GB2095924A

GB2095924A - An electric plug

Info

Publication number: GB2095924A
Application number: GB8207991A
Authority: GB
Original assignee: BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1981-03-19
Filing date: 1982-03-18
Publication date: 1982-10-06
Also published as: GB2095924B

Abstract

A plug moulded to an end of a flexible electric cable includes a pre- formed base insert 1 of electrically insulating material having holes through which plug pins 4, 5 protrude from the rear face of the insert. A vacuum-formed membrane 24 of electrically insulating material closely fits around the conductor terminals and is wholly or partially encapsulated within the moulded body 25 of the plug assembly. The insulating material of the membrane 24 is tougher than the insulating material of the moulded body 25 and the membrane substantially reduces risk at a conductor wire will protrude through the moulded plug body. <IMAGE>

Description

SPECIFICATION An improved electric plug assembly This invention relates to an electric plug assembly of the kind in which line and neutral plug pins, and usually but not necessarily an earth plug pin, and their associated conductor terminals are mounted in a preformed body of electrically insulating material, the conductors of a length of flexible insulated multi-conductor cable are electrically connected to appropriate terminals of the plug, and a moulded plug body of electrically insulating material wholly or partially encapsulates the preformed body and the plug pins and associated conductor terminals with an appropriate length of each pin protruding from the plug assembly and is permanently bonded to the insulating covering of a part of the length of cable. Electric plug assemblies of this kind will hereinafter, for convenience, be referred to as "of the kind described".

Three pin eletric plug assemblies of the kind described are especially suitable for use with domestic appliances because such appliances can be sold to the public with an electric plug permanently bonded to the flexible cable of an appliance, thereby eliminating the risk that an unskilled user of an appliance may connect a conventional rewirable three pin plug to an end of the flexible cable of the appliance in an incorrect manner which, when the appliance is used, may result in injury to the user and/or permanent damage to the appliance.

It has been found that, in manufacturing electric plug assemblies of the kind described, there is a risk that, during moulding of the plug body, a wire or wires of the exposed end of a cable conductor connected to one of the terminals will become detached from the terminal and will protrude through the moulded plug body. A plug assembly which is connected to a domestic electrical appliance and which has a live wire or wires protruding through the plug body is extremely dangerous, especially if handled with damp hands - as may be the case when the plug assembly is connected to a domestic washing machine.

It is the object of the present invention to provide an improved electric electric plug assembly of the kind described in which the aforesaid risk is eliminated or at least substantially reduced.

According to the invention, the improved plug assembly of the kind described comprises a preformed body of electrically insulating material having holes therethrough in which are fitted plug pins which protrude from the rear face of the preformed body; a vacuum-formed membrane of electrically insulating material closely fitting around at least the conductor terminals associated with the live and neutral pins of the plug, and preferably the conductorterminals associated with all the plug pins; and, wholly or partially encapsulating the vacuumformed membrane, a moulded body of electrically insulating material which is bonded to the preformed body, the vacuum-formed membrane and the insulating covering of an adjacent part of the flexible cable, the insulating material of the membrane being substantially tougher than the insulating material of the moulded body.

By the expression "vacuum-formed membrane" is meanta membrane formed by applying over said conductor terminals and sealing to the preformed body a thin-walled shell of electrically insulating material to form, between the shell and preformed body, an air-tight enclosure, and evacuating air from within the enclosure to cause the shell to collapse and closely fit around said terminals.

The provision of a vacuum-formed membrane which is of an insulating material that is substantially tougher than that of the moulded body, which closely fits around at least the live and neutral terminals and which thereby lies between them and the moulded body, eliminates or substantially reduces the risk that a conductor wire or conductor wires may protrude through the moulded plug body.

Where, for example, the moulded body is of nylon or polyvinyl chloride, preferably the vacuum-formed membrane is of a polyester or of any other material that will withstand a test temperature of at least 750"C. The vacuum-formed membrane may be of a colour different and readily distinguishable from that of the moulded body, and preferably, at least a part of the vacuum-formed membrane is visible from a face of the plug assembly to provide an indication that the membrane is present within the moulded body.

Preferably, each plug pin has at least one shoulder which bears against the front face of the preformed body to limit the extent of protrusion of the pin. The plug pins and/orthe associated conductor terminals may be held in position in the holes with the shoulders bearing against the front face of the preformed body by the vacuum-formed membrane or by a preformed spider of electrically insulating material which underlies and is tightly enclosed within the vacuum-formed membrane and which is supported by a plurality of limbs on, and is connected to, the front face of the preformed body and has protrusions bearing against parts of the plug pins protruding from the front face of the preformed body and/or against the conductor terminals or fuse contact associated with the pins.

Preferably, when present, the preformed spider is detachably connected to the preformed body and, in a preferred embodiment, the preformed spider has protuberances which are snap fits in appropriately located holes or recesses in the preformed body.

The preformed spider is preferably of an insulating material which is harder than the insulating material of the moulded body and which may be the same material as that of the preformed body. The preformed spider is preferably of a material which will withstand a test temperature of at least 750 C.

Preferred materials of which the preformed spider may be made include a glass-filled polyester and nylon.

