Into the Great Outdoors:  Running Ethernet Cable Outside

Into the Great Outdoors:  Running Ethernet Cable Outside

Written by Don Schultz, Technical Sales Representative and Fluke Networks Certified Technician

Occasionally it's necessary to use exterior Ethernet cable (CMX). These are the common scenarios:

  • Outdoor Wi-Fi access points
  • To connect two or more distinct structures
  • Outdoor IP based (Internet Protocol) surveillance cameras

Depending on the environment, it may make more sense to bury the outdoor Ethernet cable as opposed to open air runs. Whether open-air or buried into the ground, the selection of Ethernet cable is crucial. First, CMX rated Ethernet cable is the only appropriate cable to use outdoors. Life, not being that simple, means there are various types of CMX rated Ethernet cable. The only commonality between them is they have a UV resistant outer cable jacket, coated with PVC (Polyvinyl Chloride) or the superior LLDPE (Linear Low Density Polyethylene). Regular Ethernet cable meant for indoor use will quickly degrade in the sun, wind, rain and temperature swings.

There are two major types of CMX cable:

  1. Direct burial rated (underground Ethernet cable)
  2. …and, well, NOT direct burial rated

Direct burial rated means the cable jacket is thicker and therefore tough. It can withstand burial into the ground, either directly or inside conduit. Further, direct burial CMX cable provides additional waterproofing in the form of a flooded gel core or waterproof tape. Flooded gel core and the waterproof tape methods both perform the same function. But flooded gel core is messy to deal with. It requires solvents to clean up, must be wiped off the conductors before termination, and has the propensity of drying out over time. trueCABLE utilizes waterproof tape.

Sun UV Resistant Umbrella Waterproof Direct Burial

 

CMX cables can be shielded to help channel away EMI/RFI (Electromagnetic Interference/Radio Frequency Interference). The shielding, usually in the form of foil referred to as FTP (Foil Twisted Pair), will be accompanied by a ground wire as well. Generally, I recommend using unshielded cabling unless there is a valid need for shielded, such as when burying the cable within 8” of electrical wire on parallel runs.  The other primary reason to use shielded is for ESD (Electrostatic Discharge) drain off such as when running outdoor Ethernet cable above ground in structure-to-structure scenarios.  ESD build up occurs with dry air movement across cabling, and could ruin your network equipment if not allowed to discharge to ground.  

trueCABLE carries a number of CMX rated Ethernet cable types, and further information around selection is found in Selecting the Correct Outdoor Ethernet Cable 

Let’s talk about the construction of trueCABLE’s Shielded Cat6 CMX Direct Burial Cable. It’s a great example of cabling designed for either a burial or open-air scenario. At its core, this cable functions like any other Cat6 Ethernet cable. It has eight wires twisted into four pairs and is terminated to the TIA 568 A or B color code standard. Termination should be to a shielded Cat6 patch panel or shielded Cat6 keystone jack. Proper electrical grounding must be at the patch panel or switch end of the run. Due to the thickness of this cable shielded RJ45 plugs can be used, but the selection is limited and prepare for a challenge!

A picture helps…

Close Up of Construction of Outdoor Ethernet Cable

Now, the next step is deciding on whether to bury.

First…STOP! Before digging it is vital that you contact all local utilities and have a representative come to the property and mark any buried gas lines, water lines, etc. You won’t be charged for this service as the utility company is more than happy to help avoid a major incident that could cause loss of service or even life.

Second, since this cable is rated for direct burial you may indeed bury it without conduit. In fact, based upon my experience, direct burial is actually superior to putting it into a conduit as conduit will allow water in over time (especially PVC).  If you live in an area that has a frost line only 3” down, then simply bury the cable without conduit at least 10” down to avoid mechanical damage from shovels and the like.  For areas that have frost lines measured in feet, freeze/thaw cycles can play havoc with PVC conduit.  Consider that a conduit full of water will have nowhere to go when it freezes and potentially ruin your underground run.  The best bet in this scenario is to direct bury the cable 18 to 24 inches down bedded on top of a couple inches of pea gravel to help with water drainage.  Further, it is a good idea to leave some “lazy” curves in the run to allow for ground movement.  If you are determined to use conduit, metal conduit will be more durable, but costly.It is also wise to pull twine/string through the conduit with the cable and leave it in place to make cable replacements easier.

To make burying cable efficient, a trencher machine can be rented from the local equipment rental store. Sure, a shovel can be used but it will result in far more mess, take longer and result in a less consistent trench. In the event operating the trencher is beyond your comfort zone, then hire a local handy person with experience. Eye and ear protection are important.

Good to Know 

  • According to the NEC (National Electric Code) section 800.113, since CMX Ethernet cable is not fire rated it must not run indoors more than 50 feet before termination in any commercial structure.  For residential single family and duplex dwellings, CMX Ethernet cable is permitted to be used as indoor/outdoor cable without restriction with the caveat that it cannot exceed 0.25” thickness (OD or outer diameter).
  • If you have an underground rodent problem in your area (moles) your buried Ethernet cable is at risk. It is advisable to use conduit in this circumstance, and preferably metal conduit. The costs are higher, but the benefit is the conduit need not be buried as deeply.
  • If running a CMX shielded cable between two buildings (buried or not), it is very important to avoid what is known as a ground loop. This situation arises when the building electrical mains have different ground potentials. This can result in voltage injection through the cable if the cable is running to ground at both ends through the different AC grounds. Mitigation strategies can be found in How to Fix a Ground Loop.
  • Can CMX cable be run in the air between two poles or structures? Absolutely, CMX cable is meant to withstand outdoor conditions but a “messenger” must be used. A messenger is a thin high strength wire. The best way is to buy outdoor CMX above-ground shielded cable where the messenger is already built-in. If using a CMX cable without a built-in messenger there is a work around. Run thin stainless-steel wire between two sturdy attachment points and attach the Ethernet cable to the messenger. When running cable in this fashion, support the Ethernet cable along the entire length with zip ties every few feet as high wind speeds or freezing rain can do terrible things to cabling.

trueCABLE presents the information on our website, including the “Cable Academy” blog and live chat support, as a service to our customers and other visitors to our website subject to our website terms and conditions. While the information on this website is about data networking and electrical issues, it is not professional advice and any reliance on such material is at your own risk.

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