The invention refers to a protective appliance on the basis of a fuse with a melting member. Such inventions in the view of the International Patent Classification belong to electricity, namely to basic electric components, more precisely to protective appliances in which the current is flowing through a part of melting material, so that by excessive current the circuit is interrupted due to transposition of said melting material, and in particular refers to casings of such appliances.

In this, the invention is rest on a problem, how to improve efficiency of heat transfer from the interior of a casing of a protective appliance, wherein said casing ought to be suitable either for receiving of a single fuse, or of a pair of separate or mechanically interconnected fuses, by simultaneously preventing the material of the casing against negative impacts of the heat generated within the casing and maintaining efficient and long-term electric insulating properties of such casing.

A protective appliance on the basis of an electric fuse with a melting member is disclosed in EP 0 718 862, and comprises a casing with a cover, into which an electric fuse with a melting member is insertable. Said casing generally consists of an electric insulating material and is on its back side furnished with a seat and an arresting means, which allow mounting of such casing onto a standardized ledge. The casing is open on its front side and is adjusted to receive said casing, which also consists of an electric insulating material and is pivotally attached to the casing by simultaneously matching the shape of the casing, so that the cover can be either pivoted apart from the casing in order to allow access towards the interior of the casing, or may also be pivoted in opposite direction in order to close the casing by perfectly matching the cover to the casing. Besides, two electrically conductive connectors are foreseen on the external surface of the casing, by which said protective appliance can be integrated into an electric circuit. Lateral walls of such casing are generally flat and parallel with each other, which allows placing of a plurality of such casing onto a single ledge. Such cover is suitable for receiving of an electric fuse with a melting member, namely of a standardized fuse having a cylindrical i.e. tubular and electrically insulating cover, which consist of ceramics and is in both terminal areas closed with electrically conductive covers, which are electrically interconnected via a suitable melting member, which extends along the interior of said tubular casing of the fuse. Whenever the cover is pivoted apart from the casing, a suitable fuse can be inserted into the casing or also removed there-from, wherein in such case the fuse is disconnected from the electric circuit, in which the protective appliance as such is integrated. Two electrically conductive contact members are available within said casing, between which said electrically conductive covers of the fuse can be inserted and arrested, and which are separately i.e. each per se electrically interconnected with one of said electrically conductive connectors on the external surface of the casing and consequently integrated into the electric circuit. Upon closing said cover, the casing is closed and the cover perfectly matches the casing, while the fuse inserted within said casing is integrated into the electric circuit thanks to arresting of its electrically conductive covers between said contact members within the casing. Said contact members can be made as e.g. semi-circular metallic bands, or U-shaped electric conductive band as proposed e.g. in US 6,692,315 B 1 , or as a pair of resilient rests, which are displaceable apart from each other, as it is disclosed in WO 2007/131868 Al. A suitable electric fuse is one of standardized fuses according to the standard IEC 60947-1:2004 (E) i.e. 60947-1:2020, and moreover, such a fuse is also disclosed in WO 2021/101453 Al.

The protective appliance according to EP 0 718 862 comprises a pretty bulky casing, which is intended for cooperating with a relatively small fuse, having correspondingly low breaking capacity. In such case by conducting the electric current through the melting member of the fuse some heat is generated, the intensity of which is small and is practically neglecting, and cannot lead to essential increasing of temperature within the protective appliance casing, and in particularly not to such temperature, which could lead to structural changes in the material of the casing, which could result in decreasing of insulating properties of the casing as such. This is the reason why said lateral walls can be flat and why several casings can be simply placed closely to each other onto the came ledge.

