Crimp UTP cable and pinout RJ45: T568A, T568B and check connection

What is the difference between T568A and T568B

T568A and T568B are two color-coding standards for crimping eight-pin RJ45 connectors. Both are recognized by the current ANSI/TIA-568.2-D standard and provide identical electrical characteristics and support for network protocols, including Gigabit Ethernet. The only difference is the order in which the orange and green pairs are connected: in T568A, the green wires are connected to pins 1 and 2, and the orange wires to pins 3 and 6; in T568B, the orange wires are connected to pins 1 and 2, and the green wires to pins 3 and 6. The remaining wires are connected to the same pins in both standards.

T568A is considered the preferred standard because it provides backward compatibility with earlier USOC schemes for one and two pairs. T568B corresponds to the older AT&T 258A color code and has become more widespread. There is no technical advantage of one standard over the other. The choice is guided by the established practice of the facility: T568B is more often used in commercial and home networks, T568A in government projects. Both standards are permitted for use by the current ANSI/TIA-568.2-D.

RJ45 pinout table by colors

Pin positions are shown from the front of the connector (contacts facing the reader). Numbering goes from left to right.

Source: ANSI/TIA-568.2-D. The scheme has been verified against Fluke Networks and Fiber-Mart documentation. The RJ45 connector is also designated as 8P8C — eight positions, eight contacts. For 100Base-T networks (100 Mbit/s), pins 1, 2, 3 and 6 are used; the other four are reserved. For Gigabit Ethernet, all eight pins are used.

When the same scheme is needed on both ends

For a straight patch cord connecting a computer to a switch or router, the same scheme is used on both ends: T568A-to-T568A or T568B-to-T568B. Mixing standards on the ends of one cable disrupts pair matching and leads to transmission errors. The cable must be crimped “color to color, stripe to stripe” on both ends.

A patch cord is a ready-made cable with connectors on both ends for connecting active equipment. The pinout of a patch cord for the internet follows the same rule: the same scheme on both ends. If you are making a cable to connect an IP camera or an access point with PoE power, a straight scheme is also used. A cable for the internet over twisted pair does not require crossover when connecting to modern equipment.

Is a crossover cable needed today

A crossover cable is made with different standards on the ends: one end is T568A, the other is T568B. Such a cable was necessary for direct connection of two computers or two switches without an intermediate device. However, modern network equipment supports the Auto-MDIX function, which automatically detects the cable type and corrects transmission and reception. With Auto-MDIX, a crossover cable is not required: a direct connection works with an ordinary patch cord.

Crossover cable remains relevant only for legacy equipment without Auto-MDIX support. In most modern networks, there is no need for it. If you are not sure whether a specific device supports Auto-MDIX, check its documentation. For standard connections “computer — switch”, “computer — router”, a straight cable with the same scheme on both ends is used.

Crimping features for Cat5e and Cat6

Cat5e and Cat6 differ in construction. Cat5e supports frequencies up to 100 MHz and speeds up to 1 Gbit/s over the full 100-meter length. Cat6 is rated for 250 MHz and transmits 10 Gbit/s over a distance of up to 55 meters. Cat6 cable has a larger outer diameter due to thicker conductors, tighter pair twisting, and a central separator (spline) that separates the pairs.

Due to its greater thickness, Cat6 requires connectors designed for the increased cable diameter. Connectors for Cat5e are smaller internally and do not account for the spline. Using a Cat5e connector for Cat6 cable makes it difficult to insert the wires and can result in poor contact. Many Cat6 connectors have a two-piece construction: the wires are first inserted into a separate load bar, which is then inserted into the connector body. This simplifies wire arrangement and reduces the risk of mixing up the order. When crimping Cat6, the central spline is cut flush with the sheath.

If you are choosing between Cat5e and Cat6, focus on the required speed and line length. For office networks with gigabit connections, Cat5e is sufficient. For lines where 10 Gbit/s over a distance of up to 55 meters is planned, Cat6 is used. A comparison of categories is analyzed in the material UTP Cat5e or Cat6: which to choose. If the line runs near sources of electromagnetic interference, consider shielded solutions: UTP or FTP.

