smoke zero halogen rated cable
  • CM/CMG/CMx: General purpose cable
  • PVC: Unrated cable

CMP burning:

enter image description here

CMR burning:

enter image description here

Notes

  • CAT6 is still very precise about how the cables are terminated. Sloppy termination will reduce the capacity of the run. This is generally not the case with CAT5.

  • The linked wikipedia article, has good diagrams illustrating what is plenum space and what isn't. Generally, you should use plenum cable in a dropped ceiling unless you are certain that it is not air-handling space. If a duct in your drop ceiling is missing a section: your drop ceiling suddenly, inadvertently, becomes an air-handling space.

See also

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Great answer, and neat videos, thanks! – Michael Haren Oct 30 '09 at 16:15
    
@Ian - Good info .. hope you don't mind the edit to clarify. If you do, feel free to undo it! – tomjedrz Oct 30 '09 at 17:03
    
That's fine, tomjedrz. i just changed it SO IT WASN'T ALL IN BOLD BECAUSE THAT WAS A BIT MUCH. Don't you think? :P – Ian Boyd Oct 30 '09 at 17:06
    
+1 and accepted. Thanks! – romandas Oct 30 '09 at 17:11

Put simply, PVC Cable is the most common type of cable used today and consists of a chemical compound called Poly Vinyl Chloride. If a fire occurs, burning PVC Cable can emit large quantities of dense black toxic smoke, and significant amounts of hydrochloric acid.

If you have a Plenum ceiling, having PVC cable in the ceiling during a fire would cause a concentration of these fumes to be spread throughout the building. Exposure to these fumes could then hinder the safe evacuation of persons in the vicinity and result in increased fatalities. Plenum Rated Cable has a special coating on the wire, which causes it to burn at a much higher temperature and emit fewer fumes than conventional PVC. As a result, the National Electric Code (NEC) requires that only plenum rated cables be installed in plenum air spaces.

Therefore, for fire safety and code compliance concerns, choose PLENUM rated cable. If fire safety is not any concern or local code requirement, choose PVC for ease of installation and lower cost.

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