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. Performing cutting, stripping, and terminating operations right the first time and avoiding the need for expensive follow-up troubleshooting can mean the difference between making a profit on the job and taking a loss.
To ensure maximum return on every LAN installation project, well-trained field installers should understand the fundamental techniques necessary for handling high performance cabling. 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.
Achieving consistent quality depends on a balance of having both the right tools and understanding the proper installation techniques. By using the proper tools and maintaining them in good operating condition, installers are able to get the same results time after time and minimize the risk of leaving behind any potential land mines or troubleshooting challenges for the certification and testing staff.
It starts with a snip. The first step in the process is cutting the proper length of cabling and ensuring that you have adequate margin for attaching the connectors without creating problems by leaving excess cabling at the termination point. Typically, it's 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, but you should typically leave only enough slack to fit neatly within the wire management structure.
When cutting the cable it's important to use snips that provide a good clean cut every time. The tool should also be ergonomically suited for repeated usage without undue fatigue or stress to the user. The use of a blade with a serrated edge can help keep the cabling jacket from slipping along the blade face during the cutting process. When using snips equipped with a smooth blade you run the risk of cutting yourself while trying to hold the cabling in place for a clean cut. Another important feature to look for in a good snip is an elongated handle, which allows you to easily exert the needed pressure using the palm of the hand rather than your fingers.
Grip it and strip it. Stripping 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 that can be used to score a “ring” around the diameter of the cabling jacket, which allows it to easily be pulled off, exposing the twisted pairs. When using such a stripping tool it's very important to select one with adjustable blades and to be sure that the blades are properly adjusted for the cable type you're working with, so it doesn't cut or nick the insulation on the underlying conductor pairs. Even an unnoticeable nick in the insulation on the wiring pairs can create an unacceptable result on the return-loss test that is critical for passing Cat. 6 certification. Using a tool with replaceable blades allows you to make sure that you always get a clean cut around the cable jacket. This clean cut helps 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.
It's termination time. With 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's untwisted shouldn't exceed ½ inch.
For high-speed installations, such as Cat. 6 and Cat. 7, it can also be very important to match the cabling and connector hardware in order to ensure the same characteristics are maintained throughout the termination circuit, thus avoiding signal “speed bumps” in the connector that can negatively affect performance.
An overriding issue with terminating the UTP is consistently following the color-coding conventions for the installation. The two major standards to follow 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, but in residential applications it's important to note that 568-A will allow for two-line service while 568-B will only allow for one. Therefore, residential installations should use either 568-A or USOC (Universal Service Order Code) conventions to ensure 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, you 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's important not to untwist too much length, but it's also important not to re-twist too much. Especially with cabling such as Cat. 5e, which isn't very tightly twisted, some installers can be prone to add a bit of additional twist, thinking that it can't hurt, but it actually can. Over twisting can change the impedance of the cabling just as significantly as untwisting. To keep this concern to a minimum, you should be careful not to have too much wiring exposed. Typically the rule is to not 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 you 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 insulation displacement connector (IDC) terminals. For tools that have a dual settings (“Low” and “High”), it's recommended that you always use the low setting in order to avoid bending apart the connector tines of the IDC, 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're 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's also important to use a tool with replaceable blades and make sure you're 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.
The final step. The field installer should also be responsible for initial testing of the terminated circuit in order to ensure that the workmanship is correct and that it's ready for subsequent testing by the certification staff. You should test for shorts, opens, miswires, reversals, split pairs, and shield continuity while also measuring the length of all cable runs.
You're also 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 depends on 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.
Payerle is LAN certifier product manager, San Diego, Calif., and Lindhart is datacom product coordinator for Ideal Industries, Inc. in Sycamore, Ill.
Sidebar: Special Considerations for Coax
While 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 overall wiring in most residential applications and is also a factor for many commercial environments where video, cable broadband, or CCTV security systems is a consideration.
Cutting — When cutting coax cabling, it's 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 — You should use a stripping tool that's 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's very important to use a ratcheting tool that doesn't release until the proper crimping displacement has been applied for the specific cabling and connector type. Proper crimping force can be especially important for coax with stranded center conductors (data/CCTV applications) where you can't 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.
Sidebar: Keep an Eye on That Twist
The fundamental characteristics of twisted-pair cabling must be maintained in a consistent manner along its 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.