What Happens If Water Gets Inside Ethernet Cable?
Written by Don Schultz, Technical Sales Representative and Fluke Networks Certified Technician
Have you ever been tempted to run indoor rated Ethernet cable outside? That might seem like a good idea if it is a short run or put it into a PVC conduit. Admit it, you have been tempted. So, incidentally, have I. In fact, I had to learn the hard way just how wrong of an idea this is. See Selecting the Correct Outdoor Ethernet Cable for more about why this is not the way to go.
Liquid water inside an Ethernet cable is evil--even direct burial rated Ethernet cable with waterproof tape can only provide a certain degree of protection. If the tough cable jacket gets breached, the waterproof tape will mitigate the issue, but there will still be measurable consequences. Why? Waterproof tape is designed to activate in the presence of water and results in a gel that is somewhat conductive by nature. See Direct Burial Ethernet Cable: Gel-Filled vs. Waterproof Tape for a neat experiment I performed that illustrates this.
This started me on the path to investigate further. Is the water-activated gel bad for data transmission? Is there any signal degradation at all? How much worse would liquid water be given the same circumstances? Of course, I had to conduct more experiments to find out!
So, what exactly happens to the Ethernet cable when water does get inside? Fortunately, trueCABLE uses a very advanced tool to measure Ethernet performance--a Fluke DSX-8000 Versiv CableAnalyzer. It is this tool and some cool testing that will tell the tale. As I like to repeat to anyone who listens, “There is no hiding from Mr. Flukey”.
The Mad Scientist Strikes
I love doing “what-if” experiments, so I obtained the following:
- Cat6 Shielded Riser bulk Ethernet cable, 213 feet long
- Cat6 Unshielded Direct Burial bulk Ethernet cable, 180 feet long
- ...a bucket with water in it
Both cables were terminated from keystone jack to keystone jack, known as a permanent link configuration. What is a permanent link? See What is an Ethernet Patch Cable? ANSI/TIA Permanent Link testing is strict, and the Fluke DSX-8000 provides more diagnostic data when this type of test is run. Exactly what I wanted.
I grabbed my cut and strip tool and popped open the cable jacket on both cables, about half-way through their length. I then Fluke tested as follows:
- Immediately after termination (to make sure the cable is good, setting a baseline)
- Right after breaching the cable jacket, to be sure the cable was not damaged
- After submersion in the bucket of water, and at periodic intervals
The idea was to show how quickly the cable would fail, and if it did fail, just how bad the failure really was. Believe it or not, there are various degrees of failure.
Yikes. Not good at all. As expected, the Cat6 Riser indoor cable failed miserably the moment water got inside it. Two hours in, it failed not only the ANSI/TIA Cat6 Permanent Link + PoE test, but also the 5GBASE-T + PoE bandwidth test. For the record, this cable is quite dead. Anyone need a clothesline?
So, what does some waterproof tape get you? At the two hour mark, the CMX jacketed Cat6 outdoor cable still passes the ANSI/TIA Cat6 Permanent Link + PoE test, but after the waterproof tape absorbs enough water, it will cause a failure on that test eight hours in. What is unique, though, is the bandwidth tests kept passing. In fact, there were multiple bandwidth tests taken all the way out to the 24-hour mark and using 5 Gigabit with PoE. All passed and kept passing with no apparent additional degradation. Impressive results compared to the riser rated cable, which failed miserably immediately.
This illustrates there are multiple degrees of “failure.” A failure on a strict ANSI/TIA test does not necessarily translate into an inability to pass data.
In order of least to most strict, here are the various ways you can test a cable:
- Verification (looking for shorts and miswires, says nothing about performance)
- Qualification (bandwidth or speed testing to 1 Gigabit or higher, minimum for your cable to work to your expectation)
- Certification (the measurement of cable performance using electrical metrics, provides built-in safety factors to ensure a working network under any condition)
Generally, unless you are installing a complex network and have higher-end needs, you won’t start to notice issues until the speed tests start failing. If the verification tests fail, you will definitely notice because your cable will not work at all. See The ANSI/TIA 568 C Series of Specifications: What is Most important to Know for Copper for more detailed information.
Would gel-filled (icky pic) do any better here? For all practical purposes, for the average network, the answer is no. Bandwidth is where it counts in the end. If the cable can still pass data, it will still work. You would never know the difference unless you happen to own a Fluke DSX-8000. That is not to say I won’t test gel-filled in the future, because I will and compare it to waterproof tape.
The Fluke Screen - How to Spot Water In Your Cable for DSX-5000/8000 Users
Water in your Ethernet cable shows up as Return Loss. Return Loss is one of many ANSI/TIA metrics that describes how your Ethernet cable signaling is behaving. The limit for how much Return Loss you can have is represented by a red line on the graphic. Return Loss can be caused by multiple factors, but water in the cable is quite unique in how it looks.
First, here is a good Return Loss graphic:
See how the signal results are all staying above the red line? That is what you want.
Here is a bad Return Loss graphic:
This is a classic example of water in your cable. The giveaways are:
- The test is failing at lower (10 to 150 MHz), not higher frequencies
- The lines (representing the wire pairs) are all following the same trend in a significant downward dip
So, what is the “moral of the story”? Don’t get water in your Ethernet cable! Seriously, though, the main takeaway is to avoid a cable jacket breach in the first place when using CMX direct burial cable. There are ways to avoid issues with freeze/thaw cycles, as I detail in Into the Great Outdoors: Running Ethernet Cable Outside.
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