Temperature's Effect on Ethernet Cable Length
Imagine this: You are running Ethernet cable through an attic in the “dog days” of summer. You wonder, “Is this going to affect my data somehow? I am melting up here!”
On the opposite side of the spectrum, you are running Ethernet cable outside during the dead of winter. Your face is turning a beautiful shade of blue. The same thoughts occur to you, “If I am freezing, what about my data?”
Is it true that temperature can affect how your Ethernet data cable operates?
The quick answer is yes. If you have read my other blogs, you know the real answer is never simple.
Ambient Temperature Extremes
Extremely high or low temperatures can introduce a number of factors that you may not be aware of. Any reputable Ethernet cable manufacturer will list the temperature ranges, and these temperatures are set by the manufacturer and/or per ANSI/TIA 568. When speaking in regards to temperature extremes, we have the absolute “do not exceed” temperatures for installation, operation, and storage -- for ambient temperatures.
Ambient temperature is the temperature around you. Inside your room is one ambient temperature. Walk outside and that ambient temperature is likely different. For example purposes, let’s take a look at our Cat6A Unshielded Direct Burial trueCABLE spec sheet to find out where we can go:
So we have a maximum ambient temperature limit of 167º F. This means the cable will not reliably pass data above that temperature. What about the lowest temperature?
- -40º F (or C) as the lowest possible operating or storage temperature
- -4º F (or C) as the lowest possible installation temperature
What that all means is you dare not try and install Ethernet cable below -4º F because your cable is likely to crack and get annihilated in your effort to run it. Plastic (and likely you too) get brittle at extremely low temperatures. Not that you really want to install at that low of a temperature anyway? Right? I hope you are nodding “yes”. Honestly, I do.
Once installed and not moving, the colder operating temperature limit of -40° F comes into effect. This is also the lowest temperature for storage.
The maximum operating temperature extremes is the same for our outdoor and indoor cables--but with a catch.
The big environmental advantage to outdoor cable is its ability to shrug off ambient temperature extremes (temperature swings). You likely already know that outdoor CMX cable jackets fight off UV rays, water, ice, and other bad stuff. What you may not know is that CMX cable jackets are designed to be impermeable to water vapor. Riser rated and plenum rated communications cable is based upon PVC and is permeable to water vapor. This means water vapor (not liquid water) will migrate through the pores of the plastic jacket. When dealing with stable indoor temperatures this phenomenon goes unnoticed since the cable will “breath”. Water vapor has a chance to enter and leave as it desires, and all is well. In severe temperature swings, however, if you use the wrong cable you will have a problem.
Outdoor cables are LLDPE jacketed, which does not allow moisture vapor to intrude at all. We are not talking about water you can see. Remember that idea you had of saving money and running Riser rated cable through sealed PVC conduit outside? That is a bad idea. Over time, indoor Ethernet cable installed outdoors will allow water vapor in and then due to temperature swings that water vapor will condense back into liquid water before it has a chance to escape. For the record, that will ruin your cable.
We won’t really talk about that here, but suffice it to say you should not run your Ethernet cable through vats of liquid Nitrogen or on top of a pizza oven. M’kay? Again, I really hope you are nodding “yes”.
Insertion Loss Due to (Higher) Temperatures
You know how everything in life has a catch of some kind? Well, except for death and taxes. This applies to Ethernet cable too. In my blog Ethernet Cable Lingo I point out that “usually but not always…” means that there are always exceptions and that technical information needs to be taken in context.
For indoor temperature regulated environments, or if you live in a place that is 68° F or less year round, the generic rules around maximum distance for Ethernet cable length apply. This means that any one Channel can be 328 feet or 100 meters long. For Permanent Links or Modular Plug Terminated Links (MPTL) the distance limit is defined by ANSI/TIA 568 2.D as 295 feet or 90 meters.
So, how does this change when temperatures rise past 68° F? As temperatures rise, the lengths of your runs need to get shorter. Otherwise, you will get signal degradation over distance, also known as attenuation, to the point where the cable will not work reliably or at all. In the ANSI/TIA and Certification realm, this is called Insertion Loss.
What’s happening is the cable becomes “thine own enemy”. The very construction of it, to include the conductor insulation, can actually become slightly conductive as temperatures rise and chlorine atoms present in the plastic get “weird”.
How significant is this effect?
All stated lengths are using a miminum of 24AWG solid copper Ethernet cable of Cat5e or above.
Note** Maximum Channel length is predicated on Field Term to Field Term or RJ45 to RJ45. No additional patch cables are involved.
Note*** Maximum Permanent Link length allows the use of (2) patch cables at either end of the link, up to the total 328 feet maximum length allowed.
So, putting this into context:
- At or below a certain temperature (baseline) the distances you can run your cable are not affected. It is going above the baseline that will trigger a need to reduce lengths.
- Shielded cable can go further than unshielded as temperatures rise and still maintain reliability, but only to a certain extent.
- If your ambient temperature exceeds 167 °F, then you are advised to use fiber optic cable.
Advice? Keep your expected maximum temperatures in mind for your installation and then set your distance limits for your drops based on the most extreme temperature possible. For example, if you have a MPTL style shielded cable link going outside (keystone jack to RJ45 connector for a camera or something), and your area sees 110º F temperatures in the summer, then keep your distance down to less than 280 feet. But, that is not the end-all answer.
What about PoE or Power over Ethernet? Since you are putting DC voltage across an Ethernet cable in this situation, you are right to ask if that adds heat to a cable. It does, and it gets worse with thinner conductors. This is why I often suggest 23AWG pure copper solid conductors for PoE runs that exceed 150 feet. In other words, Cat6 or Cat6A is king when it comes to PoE over distance in higher temperatures. Cat5e may work when you throw PoE into the mix, but not as reliably when temperatures are high and are distances long.
Unfortunately, there is no handy chart or guide for the effects of PoE because there are so many variations of PoE and each device that needs power will draw different wattages at different times.
What it all comes down to is...
Testing. This step is skipped by some folks, but it should not. The best of the best testing involves the use of a Fluke Versiv DSX CableAnalyzer. When lacking one of those, a good way to test is found in this free white paper: Testing 10 Gigabit Ethernet Over Copper on a Shoestring Budget.
With that said, HAPPY NETWORKING!
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