Minimum Run In Data Center

[kcbell]

Hi

I am getting quote to run some horizontal cables between servers rack and the new network rack in the Data Center. Most of the runs are between 15' to 50'. The electircal contractor came back with a EIA/TIA spec and said the minimum for CAT 6 for horizontal cabling is 15m. I did find the following on the web somewhere.

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ANSI/TIA/EIA 568-B.2-1
This is much better cable, better quality copper and contains a physical separator between the 4 pairs to further reduce electromagnetic interference. It provides higher performance than CAT5e and its upper frequency for testing is 250MHz. All the components for this system, basically from the wall plate to the wiring closet must conform to CAT 6 standards. The minimum length for this system is 15 meters and the maximum distance is still 100 meters.

Poor terminations of the cables can have massive effect on the overall performance of the system so make sure the patch cords and fly leads are of CAT6 standard. The components of this system are also of high standard and must be backwards compatible.

It is always good practice to install the best cable available as its difficult to replace cabling inside wall, ducts and floors. As most cabling systems last 10 years or more, UTP CAT6 cable will future proof your investment, giving you much higher data rates than CAT5e
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Should I go with the contractor that stated a minimum of CAT 6 run is 15m or go with the one that did not specify? That means they will run 10' if that is the distance between servers rack and network rack.

Thanks!

 

[mikeydidit]

I would call one of the cable manufactures’ (Berk-tek, General cable) technical support and run the idea by them. If it is something that could be a problem they will let you know for sure before buying something that may or may not work.

Hell, there are no rules here - we're trying to accomplish something.
Thomas A. Edison

For the best response to a question, read thread690-1323977

 

[franklin97355]

The minimum length for this system is 15 meters and the maximum distance is still 100 meters.

I think they are talking of the end to end distance not each segment. Otherwise the jumpers at the patch panel would have to be 15m long.

The answer is "42"

 

[RobKorn]

I was not aware of a minimun length for a cable run. Fiber does have such issues, but I've never heard of it in copper.

If there is such a rule, then how can you attach a server to a switch with a 6' patch cable, if there was such a rule there would only be huge patch cables.

I say "Shenanagons", I wouldn't run extra length (except service loop) because there would be a tendancy to "coil" the 15' extra and tie it up... don't do it.

 

[dagwoodsystems]

There is an ANSI/TIA/EIA-568-B.1 guideline that suggests the Consolidation Point (Zone enclosure box) be at least 15 meters from the telco room. You wouldn't bring a short run to a consoldation point anyway, so the recommended distance doesn't even come into play. It says nothing at all about the length of individual cable runs. Anyone claiming that it does has a misunderstanding of the suggestion.

This is all about minimizing crosstalk at Consolidation Points. Check out

http://www2.ampnetconnect.com/displaydocument.asp?iDocID=721&iDocLinkID=142&iDocLinkType=html

for a visual definition of "Consolodation Point". It's a lot quicker to explain by having you look at a picture. Consolidation points are part of newer cabling techniques known as "Zone Cabling".

Anyway, the point of the recommendation has to do with Near-End Crosstalk (NEXT), and NOT some "minimum cable length". Multiple connections that are very close to each other are susceptible to NEXT, which can be reduced or eliminated by keeping it away from a "noisy" area (such as a server room).

It's good practice regardless of what level of cable you're pulling. But to answer your questions directly: there is no short length limit.

 

[franklin97355]

from

http://www.tiaonline.org/standards/technology/cat6/faq.cfm

What is the shortest link that the standard will allow?

There is no short length limit. The standard is intended to work for all lengths up to 100 meters. There is a guideline in ANSI/TIA/EIA-568-B.1 that says the consolidation point should be located at least 15 meters away from the telecommunications room to reduce the effect of connectors in close proximity. This recommendation is based upon worst-case performance calculations for short links with four mated connections in the channel.

The answer is "42"

 

[dagwoodsystems]

Nice! Far more concise than my wall of words! I think I like the term "recommendation" better than my use of "suggestion" or "guideline" as well.

Anyway, the CP can be a weak point so it's worth pointing out. But some cabling designs don't include one, making it a non-issue. Frankly, I would be far more concerned about the patch panel termination, which is something that IS a part of most cabling jobs.

The patch panel is often located IN the telco room, and it's where all the wire untwisting and over-zealous use of cable ties often comes into play. And while I love dressing cables, I've been told that a somewhat more random approach to landing the cable is preferred.

Traditionally, cable number 1, 2, 3 and 4 are neatly tied together and groomed all the way to the termination point on the patch panel. But I have been instructed NOT to do this with CAT6. Instead, try to remove the "parallalism" of the cables as they approach the patch panel. And by all means, don't kink the twisted pairs backwards just to make the landing of the cable look "tight". Bending the pairs in this fashion is akin to having a kink in the middle of the run...only this time it's susceptible to EMF from the server, the cooling fan, the big monitor and all kinds of other telco room "noise" sources.

You are in greater danger of contaminating your data due to inappropriate cable termination techniques at the patch panel, than you are at the CP.

 

[kcbell]

Folks:

I was away for several days and found many replies. Appreciate all the comments.

I did send an email to one of the cable vendor and the reply was: Yes, the minimum segment is 15 meters. This is especially true for data center application. I was told if the length is shorter than 15 meters then it will give bad result on the NEXT test. I also talked with the contractor that will run the cables. He said the cable would be looping around the cable tray instead of cut exact length between two points.

Thanks again!

 

[dagwoodsystems]

I'd love to see a comparison of Attenuation, NEXT and FEXT on a properly terminated CAT6 that is 50 feet long (a.k.a. the suggested minimum length) against one that is 150 feet long.

franklin97355 brings up a great point: What happens when you use "short" patch cables to uplink two Gigabit switches together? Does the collision domain just completely fall to pieces? The reason is doesn't is because crosstalk tends to happen where cable untwisting is done...like landing the cable on jacks. The untwisting that occurs in patch cords is insignificant.

That's why I keep insisting that attention be paid to the installation practices, especially with all the junk science going around about the cable itself.