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.

Shielded Twisted-Pair Connectors

In the United States, the most common connectors for cables that have individually shielded pairs in addition to an overall shield are based on a pre-1990 proprietary cabling system specified by IBM. Designed originally to support Token Ring applications using a two-pair cable (shielded twisted-pair, or STP), the connector is hermaphroditic. In other words, the plug looks just like the jack, but in mirror image. Each side of the connection has a connector and a receptacle to accommodate it. Two hermaphroditic connectors are shown in Figure 1. This connector is known by a number of other names, including the STP connector, the IBM data connector, and the universal data connector.

 
Figure 1: Hermaphroditic data connectors

The original Token Ring had a maximum throughput of 4Mbps (and later 16Mbps) and was designed to run over STP cabling. The 16Mbps Token Ring used a 16MHz spectrum to achieve its throughput. Cables and connectors rated to 20MHz were required to allow the system to operate reliably, and the original STP hermaphroditic connectors were limited to a 20MHz bandwidth. Enhancements to these connectors increased the bandwidth limit to 300MHz. These higher-rated connectors (and cable) are designated as STP-A.

STP connectors are the Jeeps of the connector world. They are large, rugged, and versatile. Both the cable and connector are enormous compared to four-pair UTP and RJ-type modular plugs. They also have to be assembled and have more pieces than an Erector set. Cabling contractors used to love the STP connectors because of the premium they could charge based on the labor required to assemble and terminate them.

Darwinian theory prevailed, however, and now the STP and STP-A connectors are all but extinct—they've been crowded out by the smaller, less expensive, and easier-to-use modular jack and plug.

Crossover Cables | Modular Jacks and Plugs

One of the most frequently asked questions on wiring newsgroups and forums is "How do I make a crossover cable?" Computers that are equipped with 10Base-T or 100Base-TX network adapters can be connected "back-to-back"; this means they do not require a hub to be networked together. Back-to-back connections via crossover cables are really handy in a small or home office. Crossover cables are also used to link together two pieces of network equipment (e.g., hubs, switches, and routers) if the equipment does not have an uplink or crossover port built-in.

A crossover cable is just a patch cord that is wired to a T568A pinout scheme on one end and a T568B pinout scheme on the other end. To make a crossover cable, you will need a crimping tool, a couple of eight-position modular plugs (a.k.a. RJ-45 plugs), and the desired length of cable. Cut and crimp one side of the cable as you would normally, following whichever wiring pattern you desire, T568A or T568B. When you crimp the other end, just use the other wiring pattern.

Warning

As mentioned several times elsewhere in this book, we recommend that you buy your patch cords, either straight through or crossover, instead of making them yourself. Field-terminated patch cords can be time-consuming (i.e., expensive) to make and may result in poor system performance.

Table 1 shows the pairs that cross over. The other two pairs wire straight through.

Table 1: Crossover Pairs 

Side-One Pins	Wire Colors	Side-Two Pins
1 (Transmit +)	White/green	3 (Receive +)
2 (Transmit –)	Green	6 (Receive –)
3 (Receive +)	White/orange	1 (Transmit +)
6 (Receive –)	Orange	2 (Receive –)

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.

ANSI/TIA -568-C Wiring Schemes T568A and T568B

ANSI/TIA-568-C does not sanction the use of the USOC scheme. Instead, two wiring schemes are specified, both of which are suitable for either voice or high-speed LAN operation. These are designated as T568A and T568B wiring schemes.

Both T568A and T568B are universal in that all LAN systems and most voice systems can utilize either wiring sequence without system errors. After all, the electrical signal really doesn't care if it is running on pair 2 or pair 3, as long as a wire is connected to the pin it needs to use. The TIA/EIA standard specifies eight-position, eight-contact jacks and plugs and four-pair cables, fully terminated, to facilitate this universality.

The T568B wiring configuration was at one time the most commonly used scheme, especially for commercial installations; it is shown in Figure 1. The TIA/EIA adopted the T568B wiring scheme from the AT&T 258A wiring scheme.

 
Figure 1: The T568B wiring pattern

The T568A scheme (shown in Figure 10.9) is well suited to upgrades and new installations in residences because the wire-termination pattern for pairs 1 and 2 is the same as for USOC. Unless a waiver is granted, the U.S. government requires all government cabling installations to use the T568A wiring pattern. The current recommendation according to the standard is for all new installations to be wired with the T568A scheme.

