Fuse units are used in switch fuses. A switch fuse refers to a combination of a load switch and a fuse base. In modem switch fuses of this kind, the fuse is fitted to a detachable unit, a fuse unit, for safety reasons. The fuse unit is thus intended to receive the fuse and act as protection for the fuse and as a setting device, which will facilitate placing the fuse in the switch fuse. In addition, fuse units help to create an electrical contact between the fuse and the switch fuse.

A cartridge-model switch fuse is generally designed in such a way that the fuse unit can only be detached from the body of the switch fuse once the switch is open. Thus the power must first of all be cut by setting the switch fuse to the open position. After this, the units, which are now in a dead state, are pulled out of the switch fuse to allow the fuse to be changed. The actual fuse changing thus takes place in complete safety entirely outside the switchgear. This permits the work to be carried out in well-lit conditions, well clear of the live components. It is also possible to keep spare units, in which an operational fuse is ready installed, thus achieving a very rapid fuse change.

The invention concerns fuse units, which are intended for substantially cylindrical fuses.

In particular, the invention relates to fuse units for Neozed and Diazed types of fuses, according to standard IEC60269-3-1. The invention also relates to fuse units for other fuses, which are described in the standard CEI/IEC 269-3-1. Applicable examples of fuses according to standard UL 198C are fuse types CC and J.

The invention is intended to further improve the usability of fuse units and to create a fuse unit, in which the fuse can be changed easily and reliably without using tools.

The invention is based on equipping the fuse unit with a spring-loaded movable part, a carrier, which is arranged to push the fuse in the operating position of the fuse unit.

Further, the fuse unit is equipped with locking means, which can be used to lock the carrier into the pulled-out position while the fuse is changed. Once the new fuse has been set in place, the carrier can be released and the fuse unit pushed into place in the switch fuse. In this position, the spring pressure ensures that sufficient contact pressure to create a good electrical contact is formed between the contact parts of the fuse and fuse unit.

More specifically, the fuse unit according to the invention is characterized by what is stated in the characterizing section of Claim 1.

Considerable advantages are gained with the aid of the invention.

In the fuse unit according to the invention, the fuse can be changed easily and manually.

No separate tools are necessarily required. In addition, the spring loading of the carrier ensures a sufficient contact pressure.

The invention also has a great many preferred embodiments, by means of which significant additional advantages are gained.

For example, the carrier can be designed to travel along a track in the fuse unit, in such a way that the carrier cannot accidentally fall of the track. Thus, as the fuse unit actually has no detachable securing components, the possible loss of securing components is eliminated. Certain other solutions use a bolt, for example, to secure the fuse, for example, in which case the bolt can be lost when the fuse is changed.

If the contacts connecting the fuse unit to the external circuit are made to travel with the carrier, the additional advantage is gained that the placing of the opened fuse unit into the switch fuse is prevented.

There is also a preferred embodiment of the fuse unit, in which the fuse unit includes an angled surface, which is arranged to receive the indicator stud released by a blown fuse.

This embodiment significantly facilitates checking the condition of the fuse and

detecting a blown fuse. In a particularly preferred embodiment, a mirror-like component is also attached to the angled surface of the fuse unit, which for its part also facilitates detecting the indicator stud. Further, the fuse unit can be designed in such a way that the indicator stud is held inside the unit until the fuse is changed. This brings the advantage of preventing the indicator stud from dropping into places where it may cause disturbances.

In the following, the invention is examined with the aid of examples and with reference to the accompanying drawings.

Figure 1 shows components of one fuse unit according to the invention separated from each other.

Figure 2 shows the fuse unit of figure 1 assembled and seen at an angle from its front side.

Figure 3 shows the changing of the fuse in the fuse unit of Figure 1.

Figure 1 shows the body part 1 of the fuse unit, to which the other components are attached and inside which the fuse is fitted. The body part is manufactured from an electrically insulating material of suitable strength, for example, from a suitable plastic.

In Figure 1, the front side of the body part 1 of the fuse unit is downwards and the rear part of the body part is partly visible. In this case, the term front side of the fuse unit refers to the side of the fuse unit that remains visible when the fuse unit is set in place in the switch fuse. The rear side, in turn, refers to the part that remains at least partly inside the structure of the switch fuse. Figure 1 also shows a fixed contact 2, which is placed in a recess made for this purpose in the body part 1. The fixed contact 2 is made from a suitable electrically conductive material and a contact point 2a and contact surface 2b are formed in it. The contact point 2a is intended to form an electrical contact with the contact components of the switch fuse when the fuse unit is placed in the switch fuse.

The contact surface 2b is, in turn, intended to form an electrical contact with the fuse

placed in the fuse unit. The contact 2 also has an opening 2c, for a purpose to be disclosed later.

Figure 1 also shows a moving component 3, which in this publication is called a carrier.

Like the body part 1, the carrier can be made from electrically insulating plastic. A recess for one end of the fuse is formed in the front part of the carrier 3, while a moving contact 4 is attached to the rear part, so that the fuse pushed into the recess in the carrier 3 forms a contact with the contact surface 4b of the moving contact 4. In addition, the moving contact includes a contact point 4a, for forming an electrical contact with the contact components of the switch fuse when the fuse unit is placed in the switch fuse.

