A 1 - Leoni

162Rodent protection for fiber optic cablesFiber optic cables are relatively thin and therefore verysusceptible to rodent damage. Depending on the application it isimportant that fiber optic cables can offer protection against thistype of damage. There are no national or indeed internationalstandards or test specifications covering the correspondingrequirement for rodent protection.The following construction has been customary in the market inEurope (particularly in Germany, Austria and Switzerland) sincethe early 1990s:For outdoor cables, the usual aramid yarns for strain relief arereplaced with glass rovings. These glass yarns shatter and getinto the mouth and throat of the rodents. The animals associategnawing on cables with pain and usually stop.The general rule is:The more glass rovings, the greater the protection forthe cable.The overall diameter should also be as large as possible.Constructions with stranded loose tubes give even lessfavourable leverage in combination with the larger corediameter. The cable then acts like a gag bit. Before the rodentreaches the glass rovings, however, it first has to gnaw throughthe outer sheath. Constructions with an additional polyamidesheath (thickness 0.5 mm) have also proven themselves hereas polyamide is very hard and smooth.Metal armouring must be recommended as rodent protectionfor all applications where rodent damage is to be expected. Thisis the case, for example, with installation in shafts or conduitswith a correspondingly large diameter, e.g. along railway linesor motorways.The following types of metal armouring are available:■■■■■■Corrugated steel claddingThe most common metal armouring is the 0.155 mm thickcorrugated steel cladding due to its very good flexibility.Steel wire armourThe steel wire armour made from wires with a thicknessof up to 1.25 mm is very robust.Steel bandSteel band sheathing consists of two overlapping layersof steel band that are wound around the cable.In the case of cables with two sheaths with sheathing betweenthem, the ingress of water into the cable core is also preventedprovided the internal sheath is not damaged.This combination of plastic, glass and moisture-absorbingswelling material has to be gnawed through before rodentreaches the loose tubes containing the internal optical fibers.Despite all precautions, however, damage to the outersheath can never be fully ruled out.www.leoni-infrastructure-datacom.com