The invention refers to a protective appliance on the basis of a fuse with a melting member, which is prevented against insertion of a false fuse and consequences, which could result from such action. In accordance with the International Patent Classification, such invention belongs to electricity, namely to basic electric components, and in particular to protective appliances, in which the current is flowing through a part of melting material, so that the electric circuit, when exposed to overcurrent, is interrupted due to displacement of melted material, wherein the invention in particular refers to casings used in such appliances, and is included in the Class H 01 H 85/165.

In this, the purpose of the invention is to prevent insertion of an inappropriate single fuse into a protective appliance, which is adjusted for receiving of a double i.e. a tandem fuse, since such irregularity would lead to essential exceeding of a nominal capacity of the fuse with the possibility of burning of arc due to insufficient contact pressure during insertion thereof, which may be later also followed by unnecessary interruption of the electric current due to insufficient nominal value of the fuse, despite to regular operation of the electric circuit. A protective appliance on the basis of a fuse with a melting member is disclosed in EP 0 718 862 Al and comprises a casing with a cover, into which a suitable fuse with a melting member is insertable. Said casing generally consists of an electric insulating material and is on its rear side furnished with a seat and arresting seat, which are arranged for mounting said casing on a standardized connecting ledge. The casing is opened on its front side and is adjusted for receiving of a cover, which is on the one hand pivotally attached to the casing and on the other hand matches the casing, so that the cover may be either pivoted away from the casing in order to allow access towards to the interior of the casing, or may also be pivoted in opposite direction towards the casing, upon which the casing is closed and the cover matches the casing. Besides, two electric conductive connectors are foreseen on the external surface of the casing, via which the protective appliance can be integrated into an electric circuit. Lateral walls of the casing are generally flat and extend parallel with each other, which leads to possibility of mounting a plurality of casing on the same connecting ledge tightly one adjacent the other. Said cover is adapted for receiving of an electric resistance fuse with a melting member, namely a standardized fuse with a cylindrically tubular and electrically insulating ceramic body, which in its both terminal portions closed by means of electric conductive cups, which are electrically interconnected with each other via a melting member, which extends along the interior of said tubular fuse body. Whenever said cover is pivoted away from said casing, such a fuse may be either inserted there-into, or may be removed from it, and in such case the fuse is disconnected from the electric circuit, in which the protective appliance is integrated. Two electrically conductive connectors are available within said casing, between which the fuse is arrestingly insertable in the area of said electric conductive cups thereof, and which are each per se electrically connected with corresponding electrically conductive terminals on the external surface of the casing, and are thus connectable with the electric circuit. Upon closing said cover, which then perfectly matches to the casing, the casing is completely closed and the fuse within the cover within the casing is integrated into the electric circuit thanks to said arresting if its electrically conductive cups between both electrically conductive terminals within the casing. Said terminals may be formed of semicircularly bent metallic bands or of a metallic band, which is bent in form of letter U, which is disclosed e.g. in US 6,692,315 Bl, or as a pair of elastically mounted rests, which are deflectable apart from each other as it is disclosed in WO 2007/131868 Al.

Said electric resistance fuse is meant as one of standardized fuses pursuant to IEC 60947-1:2004 (E) or 60947-1 :2020 standard, and one of suitable embodiments is also disclosed in WO 2021/101453 Al.

Regarding said protective appliance according to EP 0 718 862, a relatively bulky casing is required, which is however foreseen for inserting of a relatively small fuse with correspondingly low nominal capacity. In such case, by flowing of electric current through the melting member certain amount of heat is generated, which is however practically neglectable and cannot lead to essential increasing of temperature within the interior of the casing, and in particularly not in such extend that overheating could result in structural changes in the material of the casing, which could reduce insulating properties of the casing as such. Consequently, the lateral walls of the casing can be flat, smooth and can extend parallel with each other, which allows placement of numerous casings adjacent to each other on the same connecting ledge. The width of the casing depends on diameter of the fuse inserted therein, and there is always a tendency on reducing the casing width, since the protective appliance then requires less space on said connecting ledge and more protective appliances and more fuses can then be installed on the same connecting ledge.

