GB2322742A

GB2322742A - An electrical isolation device

Info

Publication number: GB2322742A
Application number: GB9803385A
Authority: GB
Inventors: Shepherd Richard; Ian Harrison
Original assignee: British Nuclear Fuels PLC
Current assignee: Sellafield Ltd
Priority date: 1997-02-21
Filing date: 1998-02-19
Publication date: 1998-09-02
Anticipated expiration: 2018-02-19
Also published as: GB9803385D0; GB9703654D0; GB2322742B

Abstract

An isolation device 17 for use with an electrical component which has a fuse holder 6 movable to a position in which a fuse element can be removed from the holder comprises a locating member 18 adapted to retain the fuse holder in this position and to prevent re-insertion of a fuse element. A padlock 30 secures the locating member 18. The fuse holder 6 is retained by a catch 25 which extends into a recess provided to accommodate the fuse holder. The locating member 18 is shaped so that it can be used to retain the fuse holder only when a switch actuator 5 on the component is in an inoperative position.

Description

An Electrical Isolation Device The present invention relates to an isolation device for use with an electrical terminal component. In particular, the invention relates to an isolation device for use with an electrical terminal component of the type incorporating a fuse element normally establishing an electrical connection between two contacts of the terminal component.

In the maintenance or inspection of electrical equipment it is often desirable for safety reasons to isolate the equipment requiring attention from the source of electrical supply. This can be achieved by removing a fuse element from a terminal component arranged in the circuit serving the equipment. In certain circumstances it is essential that unauthorised or inadvertent replacement of a fuse element is prevented. Known methods of ensuring that the fuse element cannot be replaced without authority to do so have not proved to be satisfactory.

It is an object of this invention to provide an isolation device which prevents the undesired insertion of a fuse element in an electrical terminal component.

According to the invention there is provided an isolation device for use with an electrical component of the type comprising a fuse holder in which is mounted a removable fuse element, the fuse holder being movable between a first position, in which a fuse element mounted in the fuse holder establishes a connection between electrical contacts on the electrical component, and a second position, in which the fuse element can be removed from the fuse holder, the isolation device comprising a locating member adapted to retain the fuse holder in the second position and to prevent insertion of a fuse element into the fuse holder.

Preferably, locking means are provided for securing the locating member.

The locking means preferably comprises a padlock having a pivoted hook portion arranged to pass through the locating member.

The locating member may include a cut-away portion which accommodates the fuse holder, and wherein a catch extends into said cut-away portion to engage and retain the fuse holder in the second position.

The cut-away portion may be bounded by two arms which pass on either side of the fuse holder, wherein the hooked portion of the padlock passes through each of the two arms.

The electrical component may further include a switch actuator positioned adjacent to the fuse holder, the locating member being provided with a cavity for receiving the switch actuator.

Advantageously the locating member is shaped so as to retain the fuse holder in the second position only when said actuator is in the inoperative position.

The cavity may include an inclined surface having an angle of inclination which corresponds substantially to an angle of inclination of a surface of the switch actuator when the actuator is positioned in an inoperative position.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a front elevation of an electrical terminal component to which an isolation device according to the present invention can be fitted; Figure 2 is a part cross-sectional elevation taken on the line II-II in Figure 1; Figure 3 is an isometric view showing an isolation device according to the present invention mounted on the electrical terminal component shown in Figure 1; Figures 4 and 5 show two elevations of a locating member forming part of the isolation device illustrated in Figure 3, and Figure 6 is a view taken in the direction of arrow A shown in Figure 3.

Referring to Figures 1 and 2 there is shown an electrical terminal component in the form of a known type of junction box 1. The junction box 1 houses terminals to which electrical wires can be secured and comprises a casing 2 and a removable cover 3 attached to the casing by two screws 4. Incorporated in the junction box is a pivotable switch actuator 5 and a fuse holder 6. Mounted in the fuse holder 6 is a removable fuse element 7 of a known type comprising a piece of fusible metal which melts and interrupts the electrical current when an excess current flows, thereby protecting the electrical equipment served by the circuit. The switch actuator 5 and the fuse holder 6 are arranged in a moulded plastic mounting 8 attached to the cover 3. The fuse holder 6 extends into a recess 9, at least a portion of which is formed in the mounting 8.

The fuse holder is a moulded plastic component comprising a head 10 from which extends a body portion 11. Beneath the head 10 and extending transversely to the length of the body portion 11 are an upper rib 12 and a lower rib 13. When the junction box 1 is in service, the fuse element 7 is mounted between the upper and lower ribs 12, 13 so as to establish an electrical connection between the contacts in the junction box 1. The fuse holder 6 is secured in the junction box 1 by a captive screw 14 which extends through the head 10 to engage with a screw threaded boss 15 fixedly mounted within the casing 2. A catch 16 protrudes from the body 10 at an end thereof remote from the head 10 for a purpose hereinafter to be described.

