Antitheft device for cables, particularly electric cables and in cable ducts or the like The present invention relates to an antitheft device for cables, particularly electric cables and in cable ducts or the like.

The theft of electric cables directly from their laying site, such as public lighting installations or railroad systems or even electric power distribution systems is an increasingly frequent event.

In addition to the loss of materials, i.e. the cable, and to the costs incurred for replacement of the cable section that has been removed, damages also involve the service, i.e. the installation functions that relied on the cable line. Therefore, such damages may cause essential services to be suspended, possibly for long periods of time, and while they may be limited to lamps being extinguished in public lighting installations, in railroad systems they might lead to railroad traffic being stopped for several hours, with great inconvenience possibly extending over very large areas of the railroad line.

Therefore, the need has been felt for effective, simple and inexpensive protection of cables, and has not been satisfactorily fulfilled yet, in a manner that would allow implementation in both new installations, and in existing lines.

Cables, namely electric cables that have been laid in cable ducts or the like, are stolen by accessing such cables in ducts or channels through accesses closed by removable covers. When cables lie in channels, such channels are closed at one of its sides by a number of adjacent covers of predetermined length, whereby when the channel is opened at two locations at a desired distance and one or more cables are cut, this cable segment/s may be pulled off the channel, and wound, for instance, in coils and carried away.

When cables are laid in tubular ducts that are closed all along their shell surface, manholes are currently provided. These are located at predetermined distances from each other, whereby cables are stolen by accessing them through these manholes, cutting them at the manholes and pulling the cable segment/s that were cut out from the rest of the line at the two manholes out of the conduit. This process may be complemented by the step of winding the cable/s in coils as they are being pulled off. Then, the segments that have been pulled off and wound in coils are carried away.

The invention has the object of providing an antitheft device for cables, particularly electric cables and in cable ducts or the like, that might both provide easy and inexpensive installation even in existing lines and ensure high safety against theft.

In a first general embodiment, the invention fulfills the above objects by providing an antitheft device for cables or the like, particularly cables laid in cable ducts or the like, which comprises at least one fiber-optic cable laid along at least one cable or cable bundle, said fiber-optic cable being attached to said cable and/or said cable bundle at least at one point or a plurality of a succession of multiple points arranged at predetermined distances from each other over the length of said cable or said cable bundle, or said fiber-optic cable is attached to said cable or said cable bundle in continuous fashion over the entire length of said cable or cable bundle, whereas said fiber-optic cable has two opposite ends, i.e. one input end for a predetermined light signal and one output end for said light signal transmitted by said fiber-optic cable, a unit being provided for generating said predetermined light signal, and transmitting said signal at the input end of said fiber-optic cable and a unit being provided for receiving said light signal transmitted by the fiber-optic cable, and receiving said light signal from the output end of said fiber-optic cable, a unit being further provided for processing/comparing the light signal detected by the receiving unit, said processing/comparing unit determining the changes of a few characteristic parameters of said actually received light signal as compared with the nominal reference values of said characteristic parameters of the light signal, which are or can be stored in said processing/comparing unit, said processing/comparing unit triggering alarm warning means when the actual values of said characteristic parameters of the received light signal deviate from the nominal reference values of said characteristic values beyond a given tolerance.

The principle of measuring the change of the characteristic parameters of a light signal transmitted through an optical fiber for detecting fiber-optic cable deformation actions is known and widely used as a sensor in various applications. In the present context, this principle cannot be directly implemented using prior art devices, but requires substantial changes, as it is used to non- rigid elements to be supervised. Therefore, the existing devices cannot be adapted to the structural cable specifications by simple and obvious changes.

In a first particular embodiment of the general device of the invention, the fiber-optic cable is attached to the cable or cable bundle at each point in stationary, i.e. stable fashion, using an annular element for circumferentially fastening said cables together.

