What should you do if the network cable inside the wall breaks? Out of eight lamps on the line tester, only 4 lit up. I used the dichotomous method to find the break point where the mouse bit me

early autumn last year, the desktop computer in the study suddenly started getting a bit slow. Gigabit broadband, and the living room computer was always around 940Mbps when I ran the cable, but the study unit was stuck at 93 or 94Mbps, the numbers so steady it felt like someone had soldered them together. I suspected broadband at first, but the unit in the living room was clearly full-speed; I also suspected the computer's network card, and after fiddling with drivers all night, it didn't work. Finally, I grabbed my laptop and went to the study, plugged it into the wall panel—also 93MB. At that moment, I realized: problem wasn't with the device, but with the network cable embedded in the wall for five years. This article will cover the entire process of locating breakpoints, reading and measuring wiring, and the three repair methods. Anyone who has completed wiring will find it useful sooner or later.

spend ten minutes first to eliminate both ends, don't blame the wires in the wall

wall internal lines are the most difficult sections to maintain, so they should be the last to be suspected. I set a rule for myself: only after checking both ends can I have the right to move on the idea of the wall.

first thing is to replace the jumper. The jumper wires from the router to the panel and from the panel to the computer are all flexible. It's common to get caught by the door, oxidized connectors, or snapped clips. Try replacing one wire each for two minutes. I conveniently swapped the router end from LAN1 to LAN2—it's not uncommon for a router to fail on a single network port, so replacing the port would rule out that. If your home doesn't have enough network ports and needs to rely on a switch, don't overlook the switch step. How do you choose and connect it? I've written a .

second thing is cross-validation. Plug the laptop directly into the router's LAN port and run a speed test: 940 Mbps, indicating both the router and broadband are fine; Then I plug the same laptop into the study panel, 93MB. Both jumpers had been replaced, the equipment had been replaced, and only the wire inside the wall remained in the middle—the suspect was identified. The 93 Mbps number is also important. In a gigabit environment, being stuck between 90 and 95 Mbps is basically a typical characteristic of "running on a 100 Mbps link." the optical modem plugged in the wrong 100 Mbps port it was the same number. At the time, I even blamed the optical modem for quite a while.

How to read the light on a

line tester: 1236 on, 4578 off, gigabit has dropped to hundreds

found the fifteen-yuan line gauge I bought the year I pressed the crystal head. There were two boxes, one for the main and auxiliary parts, one plugged in at each end. When the switch was set to ON, the lights would flash in order from 1 to 8. lights on all don't mean the cable is fine; the number of lights is the most information-rich part.

the results I measured: lights 1, 2, 3, and 6 were normally on, while lights 4, 5, 7, and 8 just wouldn't light up. The reference line is blue, blue-white, brown-white, brown-white, and brown—these four wires are broken. Those in the know probably laughed at this—10MB only requires four cores—1, 2, 3, and 6—to work, so this computer "can still go online," but quietly dropped from gigabit to 100MB. This is the most problematic part of the wall disconnection: it doesn't alarm, just slowly. I calculated the score for four-core and eight-core in the of the for pressing the crystal head. Here, you just need to remember the conclusion: only with all eight cores fully integrated can you get Gigabit.

To summarize the pronunciation of

lamp, there are three main situations. If all 8 lights are on but the internet speed is still slow, that's not a broken wire. Check the negotiation speed and cable type. Some old houses have electricians directly threading four-core wires for you, naturally 100Mbps wires without issue; All eight lights are completely off, and the computer network port is directly red X, which is actually the easiest way to locate; Someone like me, half-bright, is the most hidden and also the main character of this article. Another type of pitfall is misaligned lights, such as the main and secondary lights not matching their numbers. That's a wiring error and a problem with the connector, unrelated to broken wires.

breakpoints are hidden: first check these three places, then use binary methods

confirm that the four cores are broken, the next step is to find where the breaks are. The network cable runs through the wall, so you can't just smash it, right? Actually, it's not necessary. There are only three high-incidence breakpoints, and checking these three spots first can solve most of the problems.

the first point: ceiling and maintenance opening. The ceiling line is exposed, which is where mice love to bite—believe it, it's perfectly normal for mice to be in old residential building ceilings. Second, the panel boxes at both ends. The inner wire of the box was snapped and caught, smeared with putty from renovation, and later damaged by the electric hammer—all here. The third location, near the weak current box. The box door is often left open for mice to enter, and the wire at the corner of the box door can easily be cut by the metal sheet of the box body. I had just lifted the flashlight from the study ceiling maintenance port and shone a flashlight: the outer shell of that wire had been bitten open, four of the eight cores broken, the bite marks were clear, and the four wires from the Lan and Zong families were all out, perfectly matching the wire detector's readings.

if you haven't finished all three sections, you need to apply the binary method. The premise is that there is a removable point in the middle of the circuit: cable box, 86 box, or the panel from another room—all are fine. Cut the wire from the middle point, use a wire gauge to measure both sections: the good segment has all eight lights on, the bad segment continues to show broken core—cut the range in half. If the broken half has another dismantling point, do another round. When renovating your home, you have a single conduit and a wire running straight through, with no disassembly points in between. If you can't use binary methods, then the only option is to replace the entire wire for a single route, which is actually straightforward.

a quick mention of the tools to avoid buying the wrong ones. If you search online for 'network cable breakpoint,' you'll find a wire finder. That device is for audio cable finding—you can find 'which cable is which' among a pile of wires. You can't measure the breakpoint, so don't place an order impulsively. If you really want to take it apart, the device that reports the breakpoint distance in meters is called a time-domain reflectometer. It sends a pulse onto the line, bounces back after touching the breakpoint, calculates the time difference and distance, and only has it in the installer's toolbox. Buying it for home use is a waste of money.

