Coaxial Cable Connectors

Unless you have operated a 10Base-2 or 10Base-5 Ethernet network, you are probably familiar only with the coaxial connectors you have in your home for use with televisions and video equipment. Actually, a number of different types of coaxial connectors exist.

F-Series Coaxial Connectors

The coax connectors used with video equipment are referred to as F-series connectors (shown in Figure 1). The F-connector consists of a ferrule that fits over the outer jacket of the cable and is crimped in place. The center conductor is allowed to project from the connector and forms the business end of the plug. A threaded collar on the plug screws down on the jack, forming a solid connection. F-connectors are used primarily in residential installations for RG-58, RG-59, and RG-6 coaxial cables to provide CATV, security-camera, and other video services.

 
Figure 1: The F-type coaxial-cable connector

F-connectors are commonly available in one-piece and two-piece designs. In the two-piece design, the ferrule that fits over the cable jacket is a separate sleeve that you slide on before you insert the collar portion on the cable. Experience has shown us that the single-piece design is superior. Fewer parts usually means less fumbling, and the final crimped connection is both more aesthetically pleasing and more durable. However, the usability and aesthetics are largely a function of the design and brand of the two-piece product. Some two-piece designs are very well received by the CATV industry.

A cheaper F-type connector available at some retail outlets attaches to the cable by screwing the outer ferrule onto the jacket instead of crimping it in place. These are very unreliable and pull off easily. Their use in residences is not recommended, and they should never be used in commercial installations.

N-Series Coaxial Connectors

The N-connector is very similar to the F-connector but has the addition of a pin that fits over the center conductor; the N-connector is shown in Figure 2. The pin is suitable for insertion in the jack and must be used if the center conductor is stranded instead of solid. The assembly is attached to the cable by crimping it in place. A screw-on collar ensures a reliable connection with the jack. The N-type connector is used with RG-8, RJ-11U, and thicknet cables for data and video backbone applications.

 
Figure 2: The N-type coaxial connector

The BNC Connector

When coaxial cable distributes data in commercial environments, the BNC connector is often used. BNC stands for Bayonet Neill-Concelman, which describes both the method of securing the connection and its inventors. Many other expansions of this acronym exist, including British Naval Connector, Bayonet Nut Coupling, Bayonet Navy Connector, and so forth. Used with RG-6, RG-58A/U thinnet, RG-59, and RG-62 coax, the BNC utilizes a center pin, as in the N-connector, to accommodate the stranded center conductors usually found in data coax.

The BNC connector (shown in Figure 3) comes as a crimp-on or a design that screws onto the coax jacket. As with the F-connector, the screw-on type is not considered reliable and should not be used. The rigid pin that goes over the center conductor may require crimping or soldering in place. The rest of the connector assembly is applied much like an F-connector, using a crimping die made specifically for a BNC connector.

 
Figure 3: The BNC coaxial connector

To secure a connection to the jack, the BNC has a rotating collar with slots cut into it. These slots fit over combination guide and locking pins on the jack. Lining up the slots with the pins, you push as you turn the collar in the direction of the slots. The slots are shaped so that the plug is drawn into the jack, and locking notches at the end of the slot ensure positive contact with the jack. This method allows quick connection and disconnection while providing a secure match of plug and jack.

Be aware that you must buy BNC connectors that match the impedance of the coaxial cable to which they are applied. Most commonly, they are available in 75 ohm and 50 ohm types, with 93 ohm as a less-used option.

Tip

With all coaxial connectors, be sure to consider the dimensions of the cable you will be using. Coaxial cables come in a variety of diameters that are a function of their transmission properties, series rating, and number of shields and jackets. Buy connectors that fit your cable.

Using a Single Horizontal Cable Run for Two 10Base-T Connections

Let's face it, you will sometimes fail to run enough cable to a certain room. You will need an extra workstation in an area, and you won't have enough connections. Knowing that you have a perfectly good four-pair UTP cable in the wall, and that only two of those pairs are in use, makes your mood even worse. Modular Y-adapters can come to your rescue.

