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In planning an Ethernet network, the first choices you will make when laying cable are as follows. There are two cabling standards for Ethernet cables, the most common being T568A and T568B. While both standards serve the same purpose (connecting devices such as computers, routers, and switches via twisted-pair cables), the pinouts for the RJ45 connectors are different.
In this blog, we’ll analyze the differences between the T568A and T568B, discuss when to use both networks, and answer some frequently asked questions to help you make the best choice for your network.
What Are T568A and T568B?
T568A and T568B are the Telecommunications Industry Association (TIA) cabling standards for Ethernet cables such as Cat5e or Cat6. These standards define the pinout of the eight wires of a twisted pair of Ethernet cables connected to an RJ45 connector.
Here’s a comparison of how the wire pairs are arranged in each standard:
| Pin Position | T568A Wire Color | T568B Wire Color |
|---|---|---|
| 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 |
As you can see, the main difference between the two is the order of the wire pairs. T568A starts with the green pair (Pins 1 and 2), while T568B begins with the orange pair (Pins 1 and 2).
Key Differences Between T568A and T568B
- Pair order: The only physical difference is the ordering of the green and orange wire pairs. T568A places the green pair on pins 1-2 and the orange pair on pins 3-6; T568B flips this.
- Performance: Both standards support identical Ethernet speeds and reliability. Choosing one or the other has no impact on network throughput, as long as each cable is terminated the same way at both ends.
History and Usage
- T568A: Provides backward compatibility with legacy telephone (USOC) wiring and is common in government or older installations. It was the original preferred TIA scheme (for example, U.S. federal contracts specify T568A).
- T568B: Derived from the AT&T 258A color code and has become the default scheme for most new Ethernet installations in the U.S.. Today, T568B is widely used in commercial and residential networks, whereas T568A mainly appears in older or specialized systems.
Which Wiring Standard Should You Use?
So, how do you choose between T568A and T568B? Well, it depends on a few factors:
1. Existing Network Setup
If you are expanding an existing network, follow the cabling standards being used. Using T568A with T568B may cause signal interference or slow download and upload speeds.
2. New Network Installation
T568B is usually the safer choice if starting over (this standard is more commonly used in the United States). T568A is acceptable for government facilities or networks that use older telephone systems.
3. Backward Compatibility
The T568A is preferred if compatibility with older telephone systems (USOC lines) is required; however, most modern network equipment supports both standards, so backward compatibility is no longer an issue today.
4. Network Performance
The good news is that both standards enable your network to perform equally well. However, you will get the same data speeds and performance if you configure only the T568A or T568B, with similar routing at both Ethernet cable ends. …… You will get the same data speeds and network reliability.
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Straight-Through vs. Crossover Cables
In most cases, you will use straight-through cables to connect devices such as a computer to a router or a switch to a router. These cables are wired the same way at both ends, either T568A or T568B.
However, crossover cables connect similar devices (such as a computer to a computer or a switch to a switch). Crossover cables use the T568A on one end and the T568B on the other to “crossover” the transmit and receive pairs to establish the correct connection.
But here’s a helpful hint: Most modern network devices now support Auto MDI-X, which automatically detects and adjusts the connection type. This means that crossover cables are not as necessary as they once were!
How to Identify T568A vs. T568B
- T568A: When looking at the RJ45 plug with the clip down, the first pair of wires (pins 1-2) will be white/green and green.
- T568B: The first pair of wires (pins 1-2) will be white/orange and orange.
In addition, you can check the wiring sequence with a cable tester.
Frequently Asked Questions (FAQ)
Q: What’s the difference between T568A and T568B?
They use the same pinouts except that the green and orange pairs are swapped between the two schemes.
Q: Can I mix T568A and T568B in the same network?
No. Mixing them on one cable will cause pin mismatches and link failures. Use only one standard throughout your network.
Q: Which standard is more common in the US?
T568B – it’s used in the vast majority of modern U.S. networks.
Q: Do T568A and T568B affect network performance?
No – they deliver identical Ethernet speeds and reliability.
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Conclusion
When choosing between T568A and T568B, the single best advice is: pick one scheme and be consistent. Either standard delivers the same electrical performance, so consistency matters most. If you’re extending an existing network, simply match its wiring. For new installations, many installers default to T568B (especially in the US) because it’s common in modern equipment. In any case, wiring all cables to one standard end-to-end will keep your network reliable and trouble-free.
Apple Liu is Romtronic’s Marketing Manager, focusing on business growth across the Asian market. With a background in International English and eight years of sales experience in the electronic cable and harness industry, she brings both in-depth industry knowledge and a global outlook to her role.
In addition to leading market strategy, Apple also oversees content development and editorial work—crafting clear, engaging messaging that reflects Romtronic’s values and technical strengths. She is passionate about digital engineering and is committed to strengthening Romtronic’s brand presence and innovation in a competitive global landscape.
