# RJ45 / 8P8C Ethernet: T568A and T568B

Match numbered contacts and twisted pairs when terminating Ethernet cable.

**Applies to:** Contact assignments for T568A/B. This is not a rear punch-down layout or a PoE injection circuit.

## When to use it

Making a straight-through patch lead or terminating a compatible data jack.

## Why it works this way

Keeping each twisted pair together matters even when a basic continuity test passes.

![RJ45 / 8P8C Ethernet: T568A and T568B — Contact assignments for T568A/B. This is not a rear punch-down layout or a PoE injection circuit.](https://valleytech-black-wire-guide.pages.dev/library/wiring/ethernet-t568.svg)

[Open / save the original SVG](https://valleytech-black-wire-guide.pages.dev/library/wiring/ethernet-t568.svg)

## Connection reference

| Contact | 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 |

## Make the connection

1. Identify contact 1 using the connector drawing; plug and socket views can appear mirrored.
2. Use A at both ends or B at both ends for a straight-through lead. Preserve pairs 1-2, 3-6, 4-5 and 7-8.
3. Use a suitable cable tester; check pair assignment as well as opens and shorts.

## Check before powering

- Rear IDC terminal order varies by jack; do not copy the plug's left-to-right order onto it.
- An 8P8C socket may carry non-Ethernet signals. Confirm the equipment documentation before connecting it.

## Matching module references

This is a general interface guide; match your own hardware documentation.

## Sources & review

Source documents inspected; independent electrical and bench review pending. Reviewed 2026-09-27.

- [Leviton Cat 5e / Cat 6 jack instructions](https://leviton.com/content/dam/leviton/network-solutions/product_documents/instruction_sheet/Leviton_IST_5G110_61110_eXtreme_Cat5e_Cat6_Jacks.pdf) — Table 1: T568A/B contact assignments and jack termination labels; checked 2026-09-27
- [Fluke Networks: RJ connector naming](https://www.flukenetworks.com/blog/cabling-chronicles/history-rj45-case-mistaken-identity) — RJ11 / RJ14 / RJ25 versus modular connector contact counts; checked 2026-09-27

Original writing and diagram by Kal / Valleytech Solutions, CC BY 4.0. Manufacturer artwork and documentation retain their own rights.

[CC BY 4.0](https://creativecommons.org/licenses/by/4.0/) · SHA-256: `26d108697685fa6266358f15630b133eef2972878f762bb375bd4560a7289400`

[Open the interactive guide](https://valleytech-black-wire-guide.pages.dev/?tab=wiring&guide=ethernet-t568) · [All wiring guides](Wiring.md)