GB2193053A - Fuse unit - Google Patents

Abstract

A fuse unit includes a removable fuse link carrier 1A, 1B and a base assembly including terminals for cables, each terminal having a female socket recess with opposed side walls, said assembly further including a shroud member 11 and a base member 12 releasably connectable thereto whereby, in use, to shroud said cable terminals. The fuse link carrier includes at least one fuse link having a pair of probe contacts 3 with downwardly depending contact blades 4, 5, each blade being provided, at or adjacent the free end thereof, with at least one outwardly extending protrusion 34, wherein, during location of a fuse link within said unit, each protrusion 34 engages the associated side wall of a socket recess of a cable terminal. The leading ends of said blades initially enter the female socket recess thereby assisting in the correct disposition of said blades relative to the cable terminal, and thereafter said protrusions 34 first come into engagement with upper corners or edges of said opposed side walls of said female socket recess and thereafter with said side walls themselves whereby to afford improved physical and electrical contact between said blades and said cable terminal. <IMAGE>

Description

SPECIFICATION Fuse unit The present invention relates, in general, to a fuse unit of the type including a fuse cartridge carrier member of a suitable material, such as for example a dielectric material, enclosing a cartridge and having probe contacts associated therewith and adapted to be inserted into terminals provided in a fuse base assembly.

The invention relates more particularly to improvements in such fuse units.

In accordance with the known art fuse units of the type under consideration are generally manufactured from mouldable materials, with what might be termed the housing being manufactured from a material such as, for example, a phenolic resin or a thermoplastic material, and with metal parts being employed as current-carrying components.In one known embodiment a fuse unit of this general type will comprise two distinct and separable assemblies, including at least one removable fuse link carrier or top containing appropriate fuse contacts and furthermore having means for securing, in use, a suitably rated fuse link thereto, and further including a base assembly comprising moulded components and containing at least two cable terminals having provision for engagingly accepting the fuse contacts so as to provide electrical continuity from at least one incoming cable, through the fuse link, to at least one outgoing cable.The components of such a base assembly usually include a base section containing the cable terminals or terminal blocks and a top section or so-called top plate or shroud, which in use is adapted to be separable from said base section to allow for access of or to cable terminals during installation, or alternatively for purposes of maintenance. When such a fuse unit is in use removal of the top plate portion would result in the exposure of live terminals and therefore, for purposes of safety, at least those terminals associated with the incoming cable or cables need to be separately shrouded.The cable terminals used in such fuse units are generally speaking of the tunneltype containing appropriate means, such as for example slotted-head type pinching screws or the like, which are adapted to be brought into contact with the ends of cables inserted into the tunnels of the cable terminals or terminal blocks whereby to clamp the cable conductors in position relative to the terminals.

In accordance with the present invention, therefore, there is provided a fuse unit including a removable fuse link carrier and a base assembly including terminals for cables, each terminal including a female socket recess having opposed side walls, said base assembly further including a shroud member and a base member connectable thereto whereby, in use, to shroud said cable terminals, wherein said fuse link carrier includes at least one fuse link including a pair of probe contacts in the form of a pair of downwardly depending contact blades, in spaced-apart parallel relationship, each contact blade being provided, at or adjacent the free or leading end thereof, with at least one outwardly extending shaped protrusion, and wherein, during location of a fuse link within said unit, the or each protrusion on each contact blade comes into engagement with the associated side wall of a socket recess of a cable terminal, the arrangement being such that the leading ends of said blades initially enter the female socket recess, thereby assisting in the correct disposition of said blades relative to the cable terminal, and thereafter said protrusions first come into engagement with upper corners or edges of said opposed side walls of said female socket recess and thereafter with said side walls themselves whereby, in use, to afford improved physical and electrical contact between said blades and said cable terminal.

