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Chele

join:2003-07-23
kudos:1

Plenum or non-plemum

We just started doing some work for a private school. They asked us to pull 3 CAT5e cable runs within the office building. We used Plenum cable as the cable is strung right above the ceiling tiles(typical office ceiling). AC/heating is vented via ducts into the habitable space but it obviously "leaks" above the ceiling tiles. We did notice that none of the existing cable is plenum, including a job they had done somewhat recently(aprox 50 cable runs). The work seems to be professionally done, the cable is well supported above the ceiling tiles and it has been dressed very nicely in the server room. From all I have read, it seems the previous job was not done to code. Can someone shed some wisdom on this?

Thanks


Porch

join:2005-06-19

The only time I have seen plenum used is in government installs or other high dollar or sticker for the rules outfits. I have never installed the stuff even in new or remodels and no inspector has even looked twice at it.



54067323

join:2012-09-25
Tuscaloosa, AL

2 recommendations

reply to Chele

said by Chele:

From all I have read, it seems the previous job was not done to code. Can someone shed some wisdom on this?
Thanks

It very well could be up to code, plenum cable is only required above a drop ceiling if that space is used for return air, if the area above the ceiling is just dead space then standard CM3 is legal.


WHT

join:2010-03-26
Rosston, TX
kudos:5
reply to Chele

Determine if the space above the tiles is used for air return. The feed air will obviously be in ducts and the grills can easily be identified. Fine some grills that look different and see if they have ducts above them - if they do it's a ducted return, if they don't then the space is used as the air return and plenum cable would be required.

I spent several years in a city that required plenum rated cable and I don't think I ever say a ducted air return. One of the telecom/data cable contractors installed the cables after the grid work was done, but before the tiles were installed. I was there when the inspector dropped in and the only thing he said that had to be changed was to suspend the cables from the steel work, and not have them laying on the grid work. Nothing was mentioned about non-plenum cables used.


gunther_01
Premium
join:2004-03-29
Saybrook, IL
reply to Chele

Yes, Plenum is used only if the air space is used, as, guess what, a plenum.. And also, yes, you are supposed to NOT just lay your cables on the tiles. There are supposed to be properly suspended above the tiles, by their own means.

Both of these items are NEC code and should be followed regardless of inspectors. You will not be happy if someone dies from a fire in that air space. If your CMR cable was put in a plenum space and someone died from the fumes.. That's why you use plenum cable in plenums, it doesn't burn the same and has less toxic fumes. Or if you ever need to fix something and the tiles are all stuck down from idiots just laying stuff on top. (I can't stand that one, especially since it's code not to do it, and is unprofessional as hell)
--
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WHT

join:2010-03-26
Rosston, TX
kudos:5

Not to detract from the thread, but the environment would be pretty toxic anyway long before non-plenum PVC jacketed cable starts to burn generating chlorine based combustion components.

Curiously Europe has banned the use of PVF cable all together (as I recall) because of the far more toxic fluorine combustion byproducts of plenum rated cable. The genesis of this was the high injury rate involving PVF fire rated cables in British ship board fires during the Falkland Islands battle.



nunya
Premium,MVM
join:2000-12-23
O Fallon, MO
kudos:12
Reviews:
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reply to Chele

In today's "sue them all" society, you want to make sure your installation is up to snuff. Even if everybody else' is total shit.
In the off chance there was a fire in the plenum and somebody died or was injured by smoke inhalation, what the lawyers do is add everybody to the lawsuit (HVAC contractor, electrical contractor, plumbing contractor). They are most likely to get settlement if each party is assigned X% responsibility. The more parties you add, the less the percentage is for each - thus the willingness to settle rather than fight.

The easiest way to tell if a ceiling is used as the plenum has already been mentioned in this thread. Look for the "double pipe" (supply and return) or if there are "blank" grilles in the ceiling. "Blank" grilles usually indicate that the ceiling space is used for return air (plenum).
--
If someone refers to herself / himself as a "guru", they probably aren't.


Chele

join:2003-07-23
kudos:1
reply to Chele

Thanks to all! We will be visiting the site again to make a final determination. BTW, to those that do this on a regular basis, how often do you see installations that should have plenum cable--but don't? I ask because looking back, I have never seen plenum cable used and it seems too much of a coincidence that none of the sites required it:( Plenum seems to be fairly easy to spot because it just looks "cheap" compared to the non-plenum.



nunya
Premium,MVM
join:2000-12-23
O Fallon, MO
kudos:12
Reviews:
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I think it depends on your geographical location. Around here, code enforcement is pretty tight on new construction and commercial work. Inspectors pretty much go by the book. I'd say the worst offenders for non-plenum in plenum installations would be the phone company, satellite, and CATV installers. Their work is usually total crap (in general) anyway. Municipal workers also do not seem to give a shit.
In my neck of the woods, the drop ceiling is almost always used for return air - so plenum is more common than CMX or CMR.
Any time plenum isn't required, I do not use it. #1) it's more expensive. #2) the sheath is more brittle and tends to snag, rip, twist, catch, etc...
It sucks re-pulling 250' of a cable though a bundle because it got a loop snag and caught on a ring.
--
If someone refers to herself / himself as a "guru", they probably aren't.