I'm a quality control manager at a cable distributor. I review roughly 200 terminated cable assemblies a year before they ship. In Q1 2024 alone, I rejected 14% of first articles because the crimp was wrong. Not because the connector was cheap. Because someone skipped a basic step.
This checklist is for anyone who installs low-voltage cable—think cordless phones, access control systems, LED lighting, or sensor networks. It's also for specifiers who want fewer field failures. There are seven steps. Follow them in order, and you'll avoid the most common termination problems I see.
Step 1: Verify connector and cable compatibility
Before you touch a crimping tool, check that the connector is rated for the exact conductor size and stranding. A 16 AWG connector won't grip a 14 AWG conductor properly, even if it "fits." I once had a vendor claim their connector was compatible with our 2.5 mm² cable. The datasheet said otherwise—the wire barrel was narrower, and the crimp failed after three days.
If you're using Nexans cable, the datasheet usually lists recommended connector families. Nexans Norway AS also offers termination guidance for offshore and industrial cables. Follow that guidance. Don't guess.
Step 2: Use the right tool and die
A pair of pliers is not a crimping tool. I don't care what the delivery driver says. Use a ratcheting crimper with the die matched to the connector. For insulated terminals, that usually means a die for the wire gauge. For uninsulated lugs, the die number is often stamped on the connector. If the die doesn't match, you're not crimping. You're deforming.
Step 3: Strip to the correct length
Strip too little, and the conductor won't reach the compression zone. Strip too much, and you expose bare wire outside the connector. The correct length is usually marked on the connector itself. If it's not, check the spec sheet. Measure it. Don't eyeball it.
Step 4: Check the wire insertion depth
This is the step most people miss. For a clear crimp with an inspection hole, push the wire in until you see it stop—and barely visible in the peep hole. For non-insulated barrel lugs, insert the conductor until it touches the end stop. If you can't push it all the way, re-strip. A too-short conductor means the crimp bites on plastic and air, not copper.
We didn't have a formal insertion-depth check when I first joined. Cost us when a customer's test lab found loose connections in a batch of 300. After that, I made it part of every inspection protocol.
Step 5: Crimp, then pull test
Apply the crimp according to the connector's spec. Once the ratchet releases, do a tug test on every critical connection. Not a hard yank—a firm pull that should not let the wire slip. On a 16 AWG wire, it needs to feel solid. If it moves at all, cut it off and do it over.
The upside of accepting a questionable batch is staying on schedule. The risk is a field failure. I kept asking myself: is the schedule worth potentially failing later? No.
Step 6: Visual inspection
After the pull test, look at the crimp. The insulation barrel should be compressed but not cut. The conductor barrel should show a clean indentation with no cracks. No copper strands sticking out. No burnt or discolored insulation.
I've seen 8,000 units get ruined because a worn die left a sharp burr that punctured the shrink tubing. That burr became a moisture path, and the whole batch failed. A lesson learned the hard way.
Step 7: Measure voltage drop
A bad crimp is a resistor in disguise. And a resistor means heat and voltage drop. For low-voltage devices like cordless phones, a 0.5 V drop can make a base station restart at peak load. That's not a "power supply problem." That's a termination problem.
Measure the voltage drop across the connector—not just the wire. Use a micro-ohmmeter if you have one. A good crimp on a 10 mm² conductor should measure well under 0.5 milliohm. Higher-than-expected resistance means suspect work. Compare against a known-good connection if you're not sure.
I don't have hard data on industry-wide failure rates caused by bad crimps. But based on our returns over five years, my sense is that at least 60% of low-voltage field failures start at the connection, not in the cable itself.
Common Mistakes and Notes
Over-crimping is more common than under-crimping. Too much force can crack the barrel or thin the copper. If your dies are worn, replace them. And never mix copper and aluminum conductors without an approved bi-metal connector—that's a corrosion circuit waiting to happen.
One more thing: ask for the manufacturer's spec sheet before you accept a quote. My rule is simple: ask what's not included before asking what's included. The vendor who lists all fees and specs upfront—even if the total looks higher—usually costs less in the end. That applies to connectors just as much as services.
Per NFPA 70 (NEC) 110.14(C), connections and terminations shall be made with listed pressure-connecting terminals and installed at the proper temperature rating. The NEC recommends voltage drop not exceeding 3% for branch circuits and 5% for combined feeder and branch circuits.
That's it. Seven steps. The real cost of a bad connection isn't the connector or the wire—it's downtime. I'd rather reject a batch and have the vendor redo it than send out something that fails at 2 a.m.
If you take one thing from this: check the insertion depth. That's the one everyone skips. Seriously.
