GB2119179A - Cooling a terminal of a plug - Google Patents

Abstract

The live wire of a plug is connected to a terminal (16) shaped to have good thermal contact with a recess (46, 48) in the plug base (10). A cover (24) welded onto the base (10), also thermally contacts the terminal (16) via a hollow, finned depending abutment (56). <IMAGE>

Description

SPECIFICATION Electrical plugs This invention is concerned with electrical plugs, especially but not exclusively non-rewirable plugs; by a "non-rewirable plug" is meant, where the expression is used herein, a plug and flexible cord assembly in which a plug and leads of the cord electrically connected to conductors within the plug are permanently assembled together to prevent access to the lead connections within the plug.

A form of electrical plug has been proposed which comprises an electrically insulating base in which conductor pins of the plug are mounted. The pins extend through the base from a connecting zone adjacent an inner side of the base, to project beyond an outer side of the base. The base provides a fuse cavity to which access can be gained, for introduction or removal of a fuse, from the outer side of the base. In use of the plug a fuse is held in the cavity by fuse clips, to connect electrically a live pin of the plug with a live lead of a flexible cord. One of the fuse clips is associated with, and may be integral with, a live lead termination adjacent the inner side of the base. A base cover is secured to the base to shield said termination and other otherwiseexposed conductors adjacent the inner side of the base.A plug of this form is hereinafter referred to as an electrical plug of the kind referred to.

Problems of overheating have been found to arise in plugs of the kind referred to. In particular it has been found that the live lead termination and its associated fuse clip can be especially prone to overheating.

It is an object of the present invention to provide an improved electrical plug of the kind referred to in which heat can be conducted away from the live lead termination, and associated fuse clip, more efficiently, to prevent overheating.

The invention provides in one of its aspects an electrical plug of the kind referred to in which the live lead termination is mounted in a recess formed in the inner side of the base and is in contact over a substantial area with portions of the base providing side walls of the recess, the base cover being arranged to abut the side walls in order that heat from the termination can be conducted away through the side walls to the cover.

Preferably the base cover comprises a portion in the form of an abutment arranged to enter the recess and abut the termination.

This abutment may serve to retain the termination in position on the base, but furthermore it can assist in conducting heat away.

For this latter purpose, the abutment preferably contacts the termination over a substantial area, and may be of a substantial volume to act as a heat sink; in a most preferred construction the abutment has a finned construction.

The termination may comprise a plurality of upturned flanges which lie flat against the side walls bounding the recess.

Where the base cover is secured to the base by ultrasonic welding, in construction of a non-rewirable plug, advantage may be taken of the welding process to cause the base cover to adhere to the side walls and to cause said abutment of the cover (where provided) to adhere to the termination. Such adherence of the cover to the side walls and the termination can be of value in ensuring efficient heat transfer to the cover.

There now follows a detailed description, to be read with reference to the accompanying drawings, of an electrical plug of the kind referred to which illustrates the invention by way of example.

In the accompanying drawings: Figure 1 is a perspective view showing a base of the plug, and fuse clips, conductor pins and a cover to be assembled with the base; Figure 2 is a plan view of the base cover, from beneath; Figure 3 is a view of the cover in section on the line Ill-Ill of Fig. 2; Figure 4 is scrap section showing a live lead termination and fuse clip held in place on the base by the cover; and Figure 5 is a view similar to Fig. 4 but showing the components immediately prior to final assembly of the cover with the base.

As shown in Fig. 1, a 13-amp non-rewirable plug meeting British Standard 1 363 comprises a base 10 of an electrically insulating material, two metal spring-clips 12 and 14, a live lead termination 1 6, three conductor pins comprising a live pin 18, a neutral pin 20 and an earth pin 22, and a base cover 24 of an electrically insulating material.

Legs of the two spring-clips 1 2 and 14 are arranged to be introduced, in assembly of the plug, through slots 26 and 28 in the base from an inner side of the base (the upper side as seen in Fig. 1) in order to project into a fuse cavity (not shown) which opens out of the outer side of the base. The legs of the spring-clips, projecting into the fuse cavity, are arranged to hold the two metal-capped ends of a conventional cartridge fuse (to British Standard 1362).

The three conductor pins are arranged to be mounted in slots 30, 32 and 34 in the base 10, the pins extending right through, and beyond, the base from a connecting zone adjacent the inner side of the base. The live pin 1 8 comprises an integral tab 36 which is arranged to be welded to one of the springclips 1 2 to provide an electrical connection between the pin and a fuse held, in use of the plug, by the spring-clip. The neutral pin 20 and the earth pin 22 comprise integral termi nations 37 and 38 whereby the neutral and earth leads of a flexible cord can be connected to the pins.

The live lead termination 1 6 is pressed from sheet metal and comprises a flat base portion 39 from which three edge portions 40, 41 and 42 are turned up, as seen in Fig. 1. A projecting portion 44 enables the live lead of the flexible cord to be connected up to the termination 1 6. Just as one of the spring-clips is welded to the tab 36 of the live pin 18, the other spring-clip 1 4 is arranged to be welded to the underneath of the base portion 39 of the live lead termination 1 6.

