Monday, September 26, 2011

Twisted-Pair Continuity Tester & Coaxial Tester

Twisted-Pair Continuity Tester

Many of the common problems of getting cables to work are simple ones. The $5,000 cable testers are nice, but for simple installations they are overkill. If the cable installer is not careful during installation, the cable's wire pairs may be reversed, split, or otherwise incorrectly wired. A simple continuity tester can help you solve many of the common problems of data and voice twisted-pair cabling by testing for open circuits and shorts.
Figure 1 shows a simple continuity tester from IDEAL DataComm; this tester (the LinkMaster Tester) consists of the main testing unit and a remote tester. The remote unit is patched into one side of the cable, and the main unit is patched into the other side. It can quickly and accurately detect common cabling problems such as opens, shorts, reversed pairs, or split pairs. Cable testers are available from many vendors and sell for under $100. Testers such as these can save you many hours of frustration as well as the hundreds or even thousands of dollars that you might spend on a more sophisticated tester.

Figure 1: IDEAL's LinkMaster Tester

Coaxial Tester

Although coaxial cable is a little less complicated to install and terminate, problems can still arise during installation. The tester shown in Figure 2 is the IDEAL DataComm Mini Coax Tester. This inexpensive, compact tester is designed to test coax-cable runs terminated with BNC-style connectors. It can test two modes of operation: standard and Hi-Z for long runs. Coaxial-cable testers will quickly help you identify opens and shorts.

Figure 2: IDEAL's Mini Coax Tester

Friday, September 23, 2011

Cable Testing - A Cable-Toning Tool

A cable toner is a device for determining if the fundamental cable installation has been done properly. It should be noted that we are not discussing the sophisticated type of test set required to certify a particular level of performance, such as a Category 5e link or channel. 
In its simplest form, the toner is a simple continuity tester that confirms that what is connected at one end is electrically continuous to the other end. An electrical signal, or tone, is injected on the circuit being tested and is either received and verified on the other end or looped back for verification on the sending end. Some tools provide visual feedback (with a meter), whereas others utilize audio feedback. Testing may require that you have a partner at the far end of the cable to administer the inductive probe or loop-back device (this can also be accomplished with a lot of scurrying back and forth on your part). Figure 1 shows a tone generator, and Figure 2 shows the corresponding amplifier probe.

Figure 1: A tone generator

Figure 6.20: An amplifier probe
More sophisticated testers will report not only continuity but also length of run, and will check for shorts and crosses (accidental contact of one conductor with another), reversed pairs, transposed pairs, and split pairs.

Tuesday, September 20, 2011

Common Cabling Tools - Punch-Down Tools

Twisted-pair cables are terminated in jacks, cross-connect blocks (66-blocks), or patch panels (110-blocks) that use insulation displacement connectors (IDCs). Essentially, IDCs are little knife blades with a V-shaped gap or slit between them. You force the conductor down into the V and the knife blades cut through the insulation and make contact with the conductor. Although you could accomplish this using a small flat-blade screwdriver, doing so is not recommended. It would be sort of like hammering nails with a crescent wrench. The correct device for inserting a conductor in the IDC termination slot is a punch-down tool.

Different blades are used depending on whether you are going to be terminating on 110-blocks or 66-blocks. Although the blades are very different, most punch-down tools are designed to accept either. In fact, most people purchase the tool with one and buy the other as an accessory, so that one tool serves two terminals.
A punch-down tool is really just a handle with a special "blade" that fits a particular IDC. There are two main types of IDC terminations: the 66-block and the 110-block. The 66-block terminals have a long history rooted in voice cross-connections. The 110-block is a newer design, originally associated with AT&T but now generic in usage. In general, 110-type IDCs are used for data, and 66-type IDCs are used for voice, but neither is absolutely one or the other.
Blades are designed with one end being simply for punch-down. When you turn the blade and apply the other end, it punches down and cuts off excess conductor in one operation. Usually you will use the punch-and-cut end, but for daisy-chaining on a cross-connection, you would use the end that just punches down.
If you are terminating cables in Krone or BIX (by NORDX) equipment, you will need special punch-down blades. These brands use proprietary IDC designs.
Punch-down tools are available as nonimpact in their least expensive form. Nonimpact tools generally require more effort to make a good termination, but they are well suited for people who only occasionally perform punch-down termination work. Figure 1 shows a typical nonimpact punch-down tool.

Figure 1: IDEAL DataComm's nonimpact punch-down tool
The better-quality punch-down tools are spring-loaded impact tools. When you press down and reach a certain point of resistance, the spring gives way, providing positive feedback that the termination is made. Typically, the tool will adjust to high- and low-impact settings. Figure 2 shows an impact punch-down tool. Notice the dial near the center of the tool—it allows the user to adjust the impact setting. The manufacturer of the termination equipment you are using will recommend the proper impact setting.

