under-floor slack spools

[Zitibake]

I'd like to make a 6-foot slack loop under a raised floor. It will eventually hold a couple hundred cat6 cables, so the bundle will be about 6 inches in diameter.

I've seen a "snake loop" product, but I was imagining something more like a row of vertical fiber spools... except horizontal, under the floor. Maybe a row of coffee cans, glued to the deck below the floor :) .

Any pointers to under-floor slack spool tricks, or solutions?

[cernst]

a few quick questions and concerns.

- are there reasons not to have cables made/cut to length?

- I know my server floor doesn't change all that often, but I do have some servers that are on a rotation to be retired. I would think that pulling old cabling out would be a very hard chore if the cables were towards the center/bottom of this "spool"

[Zitibake]

a few quick questions and concerns.

- are there reasons not to have cables made/cut to length?

TIA-942 suggests leaving several feet of unused slack cable at the end of every horizontal cable run (the number of feet depends on the classificaion of cable run). The cable could be left above the floor, but 6 feet of slack cat6 cable takes up a lot of volume, no matter where you store it.

What I ended-up doing was putting a pair of Snake Loop trays end-to-end under the floor, at a 90-degree spur off the cable tray, and near punch-down Zone Distribution Area:

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O O )
/ ------------
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(punchdown frame here)


If I have to shorten a cable (due to a need to repunch on the frame, etc.) then I'd pull the cable free as far back as the slack loop, and wrap the cable around the nearer spool. There's room for a third Snake Loop in the row, if I needed to shorten cables even more.

I wonder if the TIA folks really care about under-floor airflow? The amount of cable they're requiring to be left coiled-up is more than is really necessary for most applications. Also, as they push people to preterminated wiring harnesses, slack is pretty pointless. If you have a bad cable in a premade bundle, you're just going to mark it bad and never use it.

[attagirl]

a few quick questions and concerns.

- are there reasons not to have cables made/cut to length?

- I know my server floor doesn't change all that often, but I do have some servers that are on a rotation to be retired. I would think that pulling old cabling out would be a very hard chore if the cables were towards the center/bottom of this "spool"


Enjoyed reading this post because I have to tend to agree with this one. There would be issues if you do rotate the servers and are pulling cables out. I think that this might be more of a mess then you might think.

How do you plan to avoid something such as this.

[Neoeclectic]

TIA-942 suggests leaving several feet of unused slack cable at the end of every horizontal cable run (the number of feet depends on the classificaion of cable run). The cable could be left above the floor, but 6 feet of slack cat6 cable takes up a lot of volume, no matter where you store it.

What I ended-up doing was putting a pair of Snake Loop trays end-to-end under the floor, at a 90-degree spur off the cable tray, and near punch-down Zone Distribution Area:

|
|
\
-------------
O O )
/ ------------
|
|
(punchdown frame here)


If I have to shorten a cable (due to a need to repunch on the frame, etc.) then I'd pull the cable free as far back as the slack loop, and wrap the cable around the nearer spool. There's room for a third Snake Loop in the row, if I needed to shorten cables even more.

I wonder if the TIA folks really care about under-floor airflow? The amount of cable they're requiring to be left coiled-up is more than is really necessary for most applications. Also, as they push people to preterminated wiring harnesses, slack is pretty pointless. If you have a bad cable in a premade bundle, you're just going to mark it bad and never use it.

I don't agree with a lot of the stuff found in the TIA-942. They seem to disregard airflow dynamics and things along those lines. If you're raised floor is only 10" over foundation then you have a real problem on your hands. But they're expecting probably 36" raised providing plenty of clearance for under floor work and air flow. The 942 is based off of presumptions that most likely aren't true across the board.

Personally, I don't see the need for slack more than 1' which is what I leave with horizontal cabling. That allows me to not have to loop them but to let the cables flow in a natural manner within the tray. If you know what you need and what you're doing 6' is a heck of a lot. I'm going to have reread that though I must have missed that part.

[Keith]

While I must say that I do prefer to have some cable slack left before the termination point, I have my concerns regarding having the slack under the floor. My main concern is airflow. Putting a large bundle of cabling that is 3ft long doubled over makes the bundle to essentially be 12" in diameter. Depending on how your floor is laid out with HVAC, this may lead to some blockage under the floor and cause some serious hot spots to occur. If it were up to me, i'd prefer to have my slack going vertical via a spindle cable management system. Not only will this allow you to keep as much airflow under your floor as possible, but it will allow tracing cables through the bundle much easier, in the event that you find that you need to do so.

On the topic of the coffee can. I would recommend going to costco and buying your coffer since the normal retail coffee may not offer the most efficient bend radius.

Let us know how it works out!

[Neoeclectic]

The interesting thing about raised flooring though is that it's backwards to not consider doing overhead cabling exactly for the reason of airfloor obstructions underneath. To really do it right one would have to have an air plenum that feeds air down ducts that carries the air exactly where it needs to be and not let things like cable trays disrupt the flow.

That's how some of the more expensive centers are designed. They might have several rows of trapezoid-shaped ducts where it gets smaller from the main feed. That's so the pressure is equalized through the entire duct. Then there are upper valves that are opened to release air directly straight up from where they are. You lay them out so their not blowing directly underneath a cable tray or a power junction, and then directly up and out the vented floor tile.

My data center isn't designed that way. It's basically just air blowing in random directions under the floor. No duct work at all, and its having to fight its way around miles of cable trays. We're about to deploy a system of rerouting the airflow to equalize the pressure under the floor. We had a company called Flowlogix come out and perform a comprehensive airflow study. Basically, they're going to take sheets of canvas and use it to direct the air to where it needs to go and to equalize the pressure. It's just like duct work except made out of canvas. They also guaranteed us a 40% power consumption savings in the first year or we get our money back which isn't a bad deal at all.

[Keith]

Sounds like an interesting idea. The one thing that I dig about traditional raised flooring is the diversity you can achieve in regards to cooling...I have a personal preference to not being tied in to a specific layout. Over time, the requirements most likely will change, you will of course have to account for growth and higher density applications.

It is all about aerodynamics...No, we are not designing a race car, but we are fighting against wind resistance. I really wish somebody would come out with a cable tray for under the floor that was more aerodynamic in order to decrease the resistance. I cannot wait until the day when they finally develop wireless electricity! Physical security and functionality, all built in to one.

[Neoeclectic]

I don't think I'd want to be in the same room as wireless electricity! I am a strong proponent of raised floor horizontal cabling. Overhead cabling is fine but I hate having to use a ladder and trying to pull bulk cable through. Also it gets pretty hot up there since heat rises and all.