In a second embodiment, the fiber-optic cable is attached in sliding fashion relative to a fastener element for fastening the cables of the bundle together, or a single cable or the bundle cables together or to a wall of a channel or duct that houses said cable or said bundle, each fastener element having an annular or tubular element for the passage^ of the fiber-optic cable, said fiber-optic cable being passed through said annular or tubular element to form a loop, a curl or an eyelet on one of the two sides of said annular or tubular element.

Preferably, in an improvement of the above described variant embodiment, the fiber-optic cable is passed through said annular or tubular element, to form a loop, a curl or an eyelet on the side of said annular or tubular element opposite to the fiberoptic cable entry side.

Here, the fiber-optic cable is attached to the cable or cable bundle by the fastener elements for fastening the bundle cables together or the cable and the cable bundle together and to a wall of a channel or conduit that houses the cable or the cable bundle.

In a more specific construction of the above described second embodiment, the fiber-optic cable is attached to the cable or cable bundle by separate fastener elements, arranged in positions that do not coincide with those of said fastener elements for fastening the bundle cables together or the cable and the cable bundle together and to a wall of a channel or duct for housing the cable or the cable bundle.

In this more specific construction, the fiberoptic cable is attached to the cable or the cable bundle using an annular or tubular element for the passage of the fiber-optic cable, which is integral with said fastener elements for fastening the bundle cables together or the cable and the cable bundle together and to a wall of a channel or duct that houses the cable or cable bundle; said fiber-optic cable is passed through said annular or tubular element to form a loop, a curl or an eyelet on the side of said annular or tubular element opposite to the fiber-optic cable entry side, whereas the incoming fiber-optic cable section and the outgoing fiber-optic cable section that comes out of said annular or tubular element on the side opposite to said curl or said loop are in turn attached, separately from the other cables, by fastener elements to the wall of the channel or duct for housing said cable or cable bundle.

In a preferred embodiment, the incoming fiberoptic cable section, that comes into said annular or tubular element is attached to a wall of the channel or duct on the entry side of said annular or tubular element, and at a certain distance from the entry- side of said annular or tubular element, whereas the outgoing fiber-optic cable section that comes out of said annular or tubular element downstream from the loop or curl is attached to a wall of the duct or channel on the exit side, through which the curl comes out of said annular or tubular element, and at a certain distance from said annular or tubular element, such that said annular or tubular element with the curl of the fiber-optic cable, is placed in an intermediate position between said two points of attachment of the fiber-optic cable sections to a wall of the duct or channel.

It shall be noted that a combination of the first and second embodiments may be also provided, in that the means of these two embodiments may be arranged in alternate relationship over the length of the cable in a predetermined order.

As a result of the above, even when cutting one or all of the cables of a bundle without cutting the fiber-optic cable, the action of pulling the cables off the housing conduit or channel causes deformation of the fiber-optic cable and hence a change of the characteristics of the light signal that comes out of the fiber-optic cable. This change may be detected and trigger the alarm warning means .

Furthermore, the fastener elements for fastening the bundle cables together or the cable and the cable bundle together and to a wall of a channel or duct that houses the cable or cable bundle, i.e. the various embodiments of the brackets secured to the bottom of the cable duct or the cable ties for fastening multiple cables of a bundle together and to said housing element, especially when there are many of them, secure the cables to an unremovable element (generally a concrete part), and slow down the theft. This hindrance, in combination with an alarm warning through a siren or a light may effectively act as a disturbance for the thieves and later on as a dissuasion, during the theft.

The presence of the annular or tubular element with the fiber-optic cable extending therethrough to form a loop, a curl, or the like, increases the change of the bending radius at each pulling action on the fiber-optic cable, and hence improves cable tamper detection sensitivity.

When the cable or cable bundle lies in a tubular duct or a housing channel having at least one inspection opening, said opening or said channel being designed to be opened and closed by a removable inspection cover, the invention further suggests that the fiber-optic cable may be fixed to said inspection cover at least at one point.

This fiber-optic cable may be the same fiberoptic cable that is associated with the cable/s or a separate fiber-optic cable, whose function is limited to detection of displacement of the covers to the open state.

