Whether you are troubleshooting an existing Ethernet cable or planning for a new installation it is important to understand the limitations of your materials so that you can be sure of what it is and is not capable of doing. One limitation that commonly comes up in my projects is the max length of Ethernet cable before data loss or attenuation begins to happen.
The maximum length of an Ethernet cable from one network device to another is almost always 100 meters or 328 feet. This effective max distance of Ethernet is the same from category 5 through to category 8 Ethernet cable but can be reduced because of a hand full of external factors. These factors included electromagnetic noise in the area, the quality of the installation, cable temperature, and the number of terminations across a single cable. Anyone who needs to extend their network beyond this limit can do so by using a network cable type designed for the increased distance or by installing a network device at some point along the run to boost, or extend, the signal.
Why Does Ethernet Have a Length Limit?
The first question that many people have when they find out that Ethernet cable only works up to 100 meters is why does Ethernet have a length limit? The reason for this limitation has to do with the nature of electricity as it travels down a cable.
All materials, including the copper inside of an Ethernet cable, have what is called internal resistance. Internal resistance is nothing more than a measure of how difficult it is for electricity to travel through any given material. The lower the resistance of a material the more easily electricity can travel down a cable made of said material. Copper is a great conductor of electricity but it still has some internal resistance. This resistance puts a physical limit on just how far signals made of electricity can effectively be transmitted down a cable.
A theoretical Ethernet cable made of gold would have lower internal resistance and would work for longer distances. Another theoretical Ethernet cable made of tin would have much higher internal resistance and would not work well at all. The engineers who designed the original standards for Ethernet cable chose to target a distance of 100 meters as it strikes a good balance between utility and cost of materials.
| Cable Type | Media Type | Link Speed | Frequency | Max Length (Metric) | Max Length Imperial) |
|---|---|---|---|---|---|
| Cat 5 Twisted Pair | 1000BASE-T | 1 Gbps | 100 MHz | 100 Meters | 328 Feet |
| Cat 5e Twisted Pair | 1000BASE-T | 1 Gbps | 100 MHz | 100 Meters | 328 Feet |
| Cat 5e Twisted Pair | 5GBASE-T | 5 Gbps | 100 MHz | 100 Meters | 328 Feet |
| Cat 6 Twisted Pair | 1000BASE-T | 1 Gbps | 250 MHz | 100 Meters | 328 Feet |
| Cat 6 Twisted Pair | 5GBASE-T | 5 Gbps | 250 MHz | 100 Meters | 328 Feet |
| Cat 6 Twisted Pair | 10GBASE-T | 10 Gbps | 250 MHz | 55 Meters | 180 Feet |
| Cat 6A Twisted Pair | 1000BASE-T | 1 Gbps | 500 MHz | 100 Meters | 328 Feet |
| Cat 6A Twisted Pair | 10GBASE-T | 10 Gbps | 500 MHz | 100 Meters | 328 Feet |
| Cat 8 Twisted Pair | 10GBASE-T | 10 Gbps | 2000 MHz | 100 Meters | 328 Feet |
| Cat 8 Twisted Pair | 40GBASE-T | 40 Gbps | 2000 MHz | 30 Meters | 98 Feet |
In this table, you can see that while most twisted-pair Ethernet cables are designed to work at the standard 328 feet there are some unique situations where maximum lengths were sacrificed for increased performance. It is not likely that you will be using many network devices that are equipped with 10 Gbps network interface cards in a residential setting but it is something to consider if you will be using a server, NAS, or other pieces of high-end equipment. It is also something that you might want to keep in mind if you would like your network to be as future-proof as possible.
Armed with an understanding of why Ethernet cables have a max length limit, let’s take a look at what counts as a single cable when talking about length limits and how to tell how long a given cable is.
Permanent Links and Ethernet Channels
When looking at how long an Ethernet cable can run it is important to understand just exactly what counts as a cable in that context. This can be a little bit confusing because there is no reason that you cannot connect multiple cables end to end and then use them collectively as a single link to connect network devices. To resolve this confusion the term channel is usually used to refer to a network link from one active device to another. This can be a single Ethernet cable or it could be several.
The classic example of an Ethernet channel is made up of three separate cables. The first cable in this example is a 16-foot patch cord from a switch to a patch panel. The second cable is what is known as a permanent link cable and is installed in a structure in a way that it is never moved. The maximum length of the permanent link cable in this example is 295 feet. The final cable is another 16-foot patch cable that connects from the termination of the permanent link cable to a network device such as a computer or smart tv.