Several companies make Y-adapters that function as splitters. They take the four pairs of wire that are wired to the jack and split them off into two separate connections. The Siemon Company makes a variety of modular Y-adapters (see Figure 1) for splitting 10Base-T, Token Ring, and voice applications. This splitter will split the four-pair cable so that it will support two separate applications, provided that each application requires only two of the pairs. You must specify the type of splitter you need (voice, 10Base-T, Token Ring, etc.). Don't forget, for each horizontal cable run you will be splitting, you will need two of these adapters: one for the patch-panel side and one for the wall plate.

Figure 1: A modular Y-adapter for splitting a single four-pair cable into a cable that will support two separate applications

Warning

Many cabling professionals are reluctant to use Y-adapters because the high-speed applications such as 10Base-T Ethernet and Token Ring may interfere with one another if they are operating inside the same sheath. Certainly you should not use Y-adapters for applications such as 100Base-TX. Furthermore, Y-adapters eliminate any chance of migrating to a faster LAN system that may utilize all four pairs.

Additional Designations of Fiber-Optic Cables

Once you've determined whether you need single-mode or multimode fiber strands, loose tube or tight-buffered cable types, and indoor or outdoor cable capability, you still have a variety of fiber-optic cable options from which to choose. When buying fiber-optic cables, you will have to decide which fiber ratings you want for each type of cable you need. Some of these ratings are:

• Core/cladding sizes
• Number of optical fibers
• LAN/WAN application

Core/Cladding Size

The individual fiber-optic strands within a cable are most often designated by a ratio of core size/cladding size. This ratio is expressed in two numbers. The first is the diameter of the optical-fiber core, given in microns (μm). The second number is the outer diameter of the cladding for that optical fiber, also given in microns.

Three major core/cladding sizes are in use today:

• 8.3/125
• 50/125
• 62.5/125

We'll examine what each one looks like as well as its major use(s).

Note

Sometimes, you will see a third number in the ratio (e.g., 8.3/125/250). The third number is the outside diameter of the protective coating around the individual optical fibers.

8.3/125

An 8.3/125 optical fiber is shown in Figure 1. It is almost always designated as single-mode fiber because the core size is only about 10 times larger than the wavelength of the light it's carrying. Thus, the light doesn't have much room to bounce around. Essentially, the light is traveling in a straight line through the fiber.

Figure 1: An 8.3/125 optical fiber

As discussed earlier, 8.3/125 optical fibers are used for high-speed long-distance applications, like backbone fiber architectures for metro, fiber-to-the-home, transcontinental, and transoceanic applications. Single-mode fibers are standardized in ITU, IEC, and TIA.

50/125

In recent years, several fiber manufacturers have been promoting 50/125 multimode fibers instead of the 62.5/125 for use in structured wiring installations. This type of fiber has advantages in bandwidth and distance over 62.5/125 fiber, with about the same expense for equipment and connectors. ANSI/TIA-568-C.3, the fiber-optic-specific segment of the standard, recommends the use of 850nm laser-optimized 50/125 fiber instead of the alternate 62.5/125 type.

62.5/125

Until the introduction of 50/125, the most common multimode-fiber cable designation was 62.5/125 because it was specified in earlier versions of ANSI/TIA/EIA-568 as the multimode media of choice for fiber installations. It had widespread acceptance in the field. A standard multimode fiber with a 62.5 micron core with 125 micron cladding is shown in Figure 2.

Figure 2: A sample 62.5/125 optical fiber

The 62.5/125 optical fibers are used mainly in LED-based, lower-transmission-rate, FDDI LAN/WAN applications. However, as speeds have migrated to Gigabit Ethernet and above, 850nm laser-optimized 50/125 micron multimode fibers (commonly referred to as OM3 per the ISO 11801 Ed 2 cabling standard) have become more common.

Number of Optical Fibers

Yet another difference between fiber-optic cables is the number of individual optical fibers within them. The number depends on the intended use of the cable and can increase the cable's size, cost, and capacity.

