EP0568137B1

EP0568137B1 - A mounting structure for an electrical apparatus having a device indicating removal of same

Info

Publication number: EP0568137B1
Application number: EP93201118A
Authority: EP
Inventors: Antonio Aldizio
Original assignee: BTicino SpA
Current assignee: BTicino SpA
Priority date: 1992-04-30
Filing date: 1993-04-17
Publication date: 1996-11-27
Anticipated expiration: 2013-04-17
Also published as: EP0568137A1; DE69306158D1; DE69306158T2; ITMI921036A0; IT1255115B; ES2095558T3; ITMI921036A1

Description

This invention relates to electric systems, and particularly to a structure for mounting an electrical apparatus inside a box, especially an apparatus equipped with a device for indicating removal of the apparatus from the box,
In installing electric systems, it is frequently necessary to apply measures directed to prevent, or at least indicate, tampering with the system apparatus. Such is the case, for instance, with intrusion-resisting apparatus, wherein the removal of a critical system component such as a detector may render the system ineffective, or with electrical control and monitoring panels of power supply networks for industrial or civil uses, which could be tampered with by unauthorized personnel with the result that unforeseen damage may be caused to electrical apparatus connected in the system, or with elevator pushbutton strips incorporating key-operated safeguard mechanisms to only allow the elevator to be stopped at certain floors by holders of the corresponding keys, wherein an unauthorized person still could, by prying out a safeguarded pushbutton, close its respective contact and so gain access to a restricted floor.
A commonly used expedient for indicating that electric apparatus housed in wall hung or set-in boxes have been tampered with provides electric components consisting of two discrete members coupled to each other whose electrical behavior is altered as the two members are moved away from each other. A typical component of this type is the reed relay, wherein the two coupled members are a pair of ferromagnetic contacts and a permanent magnet. In operation, one of the members, e.g. the permanent magnet, would be rigidly connected to an insert unreleasably attached to the box, and the other member to the electrical apparatus, in turn attached to the box in a removable fashion. The reed relay is part of an indicator circuit, which may be the alarm circuit itself in which the electrical apparatus is connected in the instance of an intrusion-resisting system, and is connected such that the removal of the apparatus mounted in the box, and hence of the contact from the magnet, would result in an alarm being tripped upon the contact being opened or closed, depending on the reed relay type.
The member that is connected to the apparatus is usually located within the apparatus casing, close to the wall which locates opposite to the bottom of the box in which the apparatus is mounted. In conventional applications, the member that is connected to the box is attached to the latter either directly or through a specially provided support base, using screws, adhesives, or a strip of a double-sided adhesive material. These fastening arrangements have, however, some drawbacks. In fact, screw fastening is a comparatively awkward operation because the member to be fastened must be first positioned accurately, then holes must be drilled through the box bottom, and the screws tightened, and on the other hand, fastening with adhesives or double-sided adhesive material, while being simpler, is also rather awkward because it still requires accurate positioning, and tends to be unreliable as the adhesive deteriorates over time. In all cases, moreover, the level reached by the electric apparatus in its ultimate position within the box must be either known or measured, so that the two coupled members locate, on completion of the installation, at a prescribed mutual distance for proper operation, which distance should be the least possible in the instance of a reed relay. It should be noted that in many cases, in view of the different depth of the boxes used for enclosing electrical apparatus, shims would have to be fitted between the member to be fastened to the box and the box bottom.
It is the object of this invention to provide a mounting structure of the type specified above, which has none of the aforementioned drawbacks and is simple and reliable, as well as convenient to install.
This object is achieved by a mounting structure as defined and characterized in the claims appended to this description.
The invention can be more clearly understood from the following detailed description of an exemplary, and in no way limitative embodiment thereof, to be read in conjunction with the accompanying drawing, the single Figure whereof shows the inventive mounting structure and various parts prior to installation.
As shown in the drawing, a group 10 of three modular construction electrical apparatus 11, 12 and 13 held together on a frame 14 is intended to be releasably fastened, such as by means of two screws 15, to the interior of a box 16 having a rectangular cross-sectional shape and being adapted to be set in a wall. The frame 14 has lead-in walls 14a to facilitate alignment of the two parts.
One of the three apparatus, namely the one denoted by 11 in the drawing, may be an infrared detector of moving objects, and contains contacts (hidden from view in the drawing) of a reed relay on the bottom of its casing. The permanent magnet for operating the reed relay, indicated at 17, is attached to an insert 18 adapted to be secured releasably on the box 16 interior.
The insert 18 comprises an elongate body 19 made of a non-magnetic material, e.g. a plastics molding, and having a recess wherein the magnet 17 is accommodated and held. Two spring reeds 20, e.g. made of steel, are respectively attached to the ends of the body 19 by means of grooves 19a and interfitting formations 19b. The free ends of the reeds 20 are each formed with two prongs 20a and are set apart a greater distance than the inside width dimension of the box 16.
Two tabs 21 are blanked out of the reeds 20 and suitably bent to locate at a spacing from one another smaller than the distance between the lower and upper sides of the apparatus 11. These sides have each a pair of parallel ribs 11a spaced apart to receive and guide the tabs 21.
The parts described above jointly define a mounting structure for mounting the group of electrical apparatus 10 inside the box 16, which is installed by first joining the insert 18 with the apparatus, as by forcing the latter in place between the tabs 21, and then fitting the group into the box 16 with the insert in place. The group 10 will automatically align to the box by virtue of the lead-in walls 14a provided, and the insert 18 -- whose reeds 20 bend elastically inwards upon its introduction -- will also locate automatically in the box and retain its position relative to the apparatus 11. In addition, the insert 18 is held unreleasably to the box by the prongs 20a engaging the opposed longitudinal walls of the box 15 under the spring bias from the reeds 20. Thus, the insert 18 functions similar to an expansion anchor means.
Notice that once the insert 18 is secured in place, the group 10 can be disassembled and reassembled without altering the mutual positioning of the insert and the apparatus. It should be also noted that the insert 18, although unreleasably secured from the operational standpoint, may be easily taken, where required, out the box for use at another location in combination with the same or another apparatus, because of the expansion anchor-like arrangement relying on the comparatively modest spring bias provided by the reeds 20. And moreover, notice that the mounting structure of this invention affords optimum positioning of the insert 18 and the apparatus 11 irrespective of the box depth.
While a single embodiment has been described and illustrated, it is understood that many changes and modifications could be introduced as fall within the same inventive concept. For example, a cylindrical box could be substituted for the rectangular box; the tabs 21 and corresponding ribs 11a could be replaced with some other guiding and fastening arrangement between the insert and the apparatus; instead of a reed relay, other components could be employed whose electrical characteristics be tied to the distance therebetween, such as a coil with a detachable ferromagnetic core, a separable plate capacitive element, a photoelectric coupler, a monostable microswitch, etc.. If required, moreover, terminals may be provided in the insert for any supply or connection lines to the portion of the electrical device housed therein.

