Plenum Cabling in Conduit under Slab. Not Good! 2

[jonoman123]

I've got several Plenum feed cable's going to each IDF from the MDF, via conduit in concrete slab. They all have at least a minimal amount of water in them. Obviously, Plenum jackets like to harden and crack over time, which doesn't mix with water too well. In less than a year, I've had 50% failure: Cable has a crack or hole, and water gets into it. Bam! Instant short on a pair. The conduits were blown out before install, but water tends to get into them anyway.
Here's my question: shouldn't a burial grade, gel filled cable be installed in the conduit? Plenum cable is for plenum spaces, but the meatheads who installed it don't know the difference. I need good hard proof here by EIA/TIA or BICSI standards.
Can anyone help?

 

[Servamatic]

While I agree with you on using gel filled cable underground, if it is used to feed from point A to point B within a building, you would have to have a transition point at each end of the conduit. By NEC code you can only have unlisted cable extending a maximum of 50' inside a building, unless it is in rigid or IMC conduit.

Unless plenum is required by code, it would economically be my last choice, strictly due to cost.

If the conduit is run box to box underground and just a short distance between where it emerges above ground and where it is terminated you might be ok to use it, providing the local AHJ agrees. This is due to gel filled cable being extremely hazardous in a fire.

There are new types of multi-use underground cables that do have listing, I would look into that in these situations.

I would also submit a bill for replacement to the contractor that installed the cable, since plenum cable is not recognized for underground use, and the code does require you follow the "use for which intended" rule.




Richard S. Anderson, RCDD

http://www.servamatic.net

 

[jonoman123]

Thanks for the reply! When you say "since plenum cable is not recognized for underground use, and the code does require you follow the "use for which intended" rule." are you saying there is a definitive "code" appointed by BICSI or EIA/TIA. I know the difference between codes and standards. Where could I find it documented. It's so frustrating anyway. Who in their right mind, unless they were ignorant (as in my case) would spend so much on plenum cabling anyway for this app? Again, any help is much obliged.

 

[Servamatic]

I was not referring to standards, I was referring to the National Electric Code, which in most places is law.
Standards are voluntary.
I would suggest reading Article 800 of the NEC.
Specifically 800-50 and 800-52.

To be fair, it is sort of a gray area, which is why I made the statement about your local AHJ. The code does not specifically say you can't, but it does say any cables installed within a building will be listed for the purpose.
Plenum is not listed for underground.

Any cable placed in an underground conduit should be outdoor rated for wet locations.

Richard S. Anderson, RCDD

http://www.servamatic.net

 

[buitenhek]

“There is no “perfect polymer” (yet) applicable for outside water and UV protection that also will offer an inside plenum fire-rating required by the NEC.”

Inherently, plenum cables offer low toxic smoke properties and minimal abrasion/high insulating protect for the copper cables (requires jacket integrity). Water-blocking (interstitial) gels in OSP cable protect the cable from moisture but are very flammable. Usually the water blocking properties involve some form of expansion, which in turn would “break” the plenum jacket integrity allowing moisture access to the cable.

If this thought can be carried to just plain plenum cables: then if the plenum cable is subject to moisture (buried conduit) the swelling of the cable due to water logging will allow “quicker” access to the copper cable than the PVC cable since PVC cable design does not “hinge” on jacket integrity.

Enough with the "Dr. Evil quotes" and (brackets) already.

Regards,
Peter Buitenhek

 

[daronwilson]

This is a common issue, with no real easy solution in my opinion. Picture a bank with PVC conduit from floor box to floor box in/under the slab. Do we put gel filled Cat5e for phones/data and gel filled fiber, etc in there? We don't unless specified. As I understand it, technically when you penetrate that slab you are outside the envelope of the building and the product should be listed for underground use. I guess we have cheated it for many many years when the conduits are good and dry.

Obviously when it goes outside the confines of the building we use underground cable, but as I think of our office here we have gutter with maybe 30 runs of PVC going down to the floor outlets. Each one has phone and data, and it's all just PVC.

Go figure, sometimes rather awkward to do it 'right'.

Good Luck!

It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com

 

[Servamatic]

Just a point of clarification the quote that "Inherently, plenum cables offer low toxic smoke properties" is not true at all, although that is a common misconception.

The advantage plenum cable gives you is slower burning, it should die out as soon as you remove the flame, and it gives off a whiter smoke to aid vision to escape the fire.

A pound of CMP cable is just as toxic as a pound of CMR.

Richard S. Anderson, RCDD

http://www.servamatic.net

 

[buitenhek]

Thanks Richard, I was in that group of common misconception regarding plenum toxic output. Do you have any source/thread for further reading on that subject?
Regards,
Peter Buitenhek

 

[Servamatic]

Sure Peter

Try this link

http://www.wireville.com/news/news01.html

Talks about how plenum cable came to be.
If you do a search on the whole article, the word toxic never comes up. The main concern of UL and NFPA was and still is smoke and flame.

Here is a paragraph from the study.

"Cables made with complex compounds are much more sensitive to the conditions by which they are made. Processing of the polymer compounds can cause variation in the chemical reaction that is required to keep PVC and PO from generating dark smoke. Variations in flame spread and smoke generation results from changes in manufacturing speed, location, and tooling. Again, this is not the case when fluoropolymers are used."


Richard S. Anderson, RCDD

http://www.servamatic.net

 

[daronwilson]

Here is another good link:

http://www.datacable.org/issues/toxic.pdf

It certainly adds some validity to the discussion in my opinion when the results are documented like this in a published scientific study. Very good article IMHO.



It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com

 

[buitenhek]

Very good articles. No discernable difference in PVC & Plenum toxic output from fire. Plenum exhibited low fuel load, very low smoke and heat release.
Great Forum.
Regards
Peter Buitenhek