T568A vs T568B: RJ45 Wiring Standards Explained
T568A and T568B are the two standard ways to arrange the eight wires inside an RJ45 (8P8C) connector. They cause endless confusion, but the practical truth is simple: there's only one difference between them, and the golden rule is to stay consistent. This VOOHU Electronics guide gives the full pinout and tells you which to use.
The short answer
T568A and T568B are pin/pair assignment schemes defined under the ANSI/TIA-568 cabling standard. The only difference is that the orange and green pairs are swapped. Both perform identically and both support Gigabit, 10G and PoE. Use one standard at both ends of every cable — that consistency matters far more than which one you pick.
T568A and T568B pinout
Both schemes use the same four twisted pairs on the same pin groups (pair 1 on pins 4–5, pair 2 on 1–2, pair 3 on 3–6, pair 4 on 7–8). Only the wire colors on pins 1, 2, 3 and 6 change:
| Pin | T568A wire | T568B wire | Signal (10/100) |
|---|---|---|---|
| 1 | White/Green | White/Orange | TX+ |
| 2 | Green | Orange | TX- |
| 3 | White/Orange | White/Green | RX+ |
| 4 | Blue | Blue | (unused on 10/100) |
| 5 | White/Blue | White/Blue | (unused on 10/100) |
| 6 | Orange | Green | RX- |
| 7 | White/Brown | White/Brown | (unused on 10/100) |
| 8 | Brown | Brown | (unused on 10/100) |
Straight-through vs crossover cables
The two standards are how you make the two common cable types:
- Straight-through cable: the same standard (A–A or B–B) on both ends. This is the normal patch cable connecting a PC, phone or device to a switch or wall jack.
- Crossover cable: T568A on one end and T568B on the other. This swaps the transmit and receive pairs and was historically used to connect two like devices directly (PC-to-PC, switch-to-switch).
Which standard should you use?
Neither is electrically superior, so the choice is about convention and consistency:
- T568B is the most widely used scheme in US commercial installations and is what most pre-made patch cords follow.
- T568A is common in US residential work and is specified by some US government and federal projects, and is more common in certain other regions.
- Pick one and standardize. Choose the standard your customer spec, local code, or existing plant uses, document it, and wire every jack and cord the same way. Mixing schemes within a site is the real source of faults and troubleshooting headaches.
Quality RJ45 jacks and keystone modules are printed with both A and B color codes on the housing, so the same connector supports either scheme — you simply punch down to the row you've standardized on.
Common mistakes
- Accidentally wiring one end A and the other B and creating an unintended crossover.
- Splitting pairs (not following the pair groupings), which destroys twist and ruins high-speed performance — see our signal-integrity guide.
- Mixing A and B across a building with no documentation.
- Untwisting too much wire at the connector, hurting Cat6A/Cat8 margin — see Cat6A vs Cat8 selection.
Need RJ45 jacks, plugs or keystones?
VOOHU Electronics manufactures standard, shielded, integrated-magnetics, PoE and waterproof RJ45 connectors and keystones marked for both T568A and T568B wiring. Request datasheets or samples for your build.
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Frequently asked questions
- What is the difference between T568A and T568B?
- Only the orange and green pairs are swapped — pins 1, 2, 3 and 6 differ; pins 4, 5, 7 and 8 are identical. Electrically they perform the same; use one standard consistently at both ends.
- Is T568A or T568B better?
- Neither is electrically better; both support Cat6A/Cat8, Gigabit and PoE. T568B dominates US commercial work; T568A is common in US residential and some government specs. Pick one and standardize.
- What happens if I use T568A on one end and T568B on the other?
- You create a crossover cable. Modern Auto-MDI-X ports correct it automatically so it usually still works, but for structured cabling keep both ends the same standard.
- Does the wiring standard affect Gigabit or PoE?
- No. Both use the same four pairs on the same pins, so 1000BASE-T and PoE work identically with either, as long as the cable is wired consistently end to end.