Who This Is For (And Why I Wrote It)
If you're an engineer, a technician, or anyone who's ever stared at a pile of loose connectors and a crimping tool and thought, "There has to be a right way to do this"—this is for you.
I'm a quality manager at Kemet, which means I'm the person who inspects components before they go to customers. I've reviewed thousands of connector assemblies over the last four years. And I'll tell you flat out: most crimp jobs I see are either over-crimped, under-crimped, or just flat-out wrong.
I'm not here to sell you on a specific tool or brand. I'm here to give you a repeatable, testable process that works. Here are the four steps I use for every connector I approve.
Step 1: Choose the Right Tool (Don't Just Grab the First One)
Everything I'd read about crimping connectors said you need a "must-have" tool that costs thousands. In practice, I found the opposite: a mid-range, adjustable, four-indent crimper (often under $200) gives way more consistent results for 95% of applications than an expensive fixed-die tool.
Here's the checklist:
- Set a budget: Around $150–$250 for a good adjustable ratcheting tool.
- Check the jaw compatibility: Not all dies fit all connectors. If you're doing RJ45, make sure the die matches the profile.
- Call the manufacturer: I don't care if it's a pain—ask them directly: "What die do you recommend for this connector part number?"
Why I check this: I once rejected a batch of 2,000 connectors because the technician used a tool that was supposed to be "universal." It wasn't. We found the issue only after 8,000 units showed intermittent failures in storage. The rework cost us $22,000 and delayed a major client launch.
Step 2: Strip the Wire—But Not Like That
Most people think stripping is easy. It's not.
Here's what I see:
- Too much insulation removed (wire strands exposed).
- Not enough removed (insulation gets caught in the crimp).
- Nicks in the copper strands because the blade was set too deep.
How to do it right:
- Use a self-adjusting wire stripper. It's super responsive to wire gauge.
- Set the blade depth so it just barely kisses the conductor. You should see the insulation cut cleanly, but the copper strands should be completely untouched.
Take it from someone who's rejected 8% of first deliveries in 2024 for stripping defects: if you can see a single nicked strand, stop. Re-cut. Start over. That strand is a failure point under vibration.
Step 3: The Crimp—And the One Detail Most People Miss
This is where the magic—or the disaster—happens.
You line up the connector, you insert the wire, you squeeze. But there's a step most people skip: making sure the crimp die is exactly aligned with the connector's contact barrel.
Here's how I check it:
- Visually align the die so it sits exactly in the center
- On the first crimp, squeeze the tool just enough to hold the connector, then release and check alignment before the final squeeze.
- If you're off by even 1mm, the contact won't have the right pressure on both sides.
Why this matters: The industry standard, per IPC/WHMA-A-620 (the accepted standard for cable and wire harness assemblies), requires the crimp to have 4 points of contact with the conductor. If the die is misaligned, you might get 3, or even 2. That's not just a quality issue—it's a liability. I've seen connectors fail in the field because of this.
So glad I caught that on a pilot run once. Almost missed it. Would have meant 10,000 units with a 15% failure rate.
Step 4: The Pull Test (Don't Skip This)
The conventional wisdom is that you can just "feel" if a crimp is good. My experience with 200+ orders suggests otherwise. The only reliable way is a pull test.
Here's the rule of thumb:
- For 22 AWG wire: minimum pull-out force is around 15–18 N (3.4–4.0 lbf).
- For 18 AWG: about 30–35 N (6.7–7.9 lbf).
- Check the manufacturer's data sheet for exact numbers.
If you don't have a pull tester (and honestly, most small shops don't), here's a quick alternative:
- Use a pair of pliers to grip the wire, and gently pull.
- If the connector slides off with less than a firm tug, it's a reject.
- For a more precise check, buy a simple spring scale for $20. It's way better than guessing.
One last thing: I'm not 100% sure if this applies to your specific situation, but I'll say it anyway: if you're crimping for a medical or aerospace application, don't even think about skipping the pull test. Your mileage may vary if you're doing a one-off hobby project, but for production work, this is not optional.
Final Thoughts: The Mistakes I See Over and Over
Let me save you some time. Here are the top three errors I flag on inspection:
- Error #1: Over-crimping. People squeeze too hard, and the connector body deforms. If you see a bulge on the side, you've ruined it.
- Error #2: Wrong die for the connector. I can't tell you how many times I've seen someone use a modular plug die on a coaxial connector. It doesn't work.
- Error #3: Not replacing worn dies. A good ratcheting tool will last for years. The dies? They wear out after about 10,000 cycles. If you're not tracking cycles, you're guessing.
There's something satisfying about a properly crimped connector. After all the hassle of alignment, the test, and the rework, finally seeing a perfect batch go out—that's the payoff.
I get why people go with the cheapest tool or the fastest method. Budgets are real. But the hidden cost is failures, rework, and unhappy customers. Trust me on this one: spend the extra $100 on the right tool, take the extra 10 seconds per connection, and you'll save thousands in the long run.
Oh, and one more thing I should add: we keep detailed records of every rejected batch at Kemet. If you want to avoid being in that report, follow these four steps.
