The present invention relates to a power cord clamp for lamp holders with a support formed by a tube or stem, featuring very easy assembly.
Conventional lamp holders with a support formed by a tube or stem are generally constituted by a body made of electrically insulating material, wherein there is provided a seat for the lamp and wherein the electrical connection terminals for the electric power supply cord of the lamp holder are arranged. The support of these lamp holders is provided by means of an externally threaded tube which is connected, by using its external thread, to a threaded hole formed in the lamp holder, generally in the portion of the lamp holder known as dome and located opposite with respect to the region wherein the lamp seat is formed.
The electric power cord enters the lamp holder through the supporting tube or stem, which can be metallic or made of synthetic material.
These lamp holders use power cord clamps, i.e., devices having the purpose of avoiding the sliding of the power cord with respect to the lamp holder, in order to prevent any traction stresses on the cord from being transmitted to the electrical terminals, causing the separation of the power cord and therefore constituting a potential source of accidents.
Power cord clamps currently used for these lamp holders are generally substantially disk-shaped and are meant to be accommodated completely inside the lamp holder. The disk-like body of these power cord clamps is centrally provided with a passage for the power cord which is delimited by two opposite wings which allow the cord to pass only in one direction, jamming against the lateral surface of the power cord when a force is applied to said cord in the opposite direction, stopping it.
Power cord clamps currently used in lamp holders with a support constituted by a tube or stem entail the drawback that the clamping of the power cord which they achieve is not always entirely satisfactory.
These power cord clamps also have a considerable bulk inside the dome of the lamp holder and often require the production of special lamp holders.
Another drawback which can be observed in the use of these power cord clamps resides in the difficulties in assembly which are encountered in correctly accommodating the power cord clamp inside the lamp holder dome.
Moreover, these lamp holders, if they use a supporting tube or stem made of metallic material, entail the drawback of requiring the use of an insulating bushing to be fitted on the end of the tube inside the lamp holder, in order to prevent damage to the power cord as a consequence of movements of said cord with respect to the tube which might cause the electrical connection of the tube to the electrical power supply wires of the lamp holder.
Examples of lamp holders and related power cord clamps, could be found in the following documents: FR-A-2509514, US-A-4386817 and US-A-5276280. DE 295 16 288 U discloses a lamp holder and related power cord clamp of the same kind of the one set forth in the preamble of claim 1.
A principal aim of the present invention is to obviate the above-described drawbacks by providing a power cord clamp for lamp holders with a support formed by a tube or stem which is highly reliable as regards the locking of the power cord.
Within the scope of this aim, an object of the present invention is to provide a power cord clamp which can be very simply and rapidly assembled to the lamp holder.
Another object of the present invention is to provide a power cord clamp which avoids the need to use insulating bushing even in the case of lamp holders having a metal tube.
A further object of the present invention is to provide a power cord clamp having a reduced bulk and competitive production costs.
This aim, these objects, and others which will become apparent hereinafter are achieved by a power cord clamp for lamp holders with a support formed by a tube or stem, comprising a body having at least one elongated region which can be inserted in the end of the tube or stem which is connected to the lamp holder, said elongated region being crossed longitudinally by a passage for the electric power supply cord of the lamp holder, said body having, in the region crossed by said passage, at least one portion which can flex towards or away from the longitudinal axis of said passage, said flexible portion being provided, on its side directed towards said passage, with power cord clamping means which can engage the cord as a consequence of the flexing of said portion towards the axis of said passage caused by the engagement of the outer surface of the flexible portion against the inner surface of the tube or stem when said elongated region is inserted in said tube or stem, characterized in that said elongated region has no lateral openings, the flexibility of said portion being increased by a reduction in the thickness of said body in the region crossed by said passage proximate to said flexible portion.
Further characteristics and advantages of the present invention will become apparent from the description of the preferred but not exclusive embodiment of the power cord clamp according to the invention, illustrated only by way of non-limitative example in the accompanying drawings, wherein:
With reference to the above figures, the power cord clamp according to the invention comprises a body, generally designated by the reference numeral 1, which is preferably made of molded synthetic material and has an elongated and preferably substantially cylindrical region 2 which is crossed coaxially by a passage 3 for the electric power cord 4 of a lamp holder, generally designated by the reference numeral 5, of the type with a support provided by a tube 6 or stem.
The region 2 has at least one lateral portion, preferably two lateral portions 7a and 7b, which are formed in two diametrically opposite regions of the skirt of the region 2 and can flex towards or away from the axis of the passage 3.
Each one of the portions 7a and 7b is provided, on its face directed towards the passage 3, with cord clamping means which can engage the cable 4 as a consequence of the flexing of the corresponding portion 7a, 7b towards the axis of the passage 3.
