The Quick Answer
Whether you are terminating your first cable or your thousandth, these are the same mistakes that cause intermittent connections, failed cable tests, and callbacks. The good news is every single one is avoidable once you know what to look for.
This guide walks through each mistake in order: what goes wrong, why it happens, and exactly how to fix it. If you just want the summary, jump to the quick reference table at the bottom.
Wrong Connector for Your Cable Type
What goes wrong
When you force a connector designed for a thinner cable onto a thicker one, the jacket cannot seat in the strain relief, the wires cannot align in the channels, and the contact blades cannot pierce the conductors at the correct depth. The result is open pins, intermittent contacts, or a termination that pulls apart with minimal force.
Why it happens
Cat5e, Cat6, and Cat6A connectors all look like RJ45 plugs from the outside. The differences are internal: channel width, strain relief bore diameter, and contact blade geometry. Installers who work with multiple cable types often grab whichever connector is closest without checking the rating.
How to fix it
Match the connector to the cable. Always. For Cat5e, use the EZ-RJ45 Cat5/5e. For Cat6, the EZ-RJ45 Cat6 or ezEX44 Cat6. For Cat6A, the ezEX48 Cat6A. If you work with multiple cable types, the ezEX-RJ45 Universal covers Cat5e through Cat6A and eliminates the guessing.
Untwisting Pairs Too Much
What goes wrong
The twist in each pair is not decorative. It is the primary mechanism that cancels electromagnetic interference (EMI) between adjacent pairs. When you untwist too much, the wires act like parallel antennas at the termination point. The result is elevated Near-End Crosstalk (NEXT), which is the most common cause of Cat6 and Cat6A certification failures.
Why it happens
Untwisting more wire makes it easier to arrange the individual conductors into the correct color order. With Cat5e, you could get away with an inch or more of untwist because the bandwidth requirements are lower. Cat6 and Cat6A do not tolerate that slop. Installers who learned on Cat5e carry the habit forward.
How to fix it
Untwist only enough to fan the wires into the correct order, then hold them flat and trim to length. With pass-through connectors like the EZ-RJ45 Cat6 or ezEX48 Cat6A, you can push the wires through and verify the color order from the front before trimming. This means you need less untwist because you get visual confirmation without needing extra wire to work with. Aim for half an inch maximum, measured from the point where the twist ends to the jacket.
Wrong Wire Color Order
What goes wrong
A swapped pair means two wires are in the wrong position. Depending on which wires are crossed, the link may not come up at all, negotiate at a lower speed, or produce high error rates. A split pair (where one wire from two different pairs is swapped) is worse because it can pass a simple continuity test while still failing performance testing.
Why it happens
The T568B color order is: white-orange, orange, white-green, blue, white-blue, green, white-brown, brown. That is eight wires to arrange in the correct sequence, and two of the pairs cross over each other (the green pair splits around the blue pair). It is easy to swap the green and blue positions or accidentally put a solid-color wire where the striped one should be.
How to fix it
Pick one standard (T568B is the most common in North America) and use it on every single termination. Print the color order or keep a reference card in your tool bag. With pass-through connectors, verify the color sequence from the front of the connector before crimping. A VDV MapMaster 3.0 will catch any wire map errors in seconds. For a deep dive on the two standards, see T568A vs T568B: Which Should You Use? and our RJ45 Pinout Guide.
Uneven Wire Lengths Before Insertion
What goes wrong
When the eight wires are cut to different lengths, the shorter wires do not extend far enough into the connector to make contact with the piercing blades. You end up with one or more open pins on the wire map test. In some cases, the short wire makes partial contact, which is worse because the termination passes initial testing but fails intermittently under vibration or temperature changes.
Why it happens
After arranging the wires in the correct color order, installers often trim them with angled cutters or trim from an angle instead of straight across. The wires on one side end up a few millimeters shorter than the other side. At the scale of an RJ45 connector, a couple of millimeters is the difference between a solid contact and an open pin.
How to fix it
After arranging the wires flat in the correct order, hold them firmly between your thumb and forefinger and make one clean, straight cut with flush cutters. All eight wire ends should be perfectly even. Before inserting into the connector, visually inspect the cut ends from the side. If any wire is visibly shorter, trim again. With pass-through connectors, you have extra insurance because you can see each wire emerge from the front before crimping.
Not Pushing Wires Far Enough into the Connector
What goes wrong
The contact blades inside an RJ45 connector are at the very front. When you crimp, the blades are pushed down and pierce through the insulation of each conductor to make electrical contact. If a wire stops short of the blade, the blade pierces air instead of copper. The pin shows as open on the tester, or worse, makes a marginal contact that works until the cable is moved.
Why it happens
It takes more force than you might expect to push eight wires simultaneously through the tight channels inside an RJ45 connector. If the wires are slightly fanned, or if the cable jacket is gripping them, one or more conductors can hang up partway through. With standard (non-pass-through) connectors, there is no way to verify insertion depth visually.