All three of these cables combined come out to a total of 327 feet and do not exceed the maximum allowable length of Ethernet cable. When planning a network most people only think about the permanent link cables that will be installed. After all these cables are what you will be working with throughout the project. It is important however to remember that the patch cords will be added later in most situations so the maximum length of the permanent link cable should be reduced to allow room for the patch cords to be installed.
How Do I Tell How Long My Cable Is?
At this point, we know how long our cables can be and we are ready to apply that knowledge directly to your project. The length of a cable is important to think about in two major situations. The first situation is during the planning stages when one needs to make sure that a planned cable will not go over the max useable length. The second is after a cable is already installed and is not performing correctly.
If you have not yet installed any cable and you are still in the planning stages your next step is to look for the longest cable run on your project and estimate how long that cable will be. This will allow you to ensure that all of the cables in your network will be under the maximum length limit. The only real way to do this is to think about everywhere that the cable needs to go and then add up all of the lengths to get an estimate of how much cable will be needed to install that link. As an example, I will go over the pathway for an Ethernet cable in my home office to show what needs to be considered when estimating the total length of cable. This cable;
- Starts on a patch panel in my garage
- Service loop behind patch panel – 15 feet
- Up the wall and along the ceiling – 15 feet
- Though the pathway to the attic – 12 feet
- In attic – 35 feet
- Service loop -15 feet
- In Wall – 8 feet
- Total – 100 feet
Because this is the longest cable in my home I can be sure that everything on this property is well under the maximum length requirement of a cat 6 cable. The same technique can be used in any other project to estimate the length of the cables that will be installed.
In cases where you need to find the length of a cable that is already installed in a home, there are two major methods. The first way to measure the length of a cable is to use a cable tester. All but the cheapest cable testers have a function that allows you to see the length of an Ethernet cable with a quick and simple test. The second method is great because it does not require any special tools and can be done by anyone.
The second way to measure an existing cable is to use the length marks on a cable. The length markings can be set up in a variety of ways in a box of cable but they all allow you to look at the length measurements on a cable and know exactly how long your cable is with some simple math. The most common way that these length markings are set up is for there to be the longest length measure of the box on the first bit of cable that comes out of the box. The measurements then count down from there until the box is empty. In some brands, the numbers will match up with the total amount of cable in a box. In this case, a thousand-foot box would have a 1000 foot marking at the beginning, a 500-foot mark right in the middle, and a 3-foot mark just before the end.
Because of this, all you need to do to get the length of an existing Ethernet cable is to note down the nearest length marking on each end of the cable. For the cable in my office, one end of the cable says 14 feet while the other end says 117 feet. That means that the total length of this cable is 103 feet.
What Things Can Decrease My Cables Effective Maximum Length?
While it is true that an Ethernet cable that is configured correctly is rated to work at up to 328 feet without any problems some situations can reduce this number significantly. These situations include EMI (or electro-magnetic interference) in the area, cable temperature, the quality of the installation, and the number of terminations across a single cable.
While Ethernet cables are designed to perform well in an electro-magnetically noisy environment, there is a certain amount of noise that is too much for the cable to be able to perform well in. There are techniques, such as cable shielding, that can make the cable perform better in said environments but in the absence of these techniques, the effective maximum distance of the cable is reduced. One of the hard things about this sort of situation is that it is extremely hard to identify and estimate the effect of this kind of noise. The good news is that environments that are bad enough to cause problems with Ethernet cable are extremely rare in the residential setting.
A problem that is far more likely to reduce the max effective length of a cable in a home is cable temperature. I explained earlier that the effective length of a cable is determined by its internal resistance. One interesting thing about electrical resistance is that it tends to increase as temperatures go up. The 328-foot standard that we have been talking about up to this point only applies to cable that is at or below 68 degrees Fahrenheit. As temperatures rise the effective distance that a signal can travel down a cable is reduced. Because of this, there are situations where a cable will perform well in the morning but as the day burns on and the temperature in your attic increases some of the longest cables in your home may begin to lose performance. On the hottest days of the year, my attic can easily reach some of the higher temperatures on the chart below. Because of this, the maximum effective length that I can run a cable in my home is only 279 feet (328 feet minus 49 feet.)
