2.4 T568A and T568B Color Codes

The Two TIA Pinouts

TIA-568 defines exactly two 8-position modular jack pinout schemes, T568A and T568B. Both assign all four twisted pairs to the same eight pins on an RJ45; the only difference is the positions of the orange and green pairs. The blue pair (pins 4–5) and the brown pair (pins 7–8) are identical in both schemes.

The mnemonic: T568A starts with the green pair on pins 1–2; T568B starts with the orange pair on pins 1–2. Either scheme is electrically equivalent — the channel performs identically because the cable's pair geometry and twist rates are pair-color-agnostic. The choice of scheme is administrative, not performance-driven.

When to Use Each

• T568B is the de facto convention for commercial new construction in North America. Most patch panels, keystone jacks, and pre-terminated cords sold in the US default to T568B.
• T568A is mandated by TIA-568 for federal government contracts and is common in legacy US government and Department of Defense sites. Some state and local government specifications also require T568A.
• Residential cabling under TIA-570 defaults to T568A.

The Technician must follow the customer's documented specification and the existing scheme in retrofit work. Where the spec is silent, match the existing infrastructure — a building wired T568B should remain T568B.

The Hard Rule: Never Mix Within a Channel

Both ends of a single horizontal channel — the work-area outlet and the patch panel port — must use the same scheme. A channel with T568A at the workstation outlet and T568B at the patch panel is a wiremap failure: the orange and green pairs are crossed, and 1000BASE-T will not link.

A common error in retrofit work is replacing one end of a run (for example, replacing a damaged keystone jack) and using the wrong color code. The link that worked before the re-termination now fails wiremap. The Technician's rule: before terminating, verify the scheme at the opposite end.

Patch cords are straight-through and use the same scheme as the cable plant. T568A patch cords work in a T568A channel; T568B patch cords work in a T568B channel. Mixing patch cord schemes is fine if both ends of the cord are the same — the cord is straight-through — but document the choice to avoid confusion later.

Crossover Cables (Historical Note)

A crossover cable uses T568A on one end and T568B on the other, deliberately crossing pairs so two like devices (switch-to-switch, PC-to-PC) could connect without an uplink port. Crossover cables are obsolete for 1000BASE-T and beyond — gigabit and faster PHYs implement automatic MDI/MDIX crossover in hardware. The Technician may still encounter legacy 100BASE-TX crossover cables in older installations; they are not TIA-568 compliant channels and should not be used as horizontal cabling.

Pair-to-Pin Mapping (Why It Matters Electrically)

Pins 1–2 and 3–6 are the two pairs used by 10BASE-T and 100BASE-TX. The split of one pair across pins 3 and 6 (with pins 4 and 5 occupied by the blue pair between them) is the source of many wiring errors. The most common field error is terminating pins 3 and 6 from different pairs — for example, white/orange on pin 3 and white/green on pin 6, with the solids on the wrong pins. This creates a split pair, which passes a simple continuity test but fails NEXT catastrophically because the two conductors of a pair are no longer twisted around each other.

The wiremap test on a certification tester detects split pairs by verifying that each pair is on the correct pins and that the two conductors of each pair are paired correctly. A multimeter continuity check does not detect split pairs — this is a common exam scenario.

Pin Numbering

Pins are numbered 1 through 8 when viewing the connector from the contact side (metal contacts facing up), with the clip facing away from you. Pin 1 is on the left. Reversing the connector flips pin 1 and pin 8; this is a frequent error for inexperienced terminators and produces a complete wiremap failure (reversed pair).

Keystone jacks and patch panels label color positions for both T568A and T568B, typically with two color-coded strips. Use the strip that matches the project specification and verify before crimping. Modular plugs (male RJ45) are not labeled — the Technician must apply the color order from memory.

Documentation and Labeling

TIA-606 administration requires that the pinout scheme be documented on the project record. In practice, this is usually the project's cabling standard document, which states "All horizontal cabling shall be terminated T568B" (or A). Patch panels and keystone jacks carry T568A/T568B labels; the installer marks or selects the scheme in use. Mixed-scheme installations are documented at the outlet level where they exist.

Exam Traps

• "T568A performs better than T568B at high frequency." — False. They are electrically equivalent.
• "A channel can mix T568A at one end and T568B at the other for a straight-through connection." — False. That produces a crossed pair (wiremap failure).
• "Federal contracts require T568B." — False. TIA-568 specifies T568A for federal contracts.
• "A multimeter continuity test confirms a correctly wired channel." — False. Continuity cannot detect split pairs; only wiremap can.

Hands-On Exam Implication

A Technician hands-on task is typically: terminate a Cat 6A keystone jack and patch panel port to the project specification, then pass wiremap and certification. The candidate who must pause to look up color codes will run out of time on the 20-minute-per-task limit. Memorize the table at the top of this section — both schemes, both directions — before sitting the hands-on exam.