This is the reason why a protective appliance has been developed, which is in different context described in a non-published Slovenian patent application SI- 202200071 and which is suitable for receiving of a double i.e. a so-called tandem fuse, where two fuses are joined, e.g. welded, in the area of their cups in such position, in which their cups are placed adjacent to each other, the longitudinal axles of both fuses extend parallel with each other, and the common length of such assembled fuses corresponds to the total length of each of them. Such fuses are in parallel electrically connected with each other, so that the nominal capacity of such tandem fuse corresponds to nearly a double nominal capacity of a single fuse, but such tandem fuse can despite to that be inserted into a casing, the width of which corresponds to the width of a casing, which is adjusted to a diameter of a single fuse in said tandem. Consequently, when compared with using of a single fuse, the benefit of using said tandem fuse is placing of a fuse with practically double nominal capacity into a casing of equal width as the width of the casing suitable for using a single fuse. There is however a problem, which must be bom in mind, and this is at least a theoretical probability that an user would attempt to inserting a classic single fuse instead of a tandem fuse, since the nominal capacity of such single fuse is inappropriate for the electric circuit, in which the tandem fuse should be used. In such case, by insertion of a single fuse an electric arc could be generated due to insufficient contact pressure, which might lead to fire, and moreover, such inappropriate single fuse would interrupt the electric circuit even if the last would be quite regularly operated. Of these reasons it would be therefore quite useful, if even a theoretical possibility of application of a single fuse in such a protective appliance, instead of a double i.e. tandem fuse, could be a priori excluded.

Moreover, one of known protective appliances on the basis of a fuse with a melting member is also disclosed in EP 1 296 342 Al.

The present invention refers to a protective appliance on the basis of a fuse with a melting member, which is prevented against insertion of a false fuse. Such protective appliance generally comprises a casing, a cover and a fuse.

A box-shaped casing is opened on its front side and consists of an electric insulating material, and is moreover on its rear wall furnished with an arresting seat, which is suitable for attachment of said casing onto a connecting ledge or similar mounting means. Lateral walls of said casing are arranged parallel with each other, and two apart from each other spaced electrically conductive terminals are foreseen on the external surface of the casing in the area of said front side thereof, by means of which said protective appliance is connectable with suitable electric conductors and is such enabled to be integrated in an electric circuit. Two electric conductive connecting seats are foreseen within the interior of said casing adjacent to said rear wall, and are adapted for insertion of an electric fuse therebetween, so that a required contact pressure between each of them and said fuse can be established, wherein each of said connecting seats is per se electrically connected with one of said electric conductive terminals on the front side of the casing, via which then also the fuse is also integrated in said electric circuit.

Said cover also consists of an electric insulating material and is on the one hand adapted for tightly matched closing of said opened front side of the casing, while on the other hand, said cover is also adapted for receiving of said fuse. Said cover is pivotally attached to the casing in a pivot point, which is arranged on the one terminal area on the front side of the casing, so that the cover is pivotal relatively to the casing at a pre-determined angle, which is sufficient to allow insertion or removal of said fuse, wherein the geometric axis, around which said cover is pivotal relatively to said casing, extends perpendicularly with respect to said parallel with each other arranged lateral walls of the casing. Said cover is on its other terminal area, i.e. oppositely to said pivot point, furnished with a handling grip, which is arranged on the front i.e. external surface. Moreover, said cover is furnished with a seat, which is suitable for placement of the fuse there-into, and which is due to ensuring of required electric insulating properties arranged at a sufficient distance apart from said front surface and simultaneously also at a sufficient distance apart from said pivot point between the cover and the casing, but also in a suitable position in the area sufficiently close to said connecting seats, so that on the one hand, in opened state of the cover, namely when the cover is pivoted around said pivot point in a direction away from the casing, an electric fuse can be either inserted into said seat on the cover, or also removed there-from, while on the other hand, when said cover is closed i.e. pivoted around said pivot point in a direction towards the casing, the electric fuse, which is placed within said seat, is maintained in an electrically conductive contact with said connecting seats within the casing, wherein in such a state also a sufficient contact pressure between the fuse and said connecting seats is established.