Claims

A structure for mounting an electrical apparatus inside a box (16), especially an apparatus (11) which is attached releasably to the box (16) and equipped with a device for indicating removal of the apparatus (11) from the box (16), said device comprising two members coupled together within the box (16) and means operative to generate a signal upon the two members being parted together, and said members being affixed, the one to the apparatus (11) and the other (17) to an insert (18) attached to the box (16) by unreleasable fastening means, the structure being characterized in that the unreleasable fastening means comprise expansion anchor means (20) engaging the box (16) walls.
A mounting structure according to Claim 1, characterized in that it further comprises fastening means (21,11a) effective to hold the insert (18) removably to the apparatus (11) in a predetermined position prior to fitting the apparatus (11) and the insert (18) into the box (16).
A mounting structure according to either Claim 1 or 2, characterized in that the expansion anchor means (20) comprise two spring reeds (20) being attached to the insert (18) on two opposed sides of the latter and having at least one prong (20a) on their free ends, the distance between the free ends of the reeds before fitting the insert (18) into the box (16) being larger than the distance between said box (16) walls engaged by said expansion anchor means (20).
A mounting structure according to Claim 3 as dependent on Claim 2, characterized in that the means of fastening the insert (18) to the apparatus (11) comprise two spring tabs (21) being formed each from one of the spring reeds (20) integrally therewith, and guide and bearing means (11a) on opposed sides of the apparatus for receiving the two tabs (21) in push fit relationship on said opposed sides.