Figure 2: IDEAL DataComm's impact tool with adjustable impact settings
With experience, you can develop a technique and rhythm that lets you punch down patch panels and cross-connections very quickly. However, nothing is so frustrating as interrupting your sequence rhythm because the blade stayed on the terminal instead of in the handle of the tool. The better punch-down tools have a feature that locks the blade in place, rather than just holding it in with friction. For the occasional user, a friction-held blade is okay, but for the professional, a lock-in feature is a must that will save time and, consequently, money.
You should always carry at least one extra blade for each type of termination that you are doing. Once you get the hang of punch-downs, you'll find that the blades don't break often, but they do break occasionally. The cutting edge will also become dull and stop cutting cleanly. Extra blades are inexpensive and can be easily ordered from the company you purchased your punch-down tool from.
Some brands of 110-block terminations support the use of special blades that will punch down multiple conductors at once, instead of one at a time.
If you are punching down IDC connectors on modular jacks from The Siemon Company that fit into modular wall plates, a tool from that company may be of use to you. Rather than trying to find a surface to hold the modular jack against, you can use the Palm Guard (see Figure 3) to hold the modular jack in place while you punch down the wires.

Figure 3: The Palm Guard
A 4 square of carpet padding or mouse pad makes a good palm protector when punching down cable on modular jacks.

Saturday, September 17, 2011

Common Cabling Tools - Wire Cutters

You can, without feeling very guilty, use a regular set of lineman's pliers to snip through coaxial and twisted-pair cables. You can even use them for fiber-optic cables, but cutting through the aramid yarns used as strength members can be difficult; you will dull your pliers quickly, not to mention what you may do to your wrist.
KEY TERM: aramid 
Aramid is the common name for the material trademarked as Kevlar that's used in bulletproof vests. It is used in optical fiber cable to provide additional strength.
So why would you want a special tool for something as mundane as cutting through the cable? Here's the catch regarding all-purpose pliers: as they cut, they will mash the cable flat. All the strippers described previously work best if the cable is round. Specialized cutters such as the one shown in Figure 1 are designed for coax and twisted-pair cables and preserve the geometry of the cable as they cut. This is accomplished using curved instead of flat blades.

Figure 1: Typical wire cutters
For fiber-optic cables, special scissors are available that cut through aramid with relative ease. Figure 2 shows scissors designed for cutting and trimming the Kevlar strengthening members found in fiber-optic cables.

Figure 2: IDEAL DataComm's Kevlar scissors

Monday, September 12, 2011

Common Cabling Tools - Wire Strippers

The variety of cable strippers represented in this section is a function of the many types of cable you can work with, various costs of the cable strippers, and versatility of the tools.

Twisted-Pair Strippers

Strippers for UTP, ScTP, and STP cables are used to remove the outer jacket and have to accommodate the wide variation in the geometry of UTP cables. Unlike coax, which is usually consistently smooth and round, twisted-pair cables can have irregular surfaces due to the jacket shrinking down around the pairs. Additionally, the jacket thickness can differ greatly depending on brand and flame rating. The trick is to aid removal of the jacket without nicking or otherwise damaging the insulation on the conductors underneath.
The wire stripper in Figure 1 uses an adjustable blade so that you can fix the depth, matching it to the brand of cable you are working with. Some types use spring tension to help keep the blade at the proper cutting depth.

Figure 1: A wire stripper
In both cases, the goal is to score (lightly cut) the jacket without penetrating it completely. Then, you flex the cable to break the jacket along the scored line. This ensures that the wire insulation is nick-free. In some models, the tool can also be used to score or slit the jacket lengthwise in the event you need to expose a significant length of conductors.
When working with UTP, ScTP, or STP cables, you will rarely need to strip the insulation from the conductors. Termination of these cable types on patch panels, cross-connections, and most wall plates employs the use of insulation displacement connectors (IDCs) that make contact with the conductor by slicing through the insulation. In case you need to strip the insulation from a twisted-pair cable, keep a pair of common electrician's strippers handy. Just make sure it can handle the finer-gauge wires such as 22, 24, and 26 AWG that are commonly used with LAN wiring.

Coaxial Wire Strippers

Coaxial cable strippers are designed with two or three depth settings. These settings correspond to the different layers of material in the cable. Coaxial cables are pretty standardized in terms of central-conductor diameter, thickness of the insulating and shielding layers, and thickness of the outer jacket, making this an effective approach.
In the inexpensive (but effective for the do-it-yourself folks) model shown in Figure 2, the depth settings are fixed. The wire stripper in Figure 2 can be used to strip coaxial cables (RG-59 and RG-6) to prepare them for F-type connectors.

