atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Cabling Telephones Systems Wiring plenum or not???

Let's also remember that plenum-rated cable isn't "better" because it costs more. It is designed to minimize flame spread when installed horizontally. Some plenum jacket formulas when installed in a vertical (riser) environment actually burn like crazy, hence the reason for riser-rated cable. Granted, some plenum cables today are dual-rated, but not all. The only way to know for sure is to check with the manufacturer to determine their jacket material and ratings.

It is equally wrong to use plenum cable in a riser environment as it is to use riser cable in a plenum. One size does not fit all, contrary to popular belief.

When in doubt:

CMR ONLY in vertical installations.

CMP ONLY in horizontal installations in plenums.

Trust me on this. Some jurisdictions require following the NEC to the letter, specifically article 110 where it is stated that "all material shall be approved for the purpose". We had a job in Prince Georges County, MD a while back where we used 100 pair plenum cable (we had a piece in stock) for a five-story riser cable. The electrical inspector made us pull it out and replace it with cable that had the CMR rating.

Supply and demand is what causes the difference in price between the two cable jacket types. This is obviously due to the fact that there is a lot more horizontal cable being installed than vertical. While some will state that the cost difference is negligible, I respectfully disagree. With the suppliers we use, the difference is significant and well-worth it to stock both types.

Actally its hard to know what is a plenum space and what isn't anymore. Some builings are non-plenum except that an return duct has been damaged or disconnected and now the space above the ceiling tiles is active, with postitve air flow...so the non plenum space ia an accidental plenum. What cable do you use now? Is is just the code we worry about or preventing a hazard?

Well, I have run plennum on several occasions but do not often. With every city having its own specifications I and my customers are lucky I guess for the price savings. We do not have but one building that I'm aware of that uses the above ceiling area for return air. However most of our buildings are of conventional construction. The need for plennum has been listed in the bid specs from the architect. But remember, I am in a very rural area.

Maybe tell the building owner to have the "damaged" duct work fixed?

It is just the code...... i did a wiring job years ago for a company in the chemical industry... when i discussed the potential for plenum cable being needed he explained that he was a chemist and in a typical office environment if there were a fire the cable sheathing burning would be so far down the list of problems that it wouldn't matter if it was pvc or plenum.

As I stated I had one job that was Plenum. This was many years ago in a building designed for doctor offices. I ran my little 2 pair Teflon wire next to miles of PVC drain pipes going to all the exam rooms.

Air plenum return is very inefficient. In an age where technology has made heating/cooling systems very efficient it seems a waste not utilize the best distribution. Air plenum return is cheap. another example of the "low Bidder" and the cost of Plenum cabling, and the continual cost of heating/cooling for the life of the building isn't mentioned

I just came across this thread again.

It is equally wrong to use plenum cable in a riser environment as it is to use riser cable in a plenum. One size does not fit all, contrary to popular belief.

When in doubt: CMR ONLY in vertical installations. CMP ONLY in horizontal installations in plenums.

Sorry Ed but that's absolutely wrong. If you look at the hirearchy or substitution tables in any of the NFPA 70 (NEC) low voltage articles (725, 800 on) you will see that a plenum listed cable trumps all others. It's at the top of the list and can be used in place of anything. That includes riser in a vertical run.

Trust me on this. Some jurisdictions require following the NEC to the letter, specifically article 110 where it is stated that "all material shall be approved for the purpose". We had a job in Prince Georges County, MD a while back where we used 100 pair plenum cable (we had a piece in stock) for a five-story riser cable. The electrical inspector made us pull it out and replace it with cable that had the CMR rating.

That inspector plain didn't know what he was talking about. To quote something as nebulous as Art 110 when the situation is clearly covered elswhwere just shows his lack of knowledge. Many inspectors (and sparkies) are poorly versed on low voltage. I would have shown him the book and not budged, especially if it was going to cost you money.

-Hal

Always follow your local building code! If you do not know then take the steps and get the documentation to verify it. If not you could make a very expensive mistake! I am in San Diego and Plenum is a very common cable used.

When I was at AT&T back in the late eighties....the rule was always use plenum and they charged a flat rate as well with some exceptions for high celings, very long runs, cinder block walls, etc. Then they charged a frim rate of 64 hour plus parts. We AEs had a guide called "wire made simple" which of course it was anything but.