Make a network cable: proper instructions
What you are making
A straight-through Ethernet patch cable: the same wiring order at both ends. It is used to connect a computer, switch, router, access point, printer or similar network device. It carries low-voltage data, but it may also carry Power over Ethernet (PoE), so do not work on a live cable connected to network equipment.
Choose the right cable first
The connector may look the same, but the cable category and the connector must suit the speed, length and environment. Do not buy a random drum and random plugs.
| Type | Practical use | Simple advice |
|---|---|---|
| Cat5 | Old 100 Mbps installations | Do not buy it for a new job. |
| Cat5e | Gigabit Ethernet up to 100 m | Usually enough for a normal home or office run. |
| Cat6 | Gigabit Ethernet up to 100 m; 10 Gigabit on shorter runs | A sensible upgrade if you are installing new cable. |
| Cat6A | 10 Gigabit Ethernet up to 100 m | Thicker and less flexible, but the right choice for a full 10 Gb run. |
| Cat7 / Cat8 | Specialist or data-centre applications | Do not pay for the label unless you know the equipment and standard require it. |
For an ordinary loose lead between equipment, stranded-core patch cable is flexible and resists repeated bending. Solid-core cable is normally for fixed runs in walls, trunking or ceiling space; terminate it into a proper jack or patch panel rather than repeatedly bending an RJ45 plug directly onto it.
Shopping list
- Cat5e, Cat6 or Cat6A cable of the correct type and length.
- RJ45 plugs labelled for that exact cable category and conductor type: stranded or solid.
- An RJ45 crimping tool that matches the plugs.
- A cable jacket stripper or a small, sharp cutter.
- An Ethernet cable tester with a wire-map function.
- Optional strain-relief boots, labels and a spare plug or two.
Do not substitute an 8P8C/RJ45 plug designed for stranded cable onto solid cable, or the other way around. The contact teeth are different. It can appear to work initially and then fail intermittently.
Pick a wiring standard
For a normal patch cable, use one standard at both ends. T568B is common in existing UK installations; T568A is also valid. There is no speed advantage to either. The problem is mixing them by accident.
| Pin | T568B colour | T568A colour |
|---|---|---|
| 1 | White/orange | White/green |
| 2 | Orange | Green |
| 3 | White/green | White/orange |
| 4 | Blue | Blue |
| 5 | White/blue | White/blue |
| 6 | Green | Orange |
| 7 | White/brown | White/brown |
| 8 | Brown | Brown |
When checking a plug, hold it with the gold contacts facing you and the latch facing away from you. Pin 1 is on the left. Stop and re-check this orientation before crimping; reversing it is one of the easiest mistakes to make.
Make the cable
- Measure sensibly. Leave enough slack for moving equipment, but do not coil metres of spare cable tightly behind a desk.
- Cut square. Use cutters that leave the end flat. Slide a strain-relief boot on now if you are using one.
- Strip only the jacket. Remove roughly 25–30 mm of outer jacket. Do not nick the insulation on the individual wires; a nick becomes a future break point.
- Keep the pairs twisted. Untwist only the final short section required to arrange the wires. The twists are part of how the cable rejects interference.
- Arrange the eight conductors. Put them in your chosen T568A or T568B order. Flatten them gently between finger and thumb, then trim the ends evenly so they are the same length.
- Insert fully. Push the conductors into the plug until every wire reaches the front. The cable jacket, not only the individual wires, must sit under the plug’s strain-relief tab.
- Inspect before crimping. Look through the clear plug. Confirm the colour order, that all eight conductors reach the nose, and that the jacket is inside the plug.
- Crimp once, firmly. Put the plug fully into the correct tool position and squeeze the handles completely. Do not half-crimp or repeatedly squeeze a doubtful plug.
- Repeat the same standard at the other end. A normal patch cable is T568A-to-T568A or T568B-to-T568B.
Test it before trusting it
Plug each end into the cable tester. A basic tester should show pins 1 through 8 in order at both ends. Test before routing the cable behind furniture or through trunking.
- Open: one number is missing. A conductor did not reach the contact or was not pierced.
- Short: two conductors are touching. Cut off and redo the plug.
- Reversed or crossed: the colours are in the wrong order at one end.
- Split pair: continuity may look plausible, but a pair has been incorrectly matched. This can cause unreliable links or a link that falls back to a slower speed. Use a tester able to identify it where possible.
After the wire-map test, connect the cable to actual equipment. Check the link lights and confirm the negotiated speed in the operating system or switch interface. If you expected 1 Gb or 10 Gb but get 100 Mb, assume the cable or termination is wrong until proven otherwise.
Pitfalls to avoid
- Using a plug that does not match the cable’s conductor type or diameter.
- Untwisting too much of each pair at the plug.
- Leaving the cable jacket outside the plug’s strain relief.
- Using pliers instead of a proper crimping tool.
- Running Ethernet parallel and very close to mains cable for a long distance. Cross mains cable at right angles where routes meet and use appropriate separation.
- Putting a tight kink, staple, knot or crushing bend into the cable. Keep bends broad and gentle.
- Assuming a lit link proves the cable is good. A bad cable can still link at a reduced speed or fail only under load.
Best practice
- Use factory-made patch leads where a standard length will do; hand-made leads are best reserved for a custom length, repair or learning exercise.
- For a permanent run, use solid cable terminated to wall jacks or a patch panel, then use short flexible patch leads at each end.
- Label both ends with where the cable goes.
- Keep the wiring standard consistent throughout the installation.
- If the cable will carry PoE to an access point or camera, use known-good cable, correct terminations and equipment rated for the intended power.
When it is finished
You should have a cable that passes its wire-map test, gives the expected link speed, and has no exposed copper, tight kinks or loose strain relief. Keep one failed plug as a reminder of what to inspect next time; cutting it open is a useful way to see whether the conductors actually reached the contacts.