Conduit Fill With Stubs 2

[AvayaNovice]

Does the conduit fill ratio rule apply to stubs? Ie. a 2' stub (or chase) going from the cieling space, through the cieling tiles, and just a few inches down, basically allowing a path for your cabling to go from above the cieling down into the MDF or IDF. I've done it with 4" PVC a bunch of times, and since they're usually only a foot or two long, I fill them up pretty full so as to not have to have too many. Any standards info on this?

Also, are there any defined standards on whether or not flex requires a plastic bushing, or no?

 

[Servamatic]

Conduit fill ratios ONLY apply for firestopping, the NEC exempts communications cables from fill ratios. NEC 800.48 Exception.

Remember only Chapter 8 applies to communications cable installation, unless Chapter 8 refers you to a specific place in the code, such as in Article 800.6 which refers you to Article 300.4(D) for protecting your cable.

So if you are asking for firestopping purposes, you must follow the manufacturers specs on the firestop material and assembly you are installing.

You should ALWAYS use bushings on metal conduit.

Richard S. Anderson, RCDD

http://www.smartbuilthomes.com

 

[daronwilson]

Ok it's 1am and I'm not going back out to the truck to look it up, but I thought that exception refered to horizontal cabling. I'll look in the morning.

As for flex conduit, I know of no standard or requirement requiring a plastic bushing. You must have an approved fitting for each end such as a screw in connector or clamp on connector, but you aren't required to have a plastic anything on it as far as I know.

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

 

[RSKing]

If I'm reading this correctly, we're discussing a piece of EMT installed through a drop-ceiling tile for the express purpose of making the install aesthetically pleasing.

If so there are no firestopping or fill ratio issues to consider. There would be considerations for adequate bracing of the installed system, support of cable, and ensuring future expansion space is available.

Hope this helps...


Richard S. King, RCDD/LAN/OSP
TKG Consulting Engineers, Inc.

 

[Jtodd]

I think the question is more 1st Floor/2nd Floor floor/ceiling sleeves. Honestly I don't know if the NEC has any codes regarding cable fill in this case (seems to me I read somewhere it doen't, but I won't hold fast to that). BUT in my standards, and what I'm writing as specifications for the university, it does matter. 40% cable fix max with one empty conduit when finished. I'm fairly sure that's what the intent of the TDMM is, but code I'd lean towards no.
As for the firestopping, I want between floor (or hallway) sleeves plugged, regardless of how much cable is in them. But for one that is mentioned by RSKing, I wouldn't fire stop that one.

PS I wouldn't want to use flex at all, but that's my preference.

Justin T. Clausen
Physical Layer Implementation
California State University, Monterey Bay

 

[Servamatic]

Well, I did quote the code section...

Richard S. Anderson, RCDD

http://www.smartbuilthomes.com

 

[Jtodd]

Well, yes, I did see that, which actually left me with a question...
When NEC is addression conduit cable fill percentages, it is only doing so as it pertains to how a certain fill % is firestopped? (x% gets this type/amount of firestop, y% gets another). Should different amounts of cable get firestopped differently? Per code? or per manufacture?


It makes sense that NEC doesn't care to much about the crush factor in a 90% filled 4" conduit, or jack burn when trying to pull a new cable in (or old one out).

Justin T. Clausen
Physical Layer Implementation
California State University, Monterey Bay

 

[AvayaNovice]

I'll be more clear:

This was addressed as far as drop cielings, not from 1st floor to 2nd.

Let's say I've got a snake tray filled with 100 cat5e drops. I need to take them from the snake tray, down from the cieling, through the drop cieling tile, and into the MDF (all on the same floor). Usually, I put three or four 4" PVC conduit 2' sections that allow an aesthetic passage from cieling area to the MDF, and then waterfall out of those onto a ladder rack.

So the question was... is there any maximum fill for those? I stuff them all the way to the max (without damaging cable, or making it too tight to where it's not reasonable).

I thought that fill ratio's were both for fire rating, and for performance (ie. not having too many cables crammed together which could possible cause a pinch or something).

I wasn't sure as to whether or not I'd have to keep those at 40% as well.

 

[Servamatic]

You don't need to re-explain, I understood the question.
When I answer a question, it is not meant to fit one situation. So often I give a general situation answer that will fit multiple questions..

There is NO max fill ratio for communications cable...EXCEPT if you have to firestop. NEC Section 800.48 Exception clearly states fill ratios DO NOT apply to communications cables.

