Terminating an Ethernet cable (crimping an RJ45 connector onto the end) is a practical skill for anyone who manages their own network infrastructure. It’s not difficult once you understand the steps, but a poorly terminated cable is a common source of intermittent network problems that can take hours to diagnose. Here’s how to do it properly.
What You’ll Need
- Ethernet cable
- RJ45 connectors (make sure they match your cable category)
- RJ45 crimping tool
- Cable stripper or sharp knife
- Cable tester (strongly recommended)
For Cat6 and Cat6a, use connectors specifically rated for that category. Cat6a cables are thicker and may require pass-through connectors or a specific crimping tool.
Understanding the Wiring Standards: T568A vs T568B
Inside an Ethernet cable are eight wires arranged in four twisted pairs. When you terminate a cable, those wires need to be arranged in a specific order inside the RJ45 connector.
There are two wiring standards: T568A and T568B. The only difference between them is the order of two pairs.
T568B pin order (left to right, with clip facing down):
- Orange/White
- Orange
- Green/White
- Blue
- Blue/White
- Green
- Brown/White
- Brown
T568A pin order:
- Green/White
- Green
- Orange/White
- Blue
- Blue/White
- Orange
- Brown/White
- Brown
Which should you use?
T568A is the common standard in Canada and is used in most commercial installations.
The most important rule is consistency: use the same standard at both ends of every cable, and use the same standard throughout your entire installation. Mixing T568A at one end and T568B at the other creates a crossover cable; which has specific uses but won’t work as a standard network cable.
If you’re adding cables to an existing installation, check which standard is already in use and match it.
Step-by-Step: Terminating the Cable
Step 1: Cut the cable to length
Leave yourself a little extra…it’s easier to trim than to add length later.
Step 2: Strip the outer jacket
Use a cable stripper or a sharp knife to remove approximately 25–30 mm of the outer jacket. Be careful not to nick the inner wires. For Cat6 cables with an internal spline (the plastic cross-divider), remove it by cutting it flush with the jacket.
Step 3: Untwist and arrange the pairs
Separate the four twisted pairs and untwist them just enough to arrange the individual wires. Keep the untwisted section as short as possible. Excessive untwisting degrades the cable’s performance, particularly at higher speeds.
Arrange the eight wires in the correct order for your chosen standard (T568A or T568B), holding them flat and parallel.
Step 4: Trim the wires
Hold the wires flat and trim them to approximately 12–14 mm from the edge of the jacket. They need to be even and long enough to reach the full depth of the connector, but not so long that there’s excess untwisted wire inside.
Step 5: Insert into the RJ45 connector
With the connector’s clip facing down, slide the wires into the connector. Each wire should slide into its own channel and reach the front of the connector. The jacket should enter the connector body by a few millimetres, this is important for strain relief.
Double-check the wire order through the transparent front of the connector before crimping.
Step 6: Crimp
Place the connector firmly into the crimping tool and squeeze fully. The crimping action pushes the metal contacts down through the wire insulation (making electrical contact) and locks the jacket in place.
Step 7: Test the cable
This step is skipped far too often. A cable tester sends a signal through each wire pair and confirms continuity, correct pin mapping, and that there are no shorts or crossed pairs. A cable that looks fine can still have a wiring fault that causes intermittent problems under load.
Basic cable testers are inexpensive and worth having. For structured cabling installations, a certification tester (such as a Fluke DSX) verifies that the cable meets the performance specification for its category, important for any permanent installation.
Common Mistakes
Excessive untwisting. Untwisting the pairs further than necessary to straighten the wires degrades the cable’s ability to reject interference. Keep it to the minimum needed for termination.
Wires not reaching the front of the connector. If the wires don’t extend to the contacts at the front of the RJ45, the crimping tool won’t make a reliable connection. Check before crimping.
Jacket not entering the connector. The outer jacket needs to be gripped by the connector body for strain relief. If only bare wires enter the connector, the termination is fragile and prone to failure.
Not testing. A visual check is not a cable test. Always test with a tester.
Inconsistent standards. Mixing T568A and T568B within an installation causes confusion and potential connectivity issues. Stick to one standard throughout.
Patch Panels and Keystone Jacks
Terminating into a patch panel or wall outlet keystone jack uses a slightly different process, the wires are punched down into IDC (insulation displacement connector) terminals rather than crimped into an RJ45. The same wiring standard applies, and most patch panels and keystones are clearly labelled with both T568A and T568B wire colour sequences.
A proper punch-down tool is worth using, it seats the wire correctly and cuts the excess in one action. Using a screwdriver or pen is a common shortcut that produces unreliable results.