I run a low-voltage contracting crew. I've been ordering cabling and pulling wire for commercial and industrial jobs for 12 years, and in that time I've personally made six significant mistakes totaling roughly $23,000 in wasted budget. This one — the one about the multimeter and the cable order — taught me the most.
September 2022. I'm standing in a server room outside Lawrenceburg, KY, staring at a multimeter that's telling me $8,000 worth of General Cable is garbage. I'm about to authorize my crew to cut every run out of the walls.
Good thing one of my guys asked me an annoying question first: "Did you check the meter?"
I hadn't. That's how I learned the difference between a $40 Infinity Pro multimeter and a Klein Tools MM700 the hard way.
It Started With a USB Power Delivery Test
The job: pulling Cat6A for a control network in a building near the General Cable plant in Lawrenceburg. The order came through a supply house that draws stock from that facility — about 9,000 feet of cable, 22 drops, all with test reports.
Part of the commissioning work involved USB-C powered edge devices. I keep a USB power delivery recording list for those jobs — a paper log where I write down every port's negotiated voltage, current draw, and anything that looks weird. The list itself is simple: columns for port number, adapter model, negotiated PD profile, voltage under load, current, and pass/fail. But because it's a written record, it forces the person testing to slow down and actually look at each reading instead of glancing at a screen and moving on.
And that list caught one. Every port read 19.2 volts on an adapter that negotiated for 20.0. Not technically outside tolerance, but not right either. That made me nervous enough to start testing the horizontal cable runs. Then things went sideways: the same meter showed 12.6 ohms on a 120-foot run I expected to see under 2. I stopped the crew and made the call: bad cable.
Two Mistakes, One Paranoia
Here's where my history made me stupid.
In 2015, my first year running my own show, I bought a pallet of THHN from a guy who called himself a "General Cable supplier." The price was 30% under the local distributor. I checked the labels, got excited about the savings, and paid the invoice. Two days later the inspector flagged it — no UL marking on the conductor. We ripped out every run we'd landed. $3,200 in material gone, a three-day delay, and the most embarrassing conversation I've ever had with a client.
So when this meter started screaming that the Cat6A was out of spec, I wasn't objective. I was already composing an angry email to my supply house. I'd convinced myself it was 2015 all over again — another gray-market cable disaster.
For a solid hour I went back and forth. Rip out the cable and reorder? That was $8,000 of material in the dumpster, a week of schedule slip, and a very unpleasant phone call to the general contractor. Leave it in and commission it anyway? That meant signing off on something my meter said was defective. My gut was stuck on the 2015 nightmare, and the only way to break the loop was a second opinion.
It wasn't until Mike, one of the journeymen, finally spoke up that I snapped out of it.
The Infinity Pro vs Klein Multimeter Test
Mike said, "Before we cut anything, can we check your meter?"
He pulled a Klein Tools MM700 out of his truck. Nothing fancy — not the newest model, not a lab-grade instrument — just the meter he'd carried for years and trusted. We put both meters on the same USB-C PD adapter. Same outlet. Same leads, actually, because I wanted to rule out bad test probes.
Klein: 20.06 volts. Infinity Pro: 19.21.
Then the cable run, same leads. Klein: 1.9 ohms. Infinity Pro: 12.6.
The cable was fine. The meter was lying.
I tested a known 1k resistor from my tool bag. The Klein hit it dead-on. The Infinity Pro read nearly 15% high. Then I checked the folded paper manual that came with it — a tiny 'accuracy: ±(2.5% + 5 digits)' disclaimer that I'd never bothered to read. On a good day, that's a guess. On a modern switch-mode power supply, it's worse than useless.
And the supply house, to their credit, answered the phone, put the order on hold, and emailed the test reports within the hour. The reels had traceability back to the General Cable facility in Lawrenceburg, KY, with matching reel numbers. I just couldn't see that through my own panic until the meter problem was sorted.
What the Cheap Meter Got Wrong
I'm not saying every Infinity Pro unit is garbage. I'm saying I had no business trusting a budget meter for USB power delivery verification in 2022.
Here's the part that took me a while to understand. USB-C PD adapters use switch-mode power supplies. They don't produce a clean sine wave — they produce noisy, distorted waveforms. A True RMS multimeter measures that properly. A meter that reads 'average RMS' and scales it up by a sine-wave constant will report wrong numbers on those circuits. The Infinity Pro wasn't True RMS. It also hadn't been calibrated since I bought it, if it ever was, and it had spent eight months bouncing around in my truck door before this job.
Think of it like a camera with a fixed shutter speed pointing at a strobe light. Sometimes it catches the bright flash, sometimes it catches the dark gap. Either way, the photo doesn't match what your eye actually sees. That's what a non-TRMS meter does on a switch-mode supply — it gives you a confident-looking number that just isn't true.
The Klein MM700, per Klein Tools' spec sheet, is True RMS and rated CAT III 1000V / CAT IV 600V. That rating isn't marketing. It means the meter is designed to handle non-linear loads and to protect the user on real industrial circuits. The cheap meter wasn't rated for that work — and a meter that's not rated for the circuit you're testing isn't just inaccurate, it's a safety hazard. I'm glad the worst outcome here was a bad reading instead of a flashover.
The Checklist That Caught 47 Mistakes
That afternoon I bought an MM700 for every vehicle on my crew. About $160 each. Hurt a lot less than $8,000.
And I built a pre-check list that's now in every project folder:
- Test the meter against a known reference before trusting any critical reading.
- Use True RMS for USB-PD, PoE, VFD, and any other non-sinewave circuit.
- Record every reading on the USB power delivery sheet — voltage, current, and which meter was used.
- Demand the mill test report and verify the supplier is authorized to sell General Cable product.
In the first 18 months, that list caught 47 potential errors on our projects — a transformer tap set wrong, a mislabeled breaker, and a whole batch of adapters that would have been a fire risk if installed. And the cable order from the Lawrenceburg plant? It passed every test once I used a meter that could see the truth.
What's Changed, What Hasn't
The fundamentals don't move. Verify before you blame. A test instrument is only as good as its calibration. A supplier's word means nothing without documentation.
But the industry has changed underneath us. Best practice in 2015 isn't best practice in 2025. The circuits we install now — USB-C PD, PoE++, variable frequency drives, LED drivers — generate noisy, distorted electrical environments. The cheap test tools that were acceptable back then don't cut it anymore. Neither do vague supply chains. General Cable is part of the Prysmian Group now, which changed how distribution works, and there are plenty of unauthorized 'wholesalers' out there selling reels that wear familiar labels. Some of that product is fine. Some of it isn't. The only way to know is to verify the source and ask for paperwork.
The question everyone asks when they buy a multimeter is 'what's the price?' The question they should ask is 'can I trust this reading on the circuits I actually work on?' And the buyer who orders cable shouldn't ask 'what's your best price?' — they should ask 'where was this made, and can you prove it?'
For me, the answers were a Klein MM700 in every van, and a rule I've never broken since: the meter gets verified before the material gets condemned.
When I train new guys now, I start with the same speech: tools lie, supply chains muddy the water, and the answer is always verification. This checklist is the cheapest insurance you'll ever buy.
That rule is why we didn't rip out $8,000 of good cable. It's also why I'm telling you this story — so you don't have to learn it the expensive way.
