GB2314210A

GB2314210A - A flameproof enclosure for electrical switchgear

Info

Publication number: GB2314210A
Application number: GB9711937A
Authority: GB
Inventors: Guy Kevassay
Original assignee: Legrand SA; Legrand SNC
Current assignee: Legrand SA; Legrand SNC
Priority date: 1996-06-11
Filing date: 1997-06-09
Publication date: 1997-12-17
Anticipated expiration: 2017-06-09
Also published as: DE19724652A1; GB2314210B; FR2749734B1; FR2749734A1; GB9711937D0

Description

2314210 A FLAMEPROOF ENCLOSURE FOR ELECTRICAL SWITC11GEAR The invention

relates to flameproof enclosures for electrical switcligear.

Particularly, the invention is concerned with enclosures which are intended to receive any kind of junction, operating, instrumentation or other electrical switcligear, particularly electrical switcligear capable of causing sparks or overheating, such as switches or relays, said covering having to be flameproof and therefore mechanically resistant to the excessive pressure of a blast inside the enclosures without causing it to spread into the outside atmosphere which may be explosive.

Enclosures of this kind are known; they usually comprise a housing of the parallelepipedic kind, which, on one of the faces thereof, usually the front face, has an opening which is closed by a cover. In order to provide flameproof closure of the opening by way of the cover, closure is performed by screwing the cover into the opening, these two members therefore being circular in shape and provided with complementary screwthreads. It will readily be appreciated that it is the quality of said screwthreads which conditions the resistance of the enclosures to blasts; not only do these screwthreads have to be of sufficient length, but the gap between the flanks of the external screwthread of the cover and those of the internal screwthread of the opening of the housing of the covering must be small, and the same all along said length, this gap also having to permit the gradual reduction in pressure of pressurised gases contained inside the enclosure which have been caused during an internal explosion.

The housing and its cover can be made of sheet steel, or of an alloy of bronze, cast iron, aluminium casting, or other, and be large in size. To facilitate handling of the cover, which can be heavy, and particularly to avoid it being dropped after being unscrewed which would certainly result in damage to its external screwthread, a proposal has already been made to support the cover in relation to the housing by means of support means, which, whilst being pivotally connected to the housing, are connected to the cover in such a way that it can be rotated in order to open and close the housing.

Hitherto, these means have been most frequently made in the form of an arm, one end of which is pivotally mounted to the housing by means of a hinge type 2 connection and the other end of which is also pivotally attached to a pivot which pivotally receives the cover in the centre thereof. Such an arrangement is illustrated schematically in Figure 8 of the accompanying drawings and has drawbacks: firstly, when the enclosure is open, since the hinge is inevitably placed inside the housing, the opening is not completely freed, and, secondly, the outer screwthread of the cover is not protected, said screwthread thus being able to be knocked by the housing when the cover is being handled during closure of the housing; moreover, the central pivot of the cover prevents an inspection window from being fitted; to avoid this, and, more particularly, to free the central region of the cover, a proposal has already been made to make the cover integral with the arm by means of a ring which is located inside the cover and provided in the form of a cup member, the cylindrical skirt of which externally bears the outer screwthread, the cover being rotatably mounted in relation to the ring; however, the space requirement of this arrangement limits the inner useful volume of the enclosure, or, if the useful volume is well-proportioned, results in a covering of large dimensions.

According to the invention, there is provided a flameproof enclosure for electrical switcligear, comprising a housing, which, in one of the faces thereof, has an opening which is closed by a cover, the opening and the cover being of circular shape and provided with complementary screwthreads comprising an internal screwthread in the opening and an external screwthread on the cover to permit closing of the opening by screwing in the cover and support means to support the cover in relation to the housing, wherein the support means comprises a plate disposed transversely to and surrounding the cover so as to permit rotation of the cover therein and the plate is connected to the housing by a hinge joint disposed outside the housing.

Locating the hinge joint outside the housing is advantageous in that it can allow complete access to the inside of the enclosure.

Preferably, the external screwthread of the cover is extended along a groove which is delimited by a flange, which, when the cover is closed, is k of abutting on the plate which itself abuts on said one of the faces of the inm-Ig-i-n line with which the opening is disposed, the cover being engaged ire bore in the 3 internally screwthreaded plate, the screwthread of the bore and the external screwthread of the cover being complementary, the base diameter of the groove being slightly less than the minimum diameter of the screwthread of the bore, and the flange being of greater diameter than said diameter.

Advantageously, the internal screwthread of the opening is arranged inside the housing, being slightly offset from said one of the faces in line with which the opening is disposed.

Preferably, said one of the faces which has the opening is rectangular and the plate is also rectangular.

