How to Test an Ethernet Cable – Without a Cable Tester

Ethernet cables play a vital role in computer networks, enabling computers and networking devices to connect to each other and exchange information. If you’re experiencing network difficulties, setting up new devices on a network with extra cables, or doubting the work that a network engineer performed, you’ll want to spend some time testing your network cables.

Depending on your goals and equipment, this process can be very quick or very time consuming. Here’s a quick rundown on how to test ethernet cables without a cable tester, some common things you should look for when testing cables, and when you should definitely buy a cable tester to save yourself some time and effort.

Ethernet Cable Test Without Tester

Basic Troubleshooting

If you think that a faulty ethernet cable is causing problems on your network, you may want to try some basic troubleshooting first. This step is a lot easier if you can remove the cable and replace it easily or if you’ve got an extra device that you can plug into the cable. If you’ve only got a single computer that can’t move and the cable runs through your wall, you’re going to have a hard time performing this step.

Your goal here is to prove that the cable isn’t the point of failure in your network. In order to do this, you’ll want to try to test two things. First, test your current device on your current network with a different cable. Next, test your current cable on a different device, ideally on a different network. If the new cable doesn’t fix things and your old cable works fine on a different device, your network issues probably aren’t a result of your ethernet cable.

You’ll need an additional ethernet cable in order to perform the first part of this test. You can usually borrow an ethernet cable from another device on a home network. Make sure that you use an ethernet cable that works well and doesn’t connect to a service you need to test your network.

In other words, if you’re going to run a speed test to check your cable, don’t pillage the cable between your router and your modem to plug in your laptop. In most cases, doing a quick ping of another device on the network, sending a small file, or loading a single web page is more than enough to verify that the new cable works.

When performing the second step, you’ll ideally want to plug your old cable into a totally different network environment. This isn’t always possible at home. Try to at least use a different port in the back of your router, however. It’s best to use a totally different device for this test, but you’ll sometimes find that just switching ports or networks is enough to prove that your cable works fine. Again, if you can successfully ping other devices, transfer small files, or load small webpages, you’re almost certainly fine.

DNS Ping

Visual Checks

Before you break out the multimeter, it’s worth spending a bit of time examining your cable. Are there any visible breaks or kinks? If so, there’s a much higher chance of a short or other internal damage in the cable.

The plug on each end of the cable should be clear, with 8 colored wires inside. Four should have white stripes, while the other four should be solid in color. Make sure that the wires are arranged in the same order on each end. In the US, this order should be white/orange, orange, white/green, blue, white/blue, green, white/brown, and brown. This cable standard is called TIA 568B.

In many cases, ethernet cables are created by hand. Creating networking cables is an annoying, time consuming process that involves a fair amount of dexterity, patience, and finger strength. It’s not uncommon for cables to switch places sneakily while someone is crimping on the cable end. If this happens, the wires will be out of order inside of the clear cable head and the cable won’t work.

If you’re having trouble seeing the color of the wires, consider taking a picture with your phone on a high zoom level. This makes it much easier to see the order and gives you a static image that you can use when comparing both ends of the cable.

It’s okay if your cable has the green and orange wires swapped, but they should be reversed on both sides, this is a TIA 568A cable. If your cable has the green and orange wires swapped on one side but not the other, it’s something called a “crossover cable” that can only be used for specific connections, like plugging two computers directly into each other. In modern computing, crossover cables are incredibly rare, so it’s much more likely that any issues with colors involve someone putting the wires in the wrong order rather than deliberately creating a crossover cable.

Ethernet Switch

Using a Multimeter

Once you’ve quickly checked over the outside of your cable, it’s time to break out the multimeter. You’ll want to use the multimeter to create a circuit across each pin of your ethernet cable in turn. This means you’ll need to get both ends of the cable fairly close to each other and you’ll want a way to hook up the probes of your multimeter to the small conductor at the end of each pin on the cable end.

Alligator clips and t-pins or sewing needles work great, if you have them. If not, you may have to get creative. Remember to use the multimeter to make sure that the device you’re using to pinpoint each pin is fully conductive.

You can streamline your use of your multimeter by setting it up so you’re just checking for a successful connection. The “diode check” mode on many multimeters is ideal for this. It should beep when it finds a successful connection.

With your cables held in place by a weight, clamp, or helper, carefully touch your probes to each terminal at the cable head in sequence, with the probes on the same position on each end of the cable. You should get a beep in each position.