How to fix

breakpoints found: I tried each of the three paths once

find the breaking point, amend the law according to the situation, and I'll rank from highest to lowest recommendation level.

first, let's talk about replacing the whole one—this is my top recommendation. Don't pull out the old wire; tie it tightly to the new wire and wrap it with tape. Use it as a "wire" to "pull the wire." Bringing the new wire over from the other end of the pipe is much easier than threading new wire through an empty pipe. The only downfall was that more than one cable was stuffed inside the pipe, so the resistance was so strong it couldn't be pulled. If you did, don't force it—if you broke the neighboring wire, you'd be so sad you'd have no time. That's how I replaced the ceiling section—cut a section of Cat 5 and put it up, and it took half a day to finish.

connectors are emergency solutions. One is two or three mao, two core wires are inserted, and with pliers, the blade inside pierces the insulation and bites the copper wire. Breaking four of eight cores means connecting four pairs. To be honest, gigabit is very sensitive to crosstalk. The connection point in the line is a "scar," and after connecting, you might negotiate back to gigabit but send large files with bits and retransmissions, which looks fast but is actually unstable. So after connecting, you must retest, which will be explained in detail in the next section.

really don't want to move the wall, here are two backup plans. Exposed PVC cable trays run along the corners of walls, and it's all done in one day. The appearance is subjective. Even easier, I just gave up on that cable and replaced it with wireless backup: the old router was relayed, Mesh wireless backhaul worked, the Mercury wireless bridging article wrote the full steps. Cutting the speed in half is a physical rule, but it's more than enough for a study to brow or hold a video conference.

Finish the work after wiring: Retest the negotiation rate before it counts

whether it's replacing cables or connecting wiring, you must check one number before finishing work: network card negotiation speed. In Win11, go to Network, Internet, or Ethernet in the settings, scroll down to "Connection Speed (Receive/Transmit)," and it will show that only 1000/1000Mbps counts as a gigabit link. On old systems, pressing Win+R to enter ncpa.cpl and double-clicking Ethernet would still work. Shows 100/100, all dry white on the front.

But negotiating over gigabytes is just the passing line. I need to remind you one more word about the way the wires are connected. I helped a friend disconnect once, negotiated a speed of 1000Mbps, but when copying files from the internal network, a 40GB folder got a verification error halfway through. Two tries both times both disconnected at the same location—the connection was a bit error, and the retransmission slowed the effective speed down to just 20 to 30MB/s. Eventually, they replaced the entire cable and finally calmed down. So for emergency wiring, you need to add an acceptance criterion: the internal network copies a large file once, and after dozens of gigabytes of files without errors, it can be considered truly repaired. How to test speed reliably follows the same as broadband speed test: don't just look at web speed tests; check internal network copy and negotiated speeds together.

three preventive actions to avoid getting bitten a second time

after this repair, I reflected a bit. If I had done all three things properly, I wouldn't have gone through this ordeal.

First, don't be greedy for too many in your renovation. Ideally, one conduit runs through one network cable, at most two. Once the conduit is full, you can't pull it when switched, which basically seals the wire. the article about installing network cables during renovation, I wrote an acceptance checklist before. Here's an even tougher one: when handing over, use a wire tester to run through each wire, then sign off only after all eight lights are on. If there are any issues, have the technician replace them on the spot. Afterwards, a wall seal will make it hard to explain.

second, leave maintenance openings for the ceiling and weak current box, and keep the weak current box door always closed. The rats are running through cable trays and pipelines inside the ceiling, leaving the inspection port open. Every year, they lift the flashlight to shine a photo, so teeth marks are detected and treated early, but the cost is five minutes.

third, don't stretch the wires inside the panel box too tight. Leave some U-shaped margin so the thread doesn't get caught by the clip, and you can still cut off a section and re-press the head during future maintenance.

finish, lay out the entire sequence: replace jumpers and ports to exclude both ends, cross-verify the laptop to lock the inner wall section; The line gauge reads the light; remember, 1236 on 4578 is off means Gigabit drops to 100 Mbps; Ceiling removal, panel boxes, and weak current boxes are three high-risk points; if there is an intermediate box, use a binary method; The method of renovation follows the order of replacing the entire wire, connecting the wire, then the exposed wire or wireless; Finally, let's look at the negotiation speed and the internal network review to wrap up. The only tool was a fifteen-yuan line gauge throughout the process, and the incident of smashing the wall never happened.