WO2000046881A1

WO2000046881A1 - Electrical coupler

Info

Publication number: WO2000046881A1
Application number: PCT/AU2000/000063
Authority: WO
Inventors: Milos Starec; Rado Starec; James Gerard Cowhey
Original assignee: Modular Connections Australia Pty Ltd.
Priority date: 1999-02-03
Filing date: 2000-02-03
Publication date: 2000-08-10
Also published as: AUPP845699A0; GB2362767A; GB2362767B; GB0121309D0

Abstract

A plug (50) for an electrical coupler including a conducting pin (94) with an exposable forward end (51) for establishing electrical contact with an electrical contact of a corresponding socket; and a sleeve (62) for selectively providing or restricting access to the pin (94), moveable between a first, rearward position and a second, forward position; wherein when the sleeve is in the first position the sleeve is substantially rearward of the forward end of the pin whereby the forward end of the pin is exposed to allow access to the forward end of the pin, and when the sleeve is in the second position the forward end of the pin is substantially concealed by the sleeve to restrict access to the forward end of the pin.

Description

ELECTRICAL COUPLER

The present invention relates to an electrical coupler, of particular but by no means exclusive use with ring mains.

Existing electrical couplers comprise a plug, with one or more exposed conducting pins, and a socket with electrical contacts generally concealed within a casing or housing.

In some existing couplers, the pins of the plug are surrounded by an insulating sleeve to protect or shield the pins. This sleeve may also be adapted to receive at least part of the socket housing so that any mechanical load to which the coupler is exposed (when the plug and socket are coupled) is borne by the sleeve-housing connection rather than the pin-contact connection(s) .

The benefit provided by this sleeve's shielding the pins is twofold: the pins are shielded from damage (if, for example, a heavy article is dropped on the plug), and in those cases where the plug (i.e. one or more of the pins) is live, a person handling the plug is less likely to touch the live pins and thereby risk an electric shock. However, the protection thus offered will be, in some applications, far from optimal as the pins are still readily accessible at their forward end. Indeed, safety regulators in some jurisdictions recjuire that such pins, even if surrounded by such a sleeve, should never be live or able — in the course of normal use — to be made live.

In certain countries, such as the United Kingdom, this issue is of particular significance owing to the standard use of ring mains. In such mains the live wire and therefore pin remains live even when the ring main is interrupted. This is generally of little concern as an occupant of a building wired in this manner can only gain access to the electrical supply via a general power outlet comprising a socket with fully recessed electrical contacts. However, the more recent development of modular building wiring systems, which comprise cabling and power outlets connected with plug and socket couplers and which are designed for quick installation and convenient reconfiguration, has meant that electricians may frequently be required to interrupt a ring main by unplugging a component of the wiring system, generally either a cable or power outlet. In many cases it may be either undesirable to switch off the power supply at the mains (so that vital electrical equipment can be kept running) , or simply inconvenient, but — with a conventional electrical coupler — this would expose the electrician to often unacceptably high risk of contact with the live pins of the plug, whether or not they are surrounded by a conventional sleeve.

Examples of a prior art plug and socket are illustrated in figures 1A and IB respectively. Referring to figure 1A, the prior art plug 10 includes a casing 12 of moulded plastic and three conducting pins 14. The casing 12 includes a sleeve 16 around pins 14: the sleeve 16 shields the pins 14 from damage, and reduces the likelihood of a user inadvertently coming into contact with pins 14, should they be live. The sleeve 16 also includes a number of keyways 18, 20a and 20b, which correspond to ridges provided in prior art socket 30 (see figure IB), to ensure that plug 10 and socket 30 can be connected with only the intended relative orientation.

Plug 10 further includes latch 22 with two catches (not shown but projecting downwards as illustrated from the lower surface of latch 22) for engaging corresponding rebates 32a and 32b in socket 30, to more securely engage plug 10 and socket 30 in use.

Referring to figure IB, prior art socket 30 includes a casing 34 of moulded plastic and containing conducting electrical contacts (not shown) accessible through slots 36, which are adapted to receive pins 14 of plug 10, but otherwise concealed. Socket 30 includes ridges 38a and 38b, corresponding to keyways 20b and 20a respectively, and a bottom ridge (not shown) corresponding to keyway 18 of plug 10. A groove 40 is provided between adjacent rebates 32a and 32b, so that—in use—a screwdriver or the like may be inserted under latch 22 to lift latch 22 and withdraw the catches of latch 22 from rebates 32a and 32b and hence allow the decoupling of plug 10 and socket 30.

