When installing optical fiber cable for a network there are always questions to ask – like should we bury it or hang it? Although I am not an architect, we will try to go over some different scenarios and types of fiber cable that are used in both applications. There are several factors that come in to play when deciding if you should hang fiber on poles or bury it in the ground. The factors include type of terrain where you are installing the cable, as well as whether you are in a rural or urban location are just two. The weather patterns for the area where the cable is being installed is another important factor to consider. Another one is the structures that are in place or not in place, like the existing poles that would be used to hang your cable on.



Which Cable is Used for Each Application?


When looking at fiber cables for these two applications we will look at them separately. There are some cables that are appropriate for both applications and then some that are better suited for one or the other. The fiber cables used will always be meant for outdoor applications and will have outer jackets that will assist in keeping the fiber inside safe from different conditions, whether extreme or not. One thing you will notice is that all the jackets will have the same black color. This is to prevent that big thing in the sky known as the sun and its ultraviolet rays from messing with the optical signals traveling along the fibers.



Different Types of Aerial Cable


When looking at aerial applications there are a couple different options that can be used. You also have restrictions for span length as well as the environmental conditions where you are located for sag allowance when the ice builds up. Not only do you have to know the strength limits of the cable, but you also need to calculate how much weight the poles you will be using can handle. The first type is known as ADSS or All Dielectric Self Supporting cable. This cable is non conductive and has a strong jacket that is reinforced and does not require a messenger wire. When installing this type of fiber cable you will use several different types of accessories to assist in hanging the cable on your poles.

There is also Figure 8 Self Supporting cable that has a messenger wire incorporated into the cable. When you look at an exposed end, the outer profile looks like the number eight. This also has hardware that will need to be purchased to hang it on the poles.

So these two types are your self-supporting cables that do not need a separate messenger wire installed before you can install the cable. Messenger wire is a piece of galvanized, stranded, aluminum clad steel wire that is run ahead of the fiber cable. This wire is used to attach the fiber cable to add strength and stability. When using this method, you should be sure the cable you will be running can be lashed to the messenger wire. Lashing is the process in which the fiber cable run is spiral wrapped with lashing wire to the messenger wire to hold it in place without placing undue stress on the cable or the fibers inside it. When working in an aerial application one key factor is if there is any infrastructure (poles) already in place where you will be running the cable. In urban areas and in the suburbs where houses are closer to each other, the distance between telephone poles will allow you to not exceed the maximum length that is tolerable.



Different Ways to Bury Fiber Optic Cable


There are two main ways that you bury fiber optic cable. When burying cable in the ground there are a couple things that you will need to watch out for and to follow. The frost line is a very important consideration when you are going to bury cable, especially in the north where how deep you will need to dig is much greater. The frost line is the level at which the ground and soil will no longer freeze. The farther down you need to dig in order to get below the frost line can have a direct impact on the amount the project will cost.

Direct burial is when you have an outside plant cable that is armored with corrugated steel tape. In this situation, you do not need anything else to protect your cable - hence the name direct burial. The other way that it is done is to use conduit and armored fiber is no longer needed. This process typically takes a more time and expense because you have to run the conduit and then the cable is run through the conduit.

There are some benefits that exist when the cable is being buried. As long as it is done properly and below the frost line, weather will not have an effect on your cable run. It will be immune to the wind and ice problems that typically wreak havoc in aerial applications. You generally see buried cable when there is no existing infrastructure in place where you will be running the fiber cable. Typically in rural areas you will see cable buried compared to an aerial installation. This has to do with the distance between poles, and in cases where it would not be cost effective to put in new ones.

Although there are many positives for each application, even when installed correctly there can be some negatives to each as well. There are several factors for both that can not only add to the cost but can also change the plans for your build. One of these factors is the type of terrain that you are running through. If you are going through a rocky environment when doing an underground application the costs associated with this will increase drastically due to the equipment, hours and manpower needed to dig in the rocky terrain. In this instance, it would be cost effective to install poles because the amount of digging that needs to be done will be less. A negative for aerial cable is the likelihood that you will need to repair a broken fiber in extreme weather conditions. It is much more likely that the cable will be damaged by ice, wind, or fallen branches or trees in bad weather conditions. When dealing with both it is beneficial to work with an architect that will survey the route all the way through and provide you with the best solution. Sometimes a job will require you to use aerial cable for some of the job and to bury cable in other areas.

The bottom line is you want to run your cable in a path that is the most cost effective way possible. If this means using existing infrastructure or knowing the terrain and the proper techniques that will be the most beneficial when deciding or figuring out where the new path for the cable will need to go.