Connectors for solid and stranded cable

UTP cable is available with solid and stranded conductors. Solid cable is used for permanent installation in walls and ceilings. Stranded cable is more flexible and is used for patch cords, where resistance to repeated bending is important.

Connectors for these cable types differ in the design of the contact blades. For solid cable, connectors with spring contacts that grip the conductor on both sides are used. For stranded cable, connectors with sharp blades that penetrate between the fine wires without cutting them are used. There are universal connectors suitable for both types. When crimping stranded cable with an ordinary connector for solid cable, poor contact or breakage of some wires is possible. Check the applicability of the connector for your cable type: UTP communication cable: complete guide.

Step-by-step crimping instructions

Tool preparation

For crimping you will need: a crimper (crimping tool), a stripper or knife for removing the sheath, side cutters for a clean cut of the wires, RJ45 connectors, a cable tester. A ratchet crimper provides uniform crimping force. Pass-through connectors allow you to check the wire order before crimping, as the wires exit through the front of the connector.

Step 1. Stripping the sheath

Remove the outer sheath from the cable to a length of about 1.5 inches (approximately 3–4 cm). Use a stripper or the cutting blade of the crimper so as not to damage the insulation of the twisted pairs. The cut must be neat: damage to the wire insulation changes the characteristic impedance and causes signal loss.

Step 2. Arranging the wires

Untwist the pairs and align the wires in a single row according to the chosen T568A or T568B scheme. For Cat6, cut the central spline flush with the sheath. Try not to untwist the pairs more than necessary: the longer the untwisted section, the higher the crosstalk. The maximum length of the untwisted section is no more than 13 mm.

Step 3. Aligning and trimming

Align the wires to the same length and press them tightly together. Cut the wires evenly, leaving about 0.5 inches (12–13 mm) from the edge of the sheath. A clean cut is necessary for all eight wires to make simultaneous contact with the connector blades.

Step 4. Installing the RJ45

Hold the connector with the latch away from you, contacts toward you. Insert the wires into the connector, observing the order. Make sure each wire reaches the front wall of the connector and the cable sheath is secured in the body. If using a pass-through connector, check the color order through the front. If using a two-piece Cat6 connector, first put the load bar on the wires, then insert the assembly into the body.

Step 5. Crimping

Insert the connector into the crimper socket and press the handles smoothly but firmly until they stop. The ratchet mechanism will not release the handles until crimping is complete. The connector blades will cut through the wire insulation and make contact with the copper conductors. At the same time, the strain relief will clamp the cable sheath.

Step 6. Testing

Connect both ends of the cable to the tester and start the test. The indicators should light up one after another on both tester units in the correct order (1-2-3-4-5-6-7-8). If any indicator does not light or lights in the wrong order, the cable is crimped incorrectly.

How to test the cable after crimping

A network tester is the main verification tool. Simple models check wire continuity and pair order. More functional testers additionally measure cable length, determine the distance to a fault, and detect crosstalk. The tester is connected to both ends of the cable. The indicators on the main and remote units should light up one after another for each wire.

When checking, pay attention to:

• Wire break. The indicator for the corresponding wire does not light on one of the units. Cause: the wire did not reach the contact or is not crimped firmly enough.
• Short circuit. Indicators light in the wrong order or simultaneously. Cause: a short between wires due to damaged insulation or a burr.
• Mixed pairs. Indicators light in the wrong order. Cause: the wire arrangement is incorrect.
• Split pair. One wire of a pair lights, the other does not. Cause: a break in one wire of the pair.

If the tester shows an error, cut off the connector and crimp again. Re-crimping the same connector is not allowed: the blades have already cut the insulation, and the contact will be unreliable. To test the line after installation, cable analyzers are also used, which measure attenuation, crosstalk and characteristic impedance. The procedure for laying and installing UTP cable is analyzed in the article UTP cable installation.

Typical mistakes

Mixed-up wire sequence. The most common mistake. The wires are arranged not according to the T568A or T568B scheme, but arbitrarily. The network may work at low speed or not work at all. Before crimping, double-check the color order using the pinout table.

