Plenum and non Plenum?

Old 11-18-04, 05:23 PM
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Plenum and non Plenum?

When dealing with co-ax, what is the difference between plenum and non plenum cable? What does NEC say about installation specs into commercial buildings. Does it always have to be plenum?

Thanks, always wondered about that.
Old 11-18-04, 06:06 PM
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It depends on the installation/application. It doesn't always have to be one or the other, unless the environment calls for it.
Old 11-18-04, 07:03 PM
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Someone can correct me if I am wrong, but I believe the term "plenum" and "non-plenum" is actually self-describing.

When the space above a ceiling (drop in tile or sheetrock) in a building is being used as a return airway path for the HVAC system, that area is considered a plenum. Any cables installed in that area must be in metal conduit due to the fact that if a fire occurs, many of the PVC casings used on wire is toxic when melted and the fumes would circulate throughout the building.

Plenum rated cable gives off no toxic fumes when burned. However it is much more costly than regular PVC cable. But then again, when you factor in not having to install conduit, it's much less.

Years ago, we used to mix match PVC and plenum cables on jobs. Supposedly saving the Plenum rated stuff for the ceilings and the PVC would go everywhere else.

However, there is always one installer who doesn't think and you would have to rip out a whole installation due to the inpector picking up the PVC cable in a Plenum rated area.

We don't take the chance anymore. We only buy Plenum now for all jobs, even though it costs more. One wrong use of non-plenum cable in the wrong area could be a 100k mistake. It's not worth the risk.

As I stated earlier, this is my understanding. If I'm wrong I would like to hear more from someone more up on the codes.

paul o's

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