Cabling for the Color-blind

One challenge for the colorblind individual in IT is being able to make patch cables from some Cat5 or Cat5e cable and RJ-45 connectors. The problem for us is, of course, that the industry standards are all based on color codes.

I have studied the manufacture of Cat5 cable in order to find other visual cues as to the identities of the twisted pairs.

Simply as a matter of technique, I was taught to “banana” the twisted pairs after stripping the outer insulation. This turned out to be beneficial as it provides our first, non-color, clue as to which pairs are which color.

Understand that I am writing from the perspective of my own color perception. I am Red-Green deficient. As a result the one color that I can always easily identify is the Blue pair. This may not be the case for someone who is Blue-Green deficient. However, the principle I will describe still holds true, you’ll just have to adjust based on what you can perceive.

After “banana”-ing the pairs, I turn the cable until the Blue pair is pointing away from me (Fig. 1). I have not yet encountered a manufacturer who arranges the pairs in the insulation differently, and I believe that to do so would interfere with the purpose for which the pairs are twisted at different intervals (more on that later).


So with the Blue pointed away from my body, the pair that is pointed back at my chest is the Green pair. For me, that solves the issue, as it is the Green and Orange pairs that I have difficulty distinguishing. The Orange pair is either to the left or right
depending on which end of the cable you are working from.

Let’s say that you can reliably identify the Orange pair. Point it away from you. The Brown pair is the one pointing back at you.

Now, let’s assume that you cannot reliably identify any one color. Or maybe you just don’t trust the result of the test above. Or, maybe, you’ve run into the one manufacturer out there that doesn’t arrange the pairs in the insulation the way all the others do.

The key now, is the number of twists in each pair.

 

Pair color

[cm] per turn

Turns per [m]

 

Green

1.53

65.2

 

Blue

1.54

64.8

 

Orange

1.78

56.2

 

Brown

1.94

51.7

 

Without worrying about the specifics of the table above, the point is that the Green pair is the most tightly twisted. The Blue pair next, then Orange, and the Brown pair has the fewest twists. So by closely looking at the pairs before untwisting them you can verify their identities. This is another strength of the banana technique—once you have identified the pair colors, you’ll be better able to keep them straight as you order the individual wires by the 568A or 568B standard.

A brief explanation: You may wonder why the pairs are twisted at different rates. When two wires are lying next to each other, and one carries a current, that current will be inducted into the other wire. You can see, then that that would be a problem for wires carrying packets of data. The solution is to twist the wires at different rates. This way no one wire is laying next to any one other wire, except for the one it is twisted with.

This leads to another issue in making cables. A common poor practice is to strip off a lot of insulation, get the individual wires into their proper places in the RJ-45 connector and crimp the connector on with a lot of untwisted wire between the base of the RJ-45 and the outer insulator. If you do this, if more than about a ½ inch of wire is untwisted at the connector, you have undone the purpose for which the twists were made and this will allow induction to happen. Your 100Gb NIC will never receive 100Gb. Each patch cable made this way will degrade the network. As a separate but important matter, some of the outer insulator should be inside the RJ-45 connector, enough to be under the rear crimp. This takes the weight of the cable off of the soft copper wires and puts it on the insulator and that little nylon string that is inside the insulator.

The Standards: There are two industry recognized standards for making patch cables. They are called 568A and 568B. The letter designators are not, as is usually assumed, a serial identification. “A” stands for AT&T and “B” stands for Bell. Before the enforced breakup of AT&T, they developed their standard for 4 pair cable wiring. The regional Bell companies, which were part of the AT&T system, did too, and it was a little bit different. AT&T was responsible for their internal wiring and between the Bells. The Bells did wiring all the way to the customer. Simply because there was much more wiring done the Bells way, the “B” standard is the prevailing industry standard. There is nothing wrong with using the “A” standard to make a patch cable, but it can lead to confusion if someone is trying to repair a line without inspecting the opposite end. It’s also important to know both standards, as a cable made with the “A” standard on one end and “B” on the other is known as a cross over cable, which has its own uses. Specifically to connect “like” devices, such as a router to a router or a computer to a computer, where the patch, or straight through cable with matching standards at both ends, connects “unlike” devices; a computer to a switch or hub, for example.

568B:

Pin

Pair

Wire

Color

1

2

1

Orange White

2

2

2

Orange

3

3

1

Green White

4

1

2

Blue

5

1

1

Blue White

6

3

2

Green

7

4

1

Brown White

8

4

2

Brown

568A:

Pin

Pair

Wire

Color

1

3

1

Green White

2

3

2

Green

3

2

1

Orange White

4

1

2

Blue

5

1

1

Blue White

6

2

2

Orange

7

4

1

Brown White

8

4

2

Brown

 

Notice that the only real difference is that the Green and Orange pairs switch places.

Some technique tips:

Strip the outer insulator by about 1 ½ inches. You’ll end up cutting off about an inch, but it makes the wires long enough to work with when getting them in order. Cut off the exposed string at the insulator now. Leaving the string to hang out of the RJ-45 connector isn’t tidy or professional.

 

After making the “banana” and identifying the colors, untwist the pairs and get the individual wires as straight as you can, by pinching a pair hard between a finger and thumb and pulling the wire through from the insulator to the cut end. IT may curl a little, but that’s okay.

 

Pinch finger and thumb together in the same manner and pull one wire at a time between them, working to get the wires as close together as possible. If the fleshy part of your thumb is pressed on the edge of the outer insulator, you’ll have that good ½” or so of copper trapped.

Just as you straightened the pairs, now do it again with all 8 wires. The goal is to get a nice straight ribbon of wire all in their proper order.

 

Using your crimping tool’s cutter, with the 8 wires still pinched down with finger and thumb, put the wires in the cutter right up to the end of your thumb and cut the wires. Ideally, the cut will be straight across. (Don’t cut your thumb!)

With the Orange White (for the “B” standard—Green White if “A”) wire to the left of the ribbon place the wires into the RJ-45 connector with its clip pointing down. Work the wires into their individual channels. Look at the end of the RJ-45. If all 8 wires are in their place, you should see 8 flashes of copper through the clear plastic.

 

Put the connector in the crimper and press. Press hard.

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