How to Identify, Verify, and Test an RJ45 Pinout

RJ45 Pin Numbering: How to Orient the Connector

Before you can follow any wiring diagram, you need to know which pin is which. Every RJ45 connector has 8 gold contact pins inside the clear plastic housing. To identify them correctly, hold the connector in this position:

This orientation is universal across all RJ45 documentation, testers, and wiring standards. When you look at a pass-through connector during termination, the wires you see coming out the front should be in order from pin 1 (left) to pin 8 (right) using this same orientation.

This numbering applies to every wiring standard. Once you can identify pin 1 through pin 8, you just need to know which color wire goes to which pin.

T568B Wiring Standard

T568B is the most widely used wiring standard. If you are terminating cable in a commercial building, data center, or home network in the United States, T568B is almost certainly the standard you should follow.

Notice that the transmit and receive pairs are not on consecutive pins. Pin 3 and pin 6 form the receive pair, with pins 4 and 5 (the blue pair) sitting between them. This is not an error - it is intentional. The RJ45 pinout was designed to be backward-compatible with older telephone wiring standards, which placed the first pair on the center pins.

T568A Wiring Standard

T568A swaps the orange and green pairs compared to T568B. It is the standard specified by the U.S. federal government (TIA/EIA-568) and is sometimes used in residential installations. If you are working on a government building or following a spec that calls for T568A, use this table.

The blue pair (pins 4-5) and brown pair (pins 7-8) are identical in both T568A and T568B. The only change is that the green pair moves to pins 1-2 and the orange pair moves to pins 3-6.

T568A vs T568B: Which Should You Use?

Both standards deliver identical Ethernet performance. The difference is purely about which color wires land on which pins. As long as both ends of the cable use the same standard, the cable will work perfectly.

The choice comes down to context:

• T568B is the de facto standard in commercial installations, data centers, and most residential networks. The vast majority of pre-made patch cables, patch panels, and wall jacks ship with T568B diagrams.
• T568A is specified by the U.S. federal government and is required by some local building codes for government and residential construction. It also aligns with the older USOC wiring standard used for telephone systems.
• Consistency is what matters. If you are adding drops to an existing building, match whatever standard is already in place. Mixing T568A and T568B within the same installation creates confusion and increases the chance of wiring errors.

Crossover Cable Pinout

A crossover cable has T568A on one end and T568B on the other. This swaps the transmit and receive pairs so that two like devices (switch-to-switch, PC-to-PC) can communicate directly without a switch between them.

The only scenario where you might still encounter a crossover requirement is connecting legacy equipment that predates Auto-MDI/MDI-X, or certain specialized industrial or embedded devices. In those cases, check the device documentation before terminating.

How to Verify a Pinout with a Cable Tester

A cable tester is the only reliable way to confirm that your termination matches the intended pinout. Visual inspection through a pass-through connector is a good first check, but it cannot catch split pairs or subtle miswires.

What to test

• Wiremap. Verifies that each pin on one end connects to the correct pin on the other end. This catches opens, shorts, miswires, and reversed pairs.
• Split pair detection. Confirms that each pair of pins uses wires from the same twisted pair. A wiremap test alone does not catch split pairs.
• Continuity. Ensures there are no open (disconnected) pins or intermittent connections.
• Length. Measures cable length and can identify the distance to a fault, which helps locate where a problem is along a long run.

Testing workflow

After terminating both ends of the cable:

1. Plug one end into the tester's main unit and the other into the remote.
2. Run a wiremap test. All 8 pins should show a direct 1-to-1 mapping with no crosses, opens, or shorts.
3. If your tester supports split pair detection, run that test next. Even if the wiremap passes, a split pair will cause crosstalk problems at higher speeds.
4. For critical infrastructure, run a length measurement to confirm the cable is within the 100-meter maximum for Ethernet.

Recommended Testing Tools

The right tester depends on the scope of your work. For occasional terminations, a basic wiremap tester is sufficient. For professional installations requiring documentation, invest in a tester that generates reports.

Common RJ45 Pinout Mistakes

Most wiring failures come down to a handful of repeatable errors. Knowing what to watch for eliminates the majority of rework.

Reversed pairs

The solid and striped wires within a pair are swapped. For example, orange goes to pin 1 and white/orange goes to pin 2, instead of the correct order. This reverses the polarity on that pair. Most modern switches can compensate for a single reversed pair, but it degrades signal quality and should be fixed.

Split pairs

This is the most dangerous mistake because it often passes a basic wiremap test. A split pair occurs when pin continuity is correct but the wires come from different physical twisted pairs. For example, pin 1 uses white/orange (correct) but pin 2 uses white/green instead of orange. The wiremap shows pins 1 and 2 connected, but the two wires are not twisted together, so they act as an antenna instead of a balanced pair. The result is severe crosstalk that kills performance at gigabit speeds and above.

Wires not fully seated

If a conductor does not reach the front of the connector before crimping, the contact blade cannot pierce the insulation and make contact with the copper. This is the most common reason for open pins on a wiremap test. With pass-through connectors like the EZ-RJ45, you can visually confirm that all 8 wires extend through the front before crimping, which virtually eliminates this problem.

Mixing T568A and T568B on the same cable

If one end is wired T568A and the other is T568B, you have created a crossover cable. This used to cause link failures, but modern Auto-MDI/MDI-X handles it automatically. Still, it creates confusion for the next person who works on the cable and should be corrected.

Connectors and Tools for Clean Terminations

Getting the pinout right is easier with connectors that let you verify wire order visually before you crimp. Pass-through connectors are the standard for this reason - the wires extend through the front of the connector so you can confirm the color sequence before committing.