GB2242079A - Plug with transparent cover - Google Patents

Abstract

A domestic plug for use with an electrical socket comprises a base (12), pins (24, 26, 28), and a transparent cover (14) through which the internal wiring connections may be viewed and examined for integrity without dismantling the plug. An opaque cover plate (38) may be snap-fitted over the transparent cover portion. A spring contact, fig 4 or fig 5 may be provided. <IMAGE>

Description

PLUG FOR USE WITH ELECTRICAL SOCKET The present invention relates to a plug for use with an electrical socket and particularly, but not exclusively to such a plug having three pins of generally rectangular cross-section, commonly referred to as a three-pin square plug.

When a plug is repeatedly inserted and removed from a socket, the wiring connections of that plug may become loose or even disconnected. This is particularly true if the plug is removed from the socket by pulling the cable.

It is a relatively simple operation to check the wiring connections of a plug; however, doing so involves dismantling the plug and this requires the use of a screwdriver.

It is an object of the present invention to provide a plug which obviates or mitigates the aforementioned problem.

According to the present invention, there is provided a plug for use with an electrical socket, said plug having a substantially transparent cover portion whereby the wiring connections of the plug may be examined for integrity without dismantling the plug.

Preferably an opaque cover plate is fitted over the transparent cover portion. Conveniently the cover portion has a recessed area for receiving the cover plater which, when in place in said recessed area, obscures view of the wiring connections of the plug. Advantageously said cover plate snap-fits into said recessed area and may be simply removed from said recessed area to allow viewing of the wiring connections of the plug.

Conveniently only the recessed area of said cover portion is transparent. Alternatively, the entire cover portion is transparent.

According to conventional practice the plug may comprise three pins arranged to be inserted into the live, neutral and earth socket connections of a socket. The pin arranged to be inserted into the live socket connection is connected to its wire connection means through a fuse.

Preferably indication means are provided to give an indication of whether this fuse is intact. Conveniently, the indication means is provided by neon indicator arranged to illuminate to indicate that said fuse is intact. The wire connection means of the neutral and earth pins are integral with the respective pins and are disposed at the top of said pins.

The wire connection means of each of said pins preferably includes a channel into which a wire may be inserted to establish an electrically conductive connection between said wire and said pin, a wire securing member movable in a direction transverse to said channel, said member being arranged to clamp said wire in said channel when in its securing position, a compression spring disposed around said securing member biasing said securing member into said securing position, the arrangement being such that when said member is moved against the influence of said spring and a wire is inserted into said channel, subsequent release of said member causes the securing member to return to its securing position to clamp the wire within said channel.

A preferred embodiment of the invention will now be described. This description is made by way of example and not by way of limitation and is made in combination with the accompanying drawings in which: Figure 1 is an exploded perspective view of a plug in accordance with an embodiment of the present invention; Figure 2 is a plan view of the assembled plug as shown in Figure 1.

Figure 3 is a plan view of the plug shown in Figure 1 with part of the body of the plug removed; Figure 4 is a perspective view of part of one of the electrical connection pins of the plug shown in Figures 1 to 3; Figure 5 is a perspective view of part of an alternative electrical connection pin which may be used with the plug shown in Figures 1 to 3; Figure 6 is a diagrammatic view of a fastening mechanism for the plug shown in Figures 1 to 3, and Figure 7 is a plan view of a locking member which is part of the mechanism shown in Figure 6.

Reference is firstly made to Figure 1 of the drawings which shows a plug generally indicated by reference numeral 10. The plug 10 has a base portion 12 and a cover portion 14 which may be fastened together to define a chamber 16 therebetween. The base portion 12 and cover portion 14 are made of a plastics material and are fastened together by a fastening mechanism (not shown) which will be described later in detail. The wiring connections of the plug 10 are contained within chamber 16 as will also be described later in detail. The cover portion 14 is substantially transparent, therefore the wiring connections in chamber 16 may be examined without separating the cover portion 14 and the base portion 12.

