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?

 

[daronwilson]

OK, lets clarify a bit.

According to the NEC, there is no maximum fill ratio required for communciations cabling, we've hit that. Article 300-21 says " ...Openings around electrical penetrations through fire-resistant-rated walls, partitions, floors or ceilings shall be firestopped using approved methods to maintain the fire resistance rating." Bascially, if you penetrate a rated assembly, you are responsible for restoring it to it's original rating. The proper way to do this is with a listed fire stopping material installed according to the manufacturers listed procedure.

Personally, I would try to adhere to the 40% or so all the time. Why? Because you could almost always come back and firestop that if you needed to, and I try to keep the installations standards compliant. If you install it and push it to 80% fill, then they remodel a bit, partition and the wall you are in becomes a rated wall, you have to fix it. Also it leaves room for expansion which is pretty much common sense.

Now for ceiling tile, yes they have a rating. Depending on the installation, that rating may be considered in the total ceiling rating. One hospital we work in has drop ceiling and then hardpan sheetrock 12" above that. Everything going in or out of that sheetrock must be restored to the original rating, the AHJ won't allow any holes in the drop ceiling because it decreases the rating so we caulk around all penetrations there as well.

Putty is hardly much of a bother, if installed carefully it can be pulled out from both ends, new wires added and the replaced. Bother or not, it's what is required in many installations.

Oh, keep in mind we are only really dealing with intumescent fire stopping materials, that is those that expand when heated to seal off. Pillows are a great example of this, as well as many caulks and puttys that expand as the insulation burns or melts off the wire in a fire. There are many other types including cementitious, elastomeric and endothermic.

I sense the frustrtation, but please keep in mind that firestopping is not the type of question one asks and can get a simple answer. If it were, the STI firestopping data sheet book wouldn't be 580 pages long. We are all offering suggestions based on our experience, your individual mileage may vary.

I don't use PVC stubs inside generally. We use PVC outside and underground, and primarily EMT inside. My install would be 3 or 4 4" EMT pipes strapped on with kindorf straps to a piece of strut and poking through the ceiling. In our hospital example, I'd even caulk around the EMT because they don't like to have any dust coming down, or smoke going up, and when they see the red caulking they are happy. Go figure. The EMT would have a connector on each end, and generally inside the room would be those nice grounding devices that allow you to bond all the EMT together and tie it to the racks/ladder/bus. Depending on where it is, we might have to putty it when we are done or caulk it.

Please check out this link. I'm not touting one fire stop product over another, but this was the closest on my bookshelf and has great illustrations.

http://sti.fmpdata.net/ftp/Tech_Updates/TU-Cables.pdf

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