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(11) | EP 0 746 004 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
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| (54) |
Lamp holder for a wall-mounted switch assembly and the related switch assembly Lampenhalterung für an einer Wand befestigte Schalteinrichtung und ensprechende Schalteinrichtung Support de lampe pour dispositif de commutation monté au mûr et dispositif de commutation y relatif |
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| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
[0001] The present invention relates to a lamp holder for a wall-mounted switch assembly and the related switch assembly.
[0002] It is known that modular electrical switches are available on the market for installation on walls with the aid of an intermediary plate or support frame to which a plurality of switch modules or "fruits" may be fixed.
[0003] These switches are often provided with a housing for a lamp for indicating the open or closed state of the switch, the lamp being located beneath a rocker key (transparent or provided with a transparent window) which operates the switch.
[0004] Usually the indicator light, which is preferably a neon lamp, enables the location of the switch to be seen even in the dark and thus is energised and hence switched on when the switch is open and is off when the switch is closed.
[0005] In some cases, however, it may be necessary for the closed state of the switch to be made visible by the corresponding switching on of the lamp.
[0006] This is particularly the case for switches which control remote light sources, for example external lights, operated from the interior, or electrical apparatus other than light sources such as fans, heating elements, air conditioners and the like.
[0007] At present, in order to provide such locating and indicating functions, use is made of lamps or illuminating systems including load-stabilising resistances provided with cables which connect them to the clamping terminals of the switch assembly or at least to voltage supplies controlled by the switch.
[0008] It is not very easy to use these lamps since their supply cables are of small section and are difficult to insert in the terminals provided for the power cables or, once inserted, may easily slip out or may not be clamped and held very reliably to the detriment of the functioning ability and safety of the system.
[0009] Although, on the one hand, such lamps are versatile to use since their supply cables may be connected in different ways according to the very different requirements of different systems, they have the further disadvantage that the installer must necessarily study the electrical system and the switching apparatus to effect the most appropriate connections.
[0010] By the term switch is in fact intended electrical apparatus of essentially two types:
- simple single pole open-contact switches (known by the acronym SPST for single pole-single throw)
- two-way contact-switching, single pole switches known by the acronym SPDT for single pole-double throw.
[0011] It is clear that the connection of a locator lamp to the electrical apparatus or system must be carried out in different ways according to the type of electrical apparatus and the desired function.
[0012] In the case of a locator lamp associated with a simple switch, which is lit when the switch is open, it is clear that the lamp must be connected in parallel with the switch, that is to its two electrical terminals.
[0013] In the case of an indicator lamp associated with a switch which is lit when the switch is closed to supply an electrical load, the lamp must be connected in parallel with the load, that is, its terminals must be connected respectively to a terminal of the switch from which the load receives its supply and to the return wire to the mains supply.
[0014] For this application, which is not very frequent, modular switches may be provided with an auxiliary terminal which is insulated electrically from the switch contacts and which allows the mechanical fixing of a mains return wire to a lamp terminal and their electrical connection.
[0015] In the case of a two-way switch, the locator lamp must be connected between the two terminals corresponding to the switched terminals.
[0016] These different requirements have up till now prevented the manufacture of a modular device or lamp holder which can be coupled safely, reliably and in only one way to a plurality of different electrical apparata.
[0017] DE-A-1790264 discloses a lamp holder and an electrical switch assembly, according to the preamble of claim 1 and, respectively, claim 4.
[0018] The present invention remedies this problem by providing a lamp holder for electrical switch assemblies which can be connected electrically in the appropriate manner to electrical switch assemblies with different functions, by simple mechanical coupling without the possibility of error and in a very reliable manner.
[0019] The present invention also provides a family of functionally different pieces of electrical equipment which can couple with the lamp holder and are constituted by a plurality of common structural elements, the different functions resulting from very small modifications during assembly which do not affect the mass production of the individual components and their combinations.
[0020] These results are achieved by the provision of a lamp holder in which a generally rectangular-box-shaped insulating block acts as a lamp support and as a housing for rheophores for the electrical connection of the lamp to a plurality of electrical pressure-contacts, preferably three, projecting from a pair of opposite sides of the block which, on tight fitting of the block between two insulating tenons formed by the insulating body of a switch assembly, contact clamping electrical terminals housed in the insulating tenons of the body of the assembly by passing through corresponding slots which are formed in the insulating tenons and extend in the direction of fitting of the block.
