GB2044877A

GB2044877A - Retaining and safety cap for electrical terminal screws

Info

Publication number: GB2044877A
Application number: GB8007795A
Authority: GB
Original assignee: BBC Brown Boveri France SA
Current assignee: BBC Brown Boveri France SA
Priority date: 1979-03-09
Filing date: 1980-03-07
Publication date: 1980-10-22
Also published as: FR2451151A1; DE2909202C2; CH651718A5; DE2909202A1; FR2451151B1; GB2044877B

Abstract

A cover and safety cap for terminal screws is disclosed to protect against accidental contact with terminal screws (13, 14) and to inhibit these screws from falling out in transit if they are not fully screwed home. Each cover (15, 16) includes a radially resilient ring attachment (33) the inner diameter of which is smaller than the outer diameter of the screws (13). <IMAGE>

Description

SPECIFICATION Cover and safety cap for terminal screws on electrical devices The invention relates to a cover and safety cap for terminal screws on electrical devices, in particular on switching devices such as contactors, circuit breakers and the like, and comprising openings coaxial to the terminal screws to be covered, and ring attachments bounding these openings, and with locking means for snapping the cover and safety cap on to the electrical device.

Such cover and safety caps simultaneously serve various purposes, namely they prevent or at least make more difficult any unintentional contact with the electricity-carrying terminal screws and the bared cable ends connected thereto, and in addition they can also serve for preventing loose screws from falling out, for example during transport, or screws which have loosened due to operational vibration from falling out and producing damage in the form of a short circuit or the like, apart from the loss of the terminal screw itself, and finally such caps serve, when provided with openings coaxial to the terminal screws to be covered, for guiding a screwdriver when connecting the associated wires. This latter is of particular importance when using motordriven screwdrivers.

Preventing screws from falling out is particularly important here, because within the framework of the known rationalisation attempts by the manufacturers of electrical devices there has been an increasing changeover to screwing those terminal screws which have to be connected to wires on site only a few thread pitches deep into their female threaded socket, so that the erection personnel does not need to unscrew the terminal screws on site before inserting the end of a wire. However, for the manufacturer of the electrical device it is still necessary, as previously, to screw the said terminal screws a few thread pitches deep into the associated female screwed socket. This must either be done manually or special screws be used which enable each individual screw to be mechanically inserted into the threaded socket.Such special screws comprise at their screw end either a pin-type guide portion, the outer diamter of which must be smaller than the diameter of the thread core, or they comprise at their screw end a conical region, i.e. a type of point or a similar arrangement, which however leads to a lengthening of the total screw length and requires the use of a special screw.

Alternatively, funnel-shaped countersunk portions in the threaded sockets are possible, but this affects the material thickness of this portion, as the threaded sockets have to be machined.

In spite of the latter arrangements, there is the danger in the case of completely mechanical, i.e. fully automatic assembly of terminal screws, that some screws become tilted and lead to thread damage both on the terminal screw and in the threaded socket. Such mistakes either increase the reject level or lead to undesirable delays on the site of assembly of the corresponding electrical device. It is also possible that due to vibration during transport, some of the terminal screws become screwed down into the female screwed socket, so that when connecting the wire on the assembly site, either these screws must previously be unscrewed, or the end of the wire to be connected becomes improperly inserted.

The object of the present invention is to eliminate or at least reduce the aforesaid drawbacks, and in particular to take measures which allow the use of normal screws without angular faces or pin-type screw ends, or female threaded sockets without lead-in or countersunk portions even for mechanical fully or partly automatic factory assembly.

This object is attained according to the invention in that the ring attachments whicbh extend from a leg of the cap which is substantially L-shaped or U-shaped in cross-section are at least slightly resilient in a radial direction, and when in their unstressed state they are sightly smaller in their inner diameter than the outer diameter of the heads of the terminal screws.

