GB2040605A

GB2040605A - Electric plugs

Info

Publication number: GB2040605A
Application number: GB8000494A
Authority: GB
Original assignee: BICCBURNDY Ltd; BICC PLC
Current assignee: BICCBURNDY Ltd; Balfour Beatty PLC
Priority date: 1979-01-08
Filing date: 1980-01-08
Publication date: 1980-08-28
Also published as: GB2040605B

Abstract

In an electric plug having at least two line pins 2 projecting from the insulating plug body 1, e.g., a 13 amp three pin plug, each line pin 2 is, over a substantial part of its length adjacent the plug body 1, of reduced overall cross-section and has a separate sleeve 4 of plastics insulating material heat-shrunk about and gripping the reduced part of the length of the pin. The heat-shrunk sleeve 4 is so shaped and dimensioned that its outer surface forms a smooth continuation of the surface of the unreduced part of the length of the pin. The pin may be of solid or hollow form. <IMAGE>

Description

SPECIFICATION An improved electric plug This invention relates to electric plugs and is especially, but not exclusively, concerned with electric plugs for use in domestic and similar wiring systems.

When an electric plug is electrically connected in a socket outlet but the faces of the plug and outlet are not in interfacial engagement, there is a substantial risk that a child or other person will introduce a finger or other object between these faces and receives an electric shock. To reduce this risk, it has been proposed and is sometimes the practice to provide on at least each line pin of the plug an insulating protective covering which extends around and along a substantial part of the length of the pin projecting from and adjacent to the insulating plug body.Such insulating protective pin-coverings may be integral parts of the plug body but more recently it has been proposed to use, for each insulating pin-covering, a separate sleeve of insulating material which fits over a part of a length of a pin or a separate body of insulating material which is moulded in situ on a part of a length of a pin, each of which parts is of reduced cross-section.

According to the present invention, we provide an electric plug having an insulating plug body from which at least two line pins project, wherein a substantial part of the length of each line pin adjacent the plug body is of reduced overall crosssection and has a separate sleeve of plastics insulating material heat-shrunk about and gripping said reduced part of the length of the pin, the heat-shrunk plastics sleeve being so shaped and dimensioned externally that its outer surface forms a substantially smooth continuation of the surface of the unreduced part of the length of the pin.

Each line pin may be of solid form or it may be a hollow pin formed by folding or otherwise shaping a sheet metal preform.

Preferably, the part of the length of the pin of reduced overall cross-section extends to the end of the pin within the plug body.

The transverse configuration of each line pin may be rectangular, circular or any other desired transverse cross-sectional shape and the transverse configuration of said reduced part may be of the same transverse cross-sectional shape as that of the pin or may have a transverse crosssectional shape differing from that of the pin.

In all cases, the external surface of said reduced part of the length of each line pin may be serrated, etched or otherwise roughened to enhance the grip of the heat-shrunk plastics sleeve. In some cases, the heat-shrunk plastics sleeve may be bonded to the reduced part of the pin.

By the expression "heat-shrunk" is meant that condition to which a sleeve or other article of one shape made from a heat-shrinkable plastics material, that has been caused to expand or otherwise deform into another shape at an appropriate temperature, will at least partly contract or otherwise recover when it is subsequently subjected to a sufficiently high temperature.

Heat-shrinkable plastics materials that may be used for the sleeve include cross-linked polyethylene, which can be caused to contract to an extent sufficient for the sleeve to grip said reduced part of the length of the pin when the sleeve is heated to a temperature of about 1 500 C, polyester material, polyvinyl chloride, ethylenevinyl acetate and certain grades of polytetrafluoroethylene and other fluorocarbon polymers and copolymers.

The invention also includes an electrically insulated electric plug pin substantially as hereinbefore described.

The invention will be further illustrated by a description, by way of example, of a preferred 13 amp three pin plug with reference to the accompanying drawings, in which: Figure 1 is a pictorial view of the electric plug; and Figure 2 is a fragmental perspective view of a hollow line pin of the electric plug shown in Figure 1.