[0021] Other characteristics being the same, the selective presence or absence of one of three slots in the tenons of the electrical assembly enables its function as a one or two-way switch to be determined.
[0022] The provision of an electrically insulated terminal in one of the tenons also allows the switch to operate with indication of the closed state of its contacts.
[0023] The characteristics and advantages of the invention will become clearer from the description which follows and from the appended drawings, in which:
Figure 1 is an exploded perspective view of a switch module known in the art which can easily be modified to convert it into a simple switch or a two-way switch in accordance with the present invention;
Figure 2 is an electrical circuit diagram showing the connection of a locator lamp to a switch;
Figure 3 is an electrical circuit diagram showing the connection of a locator lamp to a two-way switch;
Figure 4 is an electrical circuit diagram showing an indicator lamp for indicating the closed state of a switch;
Figure 5 is an exploded perspective view of a preferred embodiment of a lamp holder block for coupling with a switch module in accordance with the present invention and a component element of a switch module modified in accordance with the present invention;
Figure 6 is a perspective view of a component element of a switch module which acts as a simple switch, modified in accordance with the present invention for coupling with a lamp holder for a locator lamp;
Figure 7 is a perspective view of a component element of a switch module, which acts as a two-way switch, modified in accordance with the present invention for coupling with a lamp holder for a locator lamp;
Figure 8 is a perspective view of a component element of a switch module which acts as a simple switch, modified in accordance with the present invention for coupling with a lamp holder for an indicator lamp for indicating the closed state of the switch.
[0024] For a better understanding of the invention, a switch assembly of modular type known in the art is shown in Figure 1.
[0025] The assembly comprises a box-shaped insulating housing formed by two shells 1, 2 moulded from plastics material and joined together by glueing or heat-sealing.
[0026] The shell 1 constitutes a prismatic frame having internal ribs 3 and eyes 4. The eyes 4 support a front rocker key 5 operable by the user and provided with a hollow rod 6 housing and guiding an operating pin 7 which is urged by a compression spring 8 to act on a rocker arm 9 of conductive material.
[0027] The internal ribs 3 form a suitable seat for a transparent plastics block 10 with a high refractive index which acts as a reflector for a light source housed in a cavity 11 in the reflector.
[0029] With reference to the condition of use and installation of the switch assembly, the shell 2 closes the rear end of the frame 1 and consists essentially of a flat element with a pair of hollow box-shaped elements 12, 13 projecting from the rear face of the shell 2.
[0030] The box element 12 is formed with two prismatic housings which are separated and insulated from each other by an insulating partition, not visible, for receiving first and second electrical clamp terminals 14, 15 respectively.
[0032] The structure of each terminal 14, 15, 16 is conventional and, with reference to the terminal 16, includes a fixed metal clamp member 17 formed by bending a flat element into a C-shape or right-angled annulus, and a nut element 18 with a threaded seat housed between the arms 18A, 19 of the fixed clamp member. A hole 20 is formed in the fixed clamp member for the passage of a screw 21 which engages the nut element 18 and acts as a movable clamp member.
[0033] The ends of electrical wires may be inserted through apertures 22, 23 in an end wall of the box element 13 and between the clamp members to be clamped thereby.
[0034] The clamping screw 21 of the terminal 16 is rotated through an aperture 24 formed in one face of the box element 13.
[0035] The structure of the terminals 14, 15 is entirely similar and their clamping screws 25, 26 can be rotated through apertures (not visible in Figure 1) while apertures 27, 28 are provided for the insertion of the wires.
[0036] The structure of the terminals 15, 16, 17 is completed by a conductive wing member which differs according the function to be acchieved.
[0037] In the case of the terminals 15 and 16 which each have the same function of forming a fixed contact of the switch, each fixed clamp member has an extended wing member 29, 30 respectively which supports a contact boss intended to be contacted by a corresponding boss 31, 32 on one of the two ends of the rocker arm 9.
[0038] In the case of the terminal 14, which acts as a sliding contact and support for the rocker arm 9, the fixed clamp member has an extended wing member 33 which terminates in a transverse support blade 34 for sliding contact with the central portion of the rocker arm 9.
