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My MacBook pulled down 800+ Mbps on speed tests, but the smart TV I’d hardwired in my great room couldn’t break 90 Mbps no matter what I tried. I spent weeks convinced the TV had a crappy network adapter. Nope, it turns out one of the Ethernet cables our home builder’s subcontractor ran during construction was Cat5—not Cat5e or Cat6—and it was choking everything connected through that run. I spent 10 minutes running and crimping a new Cat6 cable to fix the whole thing.
My wired speeds made no sense
Same network, wildly different results
My network setup isn’t exactly basic. I’ve got a Ubiquiti Dream Machine handling routing duties, multiple Ethernet runs throughout the house, and 1,200 Mbps internet service. When I optimized my Wi-Fi channels a while back, my wireless performance got way better. But the wired connections should’ve been even faster—that’s kind of the whole point of running cable. My setup in the great room has one Ethernet wall plate behind the TV. I added a mini Ubiquiti network switch so I can have both my PS5 and TV hardwired to the router.
Most of my hardwired devices elsewhere in the house were hitting 750–850 Mbps on speed tests. That’s totally reasonable given some overhead. But the cable for the smart TV and PS5 in our great room maxed out around 90–95 Mbps on a good day when I used my tester on it and checked my Ubiquiti app. Before that, I rebooted the TV and PlayStation probably a dozen times and power cycled the network switch. I even did a factory reset to the network adapter thinking maybe some settings got corrupted. Nothing changed.
My breakthrough came when I dug a spare Ethernet cable out of a drawer and connected it to the same port on my Ubiquiti router. I wanted to completely rule out the TV, PS5, and mini switch as the problem. It got to 780 Mbps just like that. It was the same port as the TV, same network, and same everything—except the cable. The in-wall cable running to that location was clearly the issue, but at that point, I was thinking the cable was damaged.
Ethernet cables aren't all created equal
Cat ratings determine maximum speeds
Credit: Unsplash
In case you don’t already know this—Ethernet cables have hard speed limits based on the type. If you look at any Ethernet cable, there’s a «Cat» rating printed along the jacket. Cat5 cable maxes out at 100 Mbps, which seemed fast when we were all excited about getting off dial-up but doesn’t cut it anymore. Cat5e pushes that up to 1Gbps, so it handles gigabit connections fine. Cat6 goes higher still, up to 10Gbps on shorter runs, and it maintains gigabit speeds reliably even on longer ones. Cat6a and Cat7 exist, too, but those are more than most people will ever need at home.
The part that bit me: your slowest cable determines the speed for that whole connection. I’ve heard people compare it to highway lanes, and that’s basically right—doesn’t matter if you’ve got six lanes for most of the drive when everything grinds to a halt at that one spot where it narrows to a single lane. My router, network switch, PS5, and TV support gigabit. But one Cat5 cable in the chain forced everything down to 100Mbps, and 90-something Mbps is about what you actually get after protocol overhead.
When I crimped my own Ethernet cables for the basement network project a year or two after we moved in, I specifically bought Cat6. I knew those cables were good. But I’d never actually verified all the cables my builder’s contractor installed on the main floor during construction a few years prior.
Finding the bottleneck cable
The jacket tells you everything
For the most part, you can’t eyeball the difference between Cat5 and Cat6 cables just by looking at them. The RJ45 connectors are identical. The cable thickness is basically the same. But every Ethernet cable has its rating printed right on the outer jacket—usually something like «CAT5E» or «CAT6 UTP» repeated every foot or so along the length.
I went down to the basement, where all my cable runs terminate, and started tracing. The cables I’d run myself were obviously Cat6—I bought the spool and crimped every connector. But I never checked the cables the contractor had done on the main floor during our build. Most of them were clearly marked Cat6 on the jacket. But the run going to the great room wall plate location had a plain old «CAT5» printed on the cable. There was no «e» after it, just Cat5.
My theory is the contractor got to the end of the job and ran out of Cat6, so he finished up with whatever random cable he had in his truck. I mean, I get it—deadline’s coming, the homeowner definitely isn’t going to inspect every cable jacket, and once it’s in the wall nobody can tell the difference anyway. I’m still annoyed by it, though. That one lazy choice meant I’d been stuck at a fraction of my actual internet speed since we moved into the house. The cable technically worked. It just couldn’t do gigabit.
The 10-minute fix that unlocked gigabit speeds
Replacing one cable changed everything
Luckily, I had part of a Cat6 spool sitting in the basement from when I wired down there, so this wasn’t going to cost me anything. I measured from my basement router location to the wall plate—roughly 23 feet. I grabbed my crimping tool, cut a fresh piece, and put a connector just on the router end for now (it’s easier to snake this way). The trick was taping the new Cat6 to the old Cat5 before pulling it out up from the wall plate location.
Once I got the new cable routed and the old one out, I crimped the wall plate end of the new Cat6 cable. Then, I checked the speed with my tester—750+ Mbps. The same wall plate couldn’t crack 95 Mbps an hour earlier. All because of one subpar cable I’d never thought to check.
I spent the next hour verifying every other contractor-installed run in the house, reading jacket labels with a flashlight in the basement ceiling. I had no other Cat5 surprises, thankfully—just that one lazy substitution. While I was at it, I finally cleaned up the cable management around my network rack—something the internet had been bugging me about for a while, anyway.
A $5 cable might be your gigabit bottleneck
A corner-cutting contractor cable held my entire great room connection hostage at 100Mbps while I blamed the TV, PS5, the switch, and pretty much everything except the actual problem. If you’re paying for gigabit and certain wired devices seem weirdly slow, don’t immediately assume the hardware is bad or start shopping for replacements. Check your cables first. You’re looking for «CAT5» printed on the jacket—specifically without the «e» after it. Pay extra attention to any cables installed by contractors during construction, even in new builds. Replacing a Cat5 cable with a Cat5e or Cat6 might cost you $15–$20 at most, and it could be the difference between getting the 100Mbps you’re getting now, and the gigabit speeds you’re actually paying for.
