Calculating Ethernet Cable Overall Channel Length for Success
Written by Don Schultz, trueCABLE Technical Manager, Fluke Networks Copper/Fiber CCTT, BICSI INST1, INSTC, INSTF Certified
Consider this situation: An installer runs 290 feet of solid copper Ethernet cable and dutifully punches down both ends of the cable into patch panels and/or keystone jacks. The installer then plugs in some stranded copper patch cords at both ends, both totalling about 30 feet and turns the equipment on. The speeds are not what is expected and there is severe packet loss. What’s worse is the cable system does not seem to work well in the afternoons. On very hot days, it does not work at all. The next morning everything seems OK. What the heck is going on? Isn’t 328 feet (100 meters) the magic number? The answer is sometimes “no”. It all depends on the installation. Please note the video is a short demonstration. The written blog that follows is far more detailed and gives actual calculation tables.
When installing solid copper Ethernet cable you might have heard terms like “permanent link” and “channel”. Being aware of these terms, and the restrictions associated with them, will help you design and install a working SCS (structured cabling system). This blog is dedicated to helping you figure out how to create an overall working channel, which is more complicated than it first appears. So, buckle up because we are going to talk about:
- What makes up an overall channel and what are the components?
- Does Category and conductor gauge of the solid copper permanent link (also called “horizontal cable” affect your length?
- How long can permanent links and channels be and how are they related?
- How long can patch cords be?
- How temperature can affect the length of your permanent link and therefore the overall channel length
- Example calculation of a properly constructed overall channel
What makes up an overall channel and what are the components?
If you are an experienced installer and frequently work with business communications cable installations, this concept will not be new to you. Traditional channels are comprised of:
- Solid copper Ethernet cable (Cat5e, Cat6, Cat6A, for example)
- The solid copper Ethernet cable is terminated at both ends to IDC (insulation displacement contact) terminations such as patch panels and/or keystone jacks. This provides female ports on both ends. The result is a permanent link.
- The permanent link is then patched into with patch cords at both ends. An example would be a short patch cord in your telecommunications room to patch your switch into your patch panel and then on the other end a longer patch cable to plug a computer into a wall outlet.
- The overall Ethernet channel ends up with male plugs on both sides when the patch cords are plugged in
There are slight variations upon this theme, but the key item is IDC terminations and patch cords are used somewhere in this overall channel.
Example overall Ethernet channel
Does Category and conductor gauge of the solid copper permanent link affect your length?
No, assuming you are constructing your permanent links according to the ANSI/TIA 568 series of specifications and guidelines. There is a hard rule on the maximum length of permanent links. This hard limit is regardless of whether the solid copper Ethernet cable is 24 AWG Cat5e or 23 AWG Cat6A.
There can be variations that exceed the rules, but they require very thick 22 AWG conductors and trade-offs in your expected speeds. There are specialty “Ethernet” cables designed to carry data reliably at longer distances, subject to limitations. To see more on this, please read Breaking the law! Violating Ethernet Cable 328 Foot Length Limitations.
Myth debunked: Many novice installers are under the impression that higher Category rating will provide “more feet”. This is flatly incorrect.
How long can permanent links and channels be and how are they related?
No doubt you have heard by now this statement: “Ethernet cable can be 328 feet long”. Please get that phrase out of your vocabulary. It is misleading and only tells 10% of the story. The correct way of wording that phrase is:
“Copper twisted pair Ethernet cable channels, under ideal conditions and within certain limitations, may reach 328 feet maximum.”
Here are the actual guidelines from the standard to reach this maximum limit:
- The permanent link must be constructed of 22 to 24 AWG solid copper conductors. Category is not relevant.
- The two patch cords must be constructed of 24 AWG stranded copper conductors
- The solid copper permanent link has a maximum length of 295 feet at 68℉
- Each patch cord may be up to 16.5 feet long
- In totality, under the above conditions and circumstances, you achieve 328 feet. This means up to 295 feet of solid copper cable and up to 33 feet (total) of stranded copper patch cord.
As far as relationship between the channel and permanent link, the permanent link is part of the channel and is the permanently installed cable. Permanent links are the solid copper portion running inside walls and above your ceilings (or below your floors) that end up at patch panels and keystone jacks (called drops). Once you have plugged in two patch cords on either side of the permanent link you have created the overall channel. Keep these criteria in mind:
- ALL channels always end up with two 8P8C (aka RJ45) style connectors at both ends. This includes your typical “RJ45” modular plug or it might be a field termination plug as well.
- Permanent links end up in female ports on both ends and are effectively useless until you create your overall channel by plugging in patch cords
How long can patch cords be?
As you might have noticed above, there were some caveats around patch cords. You may have noticed that I pointed out 24 AWG and 16.5 feet very specifically. There is a reason for that! As patch cords are constructed from stranded copper conductors they have far more attenuation (also called signal loss) associated with them. This attenuation gets more severe as the patch cord copper conductor gauge gets thinner. Therefore, a 26 AWG patch cord has more signal loss than a 24 AWG patch cord. If the difference between solid and stranded copper conductors confuses you, please read Solid vs. Stranded Ethernet Cable.