It will readily be seen that the level of shielding of a user provided by sleeve 16 will generally be adequate in those electrical arrangements where plug 10 ceases to be live when it is disconnected from socket 30.

However, when employed in a ring main, both plug 10 and socket 30 remain live even when disconnected from one another. The electrical contacts of socket 30 will be satisfactorily concealed in these circumstances, but a greater level of shielding of the pins 14 is clearly desirable.

Accordingly, it is an object of the present invention to provide an electrical coupler where the pins of the plug are shielded from contact by a user to a comparable extent to the electrical contacts of the socket .

The present invention provides, therefore, a plug for an electrical coupler including: a conducting pin with an exposable forward end for establishing electrical contact with an electrical contact of a corresponding socket; and a sleeve for selectively providing or restricting access to said pin, moveable between a first, rearward position and a second, forward position; wherein when said sleeve is in said first position said sleeve is substantially rearward of said forward end of said pin whereby said forward end of said pin is exposed to allow access to said forward end of said pin, and when said sleeve is in said second position said forward end of said pin is substantially concealed by said sleeve to restrict access to said forward end of said pin.

Preferably said sleeve defines a slot or aperture through which said forward end of said pin projects when said sleeve is in said first position. Preferably said slot or aperture is sized to fit said pin.

Preferably accessibility to said pin is limited to said slot or aperture when said sleeve is in said second position.

Preferably said plug includes biasing means for biasing said sleeve toward said second position

Preferably said biasing means is a spring, and more preferably a helical spring.

Preferably said plug includes disengagable locking means for locking said sleeve in said second position, to restrict the undesired movement of said sleeve from said second position towards said first position.

Preferably said locking means includes detent means. Preferably said sleeve is provided with said detent means.

Preferably said plug is provided with an engagement surface for engaging said detent means .

Preferably said locking means is disengagable by means of unlocking means provided in said socket . Thus, when the plug is unplugged from the socket, the sleeve is pulled by the socket to the second position irrespective of the presence or otherwise of a spring.

The pin may be one of a plurality of pins, in which case the plug preferably has a plurality of slots or apertures each corresponding to one of said pins .

The biasing means may be one of a plurality of biasing means, and the detent means may be one of a plurality of detent means, in which case the plug preferably has a plurality of corresponding engagement surfaces.

Preferably said sleeve has a disengagable engagement means for engaging a portion of said socket when said plug and said socket are coupled, whereby said sleeve may be moved away from said first position and towards said second position by separating or decoupling said socket and said plug.

The present invention also provides a socket for use with a plug as described above, including: a portion for engaging said engagement means.

The invention further provides a socket, for use with a plug as described above, including: unlocking means for unlocking said locking means .

According to a further aspect of the present invention, there is provided a electrical coupler, including a plug and a corresponding socket, the plug including: a conducting pin with an exposable forward end for establishing electrical contact with an electrical contact of a corresponding socket; and a sleeve for selectively providing or restricting access to said pin, moveable between a first, rearward position and a second, forward position; wherein when said sleeve is in said first position said sleeve is substantially rearward of said forward end of said pin whereby said forward end of said pin is exposed to allow access to said forward end of said pin, and when said sleeve is in said second position said forward end of said pin is substantially concealed by said sleeve to restrict access to said forward end of said pin.

In order that the present invention may be more clearly ascertained, preferred embodiments will now be described, by way of example, with reference to the accompanying drawing in which:

Figure 1A is a view of a prior art plug;

Figure IB is a view of a prior art socket; Figure 2A is view of a plug according to a preferred embodiment of the present invention;

Figure 2B is a view of the sleeve of the plug figure 2A;

Figure 2C is a view of a socket according to a preferred embodiment of the present invention;

Figure 3A is a cross-sectional view of the plug of figure 2A;

Figure 3B is a cross-sectional view of the socket of figure 2C; Figure 4A is a front view of the plug of figure

2A;

Figure 4B is a front view if the socket of figure 2C;

Figures 5A to 5D are a sequence of cross- sectional views of the plug of figure 2A and socket of figure 2C been connected;

Figure 6 is a view of a socket and sleeve according to a further preferred embodiment of the present invention; Figures 7A and 7B are details of the socket and sleeve of figure 6 illustrating the manner in which they may be connected. Figure 8 is a view of a socket and sleeve according to a still further preferred embodiment of the present invention;

Figures 9A and 9B are details of the socket and sleeve of figure 8 illustrated in a manner in which they may be connected;

Figures 10A to 10B illustrate process of connecting the socket and sleeve of figure 6.

