What is the maximum length of a network cable that can be stretched in meters? What happens if you go over 100 meters? A real record of a 130-meter attempt and a crash

last year, I installed surveillance cameras in the yard, from the weak current box in the living room to the rear wall camera. I measured with a tape measure, and the wiring should be about 130 meters long. At the time, I thought, 'It's a network cable, just plug it in and it will work.' But the day after plugging it in, it started losing packets. A week later, the camera dropped at night, and my phone kept spinning when I clicked it. After much effort, I realized the problem was that "network cables have a maximum distance"—and this upper limit was much more severe than I had imagined.

to get to the bottom of the line: 100 meters is the deadline written into the standard

The maximum transmission distance for a single segment of

network cable (twisted pair) is 100 meters . This is not a manufacturer's recommendation; it is written in the IEEE 802.3 Ethernet standard. No matter if you use Cat5, Category 6, or Category 7, the electrical signal running through copper wire attenuates more sharply. 100 meters is the standard passing line for "signal that can still be correctly confirmed."

actual construction is even more conservative: the standard plans for a 90-meter permanent link plus a total of 10 meters of jumper at both ends. In other words, for the section embedded in the wall during renovation, don't exceed 90 meters, leaving some margin at both ends. How to plan wiring and leaving openings? I wrote more in detail in the renovation network cable planning , and here I only discuss distance.

Why

choose 100 meters? In plain terms, it's two accounts. First is attenuation: electrical signals running over twisted pair cables get weaker and weaker, reaching the hundred-meter level, so weak that the receiving end can almost no longer distinguish between 0 and 1. Second is the time account: In the early days, Ethernet was designed as half-duplex, so the signal had to be echoed within a fixed time window, which converted to a line length of about 100 meters; Later, when full duplexing was implemented, the time limit was tight, but the decay account remained, and the 100-meter distance became the current standard.

my 130-meter crash scene

details of the failure are worth discussing, because the symptoms are typical and gradually worsen:

• first night: The camera could connect, but the negotiated speed was only 100M (100Mbps). I thought it was the camera itself at 100Mbps and didn't pay much attention;
• Day 3: Daytime is fine, but as soon as the courtyard lights come on at night, the screen starts to freeze and spin;
• a week later: Ping camera packet loss rate is 3% to 5%, it drops in the middle of the night, and the next morning it climbs back up on its own.

how to choose camera positions and power supply, I came from the home surveillance network planning article, but that's not the issue. Later, I tested it directly with a laptop cable plug: for a 130-meter cable, the gigabit connector was negotiated for less than 1000M, and they only agreed to 100MB; Switch to a 20-meter line of the same type and immediately negotiate gigabit as usual. I followed the method of connecting the connectors to network cables step by step, and it worked perfectly. At this point, there are only two suspicions left: distance and cable.

Why do some cables fail after seventy or eighty meters: the cable pit

standard has a prerequisite for the 100-meter mark: oxygen-free copper wire that meets the standard. How far you can actually stretch depends on the cable.

oxygen-free copper (OFC) resistance is within 10Ω per 100 meters. Actual tests show that this type of wire can still hold 120 to 150 meters and still hold gigabits—but that's beyond the usual limits. The standard doesn't endorse it; if it passes, it's luck; if not, it's the norm. Copper-clad aluminum (CCA) is a completely different story: aluminum has 40% to 60% higher resistance than copper, and at the same distance, signals drop even harder. The common saying in the industry is not to exceed 70 to 80 meters. Even worse, when the copper-clad aluminum is powered by POE, it heats up noticeably. My camera is powered by POE, and in summer, the wire insulation is always warm. Just thinking about it makes me uneasy.

