GB2128282A

GB2128282A - Tamperproof plug

Info

Publication number: GB2128282A
Application number: GB08326341A
Authority: GB
Inventors: Brian David Hamblin
Original assignee: Hawke Cable Glands Ltd
Current assignee: Hawke Cable Glands Ltd
Priority date: 1982-10-09
Filing date: 1983-10-03
Publication date: 1984-04-26
Also published as: GB8326341D0

Abstract

Unused apertures in electrical and other fittings need to be closed by a tamper proof plug having an externally threaded body 10, a bore (16, 22) extending from one end of the body. As shown in Fig. 1, the bore can define a weakened wall (20) section which is the only part of the body to project from an aperture in which the plug is secured so that if the projecting part is gripped in an attempt to remove the plug the weakened wall will break. Alternatively, as shown in Fig. 2 the bore can be used to secure a cap 34 to the body 10, by means of a screw 32, which cap 34 covers the exposed part of the body 10 when the plug is located in an aperture. <IMAGE>

Description

SPECIFICATION Stopping plug This invention relates to a plug for closing an aperture for example an aperture in the wall of a junction box or other electrical fitting.

It is common practice to provide a number of apertures for cable glands in a junction box or other electrical fitting. However, it often happens that in the particular circumstances of the electrical wiring, cable conductors do not need to pass through all the apertures. The unused apertures, therefore, need to be closed off. Such closing-off must frequently be such as to maintain the flameproof "integrity" of the junction box or other fitting. Moreover in many environments it is a requirement that the closure shall not be removable except with the aid of a tool designed for that purpose.

The most common form of closure is an externally threaded plug which is received in the aperture which has been correspondingly tapped.

The intention is that the plug should be virtually completely received in the aperture so that no part, or only an insufficient part, projects from the junction box or other fitting which could enable someone to remove the plug. This is not too difficult to arrange in a plug of uniform section.

However, problems can arise with tapered plugs which may reach a condition where it is tight in the aperture while a part is still projecting from the wall of the junction box or other fitting.

The present invention has been made from a consideration of these problems.

According to the invention there is provided a tamper proof plug comprising a plug body having an external thread form for engagement in a corresponding thread form in an aperture, an axial bore extending from one end of the body, said bore defining a weakened wall portion adapted to break if gripped for removing the plug from the aperture and/or being adapted to secure a cap to the body for surrounding the end of the plug that is exposed after the body has been tightened in the aperture.

In one embodiment of the invention the axial bore provided at one end of the body defines a weakened wall wherbey in use when the plug is tightened in the aperture only the part of the body having the weakened wall projects from the fitting in which the aperture is located.

The invention is preferably applied to plug bodies of tapered form but it may also be used with plugs of uniform cross-section.

Specific embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Fig. 1 is an axial section through a plug in position in an aperture; and Fig. 2 is a section similar to that of Fig. 1 of another embodiment.

Referring to Fig. 1 the plug comprises a tapered body 10, which is externally threaded for engagement in a tapped bore 12 in the wall 14 of a junction box or other fitting. An axially aligned bore 16 is formed at the larger end of the plug body, the dimensions of the bore being chosen so that the wall 20 thereby defined is relatively weak.

in the embodiment shown in Fig. 1 the surface of the bore is smooth so that the thickness of the weakened wall is not uniform. In other words there will be places at the troughs of the thread where the wall 20 is most weak. Other configurations can be provided if desired. For example the surface of the bore can follow the threaded profile so that wall 20 is of uniform thickness.

At the base of the bore 1 6 an axially aligned, hexagon, or other suitable section, recess 22 is provided. The recess 22 is adapted to receive a correspondingly shaped key so that the plug can be tightened (or slackened) in the aperture 12.

If, as illustrated, a part of the plug projects from wall 14 when the plug is fully tightened in the aperture 12 then any attempt to undo the plug by gripping the projecting part will only result in the projecting part breaking off due to the weakened walls 20. The plug can stiil be removed, however, using the correct key.

In the embodiment of Fig. 2, the plug 10 has no bore 1 6. Instead the hexagon section recess 22 extends axially from the larger end of the plug body. As with the embodiment of Fig. 1, the recess 22 can receive a key for authorised insertion and removal of the plug.

A tapped bore 30 extends axially from the base of the hexagon recess 22. The bore 30 receives a bolt 32 which holds a dished cap 34 over the exposed end of the plug. The cap is provided with a recess 36 which receives the head of the bolt 32, the shank of the bolt extending through a hole 37 in the base of recess 36. The bolt head has a hexagon recess 38 which can receive a key for tightening, or slackening, the bolt 32.

The invention is not confined to the described embodiments. For example the shape of the cap 34 need not be as shown in the drawing. If desired seals may be provided to close any gap between the cap 34 and the wall 14 and also between the bolt 32 and the cap 34. In some cases it may be useful to provide for the plug to be tightened from within the fitting or other enclosure. To effect that the hexagon recess 22 can extend from the inner (left hand) end of the plug body instead of, or as well as, the hexagon recess at the other end of the plug body. In the embodiment of the kind shown in Fig. 2 where the hexagon recess extends from the inner end of the plug body and there is no such recess at the other (right hand) end, the tapped bore 30 will extend from the said other end.

