GB2274026A

GB2274026A - Electrical plug

Info

Publication number: GB2274026A
Application number: GB9305290A
Authority: GB
Inventors: E J Obee
Original assignee: KAINSTAR Ltd
Current assignee: KAINSTAR Ltd
Priority date: 1992-05-15
Filing date: 1993-03-15
Publication date: 1994-07-06
Anticipated expiration: 2013-03-15
Also published as: GB9210490D0; GB2271472A; GB2274026B; GB9305290D0; GB2271472B

Description

2274026 Electrical Plug Assembly This invention relates to electrical plug

assemblies and in particular it relates to pre-wired, three pin plugs commonly known as "13 amp plugs".

Because of the increasing number and variety of electrical appliances and communication channels in use, electrical plug assemblies incorporating interference suppression filters are becoming more desirable. Electrical plug assemblies are effectively limited in overall size and the incorporation of a suitable filter can be difficult to achieve.

It is an object of the present invention to provide a three pin electrical plug which is simple to assemble, safe and robust in use and incorporates a filter.

A further object is to provide for increased safety and convenience by the provision on the plug of an identifying mark or legend descriptive of the appliance to which it is to be connected.

According to the invention there is provided a three pin electrical plug with a main body portion having a side wall with an opening to admit a power cable and a lid for engagement with said main body portion and characterised by retaining means formed as integral parts of the lid and side walls.

Also in accordance with the invention there is provided a a three pin electrical plug with a main body portion from which the three pins depend characterised by retaining means for the pins formed integrally with said main body portion.

2 the three pins depend characterised by retaining means for the pins formed integrally with said main body portion.

The said lid and main body portions are made from insulating material and are moulded to include the retaining means as integral parts. The main body portion has a side,wall with a gap to admit an electrical cable. The interference suppression filter is preferably in the form of two in-line insulated wire coils wound on a ferrite ring as described in the exemplary embodiment below.

The plug has an outer body comprising separate main body portion and lid held together by retaining means such as a number of clips depending from the lid and securing with corresponding recesses in the main body portion. Both main body portion and lid are made as separate mouldings of plastic material. Standard electrically conductive rectangular pins depend from the main body portion and are connected on the inside of the plug to the appropriate live, neutral and earth wires. A filter inside the plug is held in place by means of two clips formed integrally with the main body portion. Pairs of clips, formed integrally with the main body portion are also provided to retain each of the pins. Where a clip is referred to in this text the reference is descriptive of a flexible member upstanding from the lid or main body portion and increased in cross section at its distal end. The design and operation of the clips are described and illustrated more fully in the specific embodiment below.

The otherwise empty space between the lid and main body portion is filled with an insulating material. This in-fill 3 may be e.g. PVC and can be extended as a moulding to form a strain relieving block surrounding the cable for a short distance from the plug. Successful injection of hot melt PVC under pressure as an in-fill moulding into a polyamide casing was made after experiment and is believed to be novel. It was a view previously held that the melt temperatures of polyamide and PVC were too close for in-fill moulding.

The lid is moulded with the letters or device to indicate the type of appliance to which it will connect.

By way of example one embodiment of the invention will now be described with reference to the accompanying figures in which: Figure 1 is a plan view of the inside of the main body portion Figure 2 is a simplified cross sectional view of a plug. Figure 3 demonstrates the use of legends.

With reference to the figures, a main body portion 1 and lid 17 are polyamide mouldings and embody as part of the moulding process clips for retaining the pins and interference suppression filter and clips for holding the lid in engagement with the main body portion. Figure 1 shows a plan view of main body portion 1 with live terminal 2, neutral terminal 3 and earth terminal 4. A filter 5 is retained at the centre of 1 by the two clips 6. Figure 2 illustrates the manner in which the two clips 6 operate. The ferrite ring carrying the two coils 8, 9 is located simply by pushing it down on to the two 4 prongs of the clip which move toward each other to allow passage of the ring. Once the ring is seated the two prongs forming the clip 6 are in the position shown in figure 2 and subsequently arrest any movement of the ring. Similarly the clips 19 are shaped at their distal ends so as to move apa:rt when the pin 20 is inserted and to spring back once the pin 20 is seated so as to retain it in position thereafter. The filter 5 comprises a ferrite ring with two separate coil windings 8, 9 whose ends are connected as shown in figure 1. The live wire 10 connects via terminal 11 to the coil 9 and the other end of coil 9 is connected to terminal 12. A fuseholder section 8 is incorporated and the fuse connects the terminals 12, 13. Connection from terminal 13 to the live pin at 2 is by means of the insulated wire 23. Entry to the fuseholder section which is identified as 22 in figure 1 is made from the bottom of the main body portion 1. This type of arrangement is well established in the prior art and requires no further explanation here.

The neutral wire 14 from the cable is connected to coil 8 via terminal 15. The other end of coil 8 is connected to terminal 3. Insulated earth wire 24 is connected directly to the earth pin at 4. Internal wall section 16 around filter 5 provides the required path lengths between various components. Connections of the wires at the terminals may be made by various well established means such as welding.

When each of the wires and the filter are connected and in place the lid 17 is attached to the main body portion 1 by pushing them together to engage the clips 18. The clips 18 are formed as integral parts of the lid as shown in the simplified cross sectional diagram of figure 2 and are close to the periphery of the lid so as to engage with the corresponding clips or recesses in the side wall of the main body portion. PVC is then injected into the plug to fill the void and to provide the moulding for the strain relieving block 11, if required. Because of small wall thicknesses of the main body portion in this embodiment a metal jig was used for the in-fill process. The jig clamped the complete casing firmly allowed the infill of hot melt PVC to take place without deleterious effect on the polyamide plug casing. Furthermore shaping of the jig provided the mould for the strain relieving block around the cable. When the lid is manufactured the name of the appliance to which the plug will connect is moulded in the lid body section so as to be visible to the user when the plug is assembled. This feature is illustrated in figure 3. The projections 25 depending from the lid 17 bear against the clips 19 to hold them in position further to restrain movement of the pins 20. A pair of these projections cooperate with each pair of clips for the three pins.

6

Claims

Claims 1. A three pin electrical plug comprising a main body portion and a

lid for engagement with said main body portion via retaining means, said main body portion having a side wall with an opening to admit a power cable and said plug characterised by retaining means formed as integral parts of the lid and side wall.
2. A three pin electrical plug as in claim 1 with a main body portion from which the three pins depend characterised by retaining means for the pins formed integrally with said main body portion.
3. A three pin electrical plug as in claim 1 or 2 where the retaining means are in the form of clips as described herein.
4. A three pin electrical plug as in claims 1 to 3 with an interference suppression filter incorporated in the main body portion and retained by retaining means formed integrally with said main body portion.
5. A three pin electrical plug as in claim 4 where the retaining means are in the form of clips as described herein.
6. A three pin plug as in claims 1 to 5 with an insulating material filling the space between lid and main body portions.
7 7. A three pin electrical plug as in any of the preceding claims where the interference suppression filter is in the form of insulated conducting coils wound on a ferrite ring, said coils connected in-line to the live and neutral terminals respectively.
8. A three pin electrical plug as in claims 3 to 6 where the insulating material is extended as a moulding to form a strain relieving block around the cable adjacent the plug.
9. A three pin electrical plug as in claims 3 to 7 where the in-fill insulating material is PVC injected as a hot melt under pressure.
10. A three pin electrical plug as in any of the preceding claims, moulded to provide an identifying mark or legend descriptive of the appliance to be connected to the plug.
11. A three pin electrical plug as shown and described herein with reference to the accompanying drawings.