On the other hand, however, WO 2007/131868 Al teaches that the lateral walls of the casing should be furnished with throughout slots, which support heat transfer from the interior of the casing. If upon integrating of such fuse with a melting member into an electric circuit an essential amount of heat is generated, then the heat is transferred out from the casing partially by means of conduction and partially due to convection by means of heated air, which leaves the interior of the casing. However, such approach may often be insufficient for several reasons. The main reason are operational conditions, which in practice result from increasing of requirements due to the need of applying fuses with higher and higher interruption rating, and also to the need on placing of more and more casings onto the existing ledge. In such case the slots in lateral walls of casings of each neighboring casings overlap each other, so that in fact the heated air may flow from the interior of a casing through the slots out of the casing but simultaneously also through the slots of the neighboring casing towards the interior thereof. As soon as the temperature with the neighboring casing sufficiently increases, then ventilating of one or another casing becomes inefficient. In particular in direct current circuits, e.g. in photovoltaic appliances, an electric circuit may operate in heavy but still regular conditions during a pretty long time period, namely without e.g. a short circuit or excessive current, in which also the environmental temperature may be pretty high. In such circumstances a lot of heat may be generated within the area of the fuse, wherein transferring of the heat towards the exterior of the casing is quite difficult. In such case, the walls of the casing are exposed to essential temperature increasing, in particular in the area adjacent to the fuse. By long-term exposure to such increased temperature, the structure of the material of the casing may change, which is usually at the first glance visible as a change in color thereof, but from quite physical point of view this may also lead to changes in strength of material as well as in roughness and porosity on the surface, which consequently lead to change of electric insulating capability and insulating permeability.

Increasing of roughness on the surface enhances the presence of moisture and impurities on the surface, which may lead to establishing of electric conductivity on the surface of the casing. In this context, the most problematic areas occur between each neighboring slots, in which in most vases said changes can be visually detected. Consequently, security measures in the practice require replacement of the complete protective appliance as soon as such changes in color, like e.g. bright spots or the like, are identified on the surface.

The proposed invention generally refers to a protective appliance on the basis of a fuse with a melting member, such appliance comprising - a box-shaped casing, which generally consists of an electric insulating material and is on its front side open and suitable for receiving of a cover, into which said fuse is insertable, and which is on its rear wall furnished with an arresting seat, which is suitable for attachment of said casing onto a suitable connecting ledge, and which is on each of its dominant lateral walls, which are substantially flat and smooth, furnished with a group of ventilating slots, which are equidistantly spaced apart from each other, wherein said casing is, outside of the area of said open front side, furnished with a pair of electrically conductive connectors, which are suitable for integration of said protective appliance into an electric circuit, and in addition to that, two electrically conductive arresting seats are available on suitable locations within said casing, and are suitable for receiving and arresting of said fuse, and are moreover each per se electrically connected with corresponding connectors on the said appliance casing,

- an electric fuse, comprising a cylindrical tubular casing consisting of an electric insulating material, which is on both terminal areas closed by means of electrically conductive covers, between which a melting member is arranged within the interior of said casing and is moreover also electrically connected with each of said fuse covers;

- a cover, which consists of an electric insulating material and is sufficiently rigid to be pivotally around a pivoting axis mounted on said appliance casing in the area of said front side of said appliance casing, and is suitable for receiving of said fuse, such that by pivoting of said appliance cover in a direction away from the casing, the interior of said casing is accessible from outside, and that each fuse is either insertable into said casing, or is also removable there-from, by which the fuse is simultaneously disconnected from the electric circuit, and that upon pivoting said cover in a direction towards the appliance casing the cover matches the casing, while the fuse inserted therein becomes arrested between said arresting seats within the casing and is then via said connectors on the casing electrically connected with the electric circuit; wherein said electric fuse with a melting member is such kind of a fuse, which comprises a cylindrical tubular casing, which consists of an electric insulating material and is on its both terminal areas closed with electrically conductive covers, in the area of which such a fuse is insertable and arrested between said electrically conductive arresting seats, which are arranged within the appliance casing, and between which a melting member is arranged, which extends along the interior of said fuse casing and substantially along the longitudinal geometric axis of the fuse and is electrically connected with each of said fuse covers; and wherein said slots on both lateral walls of the appliance casing are arranged along the central area of each lateral wall at a sufficient distance apart from electrically conductive covers of the fuse as well as from the arresting seats which are arranged within said casing.

