To enable maintenance and inspection of electrical equipment to be carried out safely it is necessary to isolate the equipment requiring attention from the source of electrical supply. This can be achieved by removing a contact member, for example a fuse element, from the contacts of a terminal component arranged in the circuit serving the equipment. To prevent inadvertent insertion of a fuse element or otherwise bridging the terminal contacts it is known to place an adhesive label bearing a cautionary warning over the recess normally accommodating the fuse element. A disadvantage of this arrangement is that the adhesive label can become detached, or can be easily removed, thus rendering the isolation potentially ineffective.

It is an object of this invention to provide an isolation device which prevents or deters inadvertent or unauthorised activation of an electrical component from which a contact member, normally establishing a connection between the terminal contacts, has been removed.

According to the invention there is provided an isolation device for use with an electrical component of the type having a removable contact member normally establishing a connection between electrical contacts on the component, the isolation device comprising an insert member provided with a projection extending along an axis, the projection being capable of lateral expansion with respect to the axis, the projection having a passage extending along the axis, the projection being adapted, in use, to extend into a recess vacated by the contact member, and an actuating member insertable in the passage, wherein movement of the actuating member through the passage causes lateral expansion of the projection whereby to locate the isolation device on the electrical component.

In a preferred embodiment a locking means secures the insert member and the actuating member together.

Preferably the projection includes at least one longitudinal slit.

The projection is preferably generally cylindrical in shape, the slit being formed diametrally in the projection.

A catch may be provided at a leading end of the projection, the catch being adapted in an unexpanded state of the projection to pass through an aperture provided in one of the electrical contacts and in a laterally expanded state to prevent passage of the catch through the aperture.

The passage may be of circular cross section, the diameter of which is less at the leading end of the projection than at an entrance to the passage.

The diameter of the passage may decrease gradually in a direction from the entrance of the passage to the leading end of the projection.

Preferably releasable retaining means are provided on the insert member to retain the actuating member in the operating position.

The insert member may comprise two walls extending in parallel relationship, the retaining means comprising a shoulder at an outward end of each wall, and the actuating member may comprise two side members extending in parallel relationship, wherein a rib is provided on each of the side members, each rib locating behind a shoulder when the actuating member is in the operating position.

Preferably the walls and/or the side members are flexible whereby the ribs on the actuating member can be snapped behind the shoulders on the insert member.

Each of the side walls preferably has a foot portion extending outwardly therefrom, and wherein each foot portion can engage behind a corresponding shoulder on the insert member whereby to inhibit separation of the insert member and the actuating member.

A hole is preferably provided in at least one of the walls of the insert member and a further hole is preferably provided in at least one of the side members of the actuating member, the two holes being in alignment when the actuating member is in the operating position, and wherein a locking means may pass through the aligned holes.

Preferably the locking means comprises a padlock having a body in which a pivotable hook portion can be releasably locked, the hook portion being arranged to pass through the aligned holes.

An upwardly and inwardly inclined resilient finger may be provided at an outer end of each side member of the actuating member, the fingers being biassed into engagement with the body of the padlock.

The invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a part cross-sectional end elevation of an electrical terminal component equipped with an isolation device according to a preferred embodiment of the invention.

Figure 2 shows a front elevation of a plurality of electrical components, one of which is equipped with an isolation device as shown in Figure 1, and; Figure 3 and 4 illustrate components of the isolation device shown in Figures 1 and 2.

Referring to Figures 1 and 2, an electrical terminal component 1 of a known type, is releasably attached to a mounting rail 2. The terminal component 1, which is moulded from a flame- resistant plastics, provides a fused junction between two electrical cables 3,4 forming part of an electrical circuit.

The cable 3 passes through an access opening 5 into a clamp 6 in which the cable is held firmly against a contact strip 7 by means of a screw 8. Similarly, the cable 4 passes through an access opening 9 into a clamp 10 in which the cable is held firmly against a contact strip 11 by means of a screw 12.

Countersunk holes 13,14 are provided in an upper surface 15 of the terminal component for accommodating the heads of the screws 8,12. The contact strips 7,11 extend from their respective clamps 6,10 and are formed so as to provide a gap between the strips within a recess 16. The recess extends into the terminal component 1 from the upper surface 15 thereof.

When the terminal component 1 is in use to supply an electrical current to an electrical circuit, a contact member comprising a fuse element (not shown), is located in the recess 16 so as to bridge the gap between the contact strips 7,11. An aperture 17 is provided in the contact strip 7 to enable a fuse element to be inserted into the gap. The fuse element is of a conventional type and includes a piece of fusible metal which melts and interrupts the electrical current when an excess current flows. Thus, the electrical equipment served by the circuit is protected against the effects of excess currents.