How to tell

? The most basic method: cut a small piece and peel off the wire core, scrape it with a knife, and after scraping off the copper layer from the copper-clad aluminum, the white color remains; Another hard method is to test the single-core resistance with a multimeter. A single core of 100 meters of oxygen-free copper is about 9 ohms, while copper-clad aluminum is noticeably higher, so the test yields accuracy. There's also the price barrier: the cost per 100 meters of oxygen-free copper is there, and the 'gigabit line' sold at prices lower than cabbage is basically copper-clad aluminum. For scenarios with high rework costs, like installing surveillance cameras or burying hidden wires, just buy oxygen-free copper and don't save money. If you want more margin, go for Category 6, with thicker wire cores and greater comfort over long distances.

really exceeds 100 meters: Three remedial routes

distance is unavoidable, so you have to find a way. I tried three options, with significant differences in cost and applicable scenarios:

switch relay is easiest to understand: when the signal gets tired, a switch is placed in the middle to restate the signal as it is, and the later segment is recalculated at 100 meters. That's how my yard was ultimately saved—there's a storage room in the middle of the yard, with a power outlet for the freezer, a lightning protection strip, and a five-port gigabit switch (how to choose home switch article). The 130-meter switch was split into two sections: 65 plus 65. The gigabit was back on the spot. Two things to note: don't save on metal shells and lightning protection sockets for outdoor equipment; Don't nest with cascading machines—within two or three floors, it's solid. Don't expect five switches to string together candied hawthorn for 500 meters and still be as steady as an old dog.

wireless bridges the third way, suitable for situations where there's no cable routing in the middle: a pair of 5G bridges, one end mounted on the rooftop and the other at the courtyard gate, aligned and powered on, ready to use the same day. Running two or three hundred Mbps in a 200-300 yuan range is not difficult. Its flaw is straightforward—on stormy days, it shivers slightly, and both ends must be visible without obstruction, with even a tree in between, making you suspicious. I didn't choose it at home because it can bypass cables. In scenarios where wired can be used, wired ones always sleep soundly.

Fiber Optic Transceivers: They sound intimidating, but they're actually the most worry-free for long distances

If you build a self-built building between buildings, or between the main gate and the back of the yard a few hundred meters, I advise you to go straight to fiber optic and not to fight with copper wires.

fifty to sixty pairs of 100M single-mode transceivers (like Mercury MC11A-20/MC11B-20, single-fiber bidirectional, rated at 20 km); For gigabit, models with one optical and four electric systems (like Tenda TFC304B, 3 km) are just over 100 km, the optical port can run gigabit, and the electrical port can connect to four devices, basically acting as a small switch. Fiber itself is ridiculously cheap—leather cables cost only a few cents per meter, and after two or three hundred meters, they're even cheaper than Category 5.

installation is simpler than expected: one transceiver at each end, electrical port connected to network cable, optical port to fiber. The only trouble lies in the joints—the fiber end face must be cut flat. You can do it yourself with a cold splice (align and press the V-shaped slot, costing a few yuan each); If you're worried about a mess, have the seller melt both ends according to your length, then plug and play as soon as you get it. Fiber optic connectors are sensitive to dust; don't remove the protective cap before connecting.

Also, remember the temperament of optical fibers: afraid of bending, not pulling. The bending radius of the leather cable should not be less than 3 centimeters. If a right-angle dead bend is bent, the light decay will keep rising, indicating that "the bending is open, but the speed is halved." When planning the route for my hometown house, I suffered losses here—better to take longer routes than take a detour. I've written article on rural self-built house network planning, but I won't elaborate here.

Conclusion: Taking the Position Appropriately, Including My Inspection Order

gather the lessons learned from this time into a single table, and first check the long-distance cables:

the long route I've been running is already having issues. Check in this order, don't switch lines right away:

• check the negotiation speed: check the network card details or switch management page to see whether the connection is 1000M or 100M. Dropping to 100Mbps is usually due to distance, cable, or connector factors;
• keep ping longer to check packet loss: ping -t camera IP down for half an hour, packet loss is a physical layer issue, and the software settings don't blame it;
• double connectors are pressed hard; connector oxidation in long circuits is a common fault. Follow the T568B wiring sequence that article for pressing methods;
• still doesn't work, use a binary method: cut open the middle and connect the straight connector, then test in half. Repair which half is broken. The idea is exactly the same as locating broken network cables inside walls.

end with one sentence: the 100-meter length of the network cable is a physical law, not a suggestion. Before renovating or installing surveillance cameras, measure the distance first; if it exceeds 90 meters, budget based on fiber optics, which is much cheaper than redoing the ladder afterward.