 
Figure 2: The T568A wiring pattern

The wire colors and the associated pin assignments for the T568B wiring scheme look like this:

Pin	Wire Color
1	White/orange
2	Orange
3	White/green
4	Blue
5	White/blue
6	Green
7	White/brown
8	Brown

The pin assignments for the T568A wiring schemes are identical to the assignments for the T568B pattern except that wire pairs 2 and 3 are reversed. The T568A pattern looks like this:

Pin	Wire Color
1	White/green
2	Green
3	White/orange
4	Blue
5	White/blue
6	Orange
7	White/brown
8	Brown

Note that when you buy eight-position modular jacks, you may need to specify whether you want a T568A or T568B scheme because the jacks often have IDC connections on the back where you punch the pairs down in sequence from 1 to 4. The jacks have an internal PC board that takes care of all the pair splitting and proper alignment of the cable conductors with the pins in the jack. Most manufacturers now provide color-coded panels on the jacks that let you punch down either pinout scheme, eliminating the need for you to specify (and for them to stock) different jacks depending on which pinout you use.

Tip

Whichever scheme you use, T568A or T568B, you must also use that same scheme for your patch panels and follow it in any cross-connect blocks you install. Consistency is the key to a successful installation.

Be aware that modular jacks pretty much look alike even though their performance may differ dramatically. Be sure you also specify the performance level (e.g., Category 3, Category 5e, Category 6, Category 6A, etc.) when you purchase your jacks.

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Tips for Terminating UTP Connectors

Keep the following points in mind when terminating UTP connectors:

• When connecting to jacks and plugs, do not untwist UTP more than 0.5″ for Category 5e and not more than 0.375″ for Category 6.
• Always use connectors, wall plates, and patch panels that are compatible (same rating or higher) with the grade of cable used.
• To "future-proof" your installation, terminate all four pairs, even if the application requires only two of the pairs.
• Remember that the T568A wiring scheme is compatible with USOC wiring schemes that use pairs 1 and 2.
• When terminating ScTP cables, always terminate the drain wire on both ends of the connection.

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When working with ScTP wiring, the drain wire makes contact with the cable shield along its entire length; this provides a ground path for EMI energy that is collected by the foil shield. When terminating ScTP, the drain wire within the cable is connected to a metal shield on the jack. This must be done at both ends of the cable. If left floating or if connected only on one end, instead of providing a barrier to EMI the cable shield becomes a very effective antenna for both emitting and receiving stray signals.

In a cable installation that utilizes ScTP, the plugs, patch cords, and patch panels must be shielded as well.

USOC Wiring Scheme

The Bell Telephone Universal Service Order Code (USOC) wiring scheme is simple and easy to terminate in up to an eight-position connector; this wiring scheme is shown in Figure 1. The first pair is always terminated on the center two positions. Pair 2 is split and terminated on each side of pair 1. Pair 3 is split and terminated on each side of pair 2. Pair 4 continues the pattern; it is split and terminated on either side of pair 3. This pattern is always the same regardless of the number of contacts you populate. You start in the center and work your way to the outside, stopping when you reach the maximum number of contacts in the connector.

 
Figure 1: The Universal Service Order Code (USOC) wiring scheme

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Tip and Ring Colors

When looking at wiring schemes for modular plugs and jacks, you may see the letters T and R used, as in Figure 1. The T identifies the tip color, and the R identifies the ring color. In a four-pair cable, the cable pairs are coded in a standard color coding, which is on the insulation of the individual wires. In a four-pair cable, the tip is the wire that is predominantly white, and the ring identifies the wire that is a predominantly solid color.

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The wire colors and associated pin assignments for USOC look like this:

Pin	Wire Color
1	White/brown
2	White/green
3	White/orange
4	Blue
5	White/blue
6	Orange
7	Green
8	Brown

Warning

Do not use the USOC wiring scheme for systems that will support data transmission.

USOC is used for analog and digital voice systems but should never be used for data installations. Splitting the pairs can cause a number of transmission problems when used at frequencies greater than those employed by voice systems. These problems include excessive crosstalk, impedance mismatches, and unacceptable signal-delay differential.

Solid- vs. Stranded-Conductor Cables

UTP and ScTP cables have either solid copper conductors or conductors made of several tiny strands of copper. Solid conductors are very stable geometrically and, therefore, electrically superior, but they will break if flexed very often. Stranded conductors are very flexible and resistant to bend-fatigue breaks, but their cross-sectional geometry changes as they are moved, and this can contribute to electrical anomalies. Stranded cables also have a higher attenuation (signal loss) than solid-conductor cables.

Note

Solid-conductor cables are usually used in backbone and horizontal cabling where, once installed, there won't be much movement. Stranded-conductor cables are used in patch cords, where their flexibility is desirable and their typically short lengths mitigate transmission problems.