By this means, instead of screwing the terminal screws into their female threaded sockets, they can be inserted by their screw heads into the ring attachments on the cover and safety caps, to which they then remain adhering by virtue of the said resilient effect, the caps fitted out in this manner then being assembled on the electrical device. The terminal screws remain in this position, in which they are not screwed in, until the connection of the wire ends. It should be noted here that no particular lead-in aids are required for screwing in the terminal screws on the assembly site, even when they are screwed in by motor-driven screwdrivers.According to the invention, it is possible without difficulty to unconsciously insert the screw correctly into the associated female threaded socket by small swivel movements of the manual or motor-driven screwdriver, even after a short period of training, in contrast to fully automatic assembly devices in factory assembly. A further advantage is that the screws held in the ring attachments and which become loosened by vibration during transport or the like cannot automatically become screwed into the female thread, and certainly not to a deeper extent than desired.

In a desirable embodiment of the invention in the case of a cap which is substantially Ushaped in cross-section, the said ring attachments extend from the connection leg in the direction of the free U-legs, so that these ring attachments lie between the free legs. The Ushaped cross-section gives the cap a high rigidity, and the said position of the ring attachments has the advantage that when the cap is assembled on the electrical device, the screws which are held in the ring attachments are enclosed in the manner of a cage by the free U-legs. This then prevents screws which due to especially large vibration or manual handling have fallen from the ring attachment from becoming lost.Such an effect is also obtainable with caps which are substantially Lshaped in cross-section, if they are assembled on to a wall which is raised up from an assembly plane and which covers the cap interior on one side. This also makes it impossible for screws which have slid out of the ring attachment to become lost, and likewise strongly reduces the danger of any unintentional contact with live terminal screws.

According to a desirable embodiment of the ring attachment, it is provided with at least two slots extending in an axial direction, whereby its properties of resilience can be attained in a simple and reliable manner.

According to a further desirable embodiment, at least a part of the individual ring attachments is in the form of bounding leg zones of the cap leg. This allows a small saving of material, and in addition a simplification of the cap construction.

Particular attention must be given to the interior wall of the ring attachments, in order to attain the required reliable adhesion of the terminal screws, which can even be attained for those mechanically inserted. According to one embodiment, the inner walls of the ring attachments are conically formed over part of their longitudinal region, whereas the remaining longitudinal region is formed cylindrically.

This latter cylindrical region provides an especially reliable and lasting grip for the inserted terminal screw head, which is better than in a conical region. In contrast, a conical attach ment facilitates insertion of the screw head and the resilient opening-out of the ring attachment. On this basis, it is also possible to make both longitudinal ends of the ring attachments conical, and to make the intermediate middle region cylindrical. Such a construction gives the aforesaid advantages, and also has the virtue of facilitating insertion of a screwdriver.

According to a further embodiment, which is more expensive in terms of the tool construction, but represents a particularly reliable form of ring attachment from the point of view of its gripping ability, the ring attachments are provided with multiple slots so that they become made up from several ring attachment segments, of which some are conical in one longitudinal direction, and the re mainder, preferably respective adjacent ring attachment segments, are conical in the opposite direction. As already stated, this allows particularly reliable gripping of the head of the associated terminal screw.As a modification of this latter embodiment, the ring attachment segments are provided with a small bead on their circumferential zone which next follows the middle point of the ring attachments, so that annular bead sections extend in a circumferential direction at both longitudinal ends of the ring attachments. Such an embodiment.is especially to be recommended if either the terminal screws themselves or clamping plates which are held and received thereby have such a weight that the heads of the terminal screws which have been gripped in the ring attachments threaten to fall out of the ring attachment due to vibration.

According to a further desirable embodiment of the cap according to the invention, at least one locking element in the form of a lip, a projection or the like is disposed on that leg not provided with the ring attachments in the case of the substantially L-shaped cross-section, or on at least one of the free legs in the case of the substantially U-shaped cross-section. By means of such locking elements, it becomes very easy and reliable to assemble the cap fitted with terminal screws on to the electrical device, without any further components such as screws or the like being required.

According to a further embodiment, instead of providing such locking elements, at least one recess or depression is provided in the cap, namely in the leg not provided with ring attachments in the case of the substantially Lshaped cap cross-section, or in at least one of the free legs in the case of the substantially Ushaped cross-section, into which a locking element can be snapped, this locking element extending from the electrical device itself or from a part fixed thereto.