Within the context of resolving of a previously exposed technical problem, the invention proposes that each group of said ventilating slots on said lateral walls between the front side and the rear wall of the casing, of which each slot has a predetermined and uniform width, is such conceived that said width of each slot does not exceed the distance between each two neighboring slots. The invention further proposes that both disposable groups of slots on both lateral walls of the appliance casing, namely a group of slots on the one lateral wall and the group of the slots on the opposite lateral wall, are at a pre-determined distance offset with regard to each other in the longitudinal direction of said appliance casing, namely substantially in a direction along the central geometric axis of the fuse, wherein said offset distance is determined in such manner that by each pre-determined width of said slots and each pre-determined distance between each two neighboring slots, the slots on the one lateral wall and the slots on the opposite lateral wall do not overlap each others, and that even upon placing of two appliance casings onto the same connecting ledge adjacent to each other, the ventilating slots on the one lateral wall of the first casing and the ventilating slots on the opposite lateral wall of the neighboring casing do not overlap each others. Moreover, the invention still further proposes that each of generally smooth and flat lateral walls is furnished with a laterally protruding circumferential rib, which is adjusted for resting on a substantially equal rib on the casing of each neighboring protective appliance, wherein said rib is interrupted in at least two opposite areas, wherein the length of each interruption as well as the height of the rib are determined in such manner that the circumferential air is allowed to flow freely through said ventilating slots and also through said at least two interruptions in said ribs.

Still within the context of resolving of a previously exposed technical problem, the invention further proposes that said cover, which is generally intended for receiving of the fuse, is box-shaped and comprises a suitably designed front wall, which is furnished with a manipulating grip, a rear wall, which is located merely inside of the appliance casing and is intended for supporting of the fuse, as well as two grid-shaped lateral walls, which are intended for reliable positioning of said fuse within said cover. In this, said pivoting axis, around which a required pivoting of the cover relatively to the appliance casing is allowed, is located outside of said lateral walls, and each of said lateral walls is formed of a group of bearing strips, each of them having a pre-determined width, wherein said strips are equally spaced apart from each other and extend parallel with each other and transversally with respect to the longitudinal axis of the fuse, wherein the width of such a strip does not exceed said distance between each two adjacent ventilating slots on the lateral walls of the appliance casing. Also the bearing strips of the first lateral wall are offset with regard to the bearing strips of the residual lateral wall at a predetermined distance in the longitudinal direction of the appliance casing i.e. substantially along the longitudinal geometric axis of the fuse, and said distance of said offset is correlated with the offset of the ventilating slots on the lateral walls of the appliance casing and is determined in such manner that in a situation, where the cover is closed i.e. pivoted towards the interior of the casing, each one of the bearing strips of the appliance cover is located in the area between two neighboring ventilating slots on the adjacent lateral wall of the appliance casing, namely outside of said ventilating slots, so that said bearing strips do not overlap said ventilating slots, or vice versa.

In one of the embodiments of the protective appliance according to the invention, said cover is pivotally insertable into said appliance casing of a pre-determined width, which is foreseen for receiving of a single electric fuse with a melting member, which is in the area of its covers insertable between both arresting seats within the appliance casing and is via them electrically connectable with both electric connectors on the appliance casing.