Said fuse is generally either a single fuse, comprising a cylindrical tubular body consisting of an electro-thermally insulating material, which is on its both terminal portions closed by two terminally blinded tubular caps, which are electrically connected with each other via a melting member, which extends along the interior of said tubular body and is preferably surrounded with a granulated arcextinguishing material, or a tandem fuse, which consists of two single fuses of equal shape and nominal capacities with regard to each other, which are mechanically and in a non-detachable manner connected with each other in their mutually parallel longitudinal alignment and in position, in which their geometric axles extend parallel with each other, wherein said fuses are electrically in parallel connected with each other.

According to the invention, said seat on said cover of the protective appliance is furnished with two chambers and each one of these chambers is adjusted for receiving of a single cylindrical fuse, wherein on the one hand both longitudinal axles of said chambers are arranged parallel with each other, and on the other hand, both of them are arranged within the same central plane between both lateral walls of the casing, so that the first chamber within the cover is located closer to the front side of the casing and the second chamber is located closer to the rear wall of the casing. Such conceived cover is in the area of said chambers capable to receive either a single fuse, the longitudinal geometric axis of which is aligned with a corresponding geometric axis of the one of said chambers, or a tandem fuse, the longitudinal geometric axles of which are aligned with geometric axles of said chambers. Both electrically conductive resting seats are arranged adjacent to the rear wall of the casing and in such manner that each one of said seats is able to stay in contact with a corresponding electric conductive cap of just one fuse, which is placed within the second chamber of the seat in the cover, while each potential electric contact between said electrically conductive resting seats and the fuse, which is placed within the first chamber of the seat closely to the front side of the casing, is physically disabled. In addition to that, a resilient selecting means is mounted within the casing and is arranged on the side oppositely to the pivot point and, when taking into consideration the cover in a closed position thereof, in the area between both chambers of the cover, wherein said selecting means protrudes inside i.e. towards the interior of the casing, and its resiliency is determined in such a manner, that by closing of said cover, when a corresponding cap of a tandem fuse, which should regularly occupy both chambers of said cover, abuts the selecting means, the resilient selecting means is deflected and the cap of the fuse in the second chamber, which protrudes towards the resilient selecting means, is allowed to enter into the corresponding electric conductive resting seat, while on the contrary, when inserting a single fuse, by pivoting the cover due to closing it, the cap is moved towards the selecting means, which however remains undeflected, so that upon completely closing the cover, said fuse cap remains supported by such undeflected selecting means at a sufficient distance apart from corresponding electric conductive resting seat.

In a preferred embodiment of said protective appliance, the first chamber is on its side, which is located closely to the pivot point, furnished with a seat, which is adjusted for receiving of that cap of the fuse, which is to be inserted into the first chamber, which is arranged closely to the front side of the casing. Moreover, in the area of the first chamber, into which the oppositely to the pivot point located fuse cap is to be rest, said cover is furnished with a sloped resting support, which is adjusted to the circumferential shape of the fuse cap and is faced towards the interior of the casing, and is therefore by closing the cover capable to support the fuse and press it towards the interior of the casing.

The invention will be explained in more detail on the basis of embodiments and relationship with the attached drawings, wherein Fig. 1 presents a protective appliance according to the invention, with closed cover and with a tandem fuse inserted therein, in isometric view;

Fig. 2 is a protective appliance in a cross-section along the plane A - A in Fig. 1;

Fig. 3 presents a protective appliance according to Fig. 2 in its state, where the cover is open and inserting of a tandem fuse is performed;

Fig. 4 presents a protective appliance according to Figs. 1 - 3, however upon inserting of an inappropriate single fuse and closing the cover;

Fig. 5 is a cross-section along the plane B - B in Fig. 4; and

Fig. 6 similarly like Figs. 4 and 5 presents a protective appliance according to the invention upon inserting of an inappropriate single fuse, but prior to closing the cover.

