Network cables are the one thing in a workshop that always end up in a tangled pile with no labels on them. You never know how long they are, you never know which one goes where, and when something stops working you have no easy way of telling if the cable is the problem or not. So when a proper network cable tester landed on my desk, I was genuinely curious to see how much of that guesswork it could take away.
The tool is the FNIRSI LPM-10, and it is probably the fanciest piece of test gear I currently own. FNIRSI sent it over to me for free, but they are not sponsoring this review, so everything I say about it here is my own opinion. Today I want to unpack it, go through every function it has, and work out if it actually earns a place on the bench.
What Is In the Box
The box opens from the front and the first thing you see is a soft pouch that doubles as a carrying case. If you are working out on site rather than at a bench, that is a nice touch, because everything packs away into one thing you can carry.
Inside the pouch there is the user manual and a small pile of accessories. There is an adapter that breaks a telephone jack out into two crocodile clips, so you can test telephone cables and bare wires. There is a charging cable, because both units run on internal batteries. There is a quality check card, a pair of wired headphones, a small adapter I was not immediately sure about, and a male to female RJ45 adapter that lets you extend a cable or reach a socket in an awkward spot.
Then there are the two parts of the meter itself. One is the main unit that you plug the cable into, and the other is the detector, which is the probe you wave around to find a cable in a bundle.
A Look at the Main Unit
The main unit has three ports along the top and side. There is a scan port, a QC continuity port, and a third port used for length, flash, and power over Ethernet. That last detail matters, because different tests use different ports and it is easy to plug into the wrong one. The left side of the unit is blank.
On the back label you get the specs. The battery is a 3,000 mAh cell, and cable length can be measured from two and a half metres all the way up to 200 metres. At the bottom there is a charging port sitting under a rubber grommet to keep dust and moisture out.
Since I had no idea how long this had been sitting in transit, the first thing I did was plug it in to check the charge. A red light came on while charging. There is also a screen protector on the display, and peeling that off was very satisfying.
Powering it on brings up the FNIRSI logo followed by a language selection screen, and English is right there. Inside the settings you can adjust the screen brightness so the display is easier to read, change the volume for the beeper, and open an about page that shows the firmware version. Mine arrived with a good amount of charge already in it, so it came ready to use straight from the factory.
The main menu gives you cable test, scan, length, flash, QC test, speed, power over Ethernet, and settings. The M button goes into whichever option you have selected, and the power button steps back out. Hold the power button down and the unit turns off. There is no touchscreen here, so everything is done with the physical buttons.
The Detector Unit
The second unit is the detector. It has its own charging port under a rubber cover along with a headphone jack. The headphones are there so you can trace a cable by ear without filling the room with beeping and annoying everyone else working around you.
The tip of the unit is the probe, and there is a light built into it so you can see what you are doing behind a rack or in a dark ceiling void. The light will not turn on until the whole device has been powered up first, which caught me out at the start. It is not a particularly bright light, but it does the job.
There is an adjustment knob on the side for sensitivity, and a switch to pick between scan mode and NCV mode. NCV stands for non-contact voltage, and it tells you if a cable has mains voltage running through it without you having to touch a single conductor.
Testing Non-Contact Voltage
To try the NCV function I grabbed a power lead from a monitor that was not connected to anything else. Running the probe along it, the detector immediately started complaining that there was voltage present. Cranking the sensitivity dial up to maximum made it even more eager.
For comparison I tried a USB lead and got nothing at all, which is exactly what you want. On the powered cable you get a constant beeping telling you the cable is live. If you are ever working inside a cabinet full of unlabelled cables, knowing which one is carrying mains before you grab it is genuinely useful.
Testing the Cables Themselves
For the main test I pulled out a handful of network cables that came from various devices over the years, so I had no idea what was inside any of them. I selected cable test and picked the far end option, which is the mode you use when the other end of the cable is not plugged into anything.
With nothing connected at all, the screen showed everything as disconnected, which is what you would expect. Then I plugged the other end of the cable into the second port on the meter and ran the test again. What came back was interesting. Wires one, two, three and six showed as connected, while four, five, seven, eight and the ground all showed as disconnected. That cable only has four wires in it, and when I looked closely at the transparent connector I could see exactly that. The meter had read it correctly.
Testing the rest of the cables, most of them showed all eight wires connected with only the ground missing. That is not a fault. Those cables use plastic connectors with no metal shielding on the outside, so there is no ground path to detect in the first place. I do not think I even own a shielded cable to test that part with.
Being able to see exactly which wires are missing is the part I like most here. If you are crimping your own connectors, this tells you immediately if you got a wire in the wrong slot or if one of the conductors did not seat properly in the connector.
Measuring Cable Length
The length test is the one I was looking forward to most. It uses a different port on the meter, and you get to choose the unit you want in the menu. One small annoyance is that the unit selection is not saved as a preference, so you have to pick metres again every single time you run the test.