How to fix it
This is one of the strongest arguments for pass-through connectors. With the EZ-RJ45 Cat6 or ezEX48 Cat6A, you push the wires until they emerge from the front of the connector. If all eight wires are visible and in the correct order, you know every conductor is fully seated. The crimp tool trims the excess automatically. For more detail on this approach, see Pass-Through vs Standard RJ45 Connectors.
Using the Wrong Crimp Tool for the Connector Type
What goes wrong
Crimp tools apply thousands of pounds of force through a precision die. That die is shaped to match the external dimensions of a specific connector family. When you put the wrong connector into the wrong die, force is applied in the wrong places. The connector housing cracks, the contact blades misalign, and the trim blade either misses or cuts in the wrong location. The connector is destroyed and the cable needs to be re-terminated.
Why it happens
The EZ-RJ45 and ezEX connector families look similar at a glance. Both are pass-through designs from the same manufacturer. But their external dimensions differ, and their crimp tools are not interchangeable. Installers who switch between connector types throughout the day sometimes forget to swap tools.
How to fix it
Match the tool to the connector family. For EZ-RJ45 connectors (Cat5e and Cat6), the Clamshell EZ-RJ45 Crimp Tool works. For ezEX connectors (Cat6 and Cat6A), use the EzEX Crimp Tool. If you work with both families, the PTS PRO Universal Crimp Tool handles EZ-RJ45, ezEX, and standard connectors with one die set. For a detailed comparison, see EZ-RJ45 vs ezEX Connectors: Which Do You Need?
Stripping Too Much or Too Little Jacket
What goes wrong
If you strip too little jacket, the exposed conductor length is not enough to reach the contact blades after you arrange and trim the wires. You end up with short wires and open pins. If you strip too much, the cable jacket does not extend into the strain relief area of the connector. The crimp holds the wires, but there is no mechanical grip on the jacket. A tug on the cable pulls the wires out of the connector.
Why it happens
Without an adjustable-depth cable stripper, the strip length varies from one termination to the next. Eyeballing the length is inconsistent, especially when you are working quickly. Cat6A is less forgiving than Cat5e because the internal separator takes up space and needs to be trimmed, which changes the effective conductor length.
How to fix it
Use a cable stripper with a depth stop, such as the Cat5/6 Jacket Stripper for Cat5e and Cat6 work, or the Multi-Strip Cable Stripper for multi-cable-type environments. Set the depth stop once and every strip will be consistent. For Cat6A, strip about 1.25 inches to account for the separator. For more on Cat6A-specific technique, see How to Terminate Cat6A Cable.
Not Testing After Crimping
What goes wrong
You install 50 cable drops. They all look good. You patch them in and half the ports do not link up, three have intermittent errors, and one has a split pair causing packet loss. Now you are pulling patch panels apart trying to figure out which terminations are bad. Every untested termination becomes a potential callback.
Why it happens
Testing adds time. When you are terminating dozens of cables, stopping to test each one feels slow. Experienced installers develop confidence in their technique and skip the tester. The problem is that even a 2% failure rate on 100 terminations means two bad cables that will take longer to find than testing all 100 would have taken.
How to fix it
Test every single termination. No exceptions. A basic wire map test with a LANSeeker Cable Tester takes about five seconds and catches open pins, shorts, crossed pairs, and split pairs. For jobs that require performance certification, the VDV MapMaster 3.0 covers wire map, tone, and length. For Cat6A work where you need to verify actual 10 Gbps throughput, the Net Chaser Ethernet Speed Certifier validates the link end to end. For a comparison of testers, see Best Network Cable Testers.
Mixing Solid and Stranded Connectors
What goes wrong
Solid-conductor connectors have blades that straddle the single solid wire and pierce through the insulation. Stranded-conductor connectors have sharper, pronged blades that penetrate between the individual strands to make contact with multiple strands simultaneously. When you use a solid-conductor connector on stranded cable, the blades push the strands aside instead of gripping them. The initial connection may work, but it degrades as the strands shift over time.
Why it happens
Solid and stranded connectors look identical from the outside. The only difference is the shape of the contact blades, which you cannot see once the connector is assembled. Most structured cabling (in-wall runs) uses solid-conductor cable, while patch cables use stranded. Installers who do both types of work sometimes use one connector type for everything.
How to fix it
Either carry separate connectors for solid and stranded cable and label them clearly, or use dual-rated connectors that work with both. The EZ-RJ45 Cat5/5e and ezEX-RJ45 Universal are rated for both solid and stranded conductors. For a deeper explanation of the differences, see Solid vs Stranded Cable Connectors.
Skipping Strain Relief Boots
What goes wrong
Every time a patch cable is plugged in, unplugged, or shifted, the cable bends at the point where the jacket exits the connector. Without a strain relief boot, all of that bending stress concentrates at a single point. Over time, the conductors inside fatigue and break, or shift position relative to the contact blades. The result is intermittent connections that come and go depending on cable position, which is one of the hardest problems to diagnose in the field.
