How to Tell if an Ethernet Cable is Bad

Tell if Ethernet Cable Bad title page

Let’s say you’re in your house and you want to stream a YouTube video or Netflix episode. You grab your favorite internet device and start navigating to the video you want to watch. At this point, you get a notification saying you can’t stream your video because you don’t have an internet connection.

You’re confused by this alert, because nothing has changed with your internet connection since the last time you used it.

Frustrating, isn’t it?

I get it. We’ve all been in this situation.

What makes things difficult is that there are many different reasons why your internet connection can drop.

Loss of internet connection can be caused by:

  • An unplugged modem or router power cord
  • A problem with your internet service provider
  • Overheating of your modem or router
  • Trying to access the internet outside your router’s WiFi range

These are the common causes that everyone thinks about when they lose an internet connection.

What most people don’t think about is the fact that an ethernet cable going bad could be the cause of their troubles. In fact, ethernet cable failures are more common than you think.

But how do you know if a faulty ethernet cable is causing your loss of network connection?

You can tell if an ethernet cable is going bad by running a few tests. If you think an ethernet cable has gone bad, you can:

  • Visually inspect the cable for damage
  • See if the ethernet port link lights on one of your devices light up when connected to the cable
  • Swap out the cable with another one to see if the network connection is restored
  • Use an ethernet cable tester on the cable

In this post, I’ll dive into each of these methods and explain what to look for.

How to find out if an ethernet cable is not working

If you have a device that’s connected to your network with an ethernet cable and the cable goes bad, you’ll lose your network connection.

If one (or all) of your devices loses its network connection, you might suspect that a cable has gone bad. The problem is, you don’t know for sure if that’s the cause of your lost connection.

So what do you do?

There are a few different steps you can take to see if the ethernet cable you are using has gone bad.

I recommend that you run these tests on all the ethernet cables in your network if you’re experiencing connectivity issues. You should do this because there may be multiple cables that can affect one device.

For example, what if your computer is connected to your router with an ethernet cable, and your router is connected to your modem with an ethernet cable? If either one of those ethernet cables goes bad, you’ll lose your internet connectivity.

It’ll only take a few minutes to inspect all your cables, and you may be surprised by what you find.

Visually inspect the ethernet cable

The first thing you should do is inspect the ethernet cable that you think might be going bad. Look at the sheath of the cable for the following:

  • A secure connection to the devices at each end of the cable
  • Cuts or tears in the rubber jacket around the copper wires
  • If the copper wires inside the cable are exposed outside of the rubber jacket
  • Sharp bends or turns in the cable
  • If the cable is crushed by any furniture or other heavy items

If you see damage to the ethernet cable, that might be the reason it isn’t working properly.

If the cable passes the visual test and everything looks ok, take a look at the ethernet port link lights on the devices the cable is connected to (if they have them).

Inspect the ethernet port link lights

Depending upon the device your ethernet cable is connected to, it might have ethernet port link lights to aid your inspection.

Ethernet port link lights

On devices with link lights, they’ll have two lights on each ethernet port. The lights are located on the sides of the port.

For example, here are the link lights on the ethernet port of my laptop.

Link lights on laptop ethernet port

The link light on the left is orange, while the other link light is green.

The purpose of ethernet port link lights is to let you know if your ethernet port is working properly. For the devices that have them, they make it really easy when troubleshooting ethernet cable connections.

When an ethernet cable is plugged into the ethernet port, the green light will be a solid green. This is to indicate that the ethernet cable is successfully connected to the port.

Whenever data is being sent from one device to another through the ethernet cable, the orange link light will blink. This is to indicate that data is being processed.

Here’s what it’ll look like if the cable is plugged in correctly and processing data.

Laptop ethernet port link lights on

As you can see, both lights are on. You can’t tell by the picture, but the orange light is blinking on and off.

Using ethernet port link lights to inspect ethernet cables

If you think an ethernet cable is going bad, the link lights on the ethernet port won’t light up properly. In other words, you may have an ethernet cable connected to two devices, but the link lights might be off.

Let’s use my laptop as an example.

In this case, let’s say I’m using an ethernet cable to connect my laptop to my router. I need to make sure both my router and laptop are powered on and the ethernet cable is securely connected to both devices. If everything is working properly, both link lights on my laptop ethernet port should be lighting up.

I can conclude that something’s wrong with the ethernet cable if the green light isn’t a solid green or the orange link light isn’t blinking.

If you have any devices in your home with ethernet port link lights, you can use them to troubleshoot your ethernet cables. Take the ethernet cable that you think has gone bad and connect it to the device with the ethernet port link lights.

If the link lights on the device don’t light up when you connect your ethernet cable to it and power it on, it’s probably time to swap out that ethernet cable.

Try replacing the cable with another one that works

The next thing you can do if you have a cable that you think is going bad is simply swap it out.