If the equipment served by the electrical circuit requires attention, for example, for maintenance or inspection purposes, the fuse holder and fuse element are removed from the terminal component 1. To prevent inadvertent or unauthorised replacement of the fuse element, a lockable isolation device 20 is secured to the terminal component 1.

The isolation device 20 comprises an insert member 21, an actuating member 22 and a locking means, which is preferably in the form of a padlock 23 of a known type.

As seen in Figure 2, the components of the isolation device 20 have a width dimension which is less than that of the terminal component 1. This enables isolation devices to be fitted to adjacent terminal components.

Referring to Figure 3, the actuating member 22, which is moulded from a plastics material, comprises a base 24 in the form of a rectangular strip. Extending perpendicularly from the base 24 at the ends thereof are two side members 25,26.

Each side member 25,26 is located inwardly from the ends of the base 24 by a small amount to provide a foot portion 27, the purpose of which is hereinafter described. Each side member 25,26 has an outwardly projecting rib 28 and, at an end remote from the base 24, an outwardly projecting ledge 29.

A hole 30 is provided in each of the side members 25,26.

Projecting upwardly and inwardly from the ledge 29 of each side member 25,26 is a resilient finger 31, each of which terminates in a short, outwardly directed lip 32. Depending from the base 24 is a cylindrical actuator pin 33 having a lead portion 34 of reduced diameter.

Figure 4 shows the insert member 21 which is also moulded from a plastics material. The insert member 21 has a base portion 40 of a generally rectangular form. Extending perpendicularly from an upper surface 41 of the base portion 40 at the ends thereof are two resilient walls 42,43. A shoulder 44 projects inwardly from the outward end of each wall 42,43.

Each wall 42,43 is provided with a hole 45.

A hollow projection 46, of generally cylindrical shape, depends along an axis from a lower surface 47 of the base portion 40. A diametrical slit 48 in the projection provides two legs 49, each of which terminates in a catch 50 terminates at a leading end of the projection 46. A tapered passage 51 extends through the base portion 40 and the projection 46, the passage having a cross-section of continuously decreasing diameter along its length from an entrance at the surface 41 to the catch 50. Two locating dowels 52 are provided on the lower surface 47, the dowels, in use, locating in the holes 13,14 provided in the terminal component 1.

Normally, the insert member 21 and the actuating member 22 are retained together as a pair. As seen in Figure 4, in which the actuating member 22 is shown in dotted lines, the actuator pin 33 is positioned within the passage 51 of the insert member 21. Separation of the actuating member 22 is inhibited in that the shoulders 44 prevent passage of the foot portions 27. If desired, separation can be achieved by flexing the two walls 42,43 outwardly until the distance between the shoulders 44 is sufficient to allow the foot portions 27 to pass through.

Referring again to Figure 1, when the equipment served by the electrical circuit incorporating the terminal component needs to be isolated, the fuse element and holder (not shown) are removed from the recess 16. The insert member 21 is positioned over the terminal components 1, enabling the projection 46 to be inserted into the recess 16. Insertion of the insert member 21 causes the catches 50 to pass through the aperture 17 so that they locate below the contact strip 7.

The two dowels 52 register with the holes 13,14 so that the insert member 21 is positioned correctly on the terminal component 1. Downward pressure on the actuating member 22 moves the pin 33 through the tapered passage 51. Due to the decreasing cross-section of the passage 51, the lead portion 34 of the pin 33 causes lateral expansion of the projection 46 with respect to the axis along which it extends by forcing apart the legs 49. Thus, in the operable position of the actuating member 22 the catches 50 are unable to pass through the aperture 17 in the contact strip 7. As the actuating member 22 approaches the operable position, the ribs 28 contact the shoulder 44 on the insert member 21. Due to their flexibility, the walls 42,43 and the side members 25,26, deflect to allow the ribs 28 to pass the shoulders 44, so enabling the latter to snap into the recesses formed between the ledges 29 and the ribs 28.

Security of the insert member 21 and the actuating member 22 in this position is achieved by locking these members together. As seen in Figure 1, the members are locked together by means of a padlock 23, a pivotable hook 53 of which passes through the aligned holes 30,45 in one of the arms 25,26 and one of the walls 42,43. The hook is locked into a padlock body 54 which is placed in position on the actuating member 22 so as to be held by the biassing effect exerted by the resilient fingers 31 thereof. It will be apparent that other types of locking means can be used.

After locking the padlock 23, the key is removed to prevent unauthorised access to the terminal component 1. A warning legend, for example, CAUTION ISOLATED'together with a unique identification number, may be inscribed on the isolation device. The padlock key may be stored at a secure location and kept with the relevant identification number of the isolation device. Provision may be made to ensure that the key can be withdrawn only when an authorisation permit is produced.