Outdoor Ethernet Messenger Wire Support Interval : A Pole Too Far?
Written by Don Schultz, trueCABLE Technical Manager, Fluke Networks Copper/Fiber CCTT, BICSI INST1, INSTC, INSTF Certified
You have got your ladder and cable ready! You waited until winter is over in your area (or at least it stopped raining all the time) and you want to get your outbuilding wired up to your main house to get some decent Internet connectivity to it. Perhaps you are an installer dealing with a commercial environment and would like to run an Ethernet cable between two office buildings? Well, before you head up the ladder and start stringing up Ethernet cable(s) there are some best practices and perhaps even legal requirements you need to know about.
First, if you can bury your runs, that is the preferred method for running OSP (outside plant) cable from one building to another. Your cable will be less susceptible to lightning strikes and severe weather conditions. However, direct burial is not possible if you are dealing with a concrete parking lot or some other obstruction that will prevent digging. In that case, you have to go high. For more on mitigating ESD (electrostatic discharge) see When Lightning Strikes! Ethernet Data Cable and Lightning Protection.
trueCABLE is often asked a lot of questions about aerial cable installation such as:
- What kind of cable do I need for this task?
- How should I terminate the cable for this kind of project?
- What attachment point method should I use?
- How far can I suspend Ethernet cables between two structures (attachment points)? Will I need multiple attachment points?
- Are there rules about how high the cabling has to be above the ground?
This blog will address all of these questions and more! What we won’t get into are actual installation specifics as they have been addressed in Cat6 Shielded Aerial Messenger Cable: Up The Ladder You Go! Much of this information is applicable to residential and commercial installations equally, although we will note the major differences as we go.
What kind of cable do I need for this task?
For any cable that will be hung outdoors, above ground, and suspended between two attachment points it is strongly recommended you use shielded cable. Not only should you use shielded cable, but you absolutely must use CMX (outdoor rated, UV protected) Ethernet cable that can resist Mother Nature. A comprehensive blog was written about selecting the right type of outdoor cable in Selecting the Correct Outdoor Ethernet Cable. If you take a look at the blog you will see that direct burial shielded Ethernet cable can also be used in this application, although you get no tangible additional water resistance above ground and no messenger wire. If your application speed needs are 5 Gb/s or less, we offer Cat6 Shielded Outdoor UV Ethernet with a messenger that has the messenger wire already attached. Select this if you do NOT have an existing messenger wire between your attachment points. If you need to install additional runs, or already have an existing messenger wire installed, pick up our Cat6 Shielded Outdoor UV Ethernet cable that can be attached with velcro to the first messenger wire run already present. If your application speed needs are 10 Gb/s, we offer a Cat6A Shielded Direct Burial Outdoor cable, although there is no messenger wire present.
How should I terminate the cable for this kind of project?
Terminating thick shielded Ethernet cable is not what one would characterize as a “super fun” task. The cable is built using multiple layers, along with a tough outdoor LLDPE (linear low density polyethylene) cable jacket. As such, putting on RJ45 8P8C plugs is the last type of termination you want to use. Not only will you be presented with a challenge physically, but your cable may not perform up to expectations if you should use RJ45 8P8C plugs at both ends of your cable. Instead, use Cat6 shielded tool-less keystone jacks at both ends in conjunction with shielded Cat6 factory made patch cords OR Cat6A Shielded Field Termination plugs at both ends instead. Keystone jacks and field termination plugs have PCBs (printed circuit boards) inside that provide impedance matching and are component rated for maximum performance. The mechanisms make termination much easier.
Shielded keystone jack (left). Shielded Field Termination Plug (right).
That all said, there are times when you MUST use a RJ45 8P8C plug at one end of the cable (MPTL or Modular Plug Terminated Links) when the end point device is a PoE outdoor camera or WiFi access point with a tight water resistant housing. In this case, the other end (switch end) should still be a keystone jack or field termination plug. RJ45 8P8C plugs should also be used in conjunction with cable boots for best mechanical and electrical stability. The suitable RJ45 8P8C plug for this cable termination would be our Cat6/6A Shielded RJ45 Pass Through Connector. The boot should be our Large Slip On 8.00mm style.