A protective appliance 100 on the basis of a fuse 3, 3' with a melting member generally comprises a casing 1, a cover 2 and a fuse 3, 3’. In the shown embodiment said appliance 100 is adapted for insertion of a tandem fuse 3 (Figs 2 and 3), which will be in more detail described later-on, and provides for reliable protection against insertion of an inappropriate single fuse 3’ (Figs. 2 - 4).

Said casing 1 is box-shaped and is opened on its front side 11 and adapted for receiving a cover 2, which should tightly match said casing 1. The casing 1 consists of an electric insulating material, and is on its rear wall 12 furnished with an arresting seat 120, which is suitable for attachment of said casing 1 onto a connecting ledge or similar mounting means, selected among numerous known and widely used attaching means. Both lateral walls 13, 14 of said casing 1 are arranged parallel with each other, which allows placing of several casings 1 one adjacent to the other onto the same connecting ledge, which in the practice leads to the possibility of systematic and transparent arrangement of several casings 1 of appliances 100 for protection of various circuits by simultaneously rational exploitation of the space, which is fur such purpose available on a disposable switchbox or a switch panel. Two apart from each other spaced electrically conductive terminals 15, 16 are foreseen on the external surface of the casing 1 in the area of said front side 11 thereof, by means of which said protective appliance 100 is connectable with suitable electric conductors and is such enabled to be integrated in an electric circuit even in the case, when several casings are simultaneously and tightly one adjacent to the other mounted on the same connecting ledge. On the other hand, two electric conductive connecting seats 16, 17 are foreseen in the interior of said casing 1 adjacent to said rear wall 12, and are adapted for insertion of an electric fuse 3, 3’ there-between, wherein also a required contact pressure between each of them and said fuse 3, 3’ needs to be established, so that each of said connecting seats 17, 18 is per se electrically connected with one of said electric conductive terminals 15, 16 on the front side 11 of the casing 1, via which then also the fuse 3, 3’ can be integrated into the belonging electric circuit.

Said a cover 2 generally also consists of an electric insulating material and is on the one hand adapted for tightly matched closing of said opened front side 11 of the casing 1, while on the other hand it is also adapted for receiving of said fuse 3, 3’. In this, said cover 2 is attached to the casing 1 pivotally at a pre-determined angle around a pivot point 21, which allows insertion or removal of the fuse 3, 3’. Said pivot point is arranged on the one terminal area on the front side 11 of the casing 1, wherein the geometric axis 210, around which said cover 2 is pivotal relatively to said casing 1, extends perpendicularly with respect to said parallel with each other arranged lateral walls 13, 14 of the casing 1. Moreover, said cover 2 is on its other terminal area, i.e. oppositely to said pivot point 21, furnished with a handling grip 22, which is arranged on the front i.e. external surface 20 thereof. As a consequence, even when several casings 1 are mounted on the same connecting ledge tightly one adjacent to the other, the cover 2 of each of said casings 1 can be by means of said handling grip 22 pivoted around said geometric axis 210 extending through said pivot point 21 either in a direction away from the casing 1 (Figs 3 and 6) due to insertion or removal of the fuse 3, 3’, or in a direction towards the casing 1 in a position (Figs 1, 2, 4, 6), in which the cover 2 is tightly matching placed over the casing 1, which is herewith closed, so that any access to the electric conducting components within the casing 1 is impossible.

