A Cat5e pin assignment can follow either T568A or T568B. Both schemes preserve the four balanced twisted pairs and can support the same Ethernet applications when the cabling system is correctly installed. The visible difference is the position of the green and orange pairs.
For a normal permanent link, the practical rule is straightforward: use the documented wiring scheme consistently at both ends, preserve the original twisted pairs, and test the completed link rather than judging it from conductor colors alone.
This guide explains the T568A and T568B pinout, how the two schemes differ, when to use each one, how patch cords fit into the system, and why faults such as split pairs can pass a simple continuity check but still cause Ethernet problems. For current copper cable options, see the FOCC network cable range.
Quick Answer: T568A vs T568B
T568A and T568B use the same eight conductors and the same four electrical pair positions. The difference is that the green and orange pairs exchange positions:
- T568A: green pair on pins 1 and 2; orange pair on pins 3 and 6.
- T568B: orange pair on pins 1 and 2; green pair on pins 3 and 6.
- Both: blue pair remains on pins 4 and 5; brown pair remains on pins 7 and 8.
Fluke Networks describes this orange/green swap as the key physical difference between the two wiring codes and notes that the transmission performance is equivalent when they are correctly implemented. Fluke's T568A vs T568B technical guidance provides the corresponding pin assignments.
TIA announced ANSI/TIA-568.2-E as the updated balanced twisted-pair telecommunications cabling and components standard in November 2024. TIA's standards announcement provides the revision context.
Cat5e T568A and T568B Pin Assignment
| Pin | T568A Wire Color | T568B Wire Color |
Pair Position |
|---|---|---|---|
| 1 | White/Green | White/Orange | Pair on 1-2 |
| 2 | Green | Orange | Pair on 1-2 |
| 3 | White/Orange | White/Green | Pair on 3-6 |
| 4 | Blue | Blue | Pair on 4-5 |
| 5 | White/Blue | White/Blue | Pair on 4-5 |
| 6 | Orange | Green | Pair on 3-6 |
| 7 | White/Brown | White/Brown | Pair on 7-8 |
| 8 | Brown | Brown | Pair on 7-8 |
The table is more useful when read as four twisted pairs rather than eight independent conductors. Pins 3 and 6 belong to one pair even though they are not adjacent in the connector. That detail becomes important when diagnosing split-pair faults.
Cat5e describes the electrical performance of the complete cable and connecting system; it does not define a different color sequence from other balanced copper categories. FOCC's Cat5, Cat5e, and Cat6 comparison explains the Category distinction, while the broader Ethernet cable category guide places Cat5e within the wider copper cabling family.
Which Should You Use: T568A or T568B?
Neither scheme gives Cat5e a speed advantage. The better choice is usually the one that keeps the installation consistent and documented.
Existing Installation
When extending an existing building, inspect the patch panel, work-area outlets, labels, drawings, and previous test records before terminating the new cable. If the installed permanent cabling uses T568B, continuing with T568B reduces future troubleshooting ambiguity. The same logic applies to a documented T568A installation.
New Installation
For a new structured cabling project, define the wiring scheme in the project documentation and apply it consistently. Current jacks commonly provide both A and B color markings. For example, Leviton's Cat5e jacks provide dual T568A/T568B wiring labels rather than requiring a different jack for each scheme.
The rear IDC arrangement on a keystone jack does not necessarily look like pins 1 through 8 on the front modular interface. Follow the manufacturer's printed A/B diagram rather than assuming that rear terminal position equals front-pin position.
Check Pin Orientation Before Terminating an RJ45 Plug
One of the easiest ways to produce a completely reversed pinout is to copy a diagram while viewing the modular plug from the opposite side. Photos and diagrams may show the contacts, latch, or cable entry from different orientations.
Before inserting conductors, identify pin 1 from the plug manufacturer's drawing or contact numbering and confirm that the diagram you are following uses the same viewing orientation. FOCC's guide to RJ45 plug and boot selection is also useful when checking plug dimensions and cable compatibility.
For readers performing the complete crimping process rather than only checking the pin assignment, FOCC also provides an RJ45 Cat5e crimping guide.
Straight-Through vs Crossover Is a Separate Question
A standard straight-through cable preserves the same pin positions from one end to the other. In a conventional permanent link this normally means:
- T568A at both ends, or
- T568B at both ends.
Terminating one end as T568A and the other as T568B exchanges the green and orange pair positions and produces a crossover arrangement.
