This chapter covers RJ-45 crimping and the T568A/T568B wiring standards, essential skills for the CompTIA A+ 220-1101 exam under Objective 2.3 (Networking). You will learn the exact pin assignments, how to create straight-through and crossover cables, and the tools required. While only 3-5% of exam questions directly test this topic, understanding it is critical for troubleshooting physical layer issues and for the Performance-Based Questions (PBQs) where you may be asked to select the correct wiring standard for a given scenario.
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Imagine you're a telephone technician in the 1960s, wiring a large office building. Every desk has a phone, and every phone needs a pair of copper wires to carry your voice. The building has a central wiring closet where all the wires from every desk converge. Your job is to connect each desk's wire to the correct line coming from the telephone company's central office. To make this work reliably, you need a standard color code for the wires inside the cable. The industry standard is the 25-pair color code, where each pair is identified by a unique combination of tip and ring colors (e.g., blue/white, orange/white, green/white, brown/white, slate/white). When you terminate a cable at a desk, you must place the wires in the correct order on the jack's terminals. If you reverse the order (tip and ring), the phone will not work. Similarly, if you use a different color code at each desk, troubleshooting becomes a nightmare. So the industry defined two standard wiring patterns: one for connecting a desk phone directly to the wiring closet (T568A) and another for connecting two wiring closets together (T568B). The only difference is that the orange and green pairs are swapped. If you use the same pattern at both ends, the cable is 'straight-through.' If you use different patterns at each end, the cable is 'crossover' — which was historically used to connect two computers directly without a switch. Today, modern switches auto-detect and correct for crossover cables, but the pinout standards remain critical for structured cabling. Just as a telephone technician must follow the color code to ensure every desk can make calls, a network technician must follow T568A or T568B to ensure every device can communicate.
What is RJ-45 Crimping and Why Does It Matter?
RJ-45 (Registered Jack 45) is the standardized physical connector for twisted-pair Ethernet cables. Crimping is the process of attaching an RJ-45 plug to the end of a cable using a crimping tool. The 220-1101 exam expects you to know the two wiring standards (T568A and T568B), when to use each, and how to create proper cables. A miswired cable can cause link failures, excessive collisions, or intermittent connectivity — all of which you must be able to diagnose.
The Anatomy of a Twisted-Pair Cable
Ethernet cables (Cat5e, Cat6, Cat6a) contain eight copper wires arranged as four twisted pairs. Each pair is color-coded:
Pair 1: Blue/Blue-White
Pair 2: Orange/Orange-White
Pair 3: Green/Green-White
Pair 4: Brown/Brown-White
Twisting reduces electromagnetic interference (EMI) and crosstalk. The exact number of twists per inch varies by category (e.g., Cat5e has 3-4 twists per inch, Cat6 has 4-5). For proper performance, you must maintain the twists as close to the connector as possible — no more than 0.5 inches (13 mm) of untwisted wire is allowed per TIA/EIA standards.
T568A and T568B Pinouts
Both standards define the order of wires from left to right (pin 1 to pin 8) when looking at the RJ-45 plug with the clip facing away from you and the pins pointing down.
T568A (Standard): - Pin 1: Green-White (TX+) - Pin 2: Green (TX-) - Pin 3: Orange-White (RX+) - Pin 4: Blue - Pin 5: Blue-White - Pin 6: Orange (RX-) - Pin 7: Brown-White - Pin 8: Brown
T568B (Alternative): - Pin 1: Orange-White (TX+) - Pin 2: Orange (TX-) - Pin 3: Green-White (RX+) - Pin 4: Blue - Pin 5: Blue-White - Pin 6: Green (RX-) - Pin 7: Brown-White - Pin 8: Brown
Notice that pairs 2 and 3 are swapped between the two standards. Pins 4,5,7,8 are identical. The transmit pair (TX) is on pins 1-2, and the receive pair (RX) is on pins 3-6 in both standards. For 10BASE-T and 100BASE-TX, only pins 1,2,3,6 are used. For 1000BASE-T (Gigabit), all eight pins are used.
Straight-Through vs. Crossover Cables
Straight-through cable: Both ends use the same standard (A-A or B-B). Used to connect unlike devices: PC to switch, router to switch, PC to hub.