The differences in conductors mean a difference in IDC types. You have to be careful when you purchase plugs, wall plates, and patch panels because they won't work interchangeably with solid- and stranded-core cables—the blade designs are different.

Warning

Using the wrong type of cable/connector combination can be a major source of intermittent connection errors after your system is running.

With a solid-conductor IDC, you are usually forcing the conductor between two blades that form a V-shaped notch. The blades slice through the plastic and into the copper conductor, gripping it and holding it in place. This makes a very reliable electrical contact. If you force a stranded conductor into this same opening, contact may still be made. But, because one of the features of a stranded design is that the individual copper filaments can move (this provides the flexibility), they will sort of mush into an elongated shape in the V. Electrical contact may still be made, but the grip on the conductor is not secure and often becomes loose over time.

The blade design of IDC connectors intended for stranded-core conductors is such that forcing a solid-core conductor onto the IDC connector can break the conductor or fail to make contact entirely. Broken conductors can be especially problematic because the two halves of the break can be close enough together that contact is made when the temperature is warm, but the conductor may contract enough to cause an open condition when cold.

Some manufacturers of plugs advertise that their IDC connectors are universal and may be used with either solid or stranded conductors. Try them if you like, but if you have problems, switch to a plug specifically for the type of cable you are using.

Jacks and termination blocks are almost exclusively solid-conductor devices. You should never punch down on a 66, 110, or modular jack with stranded conductors.

Advantages of Biscuit Jacks

Biscuit jacks offer a few advantages in your structured-cabling design. First of all, they are very inexpensive compared to other types of surface-mount wiring systems, which is why many houses that had the old four-pin telephone systems now have biscuit jacks—you could buy 20 of them for around $25. Even the biscuits that support multiple jacks are still fairly inexpensive.

Another advantage of biscuit jacks is their ability to work in situations where standard modular or fixed-design wall plates won't work and other types of surface-mount wiring are too bulky. The best example of this is office cubicles (i.e., modular furniture). A biscuit jack has an adhesive tab on the back that allows it to be mounted anywhere, so you can run a telephone or data cable to a biscuit jack and mount it under the desk where it will be out of the way.

Finally, biscuit jacks are easy to install. The cover is removed with one screw. Inside many of the biscuit jacks are screw terminals (one per pin in each jack), as shown in Figure 1. To install the jack, you just strip the insulation from each conductor and wrap it clockwise around the terminal and between the washers and tighten the screw. Repeat this process for each conductor in the cable. These jacks are not high-speed data compatible and are capable of Category 3 performance at best.

 
Figure 1: Screw terminals inside a biscuit jack

Note

Not all biscuit jacks use screw terminals. The more modern data communications jacks use IDC connectors to attach the wire to the jack.

Disadvantages of Biscuit Jacks

The main disadvantage to biscuit jacks is that the older biscuit jacks are not rated for high-speed data communications. Notice the bunch of screw terminals in the biscuit jack shown in Figure 1. When a conductor is wrapped around these terminals, it is exposed to stray electromagnetic interference (EMI) and other interference, which reduces the effective ability of this type of jack to carry data. At most, the older biscuit jacks with the screw terminals can be rated as Category 3 and are not suitable for the 100Mbps and faster communications today's wiring systems must be able to carry.

Types of Biscuit Jacks

No discussion of wall plates would be complete without a discussion of biscuit jacks, or surface-mount jacks that look like small biscuits (see Figure 1). They were originally used in residential and light commercial installations for telephone applications. In fact, you may have some in your home if it was built before 1975. Biscuit jacks are still used when adding phone lines in residences, especially when people can't put a hole in the wall where they want the phone jack to go.

 
Figure 1: An example of a biscuit jack

Types of Biscuit Jacks

The many different types of biscuit jacks differ primarily by size and number of jacks they can support. The smaller type measures 2.25 inches wide by 2.5″ high and is mainly used for residential-telephone applications. The smaller size can generally support up to a maximum of two jacks.

The larger-sized biscuit jacks are sometimes referred to simply as surface-mount boxes because they don't have the shape of the smaller biscuit jacks. These surface-mount boxes are primarily used for data communications applications and come in a variety of sizes. They also can have any number or type of jacks and are generally modular. Figure 2 shows an example of a larger biscuit jack that is commonly used in surface-mount applications.

 
Figure 2: Example of a larger biscuit jack

Note

Generally speaking, the smaller biscuit jacks are not rated for Category 5e (or any higher categories). They must be specifically designed for a Category 5e application. Some companies offer a modular-design biscuit jack that lets you snap in high-performance, RJ-45-type jacks for Category 5e and better compliance.

