What those orange, blue, and green wires inside an Ethernet cable actually do

I started crimping my own Ethernet cables when I moved and tackled my basement networking project. Each CAT6 Ethernet cord contains eight colored wires inside—and they’re not decorative. During my first attempts, I wired several connectors completely backwards. My cable tester caught every mistake, which made me interested in learning what each wire actually does and why the order is so important. Get those twisted copper pairs wrong, and you might end up with no network connection, or your speeds will crawl compared to what you should be getting.

What each wire pair actually does

Understanding transmit and receive signals​​​​​​

Here’s how the wire pairs in a CAT6 Ethernet cable break down by function:

The orange pair traditionally handles transmitting data, while the green pair handles receiving. In older 100Mbps networks, blue and brown pairs sat idle. Once you jump to Gigabit speeds, all four pairs activate and become bidirectional.

Each pair uses differential signaling—one wire carries a positive signal while its partner carries the negative version. The receiving device reads the difference between these signals, which cancels out the interference both wires picked up along the way.

Eight wires work in four pairs

Each color pair handles different data signals

Credit: David Jancik/Shutterstock

Pop open an Ethernet cable. Inside you’ll find those four twisted pairs: orange, green, blue, and brown. A solid-colored wire pairs up with a white wire that has colored stripes (orange with white-orange, green with white-green, and so on). They’re twisted together to cut down on electromagnetic interference, screwing up your data.

Modern Gigabit Ethernet uses all four pairs transmitting data simultaneously. Back with 100Mbps networks, only two pairs did any work—orange and green—while blue and brown sat there unused. Differential signaling is why they’re twisted as pairs. Each wire carries the opposite version of the same signal, and the receiving end reads the difference to filter out interference.

Each pair gets twisted at a different rate, too, which stops them from interfering with each other inside that tight cable space.

The T568B wiring standard most people use

Why pin order matters for your network

The T568B standard arranges pins like this: white-orange, orange, white-green, blue, white-blue, green, white-brown, brown. With my backwards connector, I simply had the connector in the wrong orientation when I pulled the wires through. My cable tester let me know something was wrong right away.

T568A exists as another standard, but pretty much everyone uses T568B for home and office installs. Your cable ends need to match each other, unless you’re building a crossover cable on purpose—and that’s pretty uncommon now since modern equipment figures out the connection type automatically.

Get the order wrong, and you’ll either see no connection or experience weird intermittent failures—this happened with my new Mac Mini. That cable tester I bought with my crimping kit saved me hours of frustration by showing exactly which wires were out of place.

These aren’t just copper wires

Construction details that affect performance

The cable on my 1,000-foot spool were solid cooper wires. But those patch cables I’d bought previously had stranded copper. There’s a reason for the difference—solid wire works better when you’re installing it permanently in walls, and stranded wire can bend over and over without breaking, which is exactly what you need for patch cables.

Wire gauge makes a difference. The 23 AWG wire in my Cat6 cable is thicker than the 24 AWG you’ll find in Cat5e. That extra thickness means you can run longer cables and push higher speeds through them. The insulation quality directly affects crosstalk between pairs.

Cat6 cables usually have a plastic spine down the middle, keeping the pairs separated. Cat5e just twists the four pairs together without that spine. Cat6a takes things up another notch with better shielding and tighter twist rates to handle 10 Gigabit speeds.

The outer jacket does more than hold everything together. Plenum-rated cable can go in air handling spaces, while direct burial cable can go underground. Some cables add foil or braided shielding for environments with heavy electromagnetic interference..

When wire order goes wrong

Symptoms of incorrectly crimped cables

My backward connector was an obvious failure—no lights, no connection, nothing. The smart TV I connected it to didn’t register any network connection. I also made a couple where I’d swapped the green and orange pairs by accident. Those caused weird issues because they’d run fine at 100Mbps but started acting flaky when I needed Gigabit speeds.

Mix up the solid and striped wires in a pair, or stick entire pairs in the wrong positions, and you’ll have a problem​​​​​. Sometimes the connection drops out of nowhere, even though it was working fine seconds earlier. Other times, you’re stuck at 100Mbps when you should be hitting 1,000Mbps.

My cable tester became essential during my learning process. It shows exactly which pins have continuity and which don’t. Professional installers use certification testers costing hundreds of dollars, but a basic $20–$30 tester catches most crimping and wiring errors.

You can get physical crimp failures even with a perfect wire order. Wires that don’t reach all the way to the connector’s end, or crimps that don’t punch through the insulation right—both cause intermittent problems or complete failures.

Every wire pulls its weight

Why this knowledge actually matters

Understanding what’s inside an Ethernet cable helped me become a better cable crimper. But it’s useful beyond just making your own cables. When you’re troubleshooting network issues, knowing you need all four pairs for Gigabit speeds helps diagnose problems faster.

It helps when buying pre-made cables, too. You can spot quality differences and understand why cheap cables might not deliver the speeds you’re paying for. You’ll know why you can’t splice Ethernet cables together like a lamp cord—those twisted pairs need to stay twisted and properly terminated.

When running cables through walls, understanding what you’re protecting makes you more careful about maintaining a bend radius and avoiding sharp staples. It explains why Power over Ethernet (PoE) works with your devices by using unused pairs in older standards, or how newer PoE standards share power across all four pairs while transmitting data.

Color is important

Ethernet cables have eight wires doing specific jobs—you can’t mix up the order and expect it to work. Learning what they do helped me stop making dumb mistakes that wasted time and burned through connectors. You need the twisted pairs in the right position, crimped in the right order, or you’ll never achieve your gigabit speeds. Making your own cables or troubleshooting flaky connections—either way, knowing what’s packed in that cable helps. I handle Ethernet cables with more care now that I know how the original designers chose those colors and wire positions.