Figure 2A is a view of an electrical plug 50 according to a first preferred embodiment of the present invention.

The plug 50 (shown with attached electrical lead 52) is similar to prior art plug 10 of figure 1A. Plug 50 has a forward end 51 and a moulded plastic casing 54, which includes a keyway 56 at the forward end of its lower surface, to ensure—in use—correct orientation relative to a corresponding socket, and a latch 58 at the forward end 51 of the upper surface of casing 54 to ensure that releasably secure engagement may be formed with the corresponding socket. The forward end 51, including latch 54, for an external sleeve 55 comparable to the sleeve 16 of prior art plug 10 (see figure 1A) . The latch 58 has catches 60a and 60b at the forward end of its lower surface which, in use, are received by corresponding rebates (see 61b and 61a of figure 2C) in the corresponding socket.

In addition, plug 50 includes a moveable internal sleeve 62, located within external sleeve 55, and slidable therein between a first, rearward position (not illustrated) in which internal sleeve 62 is contained further within casing 54, and a second, forward position (as illustrated in figure 2A) in which the forward face of internal sleeve 62 is flush with the forward end of external sleeve 55.

Figure 2B illustrates the internal sleeve 62. The internal sleeve 62 includes a forward face 64 provided with three slots 66 through which the conducting pins (not shown; see pins 94 of figure 3A) of plug 50 project when the internal sleeve 62 is in the first, rearward position. Internal sleeve 62 includes two rearward projecting slides 68a and 68b which, in use, slide within casing 54 of plug 50 and thereby maintain the correct orientation of the internal sleeve 62. The rearward end of each of slides 68a and 68b is provided with an inward pointing stops 70a and 70b respectively, to limit the range of movement of internal sleeve 62 within casing 54. These stops 70a and 70b are described below.

Internal sleeve 62 also includes grooves 72a and 72b above and rearward of forward face 64, which correspond to and are for accommodating catches 60a and 60b respectively, and allow the internal sleeve 62 to advance fully to the second, forward position illustrated in figure 2A.

Internal sleeve 62 includes two outwardly inclined projecting detents 74a and 74b, mounted either side of the forward face 64 of the internal sleeve 62 and accessible from a position forward of forward end 51 via grooves 75a and 75b respectively. When the internal sleeve 62 is in the second, forward position shown in figure 2A, these detents 74a and 74b are received by corresponding indentations (not shown; see indentations 92a and 92b of figure 3A) in the internal wall of external sleeve 55. The detents 74a and 74b thus abut the generally forward facing surfaces of these indentations and thereby resist the rearward movement of the internal sleeve 62, when internal sleeve 62 in this second position. Thus, the internal sleeve 62 is not readily moved from the second, forward position rearwardly towards the first position in which the conducting pins of plug 50 would be exposed.

In order to disengage the detents 74a and 74b to allow the rearward movement of the internal sleeve 62, the corresponding socket 80 (see figure 2C) is provided, at the forward end 84 of its moulded plastic casing 82, with two prongs 86a and 86b corresponding, respectively, to detents 74b and 74a. In other respects socket 80 is similar to prior art socket 30 shown in figure IB.

Thus, in use the forward faces 51 and 88 respectively of plug and socket 80 are brought together, and prongs 86a and 86b are inserted into, respectively, grooves 75b and 75a until they press against detents 74b and 74a respectively. Urging plug 50 and socket 80 closer together causes prongs 86a and 86b to push detents 74b and 74a inwards and thereby disengages detents 74b and 74a from the corresponding indentations in the inner surface of external sleeve 55. Prongs 86a and 86b are provided with inclined inner surfaces 90a and 90b respectively to facilitate the urging inwards of the detents 74b and 74a. The flexibility of the plastic material of the internal sleeve 62 facilitates this step. The detents 74a and 74b, when withdrawn from these indentations, may either be accommodated in indentations provided in the sides of internal sleeve 62 or, by providing a space between the casing 54 of plug 50 and the internal sleeve 62, in this space. Moving plug 50 and socket 80 closer together causes the front face 88 of socket 80 to press against the forward face 64 of internal sleeve 62 and, as the detents 74a and 74b are now disengaged, the internal sleeve 62 is pushed rearward within the casing 54 of plug 50, until the conducting pins project through slots 66 of internal sleeve 62, into socket 80 and into electrical contact with the electrical contacts

(not shown) within socket 80, and catches 60a and 60b are received by corresponding rebates 61b and 61a in corresponding socket 80. When socket 80 is withdrawn from plug 50, internal sleeve 62 is pushed forwards towards the second position by two springs (not shown) within plug 50 until the forward face 64 of internal sleeve 62 is again aligned with forward face 51 of plug 50, and detents 74a and 74b are again located within their respective indentations in the internal wall of external sleeve 55.