Figure 2: Inexpensive coaxial wire strippers
To strip the cable, you insert it in a series of openings that allows the blade to penetrate to different layers of the cable. At every step, you rotate the tool around the cable and then pull the tool toward the end of the cable, removing material down to where the blade has penetrated. To avoid nicking the conductor, the blade is notched at the position used to remove material.
One problem with the model shown in Figure 2 is that you end up working pretty hard to accomplish the task. For its low price, the extra work may be a good trade-off if stripping coax isn't a day-in, day-out necessity. However, if you are going to be working with coaxial cables on a routine basis, you should consider some heftier equipment. Figure 3 shows a model that accomplishes the task in a more mechanically advantageous way (that means it's easier on your hands). In addition, it offers the advantage of adjustable blades so that you can optimize the cutting thickness for the exact brand of cable you're working with.

Figure 3: Heavy-duty coaxial wire strippers
Coaxial strippers are commonly marked with settings that assist you in removing the right amount of material at each layer from the end of the cable so it will fit correctly in an F- or BNC-type connector.

Fiber-Optic Cable Strippers

Fiber-optic cables require very specialized tools. Fortunately, the dimensions of fiber coatings, claddings, and buffers are standardized and manufactured to precise tolerances. This allows tool manufacturers to provide tools such as the one shown in Figure 4 that will remove material to the exact thickness of a particular layer without damage to the underlying layer. Typically, these look like a conventional multigauge wire stripper with a series of notches to provide the proper depth of penetration.

Figure 4: A fiber-optic cable stripper

Monday, September 5, 2011

Building a Cabling Toolkit

Throughout this chapter, a number of tools are discussed, and photos illustrate them. Don't believe for a minute that we've covered all the models and permutations available! This chapter is an introduction to the types of tools you may require, and will help you recognize a particular tool so you can get the one that best suits you. It is impossible for us to determine your exact tool needs. Keeping your own needs in mind, read through the descriptions that follow, and choose those tools that you anticipate using.
Myriad online catalog houses and e-commerce sites sell the tools and parts you need to complete your cabling tool kit. A few of these include:
If you have to scratch and sniff before buying, visit a local distributor in your area. Check your local phone book for vendors such as Anicom, Anixter, CSC, Graybar, and many other distributors that specialize in servicing the voice/data market; many of these vendors have counter sale areas where you can see and handle the merchandise before purchasing.
We can't describe in precise detail how each tool works or all the ways you can apply it to different projects. We'll supply a basic description of each tool's use, but because of the wide variety of manufacturers and models available, you'll have to rely on the manufacturer's instructions to learn how to use a particular device.

Friday, September 2, 2011

Administration Standards

After troubleshooting a network issue and figuring out that it's a problem with the physical layer, have you ever found complete spaghetti in a telecommunications room? In our consulting practices, we see this all too often. Our clients then pay two to three times the regular consulting fees because it takes so much time to sort through the mess.
Network administrators should be judged by the neatness of their telecommunications rooms.
To provide a standard methodology for the labeling of cables, pathways, and spaces, the TIA published the ANSI/TIA/EIA-606-A Administration Standard for the Telecommunications Infrastructure of Commercial Buildings. In addition to guidelines for labeling, the standard recommends the color-coding scheme shown in Table 1. This scheme applies not only to labeling of cables and connections but also to the color of the cross-connect backboards in the telecommunication rooms. It does not necessarily apply to the colors of cable jackets, although some installations may attempt to apply it.
Table 1: Color-Coding Schemes 
Color Code
No termination type assigned
First-level backbone (MC/IC or MC/TC terminations)
Reserved for future use
Second-level backbone (IC/TC terminations)
Miscellaneous (auxiliary, security alarms, etc.)
Horizontal-cable terminations
Network connections
Common equipment (PBXs, host LANs, muxes)
Demarcation point (central office terminations)
Interbuilding backbone (campus cable terminations)
Besides labeling and color coding, you should consider bundling groups of related cables with plastic cable ties (tie-wraps). Plastic cable ties come in a variety of sizes for all kinds of applications. When bundling cables, however, be sure not to cinch them too tightly, as you could disturb the natural geometry of the cable. If you ever have to perform maintenance on a group of cables, all you have to do is cut the plastic ties and add new ones when you're finished. Many companies make hook-and-loop (Velcro) type tie-wraps, and these are recommended over tie-wraps for both copper and optical fiber cables as they typically prevent over-cinching.
While hook-and-loop cable wraps are more expensive than traditional thin plastic tie wraps, they more than pay for themselves by assuring that cables are not over-cinched; be sure to have plenty on hand.
Whether you implement the ANSI/TIA/EIA-606-A standard or come up with your own methodology, the most import aspect of cable administration is to have accurate documentation of your cable infrastructure.