RJ45 Pinouts and Wiring Standards (T568A/B)
What is an RJ45 Connector?
Definition: The RJ45 connector is an 8-pin modular plug used to terminate twisted-pair Ethernet cables (Cat5e, Cat6, etc.) for network connections.
Physical Characteristics: It features 8 wire slots, a clear plastic body, and a locking tab to secure it into Ethernet ports on switches, routers, and computers.
Example: John uses RJ45 connectors to terminate both ends of his Cat6 cables connecting PCs to switches.
Pin Numbering and Layout
Holding the RJ45 connector with the clip facing down and contacts facing you:
+-----------------------+
| 1 2 3 4 5 6 7 8 | (Front view, clip down)
+-----------------------+
Pin 1 is on the left, pin 8 on the right.
Wiring Standards Overview
Purpose: Standards ensure cables are wired uniformly to guarantee compatibility and interoperability across devices and vendors.
Key Standards: T568A and T568B, defined by ANSI/TIA/EIA-568.
T568A Wiring Standard
| Pin | T568A Color |
|---|---|
| 1 | White/Green |
| 2 | Green |
| 3 | White/Orange |
| 4 | Blue |
| 5 | White/Blue |
| 6 | Orange |
| 7 | White/Brown |
| 8 | Brown |
Applications/Preferences: Often required for U.S. government contracts and preferred for new installations.
T568B Wiring Standard
| Pin | T568B Color |
|---|---|
| 1 | White/Orange |
| 2 | Orange |
| 3 | White/Green |
| 4 | Blue |
| 5 | White/Blue |
| 6 | Green |
| 7 | White/Brown |
| 8 | Brown |
Applications/Preferences: More common in the U.S. for commercial and legacy network installations.
Differences Between T568A and T568B
The primary difference lies in swapping pairs on pins 1/2 and 3/6 (green and orange pairs).
Both provide identical electrical performance; the important factor is consistency throughout the installation.
When to use:
- Choose one standard and use it consistently at a site.
- T568A is preferred for new or federal installations.
- T568B is common in legacy or commercial environments.
Straight-Through vs. Crossover Cables
| Cable Type | Wiring | Use Case |
|---|---|---|
| Straight-Through | Both ends wired same standard (T568A-A or T568B-B) | Connect host to switch/router |
| Crossover | One end T568A, other end T568B | Connect two similar devices directly (PC-to-PC, switch-to-switch without uplink port) |
Example: John uses a crossover cable to directly connect two computers.
Termination Process
Tools Needed: Cable stripper, crimping tool, RJ45 connectors.
- Strip approximately 1 inch of cable jacket.
- Untwist pairs and align wires in correct color order (per chosen standard).
- Trim wires evenly and insert fully into RJ45 connector (pins 1-8).
- Use crimping tool to firmly secure connector onto cable.
- Repeat for other end (same standard for straight-through; different for crossover).
Testing and Verification
Use a cable tester to check:
- Correct pinout and wiring sequence.
- Continuity and absence of opens or shorts.
- Proper pairing and absence of crossed pairs.
Common faults include: miswires, open circuits, shorts.
Standards Compliance
Always adhere to ANSI/TIA/EIA-568 wiring standards for reliable, interoperable networks.
Proper labeling and documentation assist future troubleshooting and maintenance.
Troubleshooting RJ45 Cable Issues
- Symptoms: No link light, slow speeds, intermittent disconnects.
- Tools: Cable tester, multimeter, visual inspection.
- Fixes: Remake connectors, replace damaged cables, verify wiring consistency on both ends.
Summary Table: T568A vs. T568B Pinouts
| 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 |
Best Practices and Exam Tips
- Always use the same wiring standard on both ends for straight-through cables.
- Label cables for easy identification and documentation.
- Test all cables after termination to verify proper wiring.
- Understand when to use straight-through versus crossover cables.
- Practice wiring both T568A and T568B schemes for certification and real-world applications.
Example Scenario
John is wiring a new office. He chooses T568B wiring for all patch panels and wall jacks, verifying with a cable tester to ensure all cables are straight-through for PC-to-switch connections. For a special lab setup connecting two switches directly, John creates a crossover cable by wiring T568A on one end and T568B on the other.