The fiber optic cable may be attached to the cover at one point and be further attached to the cable or cable bundle and/or to further walls of a manhole .

Also, in a line with multiple manholes, a single fiber-optic cable may pass through each manhole and form a curl in the eyelet of the cover of the manhole . This configuration allows multiple manholes to be monitored using the same fiber-optic cable, and the fiber-optic cable may be placed and secured with any method and configuration as described above.

In one embodiment the fiber-optic cable is attached to said cover by an annular or tubular element for the passage of the fiber-optic cable, which is adapted to be fixed to said cover or is formed of one piece with said cover, said fiber-optic cable being passed through said annular or tubular element, to form a loop, a curl or an eyelet on the side of said annular or tubular element, opposite to the fiber-optic cable entry side.

Once again, in a preferred variant embodiment, the fiber-optic cable is passed through said annular or tubular element to form a loop, a curl or an eyelet on the side of said annular or tubular element opposite to the fiber-optic cable entry side, while the incoming fiber-optic cable section and the outgoing fiber-optic cable section that comes out from said annular or tubular element on the side opposite to said curl or said loop are in turn attached by fastener elements, separately from the other cables, to the wall of the channel or duct that houses said cable or cable bundle, possibly such that the incoming fiber-optic cable section introduced into said annular or tubular element is attached to a wall of the channel or duct on the entry side of said annular or tubular element and at a certain distance from the entry side of said annular or tubular element, whereas the outgoing fiber-optic cable section, that comes out of said annular or tubular element downstream from the loop or curl is attached to a wall of the duct or channel on the exit side through which the curl comes out of said annular or tubular element and at a certain distance from said annular or tubular element, such that said annular or tubular element with the fiber-optic cable curl is placed in an intermediate position between said two points of attachment of the fiber-optic cable, sections to a wall of the duct or channel .

In a further variant embodiment of the invention, when the cable or cable bundle lies in a tubular duct or a housing channel having at least one inspection opening, said opening or said channel being designed to be opened and closed by a removable inspection cover, a fiber-optic cable deforming element is provided, which is controlled by the position of the cover, such that, in the closed position of the cover the fiber-optic cable is not deformed, whereas in the open position of the cover, the deforming element is operative on the fiber-optic cable and deforms it.

Various embodiments of the deforming element may be envisaged. In a preferred embodiment, the deforming element comprises a slider having at least one convex or tapered deforming surface, which deforming surface has its tapered or convex end facing the fiber-optic cable and the cover when the latter is in the closed position, said slider being stably biased by an elastic element in its sliding direction toward the cover and the fiber-optic cable, whereas the slider is designed to slide between two stationary stops located on the side of the fiberoptic cable opposite to the deforming terminal, and has an extension designed for contact with the cover side facing said slider, the position and the stroke of the slider being so defined that, in the closed state of the cover, the slider is retained against the biasing action of the elastic element in the undeformed fiber-optic cable state, whereas in an at least partially lifted position of the cover the elastic element pushes the slider into deformation of the fiber-optic cable between the two stationary stops and the deforming terminal on the side of the fiber-optic cable diametrically opposite to said stationary stops .

Particularly, the cover as described in the above embodiment may be the cover that closes a manhole or a channel element of a cable or cable bundle duct or channel .

One embodiment of a deforming element that is suitable for use herein, with certain structural changes, is disclosed in EP0332900B1.

This additional feature provides warning of unauthorized access to the cable duct or channel prior to any tamper or other action on the cables and has the additional advantage of preventing any cutting action and hence any damage to the line.

It shall be noted that the antitheft device requires relatively simple and inexpensive means and may be easily implemented in existing installations or lines.

The invention provides further embodiments that may be envisaged instead of or in addition to those described above.

In one of these alternative embodiments, the fiber-optic cable has the same appearance as a cable of the line to be protected. In this case, when the cable bundle is cut, the optical fiber is also cut, and the light signal output therefrom is accordingly changed.

