Is there a performance difference between T568A and T568B?

No. Both standards keep the same four pairs on the same pin pairs (1/2, 3/6, 4/5, 7/8). They only swap which pair lands on pins 1/2 versus 3/6, so electrical performance and certification results are identical when both ends match.

Which wiring standard should I use?

Use whatever the project spec or existing building standard calls for. In new commercial work in the United States, T568B is the most common convention; U.S. federal and residential projects often specify T568A. The only hard rule is that every jack, panel, and patch cord in the channel uses one standard consistently.

What happens if one end is T568A and the other T568B?

You get a crossover cable. Modern gigabit gear with Auto-MDI/X usually still links, but the run will fail a wiremap test as a crossed pair, and 10GBASE-T or PoE troubleshooting becomes unnecessarily hard. Re-terminate one end so both match.

Does the standard change how I punch down a keystone jack?

Yes. Most keystone jacks are labeled with both A and B color sequences on the body. Follow the row that matches your chosen standard, keep pair twists intact to within half an inch of the IDC contacts, and seat all eight conductors before trimming.

Field guide · Termination

T568A vs. T568B: pinouts, wiring order, and which one to use

T568A and T568B are the two conductor-order conventions in ANSI/TIA-568 for terminating 4-pair twisted-pair cable on RJ45 plugs, keystone jacks, and patch panels. They differ by exactly one swap — the green and orange pairs trade places — and everything else about the run is identical.

The 30-second answer

T568B puts the orange pair on pins 1/2 and the green pair on pins 3/6. It is the common convention in U.S. commercial installs.
T568A reverses that — green on 1/2, orange on 3/6 — and is frequently specified on U.S. federal and residential work.
Pick one standard per building and use it on both ends of every run. Mixing ends creates a crossover that fails wiremap.

RJ45 pinout: T568A vs. T568B

Pin 1 is on the left when you hold the plug with the contacts facing you and the latch away from you (looking into the front of the plug, clip down, cable pointing away).

Pin	T568A	T568B	Pair / signal
1	White / Green	White / Orange	Pair 3 (BI_DA+)
2	Green	Orange	Pair 3 (BI_DA−)
3	White / Orange	White / Green	Pair 2 (BI_DB+)
4	Blue	Blue	Pair 1 (BI_DC+)
5	White / Blue	White / Blue	Pair 1 (BI_DC−)
6	Orange	Green	Pair 2 (BI_DB−)
7	White / Brown	White / Brown	Pair 4 (BI_DD+)
8	Brown	Brown	Pair 4 (BI_DD−)

Pins 4/5 (blue) and 7/8 (brown) are the same in both standards. Only the green and orange pairs swap between pins 1/2 and 3/6.

Keystone jack and patch panel punch-down order

Jacks and panels are labeled by conductor color, not by pin number, and most NTI keystones print both sequences on the body. Left-to-right punch-down order, as printed:

T568A sequence

1. White/Green
2. Green
3. White/Orange
4. Blue
5. White/Blue
6. Orange
7. White/Brown
8. Brown

T568B sequence

1. White/Orange
2. Orange
3. White/Green
4. Blue
5. White/Blue
6. Green
7. White/Brown
8. Brown

Termination mistakes that fail a certification test

Split pairs. Wiring pins in straight color order (white/blue, blue, white/orange…) puts signal pairs across two different twisted pairs. Continuity passes; NEXT and return loss fail. Always follow A or B exactly.
Untwisting too far back. Keep pair twist to within 13mm (½ in.) of the IDC contacts or plug load bar.
Mixed standards in one channel. An A jack with a B patch cord reports a crossed pair on the wiremap even when the link still passes traffic.
Over-stripped jacket. Strip only enough to seat the conductors; excess exposed pair length degrades high-frequency margin on Cat6 at 550MHz.
No verification. Wiremap every drop. A tester catches a reversed or crossed pair in seconds, before the ceiling closes.

Straight-through, crossover, and rollover

Cable type	End 1 / End 2	Use
Straight-through	B / B (or A / A)	Every normal patch cord and horizontal run
Crossover	A / B	Legacy switch-to-switch links without Auto-MDI/X
Rollover	Pin order reversed 1–8 to 8–1	Console cables to router/switch management ports

Connectors and tooling for either standard

Pass-through plugs make conductor order easy to verify before you crimp, and our keystones print both A and B sequences. Add what you need and we return a firm quote with lead times.