Advantageously, the plate is capable of completely covering said one of the faces in line with which the opening is disposed.

Preferably, the circular cover is constituted by a ring and by a closure plate, the ring bearing on its outer periphery the external screwthread and on its inner periphery an internal screwthread, the pitch of which is the same as that of the external screwthread, said internal screwthread cooperating with an external screwthread provided on the periphery of the closure plate and immobilising means preventing rotation of the closure plate in relation to the housing when the ring of the cover is being rotated during closing and opening operations. According to one variant, the immobilising means are constituted by a fmger which is provided on one of the closure plate and the housing, said finger being capable of cooperating with two abutments provided on the other of the closure plate and the housing.

By virtue of this arrangement, the closure plate can carry at least one item of electrical switcligear passing through it.

Advantageously, the plate bears a cylindrical collar which surrounds the external screwthread of the cover, being at a slight distance radially from said external screwthread. The axial length of the collar is at least equal to that of the external screwthread of the cover.

Preferably, elastic elements are disposed functionally between the plate and the cover in order to axially take up the play which is caused by the groove of the cover.

4 The invention is diagrammatically illustrated, by way of example, in the accompanying drawings, wherein:

Figure 1 shows schematically, in perspective, an enclosure according to the invention; Figures 2 and 3 are partial front views of the enclosure of Figure 1, shown in closed and opened positions respectively; Figure 4 is a partial section through the enclosure of Figure 1, shown in the open condition; Figure 5 is a partial section, similar to that of Figure 4, of the enclosure of Figure 1, shown with the cover thereof in the position which it adopts just prior to being closed by screwing; Figure 6 is a partial section, similar to that of Figure 4, of the enclosure of Figure 1, shown in the closed condition; Figures 7 to 9 are similar to Figures 4 to 6, and show a variant of the enclosure according to the invention; Figure 10 is a partial side view, in the direction of the arrow X in Figure 9, showing immobilising means of the variant of Figures 7 to 9; Figures 11 to 13 are similar to Figures 4 to 6, and show another variant of the enclosure according to the invention; Figures 14 and 15 are similar to Figures 11 and 13 and show yet another variant of the enclosure according to the invention; Figure 16 is a sectional view along the line XVI-XVI of Figure 17; Figure 17 is a partial view, on a larger scale, in the direction of the arrow XVII of Figure 14; and Figure 18 shows schematically in perspective an enclosure of the prior art.

With reference to Figures 1 to 6, a flameproof enclosure 10 for electrical switchgear comprises a housing 11, of substantially parallelepipedic shape here, provided with vanes 16 which have holes 17 for fixture, e.g. by means of screws, to a wall which is vertical, in particular, and one face of which, the front face 22 here, has an opening 13 capable of being closed by a cover 12. To that end, the opening 13 is circular and provided with an internal screwthread 14. The cover 12, also circular, is provided with an external screwthread 15. The internal 14 and external screwthreads are complementary and the opening 13 can thus be closed by screwing in the cover 12 which can have lugs 18 to facilitate handling thereof.

Support means to support the cover 12 in relation to the housing 11 are here constituted, according to the invention, by a plate 30 which surrounds the cover 12.

To be more exact, the plate 30 is pivotally mounted by hinges to the housing 11, here by virtue of upper 34 and lower 35 ledges provided on the housing 11 in projecting relationship on the front face 22 thereof, the ledges 34 and 35 constituting fixed mountings. The plate 30 is equipped with movable mountings 40, the ledge 34 and the upper movable mounting 40, on the one hand, and the ledge 35 and the lower movable mounting 40, on the other hand, receiving a spindle 31, as can be seen in Figures 2 and 3.

The cover 12 is fitted in a bore 33, provided in the plate 30 through which it passes; the bore 33 being threaded internally at 32, its screwthread 32 and the external screwthread 15 of the cover 12 being complementary.

In the example shown, the cover 12 is in the form of a cup member with a bottom 23 and a cylindrical skirt 21, the outer periphery of which bears the external screwthread 15 which is extended along a groove 20 towards the bottom 23 around which a flange 19 is provided which axially delimits the groove 20. The base groove diameter of the groove 20 is slightly less than the minimum diameter, that is to say measured at the top of the threads, of the screwthread 32 of the bore 33 of the plate 30, and the flange 19 of the cover 12 has a diameter which is greater than said mininium diameter. By virtue of these arrangements, the cover 12 is carried by the plate 30 in the manner of a captive screw. To this end, the cover 12 is screwed completely into the bore 33 until the external screwthread 15 thereof passes beyond the screwthread 32 of the bore 33 and slips away therefrom. The plate 30 then extends transversely in line with the groove 20 of the cover 12, and the cover 12 is free to move in relation to the plate 30 rotatably and axially within the limits defined by the length of the groove 20. This length is such that when the cover 12 is in the closed position, as shown in Figure 6, the flange 19 abuts the plate 30 which itself abuts the front face 22 of the housing 11, the internal screwthread 14 of the opening 6 13 and the external screwthread 15 of the cover 12 being completely engaged; on another side, when the plate 30 is against the front face 22 of the housing 11. With the cover 12 unscrewed, as shown in Figure 5, the screwthreads 14, 15 and 32 of the opening 13 of the housing 11, the cover 12 and the plate 30 respectively are just ad. acent to each other, the internal screwthread 14 of the opening 13 being provided J inside the housing 11, being in offset relationship to the front face 22 of the housing 11 in line with which the opening 13 is disposed.