The base portion 12 has three apertures 18, 20 and 22 for receiving elongate electrical connection pins 24,26 and 28 respectively. Pins 24, 26 and 28 are received in apertures 18,20 and 22 and extend from the base portion as shown in phantom in Figure 1. Each of the pins 24, 26 and 28 has a end portion 24a, 26a, 28a of greater cross-sectional area than its elongate portion 24b, 26b, 28b. which retain the pins in the base portion. When cover portion 14 is fastened to base portion 12, the end portions 24a, 26a and 28a are retained in chamber 16. The chamber 16 includes wire passage channels 30 through which wires may be passed to allow these wires to be connected to the pins 24, 26 and 28 as will be described.When the base portion 12 and cover portion 14 are fastened together they also define a cable entry channel 32 through which a cable 34 may extend into chamber 16 (as shown in Figure 3) so that the wires may extend into the wire passage channels 30.

The upper surface of cover portion 14 has a recessed area 36 in which an opaque cover plate 38 may be disposed. The cover plate 38 snap-fits into the recessed area 36 and may be simply removed. As best shown in Figure 2, when the cover plate 38 is in place the wiring connections of plug 10 cannot be examined without separating the cover portion 14 from the base portion 12.

However, as shown in Figure 3, when the cover plate 38 is removed from the recessed area 36, the wiring connections of the plug 10 may be examined through transparent cover portion 14.

Reference is now made to Figures 1 and 3 of the drawings. Pins 24, 26 and 28 are arranged in the conventional manner so that these pins may be connected to the earth, live and neutral sockets respectively of an electrical mains supply socket (not shown). The end portions 24a and 28a of earth pin 24 and the neutral pin 28 include wire connection mechanisms whereby wires may be connected to pins 24 and 28. The end portion 26a of live pin 26 is connected to a separate wire connection member 40 through a fuse 42. The separate wire connection member 40 is retained in cavity 16 and rests in channel 30 (as best shown in Figure 3).

Reference is now made to Figure 4 of the drawings which is a perspective view of the end portion 24a of earth pin 24. The end portion 24a defines a channel 44 into which a bared portion 46 of a wire 48 may be inserted. An elongate securing member 50 having an enlarged head 52 is movably disposed in the channel 44.

The member 50 is movable in the direction of arrows 54 to allow the bared portion 46 of wire 48 to be inserted into channel 44. A compression spring 56 is disposed around the elongate portion 50a of member 50. This spring 56 biases the member 50 into the wire securing position shown in Figure 4. When the member 50 is moved against the influence of spring 56 and a bared portion of wire is inserted into channel 44, subsequent release of the member 50 causes the member 50 to move to the securing position to clamp the bared portion of wire within the channel 44 thus establishing an electrically conductive connection between the wire and the pin 24.

Neutral pin 28 has a similar wire connection mechanism to that described for pin 24. The wire connection mechanism for live pin 26 is provided by a separate wire connection member 40. An alternative wire connection mechanism for pins 24, 26 and 28 is shown in Figure 5. This wire connection mechanism is provided by a crocodile clip arrangement 58 which is provided at the end portion 24a, 26a of pins 24 and 28, and at the wire connection member 40 for live pin 26.

Reference is once again made to Figures 1 and 3 of the drawings. A neon indicator 60 is connected between the wire connection member 40 and neutral pin 28 (the connection to pin 28 is not shown in the drawings). When the plug 10 is inserted into a socket, current flows through fuse 42 and indicator 60, and the indicator 60 illuminates to indicate that the fuse is intact. A high value resistor (not shown) is connected in series with the indicator 60 to limit the level of current through indicator 60. If the indicator 60 does not illuminate when the plug is inserted into a socket, no current is flowing through fuse 42 and indicator 60 and. this means that the fuse is blown.

The internal walls of base portion 12 which define cable entry channel 32 have a serrated surface 35. This serrated surface 35 substantially prevents movement of the cable 34 relative to the chamber 16. The wires contained in cable 34 are connected to pins 24, 26 and 28 in the conventional manner and because cable 34 may not move relative to the chamber 16, it is difficult to pull these wires out of connection with the pins 24, 26, 28.

Reference is now made to Figure 6 of the drawings which shows a fastening mechanism 62 for fastening the base portion 12 to the cover portion 14. The mechanism 62 includes an elongate locking member 64 (also shown in Figure 7) having a generally circular enlarged head 66 for engaging the base portion 12 and a generally rectangular enlarged head 68 for engaging the cover portion 14 as will be described. The locking member 64 extends through a hole 17 in the base portion 12, the enlarged heads 66 and 68 being disposed one on each side of hole 17. The hole is shaped to define an annular shoulder 70 and enlarged head 66 abuts shoulder 70 when the locking member is in the locking position (as shown in Figure 6).