Moreover, said cover 2 is furnished with a seat 23, which is suitable for placement of the fuse 3, 3’ there-into and is due to providing each required electric insulating properties arranged at a sufficient distance apart from said front surface 20 and simultaneously also at a sufficient distance apart from said pivot point 21 between the cover 2 and the casing 1. However, said seat 23 is also arranged in a suitable position closely to said connecting seats 17, 18, so that on the one hand in opened state of the cover 2, namely when the cover 2 is pivoted around said pivot point 21 away from the casing 1, an electric fuse 3, 3’ can be either inserted into said seat 23 on the cover 2 or also removed there-from. On the other hand, when the cover 2 is closed i.e. pivoted around said pivot point 21 towards the casing 1, the electric fuse 23, which is placed within said seat 23, is maintained in an electric conductive contact with said connecting seats 17, 18 inside the casing 1 and a sufficient contact pressure between the fuse 3, 3’ and said connecting seats 17, 18 is also established, which allows reliable conduction of the electric current without any danger on formation of arc. In the discussed embodiment, said fuse 3, 3’ is an electric fuse, in which a base component is a single standardized cylindrical fuse 3’, comprising a cylindrical tubular body 31 , which is made of an electro-thermally insulating material and is on its both terminal portions closed by two terminally blinded tubular caps 32’, 32”, which are electrically connected with each other via a melting member, which extends along the interior of said tubular body 32 and is preferably surrounded with a granulated arc-extinguishing material, in particular silica granulate. However, if a pair of such single fuses 3’ (Figs. 4 - 6) should be simultaneously used, both of them can be replaced with a tandem fuse 3 (Figs 2 and 3), which consists of two single fuses 3’, which are however in the area of said caps 32’, 32” mechanically and in a non-detachable manner interconnected with each other in such a position that both fuses 3’ are aligned in the longitudinal direction, so that their overall length in such assembled state remains unchanged and their longitudinal axles 30’, 30” extend parallel with each other, while in the electric context both single fuses 3’ in such established tandem fuse 3 are in parallel electrically connected with each other.

The protective appliance 100 according to the invention however excels in that said seat 23 on said cover 2 is furnished with two chambers 23’, 23”, and each one of these chambers 23’, 23” is adjusted for receiving of a single cylindrical fuse 3’, wherein on the one hand both longitudinal axles 230’, 230” of said chambers 23’, 23” are arranged parallel with each other, and on the other hand both of them are arranged within the same central plane between both lateral walls 13, 14 of the casing 1.

The first chamber 23’ within the cover 2 is located closer to the front side 11 of the casing 1, while the second chamber 23” is located closer to the rear wall 12 of the casing 1. In general, said cover 2 is in the area of said chambers 23’, 23” capable to receive either a single fuse 3’, the longitudinal geometric axis 30’ of which is aligned with a corresponding geometric axis 230’, 230” of the one of said chambers 23’, 23”, or two single fuses 3’, the longitudinal geometric axles 30’, 30” of which are aligned with corresponding geometric axles 230’, 230” of said chambers 23’, 23”, or a tandem fuse 3, the longitudinal geometric axles 30’, 30” of which are also aligned with geometric axles 230’, 230” of said chambers 23’, 23”.

In this particular case, a tandem fuse 3 is planned to be used, and said electric conductive resting seats 17, 18 are arranged adjacent to the rear wall 12 of the casing 1 and in such manner that each one of said seats 17, 18 is able to stay in contact with a corresponding electric conductive cap 32’, 32” of those single fuse 3’ within the tandem, which is placed within the second chamber 23” of the seat 23 in the cover 2, while each potential electric contact between said electrically conductive resting seats 17, 18 and the fuse 3, 3’, which is placed within the first chamber 23’ of the seat 23 closely to the front side 11 of the casing 1, is physically disabled.

