METHOD AND MEANS FOR JOINTING TOGETHER AND SHIELDING OF CABLE DUCTS FOR TELECOMMUNICATION SYSTEMS

Abstract: A method and arrangement for effecting electrical connections in and for shielding the joints between mutually connected duct sections of an electric cable duct system intended for accommodating different kinds of telecommunication cables, the duct sections preferably having the form of metal profiles of preferably rectangular cross-section. According to the method the duct sections (1, 4, 7) are joined to one another with the aid of a joint fitting (12) which extends on both sides of the joint location and which is screwed or otherwise pressed against duct sections (1, 4, 7), contact means (19) being placed in a space defined between respective duct sections (1, 4, 7) and the joint fitting (12). In addition, the joint location is embraced by a shielding or screening device comprising a clamping means (14, 15) which can be opened to facilitate fitting the means and which when fitted includes at least one shielding gasket (26) which extends circumferencially around the duct.

Description: METHOD AND MEANS FOR JOINTING TOGETHER AND SHIELDING OF CABLE DUCTS FOR TELECOMMUNICATION SYSTEMS . Technical Field. The present invention relates to a method and an arrange- ment for effecting electrical connections in and for shielding the joints between the duct sections of elec¬ tric cable ducts or trunking systems intended for accommodating different kinds of telecommunication cables, said duct sections having the form of metal profiles, or profiles made of an electrically non-con¬ ductive material and provided with an outer metallic surface coating or with metallic inlays. The ducts, or trunking systems comprise duct sections in which joints between, for instance, bottom trough-like members and associated cover members incorporate conventional shielding gaskets, for example gaskets of the- kind that comprise a resilient sealing strip wound with metal wire or filament. Background Prior Art. Ducts, or trunking systems for accommodating electric cables, e.g. telecommunication cables, are known to the art. It is also known to shield or screen such ducts against the influence of radio frequency energy and electromagnetic pulses. One drawback with present day duct shielding devices is that they are relatively complicated to use. Furthermore, the task of installing the shields is highly time consuming. It is also im¬ portant that the cover members of respective duct sections can be readily removed and re-fitted securely, particularly when dismantling and re-assembling existing duct systems. Disclosure of the Invention. The object of the present invention is to provide, for the purpose of joining together duct sections that are intended to house telecommunication cables of various kinds, and for the purpose of shielding said sections against the influence of external magnetic fields, e.g. radio frequency energy and electromagnetic pulses, a novel method and novel means with which the drawbacks associated with the known methods and means are elimi- nated. This object is achieved by means of the method and the means according to the invention, which relates to the jointing of duct sections, and preferably of duct sections which have the form of metal profiles of substantially rectangular cross-section. The charac- terizing features of the method and the means according to the invention are set forth in the following Claims. A duct system, or trunking system, comprises a plural¬ ity of interconnected straight duct sections, which may be joined together by means of T-sections, X-sections or connecting sections. The T-sections and X-sections are used to connect together branches in the duct system, whereas the connecting sections are used, for instance, to connect a duct system to apparatus cabi¬ nets. All the duct sections comprise a base member, or base channel, and a cover member. A shielding seal, or gasket is arranged in -each of the joints located in the various sections of the duct system, i.e. between the base channel and the cover member of -repective straight duct section and between the base member and the cover member of the T-section, the X-section, or the connect¬ ing sections. The shielding gasket incorporated in each of said joints consists of a known sealing strip, and preferably a sealing strip that consists of a resilient plastic core wound with metal wire or filament. The shielding gasket may have a circular or rectangular cross-section- al shape, and may also be provided with outwardly pro¬ jecting tags to facilitate fitting of the gasket. When connecting a duct system to an apparatus cabinet there is left a gap which is shielded with the aid of a bellows-like shield, in the form of a metal-wire net that hangs from the underside of the cabinet and sur¬ rounds a cable port in the cover member of the connect¬ ing section. The lower end of this shield is preferably connected to a metal frame, the surface of which that lies in abutment with the cover member of the connecting section being fitted with a shielding gasket in accor¬ dance with the above. Two mutually adjacent duct sections are preferably joined together by means of at least one joint fitting which extends along both sides of the joint between said sec- tions. Furthermore, preferably at least one