[0039] Depending on the position of the operating rocker key 5, the rocker arm 9 slides and pivots on the blade 34 so as to form an electrical connection between the clamp member 14 and the clamp member 15 or between the clamp member 14 and the clamp member 16 in a mutually exclusive manner.
[0040] An aperture 35 in the shell 2 enables a light source to be introduced into the cavity in the reflector 10.
[0041] Conventional hooked teeth formed on two opposite faces of the shell 1, one 36 of which is visible in Figure 1, enable the switch assembly to be snap-engaged with a wall support plate, possibly with several pieces of electrical equipment side by side.
[0042] It is thus clear that the switch assembly described may fulfil the function either of a two-way switch or of a simple switch and may be equipped with a switch locator lamp.
[0043] In practice, if the function of the assembly is that of a simple switch, the terminal 16 is superfluous and, for reasons of economy, is not fitted in the casing of the assembly which is sold as a different product from the two-way switch.
[0044] In both cases this modular structure combined with a locator light source has the disadvantages already mentioned of difficulty of connection, poor reliability and safety and risk of errors being made in the connections.
[0045] It is in fact clear with reference to Figures 2, 3, 4 that the electrical connections which must be formed between the light source and the switch assembly differ according to circumstances.
[0046] In the case of a simple switch (Figure 2) with a locator lamp, the terminal 14 is connected to a mains supply wire (generally the live wire) and the terminal 15 is connected to a terminal of the load L, the second terminal whereof is connected to a second mains supply wire (generally the neutral wire).
[0049] In the case of a two-way switch with a locator lamp (Figure 3), the terminal 14 is connected to a mains supply wire and the terminals 15 and 16 are connected to two switching lines which are connected to a load L through a second two-way switch.
[0051] Finally, in the case of a switch with a closed-state indicator lamp (Figure 4), the switch terminals 14 and 15 must be connected to the mains supply and to the load as in Figure 2, but the lamp must be connected in parallel with the load L, hence by one fixed terminal to the terminal 15 and by its other fixed terminal to an anchoring terminal 37 which is not formed as, and does not form part of, the switch assembly considered in Figure 1.
[0052] Figure 5 shows several simple structural modifications to the switch assembly of Figure 1 which allow it to operate together with a lamp holder, also shown in Figure 5, with the different interconnections required for each type of operation being formed automatically, in a reliable manner, without difficulty or risk of error and with few complications in production.
[0053] Since the sole element of the switch assembly which is modified is the shell 2, only this is shown.
[0054] The two box elements 12, 13 of the shell 2, because of their box-shape, form two tenons between which an insulating block 40 of right angled box-shape can be fitted tightly, the block having a generally L-shaped section in a plane parallel to the closure plate of the shell 2.
[0056] The insulating block 40, which is hollow and has ribs only partially shown, forms a housing for a plurality of electrical conductors or rheophores which are located within the block by the internal ribs.
[0057] The block is closed by a cover 41, preferably on that face of the block 40 which, when the block is engaged between the tenons 12, 13, lies against the closure plate of the shell 2.
[0058] The cover 41 may be fixed to the block 40 by heat sealing or by screws or resiliently-snap-engageable teeth. The cover 41 carries a cylindrical collar 42 which partly houses and locates a small neon bulb 43, the rheophores 44, 45 of which projecting into the block 40.
[0059] The two opposite parallel walls 46, 47 of the block 40 which contact the mutually-facing parallel walls 48, 49 of the tenons 12, 13 have apertures for the passage of three electrical pressure contacts 50, 51, 52 which are conveniently, but not necessarily, formed by the ends of rheophores anchored within the block so as to form resilient, projecting supports for the contacts 50, 51, 52.
[0060] The contacts 50 and 51 are conveniently arranged in the wall 47 so that the fitting of the block between the tenons 12, 13 causes the contacts 50, 51 to be inserted in corresponding slots 53, 54 which are elongate in the direction of fitting of the block and through which the contacts 50 and 51 respectively contact the fixed clamp members of the terminals 15 and 14.
[0061] Similarly, the contact 52 is located in the wall 46 so that the fitting of the block between the tenons 12, 13 causes the contact 52 to be inserted in a slot 55 so that it comes into contact with the fixed clamp member of a terminal housed in the tenon 13.
