T568A vs T568B: the RJ45 wiring order, and which one to use
Both schemes come from the TIA-568 cabling standard and both carry Ethernet and PoE equally well. They differ in one thing: which pair lands on pins 1 and 2. Pick one and use it at both ends of every cable.
Pin by pin
Hold the RJ45 plug with the clip facing away from you and the contacts on top; pin 1 is on the left.
| 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 |
The highlighted pins 1, 2, 3 and 6 are the ones that change: the green and orange pairs swap. Blue stays on 4 and 5, brown on 7 and 8.
Which one to use
TIA-568 prefers T568A; T568B is common in commercial installations in North America. Follow the existing building, the client's specification or, failing that, T568A.
Straight-through or crossover
Same scheme at both ends makes a straight-through cable, used almost everywhere. A on one end and B on the other makes a crossover, which Auto-MDI-X ports no longer need.
PoE on the pairs
802.3af and 802.3at power over two pairs, 802.3bt over all four. Each pair stays together in both schemes, so PoE works with either as long as the ends match.
What TIA-568 covers
- Cable categories such as Cat 5e, Cat 6 and Cat 6A, and the performance each must reach.
- Pin assignments, the T568A and T568B schemes above.
- Lengths: a channel of up to 100 m, made of up to 90 m of installed cable and 10 m of patch cords. See Cat 6 maximum length.
- Installation and testing, including bend radius, untwist at terminations and the certification tests a link must pass.
- Counterparts: ISO/IEC 11801 internationally and EN 50173 in Europe.
Cabling in CCTVplanner
- Draw cable routes on the plan and every run gets its length in the cable schedule.
- The design check flags copper runs longer than 90 m and suggests Cat 6A for runs between 60 and 90 m.
- Cables and switches land in the bill of materials with the cameras. See the PoE switch guide.
T568A and T568B questions
What is the difference between T568A and T568B?
Only the green and orange pairs swap places. In T568A pins 1 and 2 are green and pins 3 and 6 orange; in T568B it is the other way round. Blue and brown stay on the same pins.
Is T568A or T568B better?
Neither performs better. The TIA-568 standard prefers T568A, and T568B is common in commercial work in North America. What matters is using the same scheme at both ends and throughout the building.
What is a crossover cable?
A cable with T568A at one end and T568B at the other. Modern switches, cameras and computers swap the pairs themselves (Auto-MDI-X), so straight-through cables work almost everywhere.
Does PoE care whether I use T568A or T568B?
No, as long as both ends match. 802.3af and 802.3at power over two pairs and 802.3bt over all four, and each pair keeps its two wires together in both schemes.
What is TIA-568?
The ANSI/TIA-568 series is the North American standard for structured cabling in commercial buildings: cable categories, connectors, pin assignments, installation and testing. ISO/IEC 11801 is its international counterpart and EN 50173 the European one.