Finally, in a further embodiment of the cap according to the invention, at least one of its L-legs or U-legs is comb-shaped, the comb spaces being provided transverse to the longitudinal direction of the cap to be mounted on the terminal screw connections in a relatively close disposition, even when separation bars which rise to a relatively high level are disposed for safety reasons between the individual connection points. These separation bars project in this case into the said comb spaces, or they even project above the upper cap surface, which makes particularly reliable manipulation with the aforesaid screwing tools possible, and also provides a type of guide for these, for the insertion of the tool point into the ring attachment opening.

The number of ring attachments which can be disposed on a cap is at least theoretically unlimited, as is the number of individual rows. However, for certain applications, it can be desirable to provide a cap comprising only a single ring attachment, and which correspondingly serves as a cover and safety cap for only a single terminal screw.

One embodiment of the invention together with some advantageous modifications thereto are described in detail hereinafter with reference to the accompanying drawings, in which: Figure 1 shows the outlines of an electrical switching device with the essential parts of the invention indicated therein, Figure 2 is a plan view of the electrical switching device of Fig. 1, Figure 3 is a partiai view of the electrical switching device shown in Figs. 1 and 2, but to a greater scale than that of Fig. 1, Figure 4 is a partial perspective view of two cover and safety caps in other embodiments than those of the aforesaid figures, Figure 5 is a view of a special embodiment of a ring attachment, Figure 6 is a section through the ring attachment of Fig. 5, and Figure 7 is a further section through the ring attachment of Fig. 5.

Fig. 1 shows the outlines of an electrical switching device, in the present case a contactor 10, shown in side view. Only those parts necessary for clarifying the invention are shown within these contours, in the manner in which they would appear in the case of a section through the switching device. These include, in an upper plane, fixed contact pieces 11 and 1 2 with terminal screws 1 3 and 14 screwed therein, and cover and safety caps 1 5 and 1 6 mounted thereover and locked. Similar parts can be seen in an underlying plane, namely fixed contact pieces 1 7 and 18, terminal screws 1 9 and 20 and cover and safety caps 21 and 22. Detailed information regarding these parts can be gained from the description with reference to Fig. 3.

Fig. 2 is a plan view of the contactor of Fig.

1, showing in a partly cut-away manner the previously said upper plane and, below the cut-away edge, the lower plane with the associated parts. The Fig. shows the terminal screws 1 3 and 14 of the fixed contact pieces 11 and 1 2 of the upper plane, these fixed contact pieces not being shown, and the terminal screws 1 9 and 20 of the (likewise not shown) fixed contact pieces 1 7 and 1 8 of the lower plane.From this view it can be seen that the cover and safety caps 1 5 and 1 6 for covering the terminal screws 1 3 and 1 4 in the upper plane, and also the cover and safety caps 21 and 22 for covering the terminals screws 1 9 and 20 of the lower plane extend approximately over the total width of the contactor 1 0. From Fig. 2 it can also be seen that all the said terminal screws 13, 14, 1 9 and 20 are accessible from the top by means of a tool, in particular a screwdriver, by way of openings (not marked with reference numerals) in the individual cover caps, these openings being coaxial to the said terminal screws when the cover caps are in their mounted position.

Fig. 3 is a view of Fig. 1 to an enlarged scale. This again shows the fixed contact pieces 11 and 1 2 in the so-called upper plane, and 1 7 and 1 8 in the underlying plane, together with the associated terminal screws 13, 14, 1 9 and 20, and finally the cover and safety caps 15, 16, 21 and 22. It can be seen that all the said cover and safety caps.have a substantially U-shaped cross-section, with locking lips moulded on to the free legs for locking the individual cover caps.For example, in the case of the cover and safety cap 15, locking lips 24 are included on the left hand free leg 25, with respect to the figure, and locking projections 26 on the right hand free leg 25, which each engage or snap under corresponding walls or projections on the casing of the contactor 1 0. In the case of the cover and safety cap 21 disposed offset thereunder, locking lips 27 and 28 are disposed on the free legs 29 and 30. Identical locking lips are provided and can be seen on the cover caps 1 6 and 22, which are mounted specularly to the cover caps 1 5 and 21, but these lips are not indicated individually by reference numerals.Ring attachments 33 (on the cover cap 15) and 34 (on the cover cap 21) for each of the said terminal screws 13, 14, 1 9 and 20 extend from the connection legs 31 of the cover cap 15 and 32 of the cover cap 21, their inner walls forming the boundary of openings 35 and 36, which are located in the connection legs 31 and 32 of the cover caps 15 and 21.