[0062] The contact 51 is connected by a rheophore to a contact clamp 57 which engages a lamp terminal 44 and, through a rheophore 58, to the contact 52.
[0063] The contact 50 is connected by a rheophore 59 to one terminal of a load limiting and stabilising resistance 60, the other terminal of which is connected through a rheophore 61 to a contact clamp 62 which engages the terminal 45 of the lamp 43.
[0064] It is clear that, instead of a neon lamp which is preferred because of the low power it uses, a photo-emitting diode or other light source may be used.
[0066] The lamp holder described is a universal, optional module which can be fitted to any switch assembly whatever its specific function as a one-way or two-way switch or a switch with a state indicator.
[0067] The switch assembly can be adapted to the various requirements with extremely small changes during production, as illustrated in Figure 6, 7, 8 which show a shell 2 of a switch assembly manufactured specifically to act as a simple switch, a two-way switch and a switch with closed-state indication respectively.
[0068] Since, in a simple switch, any locator light, must be connected (Figure 2) between the terminals 14 and 15, in Figure 6 the tenon 12 is provided with two slots 53, 54 for the connection, between the terminals 14, 15, of the series circuit formed by the contact 50, the rheophore 59, the resistor 60, the rheophore 61, the clamp 62, the lamp 43, the clamp 57, the rheophore 56 and the rod 51 (Figure 5).
[0069] The slot 55 is superfluous and, for reasons of economy and to avoid errors in connection, the tenon 13 preferably does not have a terminal.
[0070] In Figure 7 the shell 2 differs from that of Figure 6 in that it is provided specifically for a two-way electrical switch assembly and must not have the slot 54 but must, necessarily, have the slots 53, 55.
[0071] This is to allow the connection of the light source between the terminals 15 and 16 housed (Figure 5) in the tenons 12, 13 respectively and to prevent the direct, permanent connection which would otherwise be formed between the terminal 14 and the terminal 15 through the contacts 51, 52 and the rheophore 58 of the lamp holder.
[0072] Finally (Figure 8), in the case of the switch with closed-state indication, the shell 2 is identical to that of Figure 7 but the tenon 13 must house an auxiliary terminal, corresponding to the terminal 37 of Figure 4, which is electrically insulated from the switching device.
[0073] In order to ensure the electrical insulation of the terminal from the other conductive parts of the switch assembly, it is convenient to provide an insulating partition 63 separating the terminal housing in the tenon 13 from the housings in the shell 1 (Figure 1).
[0074] The above description relates solely to a preferred embodiment of the invention and it is clear that many variations may be made therein, without departing from the scope defined in the appended claims.
[0075] For example, if commercial reasons suggest that a switch assembly should be marketed which is able to operate either as a simple switch or as a two-way switch, this could be made with a shell 2 as shown in Figure 5, with three access slots 53, 54, 55, while it would be necessary to make the lamp holder especially for the two different applications, in one case by removing the contact 52 and in the other the contact 51 so as to provide two separate products for the market or, just possibly, the task of removing or insulating one of the contacts could be delegated to the installer.
[0076] Alternatively it is possible to provide the lamp holder with a selector which disconnects one or other of the contacts 51 and 52 from the internal rheophores.
[0077] It is, however, clear that these alternative solutions are a more complicated solution to the problems and disadvantages under consideration and, although ensuring greater reliability and simplicity of connection of a locator lamp to a switch assembly, do not intrinsically and entirely ensure against the risk of installation errors.
- a rectangular-box-shaped insulating block (40-42) which can be fitted tightly in a predetermined direction between two insulating tenons (12, 13) formed by a casing (1, 2) of an electrical switch assembly, with two opposite walls (46, 47) of the block (40-42) in contact with a pair of facing walls (48, 49) of the two tenons (12, 13), at least one pair of electrical clamp terminals (14, 15, 16) being housed in the tenons (12, 13);
- the insulating block (40-42) being formed with a light source support (41, 42) and a housing (40) for rheophores (56, 58, 59, 61) for connecting the light source (43) between first (52) and second (50) electrical pressure contacts each exposed on, and projecting from, the block (40-42) on one of the walls (46, 47) of the block (40-42) which is in contact with one of the facing walls (48, 49) of the tenons (12, 13) so as to establish electrical contact with at least the pair of clamp terminals (14, 15, 16) through a plurality of slots (53, 54, 55) formed in the pair of facing walls (48, 49) of the tenons (12, 13), the slots (53, 54, 55) extending in the said predetermined direction, the first contact (52) being exposed on one (46) of the two opposite walls (46, 47) of the block (40-42) and the second contact (50) being exposed on the other (47) of the two opposite walls (46, 47) characterized in that the block includes a third pressure contact (51) electrically connected to the first contact (52) and exposed on, and projecting from, the other (47) of the two opposite walls (46, 47).