Labeling Modular Wall Plates

Just like fixed-design wall plates, modular wall plates use labels to differentiate the different jacks by their purpose. In fact, modular wall plates have the widest variety of labels—every modular wall plate manufacturer seems to pride itself on its varied colors and styles of labeling. However, as with fixed-design plates, the labels are either text (e.g., LAN,Phone) or pictures of their intended use, perhaps permanently molded in the plate or on the jack.

Cabling @Work: We Don't Know What Tomorrow Will Bring, but Adding Some Flexibility Today May Make You More Prepared

A few years ago during a hotel's remodeling project, the hotel wired its rooms with only the minimum network connection points using fixed wall plates for its new local area network. Later that year the hotel had to rewire each room to accommodate an IP phone system upgrade, and to offer in-room fax machines and additional telephones on additional lines. Each room had to have additional cabling installed as well as new wall plates.

Though no precise figures have been calculated to see exactly how much would have been saved by installing modular wall plates initially instead of fixed wall plates, it was determined that the fixed wall plate design would not enable the hotel to keep up with the ever-growing number of additional network points and media types that its guests require.

Wall Plate Jack Considerations | Modular Wall Plates

Modular wall plates are the most common type of wall plate in use for data cabling because they meet the various ANSI/TIA and NEC standards and codes for quality data communications cabling. So modular wall plates have the widest variety of jack types available. All the jacks available today differ based on a few parameters, including the following:

• Wall plate system type
• Cable connection
• Jack orientation
• ANSI/TIA-568-C.2 and -C.3 wiring pattern

Wall Plate System Type

Remember how the type of wall plate you use dictates the type of jacks for that wall plate? Well, logically, the reverse is also true. The interlocking system that holds the jack in place in the wall plate differs from brand to brand. So, when you pick a certain brand and manufacturer for a jack, you must use the same brand and manufacturer of wall plate.

Cable Connection

Jacks for modern communication applications use insulation displacement connectors (IDCs), which have small metal teeth or pins in the connector that press into the individual wires of a UTP cable (or the wires are pressed into the teeth). The teeth puncture the outer insulation of the individual wires and make contact with the conductor inside, thus making a connection. This process (known as crimping or punching down, depending on the method or tool used) is illustrated in Figure 1.

 
Figure 1: Using insulation displacement connectors (IDCs)

Though they may differ in methods, any connector that uses some piece of metal to puncture through the insulation of a strand of copper cable is an IDC connector.

Jack Orientation

Yes, jack orientation. The individual wall plate systems use many different types of jacks, and some of those systems use jacks with positions other than straight ahead (which is the "standard" configuration). These days, a popular configuration is a jack that's angled approximately 45 degrees down. There are many reasons that this jack became popular. Because it's angled, the cable-connect takes up less room (which is nice when a desk is pushed up tight against the wall plate). The angled connector works well in installations with high dust content because it's harder for dust to rest inside the connector. It is especially beneficial in fiber-to-the-desktop applications because it avoids damage to the fiber-optic patch cord by greatly reducing the bend radius of the cable when the cable is plugged in. Figure 2 shows an example of an angled connector.

 
Figure 2: A faceplate with angled RJ-45 and coaxial connectors

Note

Angled connectors are found in many different types of cabling installations, including ScTP, UTP, and fiber optic.

Wiring Pattern

When connecting copper RJ-45 jacks for universal applications (according to the standard, of course), you must wire all jacks and patch points according to either the T568-A or T568-B pattern. Figure 3 shows one side of a common snap-in jack to illustrate that the same jack can be terminated with either T568-A or T568-B color coding. (You may want to see the color version of this figure in the color section.) By comparing Table 1 and 2, you can see that the wiring schemes are different only in that the positions of pair 2 (white/orange) and pair 3 (white/green) are switched. If your company has a standard wiring pattern and you wire a single jack with the opposing standard, that particular jack will not be able to communicate with the rest of the network.

 
Figure 3: A common snap-in jack showing both T568-A and T568-B wiring schemes

Table 1 shows the wiring color scheme for the T568-A pattern. Notice how the wires are paired and which color goes to which pin. Table 2 shows the same for T568-B.

Table 1: Wiring Scheme for T568-A 

Pin Number	Wire Color
1	White/green
2	Green
3	White/orange
4	Blue
5	White/blue
6	Orange
7	White/brown
8	Brown

Table 9.3: Wiring Scheme for T568-B 

Pin Number	Wire Color
1	White/orange
2	Orange
3	White/green
4	Blue
5	White/blue
6	Green
7	White/brown
8	Brown