GB2271472A

GB2271472A - Filtered electrical plug.

Info

Publication number: GB2271472A
Application number: GB9210490A
Authority: GB
Inventors: E J Obee
Original assignee: KAINSTAR Ltd
Current assignee: KAINSTAR Ltd
Priority date: 1992-05-15
Filing date: 1992-05-15
Publication date: 1994-04-13
Anticipated expiration: 2012-05-15
Also published as: GB2271472B; GB9210490D0; GB2274026A; GB9305290D0; GB2274026B

Abstract

A pre-wired three pin electrical plug with an interference suppression filter (5 - 9) incorporated within the plug can have upper and lower body sections held together by integrally formed clips. The filter comprises coils (8, 9) wound on a ferrite core (5) held in place by snap-fit catches (16) within a housing (1b). Moulding material may be admitted under pressure to the inside of the plug to provide a filling and moulding which extends as a strain relieving block (21) around cable entry. The side walls of the lower body section are turned slightly inward (19, 20) to clamp the cable. Wire to pin connection is made by crimping the wire in a slot. The name of the connected appliance is moulded on the back of the plug, which also provides a receptacle for receiving a carrier indicating status (eg. servicing). <IMAGE>

Description

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 an interference suppression filter incorporated in the body of the plug.

Also in accordance with the invention there is provided a three pin electrical plug having upper and lower body portions in engagement and held together by retaining means and having an interference suppression filter incorporated between said upper and lower body portions.

The said upper and lower body portions are made from insulating material and are moulded, conveniently to include the retaining means as integral parts. The lower 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 upper and lower body portions held together by retaining means such as a number of clips formed in the corresponding sections of the two body portions. Standard rectangular pins depend from the lower body portion and are connected on the inside of the plug to the appropriate live, neutral and earth wires. In a preferred arrangement the tops of the pins are slotted to receive the bare wires and the connection is made by the application of pressure to the sides of the slot. A filter inside the plug is held in place by means of two clips formed in the lower body portion.

The otherwise empty space between upper body portion and lower body portion is filled with an insulating material such as PVC which may be extended as a moulding to form a strain relieving block surrounding the cable for a short distance from the plug.

The ends of the side walls of the lower body portion adjacent the cable entry gap are turned slightly inward to form a cable clamp. The upper body portion is moulded with the letters or device to indicate the type of appliance to which it will connect. A receptacle may also be moulded in the upper body portion for receiving a removable carrier comprising a strip or disc of e.g. plastic material bearing an identifying mark or legend. This strip may then be used to indicate some status of the connected appliance such as servicing or calibration state. The strip may be coloured and different shapes may be used for different equipments. When the assembly is complete the integrity of the plug should not be violated and only the fuse or fuse cover replaced.

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 lower body portion Figure 2 is a simplified cross sectional view of a plug.

Figure 3 demonstrates the use of legends.

With reference to figure 1 a plan view of lower body portion 1 is shown 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 prongs of the clip which move inward 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. 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 lower 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 are made by placing the wires in slots and then applying pressure to the walls of the slots to compress or crimp the wires. In this manner the wires are held fast and in good contact with the terminals through the walls and bottoms of the slots.

When each of the wires and the filter are connected and in place the upper body portion 17 is attached to the lower body portion 1 by pushing them together to engage the clips 18. The clips 18 are formed as integral parts of the upper and lower body portions as shown in the simplified cross sectional diagram of figure 2 and conveniently, are close to the periphery of the plug. A suitable insulating material such as PVC is then injected into the plug to fill the void and to provide the moulding for the strain relieving block 11, if required.

When the upper and lower body portions of the plug assembly are manufactured the following two features are included. In the lower body portion those parts of the side wall (19, 20) that will be adjacent the cable entry gap on assembly are moulded so as to be turned slightly inward, as shown in figure 1. This feature provides a cable clamp . The name of the appliance to which the plug will connect is moulded in the upper body section so as to be visible to the user when the plug is assembled. This feature is illustrated in figure 3.

Claims

1. A three pin electrical plug with an interference suppression filter incorporated in the body of the plug.

2. A three pin electrical plug having upper and lower body portions in engagement and held together by retaining means and having an interference suppression filter incorporated between said upper and lower body portions.

3. A three pin plug as in claim 2 with an insulating material filling the space between upper and lower body portions.

4. A three pin electrical plug as in claims 2 or 3 where the retaining means is formed as integral parts of the upper and lower body portions.

5. A three pin electrical plug as in claims 2 to 4 where the ends of the side walls of the lower body portion adjacent the cable entry gap are turned inward to form a cable clamp.

6. 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.

7. 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.

8. A three pin electrical plug as in claims 3 to 7 where the insulating material is PVC.

9. 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.

10. A three pin electrical plug as in any of the preceding claims, moulded to provide a receptacle for a removable carrier of an identifying mark or legend descriptive of the status of the appliance connected to the plug.

11. A three pin electrical plug as in any of the preceding claims wherein wiring to pin connections are made by positioning the wire in a slot in the pin and applying pressure to the sides of the slot.

12. A three pin electrical plug as shown and described herein with reference to the accompanying drawings.