In a further of the embodiments of the protective appliance according to the invention, said cover is pivotally insertable into said appliance casing of a predetermined width, which is foreseen for receiving of two electric fuses with melting members, which are arranged adjacent to each other and are equal to each other with regard to their nominal braking capacity, shape and dimensions, and which are in the area of their covers insertable between both arresting seats within the appliance casing and are via them electrically connectable with both electric connectors on the appliance casing. In a still further embodiment of the protective appliance according to the invention, said cover is pivotally insertable into said appliance casing of a pre-determined width, which is foreseen for receiving of two adjacent to each other arranged, electric fuses, which are equal to each other with regard to their nominal braking capacity, shape and dimensions, and are electrically and also mechanically in a non-detachable manner interconnected with each other, and which are in the area of their covers insertable between both arresting seats within the appliance casing and are via them electrically connectable with both electric connectors on the appliance casing. In this, said fuses are preferably welded with each other in the area of their covers and in position, in which their casings are arranged adjacent to each other and their longitudinal geometric axes extend parallel with each other, so that the length of such assembled fuses corresponds to the length of each of them.

The invention will be also explained on the basis of embodiments and in relationship with the attached drawings, wherein

Fig. 1 is a protective appliance with a closed cover, in top view;

Fig. 2 presents a pair of such appliances, which are during the use placed adjacent to each other, in cross-section along the plane A - A according to Fig. 1 ;

Fig. 3 is a cross-section along the plane C - C of the appliance according to Fig. 1 ; Fig. 4 presents the assembly with a pair of fuses inserted there-into, with a closed cover and in a cross-section along the plane B - B according to Fig. 2;

Fig. 5 presents said protective appliance upon opening the cover;

Fig. 6 is enlarged cross-section along the plane A - A according to Fig. 1 ; and Fig. 7 similarly like in Fig. 2 presents pair of appliances placed adjacent to each other, in enlarged cross-section along the plane A - A according to Fig. 1. A protective appliance 100 on the basis of a fuse 3, 3' with a melting member generally comprises a box-shaped casing 1 and a cover 2, which is adapted for receiving of a fuse, namely either a single fuse 3 or a tandem fuse 3, 3’ in form of a pair of mutually assembled equal fuses, namely equal in the view of their nominal braking capacity, shape in dimensions.

Said appliance casing 1 generally consists of an electric insulating material and is on its front side 11 open and suitable for receiving of said appliance cover 2, into which said fuse 3, 3' is insertable. Said casing 1 is on its rear wall 14 furnished with an arresting seat 140, which is suitable for attachment of said casing 1 onto a suitable connecting ledge. Namely, in practice several protective appliances 100 are placed adjacent to each other onto the same connecting ledge, each of them has a width D, and may be optionally combined with other electric components, it they are also furnished with a similar arresting seat 140 for attaching to such ledge.

Said casing 1 of the appliance 100 is on each of its dominant lateral walls 12, 13, which are substantially flat and smooth, furnished with a group of ventilating slots 12', 12", 12'"; 13', 13", 13'", which are equidistantly spaced apart from each other (Fig. 2). Moreover, said casing 1 is, outside of the area of said open front side 11, furnished with a pair of electrically conductive connectors 15, 16, which are suitable for integration of said protective appliance 100 into an electric circuit. In addition to that, two electrically conductive arresting seats 17, 18 are available on suitable locations within said casing 1 , and are suitable for receiving and arresting of said fuse 3, 3', and are moreover each per se electrically connected with corresponding connectors 15, 16 on the casing 1. Such protective appliance 100 further includes an electric fuse 3, 3', which comprises a cylindrical tubular casing 31 , which consists of an electric insulating material and is on its both terminal areas closed by means of electrically conductive covers 32, 33, between which a melting member is arranged within the interior of said casing 31 and is moreover also electrically connected with each of said covers 32, 33.

Such protective appliance 100 still further includes a cover 2, which consists of an electric insulating material and is sufficiently rigid to be pivotally around a pivoting axis 21 mounted on said appliance casing 1 in the area of said front side 11 of said casing 1. Said cover is suitable for receiving of said fuse 3, 3’ in such a manner that by pivoting of said cover 2 in a direction away from the casing 1 , the interior of the casing 1 is accessible from outside and the fuse (3, 3’) can be either inserted into the casing 1, or can also be removed there-from, by which the fuse 3, 3’ is also for sure disconnected from the electric circuit until it is open. On the other hand, upon pivoting of said cover 2 in opposite direction i.e. towards the appliance casing 1, the cover 2 perfectly matches the appliance casing 1, and the fuse 3, 3’, which is inserted therein, is arrested between said arresting seats 17, 18 within the casing 1 and is via said connectors 15, 16 on the casing 1 electrically connected with the electric circuit.