Claims

1. A tamper-proof plug comprising a plug body having an external thread form for engagement in a corresponding thread form in an aperture, an axial bore extending from one end of the body, said bore defining a weakened wall portion

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Stopping plug This invention relates to a plug for closing an aperture for example an aperture in the wall of a junction box or other electrical fitting. It is common practice to provide a number of apertures for cable glands in a junction box or other electrical fitting. However, it often happens that in the particular circumstances of the electrical wiring, cable conductors do not need to pass through all the apertures. The unused apertures, therefore, need to be closed off. Such closing-off must frequently be such as to maintain the flameproof "integrity" of the junction box or other fitting. Moreover in many environments it is a requirement that the closure shall not be removable except with the aid of a tool designed for that purpose. The most common form of closure is an externally threaded plug which is received in the aperture which has been correspondingly tapped. The intention is that the plug should be virtually completely received in the aperture so that no part, or only an insufficient part, projects from the junction box or other fitting which could enable someone to remove the plug. This is not too difficult to arrange in a plug of uniform section. However, problems can arise with tapered plugs which may reach a condition where it is tight in the aperture while a part is still projecting from the wall of the junction box or other fitting. The present invention has been made from a consideration of these problems. According to the invention there is provided a tamper proof plug comprising a plug body having an external thread form for engagement in a corresponding thread form in an aperture, an axial bore extending from one end of the body, said bore defining a weakened wall portion adapted to break if gripped for removing the plug from the aperture and/or being adapted to secure a cap to the body for surrounding the end of the plug that is exposed after the body has been tightened in the aperture. In one embodiment of the invention the axial bore provided at one end of the body defines a weakened wall wherbey in use when the plug is tightened in the aperture only the part of the body having the weakened wall projects from the fitting in which the aperture is located. The invention is preferably applied to plug bodies of tapered form but it may also be used with plugs of uniform cross-section. Specific embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Fig. 1 is an axial section through a plug in position in an aperture; and Fig. 2 is a section similar to that of Fig. 1 of another embodiment. Referring to Fig. 1 the plug comprises a tapered body 10, which is externally threaded for engagement in a tapped bore 12 in the wall 14 of a junction box or other fitting. An axially aligned bore 16 is formed at the larger end of the plug body, the dimensions of the bore being chosen so that the wall 20 thereby defined is relatively weak. in the embodiment shown in Fig. 1 the surface of the bore is smooth so that the thickness of the weakened wall is not uniform. In other words there will be places at the troughs of the thread where the wall 20 is most weak. Other configurations can be provided if desired. For example the surface of the bore can follow the threaded profile so that wall 20 is of uniform thickness. At the base of the bore 1 6 an axially aligned, hexagon, or other suitable section, recess 22 is provided. The recess 22 is adapted to receive a correspondingly shaped key so that the plug can be tightened (or slackened) in the aperture 12. If, as illustrated, a part of the plug projects from wall 14 when the plug is fully tightened in the aperture 12 then any attempt to undo the plug by gripping the projecting part will only result in the projecting part breaking off due to the weakened walls 20. The plug can stiil be removed, however, using the correct key. In the embodiment of Fig. 2, the plug 10 has no bore 1 6. Instead the hexagon section recess 22 extends axially from the larger end of the plug body. As with the embodiment of Fig. 1, the recess 22 can receive a key for authorised insertion and removal of the plug. A tapped bore 30 extends axially from the base of the hexagon recess 22. The bore 30 receives a bolt 32 which holds a dished cap 34 over the exposed end of the plug. The cap is provided with a recess 36 which receives the head of the bolt 32, the shank of the bolt extending through a hole 37 in the base of recess 36. The bolt head has a hexagon recess 38 which can receive a key for tightening, or slackening, the bolt 32. The invention is not confined to the described embodiments. For example the shape of the cap 34 need not be as shown in the drawing. If desired seals may be provided to close any gap between the cap 34 and the wall 14 and also between the bolt 32 and the cap 34. In some cases it may be useful to provide for the plug to be tightened from within the fitting or other enclosure. To effect that the hexagon recess 22 can extend from the inner (left hand) end of the plug body instead of, or as well as, the hexagon recess at the other end of the plug body. In the embodiment of the kind shown in Fig. 2 where the hexagon recess extends from the inner end of the plug body and there is no such recess at the other (right hand) end, the tapped bore 30 will extend from the said other end. Claims

1. A tamper-proof plug comprising a plug body having an external thread form for engagement in a corresponding thread form in an aperture, an axial bore extending from one end of the body, said bore defining a weakened wall portion adapted to break if gripped for removing the plug from the aperture and/or being adapted to secure a cap to the body for surrounding the end of the plug that is exposed after the body has been tightened in the aperture.

2. A plug as claimed in Claim 1, wherein the bore defines a weakened wall whereby in use when the plug is tightened in the aperture only the part of the plug having a weakened wall projects from the fitting in which the aperture is located.

3. A plug as claimed in Claim 1 or Claim 2 wherein the exterior of the body is tapered.

4.,A plug as claimed in any preceding claim wherein the axial bore is of uniform cross-section.

5. A plug as claimed in any preceding claim wherein means is provided in the base of the bore for assisting insertion of the plug into the aperture or removal of the plug from the aperture.

6. A plug as claimed in any preceding claim, wherein the cap is dished to receive means for securing the cap to the body.

7. A plug as claimed in any preceding claim, wherein the plug is adapted to be secured in, or removed, from, the aperture by the same means as will secure the cap to, or remove the cap from, the body.

8. A tamper proof plug substantially as described herein with reference to Fig. 1 or Fig. 2 of the accompanying drawing.