Phone and Network Cables

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Phone and Network Cables

We will use "CAT-5" for the phone, network and ISDN runs. This page discusses the wiring for

these services. The topics covered here are:

CAT-5 cable

CAT-5 wire pairs CAT-5 connectors

568-A standard versus 568-B standard

Logically "crossed" versus logically "straight" cables

Cross-over cables for direct computer-to-computer linking

CAT-5 Cable

"CAT-5" is a nickname for cable with four wire pairs that each meet the "Catagory 5"specification for data communications. The specification defines the conductor size,insulation quality and wire twists, plus a multitude of performance characteristics. In

theory, all CAT-5 cables perform the same, supporting data transmissions up to100MB/s. A more stringent cable specification is "Catagory 6" ("CAT-6"), supporting

data transmissions up to 1GB/s. A less stringent specification is "Catagory 3"("CAT-3"), supporting data transmissions of only 10MB/s or less.

CAT-5 cables have 4 wire pairs, making a total of 8 wires. Each pair is twisted together(you've probably heard the phrase "twisted pair" before) to reduce signal interference.

The biggest factor between the catagory specifications is the number of twists perlinear unit. The more twists, the greater the signal integrity. Data signals are sent overthe wire using a differential method. With tighter twists, any interference received bythe cable is more likely to affect both wires in a pair equally, resulting in no change in

the difference between them. This allows greater data capacity over longer distances.The tighter twists also suppress noise created by the cable because the magnetic fieldfrom one wire is canceled by it's mate, making it less prone to interfering with othercables. When terminating data cables (with crimp-on connectors or at punch-downterminals), it is important to untwist the pairs as little as possible (1 cm. max.). Some

ill effects of tighter twists is they make the cable more stiff and brittle.

CAT-5 cabling can come with either "solid" or "stranded" cores. Each wire

core in "solid" CAT-5 contains a single 24 gauge wire. Each wire core in"stranded" CAT-5 is made from several thin strands. The solid cable is stifferand less suseptible to moisture contamination, making it the choice for in-wall wiring. The stranded cable is more flexible, less suseptible to fatiguefrom repeated bending and should only be used for cables no longer than 3meters, making it the choice for patch cables (the cables connecting the wall

jack to equipment). The connectors that are crimped on the end of CAT-5

are usually meant for either solid or stranded cable (though some will workwith both), so be sure you get the right kind for your cable (and make surethey are CAT-5 rated).

CAT-5 cabling can also come "shielded" or "unshielded". All the wire

pairs in "shielded" CAT-5 are contained in a wire-braid tube called a"shield". This further protects the wires from outside interferenceand reduces the amount of noise that can escape the cable. We recommend unshieldedCAT-5 for home installations, and many equipment specifications also call for

unshielded cables.

Another term you will hear a lot while shopping for CAT-5 cable is "plenum"."CAT-5 plenum" (sometimes called CMP) has the same performance characteristics asregular CAT-5 (sometimes called CMR, the "R" stands for "Riser"). The term "plenum"

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refers to the fire rating for the material making up the outer jacket of the cable.Plenum rated material does not release toxic fumes in the event of a fire. Regular CAT-5 uses aPVC jacket that will release toxic fumes when burned. Many building codes require the plenum

for commercial installations but not for residential installations. Commercial buildings typicallyrun cable through drop ceilings, and since the drop ceilings are also used for air circulation(this is called a "plenum space") there is the potential to distrubute fumes during a fire.

Residential homes typically use sealed ducts to distribute air so there is no real chance for

contamination (an exception to this is running wires in the return air space, which is typicallynot ducted). Also, homes are evacuated faster than commercial buildings, so the danger of ahazardous exposure to fumes is inherently less. With all the PVC already in most homes, in our

non-expert opinion it is not worth the price difference to get plenum (sometimes twice asexpensive), but that is a decision you should make for yourself after more carefull andthorough research. Refer to your applicable building codes regarding plenum cables before youmake any installations.

There are other practical differences between CAT-5 cables. Some have a fiber filament thattakes some of the tensil strain off the wires. Others have easier-to-distinguish colors on thewire pairs. These are just a few and it depends on the brand you buy.

CAT-5 Wire Pairs

The four wire pairs in a CAT-5 cable are distinguished by the color of theirinsulation. The four colors are (in order) blue, orange, green and brown. Thus,

when refering to the "second pair" of wires, it is the orange pair. Regular phonecable consists of two untwisted pairs, each with wires of a different solid color(the first pair is Green/Red, the second is Black/Yellow). However, we will

recommend CAT-5 for phone and concentrate there.

Strictly speaking, each colored pairconsists of (in order) a white wire with

a colored stripe and a colored wire with a whitestripe. However, the rules for cables with so few pairsare lax. Most often you will find the pairs consistingof a white wire with a colored stripe and a solidcolored wire. Sometimes the white wire may not even

have a stripe (it may have dots or just be associatedby the color of the wire it's twisted with), andsometimes it's not even white (being gray or

transparent). Some cable has all solid colors inuntwisted pairs (avoid completely as it is not CAT-5rated). We will use the common white-striped/solidscheme throughout this site.

The table at right shows the order of the wire pairs. The color standard covers cables withmore than four pairs, but that is out of the scope of this discussion.

CAT-5 Wire Order

Pair # Wire Color Abbr.