Said ventilating slots 12’, 12”, 12”’; 13’, 13”, 13’” on both lateral walls 12, 13 of the appliance casing 1 are arranged along the central area of each lateral wall 12, 13 at a sufficient distance apart from electrically conductive covers 31, 32 of the fuse 3; 3’ and also from arresting seats 17, 18 as arranged within said casing 1. Said electric fuse 3, 3’ comprises a cylindrical tubular casing 31, which consists of an electric insulating material and is on its both terminal areas closed with electrically conductive covers 31, 32, in the area of which such a fuse 3, 3’ is insertable and is usually also arrested between said electrically conductive arresting seats 17, 18 within the appliance casing 1 , and between which a melting member is arranged, which extends along the interior of said fuse casing 31 and substantially along the longitudinal geometric axis 30 of the fuse 3, 3’ and is electrically connected with each of said fuse covers 31, 32.

Said protective appliance 100 is characterized by that each group of said ventilating slots 12’, 12”, 12”’; 13’, 13”, 13’” on said lateral walls 12, 13 between the front side 11 and the rear wall 14 of the casing 1 is formed of slots, and each slot has a predetermined and uniform width W (Fig. 6), and is designed in such manner that the width W of each particular slot 12’, 12”, 12’”; 13’, 13”, 13”’ does not exceed the distance L between each two neighboring slots 12’, 12”, 12’”; 13’, 13”, 13’”.

Moreover, both disposable groups of slots 12’, 12”, 12’”; 13’, 13”, 13’” on both lateral walls 12, 13, namely a group of slots 12’, 12”, 12’” on the one lateral wall 12 and the group of the slots 13’, 13”, 13’” on the opposite lateral wall 13, are at a pre-determined distance S offset with regard to each other in the longitudinal direction of said appliance casing 1, namely i.e. substantially in a direction along the central geometric axis 30 of the fuse 3, 3’, wherein said offset distance S is determined in such manner that by each pre-determined width W of said slots 12’, 12”, 12’”; 13’, 13’, 13’” and each pre-determined distance L between each two neighboring slots 12’, 12”, 12’”; 13’, 13”, 13’” the slots 12’, 12”, 12” on the one lateral wall 12 and the slots 13’, 13”, 13’” on the opposite lateral wall 13 do not overlap each others, so that even placing of two appliance casings 1 onto the same connecting ledge adjacent to each other (Figs. 2 or 7), the ventilating slots 12’, 12”, 12” on the one lateral wall 12 of the first casing 1 and the ventilating slots 13’, 13”, 13” on the opposite lateral wall 13 of the neighboring casing 1 do not overlap each others.

Still further, each one of generally smooth and flat lateral walls 12, 13 is furnished with an laterally protruding circumferential rib 19’, 19”, which is adjusted for resting on a substantially equal rib 19’, 19” on the casing 1 of each neighboring protective appliance 100, wherein however said rib 19’, 19” is interrupted in at least two opposite areas, wherein the length of each interruption as well as the height H of the rib 19’, 19” (Fig. 6) are determined in such manner that the circumferential air is allowed to flow freely through said ventilating slots 12’, 12”, 12’”; 13’, 13”, 13’” and also through said at least two interruptions in said ribs 19’, 19”.