Crossover cable: One end uses T568A, the other T568B. Used to connect like devices: PC to PC, switch to switch, router to router. Modern switches with Auto-MDI/MDIX (Auto Crossover) can detect and correct the wiring, so crossover cables are rarely needed today, but the exam still tests the concept.
The Crimping Process Step-by-Step
Strip the cable jacket: Use a cable stripper to remove about 1-1.5 inches (2.5-4 cm) of the outer jacket. Be careful not to nick the inner wires.
Untwist and arrange pairs: Untwist each pair and straighten the wires. Arrange them in the correct order (T568A or T568B) side by side.
Trim the wires: Use a wire cutter to trim the ends evenly, leaving about 0.5 inches (13 mm) of exposed wire. This ensures the wires reach the end of the RJ-45 plug.
Insert into RJ-45 plug: Hold the plug with the clip facing down and the pins facing away. Insert the wires firmly until they bottom out. The jacket should be inside the plug by about 1/8 inch (3 mm) to provide strain relief.
Crimp: Place the plug into the crimping tool and squeeze firmly. The tool pushes the pins down into the wires and locks the strain relief.
Test: Use a cable tester to verify continuity and correct pinout. The tester should show all pins passing (1-1, 2-2, etc. for straight-through, or 1-3, 2-6, etc. for crossover).
Tools and Equipment
Crimping tool: A multi-purpose tool that cuts, strips, and crimps. The 220-1101 exam may ask you to identify the purpose of the crimping tool.
Cable stripper: A tool specifically designed to remove the outer jacket without damaging the conductors. A common mistake is using a knife, which can nick wires.
Cable tester: Verifies continuity and pinout. Advanced testers can measure length, crosstalk, and impedance. The exam expects you to know that a cable tester is used to confirm proper wiring.
Punch-down tool: Used for terminating wires on keystone jacks and patch panels, not for RJ-45 plugs. The exam may ask you to differentiate between a crimping tool and a punch-down tool.
Common Wiring Mistakes and How to Avoid Them
Split pairs: When the two wires of a pair are not twisted together, they become prone to crosstalk. For example, using the blue pair for pins 1 and 2 instead of the orange or green pair. Always keep pairs intact.
Reverse polarity: Swapping the tip and ring within a pair (e.g., pin 1 Green-White vs pin 1 Green). This breaks the differential signaling and the link will not come up.
Incorrect pinout: Using T568A on one end and T568B on the other when you intended a straight-through cable. Always double-check both ends.
Wires not fully inserted: If a wire does not reach the end of the plug, the pin may not make contact. The cable tester will show an open circuit.
Jacket not inside the plug: Without strain relief, the wires can pull out over time. Ensure the jacket is clamped by the plug's strain relief.
When to Use T568A vs. T568B
T568A is the preferred standard for residential and government installations because it is compatible with older USOC wiring. T568B is more common in commercial installations. The key point: be consistent. If you mix standards in a facility, you will create crossover cables unintentionally. For the exam, remember that T568A is the default standard per TIA/EIA-568-A, but T568B is also widely used. Both are acceptable as long as both ends match.
Cable Categories and Performance
Cat5e: Supports up to 1000 Mbps (Gigabit) at 100 MHz. The 'e' stands for enhanced. Minimum for modern networks.
Cat6: Supports up to 10 Gbps at 250 MHz over shorter distances (55 meters for 10GBASE-T). Stricter specifications for crosstalk.
Cat6a: Supports 10 Gbps at 500 MHz up to 100 meters.
Cat7: Supports 10 Gbps at 600 MHz with shielded twisted pairs (STP). Not widely used in LANs.
The exam may ask you to select the appropriate cable category for a given speed and distance. For example, to support 10GBASE-T at 100 meters, you need Cat6a or better.
Shielded vs. Unshielded Twisted Pair
UTP (Unshielded Twisted Pair): Most common. No additional shielding. Relies on twisting for noise rejection.
STP (Shielded Twisted Pair): Each pair has a foil shield, and the overall cable has a braided shield. Used in high-EMI environments. Requires specially shielded connectors and proper grounding.
