Spotting A ‘Fake’ (Or Temperamental) Ethernet Network Cable

I was recentlyre-setting up my home network, and I noticed that all devices in my study were limited to 100 Mbps read/write speeds. This was despite the fact that I have a 500 Mbps up/down package from my ISP,Hyperoptic. So I went looking into this and I tested various ethernet network cables throughout my home, and it turns out that this particular cable was the problem:

I discuss this issue in the following short video, where I demonstrate that my CAT5e cable (that I thought was rated for gigabit speeds) is only hitting 90-100 Mbps:

This video is available to view on:

Post Publishing Comments (What’s Actually ‘Wrong’ With The Cable)

Since publishing the video, there have been some really useful comments – particularly on TikTok. A few people suggested that it isn’t a fake cable after all, and that there are a few other possible causes for the slow speeds:

I dug into all of these interesting suggestions, and it has been a fun journey. It turns out that #2 (bad termination) is at fault here. Here’s a close-up shot of the Ethernet cable’s plug:

As you can see, only 4 of the 8 pins are wired up here (i.e. 2 pairs of 2 wires are in use, not the full 4 pairs). So while this is technically a valid CAT5e cable in some respects (I was wrong to say it was entirely fake in the video), it is not capable of delivering the gigabit speeds that we all expect from CAT5e cables.

Going forward, I will just use CAT6 or CAT7 cables exclusively. While I can also inspect the pins on any CAT5e cables, I had always assumed that “CAT5e = gigabit speeds” and this isn’t the case – interestingly enough. A ‘correct’ ethernet end (for the purposes of achieving gigabit speeds) should look like this:

Technical Info

Where I was wrong (in my video) is that I assumed that the cable was ‘fake’ because it didn’t provide full gigabit speeds. It’s actually the case that it is a valid RJ45 (ethernet) cable as per theANSI/TIA-568 standards, and it complies with 100BASE-TX – a 1995 era IEEE standard. However this standard (and cable wiring) only requires the use of 2 ethernet pairs (4 wires total), which can then only support up to 100 Mbps speeds.

I incorrectly assumed that any CAT5e cable could deliver gigabit (1,000 Mbps) speeds – but I was wrong. Since I want home networking speeds above 100 Mbps, I need cables that support ‘Gigabit Ethernet‘ – which is often the 1000BASE-T variant. This was introduced in 1996 and it superseded the the previous ‘Fast Ethernet’ (100BASE-*) standards.

These new gigabit standards require that all 4 ethernet pairs are used, meaning that all 8 wires of an ethernet cable are wired up at the terminated plug end:

Tristan has been interested in computer hardware and software since he was 10 years old. He has built loads of computers over the years, along with installing, modifying and writing software (he’s a backend software developer ‘by trade’).Tristan also has an academic background in technology (in Math and Computer Science), so he enjoys drilling into the deeper aspects of technology.Tristan is also an avid PC gamer, with FFX and Rocket League being his favorite games.