Your Ethernet cable can be damaged and still appear fine. I slowly mutilated one to prove it

Published Nov 9, 2026, 6:00 AM EST Aggy is a veteran writer and editor in the technology and gaming space. Having served as a Managing Editor for high-traffic digital publications, alongside being an editor and consultant for over a dozen sites. Aggy's published work spans a wide and respected array of tech and gaming outlets, including WePC, Screen Rant, How-To Geek, Android Police, PC Invasion, and Try Hard Guides. Beyond editorial work, Aggy's direct experience in the tech sphere extends to app development. Aggy has published two games under Tales and is always eager to learn and do more. He also likes working on computers and researching in his spare time. He knows about Windows, Linux, Audio, Video, and much more. My server kept throwing network errors, and I literally spent hours blaming everything else and trying to get it to work. I looked at the cable. The link light was on, the connection was up, and nothing about that patch cord looked wrong. We treat a cable as either working or dead, but there's a lot of room in between where things limp along and cost you speed. When I took my storage out, the Ethernet cord popped off. It was broken, and I had no idea. A damaged cable can still look fine Your devices will slow down before they give up A beat-up Ethernet cable can keep moving data without any obvious trouble, and that's because data doesn't care how a cable looks, only what's inside. A normal Ethernet cable holds four pairs of twisted copper wires. If you've ever taken any IT class, making an Ethernet cable is probably one of your first big projects. I took IT in high school, and that was a big project at the time. Ethernet cables are actually just those few wires, and everything else is there to protect them. Even the plug housing is there to protect the wires where they meet the port. Ethernet cords permanently installed in walls usually use thicker solid copper, while patch cords use stranded wire since it handles bending better. Every wire has plastic insulation around it, and the whole bundle sits inside an outer jacket. The pairs are twisted at slightly different rates so their magnetic fields cancel out, which cuts interference between pairs. A lot of cables also have a small plastic cross divider running down the center to keep each pair apart. Depending on where it's used, a cable might also have foil or braided shielding around the pairs or around the whole thing. At both ends, the wires land in the familiar RJ45 plug, and keeping those twists right up to the pins really matters for signal quality. When two devices connect, they run a handshake to agree on the fastest speed both can handle. They send quick pulses back and forth and use those to advertise what they support, then settle on a shared speed and mode. If the cable is in bad shape, modern network chips can spot the problem and step down to a slower speed instead of dropping the connection completely. They do this by checking whether signal quality is good enough at the higher rate; if it isn't, they drop it from the negotiation and try the next step-down. It's better than losing your signal, but you won't find out unless you check yourself. That's exactly why a beat-up cable can still show a solid link light. The device only needs to detect basic electrical activity to call the link active. But actually meeting a cable's official category rating means hitting strict signal quality targets across a wide range of frequencies, stuff like signal loss, reflections, and interference between pairs that usually come from a longer cord. When I set up my server, my cable broke without me realizing it, and it took a while to see it had fallen out of the port and was only working because it was nudged in every few seconds. A damaged cable can pass enough signal to light the link and set up a connection while failing all those standards without telling you. I broke a cable one step at a time The link was up while the signal was already failing This experiment started when a normal-looking patch cord caused errors on my server even though the link lights were on. To see how physical damage affects a cable, I took a spare and wrecked it on purpose, one step at a time. I measured after each stage instead of destroying it all at once. The damage went the way rough handling usually goes. I bent it and hit it around. I cut into it on purpose and taped it up. At the end, I even broke the connector to see if I could just hold it in place and have it work. After each stage, I checked the cable. I looked over the negotiated link speed, ran throughput tests, checked packet loss, and watched for errors like CRC failures, alignment issues, and symbol errors. A link being up doesn't mean the cable is fine. Even minor kinks and jacket cuts caused immediate reflections at the damage point, failing the signal return loss standard right away. I was terrified that there would be a spark and something would catch fire, even though I knew that a standard Ethernet cable's voltage is too low to pose any risk (PoE cables do carry some risk of sparking). To be honest, I stopped because of that fear. I've gone too far before and started a few fires. This time it didn't get that far, but it didn't take much to see problems. I'd just replace a damaged Ethernet cable instead of keeping it around. This test has limits you should know about A cable that works today can still cause trouble tomorrow You don't need to beat up a cable to know a damaged one works worse. Still, this was only one cable. Long conduit runs, cable trays packed with other cables, temperature swings, and different switch hardware can all change how damage affects a cable. So this shows damage can hide under the surface, but it can't tell you what's happening with your own cable. I know some people think that if the cable is passing traffic at its negotiated speed without obvious problems, then you shouldn't replace it. If you're looking at whether data is moving right now, a damaged cable can look totally fine. A cable running close to its noise limit becomes unstable. A little extra interference, a burst of heavy traffic, or a warm day can push it into a lot more errors. Instead of clean speeds, the link starts throwing frame errors, and TCP has to resend data, shrink its window, or back off. The link might flap or suddenly drop to a slower speed under load. These problems are hard to track down because ping still works and everything looks fine while your apps slow to a crawl. There's a world in between working great and broken This was one cable, so I can't promise your setup behaves the same way. A new patch cord costs a few dollars, which is cheap when a dying cable is causing your problems. If a link ever acts strange for no clear reason, swap the cable first. It's one of the fastest things to rule out.