Tangle-Free Design

09/01/2005


Density of cabling, its effect on cooling and air-handling systems and its interaction with other systems are some of the major challenges for communication cable layouts in telecom and data centers.

CSE: What are the key challenges in organizing cable in telecom and server rooms?

MONFORTON: From a capacity planning standpoint, building a permanent cabling infrastructure that not only meets current requirements but also anticipates future needs is tricky. One challenge is that ever-increasing quantities of cabling are being required at server and network equipment cabinets. There's also a greater density of cables being routed to main cross-connect frames. This is particularly true for data copper cross-connects, as one frequently terminates several hundred four-pair cables at each frame. This issue is only exacerbated by the larger diameters of the new augmented Category 6 designs.

BOWMAN: Without question, the single most challenging aspect of cabling in a high-density networking environment has to be cable management. The wide variety of design considerations for data center, computer room, server room and telecom spaces not only includes density of cabling, but also how it impacts cooling and air-handling systems, and even its interaction with various storage, computing and ancillary systems—not to mention maintaining separation from electrical power.

BOYLE: Another primary challenge is planning for MAC—moves, adds and changes. Any designer worth his or her keep will specify and design clean and efficient distribution pathways. A good installer will load those pathways and cross-connect patch panels to active electronics in a neat and workmanlike manner. However, follow-up is crucial, as lack of time, budget, training and manpower can make it difficult for the end user to maintain the original look.

CSE: Speaking of initial installations, what kinds of problems do you typically encounter when you go into an existing telecom/server room?

BOWMAN: The biggest problem I've observed stems directly from the rapid evolution of technology and the incredible increase in the number of servers and support systems in today's telecom rooms. Many of these spaces were not designed, but just happened. Sorting through the layers and layers of cabling supporting various systems—and often installed by numerous contractors—can be an expensive and time-consuming process. I've seen many of the end users choose to get rid of existing cabling and simply start over.

MONFORTON: For existing telecom or server rooms, by far the most common issue is a lack of adequate, if any, vertical or horizontal cable management devices for the quantity of patch cords or cross-connects. Additionally, the tangled rat's nest of patch cords in front of active equipment often makes it difficult to work on this equipment at all—an anathema to IT staffs who must work quickly when problems arise. The bottom line is that wire management must be easy to use and have sufficient capacity to accommodate "real world" quantities of patch cords and cross-connects.

BOYLE: Anyone who has spent any time at all in this business has experienced all of the proverbial skeletons in the closet: abandoned wiring; mislabeled wiring or wiring lacking labels at all; wiring that is not properly supported or secured, i.e., lying on top of duct work or piping; wiring for fire alarms, building automation or what not intermingled with telecom wiring; MAC wiring in unsleeved penetrations; and improper fire stopping and grounding measures.

GIBSON: Believe it or not, just about every existing telecom or server room has some kind of problem. One of the more common maladies is too many cables trying to occupy the same space. This is typically the result of an infrastructure addition, where abandoned cabling was merely disconnected rather than removed. We also find a lot of pathways are just not large enough to handle the amount of necessary cabling. Conduit should only be filled to 40% of its capacity, and no more than 50% of the tray should be occupied.

Another big problem is multi-category cabling misconnected to a patch panel. For example, Category 5 and 6 cabling connected to a patch panel with only Category 5 connectors. We also find split pairs on voice cabling, insufficient cable slack—which impedes replacements and increases cable stress—and inadequate or unlabeled cable terminations.

CSE: What are some effective counter-strategies?

BOYLE: IBM has a wonderful slogan: "Think." We all know that MACs are inevitable, so one must think and plan ahead to make it easier for the client to accomplish change. For example, one should provide additional sleeved penetrations into the rooms, size the pathways to accept additional cabling and specify equipment that is flexible enough to accommodate future needs and requirements. In addition, insist on proper labeling and record keeping.

GIBSON: Referencing ANSI/TIA/EIA-569-B, for the standard room size and component configuration, is also advisable. As far as cable tray, lay it out either overhead or underfloor for smooth transition between the horizontal and backbone cabling entrance and the termination points within the space. Locate sleeves or conduits entering the space in a way that effectively addresses cable-pulling and service-loop issues. For orderly installation between various components, be sure to provide vertical and horizontal wire-management systems on the equipment racks. For easier cable handling, plan on a minimum of six inches, both over and under the connecting hardware. Well-organized, color-coded cross-connect fields will also specifically identify the backbone and horizontal cables.

Finally, you can assign colors, referencing color-coding information in ANSI/TIA/EIA-606-A, to identify components such as backboards and labels.

MONFORTON: Our general philosophy is to engineer in sufficient permanent structured wiring infrastructure within the telecom or server room so that the need for anything beyond local patching is minimized or eliminated. Overhead or underfloor pathway requirements between equipment cabinets, frames or rows can then be determined and properly sized. Vertical and horizontal cable management pathways within cabinets and frames are then selected based on maximum usage possibilities. Where further expansion is a possibility, at least some level of schematic pre-planning for expansion areas is very helpful in determining pathway capacity requirements. This may, for example, mean tiered raceways to minimize disturbing existing wiring for future expansion work. For very large installations, multiple MDF or cross-connect areas become necessary to avoid overloading even the largest capacity raceways.