electrical contact is arranged between respective duct...section..and the joint fitting on each side of the joint between the duct sections. The provision of a joint fitting is necessary in order to ensure that the various sections of the duct remain connected should the duct system be subjected to tensile forces in the longitudinal direc¬ tion of the ducts. The electrical contact preferably has the form of a metal tongue or the like provided with a sprung or resilient element which projects from the plane of the tongue, and ensures that electrical contact is established between a joint fitting and the duct sections adjacent thereto. This has particular importance when the duct sections are made of aluminium alloys and earth currents pass through the duct walls. Because of the constriction resistance occuring in the screw joints of such ducts, the aforesaid earth currents must of necessity pass through small areas, and conse¬ quently the duct walls are subjected to local generation of heat. Due to the higher expansion coefficients of aluminium, the aluminium in the duct walls will expand to a greater extent than the iron screws normally used in such joints, wherewith the resultant increase in pressure in the joint causes the softer aluminium to flow away from the location of the joint. Due to this flow of aluminium at the region of the joint, the con¬ tact pressure will have decreased when current ceases to flow through the screw joint and the joint location has subsequently cooled, resulting in increased contact resistance. This sequence of events takes place each time current passes through the joint, re¬ sulting in a progressively poorer connection, or contact. The process is accelerated by the fact that the pro¬ gressively higher temperature at the location of the connection results in oxidation, which further increases the connection or contact resistance. As a result, the duct very soon ceases to function as an earthing con- ductor. Consequently, it has become practice in many known electric-cable duct systems to incorporate a separate earth cable, which is normally placed freely in the system. The present invention eliminates the need for a separate earth cable. Brief Description of the Drawings. The invention will now be described in more detail with reference to an exemplifying embodiment thereof illus¬ trated in the accompanying drawings. Figure 1 is a schematic, exploded view of the component parts of a duct system connected to an apparatus cabi¬ net, shown in chain lines. Figure 2 is a view taken on the line A-A in Figure 1 , 5 and shows a leg arrangement of the cabinet indicated in Figure 1. Figure 3 is a more detailed, cross-sectional view of the duct, taken on the line B-B in Figure 1. Figure 4 is a cross-sectional view taken on the line o C-C in Figure 3. Figure 5 is an enlarged view of a detail indicated by the arrow D in Figure 3. Figures 6 and 7 are respective enlarged views of a con¬ tact plate according to Figures 3 and 5. 5 Description of Preferred Embodiments. In the illustration of Figure 1 there is shown two straight duct sections 1 of a duct system, each of which comprises a base channel 2 and a cover member 3, of which one is joined to a T-section 4 and the other 0 is arranged for detachable connection to said T-section 4. The T-section 4 comprises a base member 5 and a cover member 6, which is shown lifted from the base member 5. The T-section 4 is joined to a connecting section 7, which comprises a base member 8 and a cover 5 member 9. The cover member 9 of the connection section 7 has provided therein ..a .port.. 10 through which cables can be passed to an apparatus cabinet 11 illus¬ trated in chain lines in Figure 1. The two straight duct sections 1 , the T-section 4 and the connecting section 7 are each joined to a respective adjacent duct section through the intermediary of joint fittings 12. A shielding seal, or gasket, 26 is arranged in each joint located in the various duct sections of the duct system, i.e. between the base channel 2 and the cover member 3 of respective straight duct sections, between the base members and the cover member 6 of the T-sec¬ tion 4, and between the base section 8 and the cover member 9 of the connecting section 7. Each joint between two mutually adjacent duct sections is shielded against the influence of external magnetic fields through the intermediary of a clamping device, which can be opened to facilitate fitting of the clamp, and which in the illustrated embodiment com¬ prises two jointing stirrups, which stirrups can be coupled one to the other and each of which is provided with a gasket or like seal. Thus, two shielding gas¬ kets 26 are arranged in a lower joint stirrup 14, which covers the joint at the bottom of the duct, and in an upper joint stirrup 15 which is joined to the lower stirrup 14 and covers the joint at the top of the duct. The two gaskets 26 extend in mutual paral¬ lel relationship around the joint, on all sides there- of. The shielding gaskets 13, 26 provided in the duct sections, and the jointing stirrups suitably comprise a sealing strip of known kind, for example of the kind that comprises a resilient plastic core covered with metal wire or filament, for example a Monelmetal, aluminium or stainless steel wire. The gaskets 13, 26 of the illustrated embodiment have a circular