As illustrated by Figs. 4 and 5, the live lead termination 1 6 is arranged to fit snugly in a recess in the base 10 between upstanding partitioning walls 46 and 48 of the base. The upturned edge portions 40, 41 and 42 of the termination are arranged to lie flat against inside surfaces of the walls in order that good thermal contact is made with walls over a substantial area. The legs of the attached spring-clip 14 project through the slots 28 in the base into the fuse cavity.

Details of construction of the cover 24 can be seen from Figs. 2 and 3. The cover comprises depending tubular abutments 50 and 52 which, when the cover is assembled on the base, serve to retain the earth and neutral pins, respectively, in position in their slots in the base. In order to retain the tab 36 of the live pin 1 8 (to retain the live pin and the attached spring-clip 12), and to retain the live lead termination 1 6 and the attached spring-clip 14, the cover comprises depending hollow finned abutments 54 and 56 which engage the tab 36 and the base portion 39 (of the termination 16), respectively.

The cover 24 is secured to the base 10 by ultrasonic welding. A stepped periphery 58 of the cover is arranged to meet a stepped periphery 60 of the base in order that a strong welded joint can be achieved.

In assembly of the plug, the three leads of the flexible cord are connected to the live lead termination 16, the neutral pin 20 and the earth pin 22, respectively, before welding the cover 24 to the base 10. A cord-protecting grommet (not shown) becomes secured between the cover and the base, in a conventional manner. A movable fuse cover (not shown), which closes the fuse cavity adjacent the outer side of the base, completes the assembly.

As referred to hereinbefore, and as illustrated by Fig. 4, the live lead termination is arranged to fit snugly between the walls 46 and 48 of the base, with the three upturned edge portions 40, 41 and 42 of the termination making good thermal contact with the walls over a substantial area. An important aspect of this arrangement is that owing to the large area of surface contact between the termination and the side walls of the recess, heat can be dissipated readily from the termination to the base, to militate against any tendency for the termination to become overheated. In order that heat can get away from the base, it is also arranged that the cover 24 makes contact over an area with walls 46 and 48; The cover would in normal use of the plug be exposed to atmosphere, and heat from the base would be dissipated to atmosphere through the cover.Furthermore, good thermal contact between the finned abutment 56 and the live lead termination 1 6 ensures that heat from the termination can also be transferred directly to the cover.

Certain provisions are made to ensure good thermal contact between the cover 24 and the walls 46 and 48 of the base 1 0. As shown in Fig. 5, before assembly of the cover with the base the base walls 46 and 48 comprise weld ribs 62 and 64 which provide pointed ridges upstanding from otherwise flat top surfaces of the walls. The arrangement is such that upon assembly of the cover with the base, flat inner portions af the cover engage the ribs 62 and 64, and in ultrasonically welding the cover to the base the material of the ribs becomes spread, and adhesion between the cover and the top surfaces of the walls is achieved (Fig.

4). The adhesion at the tops of the walls ensures that there is contact between the cover and the base over a substantial area, which assists heat transfer from the base to the cover.

Certain somewhat similar provisions are made to ensure good thermal contact between the cover and the live lead termination 1 6.

The hollow finned abutment 56 of the cover is of substantially uniform wall thickness, except that at a free end portion 66 the wall thickness is tapered down to an edge. Accordingly, when the cover is at first mounted on to the base the abutment 56 makes line contact with flat base portion 39 of the termination 16. Upon welding the cover to the base, the material of the free end portion of the abutment becomes spread and adhesion between the abutment and the termination 1 6 is achieved. The spreading of the material of the abutment, and the subsequent adhesion, ensures that there is contact between the cover and the termination over a substantial area, which assists heat transfer from the termination to the cover.

It will be appreciated that whilst in the construction described above the live lead termination 1 6 and its associated fuse clip 14 are provided by two components, in other constructions a termination and fuse clip assembly might be formed in one piece, or be provided by more than two components.

Claims (8)

1. An electrical plug of the kind referred to in which said live lead termination is mounted in a recess formed in the inner side of said base and is in contact over a substantial area with portions of the base providing side walls of the recess in order that good thermal contact is made with the walls, said base cover being arranged to abut the side walls in order that heat from the termination can be conducted away through the side walls to the cover.

2. A plug according to claim 1 in which said termination comprises a base portion and upturned edge portions which lie against said side walls, said termination fitting snugly in said recess between said walls for good thermal contact with the walls.

3. A plug according to either of claims 1 and 2 in which said base cover is welded to said side walls.

4. A plug according to any one of claims 1, 2 and 3 in which said base cover comprises a depending portion which abuts said termination within said recess.

5. A plug according to claim 4 in which said depending portion is hollow and finned.

6. A plug according to either of claims 4 and 5 in which a free end portion of said depending portion has become spread and adhered to said termination in welding said base cover to said base.

7. An electrical plug of the kind referred to in which provision is made for heat to be conducted away from said live lead termination to said base cover in a manner substantially as hereinbefore described with reference especially to Fig. 4 of the accompanying drawings.

8. An electrical plug of the kind referred to substantially as hereinbefore described with reference to the accompanying drawings.