ember Polyethylene bedding layer Paper tape Optical fibres Tubes in which fibres are located Figure 15.7 Optical fibre loose tube cable 15/14 Telecommunication cables Corrugated PE coated steel tape PE coated aluminium tape and core wrap Optical fibres Outer PE sheath Core profile Inner PE sheath Steel strength (10.5mm dia.) member PLC pair (3.2mm dia.) Figure 15.8 Slotted core cable with rodent protection a strength member of stranded steel wires. The cable is pulled regions of high lightning activity, the aluminium plastic laminate is through the duct via a mechanical fuse which ruptures if the in- omitted and dielectric strength members (e.g. Kevlar) replace the tended stress is exceeded, which is well before stress on the fibres steel core. exceeds 0.2% to 0.3%. Attenuation increments during the cabling The slotted core construction (Figure 15.8) is effective for high process are very low as shown in Figure 15.6. The same general fibre count cables. Figure 15.9 shows a more recent design with design is also used with fibres encapsulated in loose tubes and in several fibre bundles laid in a large protective soft gel-filled tube. gel-filled loose tubes (Figure 15.7). For applications where non- This cable is for direct burial and is shown completed with outer metallic cables are required - alongside electrified railways or in sheath's lightning and rodent protection. Corrugated PE coated steel and copper tapes Inner PE sheath Soft gel fill Optical fibres Outer PE sheath Middle PE sheath Steel reinforcement Figure 15.9 Alternative cable design with rodent protection Cable design 15/15 Optical Polyethylene fibre slot cap ribbon Filling Glass reinforced compound plastic rod Binder Sheath Figure 15.10 Self-supporting optical fibre cable 15.7.1 Self supporting cable The strength member is a pultruded glass reinforced plastic (grp) rod at the top of which is a small rectangular slot. Within this gel The advantages of interference free operation have encouraged the filled slot are two twelve-fibre ribbons covered with