Cat5e describes cable performance. T568A/T568B describes pair assignment. Straight-through or crossover describes the relationship between the two ends.
The complete crossover topic is better handled separately; FOCC's crossover LAN cable pinout guide covers the corresponding use cases and pair mapping.
Can a T568B Patch Cord Be Used with a T568A Wall Jack?
Yes. A correctly manufactured straight-through T568B patch cord can be used with a permanent cabling system whose jacks were terminated using T568A.
This does not mean that a permanent cable can be terminated A at one end and B at the other without consequence. The reason a normal patch cord works is that the patch cord itself maintains pin 1 to pin 1, pin 2 to pin 2, and so on at its modular interfaces.
Leviton, for example, specifies T568B-wired patch cords that function in either T568A or T568B applications.
FOCC's LAN patch cord range provides relevant product context when the required Category, connector, length, jacket, and cable construction have already been defined.
Cat5e Pin Assignment for 10/100 vs Gigabit Ethernet
Older Ethernet pinout diagrams often label pins 1 and 2 as transmit and pins 3 and 6 as receive. That shorthand is useful for traditional 10BASE-T and 100BASE-TX discussions, but it should not be carried directly into Gigabit Ethernet troubleshooting.
10BASE-T and 100BASE-TX
Traditional 10/100 Ethernet primarily uses the pairs occupying pins 1/2 and 3/6. This is why those pairs dominate older crossover diagrams.
1000BASE-T
1000BASE-T uses all four balanced pairs. IEEE material describing the development of 1000BASE-T states that all four pairs are used with full-duplex transmission on each pair.
- 1/2
- 3/6
- 4/5
- 7/8
A cable may therefore appear acceptable during a simplistic two-pair check yet still fail to establish a reliable Gigabit link when one of the remaining pairs is open, split, damaged, or poorly terminated.
Crossed Pair vs Split Pair
These faults are different and should not be diagnosed the same way.
Crossed Pair
A crossed pair occurs when a complete electrical pair arrives at the wrong standardized pair position. An unintended T568A-to-T568B permanent-link termination is a common example. A suitable wire-map test can normally reveal the crossed relationship.
Split Pair
A split pair can be more deceptive. Individual conductors may still have correct end-to-end DC continuity, but conductors that should form one balanced twisted pair have been separated and combined with wires from another pair.
Fluke Networks explains that a split pair can preserve continuity while causing excessive crosstalk that interferes with network operation. Some simple testers that check only DC continuity can therefore miss the problem.
| Fault | What Is Wrong | Why It Matters |
|---|---|---|
| Crossed pair | A complete pair reaches the wrong pair position | End-to-end pair map does not match the intended wiring |
| Split pair | Conductors from different twisted pairs are combined | Continuity may look correct while crosstalk and signal integrity become unacceptable |
How to Terminate Cat5e Without Creating Pair Errors
- Confirm the cable. Read the jacket for Category, conductor construction, gauge, shielding, and jacket rating. A current Cat5e UTP cable specification illustrates why the complete cable construction matters rather than the color code alone.
- Match the connecting hardware. Confirm that the plug, jack, or patch panel supports the actual conductor and insulation dimensions. FOCC's overview of RJ45 connectors for Ethernet termination provides additional context.
- Select the documented A or B scheme. Do not let opposite-end technicians make independent choices.
- Preserve pair twist. Keep the conductors twisted as close to the termination as the hardware allows. The twist pattern helps maintain pair balance and control crosstalk; excessive untwisting can reduce transmission margin even when the wire map is correct.
- Follow the hardware label. Use the manufacturer's T568A/T568B markings on jacks and patch panels.
- Inspect before closing the outlet. Check that every conductor is fully seated and that no pair has been accidentally divided.
- Test the finished link. A link light alone is not evidence that a new Cat5e permanent link meets its declared Category performance.
How to Test a Cat5e Termination
The appropriate test depends on what you need to prove.
| Test Level | Main Question | Typical Checks |
|---|---|---|
| Continuity / basic wire map | Are conductors connected in the intended order? | Opens, shorts, reversals and basic mapping |
| Advanced wire map | Are the correct twisted pairs preserved? | Crossed pairs, split pairs, pair length and mapping |
| Qualification | Can this existing link support the intended network application? | Application-oriented performance assessment |
| Category certification | Does the installed cabling meet the selected Category test limit? | Wire map, insertion loss, return loss, NEXT and other required transmission parameters |
Fluke Networks identifies insertion loss, return loss and near-end/far-end crosstalk among the core parameters considered when certifying copper cabling against relevant standards.