Shielded RJ45 8P8C Connector Plug (only if you MUST)
What attachment point method should I use?
NEVER, EVER, attach your communications cable run to an electrical cable that is already present!
There are a dizzying number of attachment methods. Some are specialty items like drop clamps and those cost a good bit of money. More commonly, if an attachment method needs to be purchased and attached to a structure (building side, pole, etc.) this will be an eye, P, or Q hook. This type of hardware is commonly available at any home improvement retailer. Hooks come in two types:
- Bolt on (threaded shank with nut)
- Screw in (sharp end with threads meant to be screwed into wood)
Screw in eye hook (left). Bolt on eye hook (right).
The high tensile strength steel messenger wire will thread through the hook portion and provide a way to hang your cable, and provide strain relief at the same time.
Notes on your attachment hardware and where to install it:
- Make sure your eye, P, or Q hook is large enough to take the strain. Buy stainless steel hooks.
- Attach your hanging hardware to a sturdy object that can withstand the weight of the cable run, and in severe weather. Do not attach your cable to an antenna, chimney, power mast, or lightning rod!
- DO NOT attach your hanging hardware to a structure or pole you do not own or do not have permission to attach to. If you install an eye hook to a service pole, for example, and the owner of that pole objects to it they will likely summarily rip it down and you may be subject to fines. Check if you are unsure.
- The height of the attachment must be sufficient to allow clearance for right-of-way items like sidewalks and roads. In commercial installations, there are actual height restrictions that must be met. More on that later.
- Do not attach your cable run under tree limbs or other items that might fall onto it
- On a home the ideal spot to attach an eye hook is right under the soffit on the corner of the house closest to your electrical meter
- For residential environments, install your cable attachment points so the Ethernet cable will be a minimum of 12” away from electrical service. This will account for cable sway and will also help prevent touching in severe weather.
How far can I suspend Ethernet cables between two structures (attachment points)? Will I need multiple attachment points?
One of the biggest questions I get asked is how far can an Ethernet cable be strung between two attachment points? Often, people look on the Internet for this information and come up short. There are good reasons why there is no hard data on this:
- The messenger wire built into the Ethernet cable can, theoretically, support the weight of a single run between two attachment points all the way out to 100 meters (328 feet) without breaking. Now, the astute among you will note that the cable still needs to go into one or more structures and potentially up and down poles. There is no way you could successfully string up an Ethernet cable the full 328 feet between two attachment points and get it terminated and still have it work properly. 328 feet is the maximum distance between two powered devices and that is under ideal circumstances.
- Cable sag must be accounted for. Cable sag must also be taken into account with the height of your attachment points. The lower the height of your attachment point, the lower your sag will be to the ground. You may be limited on cable run length due to the amount the cable sags between two attachment points. In other words, it is not a good idea to have an Ethernet cable a mere three feet above the ground. You might need an intermediate attachment point anyway.
- Outdoor cable installations are subject to temperature fluctuations and the worst case scenario high temperature should be used to gauge how far your run can be. In other words, your maximum cable run will often be dictated by ambient worst case scenario temperature and not the distance between two attachment points! A detailed chart on maximum true run length can be found in Temperature's Effect on Ethernet Cable Length.
The key takeaway from the above bullet points is you won’t run into a situation under correct installation conditions where the messenger wire will break. The tensile strength of the messenger wire is the least of your concerns, and actual maximum run length based on the ambient worst case temperature plus attachment height with the associated sag are far more important to consider.
Are there rules about how high the cabling has to be above the ground?
Yes. There are actually rules about distance vertically and in some cases horizontally too. There are some pretty detailed rules about how low your cable can hang, and these rules get more detailed for commercial installations. The distances provided are for the sag point (lowest point of the cable run due to gravity). The attachment points will necessarily be higher, so please take note of this. These rules may also vary by municipality, so please be sure and consult your local code inspector. Better safe than sorry!
A picture says a thousand words:
Commercial installation sag clearance minimum height
So, there you have it! The answer to how long you can string your messenger cable is not very straightforward. The question is more complex than it would first appear, due to factors that many do not consider until the project is well underway. Being prepared is key. Planning will ensure a successful installation. Be safe!
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