FTP (Foiled Twisted Pair): Overall foil shield around all pairs.
The exam may test the difference in installation requirements: STP connectors must be grounded, and improper grounding can create ground loops.
Troubleshooting Physical Layer Issues
When a cable fails, the cable tester is your first tool. Common failures: - Open: One or more wires are not connected. The tester shows no continuity. - Short: Two wires are touching. The tester shows a short circuit. - Miswire: Wires are in the wrong order. The tester shows a crossed pair or reversed pair. - Split pair: The tester may show continuity but the cable fails at higher frequencies due to crosstalk. Only advanced testers detect split pairs.
For the exam, remember that a simple continuity tester cannot detect split pairs; you need a certifier that measures crosstalk.
Interaction with Auto-MDI/MDIX
Auto-MDI/MDIX (Medium Dependent Interface Crossover) allows a device to automatically detect whether the cable is straight-through or crossover and adjust accordingly. This feature is standard on Gigabit Ethernet ports. However, some older 10/100 Mbps devices do not support it, so crossover cables may still be needed. The exam expects you to know that Auto-MDI/MDIX eliminates the need for crossover cables in modern networks.
Practical Considerations for Exam Performance-Based Questions
You may be presented with a scenario where you need to choose the correct wiring standard. For example: - "A technician needs to connect a PC directly to a laptop for file transfer. Which cable type should be used?" Answer: Crossover cable (or straight-through if Auto-MDI/MDIX is supported). But the exam may specify older equipment, so know the traditional rule. - "A new building is being wired with Cat6a cable. The IT manager wants to follow government standards. Which wiring standard should be used?" Answer: T568A.
Summary of Key Numbers
8 wires in a UTP cable
4 twisted pairs
Pins used for 10/100 Mbps: 1,2,3,6
Pins used for Gigabit: all 8
Maximum untwisted length at connector: 0.5 inches (13 mm)
T568A: Green-White on pin 1
T568B: Orange-White on pin 1
Auto-MDI/MDIX: eliminates need for crossover cables
Cable categories: Cat5e (100 MHz, 1 Gbps), Cat6 (250 MHz, 10 Gbps up to 55m), Cat6a (500 MHz, 10 Gbps up to 100m)
Strip the Cable Jacket
Use a cable stripper to remove approximately 1-1.5 inches (2.5-4 cm) of the outer jacket from the end of the twisted-pair cable. Rotate the stripper around the cable to score the jacket, then pull it off. Avoid cutting into the insulation of the inner wires, as nicks can cause breaks or impedance changes. The exposed length must be sufficient to allow the wires to be arranged and trimmed later. After stripping, you should see the four twisted pairs (eight wires) with their color-coded insulation intact.
Untwist and Arrange Wires
Untwist each pair and straighten the wires using your fingers. Arrange the eight wires in the correct order according to the chosen standard (T568A or T568B). For T568B, the order from left to right is: Orange-White, Orange, Green-White, Blue, Blue-White, Green, Brown-White, Brown. Flatten the wires so they lie side by side without overlapping. Ensure the wires are straight and parallel for at least 0.5 inches (13 mm) from the jacket to the tips.
Trim the Wires Evenly
Use a wire cutter to trim the ends of the wires so they are perfectly even. The remaining exposed length should be about 0.5 inches (13 mm). This is critical because if the wires are too long, they may not fit fully into the RJ-45 plug, causing poor contact. If too short, the jacket may not enter the plug, leaving the wires without strain relief. A clean, straight cut ensures all wires reach the end of the plug simultaneously.
Insert Wires into RJ-45 Plug
Hold the RJ-45 plug with the clip facing down and the pins facing away from you. Insert the wires firmly into the plug, ensuring each wire slides into its respective channel. Push until the wires bottom out against the end of the plug. Verify that the outer jacket is inside the plug by about 1/8 inch (3 mm) so that the strain relief clamp will hold it. The wires should be visible through the front of the plug.
Crimp the Connector
Place the RJ-45 plug into the crimping tool's connector cavity. Squeeze the handles firmly until the ratchet releases. The tool pushes the metal pins down through the wire insulation to make contact with the copper conductors, and simultaneously crimps the strain relief onto the cable jacket. A proper crimp results in the pins being flush with the plug body. Remove the cable and inspect the connector; the wires should be visible at the tip and the strain relief should grip the jacket.