The internal structure of the plug and socket of figures 2A to 2C are shown in cross section in figures 3A and 3B . Figure 3A is a cross sectional view of plug 50, in which like reference numerals to those of figure 2A have been used to indicate identical features.

In figure 3A, internal sleeve 62 is shown in the second or forward position, held in place by the engagement of detents 74a and 74b against the surfaces of indentations 92a and 92b in the inner walls of external sleeve 55. Slots 66 in the forward face 64 of inner sleeve 62 are aligned with conducted pins 94.

Plug 50 is provided with internal abutments 95a and 95b for engaging stops 70a and 70b respectively when internal sleeve 62 is in the second, forward position, to prevent the internal sleeve 62 from advancing forward beyond that position and out of external sleeve 55.

Plug 50 is also provided with two helical springs 96a and 96b for urging internal sleeve 62 forward to the second position after the disconnection of plug 50 and socket 80. Spring 96a is mounted between posts 71a internal sleeve 62 and post 98a provided inside casing 54 of plug 50 on forward facing rear wall 100, while spring 96b is similarly mounted between posts 71b and 98b.

Socket 80 is shown in cross section in figure 3B. Socket 80 is provided with slots 104 in the forward face 88 of socket 80 for receiving pins 94 of plug 50, and includes electrical contacts 102 rearward slots 104. In use, socket 80 and plug 50 are brought together with their respective longitudinal axes 106 and 108 aligned until prongs 86a and 86b depress detents 74b and 74a inwardly and out of engagement with the internal surface of indentations 92b and 92a. As the plug 50 and socket 80 are brought closer together, internal sleeve 62 is pushed rearwardly against the biasing of springs 96a and 96b until plug 50 and socket 80 are fully coupled and held together by both friction and latch 58 (see figure 2A) . When plug 50 and socket 80 are decoupled, springs 96a and 96b push internal sleeve 62 back to the forward position illustrated in figure 3A.

Figures 4A and 4B are front views of, respectively, plug 50 and socket 80 of figures 2A and 2C or 3A and 3B : like the reference numeral referred to like features .

Figures 5A to 5D form a sequence illustrating the coupling of plug 50 and socket 80. Referring to figure 5A, initially plug 50 and socket 80 are aligned coaxially and bought together. As may be seen in figure 5B, prongs 86a and 86b eventually disengage detents 74b and 74a respectively from the internal surfaces of indentations 92b and 92a in the inner wall of external sleeve 55 of plug 50, so that internal sleeve 62 may be moved rearwards. Referring to figure 5C, as the socket 80 is further advanced, internal sleeve 62 is moved further backwards, compressing springs 96a and 96b, until pins 94 project through slots 66 in internal sleeve 62, and through slots 104 in socket 80 to make contact with electrical contacts 102 of socket 80.

In figure 5D, plug 50 and socket 80 are shown fully coupled.

Internal sleeve 62 is prevented from moving further forward than the second, forward position by the engagement of stops 70A and 70B with internal abutments 95a and 95b, as described above .

In many applications the biasing force of springs 96a and 96b should be sufficient to restore internal sleeve 62 to the second, forward position following the decoupling of plug 50 and socket 80. However, such decouplings may take place, in some cases, many years after the coupling of the plug and socket at the original installation of the coupler, and springs 96a and 96b may have subsequently deteriorated or, owing to the accumulation of dust or other foreign material, be impeded from fully restoring internal sleeve 62 to the second, forward position.

Accordingly, in a further preferred embodiment of the present invention additional means are provided for restoring internal sleeve 62 to the second, forward position upon decoupling of the plug 50 and socket 80.

Figure 6 is a view of an internal sleeve 110 and socket 112 according to a further preferred embodiment of the present invention. Internal sleeve 110 is, in use, incorporated in a plug that is identical to plug 50 shown in figure 2A. Similarly, socket 112 is, other than as described below, identical to socket 80 shown in figure 2C.