Because the focus is network cabling and the majority of fiber-optic cables you will encounter for networking are tight buffered, we will limit our discussions here to tight-buffered cables. These cables can be divided into three categories based on the number of optical fibers:

• Simplex cables
• Duplex cables
• Multifiber cables

A simplex fiber-optic cable has only one tight-buffered optical fiber inside the cable jacket. Because simplex cables only have one fiber inside them, only aramid yarn is used for strength and flexibility; the aramid yarns along with the protective jacket allow the simplex cable to be connectorized and crimped directly to a mechanical connector. Simplex fiber-optic cables are typically categorized as interconnect cables and are used to make interconnections in front of the patch panel (also known as "in front of shelf" connections).

Duplex cables, in contrast, have two tight-buffered optical fibers inside a single jacket (as shown in Figure 3). The most popular use for duplex fiber-optic cables is as a fiber-optic LAN backbone cable, because all LAN connections need a transmission fiber and a reception fiber. Duplex cables have both inside a single cable, and running a single cable is of course easier than running two.

Figure 3: A sample duplex fiber-optic cable

One type of fiber-optic cable is called a duplex cable but technically is not one. This cable is known as zip cord. Zip cord is really two simplex cables bonded together into a single flat optical-fiber cable. It's called a duplex because there are two optical fibers, but it's not really duplex because the fibers aren't covered by a common jacket. Zip cord is used primarily as a duplex patch cable. It is used instead of true duplex cable because it is cheaper to make and to use. Most importantly, however, it allows each simplex cable to be connectorized and crimped directly to a mechanical connector for both strength and durability. Figure 4 shows a zip-cord fiber-optic cable.

Figure 4: A zip-cord cable

Finally, multifiber cables contain more than two optical fibers in one jacket. Multifiber cables have anywhere from three to several hundred optical fibers in them. More often than not, however, the number of fibers in a multifiber cable will be a multiple of two because, as discussed earlier, LAN applications need a send and a receive optical fiber for each connection. Six, twelve, and twenty-four fiber cables are the most commonly used for backbone applications. These cables are typically used for making connections behind the patch-panel (also known as "behind the shelf" connections).

LAN/WAN Application

Different fiber cable types are used for different applications within the LAN/WAN environment. Table 1 shows the relationship between the fiber network type, the wavelength, and fiber size for both single-mode and multimode fiber-optic cables. Table 2 shows the recognized fiber and cable types in ANSI/TIA-568-C.3.

Table 1: Network-Type Fiber Applications 

Network Type	Single-Mode Wavelength/Size	Multimode Wavelength/Size
10 Gigabit Ethernet	1300nm–8.3/125 micron	850nm–50/125 micron-OM3 (preferred)
	1550nm–8.3/125 micron	1300nm–62.5/125 or 50/125 micron to 220m (using –LRM)
Gigabit Ethernet	1300nm–8/125 micron 1550nm–8.3/125 micron	850nm–62.5/125 or 50/125 micron 1300nm–62.5/125 or 50/125 micron
Fast Ethernet	1300nm–8.3/125 micron	1300nm–62.5/125 or 50/125 micron
Ethernet	1300nm–8.3/125 micron	850nm–62.5/125 or 50/125 micron
10Gbase	1300nm–8.3/125 micron 1550nm–8.3/125 micron	850nm–62.5/125 or 50/125 micron 1300nm–62.5/125 or 50/125 micron
Token Ring	Proprietary–8.3/125 micron	Proprietary–62.5/125 or 50/125 micron
ATM 155Mbps	1300nm–8.3/125 micron	1300nm–62.5/125 or 50/125 micron
FDDI	1300nm–8.3/125 micron	1300nm–62.5/125 or 50/125 micron