Test the Cable
Use a cable tester to verify continuity and correct pinout. Connect one end of the cable to the tester's main unit and the other end to the remote unit. The tester will sequentially check each pin. For a straight-through cable, the LEDs should light in order 1-1, 2-2, etc. For a crossover cable, the expected pattern is 1-3, 2-6, 3-1, 6-2, 4-4, 5-5, 7-7, 8-8. If any pin fails (open, short, or miswire), the tester will indicate the fault. Advanced testers also measure length and can detect split pairs.
In a large enterprise deployment, structured cabling is the backbone of the network. For example, a university campus with 10,000+ drops will use T568A or T568B consistently throughout all buildings. The choice is often dictated by existing infrastructure or government mandates. In the US federal government, T568A is required for new installations (per TIA/EIA-568-A). A common scenario is a data center where hundreds of patch cables connect servers to top-of-rack switches. Technicians terminate Cat6a cables with RJ-45 plugs for short runs (under 10 meters) and use patch panels for longer runs. The crimping skill is essential for creating custom-length cables to avoid excess slack. A typical problem is that a technician might accidentally create a crossover cable when a straight-through is needed, causing a link failure. With Auto-MDI/MDIX, this is less common, but on legacy 100BASE-TX switches, it can bring down an entire segment. Another real-world issue is cable quality: using a cheap crimping tool can result in inconsistent pin contact, leading to intermittent errors. In a VoIP deployment, a single bad crimp can cause dropped calls and jitter. Performance considerations include maintaining the twist rate and ensuring the cable category matches the required speed. For 10GBASE-T over Cat6a, the cable must be tested to 500 MHz, and any untwisting beyond 0.5 inches will cause crosstalk and fail certification. Misconfiguration often occurs when a technician uses T568B on one end and T568A on the other while intending a straight-through cable — this creates a crossover cable. In a production network, this can cause a 'link down' condition on the switch port. The fix is to re-terminate one end to match. To avoid this, always label both ends of the cable with the standard used. In summary, proper crimping and adherence to T568A/B standards are fundamental to reliable network infrastructure.
The CompTIA A+ 220-1101 exam tests this topic under Objective 2.3 'Networking' specifically within the sub-objective 'Compare and contrast networking hardware.' Expect 1-2 multiple-choice questions and possibly a Performance-Based Question (PBQ) where you drag and drop the correct wire order for T568A or T568B. The most common wrong answer is confusing T568A and T568B pinouts. Candidates often remember that T568B has Orange-White on pin 1 but then forget that T568A has Green-White on pin 1. Another trap is assuming that crossover cables are never needed — but the exam may present a scenario with two legacy switches that do not support Auto-MDI/MDIX, requiring a crossover cable. The exam also loves to test the number of pins used for 10/100 Mbps (4 pins: 1,2,3,6) versus Gigabit (8 pins). A frequent distractor is 'all 8 pins are used for 100BASE-TX' which is false. Another trick: the exam may show a diagram of a cable with split pairs and ask what problem it causes — answer: excessive crosstalk. Edge cases: the exam might ask about shielded cable grounding — if a shielded connector is not grounded, it can act as an antenna and cause interference. Also, remember that T568A is the standard for government installations, but T568B is more common in commercial settings. To eliminate wrong answers, focus on the pin numbers: pins 1-2 are always a pair, pins 3-6 are always a pair. If the answer choice swaps pin 1 and pin 3, it's describing a crossover cable. If it swaps pin 1 and pin 2, it's a reversed pair (will not work). Always double-check the wire color sequence. For PBQs, practice writing out the order from memory: T568B: OW-O-GW-B-BW-G-BrW-Br. T568A: GW-G-OW-B-BW-O-BrW-Br. The exam will not expect you to memorize the color sequence for every pin, but you should be able to identify the correct order from a list.
RJ-45 connectors have 8 pins; 10/100 Mbps Ethernet uses pins 1,2,3,6; Gigabit uses all 8.
T568A: pin 1 = Green-White; T568B: pin 1 = Orange-White.