In one implementation of the above described embodiment, at least one of the cables has at least one core and at least one cladding over said core, said cladding also covering the fiber core of the fiber-optic cable.

In one variant, the core of the fiber-optic cable may be embedded, over its entire outer shell surface, in the thickness of the tubular cladding that covers the cable core, and said core of optical fibers is substantially parallel to the cable.

Therefore, the invention relates to a cable, particularly an electric cable comprising at least one core of conductive material and a tubular insulating cladding that covers said core, characterized in that the optical fiber core of a fiber-optic cable is integrated in said cable, said tubular cladding being also the tubular cladding that covers said optical fiber core of a fiber-optic cable, and said optical fiber core being incorporated in the thickness of said tubular cladding.

The invention also relates to a channel or tube or a section of a channel or tube for forming cable ducts, wherein said channel or tube element has integrated means for securing a bracket for one or more cables, said bracket having in turn an annular or tubular element for the passage of a fiber-optic cable and possibly one or more fastener means for independent attachment of a fiber-optic cable to one of the walls of the channel or tube, said fastener elements being provided in pairs of spaced fastener elements, the bracket and its fastening means being located in an intermediate position between said two fastener elements.

In one embodiment of said channel or said tube or said section of a channel or tube, said channel or said tube or said section of a channel or tube includes at least one removable cover for closing an access to said channel or said tube, said closing cover being equipped with means for attaching a fiber-optic cable thereto.

In a preferred embodiment, at least one removable cover is provided for closing an access to said channel or said tube, said channel or tube being equipped, in the area of said closing cover, with means for deforming said fiber-optic cable, the latter being controlled into the deformed fiber-optic cable state by the position of the cover, and said deformed fiber-optic cable state being actuated by at least partial displacement of said cover into the lifted or opened position.

These and other characteristics of the invention and the advantages derived therefrom will be more apparent from the following description of a few embodiments shown in the accompanying drawings, in which:

Fig. 1 is a perspective view of a first embodiment of the antitheft device of the invention.

Fig. 2 shows an enlarged detail of the embodiment of Fig. 1.

Fig. 3 shows an enlarged detail like that of

Figure 2, in a variant embodiment of the present invention. Figs. 4 and 5 are two perspective views of a first embodiment of an improvement of the device of the present invention, which is designed to detect and indicate unauthorized opening of manholes for access to the cables of a cable duct.

Figs. 6 and 7 are two views of a second embodiment of an improvement concerning detection and indication of unauthorized opening of manholes for access to the cables of a cable duct. '

Figures 8 to 10 are cross sectional views of three variant embodiments of an antitheft device of the present invention, in which the fiber-optic cable is integrated with the cable to be protected or is attached over its entire length to the cable to be protected to form a single composite cable.

Figures 11 to 14 show a variant embodiment of the fiber-optic cable and a non-limiting example of operation of this variant embodiment of a fiber-optic cable in combination with a deforming member of the type as shown in Figures 6 and 7.

The figures only show a few possible exemplary implementations, that will be described with reference to the figures, in the light of the differences from the embodiments shown herein.

Referring now to Figure 1, there is shown a first exemplary embodiment of a cable duct, generally designated by numeral 1. The cable duct 1 is composed of a plurality of channel segments 101, which are designed to be arranged in a row, one after the other. Each channel segment 101 has a cover segment 201 that is substantially as long as said channel segment 101, with the covers 210 being applied to the channel segments 101, and the cable duct forms a longitudinal compartment for the cables, which is closed on all of its sides, and can be opened on the side formed by the covers 201.

The cables, e.g. four cables referenced 2 in the illustrated example, may be electric cables, but may also be of any type and have any function.

Alternatively, the invention may be used with any type of elongate element to be protected from theft, such as pipes or else.

The cables 2 lie in the compartment of the housing channel 1 and the present invention has the object of protecting such cables 2 from theft.