Still further, said cover 2, which is intended for receiving of the fuse 3, 3’, is boxshaped and comprises a suitably designed front wall 22, which is furnished with a manipulating grip 220, a rear wall 23, which is located merely inside of the appliance casing 1 and is intended for supporting of the fuse 3, 3’, as well as two grid-shaped lateral walls 24, 25, which are intended for reliable positioning of said fuse 3, 3’ within said cover 2, and the pivoting axis 21, around which a required pivoting of said cover 2 relatively to the appliance casing 1 is allowed, is located outside of said lateral walls 24, 25, in the shown embodiment in the area of the front wall 23.

Each of said lateral walls 24, 25 of said cover 2 is formed of a group of bearing strips 24’, 24”, 24’”; 25’, 25”, 25’”, each of them having a pre-determined width T, wherein said strips 24’, 24”, 24”’; 25’, 25”, 25’” are equally spaced apart from each other and extend parallel with each other and transversally with respect to the longitudinal axis 30 of the fuse 3, 3’, and said width T of such a strip 24’, 24”, 24’”; 25’, 25”, 25’” does not exceed said distance L between each two neighboring slots 12’, 12”, 12’”; 13’, 13”, 13’” on lateral walls 24, 25 of the appliance casing 1, and wherein also the bearing strips 24’, 24”, 24’” of the first lateral wall 24 are offset with regard to the bearing strips 25’, 25”, 25’” of the residual lateral wall 25 at a pre-determined distance S in the longitudinal direction of the appliance casing 1 i.e. substantially along the central geometric axis 30 of the fuse 3, 3’, wherein said distance (S) is correlated with the previously mentioned offset of the ventilating slots 12’, 12”, 12”’; 13’, 13”, 13’” on the lateral walls 12, 13 of the appliance casing 1 and is therefore determined in such manner that in a situation, when the cover 2 is closed i.e. pivoted towards the interior of the casing 1, each one of the bearing strips 12’, 12”, 12’”; 13’, 13”, 13’” of the cover 2 is located in the area between two neighboring ventilating slots 12’, 12”, 12”’; 13’, 13”, 13’” on the adjacent lateral wall 12, 13 of the appliance casing 1, namely outside of said ventilating slots 12’, 12”, 12’”; 13’, 13”, 13’”, so that said bearing strips 24’, 24”, 24’”; 25’, 25”, 25’” do not overlap said ventilating slots 12’, 12”, 12’”; 13’, 13”, 13’”, or vice versa.

Advantage of such conceived cover 2 is, among others, that without any increasing of the width D of the appliance casing 1, which should in practice usually be 21,7 mm, it is in fact suitable for both, application of either a single fuse 3, or of a so called tandem fuse 3, 3’, which means two mutually assembled fuses having equal shape, dimensions and nominal braking capacity, which are in position adjacent to each other mechanically interconnected, e.g. welded, and are then functioning as two electrically in parallel connected classical fuses. For example, a protective appliances 100 i.e. a protective switches on the basis of a classic fuse 3 of type CH 10/14T from the ETI-catalogue and related to the standard IEC 60947-1 :2004(E) or. IEC 60947-1:2020, respectively, can be in practice used for protection of circuits against short circuit or excessive current up to the nominal current value of 32 A. If however such tandem fuse 3’ is used, then also an electric circuits with nominal current value up to 63 A at the DC voltage of 1500 V can be protected.

In one of the embodiments of said protective appliance 100, the cover 2 is pivotally insertable into said appliance casing 1 of a pre-determined width D, and is foreseen for receiving of a single electric fuse 3 with a melting member, which is in the area of its covers 31, 32 insertable between both arresting seats 17, 18 within the appliance casing 1 and is via them electrically connectable with both electric connectors 15, 16 on the appliance casing 1.

In a further embodiment of the protective appliance 100, said cover 2 is pivotally insertable into said appliance casing 1 of a pre-determined width D, which is foreseen for receiving of two electric fuses 3, 3’ with melting members, which are arranged adjacent to each other and are equal to each other with regard to nominal braking capacity, shape and dimensions, and which are in the area of their covers 31, 32 insertable between both arresting seats 17, 18 within the appliance casing 1 and are via them electrically connectable with both electric connectors 15, 16 on the appliance casing 1.