Straight-through cable: same standard both ends. Crossover cable: T568A one end, T568B the other.
Auto-MDI/MDIX eliminates the need for crossover cables on modern devices.
Maximum untwisted length at the connector: 0.5 inches (13 mm).
Use a cable tester to verify continuity and correct pinout.
Cat5e supports Gigabit; Cat6 supports 10 Gbps up to 55m; Cat6a supports 10 Gbps up to 100m.
These come up on the exam all the time. Here's how to tell them apart.
T568A
Pin 1: Green-White (TX+)
Pin 2: Green (TX-)
Pin 3: Orange-White (RX+)
Pin 6: Orange (RX-)
Preferred for government and residential installations
T568B
Pin 1: Orange-White (TX+)
Pin 2: Orange (TX-)
Pin 3: Green-White (RX+)
Pin 6: Green (RX-)
Most common in commercial installations
Mistake
T568A and T568B are interchangeable; it doesn't matter which one you use.
Correct
Both standards are valid, but you must use the same standard on both ends of a straight-through cable. Mixing them creates a crossover cable, which may not work with older equipment that lacks Auto-MDI/MDIX.
Mistake
All eight pins are used for 100BASE-TX Ethernet.
Correct
100BASE-TX uses only pins 1,2,3,6 (two pairs). Pins 4,5,7,8 are unused. Gigabit Ethernet (1000BASE-T) uses all eight pins.
Mistake
A crossover cable is the same as a straight-through cable.
Correct
A crossover cable has T568A on one end and T568B on the other, swapping the transmit and receive pairs. A straight-through cable uses the same standard on both ends.
Mistake
You can use any color code as long as both ends match.
Correct
The TIA/EIA standards define T568A and T568B specifically to ensure compatibility and performance. Using a non-standard wiring order can cause crosstalk and signal degradation due to split pairs.
Mistake
A cable tester can always detect split pairs.
Correct
Basic continuity testers cannot detect split pairs because the wires are connected in the correct pin order but not twisted as pairs. Only advanced cable certifiers that measure crosstalk can detect split pairs.
Reveal each answer, then mark whether you got it right. Score 60%+ to unlock the next chapter.
T568A and T568B are two wiring standards for RJ-45 connectors. They differ in the assignment of the orange and green pairs. In T568A, pin 1 is Green-White and pin 2 is Green. In T568B, pin 1 is Orange-White and pin 2 is Orange. Both are valid, but you must use the same standard on both ends of a straight-through cable. T568A is the government standard; T568B is common in commercial settings.
A crossover cable is needed to connect two like devices directly (e.g., PC to PC, switch to switch) if neither device supports Auto-MDI/MDIX. Most modern devices support Auto-MDI/MDIX, so crossover cables are rarely needed. However, the CompTIA A+ exam may test the traditional rule for older equipment.
Strip 1-1.5 inches of jacket, untwist and arrange wires in the correct order (T568A or T568B), trim to 0.5 inches, insert wires into the RJ-45 plug with the clip down, ensure the jacket is inside the plug, then crimp with a crimping tool. Always test with a cable tester.
You need a cable stripper (or a multi-tool with a stripper), a wire cutter, an RJ-45 crimping tool, and a cable tester. The crimping tool is specifically designed to push the pins into the wires and clamp the strain relief.
A split pair occurs when the two wires of a twisted pair are used for different signal pairs (e.g., using the blue pair for pins 1 and 2 instead of the orange/green pair). This breaks the twisted-pair geometry, increasing crosstalk and signal degradation. The cable may pass a continuity test but fail at higher frequencies.
Cat5e is not rated for 10 Gbps. It supports up to 1000 Mbps (Gigabit) at 100 MHz. For 10 Gbps, you need at least Cat6 (up to 55 meters) or Cat6a (up to 100 meters).
A punch-down tool is used to terminate wires on keystone jacks and patch panels, not on RJ-45 plugs. It pushes the wire into a slot and cuts off the excess. The exam may ask you to differentiate between a crimping tool and a punch-down tool.
You've just covered RJ-45 Crimping and T568A/B Pinouts — now see how well it sticks with free 220-1101 practice questions. Full explanations included, no account needed.
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