- an insulating switch body (1, 2) forming, on its rear wall (2), a housing for a light source (43) and two insulating tenons (12, 13) adapted for housing at least one pair of electrical clamp terminals (14, 15, 16), the tenons (12, 13) being intended for the fitting between them, in a predetermined direction, of an insulating block (40-42) of a lamp holder, with two opposing walls (46, 47) of the said block in contact with a pair of facing walls (48, 49) of the tenons (12, 13), and
- a plurality of slots (53-55) formed in the said pair of walls (48, 49) so as to allow electrical contact between each clamp terminal of at least the said pair of terminals and at least a first (52) and a second (50) pressure contact of the lamp holder block (40-42) respectively, characterized in that one (12) of the tenons (12, 13) is adapted for housing two (14, 15) clamp terminals and the other tenon (13) is adapted for housing one (16) clamp terminal.
- the plurality of slots (53-55) includes a pair of slots (55, 53) each formed respectively in one (48) and the other (49) of the pair of facing walls (48, 49) to allow electrical contact between the first (15) and third (16) clamp terminals and the first (52) and second contacts (50) respectively.
- einem rechteckigen kastenförmigen isolierenden Block (40-42), der in einer vorbestimmten Richtung zwischen zwei isolierende Zapfen (12, 13), die durch eine Umhüllung (1, 2) einer elektrischen Schalteranordnung gebildet sind, eng gepaßt werden kann, wobei zwei gegenüberliegende Wände (46, 47) des Blocks (40-42) in Berührung mit einem Paar von zueinander gerichteten Wänden (48, 49) der zwei Zapfen (12, 13) sind, wobei mindestens ein Paar von elektrischen Klemmanschlüssen (14, 15, 16) in den Zapfen (12, 13) gehäust ist;
- wobei der isolierende Block (40-42) mit einem Lichtquellenträger (41, 42) und einem Gehäuse (40) für Verbindungsdrähte (56, 58, 59, 61) zum Schalten der Lichtquelle (43) zwischen einen ersten (52) und einen zweiten (50) elektrischen Druckkontakt gebildet ist, die jeweils auf dem Block (40-42) auf einer der Wände (46, 47) des Blocks (40-42), die in einer Berührung mit einer der zueinander gerichteten Wände (48, 49) der Zapfen (12, 13) ist, freiliegen und von derselben vorstehen, um einen elektrischen Kontakt mit mindestens dem Paar von Klemmanschlüssen (14, 15, 16) durch eine Mehrzahl von Schlitzen (53, 54, 55), die in dem Paar von zueinander gerichteten Wänden (48, 49) der Zapfen (12, 13) gebildet sind, einzurichten, wobei sich die Schlitze (53, 54, 55) in der vorbestimmten Richtung erstrecken, der erste Kontakt (52) auf einer (46) der zwei gegenüberliegenden Wände (46, 47) des Blocks (40-42) freiliegt, und wobei der zweite Kontakt (50) auf der anderen (47) der zwei gegenüberliegenden Wände (46, 47) freiliegt, dadurch gekennzeichnet, daß der Block einen dritten Druckkontakt (51) aufweist, der mit dem ersten Kontakt (52) elektrisch verbunden ist, und auf der anderen (47) der zwei gegenüberliegenden Wände (46, 47) freiliegt und von derselben vorsteht.