In current theft techniques, the housing channel

1 is opened at locations separated by a predetermined distance and one, more or all of the cables 2 are cut at such two locations, to separate a segment of each cable from the remaining cable parts. Once the segment/s or the cable/s has been separated, it/they are pulled off the housing channel 1 through one of the two openings created by removing the cover 201 and carried away, possibly after being wound in coils or on spools.

The cables may be joined or gathered together using a succession of ties or other circumferential fastening means, arranged at predetermined distances from each other over the longitudinal length of the cable or cable bundle 2.

In a first illustrated embodiment, the cables 2 of the cable bundle are fastened together and attached to a wall of the housing channel (here the bottom wall) by a bracket 3. The bracket 3 fastens the cables 2 to the wall of the housing channel 1 and possibly to one another. Therefore, the brackets 3 have to be loosened for one cable 2 or more cables 2 or all the cables 2 to be pulled of the housing channel 1.

The channel 2 further houses a sensor, which is composed of a fiber-optic cable 4. Each bracket 3 for fastening/securing the cables 2 together and to the wall of the housing channel 1 is further provided with an annular element which delimits a passageway for the fiber-optic cable.

The annular element, which may be an eye, an opening in a wall or, like in the illustrated example, a tubular element 5 of predetermined length, is integrally fixed to of formed of one piece with each fastening/securing bracket 3 whereas, referring to the longitudinal length of the cable/s 2, a pair of fastener elements 6 are provided for each annular element, or each tubular element 5, for stationary attachment of the fiber-optic cable 4 to a wall of the housing channel 3.

The fastener elements 6 for stationary attachment of the fiber-optic cable 4 to a wall of the channel are arranged on each of the opposite sides of the tubular element 5 and hence the fastening/securing bracket 3, with respect to the longitudinal direction of the cable/s 2.

The fiber-optic cable is passed through a first fastener element 6 for stationary attachment thereof to a wall of the housing channel 1, to enter the tubular element 5 by an incoming section 104. This section is led out of the tubular element 5 on the side opposite to the entry side, whereby the fiberoptic cable is passed back through said tubular element 5 by an outgoing section 24 that entirely extends through the tubular element 5 thereby forming a loop, an eyelet or a curl 304. Therefore, the outgoing section is attached to a wall of the housing channel 1 by a second fastener element for stationary attachment.

Figure 2 shows this situation in greater detail. When the bracket 3 for fastening/securing the cables to the wall of the housing channel 1 is released, the displacement of the bracket causes at least one of the two sections 104 and 204 of the fiber-optic cable 4 to be pulled or pushed, and according the curl 304 to be pushed or pulled, thereby considerably changing its bending radius, due to- the constraining action of the tubular element 5. This change of the bending radius causes a change of the parameters for light signal transmission by the fiber-optic cable and hence a change of the characteristic parameters of the light signal that comes out of the fiber-optic cable, which change is detected, measured and compared with threshold values. According to the result of this comparison an alarm triggering signal is generated, for triggering alarm warning means that may be of various types and may be triggered alternately or at the same time.

The change of the bending radius is also caused if the fiber-optic cable 4 is released at least at one of the points for stationary fixation 6 to one of the walls of the housing channel 2.

In a variant embodiment, not shown, the fiber- optic cable is attached to a wall of the housing channel 1 using the brackets for fastening/securing the cables 2 together and to said wall of the housing chamber 1. The operation is essentially as described above. In this case, the incoming section 104 is attached to the cables and/or the wall of the housing channel 1 by a previous fastening/securing 'bracket 3 and the outgoing section is attached by the next one. Therefore, fastening/securing brackets 3 with a tubular element 5 and brackets without said tubular element 5 alternate over the length of the cable/s 2.