The cord clamping means comprise at least one tooth 8a, 8b, which protrudes from the face of the corresponding portion 7a, 7b directed towards the longitudinal axis of the passage 3. In the embodiment, shown in figures 1 to 5, the tooth 8a of the portion 7a faces the tooth 8b of the portion 7b.
The portions 7a, 7b have, on their outward face, at least one raised portion 9a, 9b which can engage the inner surface of the tube 6 when the region 2 is inserted in the tube 6 to cause the flexing of the portions 7a, 7b towards the axis of the passage 3 and therefore cause the engagement of the teeth 8a, 8b with the cord 4.
The raised portions 9a, 9b protrude so as to form a conical surface the apex whereof is directed towards the end of the body 1 which is meant to be inserted in the tube 6, so that the flexing of the portions 7a and 7b towards the axis of the passage 3 is gradual during the insertion of the region 2 in the tube 6.
Advantageously, the flexible portions 7a, 7b have a thickness gradually increasing starting from their end which is directed towards the end of said body 1 meant to be inserted in the tube 6. In practice, the region 2 has a substantially cylindrical shape, except for the raised portions 9a and 9b, and has no lateral openings, so as to ensure an excellent insulation degree of the cord 4 inserted through the passage 3. The flexibility of the portions 7a, 7b is enhanced through a reduction in the thickness of the walls of the body 1 that delimit the passage 3 proximate to the portions 7a, 7b.
The outside diameter of the region 2, except for the portions 7a, 7b, is such as to allow an insertion of the region 2 with a slight play inside the tube 6.
The body 1 has, at the axial end of the region 2 which lies opposite to the end that can be inserted in the tube 6, two resting tabs 10a and 10b, protruding laterally on opposite sides at right angles to the axis of the passage 3.
The tabs 10a and 10b are also provided, on their side lying opposite with respect to the region 2, with feet 11 which can be engaged inside the lamp holder 5.
Conveniently, if particular insulation is required for the electric power cord 4 of the lamp holder, the body 1 of the power cord clamp can have, at the axial end of the region 2 which is opposite with respect to the end that can be inserted in the tube 6, two protective wings 20a and 20b, which protrude between the resting tabs 10a and 10b, also preferably along opposite directions which are substantially perpendicular to the axis of the region 2. Said wings 20a and 20b, the shape whereof can vary according to requirements, have the purpose of further increasing the safety of the electrical insulation of the power cord 4 from any metallic part inside the dome of the lamp holder, allowing to classify the lamp holder in a higher insulation class.
The lamp holder 5 is preferably constituted by a dome 12 provided at its top, in a per se known manner, with a threaded hole 13 meant to couple to the tube 6.
The dome 12 also has a pair of flexible wings 14a and 14b which can engage in a snap-together fashion locators 15a and 15b formed correspondingly in the lamp holder body 16.
The seat 17 for the lamp is formed in the lamp holder body 16, which also accommodates the terminals for electrical connection to the cord 4, which are not illustrated for the sake of simplicity.
Seats 18 are formed in the lamp holder body 16, in the region thereof facing the tube 6, and are meant to couple to the feet 11 of the resting tabs 10a and 10b of the body 1 of the power cord clamp.
The lamp holder is assembled to the power cord clamp according to the invention as follows.
First of all, the electric power supply cord 4 is inserted through the tube 6 and through the passage 3 formed in the power cord clamp according to the invention, and the electrical conductors are connected to the terminals located inside the lamp holder body.
After connecting the electrical conductors, the power cord clamp according to the invention is slid along the power cord 4 and moved against the body 16 of the lamp holder until its feet 11 engage in the seats 18 specifically provided in the lamp holder body.
Assembly is completed by sliding the dome 12 of the lamp holder, together with the tube 6, along the cord 4 until the wings 14a and 14b engage, in a snap-together fashion, the locators 15a and 15b.
It should be noted that this final operation also achieves the insertion of the region 2 of the power cord clamp according to the invention inside the tube 6. As a consequence of the insertion of the region 2 inside the tube 6, the portions 7a and 7b engage the inner surface of the tube 6, flexing towards the axis of the passage 3 and therefore engaging the cord 4 and blocking it.
It should be noted that the locking of the power cord 4 by means of the power cord clamp according to the invention is achieved automatically when the dome 12 is assembled to the body 16 of the lamp holder 5.
In practice it has been observed that the power cord clamp according to the invention fully achieves the intended aim and objects, since it significantly simplifies the operations for the assembly of the lamp holder and ensures considerable strength of the clamping of the electric cord.
Another advantage of the power cord clamp according to the invention is that it avoids contact of the power cord with the end of the tube which is connected to the dome of the lamp holder, assuredly eliminating any possibility of damage to the power cord, even if the tube is made of metallic material, without requiring the use of electrically insulating bushings.
In practice, the materials employed, as well as the dimensions, may be any according to requirements and to the state of the art.
Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.