If you don’t get a beep in a position, first make sure that you’ve got your multimeter probes in the same position on each cable end. Once you’ve verified this, check the colors on the wires within the cable end. If you can’t do this, try moving the multimeter probe on one head up and down to see if you can get a beep in a different position.

If you do, or if you can see that the wires are in different orders, it’s likely that someone made a mistake and got the order of the wires wrong while assembling the cable. If you can’t get a beep at all or the wires are in the right order, your cable likely has a break or a short.

It’s worth noting that telecommunications cables can work with a frighteningly small number of wires. If your ethernet cable is from a very old network or was used for a specialized purpose, there’s a nonzero chance that it was deliberately set up with less than the 8 wires needed for modern high speed networking. If your testing suggests that this is the case, it’s definitely time to buy a more modern networking cable.

Verizon Fios WiFi

When to Buy a Tool

While ethernet cables are absolutely vital to the operation of your network, functional cables don’t stop working particularly often. Most of the time that people test cables, they’re checking cables that haven’t been used. When a professional is making new cables for a job, it’s standard practice to use a tool to quickly test each cable for correctness before moving on. Ethernet cables are tricky to get right and even the most experienced technician will mess up every once in a while, so testing is absolutely vital.

The techniques mentioned above have some big downsides when compared to using a tool. First, they take a while. Second, they don’t always give the same detailed diagnostics that a well-made modern testing tool can give. A great testing tool will tell you which wires are swapped or shorted, making cable maintenance a breeze. Plugging your networking cable into a new environment will only tell you if the cable works, which is helpful, but doesn’t make fixing the problem any easier.

Third, and most importantly, the techniques above usually require you to get both ends of your cable in the same place. This isn’t always an option for long ethernet cable, especially if the cable runs through a wall, ceiling, attic, or basement.

If your cable isn’t easy to move, you’ wont be able to split your multimeter’s probes and touch each probe to one end of the cable. The remote on specialized cable testers solves this problem, allowing you to plug part of your tester in at one end and simply walk to the other end, no matter how far away it is.

Ethernet cable testers can be pretty pricey, but a basic model with a remote can be picked up for well under $40. If you’re making a lot of cables (more than four or five), your cables can’t easily be moved, or you think you’ll be testing ethernet cables again in the future, it’s well worth the investment to get a cable tester. You’ll save a lot of time, you’ll get more useful test results, and you’ll be able to test cables in any situation, not just short patch cables that you can easily access.

Tracing an Ethernet Cable

Higher end ethernet testing tools have functionality built in that allows you to figure out where a particular ethernet cable is. By sending a signal down one end of the cable, you can use a sensitive instrument to look for that signal as you move it around a building. This can allow you to figure out where a cable is routed or quickly identify a specific cable in an unorganized or unlabeled patch room.

If you need to trace cable you will definitely either want to purchase a tool or borrow a tool from someone else. Tracking cables with out a toner / prober tool is next to impossible.

What Type of Ethernet Cable Should I Buy

If you find out that your ethernet cable is faulty, you’ll need to replace it. If you cut and crimped your cable yourself, replacing it will be simple. If you’re replacing a store bought cable, however, it’s a good idea to familiarize yourself with the modern cable standards and make sure you buy the right thing.

There are three common types of modern ethernet cable: cat 5e, cat6, and cat6a. Cat 5e is more than fast enough for most modern networking applications, but it’s not quite as robust or as fast as the other two. Cat 5e cable is guaranteed to be able to handle 1000 Mbps of data over 100 meters.

Cat 6 cable is a bit “faster.” in the cable world, “faster” means that the cable has better precautions to ensure that signals don’t interfere with each other, lose quality, or suffer interference from the outside world. These days, cat 6 cable is about the same price as cat 5e cable and is guaranteed to be able to handle 1 Gbps of data over 100 meters. This is the same as with Cat 5e. However over shorter runs Cat 6 will do up to 10 Gbps. It is also a little more resilient to interference.

Cat 6a cable is built to a much higher standard, but not in the way you might think. Cat 6a cable has better shielding and internal wire management than other types of cables, making it ideal for very high speed, very short runs. It can supports 10 Gbps speeds for lengths of up to 100 meters (328 feet) in length. Cat 6a is probably what most people should be installing these days.

Cat 8 cables are specialty cables that really have no useful applications outside of large datacenter environments. Cat 8 cable can handle up to 40 Gbps of data, which is a lot. There is absolutely no reason to even consider a Cat 8 cable for a home or small business network.