Ethernet Cable Colour Code: T568A vs T568B Wiring Explained

If you have ever crimped your own network cable, you may know the feeling: you plug it in and the switch light stays dark, or the link comes up at 100 Mbps even though both devices support Gigabit. In most cases the cable and the hardware are fine. The problem is that the wires are in the wrong order, or the RJ45 plug was not crimped properly.

This guide covers the RJ45 color code from start to finish: the eight wire colours, the T568A and T568B standards, when to use a straight-through or crossover cable, how to terminate a plug step by step, and how to test it. If you are planning cabling for a whole office or factory and want it done to standard from day one, take a look at our network installation for offices and factories.

The Eight Wire Colours in an Ethernet Cable

A standard UTP cable (Cat5e, Cat6 or Cat6A) contains eight copper wires twisted into four pairs. Each pair has one solid-coloured wire and one white wire striped with the same colour:

• Orange pair: orange and white/orange
• Green pair: green and white/green
• Blue pair: blue and white/blue
• Brown pair: brown and white/brown

The twists are there to cancel interference between wires (crosstalk). That is why it is not enough to get all eight colours into the plug. The two wires of each pair must land on the pins that the standard treats as a pair.

To number the pins, hold the RJ45 plug with the copper contacts facing you and the locking clip underneath. Pin 1 is on the far left and pin 8 is on the far right.

T568A vs T568B Wiring

There are two wiring standards, T568A and T568B. They perform exactly the same. The only difference is that the orange and green pairs swap places.

Pin	T568A	T568B
1	White/green	White/orange
2	Green	Orange
3	White/orange	White/green
4	Blue	Blue
5	White/blue	White/blue
6	Orange	Green
7	White/brown	White/brown
8	Brown	Brown

The blue pair (pins 4–5) and the brown pair (pins 7–8) are the same in both standards. The pairs that swap are on pins 1–2 and 3–6. Pins 3 and 6 are where most mistakes happen, because they belong to the same pair but are not next to each other.

Which one should you use? Either, as long as the whole building uses one standard for plugs, keystone jacks and patch panels. Many business networks use T568B as their default, while T568A tends to appear where a project specification calls for it. Whatever you choose, write it into the network documentation so whoever maintains the system later can follow it.

Straight-Through vs Crossover: When to Use Each

• Straight-through: both ends use the same standard (B–B or A–A). This is what you use to connect computers, IP cameras, access points and printers to a switch or router, which covers almost every job.
• Crossover: one end is T568A and the other is T568B. It used to be needed to connect two similar devices directly, such as PC to PC or switch to switch.

Today almost all network equipment supports Auto MDI-X, which swaps the transmit and receive pairs automatically, so crossover cables are rarely needed. Gigabit ports also use all four pairs, so a straight-through cable is the safe choice for normal installations.

How to Terminate an RJ45 Plug

What you need

• Network cable of the grade you need, for example Cat6
• RJ45 plugs that match the cable grade and type (solid or stranded). Use Cat6 plugs with Cat6 cable.
• A crimping tool and a cable stripper or knife
• Strain-relief boots, if you want a neater finish and fewer broken clips
• A cable tester

Steps

1. Slide the boot onto the cable first. This is the step people forget.
2. Strip about 2–3 cm of the outer jacket, taking care not to nick the insulation of the inner wires.
3. Untwist only as much as you need, then arrange the wires in your chosen order (for example T568B) and flatten them.
4. Trim the ends straight so they fit the plug, leaving the outer jacket long enough to sit inside the plug.
5. Push the wires in until every copper end reaches the front of the plug. Check the colours again before crimping.
6. Crimp firmly so all eight contacts are pressed down and the rear latch grips the outer jacket.
7. Terminate the other end with the same standard, then test.

Do not untwist the pairs too far. Common cabling practice is to keep the untwisted length to around 13 mm (half an inch) at the termination. The longer the untwisted section, the more crosstalk you get, especially on Cat6 running at high speed.

Testing the Cable After Termination

Do not pull the cable into the ceiling or trunking until it has passed a test. Simple ways to check:

• A basic LED cable tester: connect both ends and the lights should run 1 to 8 in step. A light that stays off means that wire has no contact. Lights out of order mean the colours are wrong.
• Plug it in: check the negotiated link speed on the computer or in the switch interface. If both sides support 1 Gbps but the link shows 100 Mbps, one or more pairs is usually not connected.
• Project work: for large building or factory installations, test with equipment that produces a report, so you have proof of cabling quality.

Also remember that a copper Ethernet channel should not exceed 100 metres, including the patch cords at both ends. For links between buildings or longer runs, fiber optic is usually the better choice.

Common Problems Caused by Bad Terminations

• Split pairs: all eight colours are in the plug, but not in matching pairs. A basic tester may pass the cable, yet in use it is slow, drops out or shows high error counts.
• Outer jacket not inside the plug: the latch grips only the thin inner wires, so the cable loosens and fails when it is pulled or moved.
• Wrong plug for the cable: plugs for stranded and solid cable have different contacts. The wrong type may work at first, then become intermittent.
• PoE devices unstable: IP cameras and access points powered over the cable need every pair terminated well. A poor contact can make them reboot on their own.
• Mismatched standards by accident: for example, the plug at one end is wired A while the patch panel at the other end is wired B, giving you a crossover instead of a straight-through link.

If the cabling checks out but the internet is still slow, the problem may be elsewhere in the network. See What Causes Slow Internet?, and once the network has many users and devices, segmenting it with a VLAN keeps it organised and more secure.

When to Call a Network Installer

Crimping one or two cables for a home or a desk is easy to do yourself. For the jobs below, having a team that designs and installs networks for a living pays off over the life of the system:

• New cabling for a whole office, hotel or factory, from dozens to hundreds of points
• Rack cabinets with labelled patch panels and cabling documentation
• Many IP cameras, WiFi access points or other PoE devices
• Runs longer than 100 metres or links between buildings, where fiber should be part of the design
• Network segmentation (VLANs) and security such as a firewall

Systems Connect designs and installs business network systems, from the site survey, cabling and standard terminations to rack work, equipment configuration and testing before handover.

FAQ

What is the correct RJ45 colour order?

Both T568A and T568B are correct. For a straight-through cable, use the same standard at both ends, and keep one standard across the building.

The colours are wrong but the cable works. Can I leave it?

It is better not to, especially if the order splits a pair. The link may work at low speed but will produce errors under heavy load or with PoE. Re-terminate it to standard.

Can I use Cat5e RJ45 plugs on Cat6 cable?

It is not recommended. Cat6 conductors are thicker and the cable often has a central spline, so use plugs made for Cat6 to get a proper fit and contact.

Do I need a crossover cable to connect two switches?

Most modern equipment supports Auto MDI-X, so a straight-through cable works. Check the specifications of older equipment first.

Need structured LAN cabling or a full network installation? Contact us: 📞 Call 033-265-438 or 096-246-2324 📱 LINE: @Nicesystem 🔗 Service details: Network installation in Pattaya, Chonburi and Rayong