The upper and lower surfaces of prongs 114a and 114b of socket 112 are each provided with a semi-cylindrical ridge 116a, b (on the upper and lower surface of prong 114a) and 118a, b (on the upper and lower surface of prong 114b) . Internal sleeve 110 is provided with corresponding rebates 120a, b and 122a,b immediately forward of detents 124b and 124a respectively. The operation of ridges 116 and 118 with rebates 120 and 122 is illustrated in figures 7A and

7B. In these figures, internal sleeve 110 is again shown removed from a corresponding plug for the purpose of clarity.

When a plug and socket of this embodiment are coupled (by advancing, for example, socket 112 in the direction of arrow 126), prongs 114a and 114b engage detents 124b and 124a and — as described in the context of the embodiment of figures 2A to 2C — internal sleeve 110 is pushed backwards towards the first, rearward position. In this position, sleeve 112 and internal sleeve 110 abut one another (see figure 7B) and, consequently, ridges 116a, b and 118a, b are received by rebates 120a,b and 122a, b. The resilience of the plastic of the internal sleeve 110 arid socket 112 allow sufficient defamation for this to occur.

When socket 112 is decoupled from a corresponding plug, the withdrawing of socket 112 draws internal sleeve 110 forward owing to the engagement of socket 112 with internal sleeve 110 formed by the respective ridges 116 and 118 and rebates 120 and 122. Thus, even if no internal springs (corresponding to springs 96a and 96b of plug 50 of figure 3A) are provided, internal sleeve 110 will nevertheless be restored to the second, forward position.

Figure 8 is a view of internal sleeve 150 and socket 152 according to a still further preferred embodiment of the present invention. Internal sleeve 110 is, in use, incorporated in a plug 180 that is almost identical to plug 50 shown in figure 2A. Similarly, socket 152 is, other than as described below, identical to socket 80 shown in figure 2C.

The upper and lower surfaces of prongs 154a and 154b of socket 152 are each provided with a recess 156a, b (on the upper and lower surfaces of prong 154a) and 158a, b (on the upper and lower surfaces of prong 154b). The internal sleeve 110 is provided with protrusions 162a, b and 160a, b immediately forward of detents 164a and 164b respectively. The interaction of the recesses 156 and 158 with protrusions 160 and 162 is illustrated in figures 9A and 9B.

When the plug 50 and socket 80 of this embodiment are bought into engagement with each other the protrusions 162a, b and 160a, b are received by recesses 158a, b and 156a, b respectively. Thus, similarly to the embodiment of figure 6, the withdrawal of socket 152 pulls internal sleeve 150 forward due to the engagement of the socket 152 with internal sleeve 15o by the recesses 156 and 158 and the protrusions 160 and 162. Furthermore, this arrangement prevents the internal sleeve 150 from detaching from the socket 152 unless the sleeve 150 is at the front of the plug. That is to say, as illustrated in figures 10A to

10d,in this embodiment the interior surface of the plug 180 diverges outwardly in regions 170a and 170b so that the internal sleeve 150 may only deform when it is located adjacent to regions 170a, b. Thus, the internal sleeve 150 must be pulled completely to the front and locked in place before the sleeve 150 will detach from the socket 152. These features combine to prevent the sleave 150 jamming midway inside the plug 180 and not closing off the live pins.

Figures 10A to 10D more completely illustrate this feature. In figure 10A the internal sleeve 150 is locked in the front position. As shown in figure 10B when the socket 152 engages the internal sleeve 150 regions 170a and 170b allow the internal sleeve to deform outwardly thereby receiving the prongs 154a and 154b. Subsequently, in figure 10C the protrusions 162a and 162b of the internal sleeve 150 are received within recesses 158a, b of the socket 152 and the plug 180 and socket 80 lock together in the manner described above.

Once the internal sleeve 150 has slid backwards into the body of the plug 180, the body of the plug 180 prevents the internal sleeve 150 deforming outwardly.

Thus, the present invention provides a coupler, and plug and socket thereof, where the pins of the plug are essentially as inaccessible as the electrical contacts of the socket when the coupler is decoupled.

Modifications within the sprit and scope of the invention may be readily be effected by persons skilled in the art. It is to be understood, therefore, that this invention is not limited to the particular embodiments described by way of example here and above .