My first attempt with a short patch lead just returned out of range. That makes sense, because the minimum measurable length is two and a half metres and this one was shorter than that. Disconnecting it gave the same result.
Then I moved to a yellow cable running to my switch. I unplugged the far end first, which turns out to be important, and ran the test. It came back with 10 metres, which is exactly how long that cable is. There is one physical quirk to be aware of, which is that the length port does not hold the connector's locking clip, so the plug wants to pop back out and you have to hold it in place while the test runs.
For sorting through a pile of cables where nobody wrote the length on the boot, this is a quick and accurate way to find out what you actually have.
Why the Far End Must Be Unplugged
This one is worth calling out on its own, because it caught me out and the results are convincing enough that you might believe them. With the cable still plugged into my switch, I ran the length test again. The meter reported pair one and two at 62 metres, pair three and six at 122 metres, pair four and five at 80 metres, and pair seven and eight at 62 metres.
That is a 10 metre cable. None of those numbers are real. Running the test again gave a completely different set of numbers. The switch is still talking on that cable, and that communication interferes with how the meter measures length. So for any length test, one end goes into the meter and the other end must be hanging free.
Testing the Speed
The speed test tripped me up at first. I kept plugging the cable in and getting a connection timeout no matter which port I tried. Going back to the manual sorted it out. For the speed test, the far end of the cable has to be plugged into a live router or switch, because the meter is negotiating a link with it rather than just measuring the wires.
Once I used a cable that was actually attached to my switch, the test ran straight away and told me it was a one gigabit full duplex link. That is a fast way to find out if a run is quietly negotiating down to 100 megabits because of a damaged pair somewhere in the wall.
Tracing a Cable Through the House
The scan function is what the detector unit was built for. You plug the cable into the scan port on the main unit, start the scan, and the meter puts a tone onto the cable that the probe can pick up.
There are two modes to pick from, normal and noiseless. In normal mode the probe starts beeping as soon as it gets near the energised cable, and the sensitivity dial lets you tune how close you have to be before it reacts. Standing right next to the meter it picks up everything, so you dial it down as you get closer to the target.
To give it a real test I set the scan running on a cable in my son's room and went back to the messy bundle coming out of my ceiling. There is a group of cables there feeding my CCTV cameras, and I knew the cable I was after was one of them. I also knew it was not the blue one, because that goes to my LoRaWAN gateway.
Running the probe along the bundle, nothing happened on any of the other cables, and then it started screaming on one of them. That is the cable. Doing this the old way means unplugging things one at a time and hoping you remember what you disconnected. This took seconds, and the light on the probe helps you see what you are pointing at up in a dark corner.
While I was there I flipped the probe over to NCV mode and ran it along the same bundle. It ignored all the network cables and reacted only on the mains cable running alongside them.
Flashing a Port on the Switch
The flash function solves the other half of the same problem. Instead of finding where a cable runs, it tells you which port on the switch it lands in.
I plugged a cable into the meter, set it to flash mode, and walked over to where my switch is. That cable goes into port three, and sure enough the third port LED was blinking on and off at a steady interval that was clearly being driven by the tester and not by network traffic. For anyone who has ever stood in front of a patch panel unplugging cables to figure out which is which, this alone might be worth the price.
Power Over Ethernet
The power over Ethernet test is the one function I could not properly demonstrate, because I do not currently own a single device that provides power over the cable. I tested a cable coming from my switch and it correctly reported that no voltage was present.
What the meter is capable of is detecting voltage up to 60 volts on the cable and showing it on screen. If you are installing cameras or access points that draw their power over the network cable, that is a fast way to confirm the injector or the switch is actually delivering power before you start blaming the device.
The Port Indicators
One detail I appreciated more the longer I used it. Depending on which test you have selected, the screen shows indicators next to each port telling you where the cable needs to go. Go into flash mode and one port lights up green while the other one greys out. Go into the scan test and an arrow appears pointing at the port up top.
Given that this meter has three ports and eight different tests, that small bit of guidance saves a lot of confusion. It is the difference between a tool you have to keep reading the manual for and one you can just pick up and use.
Conclusion
The LPM-10 covers a lot of ground for a single tool. Wire mapping tells you which conductors are actually connected, length measurement takes the guesswork out of a pile of unlabelled cables, the tone generator and probe find a cable in a bundle in seconds, port flashing identifies where a run terminates on the switch, and the speed test confirms a link is negotiating at the rate it should. Add non-contact voltage detection on the probe and you have a tool that does most of what you need when you are wrestling with network cabling.
The things to keep in mind are minor. The length test needs the far end unplugged or the numbers are pure fiction, the speed test needs a live switch at the other end, and the unit preference for length is not remembered between tests. None of that stops it being a useful bit of kit.
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