Ethernet Cable Color Coding: T568A, T568B and Crimping

Introduction

Ethernet cables (Cat5e, Cat6, Cat6a, etc.) use twisted pairs of wires inside to carry data. The way these wires are arranged and connected to the RJ45 connector follows strict standards — mainly T568A and T568B. Getting the wiring wrong causes connection failures, slow speeds, or no link at all.

This guide explains both standards, shows straight-through vs crossover cables, provides clear color code diagrams, and walks you through crimping RJ45 connectors and punching keystone jacks / patch panels.

T568B Straight-Through Cable

This is the most common wiring standard used today for connecting computers to switches/routers (straight-through cable). Both ends use the same order (T568B).

Pin	Color	Wire Name
1	White/Orange	Orange Stripe
2	Orange	Orange Solid
3	White/Green	Green Stripe
4	Blue	Blue Solid
5	White/Blue	Blue Stripe
6	Green	Green Solid
7	White/Brown	Brown Stripe
8	Brown	Brown Solid

T568B and T568A Crossover Cable

Crossover cables connect two similar devices directly (e.g., PC to PC, switch to switch) without a hub/switch. One end uses T568B, the other uses T568A to swap transmit/receive pairs.

Modern devices with Auto-MDI/MDIX support usually don't need crossover cables anymore — but older equipment still does.

RJ45 Color Code for 2 Pairs (Fast Ethernet)

Fast Ethernet (100 Mbps) only uses 2 pairs (pins 1-2 and 3-6). Gigabit Ethernet uses all 4 pairs.

Common in older installations or when only 100 Mbps is needed.

Step-by-Step RJ45 Crimping Procedure

Strip the outer jacket of the cable (about 1–1.5 inches).
Untwist and straighten all four pairs of wires.
Arrange the wires in the correct order (T568B or T568A) — hold them flat and tight.
Cut the wires evenly, leaving about 0.5 inch exposed from the sheath.
Insert the wires fully into the RJ45 connector (make sure they reach the end).
Check that the wires are in the correct pin order and fully seated.
Crimp the connector firmly with a crimping tool.
Repeat on the other end using the same standard (for straight-through) or opposite (for crossover).

After crimping, always test the cable with a cable tester to confirm continuity and correct wiring.

I/O Port (Keystone Jack) Punching Color Code

When punching down cables into keystone jacks, patch panels, or wall plates, follow the same T568A or T568B standard on both ends.

Most keystone jacks have color-coded pins labeled for both T568A and T568B — choose one standard and be consistent on both ends.

Quick Reference: T568B vs T568A Pinout

T568B Color Code

Pin	Color	Wire Name
1	White/Orange	Orange Stripe
2	Orange	Orange Solid
3	White/Green	Green Stripe
4	Blue	Blue Solid
5	White/Blue	Blue Stripe
6	Green	Green Solid
7	White/Brown	Brown Stripe
8	Brown	Brown Solid

T568A Color Code

Pin	Color	Wire Name
1	White/Green	Green Stripe
2	Green	Green Solid
3	White/Orange	Orange Stripe
4	Blue	Blue Solid
5	White/Blue	Blue Stripe
6	Orange	Orange Solid
7	White/Brown	Brown Stripe
8	Brown	Brown Solid

Conclusion

Correct Ethernet cable wiring using T568B (or T568A consistently) is essential for reliable network connections. Use T568B for new installations — it's the modern standard. Always test every cable you make with a cable tester before deploying it.

Double-check color order before crimping — fixing a bad cable is much harder after it's installed in walls or ceilings.