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A plug for an electrical coupler including: a conducting pin with an exposable forward end for establishing electrical contact with an electrical contact of a corresponding socket; and a sleeve for selectively providing or restricting access to said pin, moveable between a first, rearward position and a second, forward position; wherein when said sleeve is in said first position said sleeve is substantially rearward of said forward end of said pin whereby said forward end of said pin is exposed to allow access to said forward end of said pin, and when said sleeve is in said second position said forward end of said pin is substantially concealed by said sleeve to restrict access to said forward end of said pin.

2. A plug as claimed in claim 1, wherein said sleeve defines a slot or aperture through which said forward end of said pin projects when said sleeve is in said first position.

3. A plug as claimed in claim 2, wherein said slot or aperture is sized to fit said pin.

4. A plug as claimed in either claim 2 or 3, wherein accessibility to said pin is limited to said slot or aperture when said sleeve is in said second position.

5. A plug as claimed in any one of the preceding claims, wherein said plug includes biasing means for biasing said sleeve toward said second position.

6. A plug as claimed in claim 5, wherein said biasing means is a spring.

7. A plug as claimed in any one of the preceding claims, wherein said plug includes disengagable locking means for locking said sleeve in said second position, to restrict the undesired movement of said sleeve from said second position towards said first position.

8. A plug as claimed in claim 7, wherein said locking means includes detent means .

9. A plug as claimed in claim 8, wherein said sleeve is provided with said detent means.

10. A plug as claimed in either claim 8 or 9, wherein said plug is provided with an engagement surface for engaging said detent means .

11. A plug as claimed in any one of claims 7 to 10, wherein said locking means is disengagable by means of unlocking means provided in said socket .

12. A plug as claimed in any one of the preceding claims, wherein said pin is one of a plurality of conducting pins, each with an exposable forward end for establishing electrical contact with an electrical contact of a corresponding socket .

13. A plug as claimed in claim 12, including a plurality of slots or apertures each corresponding to one of said pins .

14. A plug as claimed in either claim 5 or 6, wherein said biasing means is one of a plurality of biasing means for biasing said sleeve toward said second position.

15. A plug as claimed in either claim 8 to 10, wherein said detent means is one of a plurality of detent means for disengagably locking said sleeve in said second position.

16. A plug as claimed in claim 15, including a plurality of engagement surfaces corresponding to said plurality of detent means .

17. A plug as claimed in any one of the preceding claims, wherein said sleeve has a disengagable engagement means for engaging a portion of said socket when said plug and said socket are coupled, whereby said sleeve may be moved away from said first position and towards said second position by separating or decoupling said socket and said plug.

18. A socket, for use with a plug as claimed in any one of claims 1 to 16.

19. A socket, for use with a plug as claimed in claim 17, wherein said socket includes a portion for engaging said engagement means .

20. A socket, for use with a plug as claimed in any one of claims 7 to 10, wherein said socket includes unlocking means for unlocking said locking means .

21. An electrical coupler, including a plug and a corresponding socket, the plug including: a conducting pin with an exposable forward end for establishing electrical contact with an electrical contact of a corresponding socket; and a sleeve for selectively providing or restricting access to said pin, moveable between a first, rearward position and a second, forward position; wherein when said sleeve is in said first position said sleeve is substantially rearward of said forward end of said pin whereby said forward end of said pin is exposed to allow access to said forward end of said pin, and when said sleeve is in said second position said forward end of said pin is substantially concealed by said sleeve to restrict access to said forward end of said pin.

22. A coupler as claimed in claim 21, wherein said sleeve defines a slot or aperture through which said forward end of said pin projects when said sleeve is in said first position.

23. A coupler as claimed in claim 22, wherein said slot or aperture is sized to fit said pin.

2 . A coupler as claimed in either claim 22 or 23, wherein accessibility to said pin is limited to said slot or aperture when said sleeve is in said second position.

25. A coupler as claimed in any one of claims 21 to 24, wherein said plug includes biasing means for biasing said sleeve toward said second position.

26. A coupler as claimed in claim 25, wherein said biasing means is a spring.

27. A coupler as claimed in any one of claims 21 to 26, wherein said plug includes disengagable locking means for locking said sleeve in said second position, to restrict the undesired movement of said sleeve from said second position towards said first position.

28. A coupler as claimed in claim 27, wherein said locking means includes detent means .

29. A coupler as claimed in claim 28, wherein said sleeve is provided with said detent means .

30. A coupler as claimed in either claim 28 or 29, wherein said plug is provided with an engagement surface for engaging said detent means.