Table 2: ANSI/EIA-568-C.3 Recognized Fiber and Cable Types 

Optical Fiber and Relevant Standard	Wavelengths (nm)	Maximum Cable Attenuation (dB/km)	Minimum Overfilled Modal Bandwidth (MHz · km)	Minimum Effective Modal Bandwidth (MHz · km)
62.5/125μ micron Multimode TIA 492AAAA (OM1)	850 1300	3.5 1.5	200 500	Not specified Not specified
50/125μ micron Multimode TIA 492AAAB (OM2)	850 1300	3.5 1.5	500 500	Not specified Not specified
850nm Laser-Optimized 50/125μ micron multimode TIA 492AAAC (OM3)	850 1300	3.5 1.5	1500 500	2000 Not specified
Single-mode Indoor-Outdoor TIA 492CAAA (OS1)TIA 492CAAB (OS2)3	1310 1550	0.5 0.5	N/A N/A	N/A N/A
Single-mode Inside plant TIA 492CAAA (OS1) TIA 492CAAB (OS2)3	1310 1550	1.0 1.0	N/A N/A	N/A N/A
Single-mode Outside plant TIA 492CAAA (OS1) TIA 492CAAB (OS2)3	1310 1550	0.5 0.5	N/A N/A	N/A N/A

Note

The philosophy of a generic cable installation that will function with virtually any application led the industry standard, ANSI/TIA-568-C, to cover all the applications by specifying 50/125 multimode or 62.5/125 multimode as a medium of choice (in addition to single-mode). The revised standard, ANSI/TIA-568-C.3, continues to recognize single-mode as well because it also effectively covers all the applications.

Multimode Plastic | Fiber-Optic Cables

Plastic optical fibers (POF) consist of a plastic core of anywhere from 50 microns on up, surrounded by a plastic cladding of a different index of refraction. Generally speaking, these are the lowest-quality optical fibers and are seldom sufficient to transmit light over long distances. Plastic optical cables are used for very short-distance data transmissions or for transmission of visible light in decorations or other specialty lighting purposes not related to data transmission. Recently, POF has been promoted as a horizontal cable in LAN applications for residential systems. However, the difficulty in manufacturing a graded-index POF, combined with a low bandwidth-for-dollar value, has kept POF from being accepted as a horizontal medium in commercial applications.

Buffer

The buffer, the second-most distinguishing characteristic of the cable, is the component that provides additional protection for the optical fibers inside the cable. The buffer does just what its name implies: it buffers, or cushions, the optical fiber from the stresses and forces of the outside world. Optical fiber buffers are categorized as either tight or loose tube.

With tight buffers, a protective layer (usually a 900 micron PVC or Nylon covering) is applied directly over the coating of each optical fiber in the cable. Tight buffers make the entire cable more durable, easier to handle, and easier to terminate. Figure 1 shows tight buffering in a single-fiber (simplex) construction. Tight-buffered cables are most often used indoors because expansion and contraction caused by outdoor temperature swings can exert great force on a cable. Tight-buffered designs tend to transmit the force to the fiber strand, which can damage the strand or inhibit its transmission ability, so thermal expansion and contraction from temperature extremes is to be avoided. However, there are some specially designed tight-buffered designs for either exclusive outdoor use or a combination of indoor/outdoor installation.

Figure 1: A simplex fiber-optic cable using tight buffering

A loose-tube buffer, on the other hand, is essentially a tough plastic pipe about 0.125″ in diameter. One or several coated fibers can be placed inside the tube, depending on the cable design. The tube can then be filled with a protective substance, usually a water-blocking gel, to provide cushioning, strength, and protection from the elements if the cabling is used outdoors. More commonly, water-blocking powders and tapes are used to waterproof the cable. A loose-tube design is very effective at absorbing forces exerted on the cable so that the fiber strands are isolated from the damaging stress. For this reason, loose-tube designs are almost always seen in outdoor installations.

Multiple tubes can be placed in a cable to accommodate a large fiber count for high-density communication areas such as large cities. They can also be used as trunk lines for long-distance telecommunications.

Figure 2 shows a loose-buffered fiber-optic cable. Notice that the cable shown uses water-blocking materials.