The circumferential fastening cable ties may be formed as pipe clamps or plastic straps 20 having a wall with a through hole or slot or a tubular bush or an annular element, integrally formed in the form of an appendage on one side of the strap element of the tie or clamp. The advantage is that the use of these ties or clamps provides simple and fast installation. Furthermore, the brackets or the fastener means 3 are inexpensive. These ties or clamps may also have extensions 220 that form slots, holes or the like, for attachment to a wall of the housing channel. One embodiment is shown in Figures 11 and 12.

The tubular element 5 or ring 5 ¹ or the slotted wall 5 ' * may be mounted to some sort of loop through which the strap element of the tie or clamp extends . Here, a commercially available tie or clamp may be used as the fastening bracket 3, upon which the tubular element 5, the ring 5' and/or the slotted wall 5'', as separately shown in Figures 13 to 15, are mounted. The fastening base 220 for attaching the tie or clamp 20 to a wall of the channel 1 that houses the cables 2 may be also formed as described concerning said tubular element, ring or slotted wall, as shown for instance in Figure 16. In the variant of Figure 3 , the cables 2 are fastened together at predetermined distances by circumferential fastening cable ties 3' that may be of any type. In this example, the fiber-optic cable 4 is passed with the cables 2 to be monitored through the fastening cable ties 3", whereas said cable is deviated at predetermined distances in an intermediate area between two fastening ties 3 ¹ , toward a fastener element 7 for attaching said fiber- optic cable 4 to a wall of the housing channel 1, which is of the type that attaches said fiber-optic cable to allow sliding thereof relative to an attachment point, i.e. the fastener element 7. Particularly, said fastener element comprises a ring, a slotted or bored wall or a tubular element 5 which are mounted to a fastener base 107 for attachment to the wall of the housing channel 1. The fiber-optic cable is passed through said ring, said slotted or bored wall or said tubular element 5, as described above with reference to the exemplary embodiment of Figures 1 and 2, to form a curl, a slot or a loop on the side opposite to the entry side of said ring, hole or tubular element.

The cables 2 and the fiber-optic cable 4 may be also possibly fastened together, in addition to being attached to a wall of the housing channel 1. This may occur either at all or some of the cable ties 3 ¹ or at intermediate points between two ties 3 for fastening the cables 2 and the fiber-optic cable together. Here, such arrangement may be provided at each intermediate area between successive ties or at some of such intermediate areas. As cable lengths are cut and pulled off the housing duct, in the above described embodiments, the fastener elements for fastening the bundle cables together or the cable and the cable bundle together and to a wall of a channel or duct that houses the cable or cable bundle (i.e. the various embodiments of the brackets secured to the bottom of the cable duct or the cable ties for fastening multiple cables of a bundle together and to said housing element) , especially when there are many of them, secure the cables to an unremovable element (generally a concrete part that is part of the housing duct) , and actually slow down the theft. This hindrance, in combination with an alarm warning through a siren or a light may effectively act as a disturbance for the thieves and later on as a dissuasion, during the theft.

Figures 4 and 5 show how the device of the present invention is mounted in a cable duct consisting of a tubular duct 1 for the cables 2, having manholes 10 for laying cables 2 and inspection, at predetermined distances over the length of the tubular duct 1. The manholes may have any construction and typically consist of a box-like body 110 having an access on one side. A removable cover 210 closes such access.

In this case, the cable sections are cut and pulled out at the manholes. Therefore, in the device of the present invention, the fiber-optic cable 4 that is laid along the cables 2 in the cable duct 4 is designed to have the purpose of detecting and indicating unauthorized opening of manholes, i.e. removal of the cover 210 to access the cables 2. Like in the first embodiment, the device comprises fastener means for stationary attachment of the incoming fiber-optic section 104 that comes into said manhole 110 to at least one point of a wall of the manhole 110, and fastener means for stationary attachment of the outgoing fiber-optic cable section, that comes out from said manhole, to at least one point of a wall of the manhole 110.

Preferably, the wall for attachment of the incoming fiber-optic cable section 104 is the wall that receives the duct 1 from which the incoming section extends 104, and the wall for attachment of the outgoing section is the wall with the duct 1 having the outgoing section 204 of the fiber-optic cable 4 extending therefrom.

