Best Practices for Terminating Copper Cabling

  • January 30, 2009
  • News
Although the process of terminating twisted-pair copper cabling may seem to be relatively simple on the surface, the issues involved with properly creating robust connections for today’s high performance LANs can be particularly challenging. While cutting, stripping and terminating operations appear to be straightforward tasks, doing them right the first time and avoiding the need for expensive follow-up troubleshooting can mean the difference between making a profit on the job or taking a loss. In the field time truly is money. To assure maximum return on every LAN installation project, well-trained field installers should understand the fundamental techniques necessary for handling high performance cabling, for preparing the connection and for properly attaching the appropriate connector hardware. The best and most efficient installers have developed a consistent pattern of activities that allow them to move quickly through the critical steps in terminating the copper cabling, without missing anything or having to stop and think about what to do next. By using the proper tools and maintaining them in proper operating condition, installers are able to get the same results time after time and minimize the risk of leaving behind any potential landmines or troubleshooting challenges for the certification and testing staff. Achieving consistent quality depends on a balance of having both the means to do the job properly and knowing the methods. While using the correct tools is always of critical importance, understanding the techniques and learning the requisite skills is also a paramount consideration. This paper provides an overview of best practices for terminating copper cabling and is intended as a reference source to give both experienced and new installers a solid grounding in the proper fundamentals, theory, methods and tools necessary for creating robust copper LAN connections.Understanding Twisted-pair CablingTwisted-pair copper cabling has become the predominent choice for copper-based LAN communications using structured wiring installations. A structured wiring configuration provides a robust method for distributing a full range data and other LAN services from a central distribution point to various end points throughout the network. Structured wiring has long been the standard methodology for providing the robustness required in business LAN applications and is also gaining signficant acceptance as the method for pre-wiring residential construction as well.Unlike telephone systems, which often reverse two or more conductors, LANs require that all lines are connected straight through from hub/concentrator to the workstation. The pairs are grouped as a transmit +/- pair and a receive +/- pair. It is very important that these lines are not crossed or shorted as the integrity of the network will suffer. Line mapping, also referred to as end-to-end connectivity, is a basic test that identifies the status of each wire in a twisted pair environment. In addition, the fundamental characteristics of twisted pair cabling must be maintained in a consistent manner along the entire link. The twists in the cable are designed to reduce crosstalk between the pairs and to allow for high-speed transmission (up to 200 MHz for Cat-6 cabling). If the cable characteristics are altered, such as by untwisting too much at a connector point or even re-twisting too much, the changes in impedance can result in a “speed bump“ that slows down some signals and/or causes crosstalk between the pairs. In addition, kinks or tight bends anywhere along the cable run can result in similar problems, which can be very hard to detect later without the use of sophisticated test instrumentation.Cutting the Cable to Proper LengthThe first step in the process is cutting the proper length of cabling and assuring that you have adequate margin for attaching the connectors - - without creating problems by leaving excess cabling at the termination point. Typically, it is a good practice to leave approximately 18 inches of cabling at the wall outlet. The amount of cabling at the wiring cabinet end will depend on the specific installation requirements, usually leaving only enough slack to fit neatly within the wire management structure.When cutting the cable it is important to use snips that provide a clean cut every time and also that are ergonomically suited for repeated usage without undue fatigue or stress to the user. From both a safety and consistency perspective, it is important that the snips have a serrated edge on the blade to keep the cabling jacket from slipping along the blade face during the cutting process. Smooth blade snips run the risk that installers can cut themselves while trying to hold the cabling in place for a clean cut. Another important characteristic to look for is an elongated handle on the snips that allow the installer to easily exert the needed pressure using the palm of the hand rather than the fingers.StrippingStripping is intended to remove a specified length of the cabling’s outer jacket in order to expose the twisted pairs that are to be attached to the connector. There are two schools of thought on stripping. The first is the use of a dedicated stripping tool (see Figure 1) that can be used to score a “ring” around the diameter of the cabling jacket and allow it to be pulled off to expose the twisted pairs. When using such a stripping tool is it very important to select one with adjustable blades and to be sure that the blades are properly adjusted for the cabling type, so that it doesn’t cut or nick the insulation on the underlying conductor pairs. Even an almost unnoticeable nick in the insulation on the wiring pairs can create an unacceptable result on the return-loss testing that is critical for passing Cat-6 certification. Using a tool with replaceable blades also enables the installer to make sure that they are always getting a clean cut around the jacketing and will help to minimize any problems with pulling the jacket away from the underlying wiring pairs.The second method, preferred by some veteran cabling installers, is to use their snips to roughly cut back about ½ inch of the cabling jacket and then pull the internal ripcord in the cable back to expose the required length of twisted pairs. Then they simply use the same snips to trim off the excess jacket. For experienced cabling installers, this method has the advantage of allowing them to carry out both the cutting and stripping operations without having to reach for a different tool.Terminating the Wiring Pairs on to the JackWith UTP cabling, the next step is to terminate the wiring pairs on to the jack. Here again, workmanship is critical to achieve consistent results. For an RJ-45 connector, the amount of wiring that should be exposed is only about 1 inch and the amount that is untwisted shouldn’t exceed ½ inch.For high-speed installations, such as Cat-6 and Cat-7, it also can be very important to match the cabling and connector hardware in order to assure the same characteristics are