Figure 2: A fiber-optic cable using loose buffering with water-blocking materials

Strength Members

Fiber-optic cables require additional support to prevent breakage of the delicate optical fibers within the cable while pulling them into place. That's where the strength memberscome in. The strength member of a fiber-optic cable is the part that provides additional tensile (pull) strength. Strength elements can also provide compression resistance. Compression is encountered when the temperature drops below room temperature.

The most common strength member in tight-buffered cables is aramid yarn, the same material found in bulletproof vests. Thousands of strands of this material are placed in a layer, called a serving, around all the tight-buffered fibers in the cable. When pulling on the cable, tensile force is transferred to the aramid yarn and not to the fibers.

Tip

Aramid yarn is extremely durable, so cables that use it require a special cutting tool, called aramid scissors. Aramid yarn cannot be cut with ordinary cutting tools.

Loose-tube fiber-optic cables sometimes have a strand of either fiberglass or steel wire as a strength member. These strands can be placed around the perimeter of a bundle of optical fibers within a single cable, or the strength member can be located in the center of the cable with the individual optical fibers clustered around it. As with aramid yarn in tight-buffered cable, tensile force is borne by the strength member(s), not the buffer tubes or fiber strands. Unlike aramid yarns, glass or steel strength members also have the ability to prevent compression-induced microbending caused by temperatures as low as −40°C.

Shield Materials

In fiber-optic cables designed for outdoor use, or for indoor environments with the potential for mechanical damage, metallic shields are often applied over the inner components but under the jacket. The shield is often referred to as armor. A common armoring material is 0.006″ steel with a special coating that adheres to the cable jacket. This shield should not be confused with shielding to protect against EMI. However, when present, the shield must be properly grounded at both ends of the cable in order to avoid an electrical-shock hazard should it inadvertently come into contact with a voltage source such as a lightning strike or a power cable.

Cable Jacket

The cable jacket of a fiber-optic cable is the outer coating of the cable that protects all the inner components from the environment. It is usually made of a durable plastic material and comes in various colors. As with copper cables, fiber-optic cables designed for indoor applications must meet fire-resistance requirements of the NEC.

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Exterior Protection of Fiber-Optic Cables

If you ever need to install fiber-optic cabling outdoors, the cable should be rated for an exterior installation. An exterior rating means that the cable is specifically designed for outdoor use. It will have features such as UV protection, superior crush and abrasion protection, protection against the extremes of temperature, and an extremely durable strength member. If you use standard indoor cable in an outdoor installation, the cables could get damaged and stop functioning properly.

Multimode Graded-Index Glass | Fiber-Optic Cables

A graded-index glass-fiber core is made of core of silica glass (SiO₂) and a small amount of Germania glass (GeO₂) in order to increase the index of refraction relative to the all-silica cladding. Graded-index multimode fibers have an index of refraction that changes gradually from the center outward to the cladding. The center of the core has the highest index of refraction. The most commonly used multimode graded-index glass fibers have a core that is either 50 microns or 62.5 microns in diameter. Figure 1 shows a graded-index glass core. Notice that the core is bigger than the single-mode core. The ANSI/TIA-568-C standard recommends the use of an 850nm laser-optimized 50/125 micron multimode fiber. This is commonly referred to OM3, as per the ISO 11801 cabling standard. This class of 50 micron fiber has higher bandwidth than 62.5 micron fiber and other versions of 50 micron fiber. It is recommended for the laser-driven 1–100Gbps applications.

 
Figure 1: A graded-index glass-fiber core

Single-Mode Step-Index Glass | Fiber-Optic Cables

A single-mode glass fiber core is very narrow (usually around 8.3 microns) and made of a core of silica glass (SiO₂) with a small amount of Germania glass (GeO₂) to increase the index of refraction relative to the all-silica cladding. To keep the cable size manageable, the cladding for a single-mode glass core is usually about 15 times the size of the core (around 125 microns). Single-mode fibers systems are expensive, but because of the lack of attenuation (less than 0.35dB per kilometer), very high speeds are possible over very long distances. Figure 1 shows a single-mode glass-fiber core. The latest class of single-mode fibers have very low loss at the 1385nm (water peak) region and are insensitive to bending. These are known as ITU-T G.652D and G.657, respectively.

