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There are plenty of videos and descriptions about how to use an RJ45 crimping tool. I've seen a few, and I have even tested a crimping tool, but I still don't understand how it does what it does.

What exactly happens to the eight wires inside the crimping tool, and why isn't it necessary to remove the insulation from the eight wires before putting the cable into the crimping tool?

Arseni Mourzenko
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    i dont know who was downvoting this question as it has a business and private xase on the same time. i really uovote it as it is a legitimate business question forsome who dont have a electrical knowledge. Please remember that not every question must have a server and a OS behind and may ve more about technical part of a component. so i believe you are the first i seen here asking for that – djdomi Jan 06 '21 at 12:04
  • This question as stated is specific to crimping plugs. It may be worth looking at the back of a wall jack (ie a socket) to compare how the same task is done there, with a punchdown tool. The knife-edges will be more visible in a jack. (comment because not really an answer) – Criggie Jan 06 '21 at 23:14

2 Answers2

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When you crimp a cable the metal contact pads inside the RJ45 head will "cut" into the isolated ethernet cable. Most one time used RJ45 connectors will also have a bit in the middle of the connector that will get crushed during crimping, ensuring that the cable doesn't get pulled out easily from the contact pads.

Before and after crimping

There are some RJ45 connectors that allow you to remove the head, but these are most of the time used in a commercial environment (and these are most of the time significantly more expensive). However these heads usually do not require any tools.

Similar approach is taken when you use a patch panel, where the patch panel's metal contact pads will cut open the isolation of the ethernet cable and create a circuit by penetrating through the plastic of the cable.

Source of image: https://www.vpi.us/installation/assemble-cat5e-rj45-plg-flt.html

Barnabas Busa
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  • good answer, i could not do it better even i learned eletrican and it techniques – djdomi Jan 06 '21 at 12:06
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    The wedge rotates on a hinge to jam between the shell and cable jacket like a doorstop in all “ice cubes” I’ve crimped. – Warren Young Jan 07 '21 at 15:09
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Because the magic happens inside the connector instead of the crimping tool, you don't necesssarily need one to make a working cable. Doing this once manually gives you the understanding what happens inside the crimping tool. It simply presses everything down simultaneously and equal amount of force, making the cable more trustworthy.

See e.g. wikiHow's Attaching RJ-45 Connectors without a Crimping Tool. As it's the pins that cut their way inside the wire, you could press them down one by one using e.g. a flathead screwdriver.

enter image description here

6 Press the pins down with a flathead screwdriver. Locate the small metal pins at the ends of the grooves of the connector. Use a thin, flathead screwdriver to push each of the pins down. Push the pins 1 by 1 so they’re pressed all the way into each wire.

Esa Jokinen
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    To be clear, a screwdriver or knife is a last-resort tool, and while it should work, its eight times as much work as a crimp tool. Any hardware geek should own the minimum basic tools of the trade, a plug crimper, a sheath-cutter, flush cut snips, and a punchdown tool for jacks. A wiring tester and tone source would be nice too. – Criggie Jan 06 '21 at 23:12
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    Please do not do this. Do not use a screw driver to manually crimp a cable. The guy who discovers it after spending hours hunting some problem you caused will hurt you. – Billy left SE for Codidact Jan 07 '21 at 06:02
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    This was meant for educational purposes alone, which wasn't worded clearly enough. I hope it's better now. Personally I've abandoned making own cables even with proper tools, because they break more easily than prefabricated molded cables. – Esa Jokinen Jan 07 '21 at 06:47
  • I thought everyone knew that WikiHow is one big inside joke that got out of hand, filled with nonsensical instructions and meme material. – CodeCaster Jan 08 '21 at 15:56