Is there a chart that shows just how long patch cords can be in various circumstances? Yup, there sure is. You will need to get familiar with the concept of “de-rating”:
Total Channel Length With Patch Cord De-Ratings. Image Courtesy of ANSI/TIA-568.0-E
Notes on using this table:
- D = De-rating factor applied using an equation, so…
- D=1.0 means solid copper is used for the patch cord, no de-rating
- D=1.2 means 24 AWG stranded copper patch cord
- D=1.5 means 26 AWG stranded copper patch cord
- D=1.95 means 28 AWG stranded copper patch cord
- Link = permanent link length
Interesting take-aways from this table:
- The length of your patch cords figures very prominently into the “maximum of 328 feet for Ethernet”
- The gauge of our patch cords may not even allow you to reach the “maximum of 328 feet for Ethernet”
- “Thin might be in” but when it comes to 28 AWG patch cord, the absolute maximum length is 49 feet assuming it is used as the entire channel. This means using a 49 foot long factory pre-terminated and tested patch cord as the only cable in the mix, like from a switch directly to a TV. If there is a permanent link being used, and the permanent link happens to be 295 feet in length, you can have a total of 20 feet of the 28 AWG patch cord (2 x 10 ft cords, for example). Even if your permanent link is less than 295 feet, you are still restricted to 49 feet of patch cord total.
- If you were to run 26 AWG patch cord from a computer to a router, assuming it is factory terminated and tested, you could get away with 223 feet maximum, and that would be in indoor temperatures. That is not 328 feet!
How temperature can affect the length of your permanent link and therefore the overall channel length
You may have noticed I keep referencing ambient temperature. One may assume that is potentially a big deal in how long your Ethernet cable can run. If you assumed that, you assumed right. Temperature can become a severely limiting factor and cause you to change your strategy such as inserting an intermediate switch somewhere along your overall channel. It has certainly happened to me!
- The higher the ambient temperature the shorter your permitted lengths are
- Higher temperatures increase signal loss (called Insertion Loss) because that is how copper behaves
- Indoor installations that have ambient temperatures in the 68 to 72℉ range are not really subject to this phenomenon
- ANY outdoor installation is absolutely subject to this phenomenon
- ANY indoor industrial installation (factory, indoor farms, etc.) that experience higher heat levels are subject to this phenomenon
Is there a chart for that? Of course! I wrote a detailed blog about Temperature's Effect on Ethernet Cable Length. It is strongly recommended you read it if you are expecting your installation to be subject to temperatures exceeding 72℉.
Here is a partial screenshot of the temperature table found in that blog which illustrates this:
Read this chart with the patch cord de-rating factors in mind too! The overall channel lengths listed above are predicated on 24 AWG patch cord. You are not getting the whole picture unless you combine the two charts together.
It just so happens that shielded Ethernet cable can mitigate this issue to some extent. Be careful, however. Shielded cable drives up installation costs and complexity to a point that inserting intermediate Ethernet “dumb” switches (AC or PoE powered) somewhere in the overall channel might make much more sense and cost less.
My recommendation is to use shielded Ethernet cable to avoid issues revolving EMI/RFI/ESD and don’t attempt to use shielded cable to avoid higher temperature length issues.
Putting it together: Example calculation of a properly constructed overall channel
We have an installer named “Joe”. Yeah, I could probably have picked a more interesting name. Joe intends to install security cameras outside his small business. He knows that he needs Cat5e at least, because his security cameras require 1 Gigabit speeds. Considering Cat5e handles up to 2.5 Gigabit this is no issue. That said, Joe is worried a bit about future upgradability and opted for Cat6. Joe selected trueCABLE Cat6 Outdoor Unshielded solid copper Ethernet cable.
Joe took a look at his climate data for his region and found out that the outdoor portion of his installation will be subjected to a worst case scenario ambient temperature of 107℉. The longest cable run will be 230 feet from patch panel to camera.
Joe further plans to use 28 AWG Cat6 patch cords at the patch panel end found in his office. The longest patch cord he will need is 5 feet. The patch panel end of the solid copper Ethernet cables will be punched into keystone jacks and mounted in a tool-less patch panel frame. The jacks are Cat6 rated. The other end of the overall channel will be directly terminated to a 8P8C (aka RJ45) connector to plug directly into the camera, so a second patch cord will not be required. This is known as a MPTL link (Modular Plug Terminated Link) and is commonly used for PoE devices. It will be treated identically to a permanent link.
Will this work? Let’s find out:
Joe is using solid copper Ethernet cable for his link, so he has potential access to all 295 feet allowed subject to temperature. His maximum worst case scenario temperature is 107℉ so his maximum link length is 269 feet. Joe stated his longest run is 230 feet, so he is fine in regards to temperature.
Joe intends to use 28 AWG patch cords. Looking at the patch cord de-rating chart we get…
As you can see, he has the ability to use 49 feet. That far exceeds his requirement of 5 feet. Joe is good on patch cord length too!
This will work!
Joe can now install his structured cabling system without fear of intermittent reliability (assuming he follows all the other rules around termination and running Ethernet cable!). By following these guidelines Joe also won’t need to worry about his cameras fritzing out on him during the hot summer months.
So, there you have it. By now you can see the discussion of how far copper twisted pair Ethernet cable can run is much more complicated than you might think. The key is being prepared with the correct knowledge. Given the amount of misinformation found on-line (most of it well intentioned) getting the details right when it comes to a reliable install. Nobody wants cameras that blink on and off randomly or blur, right? With that in mind, I will say…
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