Wire #

(Pair)

Wire #

(Cable)

1White/Blue W/B 1 1

Blue B 2 2

2White/Orange W/O 1 3

Orange O 2 4

3White/Green W/G 1 5

Green G 2 6

4White/Brown W/Br 1 7

Brown Br 2 8

CAT-5 Connectors

Phone and network connections both use a "Registerd Jack" (RJ) type connector. Phones useRJ-11 connectors, networks use RJ-45 connectors, which are a bit wider. The RJ typeconnectors are often called "modular connectors". Traditionaly when working with modularconnectors, the hook will be underneath and the contacts (pins) will be on top. The diagramsbelow and the wall jacks follow this standard.

Typical phones use 4 or 6 pin RJ-11 connectors (seeFigure 1 at left). Most phone cables have four wires,

but most phones only use the middle two. Click on





the picture to switch between CAT-5 and regularphone cable. Although they look physically straightin Figure 1, phone cables are logically "crossed".

Wires in RJ-11 connectors do not follow a

linear order (left-to-right), instead theyfollow a centric order, working from the

center pins out (see Figure 1). To makeconnections compatable with both ends of alogically "crossed" cable, it is necessary forevery pair in the cable to have each wireequidistant from the center of the connector

(either that or every cable would have tohave all 6 wires, a big waste). For example,if you have a cable with only one pair and it

is at pins 1 & 2 at one end and 5 & 6 at theother, the cable would not work if the endswere unplugged and reversed because pins 1

& 2 would then be empty (click on picture at

right).

Network and ISDN cables use 8 pin RJ-45connectors which look the same as RJ-11s, only alittle wider (see Figure 2 at left). There are two

standards for wiring RJ-45 connectors, called"568-A" and "568-B" for short, that differ on wherepair 2 & pair 3 are pinned. Click on the picture to

switch between the standards. Although they lookphysically crossed in Figure 2, network and ISDNcables are logically "straight".

Wires in RJ-45 connectors have a mix of centric andlinear ordering. The two middle pairs are centricordered, the two outer pairs are in linear order. Tofurther confuse, the two standards swap where pair2 & pair 3 go. When wiring an RJ-45 connector, first

come the centric pins; pair 1 is on the middle pins(4 & 5) for both standards. The next pins out (3 & 6) will either be pair 2 (568-A) or pair 3 (568-B).

Then come the linear pins; 1 & 2 will either be pair3 (568-A) or pair 2 (568-B), and finaly pair 4 is onpins 7 & 8 for both standards. See Figure 2.

Note that for the RJ-11 and both RJ-45 standards, the wires will alternate between white-striped and solid-colored. When crimping on a modular connector, you should never get twowhite-striped wires next to each other, nor should you get two solid-colored wires next to eachother. This is important to remember when pinning pair 1 (blue) whose second wire (solid-color) is pinned before it's first (white-striped).

Figure 1: RJ-11

Click on picture to switch cable types

Figure 2: RJ-45Click on picture to switch standards

Bad RJ

(Click)

568-A vs 568-B

The two standards reverse where pair 2 (orange) & pair 3 (green) are pinned. As it happens, these arethe only wires that are used in network cables.

Network protocol does not use pair 1 (blue) or pair4 (brown). You can click on the pictures to hide andshow the unused pairs. ISDN cables use all four

pairs.





Both standards are completely compatible with allnetwork and ISDN equipment and each other. Youcan plug a 568-A cable into a 568-B jack. The only

difference is the insulation color of the wire thesignals will travel, and electrons don't care aboutthat. As long as both ends of a cable are wired to

the same standard, the cable will work.

We recommend the 568-A standard because it issimilar to the wiring for an RJ-11 connector. Noticethat the 4 middle wires in the 568-A figure to theright are the same as the 4 wires in the RJ-11

figure above. In the 568-B figure below, only themiddle 2 wires match the middle 2 wires in theRJ-11 figure.

The

RJ-11/568-Asimilarity

isbeneficial because both phone and network cableswill be terminated with an RJ-45 connector (CAT-5will be used for both services) in the wiring closetbefore identifing each cable. We will then identify

each cable by plugging in a wire tester to eachcable. If both cable types are wired to the samestandard, testing will be easier with less re-

crimping. Another benefit is a cable can later bechanged from phone to network (or vice versa or toboth) with less confusion and work in keeping the

colors correct.

The drawback is most off-the-shelf equipment iswired to the 568-B standard. The Leviton jackshave a pin designation for both the A and Bstandards. However, the CAT-5 patch panel that we

will use to distribute the phone service is usuallymarked for one standard or the other. 568-B patch panels are common and will work just fine,but since we wire the RJ-45 connectors using 568-A, the orange wire would mate with the

green posts on the panel and vise versa. A simple solution is to use paint pens and recolor theposts on the patch panel. Finding a 568-A patch panel will be more difficult, but having a patchpanel that is marked in the same standard that you are wiring is worth the hassle.

Figure 3: RJ-45, 568-A Standard

Click on picture to hide/show unused wires

Figure 4: RJ-45, 568-B StandardClick on picture to hide/show unused wires

Crossed vs. Straight Cables

Phone cables are logically "crossed". A pin on one end of a crossed cable does

not lead to the same pin on the other end. Instead, it leads to it's mirroropposite on the other end. When you hold the two ends of a phone cable inthe same direction, one is wired in the reverse sequence of the other (seeFigure 1 above). This is not the same as a "cross-over" cable for direct

computer-to-computer connections as discussed below.

Figure 1 above and the table on the right show where a pin on one end of acrossed cable leads to on the other end. The same concept also applies to

phone cables with only 4 or 2 wires.

Note that the concept only applies to male-male (cords) and female-female (couplings) phone

cables. For male-female cables (splitters and extensions) the cable is not crossed but is

Crossed Cables

Pin Pin

1 6

2 5

3 4

4 3

5 2

6 1





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Phone and Network Cables