Why it happens
Strain relief boots add a step to the termination process. They have to be slid onto the cable before the connector is crimped, which means planning ahead. When you forget to slide the boot on first, the choice is to either re-terminate the cable or leave the boot off. Many installers leave it off, especially on cables that will not be moved frequently.
How to fix it
Make it a habit to slide the boot onto the cable as the first step in every termination, before stripping the jacket. This way you never have to re-terminate because you forgot the boot. For patch cables that will be handled frequently, boots are essential. For permanent structured cabling that terminates at a patch panel and is never moved, the boot is less critical but still good practice. For a complete guide, see RJ45 Strain Relief Guide.
Quick Reference: All 10 Mistakes at a Glance
Bookmark this table. It covers the mistake, what happens, and the fix in one place.
| # | Mistake | What Happens | Fix |
|---|---|---|---|
| 1 | Wrong connector for cable type | Wires do not seat, strain relief fails | Match connector rating to cable category |
| 2 | Untwisting pairs too much | Crosstalk (NEXT) failures | Keep untwist under 0.5 inches |
| 3 | Wrong wire color order | Crossed or split pairs, no link | Follow T568B consistently, verify before crimping |
| 4 | Uneven wire lengths | Short wires miss contact blades | One clean straight cut with flush cutters |
| 5 | Wires not pushed in far enough | Open pins, intermittent contacts | Use pass-through connectors for visual verification |
| 6 | Wrong crimp tool | Crushed connector housing | Match tool die to connector family |
| 7 | Wrong strip length | Short wires or no strain relief grip | Use stripper with depth stop (1" for Cat5e/6, 1.25" for Cat6A) |
| 8 | Skipping testing | Hidden failures become callbacks | Test every termination with a cable tester |
| 9 | Wrong solid/stranded connector | Poor blade contact, degrades over time | Use dual-rated connectors or label separately |
| 10 | No strain relief boot | Conductor fatigue from repeated flexing | Slide boot on before stripping, every time |
Recommended Products
These are the connectors, tools, and testers that prevent the mistakes covered in this article. Using the right combination from the start is the simplest way to eliminate termination failures.
Connectors
Match your connector to your cable type. Dual-rated options work with both solid and stranded conductors.
The ezEX-RJ45 Universal is the single-SKU option if you work with multiple cable types. It handles solid and stranded conductors across Cat5e through Cat6A.
Crimp Tools
Match the tool to the connector family. The PTS PRO covers all three families in one tool.
The Clamshell is for EZ-RJ45 only. The EzEX handles both EZ-RJ45 and ezEX connectors. The PTS PRO handles everything including standard connectors.
Testing and Stripping
A cable tester catches problems that are invisible. A good stripper keeps your strip length consistent.
The LANSeeker is fast for basic pass/fail. The MapMaster adds wire map, tone, and length. The Net Chaser certifies actual speed up to 10 Gbps.
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Frequently Asked Questions
What are the most common RJ45 crimping problems?
The most common RJ45 crimping problems are: using the wrong connector for your cable type, untwisting pairs too much before insertion, getting the wire color order wrong, cutting wires to uneven lengths, not pushing wires fully into the connector, using the wrong crimp tool, stripping too much or too little jacket, skipping testing after crimping, mixing up solid and stranded connectors, and not using strain relief boots. Most of these cause intermittent connections or outright test failures.
Why does my RJ45 connector fail the cable test even though it looks fine?
A connector can look perfect on the outside and still fail testing. The most common hidden causes are wires that did not seat fully against the contact blades inside the connector, wires that are in the wrong color order (swapped pairs), or pairs that were untwisted too far back which causes crosstalk failures. A cable tester checks electrical continuity and pin mapping, which catches problems that are invisible to the eye.
How much should I untwist RJ45 wires before crimping?
Keep the untwisted length to half an inch (13mm) or less. The TIA-568 standard specifies a maximum untwist of 0.5 inches for Cat6 and Cat6A. The twist in each pair is what cancels electromagnetic interference between the pairs. The more you untwist, the worse your crosstalk (NEXT) performance becomes. Untwist only enough to arrange the wires into the correct color order.
Can I use an EZ-RJ45 crimp tool on ezEX connectors?
No. EZ-RJ45 connectors and ezEX connectors have different external dimensions and require different crimp die sets. Using a Clamshell EZ-RJ45 or EZ-RJ45 HD crimp tool on an ezEX connector will crush the connector housing. For ezEX connectors, use the EzEX Crimp Tool or the PTS PRO Universal Crimp Tool, both of which have the correct die geometry.
Do I really need strain relief boots on RJ45 connectors?
For patch cables that will be handled, plugged, and unplugged, strain relief boots are strongly recommended. Without a boot, the cable jacket bends sharply at the back of the connector every time the cable moves. Over time, this repeated flexing fatigues the conductors and can shift wires off the contact blades, causing intermittent failures. Boots spread the bend radius over a longer distance and significantly extend termination life. For permanent in-wall cabling that terminates at a patch panel and never moves, the boot is less critical. For more detail, see our RJ45 Strain Relief Guide.
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