What is T568B Wiring?

Quick Definition: T568B wiring is a standardized method for organizing the four twisted pairs of wires within Ethernet cables. These wires are arranged in a specific order before they are terminated, ensuring consistent and effective communication between network devices when connected to RJ45 jacks or ports. T568B is commonly used for connecting various network devices, such as computers and switches, in Ethernet networks and plays a crucial role in maintaining uniform cable termination and communication.

The T568B standard creates essential uniformity in how ethernet cables are terminated.  Ethernet cables contain multiple individual wires. Terminating a cable is physically connecting each of those wires to hardware like a RJ45 plug or patch panel jack.

What is T568B Wiring?

T568B is one of two wiring standards established by the Telecommunications Industry Association (TIA) and the Electronic Industries Alliance (EIA). It is a standard that defines the ordering of the four twisted pairs of wires within ethernet cables.

T568B is a more recent standard, developed later than its counterpart, standard T568A.

T568B Explained

Internally, ethernet cables are made up of four twisted pairs of cables. In a T568B cable, these wires are arranged in a specific order before they are terminated. Keeping this order consistent is essential for data to flow across a cable between two devices trying to communicate.

Another standard, T568A, uses a slightly different wire arrangement that is not interchangeable with T568B.

Is TIA/EIA-568B the Same as T568B?

TIA/EIA-568B is the same as T568B.  T568B is just a shorthand version of TIA/EIA-568B.

What Is T568b Most Commonly Used For?

T568B is commonly used anywhere ethernet cables are used to connect two different network devices, like a computer’s NIC to a switch or network patch panel.

How T568B Wiring Works

Ethernet cabling is not complicated, containing only a few essential elements. If you were to cut open a cable, you would find eight individual wires and a plastic insert. Each of the wires terminates to a pin in a connector, and the order as defined by the standard is essential.

T568B Color Code

Ethernet’s four pairs of wires come in four colors: green, blue, orange, and brown. One of each pair will be a solid color; the other is striped with the color and white. The colors are used to maintain the order of the wires when they terminate.

T568B Cable Structure

Along with the four twisted pairs, a cable using T568B also contains a plastic insert, sometimes called a star filler. It helps reduce interference and add density to support the cable and minimize bending. A sheathing covers the wiring and inserts to protect them.

T568B Pin Assignments

Each of the eight wires is terminated to one of the eight pins on an RJ45 connector or patch panel jack. The wires must be terminated in a specific order that complies with either the T568B or T568A standard.

T568B Wiring Configuration

The T568B wiring standard dictates that the wires are arranged in the following order, starting with the first pin on the RJ45 jack: orange/white, orange, green/white, blue, blue/white, green, brown/white, brown. This can be seen easier in the diagram below.

T568B Wiring Diagrams and Examples

This diagram shows the wiring order for T568B as if you were looking down onto an RJ45 connector.

568B Wiring Diagram

T568A Vs. T568B

T568B isn’t the only wiring standard that exists, however. There is also the aforementioned T568A.

What is T568A?

The T568A standard is very similar to T568B, except two pairs are switched: green and orange. T568A wires are in the following order: green/white, green, orange/white, blue, blue/white, orange, brown/white, brown.

Are TIA/EIA 568A and TIA/EIA 568B Interchangeable?

No, these standards are not interchangeable. For example, if you were installing wiring and wired a patch panel with one standard and the network jacks with another standard, the devices connected via that wiring would be unable to communicate. You would essentially be connecting different pins at each end.

As long as you are consistent across all the wiring done in a network, either standard is fine to use. T568A, however, is more common and is recommended by the TIA for residential wiring installations.

Does the US Government Require T568A?

The US government requires all wiring in federal facilities to use T568A. This is for consistency across all facilities, preventing one building from using T568A and another building using T568B.

T568A and Crossover

In the unfortunate situation where the two wiring standards are both used in one network, there is a solution: crossover cables.

What is Crossover and Crossover Cables?

A cable that follows either standard on both ends of the cable is known as a “straight through” cable, as all the wires pass straight through to the same pins on both connectors. 

So what’s the opposite of “straight through?”

That would be “crossover,” where the wires instead are determined using T568B on one end and T568A on the other.

A crossover cable can be used to connect two ports that are wired with different standards. However, they are more commonly used to connect two of the same type of devices together instead of connecting them both to networking hardware like a switch.

How Do Crossover Cables Relate to T568B?

One end of a crossover cable is wired to the T568B standard, and the other end is wired to the T568A standard. The two standards must both be followed for each end of the cable. Otherwise, the devices will not be able to communicate when using a crossover cable in an appropriate situation.

Conclusion

Whether you use T568B or T568A usually comes down to personal preference. The important thing is consistency to ensure solid communication across your network. 

By adhering to one standard, a network admin can ensure every device on their network can communicate reliability with optimal performance.

Learn more about cabling and devices from CBT Nuggets’ training today!