Instead of holding the plug pins and/or the associated conductor terminals in position in the holes in the preformed body with the shoulders on the pins bearing against the front face of the preformed body by the vacuum-formed membrane or by a preformed spider, each plug pin may effect a snap fit with a resilient lug or other means integral with the preformed body, as described in the Specfication of our co-pending Patent Application No. 8133150, or each pin may have, integral with the pin, at least one outwardly extending resilient lug which engages the rear face of the preformed body when the pin is fully engaged in its associated hole with its shoulder or shoulders bearing against the front face of the preformed body and prevents withdrawal of the pin.

The invention also includes an improved method of manufacturing an improved electric plug assembly as hereinbefore described, which method comprises effecting the electrical connections between the plug pins and their associated conductorterminals and the electrical connections between the conductors of the flexible cable and the conductor terminals; introducing the plug pins, with the cable conductors electrically connected to the conductor terminals associated with the pins, into holes extending through the preformed body; applying a thin-walled shell of electrically insulating material over at least the terminals associated with the live and neutral pins, and preferably over all of the terminals, and sealing the shell to the preformed body to form an air-tight enclosure; evacuating air from the enclosure to cause the shell to collapse and form a vacuum-formed membrane which closely fits around said conductor terminals; and moulding electrically insulating material around the subassembly so formed to form a moulded body which wholly or partially encapsulates the vacuum-formed membrane and is bonded to the preformed body, the vacuum-formed membrane and the insulating covering of an adjacent part of the flexible cable.

Preferably, the moulded body is moulded by an injection moulding technique.

The conductors of the flexible cable may be electrically connected to the conductor terminals in any convenient manner, a crimped connection being preferred.

Where the plug assembly is to include means for electrically connecting a cartridge fuse between the live pin and its associated conductor terminal, preferably said means comprises two electrical contacts, one of which is electrically connected to the live pin and the other to the conductorterminal associated with the live pin, before they are intro duced from the front face of, and into spaced holes in, the preformed body so that they protrude into a cartridge fuse recess in the rear face of the pre formed body.

Alternatively, the two spaced electrical contacts may be carried on a single preformed carrier or on two separate preformed carriers of insulating mate rial, which contacts are electrically connected to the live pin and said associated conductor terminal before they are introduced into the preformed body and which are introduced from the front face of, and into a hole or holes in, the preformed body so that they protrude into a cartridge fuse recess in the rear face of the body with their carrier or carriers fitting tightly in the hole or holes. Preferably, the two electrical contacts are carried on a carrier of rectan gular shape which is a tight fit in a hole of corresponding shape.To ensure that the carrier is a tight fit in the hole, preferably the walls of the hole converge towards one another in a direction toward the rear face of the preformed body and the side faces of the carrier are of complementary shape, the tightness of the fit thereby increasing as the carrier is introduced into the hole from the front face of the body. One of each of the electrical contacts preferably is a spring clip for gripping a terminal of a cartridge fuse and also is preferably of such a shape and size, having regard to the size of its associated hole, that when the carrier on which the spring clip or clips is or are carried is fully home in the hole, the spring clip or clips effects or effect a snap fit so that the carrier cannot subsequently be withdrawn.

The invention is further illustrated by a description, by way of example, of a preferred 13 A three-pin plug assembly of the kind described with reference to the accompanying drawings, in which Figure 1 is an exploded isometric view of the preformed body and preformed spider of the plug; Figure 2 is a sectional end view of the preformed body with the preformed spider and vacuum-formed membrane thereon, and Figure 3 is a sectional end view of the three-pin plug.

Referring to Figures 1 to 3, the preformed body 1 of moulded plastics material has extending through the body three holes in which live and neutral pins 4 and an earth pin 5, each of hollow form, are inserted from the front face 2 of the body so that they protrude from the rear face 3 of the body with shoulders 6,7 on the pins bearing against the front face. The live conductor 11 of a flexible cable 10 is connected by a crimped connection 14to one spring contact 15 of a pair of spring contacts which project into a cartridge fuse recess (not shown) in the rear face 3 of the preformed body 1; the neutral conductor 12 of the cable is connected by a crimped connection 17 to the neutral pin 4; and the earth conductor 13 of the cable is connected by a crimped connection 18 to the earth pin 5. The live pin 4 is connected direct to the other of the spring contacts 15.A preformed spider 20 of moulded plastics material is supported by a limb 21 and side limbs 22 on the front face 2 of the preformed body 1, the side limbs making snap fits in holes 19 in the preformed body. The spider 20 has on its inner surface protrusions 23 which bear against parts of the earth pin and live and neutral pins and their associated conductor terminals and spring contact to urge the shoulders 6,7 against the front face 2 of the preformed body 1, so that appropriate lengths of the pins protrude from the rear face 3 of the body. A vacuum-formed membrane 24 of electrically insulating material closely fits around all the crimped connections and the preformed spider 20. An outer moulded body 25 of electrically insulating material wholly encapsulates and is bonded to the preformed body 1, the vacuum-formed membrane 24 and the sheath of an adjacent part of the flexible cable 10.