In the example shown, the enclosure 10 is parallelepipedic and the plate 30 is rectangular, being adapted to cover over the front face 22 by being inserted between the ledges 34 and 35.

The operations for opening and closing the enclosure 10 are carried out in the following way. Starting with the closed position shown in Figure 6, in order to open the enclosure 10 it is simply necessary to unscrew the cover 12, making use, if necessary, of the handling lugs 18. When the external screwthread of the cover 12 has been disengaged from the internal screwthread 14 of the housing 11, the plate 30 is disposed at a distance from the housing 11. Catches 36, 37 for gripping are provided at the edge of the plate 30 on the side opposite that by means of which it is pivotally connected to the housing 11. The plate 30 thus pivots about the axis formed by the spindles 3 1, as shown in Figures 1 and 4 in which the enclosure 10 is partly open, Figure 4, then wide open, Figure 1. In the open positions, the cover 12 retains its position in relation to the plate 30, firstly because of its weight and secondly because it is the plate 30 which is handled during these operations. Then, on being closed, the cover 12 adopts the position of Figure 5, and is quite naturally ready to be screwed on without any trial and error, the screwthreads 14 and 15 therefore being unable to be damaged. The small space requirement of the closure device in the closed position will be appreciated; in the open position, the opening 13 of the housing 11 is completely freed.

According to one variant, not shown, the bottom 23 of the cover 12 is equipped with an inspection window; as will readily be appreciated, this can easily be provided so that it has a large diameter, if so desired.

7 Figures 7 to 10 show another variant of enclosure 110 according to the invention; in these drawings, the enclosure 110 comprises a housing 11 and a plate which are identical to the housing and to the plate of the enclosure 10 described hereinabove. Here, the circular cover 112 is constituted by a ring 101 and a closure plate 25.

The ring 10 1 bears on the outer periphery thereof an external screwthread 115 and on the inner periphery thereof an internal screwthread 123 of the same pitch as the outer screwthread 115.

The closure plate 25 is provided with an external screwthread 24 at the periphery thereof which has the same features as the screwthread 123 in such a way that the closure plate 25 can be introduced into the ring 101 by screwing.

Immobilising means are provided to prevent the closure plate 25 from turning in relation to the housing 11 when the cover 112 is being rotated during opening and closing operations. According to the example shown, these immobilising means are constituted firstly by a fmger 26 provided on the closure plate 25 and extending parallel to the axis thereof, and secondly by two abutments 27 and 28 provided on the housing 11 and extending transversely thereto. These immobilising means are arranged in such a way that when the plate 30 is in abutting relationship on the housing 11, the ring 10 1 of the cover 112 being ready to be screwed into the internal screwthread 14 of the housing 11, i.e. the position shown in Figure 8, the end of the fmger 26 is accommodated between the two abutments 27 and 28, as shown in Figure 10. By virtue of this arrangement, when the ring 101 of the cover 112 is turned for opening or closing purposes, the closure plate 25 does not itself turn, the ring 101 being screwed or unscrewed into or out of the inner screwthread 14 and about the outer screwthread 24 of the closure plate 25.

Advantageously, as described hereinabove, the external screwthread 115 and the internal screwthread 123 of the cover 112 have the same characteristics, in particular the same pitch: thus, not only does the closure plate 25 not turn, but it also remains immobilised axially when the ring 101 is turned.

The closure plate 25 can thus receive electrical switcligear passing through it and accessible from the outside, such as switcligear 29 connected electrically by 8 means of electrical conductors, not shown, to the inside of the enclosure, said electrical conductors not running the risk of being damaged when the cover 112 is rotated. The electrical switcligear may be in the form of switches, operating members, indicators, monitors, or the like.