cross- sectional shape. The connecting section 7 of the illustrated duct system is connected to the cabinet 11 through the intermediary of a bellows-like screen 16, as shown in Figure 2. The screen 16 has the form of a metal-wire net which hangs down from the undersurface of the cabinet 11 and covers the cable port 10 located in the cover member 9 of the connecting section 7. The bottom edge of the screen 16 is connected to a metal frame 17, the surface of which lying in abutment with the cover member 9 of the con¬ necting section 7 is provided with a shielding gasket or like seal. Figure 3 is a cross-sectional view of a straight duct section taken on the line B-B in Figure 1 , and illust- rates in greater detail the base channel 2, the cover member 3 and the jointing components employed to join said parts together. The joints are suitably effected with the aid of two fittings 12, of which only one is shown. The fittings12 are mounted in T-shaped grooves 18 which lie opposite one another in the vertical walls of respective duct sections. The positioning of the fittings 12 is also illustrated schematically in Figure 1. The fittings 12 are securely held in respec¬ tive mutually opposing T-grooves 18 with the aid of screws which extend through threaded holes in respec¬ tive fittings 12, so as to press the fitting firmly in its associated T-groove 18. A contact plate 19 is placed in a channel-like recess provided in each fit¬ ting 12, so that a plate 19 is located between each fitting 12 and the opposing wall of a respective duct section, on both sides of the joint. The contact plate 19 is shown in an enlarged view in Figures 6 and 7, and comprises a thin bronze plate having punched therein resilient contact elements 20, which are twist¬ ed out of the plane of the plate 19 so as to form an angle therewith. The construction of the plate 19 and its orientation in the joint are such as to take up eventual dimensional changes caused by heat generated when electric currents flow through the contact points or connections, through torsional resilience in the contact plate, and the otherwise commonly occuring deformation and oxidation in the contact points has been eliminated. The joint between the duct sections illustrated in Figures 3 and 4 is shielded against said external energy by means of the lower jointing stirrup 14, which is connected to the upper stirrup 15 with the aid of a hook device 21 and stirrup 22 on one side of the joint¬ ing stirrups 14, 15 and a hook device 21 and a clamping device * 23 on the other side of the jointing stirrups 14, 15. A cross-sectional view of the bottom jointing stirrup 14 is illustrated in Figure 4. It will also be seen from this Figure that shielding gaskets 26 are located on both sides of the joints between respective duct sections. As illustrated in the Figure, the bottom jointing stirrup 14 presents a U-shaped ridge 24 which protects in between the duct sections therewith to pre¬ vent movement of the mutually connected stirrups 14, 15, along the duct. By appropriate dimensioning of the width of the jointing stirrups, it is possible to accept a certain degree of non-parallelity of the mutually opposing end surfaces of adjacent duct sections.

Claims: CLAIMS. 1. A method for effecting electrical connections in and for shielding the joints between mutually connected duct sections (1, 4, 7) of an electric cable duct system intended for accommodating different kinds of telecommunication cables, said duct sections having the form of metal profiles or profiles made of an electrically non-conductive material and. provided with an outer metal surface coating or inlay, characterized by positioning the duct sections (1, 4, 7) in end-to- end relationship and jointing together mutually ad¬ jacent duct sections with the aid of at least one joint fitting (12) which extends on both sides of the joint location and which is screwed or otherwise pressed against duct sections(1, 4, 7) ;placing in a space de¬ fined between respective duct sections (1, 4, 7) and the at least one joint fitting (12) at least one con¬ tact device (19) which ensures positive electrical contact between said sections; and by fitting around the joint location an electrically conductive clamping device (14, 15) which can be opened to facilitate fit¬ ting of the device around said joint location and which when fitted includes at least one shielding gasket (26) which extends circumferentially around the duct. 2. An arrangement for carrying out the method according to Claim 1 , characterized in that it includes an openable clamping device which when fitted in position encloses at least one shielding gasket (26) which extends circumferentially around the duct. 3. An arrangement according to Claim 2, characterized in that the clamping device comprises two mutually connectable stirrup-like components (14, 15) each of which has a shielding gasket accommodat¬ ing groove provided around an edge surface thereof. 4. An arrangement according to Claim 3, charac¬ terized in that at least one of the stirrup-like members (14, 15) presents a ridge or like promonatory which, when said stirrup is fitted, projects in-between said duct sections.

Inventors: LOEFVING STIG ARNE, LOEFVING, STIG, ARNE
Applicants: THORSMAN & CO AB
Application year: 1986
Main classification: H02G3
IPC codes: H02G3