November 4, 2009

How to Crimp Network Cable

1. Pull the cable off the reel to the desired length and cut. I have a box of cable at one end of my shop and a mark on the floor 10' away. For cable lengths which are a fraction of ten feet, I eye-ball the length as I pull the cable out of the box (also, my feet are about one foot long). For longer cables, I pull it out to the ten foot mark and go back to the box and pull the remaining fraction or another ten feet. If you are pulling cables through walls, a hole in the floor, etc., it easier to attach the RJ-45 plugs after the cable is pulled. The total length of wire segments between a PC and a hub or between two PC's cannot exceed 100 Meters (328 feet or about the length of a football field) for 100BASE-TX (and 10BASE-T).

2. Strip one end of the cable with the stripper or a knife and diags. If you are using the stripper, place the cable in the groove on the blade (left) side of the stripper and align the end of the cable with the right side of the stripper. This is about right to strip a little over 1/2" of the jacket off the cable. Turn the stripper about one turn or so. If you turn it much more, you will probably nick the wires. The idea is to score the outer jacket, but not go all the way through. Once scored, you should be able to twist the end of the jacket loose and pull it off with one hand while holding the rest of the cable with the other. If you are using a knife and diags, carefully slit the cable for about an inch or so and neatly trim around the circumference of the cable with the diags to remove the jacket.

3. Inspect the wires for nicks. Cut off the end and start over if you see any. You may have to adjust the blade with the screw at the front stripper. Cable diameters and jacket thicknesses vary.

4. Spread and arrange the pairs roughly in the order of the desired cable end.

5. Untwist the pairs and arrange the wires in the order of the desired cable end. Flatten the end between your thumb and forefinger. Trim the ends of the wires so they are even with one another. It is very important that the unstripped (untwisted) end be slightly less than 1/2" long. If it is longer than 1/2" it will be out-of-spec and susceptible to crosstalk. If it less than slightly less than 1/2" it will not be properly clinched when RJ-45 plug is crimped on.. Flatten again. There should be little or no space between the wires.

6. Hold the RJ-45 plug with the clip facing down or away from you. Push the wire firmly into the plug. Now, inspect the darn thing... before crimping and wasting the plug! Looking through the bottom of the plug, the wire on the far left side will have a white background. The wires should alternate light and dark from left to right. The furthest right wire is brown. The wires should all end evenly at the front of the plug. The jacket should end just about where you see it in the diagram--right on the line. Aren't you glad you didn't crimp the plug?

7. Hold the wire near the RJ-45 plug with the clip down and firmly push it into the left side of the front of the crimper (it will only go in one way). Hold the wire in place squeeze the crimper handles quite firmly. This is what will happen:

(Crimp it once.) The crimper pushes two plungers down on the RJ-45 plug. One forces what amounts to a cleverly designed plastic plug/wedge onto the cable jacket and very firmly clinches it. The other seats the "pins," each with two teeth at its end, through the insulation and into the conductors of their respective wires.

8. Test the crimp... If done properly an average person will not be able to pull the plug off the cable with his or her bare hands. And that quite simply, besides lower cost, is the primary advantage of twisted-pair cables over the older thinwire, coaxial cables. In fact, I would say the RJ-45 and ease of its installation is the main reason coaxial cable is no longer widely used for small Ethernets. But, don't pull that hard on the plug. It could stretch the cable and change its characteristics. Look at the side of the plug and see if it looks like the diagram and give it a fairly firm tug to make sure it is crimped well.

9. Prepare the other end of the cable so it has the desired end and crimp.

10. If both ends of the cable are within reach, hold them next to each other and with RJ-45 clips facing away. Look through the bottom of the plugs. If the plugs are wired correctly, and they are identical, it is a straight-thru cable. If they are wired correctly and they are different, it is a crossover cable.

11. If you have an operational network, test the cable. Copy some large files.

12. If the cable doesn't work, inspect the ends again and make sure you have the right cable and that it is plugged into the correct units for the type of cable. Try power-cycling (cold booting) the involved computers.

13. If you have many straight-thru cables and a crossover cable in your system, you should consider labeling the crossover cable or using a different colored cable for the crossover cable so you don't mix them up. I do not recommend implementing the crossover function, as recommended elsewhere, with two RJ-45 jacks, appropriately wired back to back, and two straight-thru cables. This method costs noticeably more, introduces more than the necessary number of components and connections, increases the complexity and time of assembly, and decreases reliability.

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