The openings 35, 36 are disposed such that when the cover caps 15, 21 etc. are mounted on the contactor 10, they are coaxial to the said terminal screws 13, 14, 1 9 and 20.

They then serve for guiding the tool, normally the point of a screwdriver, by means of which the terminal screws are screwed down after inserting wire ends (not shown) under clamping plates 37 held at the head end of the individual terminal screws (only the clamping plate on the terminal screw 1 3 is indicated by a reference numeral).

The inner diameters of the said openings 35 and 36 and thus of the ring attachments 33 and 34 are sized such that they are able to receive the head of the associated terminal screw so that it adheres to them. The terminal screw 1 9 is illustrated in such a position, and it can be seen that when in the position in which it is held by the ring attachment 33, this terminal screw has not yet been screwed into the female threaded socket 38 of the fixed contact piece 1 7. The assembly is as follows: the individual cover and safety caps 15, 16, 21 and 22 are fitted either mechanically or manually with the corresponding terminal screws 19, 20 etc., the cover caps fitted out in this manner are then mounted in their illustrated positions and then snapped into place, and the said terminal screws are then left in this position until the wires have to be connected.In this manner, transport vibration or the like can neither cause the individual terminal screws to become unscrewed and thus lost, nor cause them to automatically become screwed in so that they assume a position such as that of the terminal screw 1 3. If a terminal screw is completely screwed in, then the fitter is compelled on site to firstly partly screw the terminal screw out substantially as shown for the terminal screws 14 and 20, in order to be able to insert the wires to be connected between the fixed contact pieces 11, 12, 17 and 18 and the clamping plates 37. In addition to protecting the terminal screws from loss, the cover and safety caps also provide substantial protection against contact as the remaining gap between the outwardly facing free legs 23 and 29 and the wall portions, not shown, of the contactor 10 is relatively small.This latter cannot be seen from Fig. 3.

The present invention is based primarily on the radially resilient construction of the ring attachments. A great number of shapes are possible for this. Fig. 4 shows special constructional forms for the ring attachment. In this figure, two partly cut-away cover and safety caps 39 and 40 are illustrated, in which parts of the ring attachments also form one of the free legs of the cover caps. In the case of the cover cap 39 with the ring attachments 41, 42 and 43, parts of these latter form a type of extension or completion of a free leg 44 of the cover cap 39. In order to obtain the properties of resilience, the ring attachments 41 to 43 are slotted transversely to the direction in which the free leg 44 extends. The ring attachments 41, 42 and 43 open into passage openings in order to allow a screwdriver to pass. These passage openings cannot be seen in the figure.Aperture 45 and 46 are disposed at the two longitudinal ends of the free leg 44, for receiving locking means projecting from the casing of the associated electrical device or from parts fixed thereto.

The cover cap 40 is substantially of identical form, comprising ring attachments 47, 48 and 49, in which again parts of these ring attachments form an extension of the wall portions of a free leg 50. Slots are also provided in this case in the said ring attachments 47 to 49, in the direction of the free leg 50. The ring attachments 47 to 49 also open into openings (not shown), and again the longitudinal ends of the free legs 50 comprise apertures 51 and 52 for receiving locking means.

The ring attachments can be formed differently, according to the strength of the gripping property which it is required to give the individual ring attachments, these differences relating in particular to their inner walls. At the beginning of the description, it was stated that the interior of the ring attachments could be either conical or partly conical and partly cylindrical. Such a shape of the inner walls of the ring attachments might however not be sufficient for very reliable gripping of the individual terminal screws, because the danger of the respective heads of the terminal screws being shaken out at least by vibration cannot be excluded. In this respect, a very reliable form of ring attachment, but one however which is more costly in terms of tool formation, is shown in Figs. 5, 6 and 7.

These show, to a greatly enlarged scale, a small portion of the surface of a cover and safety cap 53, comprising a passage opening 54 for a tool, for example a screwdriver. Four ring attachment segments 55, 56, 57 and 58 extend from the edge of the passage opening 54. It should be noted that the ring attachment segments 55 and 56 which lie opposite each other are identical, but differ from the other two ring attachment segments 57 and 58. The sections A-B and C-D of Figs. 6 and 7 show this. These sections show that the ring attachment segments 57 and 58 have inner walls which are conical with their taper towards the flat portion of the cover cap 53.