The means for stationary attachment may be substantially identical to those described above and referenced 6. The incoming section 104 is passed through means for sliding attachment of the fiber- optic cable which are similar or identical to those referenced 7 and described with reference to the exemplary embodiment of Figure 3 , which are attached to the cover 210 of the manhole. The incoming section 104 and the outgoing section 204 extend through the tubular element 5 or the ring 5 ¹ or the slotted wall 5·' to form a curl, a ring, an eyelet or a loop 304 on the side of said tubular element 5 or said ring or said slotted or bored wall opposite to the entry side for the incoming section 104 and the exit side for the outgoing section 204 respectively.

The total length of the incoming and outgoing sections between the two stationary attachment points 7 is such that, if the cover is lifted, at least one of the two sections 104, 204 is pulled or pushed, and causes a change in the bending radius of the curl or loop 304 thereby causing, as described above, a change in the emitted light signal. Such change is measured and compared with predetermined threshold values and the result of this comparison will or will not trigger the warning means .

Figures 6 to 7 show a variant embodiment of the invention, in which any lifting and/or removing action on the cover are indicated by active deforming means, i.e. actuated by an element that deforms the fiber-optic cable. Such construction is described in greater detail, for other purposes, in EP0332900B1, and comprises a deforming element 30 that cooperates with two stationary stops 31 for the fiber-optic cable. This deforming member 30 has a convex or tapered fiber-optic cable deforming surface, which is oriented substantially perpendicular to the axis of said fiber-optic cable 4, whereas the two stationary stops 31 are designed to be placed on the side of the fiber-optic cable 4 diametrically opposite to that of the convex or tapered deforming surface 130 and outside the width of said tapered or convex surface, i.e. from the dimension of said surface parallel to the axis of the cable 4 and on each side thereof. Such deforming member is provided in the form of a slider, sliding between the two stationary stops 31 perpendicular to the fiber-optic cable 4 between a position in which the convex or tapered surface 130 does not interact with said fiber-optic cable 4 and an active deforming position, in which said convex or tapered surface is pushed against - the fiber-optic cable that is retained by the two stops 31 and is deformed according to the convex or tapered shape of the surface 130 over the section of said cable between said two stationary stops 31, thereby causing a change in the light signal emitted by the optical fibers as compared with the undeformed state of the fiber-optic cable.

An elastic element 32 stably biases the deforming member 30 into the active deforming state, whereas an axial extension 230 of the deforming member 30 allows exertion of a thrust by the deforming member in the position in which it does not interfere with the fiber-optic cable 4 against the action of the elastic element 32.

Such deforming member is located within the manhole 110 in such a position that, when the cover 210 is in the closed state, such cover acts upon the axial extension, thereby retaining said deforming member in a state in which it does not interfere with the fiber-optic cable 4, as shown in Figure 7 and, as the cover is lifted to a given extent or completely removed, the elastic element 32 displaces the deforming member 30 into a state in which it interferes with and deforms the fiber-optic cable thereby triggering the alarm warning state (Figure 6) .

While Figure 7 show the fastener means 6 for the incoming and outgoing sections 104, 204 of the fiberoptic cable 4 within said manhole, these fastener means 6 may be also omitted without substantially altering the function of the deforming means 30.

In the embodiments of Figures 4 to 7, which show the means for indicating the displacement of the covers 210 of manholes 110, the detection and indicator means may be also possibly mounted to one or more of the covers 210 of the channel segments 110 of the embodiments of Figures 1 to 3.

Referring to figures 8 to 10, a variant embodiment is shown, which is suitable for use both instead of and in addition to one or more of the previous embodiments.

Figure 8 shows a general cable, such as an electric cable, having a copper core 40 of monopolar, multipolar or any other type, and an outer insulation cladding 41. Here, the fibers of the optical fiber core of the fiber-optic cable or the fiber-optic cable itself are integrated in the main cable in stationary fashion and embedded in the thickness of the insulation cladding layer 41, which may be possibly enlarged. This cable may be fabricated using common techniques for fabrication of multipolar cables in which one of the cores consists of the fiber-optic cable or the optical fiber core of the fiber-optic cable.