- einem isolierenden Schalterkörper (1, 2), wobei auf der Rückseitenwand (2) desselben ein Gehäuse für eine Lichtquelle (43) und zwei isolierende Zapfen (12, 13), die angepaßt sind, um mindestens ein Paar von elektrischen Klemmanschlüssen (14, 15, 16) zu häusen, gebildet sind, wobei die Zapfen (12, 13) für das Passen eines isolierenden Blocks (40-42) eines Lampenhalters zwischen denselben in einer vorbestimmten Richtung vorgesehen sind, wobei die zwei gegenüberliegenden Wände (46, 47) des Blocks in Berührung mit einem Paar von zueinander gerichteten Wänden (48, 49) der Zapfen (12, 13) sind, und
- einer Mehrzahl von Schlitzen (53-55), die in dem Paar von Wänden (48, 49) gebildet sind, um einen elektrischen Kontakt zwischen jedem Klemmanschluß von mindestens dem Paar von Anschlüssen und von jeweils mindestens einem ersten (52) und einem zweiten (50) Druckkontakt des Lampenhalterblocks (40-42) zu ermöglichen, dadurch gekennzeichnet, daß einer (12) der Zapfen (12, 13) angepaßt ist, um zwei (14, 15) Klemmanschlüsse zu häusen, und der andere Zapfen (13) angepaßt ist, um einen (16) Klemmanschluß zu häusen.
- die Mehrzahl der Schlitze (53-55) ein Paar von Schlitzen (55, 53) aufweist, die jeweils in der einen (48) und der anderen (49) des Paars von zueinander gerichteten Wänden (48, 49) gebildet sind, um einen elektrischen Kontakt zwischen dem ersten (15) und dem dritten (16) Klemmanschluß und jeweils dem ersten (52) und dem zweiten Kontakt (50) zu ermöglichen.
un bloc isolant (40-42) ayant une forme de boîte rectangulaire et qui peut être monté de façon ajustée en direction prédéterminée entre deux tenons isolants (12, 13) formés par un carter (1, 2) d'un ensemble à commutateur électrique, deux parois opposées (46, 47) du bloc (40-42) étant au contact de deux parois opposées (48, 49) des deux tenons (12, 13), une paire au moins de bornes électriques (14, 15, 16) de serrage étant montée dans les tenons (12, 13),
le bloc isolant (40-42) comportant un support (41, 42) de source lumineuse et un boîtier (40) destiné à des conducteurs (56, 58, 59, 61) destinés à raccorder la source lumineuse (43) entre un premier (52) et un second (50) contact électrique sous pression qui sont exposés chacun sur le bloc (40-42) et en dépassent sur l'une des parois (46, 47) du bloc (40-42) qui est au contact de l'une des parois opposées (48, 49) des tenons (12, 13), afin qu'un contact électrique soit établi avec au moins la paire de bornes (14, 15, 16) de serrage par plusieurs fentes (53, 54, 55) formées dans les deux parois opposées (48, 49) des tenons (12, 13), les fentes (53, 54, 55) s'étendant dans la direction prédéterminée,
le premier contact (52) étant exposé à l'une (46) des deux parois opposées (46, 47) du bloc (40-42) et le second contact (50) étant exposé à l'autre (47) des deux parois opposées (46, 47), caractérisé en ce que le bloc comporte un troisième contact (51) à pression, connecté électriquement au premier contact (52) et exposé à l'autre (47) des deux parois opposées (46, 47) dont il dépasse.
un corps isolant (1, 2) de commutateur formant, à sa paroi arrière (2), un boîtier destiné à une source lumineuse (43) et deux tenons isolants (12, 13) destinés à loger au moins une paire de bornes électriques de serrage (14, 15, 16), les tenons (12, 13) étant destinés à loger entre eux, en direction prédéterminée, un bloc isolant (40-42) d'un support de lampe, deux parois opposées (46, 47) du bloc étant au contact d'une paire de parois opposées (48, 49) des tenons (12, 13),
plusieurs fentes (53-55) formées dans les deux parois (48, 49) afin qu'elles permettent un contact électrique entre chaque borne de serrage de la paire au moins de bornes et au moins un premier (52) et un second (50) contact à pression du bloc (40-42) du support de lampe respectivement, caractérisé en ce que l'un (12) des tenons (12, 13) est réalisé afin qu'il loge deux bornes de serrage (14, 15) et l'autre tenon (13) est destiné à loger une borne de serrage (16).
les fentes (53-55) comportent deux fentes (55, 53) formées chacune respectivement dans l'une (48) et l'autre (49) des deux parois opposées (48, 49) pour permettre un contact électrique entre les première (15) et troisième (16) bornes de serrage et les premier (52) et second (50) contacts respectivement.