The movement of the carrier 3 and the moving contact 4 refers to movement relative to the body part 1 of the fuse unit. Movement between the carrier 3 and the moving contact 4 is preferably prevented. For the movement of the carrier 3 relative to the body part 1, a track in the body part 1 and suitable counter-surfaces in the carrier 3 are formed, allowing the carrier to move along the track towards the fixed contact 2 and away from it. The track and the counter-surfaces are preferably designed to prevent the carrier 3 from accidentally leaving the track.

Further, figure 1 shows a spring 5, which is fitted between the contact 4 and the wall of the body part 1. In this position, the spring 5 pushes the carrier 3 towards the fixed contact 2, thus helping to maintain the contact pressure between the fuse and contact surfaces 2b and 4b, when the unit is in the operating position. In other embodiments, the spring 5 can, of course, be replaced by some other piece producing the necessary spring force.

In addition, Figure 1 shows a mirror-like plate 12 and a window 13, which, in a preferred embodiment, are placed at the lower edge of the fuse unit, in a manner described in greater detail later.

Figure 2 shows the fuse unit seen from the direction of its front surface. An opening, in which the window 13 is fitted, is formed in the lower edge of the body part 1. The

window 13 then prevents a finger, tool, piece of wiring, or similar from being pushed inside the fuse unit, where it could cause a hazard by coming in contact with live components. Behind the window, an angled surface 11 is formed in the lower edge of the body part 1, and slopes from the rear edge to the front edge of the body part. The contact 2 and particularly the opening 2c in the contact 2 is set above the angled surface 11. The opening 2c is positioned in such a way that it coincides with the indicator (component 10 in Figure 3) showing that the fuse has blown, so that when the fuse blows, the indicator can fall through the opening 2c onto the angled surface 11, where it can be easily detected. In addition, in a preferred embodiment, a mirror-like plate 12 is fitted on top of the angled surface 11, so that the fuse-blowing indicator can be seen in the mirror from a large area in front of the unit. The mirror-like plate 12 also facilitates the detection of a blown fuse by showing two images, a direct image and a mirror image, of the stud of the indicator. It is also possible to see through the mirror that the fuse is operational and the blowing indicator is in place. A good and economical mirror can be manufactured from polyester, for instance.

If desired, the fuse unit can also be equipped with, for example, an electrical fuse- condition indicator.

Figure 3 shows the fuse unit in two different positions. The upper fuse unit is shown in the operating position, in which it contains the fuse 6 and in which it can be pushed into the switch fuse. The lower fuse unit is in the fuse-changing position. In the following, these two different positions are described in greater detail.

In the upper figure, in which the fuse unit is thus in the operating position, the spring 5 pushes the carrier 3 of the switch fuse towards the fixed contacts, so that the fuse 6 is pressed between the contact surfaces and forms a good electrical contact between both ends of the fuse and the contacts. In this position, the position and distance between the contact points 2a and 4a also correspond to the position and distance between the corresponding contact surfaces of the switch fuse, allowing the fuse unit to be pushed into the switch fuse.

The figure also shows a catch 7 formed in the side surface of the carrier 3 and a corresponding catch 8, which is formed in the inner edge of the body part, essentially next to the catch 7. The catches 7 and 8 are shaped and located in such a way that, when the carrier 3 is pulled back, the catches 7 and 8 lock onto each other close to the other extreme end of the path of the carrier 3 and hold the carrier 3 in this position against the loading caused by the spring 5. The catches 7 and 8 are thus intended to hold the carrier 3 in the rear position while the fuse 6 is changed. In the lower figure, the fuse unit is shown in this changing position. Once the fuse has been changed, the carrier 3 can be released from the catches 7 and 8, and the spring 5 will once again push the carrier 3 forwards. The carrier 3 can be released by either pushing the carrier 3 forwards, or by pressing the wall of the body part slightly outwards at that point where the catch 8 is formed. When this is done, the catches 7 and 8 separate from each other. Alternatively, the catches 7 and 8 can be released, for example, by rotating the unit slightly around its longitudinal axis. This movement too will release the carrier 3.

An advantageous feature of the fuse unit shown in the figures and its changing position is that, in the changing position, the distance between the contact points 2a and 4a differs from the corresponding distance in the operating position of the fuse unit. This is due to the fact that the contact point 4a of the moving contact moves with carrier 3 relative to the body part 1 and to the fixed contact 2. The deviated position of the contact point 4a in the changing position prevents the fuse unit from being put into position in the switch fuse when the carrier 3 has not been released.

The path of the carrier 3 of the fuse unit can even be designed to be longer than needed, so that a fuse that has been put in position prevents, in the operating position of the fuse unit, the carrier 3 from pressing to the end position of its path. As this allowance for additional movement is clearly greater than the tolerance of the contact openings of the switch fuse, an empty fuse unit cannot be set in place. This is because, in an empty fuse unit, the distance between the contact points 2a and 4a is not the same as the corresponding distance in a fuse unit with a fuse in place. Preventing an empty unit being set in place also brings an advantage, as inserting an empty fuse unit may cause a fault that is laborious to find, if the system incorporates a large number of fuses.