 
Figure 1: An example of a single-mode glass-fiber core

Composition of a Fiber-Optic Cable

A typical fiber-optic cable consists of several components:

• Optical-fiber strand
• Buffer
• Strength members
• Optional shield materials for mechanical protection
• Outer jacket

Each of these components has a specific function within the cable to help ensure that the data gets transmitted reliably.

Optical Fiber

An optical-fiber strand (also called an optical waveguide) is the basic element of a fiber-optic cable. All fiber strands have at least three components to their cross sections: the core, the cladding, and the coating. Figure 1 depicts the three layers of the strand.

 
Figure 1: Elemental layers in a fiber-optic strand

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Optical Fiber Is Tiny—and Hazardous

Fiber strands have elements so small that it is hard to imagine the scale. You're just not used to dealing with such tiny elements in everyday life. The components of a fiber strand are measured in microns. A micron is one thousandth of a millimeter, or about 0.00004″. A typical single-mode fiber strand has a core only 8.3 microns, or 0.0003″, in diameter. A human hair is huge by comparison. The core of multimode fiber is typically either 50 or 62.5 microns, or 0.002″ in diameter. For both single-mode and multimode, the cladding usually has a diameter of 125 microns, or 0.005″. And finally, commonly used single-mode and multimode fiber strands have a coating layer that is 250 microns, or 0.01″, in diameter. Now we're getting somewhere, huh? That's all the way to one hundredth of an inch.

The tiny diameter of fiber strands makes them extremely dangerous. When stripped of their coating layer, as must be done for some splicing and connectorizing techniques, the strands can easily penetrate the skin. Shards, or broken pieces of strand, can even be carried by blood vessels to other parts of the body (or the brain), where they could wreak serious havoc. They are especially dangerous to the eye because small pieces can pierce the eyeball, doing damage to the eye's surface and possibly getting trapped inside. Safety glasses and special shard-disposal containers are a must when connecting or splicing fibers.

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The fiber core and cladding is usually made of some type of plastic or glass. Several types of materials make up the glass or plastic composition of the optical-fiber core and cladding. Each material differs in its chemical makeup and cost as well as its index of refraction, which is a number that indicates how much light will bend when passing through a particular material. The number also indicates how fast light will travel through a particular material. The refractive index of the core is higher than the cladding.

A fiber-optic strand's cladding is a layer around the central core that has a lower refractive index. The index difference between the core and cladding is what allows the light inside the core to stay in the core and not escape into the cladding. The cladding thus permits the signal to travel in angles from source to destination—it's like shining a flashlight onto one mirror and having it reflect into another, then another, and so on.

The protective coating around the cladding protects the fiber core and cladding from mechanical damage. It does not participate in the transmission of light but is simply a protective material against fracture. It protects the cladding from abrasion damage, adds additional strength to the core, and builds up the diameter of the strand.

The most basic differentiation of fiber-optic cables is whether the fiber strands they contain are single mode or multimode. A mode is a path for the light to take through the cable. The wavelength of the light transmitted, the acceptance angle, and the numerical aperture interact in such a way that only certain paths are available for the light. Single-mode fibers have a lower numerical aperture and cores that are so small that only a single pathway, or mode, for the light is possible. Multimode fibers have larger numerical apertures and cores; the options for the angles at which the light can enter the cable are greater, and so multiple pathways, modes, are possible. (Note that these ray-trace explanations are simplifications of what is actually occurring.)

Using its single pathway, single-mode fibers can transfer light over great distances with high data-throughput rates. Concentrated (and expensive) laser light sources are required to send data down single-mode fibers, and the small core diameters make connections expensive. This is because the mechanical tolerances required to focus the lasers into the core and to hold the fiber in connectors without moving the core away from the laser are extremely precise and require expensive manufacturing methods.