Here, the position selected by the closure plate 25 is such that it extends in line with, that is to say in the plane of, the plate 30. In order that this position is retained and not altered inadvertently, when the cover 112 is in the wide open position, means can be provided to rotationally immobilise the closure plate 25 in relation to the housing 11 in this position. Here, these means are in the form of a chain 3 8 which is fixed on one side to the housing 11, inside the housing 11, and, on the other side, to the end of the finger 26 carried by the closure plate 25.

In the embodiment of Figures 11 to 13, a plate 130 having a collar 131 is shown with a cover 12. Such a plate with a collar could also support a cover, like the cover 112, in the form of a ring 101 and mounting a closure plate 25.

If desired, it is possible to provide elastic members functionally between the plate and the cover in order to be sure that the play caused by the groove of the cover is taken up axially so that on closure the cover is in the proper position by virtue of its design, before being screwed on, so that in instances when a collar is provided, the collar of the plate is able to fit the outer screwthread of the cover properly when this latter is open.

Figures 14 to 17 show a variant in which elastic means of this kind are provided.

In these drawings, a plate 230 which bears the cover 12 is provided with a collar 231 in which an axially extending notch 232 is provided which opens into a cylindrical passage 234 which also extends axially and which passes across the plate 230. A guide rod 233 extends in the notch 232 and the passage 234, to which guide rod a helical spring 140 is fitted with play. The other end of the spring 140 extends in a hollow cylindrical base plate 141 which is slidingly mounted in the passage 234 and the closed end of which, advantageously of spherical shape, bears upon the transverse face opposite the flange 19 of the cover 12. In this way, the helical spring holds the cover 12 so that it is distanced from the plate 230, bearing upon each of 9 those elements by way of the base of the notch 232, on the one hand, and by the flange 19, on the other hand.

Of course, an arrangement of this kind can be applied to a cover made up of a ring and a closure plate.

Claims

1. A flameproof enclosure for electrical switchgear, comprising a housing, which, in one of the faces thereof, has an opening which is closed by a cover, the opening and the cover being of circular shape and provided with complementary screwthreads comprising an internal screwthread in the opening and an external screwthread on the cover to permit closing of the opening by screwing in the cover and support means to support the cover in relation to the housing, wherein the support means comprises a plate disposed transversely to and surrounding the cover so as to permit rotation of the cover therein and the plate is connected to the housing by a hinge joint disposed outside the housing.

2. A flameproof enclosure according to Claim 1, wherein the external screwthread of the cover is extended along a groove which is delimited by a transverse flange, which, when the cover is closed, can abut on the plate which itself abuts on said one of the faces of the housing in line with which the opening is disposed, the cover being engaged in a bore provided in the internally screwthreaded plate, the screwthread of the bore and the outer screwthread of the cover being complementary, the base diameter of the groove being slightly less than the minimum diameter of the screwthread of the bore, and the flange being of greater diameter than said diameter.

3. A flameproof enclosure according to Claim 1 or Claim 2, wherein the internal screwthread of the opening in the housing is slightly offset from said one of the faces in line with which the opening is disposed.

4. A flameproof enclosure according to any one of Claims 1 to 3, wherein said one of the faces in line with which the opening is disposed is rectangular, and the plate is also rectangular in shape.

5. A flameproof enclosure according to any one of Claims 1 to 4, wherein the plate is capable of completely covering said one of the faces in line with which the opening is disposed.

6. A flameproof enclosure according to any one of Claims 1 to 5, wherein the circular cover is constituted by a ring and by a closure plate, the ring bearing on its outer periphery the external screwthread and on its inner periphery an internal screwthread, the pitch of which is the same as that of the external screwthread, said internal screwthread cooperating with an external screwthread provided on the periphery of the closure plate and immobilising means preventing rotation of the closure plate in relation to the housing when the ring of the cover is rotated during closing and opening operations.

7. A flameproof enclosure according to Claim 6, wherein the immobilising means are constituted by a finger which is provided on one of the closure plate and the housing, said finger being capable of cooperating with two abutments provided on the other of the closure plate and the housing.

8. A flameproof enclosure according to Claim 6 or Claim 7, wherein the closure plate has at least one item of electrical switcligear passing through it.

9. A flameproof enclosure according to any one of Claims 1 to 8, wherein the plate bears a cylindrical collar which surrounds the external screwthread of the cover and is located at a slight distance radially from the external screwthread.

10. A flameproof enclosure according to Claim 9, wherein the axial length of the collar is at least equal to that of the external screwthread of the cover.

11. A flameproof enclosure according to any one of Claims 1 to 10, wherein elastic elements are disposed functionally between the plate and the cover in order to axially take up the play which is caused by the groove of the cover.

12

12. A flameproof enclosure for electrical switchgear substantially as hereinbefore described and illustrated with reference to Figures 1 to 17 of the accompanying drawings.