The cover portion 14 has a shaped aperture 72 into which the rectangular enlarged head 68 of member 64 may be inserted in order to fasten the base portion 12 to the cover portion 14. The aperture consists of a first relatively narrow channel 74 of rectangular cross-section which opens into a generally circular chamber 76. The chamber 76 provides an annular shoulder 78 and when the locking member 64 is in the locking position, (shown in figure 6) enlarged head 68 abuts this annular shoulder 78 while enlarged head 66 abuts shoulder 70 of base portion 12, thereby securely fastening the base portion 12 to the cover portion-14.

In order to fasten the base portion 12 to the cover portion 14, enlarged head 68 of member 64 is inserted into aperture 72. The shape of enlarged head 68 and the shape of channel 74 are such that enlarged head 68 may only be inserted in a particular orientation. The enlarged head 68 is pushed through the channel 74 until the head 68 extends into chamber 76 whereupon the locking member 64 is twisted about axis 80 so that the rectangular head 68 is moved out of alignment with the rectangular channel 74.

When the enlarged head 68 is not in alignment with channel 74, the enlarged head 68 abuts shoulder 78 and is retained in chamber 76.

In order to release the enlarged head 68 from chamber 76, the locking member 64 may be rotated around axis 80 until the enlarged head 68 is in alignment with channel 74. A spring 82 is disposed in chamber 72b and this spring 82 abuts enlarged head 68 and is compressed when the head 68 extends into chamber 76. Therefore, when the enlarged head is in alignment with channel 74, the spring 82 tends to push the enlarged head 68 out of chamber 76 in order to release the cover portion 14 from the base portion 12.

Various modifications may be made to the embodiment hereinbefore described without departing from the scope of the present invention. The plug may be manufactured from any suitable material. The cover portion may not be entirely transparent, only the portion disposed substantially above the chamber need be transparent so that the wiring of the plug may be examined for integrity. Such an arrangement would provide a plug having an opaque outer surface when the cover plate is disposed in the recessed area of the cover portion.

The opaque cover plate need not snap fit into a recessed area of the cover portion. The plate may snap fit onto the peripheral edge of the cover portion, thus obscuring view of the wiring connections in the chamber.

A similar transparent cover may be provided for a plug having two pins or for a plug having two or three pins of circular cross-section, commonly known as round pins. The plug need not have one pin with a fused connection.

The neon indicator could be replaced by a light emitting diode or any other suitable indicator device.

Any of such indicators would be connected between the live and earth pins of the plug. The cover portion and base portion may be fastened together by a screw fastening.

An advantage associated with the present invention is that the wiring connections of the plug may be examined without dismantling the plug. This may be done in any environment where there is sufficient light. The plug is of simple construction being simple to manufacture and assemble. Any person with a knowledge of how to wire a plug may do so in a relatively quick time. The plug also comprises means whereby an indication of whether the fuse is intact or not is provided. This may also be observed without dismantling the plug. If an appliance to which the plug is fitted is malfunctioning, it is relatively easy to observe and correct any fault in the plug. The wire connection mechanisms of the pins of the plug are simple to use and provide an effective electrical connection of wires to the pins. All parts of the plug may be assembled or dismantled without using a screwdriver.

Claims (6)

1. A plug for use with an electrical socket, which comprises a base, pins for establishing electrical contact with the socket extending through the base, and a substantially transparent cover portion whereby the wiring connections of the plug may be examined for integrity without dismantling the plug.

2. A plug according to claim 1 which further comprises an opaque cover plate fitted over the transparent cover portion.

3. A plug according to claim 2 wherein the cover plate is a snap-fit in a recess provided in the transparent cover portion.

4. A plug according to any preceding claim which further comprises a fuse, and indication means which in use indicate whether the fuse is intact.

5. A plug according to any preceding claim wherein each pin is provided with wire connection means, which comprises a channel for receiving a wire to be connected to the pin, and a resiliently biased securing member for holding the wire against the side of the channel to establish electrical contact therewith.

6. A plug substantially according to any embodiment described in conjunction with the drawings.