A Cold Field Call in December
Back in December 2024, I got a call about a packaging line that kept tripping its overload relay. The maintenance manager said they'd replaced the motor starter twice, and the problem kept coming back. It sounded like a motor issue. It wasn't.
I work in quality and compliance for a cable manufacturer, with products under the Nexans and Nexans Amercable Incorporated lines. My day-to-day is specs, inspections, and contracts, not crawling under conveyor lines. But when a customer's line won't stay running, the spec sheet starts to feel theoretical.
If you're learning how to use a multimeter, here's the first thing I'd tell you: one reading is not a diagnosis. That day made it obvious.
What the Readings Showed
I grabbed a 117 multimeter from the field kit. It's not a lab instrument, but it has true-RMS AC readings, which matters for motor circuits. At the panel, under load, I measured 120.4 volts. At the motor terminals, I measured 109.4 volts.
That is a 9.1% voltage drop. The National Electrical Code doesn't make voltage-drop limits a hard requirement for every circuit, but its informational note (NFPA 70, NEC 2023, 210.19(A) FPN No. 4) recommends 3% for a branch circuit and 5% for feeder plus branch. We were way outside that.
I opened a voltage drop calculator on my phone and entered the data: 110 feet of 10 AWG copper, 23 amps, 120V. The calculator predicted about 5.2% drop. So the wire was undersized for that distance. But the measured drop was almost double the prediction. Something else was eating voltage.
The Connector That Wasn't on the List
I opened a junction box about 20 feet from the motor. The termination looked fine at first: no burn marks, no loose screw, no visible corrosion. But when I touched the probes to the line side and load side of the same connector, I saw a 4.3-volt difference under load. A good connection should be close to zero.
The connector was a generic lug with no torque marking, no date code, and no listing mark that matched our approved materials list. I don't know why the installer used it. Honestly, I'm not sure why. My best guess is that the supply house had it on the truck and nobody wanted to make another trip.
I don't have hard data on how many intermittent trips trace back to bad connections, but based on the field failures I've reviewed, my sense is it's a lot more than most people assume.
The Nexans Connector Fix
The approved replacement was a Nexans connector. It came with a printed torque spec, which is exactly the kind of thing a quality person notices. We cleaned the surfaces, applied the right number of die crimps, and torqued the lug to the value on the packaging.
We re-checked the voltage at the motor: 114.2 volts under load. The drop was down to roughly 5.2%, matching the calculator's prediction for the wire alone. The line stopped tripping.
When I compared the panel reading and the motor reading side by side, I finally understood why voltage drop is so often misdiagnosed. The motor wasn't the problem. The wire was a problem. The connector was the extra problem that pushed it over the edge.
The Real Cost of a Cheap Lug
The generic lug cost less. The Nexans connector cost more. But by the time we added the two service visits, the line downtime, and the motor starter that failed prematurely, the cheap lug was the expensive one.
Total cost of ownership = part price + labor + downtime + risk. The cheapest part is not always the cheapest fix.
I now calculate total cost of ownership before comparing connector prices, not just the unit price. That's true for cable, connectors, and every other component in the system.
What I'd Tell Anyone with a 117 Multimeter
So, how to use a multimeter properly? Measure at the source. Measure at the load. Measure across the connection. Write down the readings. And if a voltage drop calculator says one number but your meter says another, don't ignore the gap—that gap is a clue.
I have mixed feelings about the installer who used that generic connector. Part of me wants to call them out. Another part remembers what it's like to be in the field without the right documentation and under time pressure. So I don't blame the person. I blame the process.
Now I keep spare Nexans connectors in my kit. Not because the brand name matters by itself, but because the spec is printed on the package—which, honestly, makes my job easier.