A permanent-link test evaluates the fixed installed cabling and its connecting hardware. A channel test includes equipment or patch cords that form the complete end-to-end channel. Use the test configuration specified by the project rather than treating a passing channel result as a permanent-link certificate.
FOCC's guide to testing an Ethernet cable with a network cable tester can support basic field inspection and troubleshooting.
Common Cat5e Pinout Mistakes
| Mistake | Possible Result | Better Practice |
|---|---|---|
| T568A at one permanent-link end and T568B at the other | Unintended crossover | Use one documented scheme for a normal permanent link |
| Treating all eight conductors as independent wires | Split-pair fault | Preserve the four real twisted pairs |
| Reading a plug diagram from the wrong side | Reversed pin sequence | Confirm pin 1 from the manufacturer's drawing |
| Following rear IDC position rather than the A/B label | Incorrect front-pin mapping | Follow the jack's printed termination guide |
| Untwisting pairs too far | Reduced crosstalk margin | Keep pair twist close to the termination |
| Using any plug simply because it is called RJ45 | Poor contact or mechanical incompatibility | Match conductor construction and dimensions |
| Testing continuity only | Split-pair or performance problems may remain | Use the test level required by the installation |
Does T568A or T568B Affect PoE?
Choosing T568A instead of T568B does not inherently improve or reduce PoE capability when the cabling is correctly terminated. Both schemes preserve the same four standardized electrical pair positions; they only assign the green and orange conductor colors differently.
PoE performance depends on the complete cabling system, including conductor material and resistance, connection quality, channel length, bundle conditions, ambient temperature and the applicable power-delivery mode. For higher-power installations, FOCC's discussion of cabling temperature in PoE installations provides additional planning context.
FAQ
Q: Is T568A faster than T568B?
A: No. Correctly implemented T568A and T568B have equivalent transmission performance. The installation quality and Category performance matter more than the choice between the two color schemes.
Q: Which is more common, T568A or T568B?
A: T568B is common in many installed commercial networks, while T568A has also been widely specified. For an existing site, matching and documenting the established scheme is generally more useful than changing it because another pattern appears more common.
Q: Can Cat5e use either T568A or T568B?
A: Yes. Cat5e connecting hardware can support either scheme when it is designed and installed accordingly. Current products such as Leviton's Cat5e jacks provide dual A/B wiring labels.
Q: Can a T568B patch cable connect to a T568A wall jack?
A: Yes, when the patch cord is a normal straight-through assembly and the permanent link itself is correctly terminated. Do not confuse that situation with terminating opposite ends of the same permanent cable to different schemes.
Q: Why does a cable pass continuity but fail Gigabit Ethernet?
A: Continuity does not prove that the correct twisted pairs are preserved or that the link meets Cat5e transmission limits. A split pair can maintain conductor continuity while creating excessive crosstalk.
Q: Does Gigabit Ethernet use only pins 1, 2, 3 and 6?
A: No. 1000BASE-T operates across all four balanced pairs.
Q: Does T568A or T568B change PoE support?
A: No inherent PoE advantage comes from choosing one color scheme over the other. Correct pair mapping and the electrical performance of the complete cabling channel are the important factors.
Final Cat5e Wiring Rule
For a new or existing Cat5e installation, use the following sequence:
- Identify the required Category and application.
- Confirm the project's T568A or T568B convention.
- Verify pin 1 orientation before arranging conductors.
- Follow the manufacturer's termination markings.
- Preserve the four original twisted pairs.
- Use the same scheme at both ends of a normal permanent link.
- Keep crossover wiring intentional rather than accidental.
- Test the completed installation at the level required by the project.
If the project is still at the cable-selection stage, FOCC's guide to choosing an Ethernet cable category can help compare Cat5e with higher categories before the termination method is finalized.
The key point is not memorizing eight colors in isolation. Reliable Ethernet depends on maintaining four balanced twisted pairs from the cable through the connecting hardware and proving the completed link with an appropriate test.
For Cat5e cable, patch-cord, connector or project-configuration requirements, provide the Category, cable construction, connector type, wiring scheme, required length, shielding, jacket rating, PoE requirement and acceptance-test needs through the FOCC inquiry page.