In order that the invention may be more clearly understood and put into practical effect there shall now be described in detail a preferred embodiment of a fuse unit in accordance with the invention. The ensuing description is given by way of non-limitative example only and is with reference to the accompanying drawings, wherein:: Fig. 1 is a side elevational view of an assembled fuse unit in accordance with the invention; Fig. 2 is an end view of the unit of Fig. 1; Fig. 3 is a plan view of the unit of Figs. 1 and 2; Fig. 4 is an underneath view of a unit in accordance with the present invention; Fig. 5 is a perspective view from above of the unit of Fig. 1, with parts separated; Fig. 6 is a perspective view from underneath of the unit of Fig. 1; Fig. 7 is a sectional view taken along the line 7-7 in Fig. 3; Fig. 8 is a view taken along the line 8-8 in Fig. 7; Fig. 9 is a sectional view showing the various components in partially assembled condition; Fig. 10 is an exploded view of portion of the base of a fuse unit in accordance with the present invention; and Fig. 11 is a view taken along the line ll-ll in Fig. 10.

In the drawings there is illustrated a fuse unit in accordance with the present invention, such a unit including, as principal components, a removable fuse link carrier, generally designated as 1, adapted to receive and retain a fuse link or probe contact, and a base assembly generally designated as 2. In the preferred embodiment illustrated the carrier 1 includes two such probe contacts, generally designated 3, each contact 3 being con structed from a continuous strip of an appropriate material so formed as to provide a pair of downwardly extending, spaced-apart opposed blades 4 and 5 and having a curved loop 6 adapted to join one end of one blade 4 to the adjacent end of the other blade 5.

Preferably each loop 6 will be of a substantially circular shape. The carrier 1 is preferably formed from two housing components, designated 1A and 1B, of a substantially complementary shape, each component 1A, 1B being recessed and adapted to receive and house substantially one half of a probe contact 3. In the embodiment illustrated each contact 3 is adapted in use, by means of a pin, clamping screw or the like (generally designated as 7), to provide adequate electrical contact by means of tightening the inserted fuse link and then mechanicaily securing the fuse link or probe contact in a housing component 1A.

Each housing component may be constructed from a block of insulating material (of any known type) and is so shaped as to allow for the housing therein of the loops of the probe contacts 3. The arrangement is such that, when brought into juxtaposition, the blades 4 and 5 of each probe contact 3 project downwardly from the fuse unit, as illustrated for example in Fig. 9, whereby to allow for location as desired within the base assembly 2 (in a manner to be described hereinafter).

The unit in accordance with the present invention furthermore includes a base assembly 2, that assembly 2 including a so-called topplate or shroud member 11 and a base member 12. The members 11 and 12 are to be manufactured separately from a suitable dielectric material and are adapted, in use, to be either permanently or releasably connected in any known manner. In an especially preferred embodiment, as illustrated, the members 11 and 12 are substantially permanently joined when assembled, through the use of a hollow rivet, threaded pin or the like 13 adapted to be located within adjoining and complementary bores provided in the members 11 and 12.

The base member 12 includes a cable guide assembly 14 at each side thereof, each cable guide assembly 14 having a pair of bores 15 therein in substantial alignment with and leading to respective tunnels of a cable terminal or cable block 16 adapted for location within the base member 12. The base member 12 is in the form of a recessed body of a suitable insulating material, as for example a dielectric material, the recess being divided into two compartments 17 and 18, by any suitable means, as for example a partition wall 19.

Each such compartment 17, 18 is then adapted to receive and retain a cable terminal, cable block or terminal block 16 therein. The partition wall 19 preferably includes a centrally disposed opening adapted to be in alignment with a similar opening on the top plate or shroud member 11 relative to said base member 12, whereby to allow for interconnection of the members 11 and 12 by means 13 (as previously described).

The open face of the base member 12 is, in use, adapted to be closed by the top plate or shield member 11, leaving spaced apertures each in alignment with a contact probe receiving recess or female socket recess in the associated terminal block 16.