In a still further embodiment of the protective appliance 100, said cover 2 is pivotally insertable into said appliance casing 1 of a pre-determined width D, which is foreseen for receiving of two electric fuses, which are which are arranged adjacent to each other and are equal to each other with regard to their nominal braking capacity, shape and dimensions, and are electrically and also mechanically in a non-detachable manner interconnected with each other, and which are in the area of their covers 31, 32 insertable between both arresting seats 17, 18 within the appliance casing 1 and are via them electrically connectable with both electric connectors 15, 16 on the appliance casing 1. In this, said fuses 3, 3’ are preferably welded with each other in the area of their covers 32, 33 and in position, in which their casings are arranged adjacent to each other and their longitudinal geometric axes 30 extend parallel with each other, so that the length of such assembled fuses 3, 3’ corresponds to the length of each of them.

As mentioned, the appliance 100 despite to its unchanged shape and dimensions, in particular the width D, enables application of fuses 3, 3’ with higher braking capacity, wherein at the same time also a fluent and sufficiently efficient heat transfer is assured from the interior of the appliance casing 1 towards the surroundings. Said heat transfer is assured by means of suitable arrangement of said ventilating i.e. ventilating slots 12’, 12”, 12”’; 13’, 13”, 13’” on the lateral walls 12, 13 of the appliance casing 1 in combination with a grid-shaped lateral walls 24, 25 of the cover 2, which are formed of bearing strips 24’, 24”, 24’”; 25’, 25”, 25’”, which are arranged by avoiding each overlapping thereof with said ventilating i.e. ventilating slots 12’, 12”, 12”’; 13’, 13”, 13’”. Said offset distance S between groups of slots 12’, 12”, 12’”; 13’, 13”, 13”’ on the on the one and the other lateral wall 12, 13 enables that even by assembling of tightly adjacent to eavh other positioned appliance casings 1 the slots 12’, 12”, 12’”; 13’, 13”, 13’” of each two neighboring casings 1 cannot overlap each others, and in addition to that, thanks to laterally protruding ribs 19’, 19” a gap is established between each two neighboring casings 1 , which corresponds to double height H of each rib 19’, 19”. Said gap is then sufficient that the hot air from each of such casings 1 may freely flow through said offset slots 12’, 12”, 12’”; 13’, 13”, 13’” outwards from the casing 1 and then along each corresponding lateral wall 12, 13 through the gap and interrupted ribs 19’, 19” towards the surroundings. The presence and arrangement of said bearing strips 24’, 24”, 24”’; 25’, 25”, 25”’ on the cover 2 however, in addition to said freely flowing of the hot air from the area of the fuse 3, 3’ towards the slots 12’, 12”, 12’”; 13’, 13”, 13’” on the lateral walls of the casing 1, simultaneously enables much better protection of the intermediate areas between the slots 12’, 12”, 12’”; 13’, 13”, 13’” against overheating, As mentioned, said intermediate areas the slots 12’, 12”, 12’”; 13’, 13”, 13’” are the most exposed areas with regard to thermal overloading, which may in critical situations lead even to structural changes and decreasing of mechanical and insulating properties of the appliance casing 1 a such. Thanks to the disclosed concept as proposed by the invention, said areas between the slots 12’, 12”, 12’”; 13’, 13”, 13’” are from the inside merely covered by said bearing strips 24’, 24”, 24’”; 25’, 25”, 25’” of the lateral walls 24, 25 of the cover 2, and in addition to that, also between each of said bearing strips 24’, 24”, 24’”; 25’, 25”, 25”’and each neighboring lateral wall 12, 13 of the casing 1 there is still and additional gap, which still additionally reduces the thermal impacts on the lateral walls 12, 13 due to the heat generated by the fuse 3.