maintained throughout the termination circuit - - thus avoiding signal “speed bumps” in the connector that can negatively impact performance.An overriding issue with terminating the UTP is consistently following the color-coding conventions for the installation. The two major standards are T568-A and T568-B. The recommended color coding established by the TIA is 568-A, however 568-B follows the color coding convention that originated within AT&T phone systems and therefore 568-B has long been in common popular usage. For most commercial LAN installations, either color-coding convention may be used, however, in residential applications it is important to note that 568-A will allow for two-line service while 568-B will only allow one line. Therefore, residential installations should use either 568-A or USOC (Universal Service Order Code) conventions to assure two-line service.The color coding is typically determined by the patch panel being used because in most cases the patch panel is hardwired for either 568-A or 568-B, while the modular jacks are dual coded so that they can be wired either way. Therefore installers must be sure to follow the same convention in the work area that is used in the patch panel. In placing the wires down, it is important not to untwist too much length but it is also important not to re-twist too much. Especially with cabling such as CAT-5e, which is not very tightly twisted, some installers can be prone to add a bit of additional twist, thinking that it can’t hurt, but actually it can. Over twisting can change the impedance of the cabling just as significantly as untwisting. To keep this concern to a minimum, installers should be careful not to have too much wiring exposed. Typically the rule is not to have more than 1 inch of unjacketed pairs exposed at the jack and no more than ½ inch should be untwisted. Most vendors of keystone-style modular jacks provide a channel area which is exactly ½ inch long, so if installers bring the jacketed cable up flush with the back end of the connector, it will serve as an accurate guide to avoid exposing an excessive length of the wiring pairs.A proper spring-loaded punch-down tool should always be used for pushing the wiring down into the IDC (Insulation Displacement Connector) terminals. For tools that have a dual settings (“Low” and “High”), it is recommended that installers always use the Low setting in order to avoid bending apart the IDC’s connector tines, which can result in a loose or intermittent connection. The reason that some newer installers opt for a higher impact setting is that they can’t seem to get the tool to punch down and trim off the wiring on the first try. In most cases, this is because they are holding the tool in too much of an upright position. Experienced installers have learned a technique in which they hold the punch-down tool at a slight angle, with the cutting edge of the blade toward the wire. This enables the blade to cleanly cut and consistently pop out the trimmed wire, even when using the Low setting. Here again, it is also important to use a tool with replaceable blades and to make sure that you are always using a sharp cutting edge.Once all of the wiring pairs are terminated, the final step is to assemble the connector body by snapping the cover into place and loading it into the patch panel or wall outlet.Coax Cable Termination – Special ConsiderationsWhile twisted pair has become the predominant cabling type used in most commercial LAN installations, installers should still be familiar with the special considerations of handling and terminating coax cable. Coax continues to be a key part of the wiring in most residential applications and is also a factor for many commercial environments where video, cable broadband or CCTV security systems may be a consideration. Therefore, cabling installers should be well versed in the proper termination techniques for coax as well as for UTP.Cutting:When cutting coax cabling, it is beneficial to use snips that have an oval-shaped cutting aperture, in order to apply cutting pressure “around the whole cable” and to avoid pressing the coax down into a flat cut.Stripping:Installers should use a stripping tool that is specifically designed for coax and that can handle a variety of different cable diameters. Slider adjustments on the stripper should allow for RG-58 (50-ohm data applications), RG-59 (75-ohm video applications), and RG-6 (75-ohm high-grade digital video/satellite applications). By using a simultaneous 3-step stripping process and multiple blades within the cutting surface, the stripping tool automatically exposes exactly the right length of the foam dielectric insulation layer, the shielding and the conductor wire.Crimping:When crimping slip-on BNC/TNC type coax connectors, it is very important to use a ratcheting tool that does not release until the proper crimping displacement has been applied for the specific cabling and connector type. For example, Ideal’s Crimpmaster tool uses interchangeable dies to assure the proper crimping of a wide range of coax terminations, including RG-59/6 CATV F-Connectors, 20 F-Series, Crimp-on RG-59 Plugs, and 20 F-Series, Crimp-on RG-6 Plugs. Proper crimping force can be especially important for coax with stranded center conductors (data/CCTV applications) where the installer cannot count on the rigidity of the conductor to help provide good electrical contact with the BNC plug. In these cases, the crimping tool needs to be able to attach a brass end conductor to the stranded cable to give it the required strength.Testing ProceduresThe field installer also should be responsible for initial testing of the terminated circuit in order to assure that the workmanship is correct and that it is ready for subsequent testing by the certification staff. For example, Ideal’s Linkmaster Pro provides a complete testing kit for both UTP and coax that tests for shorts, opens, miswires, reversals, split pairs, and shield continuity while also measuring length on UTP, ScTP, and coax with or without remotes. The Linkmaster also can identify up to eight twisted pair and coax remotes and includes a tone generator that sends up to four different tones. Test results are displayed in wire map format to support easy identification and documentation.Finally, installers are responsible for proper documentation and marking of the installed cabling links to provide a solid foundation for both the certification crew and for future maintenance, upgrades or troubleshooting. A properly installed and well-documented cabling network is a major point of pride for most veteran installers. They know that their employer’s overall success and profitability for each project will depend critically upon the installers getting it right the first time, quickly and efficiently. And, they also know that the certification crews generally keep tabs on which installers provide them with the best results. Installers who have the right tools and know how to use them are in a much better position to deliver on all counts. Learn More

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