GIBSON: For an optimal ability to modify and improve cabling infrastructure, keep pathway fill rates below 40% and reserve about 25% to 30% of individual rack space or plan space to accommodate additional racks for future needs. Also, the infrastructure system should be designed to anticipate changes within the next five years. One can make future infrastructure changes easier by requiring cable service loops for cable rerouting, keeping manufacturer-specific requirements to a minimum, removing all inactive cabling in existing rooms and keeping cabling records up to date and in a standard format per ANSI/TIA/EIA-606-A.

CSE: What are your thoughts on various cable-delivery products? Are they application-specific?

GIBSON: Yes. All cable trays are similar in nature or function, but they do have subtle differences that serve their own specific applications. The welded steel/wire mesh basket tray is a lightweight, inexpensive and flexible solution that can be used either in an overhead configuration or under an access floor.

Center spine tray , with its rigid support spine and lateral cable supporting ribs along its length, is generally used overhead when one needs to keep tray supports at a minimum and separate cable between the two sides.

Ladder tray is typically welded steel or aluminum featuring side rails connected by lateral cable support ribs along the length. This product is suited for supporting heavier power cabling and features wider rib spacing for maximum ventilation.

Ventilated channel has a one-piece ventilated bottom and is no more than six inches wide, so it is often used instead of j-hooks or conduit for smaller cable runs.

Ventilated troughs , similar to ladder tray, has rungs that are spaced closer together. This is better suited for communications cable and can be installed either overhead or under an access floor.

Solid-bottom tray is similar to the ventilated trough except it has a corrugated or reinforced solid bottom. In many cases, the solid-bottom tray is used with a solid top to provide physical protection or satisfy security issues. This tray type is the least flexible, but does provide some protection against electromagnetic interference.

Finally, there's ladder rack , which is similar to the ladder tray, but without side rails. Ladder rack, however, should only be used with a minimal amount of cabling, since it has to be physically fastened to the tray.

MONFORTON: Well said, but there are a number of other key non-application factors that must be taken into account, including budget and aesthetics. There's also capacity—both cross-sectional area and load-bearing—and physical mounting requirements. So I absolutely agree that different types of cable trays should be used for different applications. For example, a 2-ft. by 2-ft. drop-in basket tray for underfloor pathways can also be utilized instead of traditional ladder tray over equipment cabinets or termination fields.

CSE: Are there any helpful new products?

BOYLE: Manufacturers now provide vertical and horizontal wire management accessories in a variety of sizes that are both dual-sided and enclosed. This makes for a neater-looking installation and a more efficient method of wiring racks front to back.

Hook-and-loop re-enterable cable ties have eliminated much of the nylon cable tie trash from the floors of the telecom/server rooms by allowing clients to reuse ties when adding cabling. Additionally, they reduce the probability of over-tightening the tie and deforming the cable.

Wire basket trays, being relatively new, in many cases have replaced railed aluminum tray in both overhead and underfloor applications due to ease of installation and increased flexibility.

Finally, fiber-optic raceway has also made a noticeable improvement in the distribution and management of optical cable in the telecom/server environment by isolating the optical cable from the copper. Less damage is likely to occur, and MACs are easier to manage.

GIBSON: We're also seeing Velcro-type straps rapidly replacing nylon cable ties. These newer products are wider, tend not to pinch the bundle, and can be easily released and reused.

I've seen some good products that have been designed for managed networks and incorporate intelligent patch panels and associated software to keep cabling records up to date. Establishing the initial database can be difficult and time-consuming, but once data is keyed in, it's easily maintained.

Another product worth looking into is plastic channeling systems. These can be substituted for the more familiar metal cable trays in telecom and server rooms. The plastic systems range in size from 2-in. × 2-in. to 12-in. × 4-in. Most of these systems snap together without using any tools and offer accessories such as vertical spill-outs and vertical channels for rack cable management.

MONFORTON: There are new products that feature wider or deeper vertical cable management sections and can be used within or between equipment racks or cabinets. As far as fiber-optic applications, keep in mind products that have good bend radius control and slack management devices.

BOWMAN: I've seen some very creative designs that included intelligent patching and pushed patching for horizontal distribution areas, zone distribution areas and interconnect cabinets above the cabinets, mounted to cable tray. This allows some of the benefits of intelligent patching, like IP discovery, and work order fulfillment and disaster recovery to become part of the permanent cabling system. This also provides the ability to switch out entire cabinets and racks full of servers and switches without disrupting the integrity of the permanent cabling system.



Participants

Jerry Bowman , Director, ACE and Advanced Technology, SYSTIMAX Solutions, Richardson, Texas

James Boyle , RCDD , Associate, Senior Telecommunications Designer, Einhorn Yaffee Prescott, Boston

Michael Gibson , RCDD , Telecom Designer, HSMM, Roanoke, Va.

Steven Monforton , RCDD/NTS , Vice President, Environmental Systems Design, Chicago



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