The embodiment of figure 10 is a variant including more than one fiber-optic cable, namely four fiber-optic cables or four optical fiber cores 42 arranged along the circumference of the main cable core and embedded in the thickness of the insulation cladding 41.

In the variant of Figure 9, separate claddings are provided for the main cable and the fiber-optic cable, which claddings are joined along a longitudinal tangent strip. This may be obtained by welding of two cables in a processing step that follows the cable fabrication step or a cladding process in which both cores together are covered with an insulating material.

New Figure 11 shows a variant of an anti -rodent cable. This cable has an optical fiber core 42 covered with a tubular mesh, particularly made of steel 43, which has a rodent protection function.

The tubular steel mesh cover 43 is covered by a plastic sheath, particularly made of PVC 44.

In a preferred non-limiting embodiment, as shown in Figure 11, the optical fiber core 42 is externally covered by a first cladding 45, made of Kevlar, which is i turn externally covered by a second plastic cladding, particularly made of PVC 46. The tubular steel mesh cover 43 is provided over said second plastic cladding 46 and is in turn externally covered by a tubular plastic cover, particularly made of PVC and referenced 44.

A cable of this type is safe against rodent damage, but has the drawback of not being easily deformable such that any pulling or pushing action thereon would cause significant changes in the light signal, that might be safely detected and used as alarm triggers.

The cable comprises an optical fiber core 42 and two claddings 45 and 46 and has a diameter of about a few millimeters, particularly about 3 mm, and is thus adapted to cause changes in light signal transmission, that might be used for alarm triggering as a result of a deformation of the cable, which shall be intended as a combination of the layers 42, 45 and 46.

For effective operation, the cable with the anti-rodent protection feature, comprising all the layers from the core 42 to the outer sheath 44, may have sections of predetermined length along which the outer sheath layer 44 and the tubular steel mesh cover 43 are removed, thereby leaving an exposed predetermined length of a cable composed of the optical fiber core 42, the first cladding 45 and the second cladding 46 covering said core 42, which, as mentioned above, will have a diameter that allows tamper detection.

Depending on whether the cable is used in combination with the deforming members of Figures 6 to 7, the fastener elements having a ring, a slotted or bored wall or a tubular element 5, as shown in the Figures of any of the above described examples, the predetermined length of the anti-rodent cable along which the outer sheath 44 and the tubular steel mesh cover 43 have been removed, may range from about 3 cm to about 20 cm, also depending on whether the cable forms a curl, a loop or an eyelet. The step of removing the outer sheath 44 and the tubular steel mesh cover 43 is simple and may be carried out either mechanically during cable fabrication or manually, using scissors and wire strippers, as conventionally used, for instance by electricians and other skilled persons .

Figure 12 shows the fiber-optic cable of Figure 11, in which the outer sheath 44 and the tubular steel mesh cover 43 have been removed over the predetermined length.

Figures 13 and 14 show the use of the cable of the previous Figures 11 and 12 in combination with a deforming member of Figures 6 and 7. In Figures 13 and 14 the parts that have been already described with reference to Figures 6 and 7 and have the same function, are designated by the same numerals as in Figures 6 and 7.

Figure 14 shows a variant embodiment which is illustrated with a cable having an anti -rodent protection and sheath, but is also adapted for use with a normal fiber-optic cable, as described in the previous figures 6 and 7 and/or 8 to 10. In this figure, the fiber-optic cable length having no outer sheath 44 and no tubular steel mesh cover 43 is passed through the deforming device to form an eyelet, a loop, a curl 304 or the like, whose arched section opposite to the incoming 104 and outgoing 204 sections, the latter being in crossed relationship, is interposed between the deforming member 130 and the stop/s 31.