If it becomes necessary to isolate the electrical equipment served by the junction box 1, for example, to carry out maintenance procedures, the fuse element 9 is removed. This is achieved by rotating the screw 14 so that it is removed from the boss 15. When the screw 14 is clear of the boss 15, the fuse holder 6 can be withdrawn by an amount sufficient to enable the fuse element 9 to be removed. Complete withdrawal of the fuse holder 6 from the junction box 1 is prevented by engagement of the catch 16 with the boss 15.

To prevent inadvertent or unauthorised replacement of the fuse element, a lockable isolation device 17 (see Figure 3) is fitted to the junction box 1. The isolation device 17 comprises a locating member 18 which is more clearly shown in Figures 4 and 5, to which reference is now made.

The locating member 18, which may conveniently be a moulding of plastics material, is generally in the form of a parallelepiped. A cut-away portion 19 is bounded on either side by two arms 20, 21. Extending from cut-away portion 19 in a lower surface 22 of the locating member 18 is a wedge-shaped cavity 23 having an inclined upper surface 24. The greatest depth of the cavity 23 from the lower surface 22 lies on a continuation of the inner surface of the arm 20. Protruding into the cut-away portion 19 from the inner surface of the arm 21 is a catch 25, the lower surface of which is contiguous with the inclined surface 24 of the cavity 23. The lower surface 22 of the locating member 18 is relieved by a shallow channel 26 to provide a raised strip along each side of the member. Coaxial holes 27, 28 are provided towards the ends of the two arms 20, 21, respectively, to receive a pivoted hook portion 29 of a conventional padlock 30, as seen in Figures 3 and 6.

When the equipment served by the junction box 1 requires electrical isolation, the switch actuator 5 is pivoted to an inoperative or "off" position and then the fuse element 7 is removed. This requires unscrewing the screw 14 until it is clear of the boss 15. This will allow withdrawal of the fuse holder 6 through the recess 9 until the catch 16 comes into contact with the boss 15.

In this position the fuse element 7 can be extracted from the fuse holder 6. To install the isolation device 17, the raised strips on the lower surface 22 of the locating member 18 are moved along the surface of the cover 3 so that the arms 20, 21 pass on either side of the head 10 of the withdrawn fuse holder 6. When the switch actuator 5 is in the inoperative position, the angle of inclination of the upper surface of the switch actuator 5 with respect to the surface of the cover 3 corresponds to the angle of inclination of the cavity surface 24. Thus, the switch actuator 5 can pass into the cavity 23. It will be apparent that if the switch actuator 5 is in the operative or on' position, it will not pass into the cavity 23. By ensuring that the isolation device 17 can be fitted only when the switch actuator 5 is in the 'off' position, an additional safety feature is provided. When the locating member 18 is in position the catch 25 extends into the space formerly occupied by the fuse element and locates under the upper rib 12 to maintain the fuse holder 6 in the withdrawn position. To secure the locating member 18 to the fuse holder 6, the padlock hook 29 is passed through the holes 27, 28 and then locked into the padlock body 30. The key required to unlock the padlock 30 is stored at a secure location to prevent unauthorised access to the junction box 1. The fuse holder 6 is therefore locked in position and serves as a shielding member to prevent insertion of a fuse element into the junction box 1.

A warning legend, for example, 'CAUTION ISOLATED', together with a unique identification number, may be inscribed on the upper surface of the locating member 17.

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 upon producing an authorised permit.

Claims

1. An electrical isolation device for use with an electrical component of the type comprising a fuse holder in which is mounted a removable fuse element, the fuse holder being movable between a first position in which a fuse element mounted in the fuse holder establishes a connection between electrical contacts on the electrical component and a second position, in which the fuse element can be removed from the fuse holder, the isolation device comprising a locating member adapted to retain the fuse holder in the second position and to prevent insertion of a fuse element into the fuse holder.

2. An electrical isolation device according to Claim 1, wherein locking means are provided for securing the locating member.

3. An electrical isolation device according to Claim 2, wherein the locking means comprises a padlock having a pivoted hook portion arranged to pass through the locating member.

4. An electrical isolation device according to any one of Claims 1 to 3, wherein the locating member includes a cut-away portion which accommodate the fuse holder, and wherein a catch extends into the cut-away portion to engage and retain the fuse holder in the second position.

5. An electrical isolation device according to Claim 4 when dependent on Claim 3, wherein the cut-away portion is bounded by two arms which pass on either side of the fuse holder, and wherein the hook portion of the padlock passes through each of the two arms.

6. An electrical isolation device according to any one of the preceding Claims, the electrical component further including a switch actuator positioned adjacent to the fuse holder, wherein the locating member is provided with a cavity for receiving the switch actuator.

7. An electrical isolation device according to Claim 6, wherein the locating member is shaped so as to retain the fuse holder in the second position only when the actuator is in the inoperative position.

8. An electrical isolation device according to Claim 7, wherein the cavity includes an inclined surface having an angle of inclination which corresponds substantially to an angle of inclination of a surface of the switch actuator when the actuator is in an inoperative position.

9. An electrical isolation device substantially as hereinbefore described with reference to the accompanying drawings.