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How do you test the quality of an ethernet cable? Question
How can I confirm that an ethernet cable is free of defects?
I have a bunch of ethernet cables around my house. Some are apparently defective, and cause network problems when used. When these problems happen, they are often intermittent and hard to reproduce or diagnose.
I don't want to blindly throw out all my cable and replace it. This would be a lot of work and cost quite a bit. Some cables might be fine and not need replacement. The new cable I buy might be defective as well. I'd like to have a way to measure the quality and confirm that the old cable is bad and the new cable is better. How can I do this?
1 answer
There are two levels of testing you can do with Ethernet twisted pair cables, or technically twisted pair cables in general (e.g., telephone, serial, etc.). You can verify the wiring - i.e., does each pin go where it is supposed to go - and the quality.
The wiring test basically checks continuity between the wires from one end to the other. Typically this involves an active tester on one end, which sends a signal down each wire and sees where it ends up, and a passive device on the other end to route the signals from one wire to another to, essentially, bounce them back to the tester. The first one these that I had, the Siemon STM-8, cost a few hundred dollars but was worth every penny. The modern versions are relatively inexpensive. A typical name-brand tester which I currently have is the Klein Lan Scout Junior:
(Picture from Amazon but may be cheaper at a regular store.)
But there are plenty of less expensive models available as well, and even the $20 testers will actually do just fine for the basics. I mainly use these types of testers for testing installed wiring in a building, either when installing it or when a customer moves into a new office and I want to test the existing wiring before connecting computers.
If installed wiring fails then you check the jack on each end to fix the problem, either by rewiring the jack or installing a new jack. For almost everyone I say never install wiring with plugs on the ends, install jacks and use factory-made patch cables on each end.
The same testers will work just fine for patch cables. If a patch cable fails, toss it. Don't try to fix it. Even a 50' cable just doesn't cost very much and redoing the plugs is tricky business with high-speed connections.
As far as testing quality, that requires better equipment. For example, some testers (e.g., Klein Lan Scout Pro) can test cable length. Some can do even more quality testing, which may be helpful if you have a connection that works at 100 Meg. but not at 1 Gig.
But for most people a $20 - $60 basic tester that checks for pins 1-8 going through vs. crossed vs. mis-wired is all you need.
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