Multimode fibers can accept light from less intense and less expensive sources, usually LEDs or 850nm vertical cavity surface-emitting lasers (VCSELs). In addition, connections are easier to align properly due to larger core diameters. Since the core diameters are larger than single-mode fiber, the tolerances required to manufacture these parts are less precise and less expensive as a result. This is why lasers that are used to operate over only multimode fiber—that is, 850nm sources—are less expensive than single-mode sources. However, distance and bandwidth are more limited than with single-mode fibers. Since multimode cabling and electronics are generally a less expensive solution, multimode is the preferred cabling for short distances found in buildings and on campuses.

Single-mode fibers are usually used in long-distance transmissions or in backbone cables, so you find them mostly in outdoor cables. These applications take advantage of the extended distance and high-bandwidth properties of single-mode fiber.

Multimode fibers are usually used in an indoor LAN environment in the building backbone and horizontal cables. They are also often used in the backbone cabling where great distances are not a problem.

Single-mode and multimode fibers come in a variety of flavors. Some of the types of optical fibers, listed from highest bandwidth and distance potential to least, include the following:

• Single-mode step-index glass
• Multimode graded-index glass
• Multimode plastic

Sample Voice Installations

In many ways, voice installations are quite similar to data installations. The differences are the type of equipment that each end of the link is plugged into and, sometimes, the type of patch cables used. The ANSI/TIA-568-C standard requires at least one four-pair, unshielded twisted-pair cable to be run to each workstation outlet installed. This cable is to be used for voice applications. We recommend using a minimum of Category 3 cable for voice applications; however, if you will purchase Category 5e or higher cable for data, we advise using the same category of cable for voice. This potentially doubles the number of outlets that can be used for data.

Some sample cabling installations follow; we have seen them installed to support voice and data. Because so many possible combinations exist, we will only be able to show you a few. The first one (shown in Figure 1) is common in small- to medium-sized installations. In this example, each horizontal cable designated for voice terminates to an RJ-45 patch panel. A second patch panel has RJ-45 blocks terminated to the extensions on the phone switch or PBX. This makes moving a phone extension from one location to another as simple as moving the patch cable. If this type of flexibility is required, this configuration is an excellent choice.

 
Figure 1: A voice application using RJ-45 patch panels

Tip

Any wiring system that terminates horizontal wiring into an RJ-45-type patch panel will be more versatile than traditional cross-connect blocks because any given wall-plate port/patch-panel port combination can be used for either voice or data. However, cabling professionals generally recommend separate patch panels for voice and data. Separate panels prevent interference that might occur as a result of incompatible systems and different frequencies used on the same patch panels.

The next example illustrates a more complex wiring environment, which includes backbone cabling for the voice applications. This example could employ patch panels in the telecommunications closet or 66-blocks, depending on the flexibility desired. The telecommunications closet is connected to the equipment room via twisted-pair backbone cabling. Figure 2 illustrates the use of patch panels, 66-blocks, and backbone cabling.

 
Figure 2: A voice application with a voice backbone, patch panels, and 66-blocks

The final example is the most common for voice installations; it uses 66-blocks exclusively. You will find many legacy installations that have not been modernized to use 110-block connections. Note that in Figure 3 two 66-blocks are connected by cross-connected cable. Cross-connect cable is simple single-pair, twisted-pair wire that has no jacket. You can purchase cross-connect wire, so don't worry about stripping a bunch of existing cables to get it. The example shown in Figure 3 is not as versatile as it would be if you used patch panels because 66-blocks require either reconnecting the cross-connect or reprogramming the PBX.

 
Figure 3: Voice applications using 66-blocks exclusively

Figure 4 shows a 66-block with cross-connect wires connected to it. Though you cannot tell it from the figure, cross-connect wires are often red and white.

Figure 4: A 66-block with cross-connect wires

The examples of 66-blocks and 110-blocks in this chapter are fairly common, but we could not possibly cover every possible permutation and usage of these types of blocks. We hope we have given you a representative view of some possible configurations.