Rodents: the biggest threat to fiber access network cabling?
Installed fiber cabling faces a wide variety of hazardous conditions, such as exposure to chemicals, fire, or extreme temperatures. However, one of the greatest threats of all is… rodents.
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Because their teeth keep growing throughout their lifetime, rats, mice, gophers, and their relatives are always on the lookout for something suitable to gnaw. This dental self-care might result in (superficially) damaged cables. Sometimes they’ll gnaw through cables out of playfulness, or because the cables are blocking their path to a nest, or a source of food and water.
In the US, gophers are the main cause of animal-related buried cabling issues. Squirrels are the biggest cause of animal damage to aerial fiber. Squirrels forced Time Warner Cable to replace 87 miles of cable in New York in 2011. Recently, rats bit through a cable connecting two data centers in Estonia’s capital Tallinn, which meant online citizen services were unavailable for some time. Some years ago, rats completely took down internet access for Virgin Media customers in parts of Scotland.
Damage caused by rodents can seriously affect the reliability of indoor and outdoor fiber optic cables. These generally have a relatively small diameter, making them more vulnerable to chewing rodents than other telecommunication cables. And because rodents are nocturnal creatures, that like to chew cabling in places where they won’t be easily detected, network operators might not notice any damage until network performance begins to deteriorate. Besides service interruptions, they may also face costly and time-consuming damage-tracking procedures and repairs.
Rodent-damaged cables are generally found in underground shafts or supply ducts, where the animals can move freely. Other critical locations are locations where installation cables transition into buildings or between rooms (usually in the basement). Cabling running along cable routes, climbing zones, or internal ducts and raceways is less likely to see rodent infestations.
Different types of rodent protection
We can distinguish between two levels of protection: fully ‘rodent protected’ cables meaning “rodent secure” and ‘rodent-protected’ cables. Rodent protected cables prevent damage to the cable core in cases of moderate rodent infestation, where a limited number of rodents are chewing for the benefit of their teeth, or simply playing. We recommend using U – DQ (BN)-type armored cables with glass roving, also known as e-glass yarn, which protects the cable core as kind of an additional sheathing and can be used for applications in less rodent loaded environments. However, although this level of protection is generally adequate, it is not unlimited. Sooner or later, repeated gnawing can result in damage to the cable core and fiber breakage. This could be the result of different rats or mice chewing on the same piece of cabling at different times.
Optical fiber cables can be protected more extensively by adding a layer that ensures rodents can’t chew their way into the cable core. ‘Rodent-protected’ cables provide protection through mechanical resistance for a prolonged period, even in the event of a massive rodent infestation. The very best results are achieved with cables that feature steel armoring. Of the various steel armoring variants, steel tape armoring has the best properties. For rodent endangered environments, we recommend the use of steel-tape armored cables of types U – DQ (ZN) (SR) (one cable sheath), or U – DQ (ZN) H (SR) (two cable sheaths).
Glass roving reinforcement
A highly effective protection method is the use of ‘glass roving’ sheathing containing fiberglass yarns. This type of reinforcement is the most widespread protective measure. Glass roving is splintered during mechanical processing. As a result, tiny glass fiber fragments break off and drill into the skin of chewing rodents. This irritates their jaws and ensures they stop – the unpleasant itching prevents the animals from gnawing further. Glass roving armored cables offer sufficient protection for installations with a moderate risk of biting. The advantages of glass-roving armored cables compared to other protective measures include their low weight and unhindered flexibility. This means ease and speed of installation aren’t affected by the extra protection, while at the same time there is no compromise in the areas of robustness and durability. Cables can be used in climbing zones and in in-house cable ducts without any problems.
Steel wire armoring
Metal armor made with wires or steel tapes offers a higher level of protection. Rodents are simply incapable of biting through anything that is roughly as hard as alloy steel. Steel wire armor offers more protection against rodent infestation than glass roving armor cables. An armor constructed of galvanized steel wires is introduced between inners and outer sheath.
Tests have shown, however, that particularly stubborn rodents are capable of pulling individual wires out of the composite, thus weakening the reinforcement. As a result, even steel wire armored cables do not provide guaranteed protection against repeated attacks. Steel wire armoring is recommended for underground ducts and shafts where only occasional rodent infestation is to be expected.
Steel tape armoring
Steel tape armored cables are rodent-secure. Industry-wide, this is seen as 100% effective. The effect of taping is based on the fact that the teeth of the rodents cannot find a point of attack on the surface and cannot bite properly. Steel tape armored cables are recommended for outdoor use in cable ducts and shafts where rodent infestation cannot be prevented.
FRP rod armoring
FRP rods are round profiles that are largely made of glass and resin. These can be used to provide the strength of optical fiber cable designs. Cables with FRP rod armoring right under the outer sheath offer a level of protection similar to steel wire but are fully all-dielectric, which is an advantage in areas with electromagnetic fields (such as train tracks).
Although cables can also be treated with superficially applied additives such as chili, which acts as a deterrent, or lethal poisons, we would advise not to use such solutions, as a risk to installation personnel cannot be ruled out. After all, humans and rodents are both mammals.
Making the right choice
Selecting the most suitable cabling for use where rodents are present is essential. Steel-armored cable protects critical infrastructure against large numbers of rats, mice, gophers, and squirrels, although in many other cases, a less elaborate option will provide more than adequate protection.
If you’d like to discuss your specific situation with an expert, don’t hesitate to get in touch with us!