Short answer
In copper Ethernet cabling, the channel length set by the standards is 100 meters: 90 meters for the fixed cable in the wall and a total of 10 meters for the patch cables at both ends. Beyond this distance, the signal weakens, the error rate rises, and the connection slows down or drops. For longer runs, fiber optic cable, an intermediate switch or, for camera lines, a PoE extender is used.
Where does the 100-meter limit come from?
Structured cabling standards, such as TIA-568 and ISO/IEC 11801, specify that a channel of twisted-pair copper cable be no longer than 100 meters. The channel is the entire path from the switch port to the computer or camera. 90 meters of this path is the fixed cable running inside the wall or ceiling, and the remaining 10 meters are the patch cables in the cabinet and at the desk.
The reason for the limit is physics. As a cable gets longer, the signal weakens, the pairs inside the cable interfere with each other more, and the time it takes the signal to reach the other end increases. Ethernet devices are designed for a certain signal quality and delay. The standard expects these values to be met up to 100 meters when the cable and connecting hardware are chosen and installed correctly; beyond that, it is left to chance.
It doesn't matter whether it is Cat5e, Cat6 or Cat6A; as the category goes up, the speed and frequency that can be carried increase, but the channel length limit stays the same. Cat6A cable can carry 10 gigabit speeds over 100 meters; Cat6 reaches this speed only over a shorter distance.
What happens when the limit is exceeded?
A 110- or 120-meter run sometimes seems to work. The computer connects, the camera gives an image. The problem appears later: the connection drops to 100 megabits on its own, the video freezes now and then, the speed drops while copying large files, or the connection drops and comes back several times a day.
Intermittent faults like this are the hardest to find. The user blames the modem, the switch or the camera, devices are replaced, but the problem does not go away. The same line can cause more trouble in summer heat, because the resistance of the cable rises with temperature. In Şanlıurfa, a long line running over a sunlit roof or through a hot attic struggles even if it is below the limit.
On lines that use PoE, length causes a second problem. The power carried over the cable suffers more loss on a long line, and insufficient voltage reaches the camera or access point at the end. The device switches on and off, or restarts when the infrared lights come on at night.
Measuring the distance correctly
A line that looks like 70 meters between two points on a sketch can easily exceed 100 meters on site. A cable does not follow a straight line; it goes up to the ceiling, winds around columns along the duct, and enters the cabinet and turns on the shelf. When planning, look at the path the cable will actually follow, not the straight-line distance.
After the cable is pulled, the line is measured with a tester. A good cable tester reports both the length and the signal values. In a newly installed cabling, asking for the test report of every line weeds out later problems from the start.
Expert note: In planning, take 90 meters as the upper limit for a fixed cable and leave some margin. Later a desk moves, a camera pole shifts a few meters; a line with no margin goes over the limit at the first change.
Options for long distances
If you need to connect a point beyond 100 meters, there are a few ways. Which one is suitable is chosen according to the distance, how many devices will be connected and the condition of the space in between.
- Fiber optic cable: for hundreds of meters and kilometers, with no electrical interference
- Intermediate switch: refreshes the signal at a point midway that has power and a cabinet
- PoE extender: gives a short extension for a single camera or access point
- Radio link: sets up a wireless connection if there is line of sight between two buildings
- Zone cabinet: gathers the devices in a distant zone there and connects them to the center with a single fiber
When is fiber preferred?
For links between buildings, in a factory yard, between blocks within a housing estate and on lines to cameras along a long garden wall, fiber is usually the right choice. Fiber is far more relaxed than copper in terms of distance limit, and because it carries no electricity, it is not affected by lightning or ground potential differences.
Fiber needs modules or media converters at both ends that turn the signal into light. If the end device is powered by PoE, power and a small PoE switch are needed at the far point; fiber does not carry power. That is why, when running fiber to a distant camera pole, a power supply at the foot of the pole and an outdoor-rated box are also planned.
When deciding between copper and fiber, think not only about today's need but also the coming years. Changing a line that will be buried in the ground or enclosed in a wall later is much more troublesome than pulling the right cable the first time.
Limits of the PoE extender
A PoE extender is a small device placed midway that also takes its power from the line. It is a practical solution for taking a single camera slightly beyond 100 meters. However, every extender means one more point of failure and is limited by the power it takes from the line; as they are chained, the power left for the end device decreases.
If the extender will be outdoors or in a damp place, it must be put in a box with a suitable protection rating. Where several devices are gathered at a distant point, setting up a small cabinet and a fiber link at that point is healthier than using an extender.
If your existing long line is causing problems
If the connection of a camera or computer on an installed system drops often, first find out the length of the line. Most switches show on their management screen at what speed the link is established. If you see 100 megabit on a port that should be gigabit, the line may be struggling. Some managed switches also have a test feature that measures the cable length approximately.
If the line is really long, you do not need to tear everything out. Adding a small switch at a suitable point on the route, or replacing only the problem line with fiber, is often enough. When the line is short but still causes trouble, you need to check whether the connector ends, intermediate joints and the cable are crushed; this check is done with a tester in minutes.
Frequently asked
Does Cat6 cable work at 120 meters?
Sometimes it connects, but it is outside the standard. Speed may drop, the connection may drop intermittently and PoE devices may not get enough power. For a long run, using fiber, an intermediate switch or a PoE extender is recommended.
Are patch cables included in the 100-meter limit?
Yes. The channel length is the total of the fixed cable and the patch cables in the cabinet and at the desk. 90 meters are allotted to the fixed cable and a total of 10 meters to the patch cables.
Will the distance increase if I use thicker cable?
As the category goes up, the speed that can be carried increases, but the channel length set by the standards stays at 100 meters. For a longer distance, you need to change the method, not the cable category.
Let us plan your long lines correctly
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