The only time you need to worry about fill ratio for communication cables is if you are firestopping....since you are not firestopping...NO..by code you can put as many as you want in that sleeve.

Following the NEC to the letter does not gaurantee it will work, only that it will be safe for people and equipment.

That said, it is always a good practice to limit the fill, if for no other reason than future MAC's.


Richard S. Anderson, RCDD

http://www.smartbuilthomes.com

 

[Kwick18]

jtodd
My understanding of firestopping is that the fill ratio you get is the max. It gives you the maximum amount of fill before the firestopped system fails.

 

[Jtodd]

Richard,
I'll have to disagree with you, to a point. While from what you said before, the only CODE (NEC) for cable fill has to do with firestop (which I won't/can't argue), I think the STANDARD (TIA) addresses it (ooo, that code/standard thread could be coming back) as does BEST PRACTICES (BISCI TDMM among others).

I've got many sleeves of this type where I want to beat the person who overfilled them with a broom handle. We're talking in the 90%+ before I even started adding stuff!

So, in my opinion, any conduit used for any reason should be only at 40% fill on the original install, with and empty conduit installed at the same time. Then any MACS have plenty of space.


Justin T. Clausen
Physical Layer Implementation
California State University, Monterey Bay

 

[Servamatic]

I agree with you Justin, I personally do not like the fact that the NEC exempts comm cable from fill ratios.

But the NEC is law, and standards are voluntary as you know. As I recall (I need to verify) the standard also exempts sleeves (under 3').

My final comment in my last post is how I feel about it.

"That said, it is always a good practice to limit the fill, if for no other reason than future MAC's."

Richard S. Anderson, RCDD

http://www.smartbuilthomes.com

 

[Jtodd]

"That said, it is always a good practice to limit the fill, if for no other reason than future MAC's."

I'll absolutely agree with you on that one.
I was unaware of the under 3' exemption as far as the standards go, but I wouldn't exempt them.

Justin T. Clausen
Physical Layer Implementation
California State University, Monterey Bay

 

[mikeydidit]

Guys I have been watching this one close and I am surprised of the outcome. I have been under the impression that a conduit was a conduit and the 40% maximum fill rate was in place for all. As it comes out, this ends up being the practice that you would recommend anyway. I have been written up by our fire Marshall’s office for not having this same scenario sealed. So that being said, the fill ratio should also not exceed 40%?? Looks like to me the standards committee needs to look at this a little closer.


Mikey

 

[Servamatic]

Both the code and the standards mandate fill ratios when firestopping is required.
Most manufacturers of firestop require less than 40% fill, so lose the hard and fast number and read the manufacturers Listed Assembly Sheets (LAS). Many of which are around 30% fill. Some are developing new materials that can go as high as 48%, but those are few.
To be a legal firestop, you must follow the LAS, even if many inspectors don't know what they are.
If you fill a conduit to 40% and the LAS says it must be no more than 30%, you might as well not do it at all. The firestop material must have the right ratio or it can not expand to fill the void left by the conductors as the they burn away.
After a fire and the lawyers come through, you better darn sure have made legal and proper firestop, regardless of what some uneducated inspector thinks. Having him named in the lawsuit with you will not provide much comfort.



Richard S. Anderson, RCDD

http://www.smartbuilthomes.com

 

[AvayaNovice]

Well...

I guess my only point is: in terms of realistic fire protection -- are cieling tiles fireproof? Because I'm only talking about jumping into the cieling area of a drop cieling type building, the stub is just used to get from the room to the cieling, and no more...

 

[mikeydidit]

From what I read hear Avaya and my own experiences I would not fill the conduit over 40% (and I will check what is recommended from the manufacture Richard) and would putty both ends just to be sure. As some of you know from some of my past post I am in a hospital environment so I don’t take chances. I may only have to putty one side of a smoke wall and both on a fire wall but we putty both sides regardless. As for the write up from the fire marshals office. That employee is gone and the rest took a unexpected vacation.


Mikey

 

[AvayaNovice]

I can't see putting puddy in the conduit.

This is a frequent spot for MAC's, that would be unrealistic.

Furthermore, again, this was not a question oriented at fire protection, this was oriented at maximum fill rates before crunching the cable too much and causing potential performance problems.

 

[Servamatic]

Try some common sense for that one.
It has been exp[lained when you must follow fill ratios, the rest is up to you.

Richard S. Anderson, RCDD

http://www.smartbuilthomes.com

 

[AvayaNovice]

Sigh... nevermind.