Direct Burial Ethernet Cable: Gel Filled vs. Waterproof Tape

Written by Don Schultz, trueCABLE Senior Technical Advisor, Fluke Networks Copper/Fiber CCTT, BICSI INST1, INSTC, INSTF Certified

If the question about gel-filled and waterproof tape direct burial Ethernet cable has been keeping you up at night, or if there is a bet involving money about which is “better”, you have come to the right place! Read on, make money, and get your rest.

Gel filled cable is often referred to as “icky-pic”.  Essentially, the gel filling is a non free-flowing petroleum based product.  Is this stuff dangerous?  No.  It is not flammable and is not toxic.  Up until a few years ago this was the common way of making sure water did not get into direct burial cabling.

Waterproof tape is not icky, at least not as icky as icky-pic. Now, please say that fifteen times forwards and then backward. If anyone in earshot asks if you have finally gone and “lost it”, just point them to this article.

Waterproof tape is becoming increasingly common and has largely replaced the traditional gel filled direct burial Ethernet cable.  That said, “icky-pic” definitely still has a place and may be the superior option depending on what you are doing.

So, which one is better? First, let’s go over how each type works and what makes it “waterproof.”

Gel filled direct burial Ethernet

Cat6 Gel Filled Direct Burial Unshielded

• filled with non toxic paraffin wax and mineral oil based gel which is thick, sticky, and quite messy.
• requires more than simple water to clean up; typically 90% isopropyl will work well for tools or hands or wiping off conductors as it evaporates quickly.   For hands only,  “GoJo” hand wipes work well too as they are designed to cut through grease.
• the gel filling does not add unwanted thickness to your cable, making RJ45 plug termination easier
• excess gel should be wiped off the conductors prior to termination as much as you reasonably can; this is where a microfiber cloth and 90% isopropyl alcohol work great
• an electrical insulator. The gel does not convey an electric current.
• potentially an environmental hazard; cable should never be abandoned in place.
• non-hygroscopic, protecting against water getting past it to the copper conductors.
• tough UV protectant LLDPE (linear low-density polyethylene) outer cable jacket

Water block tape direct burial Ethernet

Cat6 Shielded Direct Burial (water block tape)

• water block material is dry to the touch, but ready to be activated by water.
• tough and adds thickness to your cable...as much as 0.5mm.  This may require “ovalization” of the end to be terminated into a RJ45 plug, as the cable typically is thick.
• water block tape resembles fabric and is not easy to remove by hand.  Get out the flush cutters, you will need them.
• requires no cleanup.
• mildly electrically conductive. The super absorbent polymer is activated by water, and water is electrically conductive. 
• will not allow liquid water to reach the copper conductors. Instead, the polymer will activate, the cloth tape will swell, and gelatinous polymer will migrate around the conductors thereby sealing it off. This results in some performance degradation, but the cable will remain usable.
• not environmentally offensive.   The super absorbent polymer is the same type used in baby diapers and feminine hygiene products. 
• tough UV protectant LLDPE (linear low-density polyethylene) outer cable jacket, exactly identical to the gel filled variant.

Installation Environment Recommendations

• Install either variation outdoors freely, whether underground or above ground.  Just be sure to follow the guidelines in Selecting the Correct Outdoor Ethernet Cable.
• For commercial installations, both types may run indoors up to 50 feet prior to termination (per the National Electric Code 800.113), but should never run into the plenum space.  
• For residential environments, you may use either type as indoor/outdoor cabling with no restrictions assuming the following rules are observed:
• Cable thickness (OD) or outside diameter may not exceed 0.25”
• The residence is restricted in size to a single family or duplex dwelling

Testing

You know that this blog would not be fun if some tests with pictures weren’t conducted. This is the type of topic that just begs for photos. So, here we go:

What happens when the water block tape gets wet? The gelatinous polymer was slippery but not sticky. It had no odor. Washing off with water was easy.

Is the water bearing gel conductive? Indeed. The handy flashlight test always works:

Now let’s take a look at the “guts” of gel filled direct burial cable.

A good view of the petroleum gel filling

• The gel filling has no odor
• The gel is definitely sticky...similar to glue sticks for paper
• No oozing happens, as this gel will not "free flow"
• Forget about regular hand soap and water for getting it off yourself....

Oh! And one more thing... The gel is NOT flammable. Watch this:

Performance Testing

A big question comes to mind (at least it did for me).  What happens when water gets past that tough LLDPE jacket and invades your cable?  Well, if you are using indoor style cable with no protection at all I can tell you very bad things happen as illustrated in What Happens If Water Gets Inside Ethernet Cable?

For direct burial Ethernet cable, you can rest assured that both the water block tape style and the gel filled style both keep your cable working.  It just so happens that gel filled does it somewhat better.  The question is, despite gel being better at blocking water does it really matter?  We will get to that later.  For now, let’s test.

A bucket of water was used for the immersion test.  The outer jacket was slashed with a razor knife simulating a simple glancing cut.  Prior to immersion, the cables were tested to be sure the conductors were not damaged while breaching the cable jacket and to set a performance baseline.  The cables were placed in the bucket for 24 hours.  The cables were periodically checked for performance at various intervals while submerged with a Fluke DSX-8000.

Before, during and after the test the Cat6 Gel Filled Direct Burial cable passed all ANSI/TIA Cat6 formal testing, demonstrating it was totally impervious to water infiltration.

The Cat6 Direct Burial Unshielded (water block tape) passed the formal tests before immersion, and up to eight hours after immersion.  After eight hours, the intensive formal TIA tests started to fail and less intensive bandwidth testing was performed.  After a full 24 hours, the water block tape cable was still passing the bandwidth testing, and at 5 Gigabit speeds.  Bandwidth testing = minimum level of performance.  What happened?  The water migrated inside the cable jacket, activated the gel, and the water bearing polymer gel had just enough conductivity to impair performance a bit.

So, which is “better”?

Well, both are good.  It really depends on what you are doing and how bulletproof you want your cable run to be.  It also depends on how much mess you wish to deal with.

• Gel filled is much messier to deal with, but immune to water
• Water blocking tape is easy to deal with, but does not protect the cable as thoroughly
• Both cable types can be a bit of a pain to terminate.  Water blocking tape adds thickness to an already thick cable.  Gel filling has to be wiped off the conductors.  Pick your battle!

In reality, though, just how likely is it that some exterior force will damage your cable jacket and not destroy your cable in the process?  That would be quite the stroke of luck to have a working cable run after it suffered enough damage to breach a very tough LLDPE cable jacket.

My recommendation is if your outdoor cable must pass formal TIA testing regardless of whether the jacket was breached or not (and the cable did not suffer other damage), then use gel filled direct burial cable.  Similarly, if PoE performance is of prime concern in this same situation, then gel filling is again probably the better option.  If those situations do not apply, then opt for the water blocking tape variety.

In the final analysis, any damage to your cable jacket while underground is not good and should trigger immediate replacement if discovered.

So there you have it! Now, if you have any bets you placed on this, and wish to send along some cash if you want…*wink*

HAPPY DIGGING (AND NETWORKING)!

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