Your home's pre-wired Ethernet might be sabotaging your internet speed—here's how to test it

If you moved into a new home with pre-wired Ethernet and noticed your internet speed doesn't match your plan, the problem might not be your ISP, router, switch, or other networking gear. Sometimes, the wiring itself is to blame.

Your Ethernet network might be using outdated cables

Cat5 cables could be the weak link

If you're living in an older house, there's a chance its Ethernet wiring uses Cat5 cables , which are only rated for 100Mbps. That said, a quality Cat5 cable should be able to deliver near-gigabit bandwidth over relatively short distances, but if a cheap option was used for your home wiring, your internet woes might be caused by cheap Cat5 wiring.

The best course of action is to test the cables, but cable testers that measure bandwidth (not just continuity) cost a pretty penny. What you could do instead is connect two computers to two wall Ethernet ports (one to the port where your router is connected and another to the port where you've noticed slow speeds), then use a tool like iPerf or NetIO-GUI to measure throughput.

If you're getting speeds that match or exceed your internet plan, the cables are likely fine, even if they're Cat5. If not, the wiring may need to be replaced. I recommend opting for Cat6 cables since they are relatively affordable and rated for 10Gbps. If your Ethernet wiring is newer than Cat5 and you still have bandwidth issues, a cable or an Ethernet wall outlet might be damaged.

Damaged cables may slow the entire network down

Or perhaps RJ45 wall outlets, which are more fragile than the cables themselves

Standard round Ethernet cables are quite durable. They use four twisted pairs of copper wires to reduce interference and maintain signal integrity, with high-quality cables including additional shielding to resist electrical noise. I used a beat-up Ethernet cable for years in my previous apartment, with its outer jacket torn, and some internal wires exposed, and it still delivered the full 500Mbps of my internet plan.

But when it comes to in-wall wiring that runs throughout a house, certain cables may be damaged enough to cause issues. A cable could be stapled through, sharply bent, or have a damaged outer jacket or insulation, any of which can degrade performance. It's not common for Ethernet cables to degrade to the point of noticeably reducing bandwidth, but these things do happen.

On the other hand, there's a higher chance that the RJ45 terminations are the culprit. For example, if only two wire pairs (four wires) are properly terminated instead of all four pairs (eight wires), the link speed may be limited to 100Mbps. Poor or inconsistent termination can also cause instability. In some cases, one or more wires may have come loose from a wall port, or the outlet itself may be worn out after years of use.

If you've visually inspected each outlet and didn't find any issues, the next step is to test them with a basic continuity cable tester. These are inexpensive and can quickly verify whether each wire is properly connected. If you discover that defective wall jacks are causing slowdowns, you can reterminate the cables with a crimping tool or outright replace the faulty Ethernet wall outlets.

If your home wiring uses a patch panel, you should check it as well. Perhaps some cables connected to it are damaged or have loose connections, or the wiring itself is damaged if you've got a punch-down patch panel.

Flat Ethernet cables might be the culprit

Easy to use, but frail and with poor shielding

Flat Ethernet cables are much easier to use than thick, round ones because they're more flexible and can be routed throughout the house more easily. But their slim design, which often forgoes shielding and typically uses a parallel wire layout, makes them more prone to picking up electromagnetic interference, as they can act like small antennas. This can result in dropped packets and reduced speeds.

They're also physically more fragile and can be easily damaged by bending or stapling, unlike regular Ethernet cables, which can take a beating and keep working as if nothing happened.

They're fine as short patch cables between a wall outlet and a client device, but they're a poor choice for in-wall runs or wired backhaul. If your home Ethernet is built with flat cables, there's a chance they're contributing to slow or unstable speeds.

If you can't upgrade the wiring, there are alternatives

If Cat5 cables are indeed what's dragging down your internet, the best course of action is to upgrade the wiring. But that's easier said than done, especially in larger homes with extensive cabling. One option is to upgrade only the runs connected to the wall outlets you actually use and leave the rest as-is.

If your house has a coax network alongside pre-wired Ethernet, you can use MoCA adapters to run wired Ethernet between rooms with coax wall ports. MoCA adapters are relatively affordable, and current standards can reach speeds up to 2.5Gbps, which is more than enough for gigabit internet.

Another option is a mesh Wi-Fi system. It won't match wired Ethernet, but if your in-wall network is in bad shape, you can't upgrade it, and you don't have usable coaxial cabling, mesh Wi-Fi is likely your best fallback.