Insofar as the terminal blocks 16 are concerned, cable conductor pinching screws 20 are seated in threaded bores 21 extending through the terminal block 16 into tunnels 22 thereof. Such pinching screws 20 (or the equivalent) serve to secure cable conductors 23 in a tunnel 22 and to provide additional electrical contact area. Preferably the pinching screws or the like 20 are of substantially the same diameter as the tunnels 22 of the terminal block 16 so as to prevent the cable conductors 23 from slipping out, whereby to prevent unwanted withdrawal of those cable conductors 23. The outer end of each pinching screw 20 may be provided with means allowing for rotation thereof for purposes of releasing or clamping conductors 23.In an especially preferred embodiment such a result may be achieved by the use of a pinching screw provided with a shaped head for engagement by or with a screwdriver or the like tool. In an alternative embodiment this result may be achieved by the provision of a shaped socket for engagement by or with a complementaryshaped wrench or the like tool.

The top plate or shield member 11 may be in the form of a substantially parallelepipedal box-like component adapted, in use, to be either releasably or permanently connected to the base member 12. As stated earlier, in an especially preferred embodiment such connection may be achieved in any suitable manner, such as for example by means of an open rivet or the like. Alternatively an adhesive or any other known joining means may be employed.

The top plate member 11 includes an intermediate wall 30 having slots or apertures 31 therein whereby to allow for passage therethrough of the probe contacts 3, and furthermore includes a plurality of circular holes so disposed as to be in alignment with the axis of rotation of a respective one of the aforementioned fixing or pinching screws 20.

As illustrated in Fig. 9, with the arrangement according to the present invention the distance between the outer surfaces of-the blades 4 and 5 is less than the distance which exists between the side walls of adjacent terminals of the associated terminal block 16, or in other words is less than the internal diameter of the cavity 16A of the terminal block 16 intended to receive the blades 4 and 5 in electrical connection. By reason of this, the leading ends of the blades 4 and 5 can be expected to be capable of being readily located within the socket recess of the terminal block 16, with there in fact existing a clearance (albeit small) between those leading ends and the walls of the cavity.

The projecting ends of the or each probe contact 3 provide electrical contact with inwardly facing surfaces of the associated cable terminal block 16 and are secured at their other ends to the top member so as to provide electrical continuity from the conductors of an incoming cable, through the fuse link or probe contact 3, to the conductors of an outgoing cable. The contact pressure of the probe contact 3 onto the surface of the terminal block 16 may be enhanced by the use of leaf springs 33 secured in any known manner (as for example by staking or crimping) at or adjacent to the free ends of the contact blades 4 and 5, the leaf spring 33 being intended to increase resistance between the free ends of the probe contact 3 and ensure greater frictional contact with the sides of the female socket recess provided in the terminal block 16.

Also associated with each free end of the blades 4, 5 of each probe contact 3 is at least one protrusion 34. Preferably the protrusion 34 may be formed integrally with the blades 4 and 5, as for example by stamping out therefrom. In an alternative embodiment, however, the protrusions may be in the form of a shaped piece of the appropriate material (metal) to be affixed to the relevant blades in any known manner. The protrusions 34, preferably in the form of a tear-drop or dimple shape, serve a dual purpose.

First of all, however, it must be remembered that the blades 4 and 5 themselves, as previously discussed, afford the probe contact 3 with a leading end of a reduced width when compared with the width of the female socket recess of the terminal block 16 thereby providing what might be termed a lead-in to assist in location of the probe contact 3 within the terminal block 16. In actual fact the arrangement is such that the distance between the outermost surfaces of each pair of contact blades is marginally less than the internal diameter of the female socket recess of a cable terminal 16, that factor initially assisting in locating the contact blades 4 and 5 appropriately or correctly within the socket recess.