If you have another ethernet cable that you know is working, use it to replace the one that you think might be faulty. If you don’t have a spare cable lying around, grab a cat5e or cat6 cable for your test. Ethernet cables are cheap, and it never hurts to have a spare lying around. You never know when you might need it.

When you replace the potentially faulty cable with the new one, does it restore the connection between the two devices?

Run a few tests after connecting the two devices with the different cable. If the connection between the two devices is now fast and reliable, it’s safe to say there was something wrong with the other cable.

Use an ethernet cable tester to check the cable

When you’re troubleshooting ethernet cables to see if they work, you can save yourself some time by using an ethernet cable tester.

Ethernet cable testers allow you to quickly tell if an ethernet cable has gone bad or not.

I got mine as part of an ethernet cable crimping kit because I also wanted to be able to shorten some of my ethernet cables. If you don’t want to mess around with cutting your ethernet cables, I suggest you just get an ethernet cable tester like this one.

Ethernet cable testers are inexpensive, and I think you’ll find that the time you save by using one is worth it. On top of that, you can say for sure whether your cables are working properly or not.

Not to mention, I think the tester is fun to use. All my non-technical friends are impressed when I can help them with their internet problems, so that’s a bonus as well.

How to use an ethernet cable tester

Ethernet cable testers are very easy to use. All you need is the tester and a 9 volt battery.

For your reference, here’s what an ethernet cable tester looks like:

Ethernet cable tester

As you can see, there are two parts to the tester (the Master and Remote). They can be joined together when you want to test shorter ethernet cables. If you want to test longer ethernet cables, you can separate the two devices.

To test an ethernet cable, all you have to do is plug each end of the cable into the two different tester devices. Then you just need to power on the tester.

Let’s take it one step at a time.

To start, make sure the Master tester has a 9 volt battery plugged into it and it’s powered off. In other words, make sure the switch on the Master device is in the “OFF” position.

Ethernet cable tester with switch off

Now all you have to do is plug each end of the ethernet cable into the tester. Start with the Master device first. Plug one end of the cable into the RJ45 port of the Master device.

Ethernet cable tester master connection

Next, plug the other end of the ethernet cable into the Remote tester device. As I mentioned, if you have a long ethernet cable feel free to detach the Remote device and bring it to the other end of the cable to plug it in.

Here’s an example of what it would look like if I detached the Remote tester.

Ethernet cable tester remote connection

Now that the cable is attached to both ends of the tester, move the switch on the Master device to the “ON” position. When you do, you’ll see the lights numbered 1 through 8 start to light up.

Ethernet cable tester power on

What to expect when testing a cable

The lights numbered 1 through 8 will light up one at a time on both your Master and Remote tester. The lights will light up in order starting with light 1:

Ethernet cable tester light 1
The Master and Remote ethernet cable tester devices with the 1 light lit up

The last light to light up will be light 8. After light 8, the cycle will start over again.

Ethernet cable tester light 8
The Master and Remote ethernet cable tester devices with the 8 light lit up

The 8 lights on the device refer to the 8 copper wires that are inside your ethernet cable. Each copper wire in the cable is individually tested to make sure it’s working properly.

If the cable you’re testing is really long or you can’t bring the two ends of the cable to the same place, you might need two people to verify that the same lights are lighting up on the two test devices at the same time.

When you watch the lights on your tester, it’ll continue testing each copper wire until you turn it off. If you’ve watched the tester test all 8 copper wires and they all light up green at the same time on both tester devices, you know your ethernet cable is in good shape.

However, your ethernet cable has problems if any of the following situations occur:

  • Any of the lights turn red
  • If the same numbered Master and Remote lights don’t light up at the same time (e.g. light 1 on the Master and light 4 of the Remote tester light up at the same time)
  • If any of the lights are “skipped” or do not light up at all during testing (e.g. during the cycle, light 4 on the Master and Remote tester doesn’t light up on the test devices)

If any find any of the situations above while testing your cable, it’s time to find a replacement.

Wrap up

Now that you can tell if an ethernet cable is bad, it makes troubleshooting your network a lot easier. If all your ethernet cables are working properly, you can narrow down the cause of any network connection problems you experience.

The best part is if you find a bad ethernet cable, it’s a quick and easy fix to replace it.

If you have any questions about the above information or you’d like to share your ethernet cable troubles, post a comment below.

If you found this information helpful, here are some other resources that might be useful as well:

Can Ethernet Cables Go Bad?

Does Ethernet Cable Length Affect Network Speed?

How to Tell What Type of Ethernet Cable You Have

Can an Ethernet Cable Slow Your Internet Speed?

Is an Ethernet Cable Faster Than WiFi?

Ross Ricky

Ross Ricky is an engineer and cybersecurity professional who wants nothing more than for you to get the most out of your home network.

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