It should also be noted that the ring attachment segments 57 and 58 comprise beads 59 and 60 where they meet the flat portion of the cover cap 53, these beads facing each other and forming a further step-like decrease in the internal spacing.

In contrast, the ring attachment segments 55 and 56 are conical in the opposing direction, i.e. the distance between the ring attachment segments 55 and 56 decreases with increasing distance from the flat portion of the cover cap 53. Beads 61 and 62 are again moulded on to the narrowest region, these beads thus being at those ends of the ring attachment segments 55 and 56 which are farthest from the flat portion of the cover cap 53.

In this manner, a terminal screw head is gripped by the ring attachment segments 55 to 58 in such a manner that it cannot slip out in any direction, not even during transport vibration or if the electrical device falls. The position of such a terminal screw is shown by the dashed line, and indicated by the reference numeral 63.

Slot-type recesses extend between the individual ring attachment segments 55 to 58, and provide a sufficient resilience to each individual ring attachment segment.

Finally, it should be noted that by means of suitable sizing, in particular of the spacingapart of the inner walls of the ring attachment segments 55 to 58, and by suitably choosing the degree of taper, a good grip for a terminal screw head can be attained even without the beads 59 to 62.

As stated at the beginning of the description, the illustrated embodiments of the cover and safety caps and their ring attachments, represent only examples. Various modifications are possible, and these fall within the scope of the invention as set out in the appended claims.

Claims

1. A cover and safety cap for terminal screws on electrical devices, and comprising openings coaxial to the terminal screws to be covered, ring attachments bounding the openings, and locking means for snapping the cover and safety cap on to the electrical device, in which the ring attachments extend from a leg of the cap which is substantially Lshaped or U-shaped in cross-section and are at least slightly resilient in a radial direction, their inner diameter when in an unstressed state being smaller than the outer diameter of the heads of the terminal screws.

2. A cap as claimed in claim 1 having a substantially U-shaped cross-section, wherein the ring attachments extend from the connection leg in the direction of, and between, the free U-legs.

3. A cap as claimed in claim 1 having a substantially L-shaped cross-section, in which the ring attachments extend from one cap leg in the direction of the other leg.

4. A cap as claimed :in any of claims 1 to 3, in which each ring attachment comprises at least two slots extending in an axial direction.

5. A cap as claimed in any preceding claim, in which at least partial regions of the ring attachments are formed from bordering leg regions of the cap leg.

6. A cap as claimed in any preceding claim, in which the inner walls of the ring attachments are conically formed over part of their longitudinal region, whereas the remaining part is of cylindrical form.

7. A cap as claimed in any preceding claim, in which the ring attachments are provided with a plurality of slots so that they become made up from several ring attachment segments of which some are conical in one longitudinal direction, and the remainder, are conical in the opposite direction.

8. A cap as claimed in claim 7, in which the ring attachment segments are provided with a small bead on their circumferential zone which next follows the middle point of the ring attachments, so that annular bead sections extend in a circumferential direction at both longitudinal ends of the ring attachments.

9. A cap as claimed in any preceding claim, in which at least one locking element in the form of a lip, a projection or the like is disposed on that leg not provided with the ring attachments in the case of the substantially L-shaped cross-section, or on at least one of the free legs in the case of the substantially U-shaped cross-section.

10. A cap as claimed in any of claims 1 to 8 in which at least one recess or depression is provided in that leg of the cap not provided with ring attachments in the case of the substantially L-shaped cap cross-section, or in at least one of the free legs in the case of the substantially U-shaped cross-section, into which a locking element can be snapped.

11. A cap as claimed in any preceding claim, in which at least one of the L-legs or Ulegs is comb-shaped, the comb spaces being provided transverse to the longitudinal direction of the cap between the ring attachments.

12. A cap as claimed in any preceding claim, comprising only a single ring attachment, which correspondingly serves as a cover and safety cap for only a single terminal screw.

1 3. A cap for terminal screws constructed substantially as herein described with reference to and as illustrated in the accompanying drawings.