The protrusions 34, by reason of their size, shape and actual location on the probe contact 3 (and associated blades 4 and 5) provide the probe contact 3 with at least one section having a width which is greater than the internal diameter of the female socket recess of the terminal block 16. In practice, therefore, the blades 4 and 5 initially enter the terminal block recess with clearance, but the protrusions 34 subsequently come into engagement with the side walls of the female socket recess. The blades 4 and 5 are then in effect forced towards one another against the base of the leaf spring 33. Such an arrangement, in a practical sense, has been found to exhibit a number of advantages as compared with the prior art.By way of example, the need for a perhaps unacceptably close tolerance relationship of the distance between the outer surfaces of the respective members of the or each pair of blades 4 and 5, and the internal diameter of the female recess of the terminal block 16, would be markedly reduced, if not removed altogether. The ramifications of this, in a manufacturing sense, should be self-evident.

Secondly, by in effect ensuring a pressuretype fit between the probe contacts 3 and terminal block 16, the protrusions in use provide for enhanced electrical contact between the probe contacts 3 and associated terminal block 16. In the preferred embodiment illustrated two such protrusions or dimples 34 are provided on each blade 4, 5 of a probe contact 3, thereby providing for or ensuring effective four-point contact between the or each probe contact 3 and its associated terminal block 16, hence affording improved physical and electrical contact.

As illustrated, for example, in Figures 1, 2 and 6, the removable fuse link carrier 1 includes, on each side thereof, finger grip means 40, in the form of a knurled or serrated section, whereby to afford improved grip.

The arrangement in accordance with the present invention exhibits a number of advantages over the prior art. Perhaps the most important of these relate to improved safety and the provision of a facility or means for sealing the unit against unlicensed or illegal usage of power on or in vacant premises.

It should be understood that the aforegoing description refers merely to preferred embodiments of the invention, and that variations and modifications are possible thereto without departing from the scope of the invention.

Claims (8)

1. A fuse unit including a removable fuse link carrier and a base assembly including terminals for cables, each terminal including a female socket recess having opposed side walls, said base assembly further including a shroud member and a base member connectable thereto whereby, in use, to shroud said cable terminals, wherein said fuse link carrier includes at least one fuse link including a pair of probe contacts in the form of a pair of downwardly depending contact blades, in spaced-apart parallel relationship, each contact blade being provided, at or adjacent the free or leading end thereof, with at least one outwardly extending shaped protrusion, and wherein, during location of a fuse link within said unit, the or each protrusion on each con tact blade comes into engagement with the associated side wall of a socket recess of a cable terminal, the arrangement being such that the leading ends of said blades initially enter the female socket recess, thereby assisting in the correct disposition of said blades relative to the cable terminal, and thereafter said protrusions first come into engagement with upper corners or edges of said opposed side walls of said female socket recess and thereafter with said side walls themselves whereby, in use, to afford improved physical and electrical contact between said blades and said cable terminal.

2. The fuse unit as claimed in Claim 1, wherein said shroud and base members are releasably interconnectable, by means of a screw or the like threaded-member adapted for insertion into a complementary-shaped threaded bore associated with each said member.

3. The fuse unit as claimed in Claim 1 or Claim 2, including two terminal blocks in said base assembly and two fuse links in said fuse link carrier.

4. The fuse unit as claimed in any one of the preceding Claims, wherein the distance between outermost surfaces of each said pair of contact blades is less than the internal diameter of said female socket recess of each said cable terminal.

5. The fuse unit as claimed in Claim 4, wherein the distance between outermost surface regions of opposed protrusions on respective blades of each said pair of blades is greater than the internal diameter of said female socket recess of each- said cable terminal.

6. The fuse unit as claimed in any one of the preceding Claims, constructed substantially of an electrically insulating material.

7. The fuse unit as claimed in any one of the preceding Claims, wherein said fuse link carrier includes, at each side thereof, means affording improved grip thereon, said means being in the form of a knurled or serrated portion.

8. A fuse unit, substantially as described herein with reference to the accompanying drawings.