Excessively untwisted pairs. An untwisted section longer than 13 mm increases crosstalk. Untwist the pairs only to the length needed to arrange the wires. For Cat6, it is critical to maintain the pair twist right up to insertion into the connector.

Sheath not secured by the connector. If the outer sheath is not clamped by the strain relief, the cable pulls out of the connector under tension, and the contact is broken. Make sure the sheath enters the connector by at least 3–4 mm and is clamped during crimping.

Unsuitable connector. Using a Cat5e connector for Cat6 cable, or a connector for solid cable for stranded cable, results in poor contact. Use connectors that match the type and category of the cable.

Poor contact after crimping. Crimping is done weakly, the blades have not cut through the wire insulation. The tester shows a break or unstable contact. Use a ratchet crimper and press the handles all the way.

Using an uncalibrated tester. A tester with a discharged battery or damaged contacts gives false results. Before testing, make sure the tester is working.

FAQ

Which standard to choose: T568A or T568B?

Both standards are technically equivalent. T568B is more widespread in commercial and home networks. T568A is used in government projects and provides backward compatibility with USOC. The main rule is to use one scheme on both ends of the cable. If you are expanding an existing network, use the standard already used at the facility.

Is a crossover cable needed to connect two computers?

For modern equipment with Auto-MDIX support, a crossover cable is not required. A direct connection of two computers or switches works with an ordinary patch cord. A crossover cable is needed only for legacy equipment without Auto-MDIX.

Can a Cat5e connector be used for Cat6 cable?

Physically, a Cat5e connector can accommodate Cat6 cable, but due to the difference in diameter and the presence of a central spline, the contact will be unreliable. For Cat6, use connectors designed for the increased cable diameter. Using a Cat5e connector for Cat6 will not provide Cat6 advantages and may degrade line performance.

How many wires are needed for internet over twisted pair?

For 100 Mbit/s, four wires are sufficient (pins 1, 2, 3 and 6). For Gigabit Ethernet, all eight wires are used. For PoE power, either the spare pairs or all eight wires are used depending on the PoE standard. If you are crimping a cable for the internet, use all eight wires: this ensures compatibility with gigabit networks and PoE.

How to test the cable if there is no tester?

Without a tester, you can connect the cable between two devices and check for a connection. However, it is impossible to visually determine an incorrect wire order or poor contact. A network tester is the minimum necessary tool for checking crimping quality. If a tester is not available, inspect the connector: all wires should be visible through the body and reach the front wall.

Sources

• ANSI/TIA-568.2-D «Balanced Twisted-Pair Telecommunications Cabling and Components Standard» — in force — TIA TR-42 committee — T568A and T568B color-coding standard.
• Fluke Networks. «Differences Between Wiring Codes T568A vs T568B» — technical article — flukenetworks.com — difference between T568A and T568B, compatibility and applications.
• Fiber-Mart. «RJ45 Pinout, RJ45 Color Coding and RJ45 Wiring» — technical guide — fiber-mart.com — T568A and T568B pinout table.
• Comms-Express. «Ethernet Cable Termination Guide: T568B Step-by-Step» — technical guide — comms-express.com — step-by-step crimping procedure, use of pass-through connectors, testing.
• Monoprice. «Can You Use Cat6 Connectors on Cat5e Cable?» — technical article — monoprice.com — differences between Cat5e and Cat6, connector compatibility, effect on signal characteristics.
• Berkeley MCB. «A Guide to Crimping RJ-45 Connectors» — methodological guide — mcb.berkeley.edu — crimping technique, wire arrangement, working with Cat6.
• Black Box. «Solid vs Stranded Patch Cable» — technical article — blackbox.com — differences between solid and stranded cable, connector types.
• KazKabel. «Прокладка UTP кабеля: нормы монтажа внутри, снаружи, в земле и на тросу» — practical guide — kazkabel.kz — installation rules, allowable untwisted section length.
• KazKabel. «UTP cable single-core or multi-core: What should I choose?» — technical article — kazkabel.kz — choosing a connector for solid and stranded cable.