| Temperature (Celsius) | Temperature (Fahrenheit) | Decreased Range (Meters) | Decreased Range (Feet) |
|---|---|---|---|
| 20 | 68 | 0 | 0 |
| 25 | 77 | 1 | 3.3 |
| 30 | 86 | 3 | 9.8 |
| 35 | 95 | 4.5 | 14.8 |
| 40 | 104 | 6 | 19.7 |
| 45 | 113 | 8.3 | 27.2 |
| 50 | 122 | 10.5 | 34.4 |
| 55 | 131 | 12.8 | 42 |
| 60 | 140 | 15 | 24.2 |
The last major group of factors that can decrease an Ethernet cable’s maximum effective range is anything that might increase the link’s internal resistance or limit its ability to withstand EMI effectively. Some of the most common things that can affect a cable in this way are;
- Pinched Cables
- Kinked Cables
- Stretched Cables
- Cables That Turn More Sharply Then The Manufacturer Approved Bend Radius
- Poorly Terminated Cables
- Cables with more than the standard two terminations on a single channel
- Oxidized or corroded connections
These types of problems can vary wildly as to how detrimental they can be to the cable’s maximum effective reach. For example, at one company I worked for in the past we were required to subtract a full fifty feet from the max range of cat 6 if we ever needed to have a third termination at some point along the channel. The best way to avoid these types of issues is to ensure that the network is installed properly and that there are no situations where moisture can affect the cables or terminations.
If you have an existing cable that is not performing up to your expectations take a look at the cable’s length and some of the above factors. Even if the cable is not quite the full advertised length of 328 feet you may be trying to send signals a bit too far if one or more of the above situations applies to you.
How Do I Extend My Network Beyond Ethernet’s Maximum Length?
While all of this is useful information, none of it will help someone that just needs to get a network connection to travel further than the standard maximum distance. If you find yourself in this situation you have two good options. The first option is to use a different type of network cable altogether. The second option is to add another network device into the middle of the cable to break a single channel that is too long into two separate Ethernet channels that are within the length limit.
The best way to extend a network channel beyond the standard maximum range is to use a cable that is purpose-built for the job. This method will likely be more expensive than just adding an Ethernet repeater to the channel but in the end, it will be a simpler and more stable solution. This table shows some of the most common multi-mode fiber optic options that you could use. If you need to go over the 1804 foot distance there are single-mode fiber-optic options that can easily go for ten or more miles but I did not include them here as I have never personally even seen someone use single-mode in a residential setting.
| Cable Type | Media Type | Link Speed | Frequency | Max Length (Metric) | Max Length (Imperial) |
|---|---|---|---|---|---|
| OM1 Fiber Optic | 1000BASE-SX | 1 Gbps | 500 MHz-Km | 220 Meters | 721 Feet |
| OM1 Fiber Optic | 10GBASE-SR | 10 Gbps | 500 MHz-Km | 33 Meters | 108 Feet |
| OM2 Fiber Optic | 1000BASE-SX | 1 Gbps | 500 MHz-Km | 550 Meters | 1804 Feet |
| OM2 Fiber Optic | 10GBASE-SR | 10 Gbps | 500 MHz-Km | 82 Meters | 269 Feet |
| OM3 Fiber Optic | 1000BASE-SX | 1 Gbps | 500 MHz-Km | 550 Meters | 1804 Feet |
| OM3 Fiber Optic | 10GBASE-SR | 10 Gbps | 500 MHz-Km | 300 Meters | 984 Feet |
| OM3 Fiber Optic | 100GBASE-SR10 | 100 Gbps | 500 MHz-Km | 100 Meters | 328 Feet |
| OM4 Fiber Optic | 1000BASE-SX | 1 Gbps | 500 MHz-Km | 550 Meters | 1804 Feet |
| OM4 Fiber Optic | 10GBASE-SR | 10 Gbps | 500 MHz-Km | 400 Meters | 1312 Feet |
| OM4 Fiber Optic | 100GBASE-SR10 | 100 Gbps | 500 MHz-Km | 150 Meters | 492 Feet |
Keep in mind that if you decide to use fiber in your network you will need to make sure that you have network equipment that is capable of using it on both ends. This may mean that you need to buy a special network card for your computer or that you will need to use a second switch that is capable of using the fiber.
The second way that you can extend a network can be quite a bit cheaper than using fiber-optic cables and is a good fit for many people. There are however some drawbacks to doing things this way. The first problem is that an additional network device can introduce unwanted latency into your network, especially if the network device being used is not of high quality. The second major drawback is that there is no good way to go beyond 650 feet using this method. The final potential issue is that there will be a network device somewhere out in the middle of the channel which can cause a hand full of problems.
The reason that you may want to avoid installing a network device in the middle of an Ethernet run is that there is a good chance that the device in question will end up installed somewhere less than ideal. There is nothing worse than having to climb into an attic to flash the firmware on a repeater. There is also the question of power. Unless you use an Ethernet repeater that is equipped to use PoE (or Power over Ethernet) you will need to find a way to power the network device.
Even with all of these potential drawbacks, there are many situations where a second network switch or a repeater can easily be installed in a utility closet or office. In these situations, it can be hard to justify the additional cost that would come along with using a fiber optic link. In these cases, adding another network device to break up an extra-long channel can end up being the best option.