One of the benefits, which are given by the present invention, although not directly connected with the problem to be solved, is the possibility of application of practically quite similar casing 1 and also the cover 2 even in the case, when the protective appliance 100 would be intended for protection of an electric circuit by means of a single fuse 3’. In such case, the second chamber 23” would have to be simplly blinded in order to prevent insertion of the second fuse 3’, and said resting seats 17, 18 would have to be displaced towards the area of the caps 32’, 32” of such single fuse 3’ inserted within the first chamber 23’. Still within the context of previously mentioned technical problem, the invention further provides that a resilient selecting means 190 is mounted within the casing 1 and is arranged on the side 19 oppositely to the pivot point 21 and, when taking into consideration the cover 2 in its closed position, in the area between both chambers 23’, 23” of the cover 2, wherein said selecting means 190 protrudes inside i.e. towards the interior of the casing 1. Said selecting means 190, although resilient, is also sufficiently strong, and its resiliency is determined in such a manner, that by closing of said cover 2, when a corresponding cap 32” of a tandem fuse 3, which should regularly occupy both chambers 23’, 23” of said cover 2, abuts the selecting means 190, by which the resilient selecting means 190 is deflected. Consequently, the cap 32” of the fuse 3 in the second chamber 23”, which protrudes towards the resilient selecting means 190, is allowed to enter into the corresponding electric conductive resting seat 18.

On the contrary, when inserting a single fuse 3’, by pivoting the cover 2 due to closing it, the cap 32” is moved towards the selecting means 190, which however remains undeflected, so that upon completely closing the cover 2, said fuse cap 32” remains supported by such undeflected selecting means 190 at a sufficient distance apart from corresponding electric conductive resting seat 18 even if the cover 2 is closed. When the cover 2 is open, the user is generally enabled to insert an inappropriate single fuse 3’ either into the first chamber 21’ or into the second chamber 21”.

In order to assure some better positioning of the fuse 3, 3’ in the seat 23 on the cover 2, the first chamber 21’ is on its side, which is located closely to the pivot point 21, furnished with a seat 231, which is adjusted for receiving of that cap 32’, 32” of the fuse 3, 3’, which is to be inserted into the first chamber 23’, which is arranged closely to the front side 11 of the casing 1. To this aim, the invention further provides that in the area of the first chamber 23’, into which the oppositely to the pivot point 21 located fuse cap 32’, 32” is to be rest, said cover 2 is furnished with a sloped resting support 202, which is adjusted to the circumferential shape of the fuse cap 32’, 32” and is faced towards the interior of the casing 1, and is therefore by closing the cover 2 capable to support the fuse 3’, 3 ’ ’ and press it towards the interior of the casing 1. Thanks to this last measure, upon insertion of the fuse 3, 3’ into said seat 23 and closing the cover 2, the cap 32” of the fuse 3’, 3”, which is arranged closer to said cover 2, is reliably supported by said resting support 303 and is therefore secured against undesired movements in a direction towards anyone of the lateral wall 13, 14 of the casing 1.

If the user would attempt to inserting of an inappropriate single fuse 3’ into the first chamber 23’, after closing the cover 2 the fuse 3’ is maintained in position, in which its longitudinal geometric axis 30’ is aligned with the longitudinal geometric axis 230’ of the first chamber 23’ (Fig. 4), and in such a position both caps 32’, 32’ of the fuse 3’ are maintained in position at a sufficient distance apart from both electric conductive resting seats 17, 18, so that on the one hand such fuse 3’ is physically separated from the electric circuit throughout the protective appliance 100, and on the other hand also the possibility of formation of arc between the caps 32’, 32 of the fuse and said electric conductive resting seats 17, 18 can be completely excluded.

If however the user would insert an inappropriate single fuse 3’ into the second chamber 23”, then by closing of the cover 2 such fuse 3’ would remain in position, in which its first cap 32’, which is located closer to the pivot point 21, could in principle stay in electric contact with the belonging electric conductive resting seat 17, but during pivoting of the cover 2 the opposite second cap 32” of the fuse 3’ would remain supported by said selecting member 190, so that the second cap 32” of the fuse 3’ is maintained at a sufficient distance apart from the belonging electric conductive resting seat 18, and consequently, each potential establishing of an electric circuit through the fuse 3’ is a priori and physically disabled.