Temperature's Effect on Ethernet Cable Length
Written by Don Schultz, trueCABLE Technical Sales Representative & Fluke Networks Certified Technician
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.
Extreme high and low temperatures affect more than just achievable speed. They can affect cable integrity as well. Any reputable Ethernet cable manufacturer will list the temperature range on the high end. The low end of the range is already defined by the industry. When speaking in these terms, we have the absolute “do not exceed” temperatures for installation and normal operation -- 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 Riser trueCABLE spec sheet to find out where we can go:
Interestingly, the maximum operating temperature is the same for our outdoor and indoor cables. Outdoor cable has the ability to shrug off ambient temperature extremes (temperature swings). Its jacket does not degrade in sunlight and is not semi-permeable like PVC. Riser rated cable is indeed semi-permeable like any PVC. This means moisture vapor can migrate through the plastic jacket, but “breath” so that vapor can escape as well. Our 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? Forget it for the same reasons.
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? UL and cETLus define this as:
- -40º F (or C) as the lowest possible operating temperature
- -20º F (or C) as the lowest possible installation temperature
What that all means is you dare not try and install Ethernet cable below -20º F because your cable is likely to crack and get annihilated in your effort to run it. 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, the colder operating temperature limit comes into effect.
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 Temperature
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 a temperature regulated environment, or if you live in a place that is temperate 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 are not regulated? 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?
The table below from the G Annex of ANSI/TIA 568 C.2 will say a million words:
Image courtesy of the Fluke Networks website
So, putting this into context:
- If you rely on our maximum cable temperature of 167º F, your runs need to be a lot shorter. You are now in 250 foot territory for U/UTP Ethernet cable, or about 260 feet for F/UTP shielded Ethernet Cable.
- If you are at a typical comfortable ambient temperature of 68 to 75º F then you can remain at the 295 foot maximum for a Permanent Link.
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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