The electrically insulating material of the vacuumformed membrane 24 is tougher than the electrically insulating material of the moulded body 25 and thereby substantially reduces the risk that a stray conductorwirewill protrudethroughthe moulded body.

Claims

1. An electric plug assembly ofthe kind described comprising a preformed body of electrically insulating material having holestherethrough in which are fitted plug pins which protrude from the rear face of the preformed body; a vacuum-formed membrane of electrically insulating material closely fitting around at least the conductor terminals associated with the live and neutral pins of the plug; and, wholly or partially encapsulating the vacuumformed membrane, a moulded body of electrically insulating material which is bonded to the preformed body, the vacuum-formed membrane and the insulating covering of an adjacent part of the flexible cable, the insulating material of the membrane being substantially tougher than the insulating material of the moulded body.

2. An electric plug assembly as claimed in Claim 1, wherein the vacuum-formed membrane closely fits around the conductor terminals associated with all the plug pins.

3. An electric plug assembly as claimed in claim 1 or 2, wherein the vacuum-formed membrane is of an electrically insulating material that will withstand a test temperature of at least 750"C.

4. An electric plug assembly as claimed in any one of the proceding Claims, wherein the vacuumformed membrane is of a colour different and readily distinguishable from that of the moulded body and at least a part of the vacuum-formed membrane is visible from a face of the plug assembly to provide an indication that the membrane is present within the moulded body.

5. An electric plug assembly as claimed in any one of the preceding Claims, wherein each plug pin has at least one shoulder which bears against the front face of the preformed body to limit the extent of protrusion of the pin.

6. An electric plug assembly as claimed in Claim 5, wherein the plug pins and/orthe associated conductor terminals are held in position in the holes with the shoulders bearing against the front face of the preformed body by the vacuum-formed membrane.

7. An electric plug assembly as claimed in any one of Claims 1 to 5, wherein the plug pins and/or the associated conductor terminals are held in position in the holes with the shoulders bearing against the front face of the preformed body by a preformed spider of electrically insulating material which underlies and is tightly enclosed within the vacuum-formed membrane and which is supported by a plurality of limbs on, and is connected to, the front face of the preformed body and has protrusions bearing against parts of the plug pins protruding from the front face of the preformed body and/or against the conductor terminals or fuse contact associated with the pins.

8. An electric plug assembly as claimed in Claim 7, wherein the preformed spider is detachably connected to the preformed body.

9. An electric plug assembly as claimed in Claim 8, wherein the preformed spider has protruberances which are snap fits in appropriately located holes or recesses in the preformed body.

10. An electric plug assembly as claimed in any one of Claims 7 to 9, wherein the preformed spider is of an insulating material which is harder than the insulating material of the moulded body and which will withstand a test temperature of at least 750"C.

11. An electric plug assembly as claimed in any one of Claims 1 to 5, wherein each plug pin effects a snap fit with a resilient lug or other means integral with the preformed body.

12. An electric plug assembly as claimed in any one of Claims 1 to 5, wherein each plug pin has, integral with the pin, at least one outwardly extending resilient lug which engages the rear face of the preformed body when the pin is fully engaged in an associated hole with its shoulder or shoulders engaging the front face of the preformed body and prevents withdrawal of the pin.

13. A method of manufacturing an electric plug assembly of the kind described, which method comprises effecting the electrical connections between the plug pins and their associated conductor terminals and the electrical connections between the conductors of the flexible cable and the conductor terminals; introducing the plug pins, with the cable conductors electrically connected to the conductor terminals associated with the pins, into holes extending through the preformed body; applying a thin-walled shell of electrically insulating material over at least the terminals associated with the live and neutral pins and sealing the shell to the preformed body to form an air-tight enclosure; evacuating air from the enclosure to cause the shell to collapse and to form a vacuum-formed membrane which closely fits around the said conductor terminals; and moulding electrically insulating material around the sub-assembly so formed to form a moulded body which wholly or partially encapsulates the vacuum-formed membrane and is bonded to the preformed body, the vacuum-formed membrane and the insulating covering of an adjacent part of the flexible cable.

14. A method as claimed in Claim 13, wherein the thin-walled shell is applied over the terminals associated with all of the pins.

15.A method as claimed in Claim 13 or 14, wherein the moulded body is moulded by an injection moulding technique.

16. A method as claimed in any of Claims 13 to 15, wherein the conductors of the flexible cable are electrically connected to the conductor terminals by crimped connections.

17. A method as claimed in any one of Claims 13 to 16, wherein the neutral and earth pins are integral with their associated conductor terminals.

18. A method as claimed in any one of Claims 13 to 17 in which the plug assembly includes means for electrically connecting a cartridge fuse between the live pin and its associated conductor terminal, wherein one of two electrical contacts is electrically connected to the live pin and the other of said two electrical contacts is electrically connected to the conductor terminal of the live pin and said two electrical contacts are then introduced from the front face of, and into spaced holes in, the preformed body so that they protrude into a cartridge fuse recess in the rear face of the preformed body.

19. An electric plug assembly substantially as hereinbefore described with reference and as shown in the accompanying drawings.