Referring to Figure 1, the electric plug comprises an insulating body 1 which houses the plug terminals (not shown) and from one face of which project line pins 2 and an earth pin 3. Each line pin 2 has, over a substantial part of its length adjacent the plug body 1, a sleeve 4 of plastics insulating material that has been heat-shrunk about and grips said part of the pin.

As will be seen on referring to Figure 2, each line pin 2 is of hollow form and is made by folding a sheet brass preform 5. The sheet brass preform 5 is of reduced thickness over a part of its length so that, when it is folded to form the hollow pin 2, a part 6 of reduced overall cross-section is formed on which the sleeve 4 of cross-linked polyethylene is heat-shrunk. The sleeve 4 is so shaped and dimensioned externally that its outer surface forms a smooth continuation of the surface of the unreduced part of the length of the pin 2.

1. An electric plug having an insulating plug body from which at least two line pins project, wherein a substantial part of the length of each line pin adjacent the plug body is of reduced overall cross-section and has a separate sleeve of plastics insulating material heat-shrunk about and gripping said reduced part of the length of the pin, the heat-shrunk plastics sleeve being so shaped and dimensioned externally that its outer surface forms a substantially smooth continuation of the surface of the unreduced part of the length of the pin.

2. An electric plug having an insulating plug body from which at least two line pins project, wherein each line pin is a hollow pin which is formed by folding or otherwise shaping a sheet metal preform and which, over a substantial part of its length adjacent the plug body, is of reduced cross-section, and wherein a separate sleeve of

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION An improved electric plug This invention relates to electric plugs and is especially, but not exclusively, concerned with electric plugs for use in domestic and similar wiring systems. When an electric plug is electrically connected in a socket outlet but the faces of the plug and outlet are not in interfacial engagement, there is a substantial risk that a child or other person will introduce a finger or other object between these faces and receives an electric shock. To reduce this risk, it has been proposed and is sometimes the practice to provide on at least each line pin of the plug an insulating protective covering which extends around and along a substantial part of the length of the pin projecting from and adjacent to the insulating plug body.Such insulating protective pin-coverings may be integral parts of the plug body but more recently it has been proposed to use, for each insulating pin-covering, a separate sleeve of insulating material which fits over a part of a length of a pin or a separate body of insulating material which is moulded in situ on a part of a length of a pin, each of which parts is of reduced cross-section. According to the present invention, we provide an electric plug having an insulating plug body from which at least two line pins project, wherein a substantial part of the length of each line pin adjacent the plug body is of reduced overall crosssection and has a separate sleeve of plastics insulating material heat-shrunk about and gripping said reduced part of the length of the pin, the heat-shrunk plastics sleeve being so shaped and dimensioned externally that its outer surface forms a substantially smooth continuation of the surface of the unreduced part of the length of the pin. Each line pin may be of solid form or it may be a hollow pin formed by folding or otherwise shaping a sheet metal preform. Preferably, the part of the length of the pin of reduced overall cross-section extends to the end of the pin within the plug body. The transverse configuration of each line pin may be rectangular, circular or any other desired transverse cross-sectional shape and the transverse configuration of said reduced part may be of the same transverse cross-sectional shape as that of the pin or may have a transverse crosssectional shape differing from that of the pin. In all cases, the external surface of said reduced part of the length of each line pin may be serrated, etched or otherwise roughened to enhance the grip of the heat-shrunk plastics sleeve. In some cases, the heat-shrunk plastics sleeve may be bonded to the reduced part of the pin. By the expression "heat-shrunk" is meant that condition to which a sleeve or other article of one shape made from a heat-shrinkable plastics material, that has been caused to expand or otherwise deform into another shape at an appropriate temperature, will at least partly contract or otherwise recover when it is subsequently subjected to a sufficiently high temperature. Heat-shrinkable plastics materials that may be used for the sleeve include cross-linked polyethylene, which can be caused to contract to an extent sufficient for the sleeve to grip said reduced part of the length of the pin when the sleeve is heated to a temperature of about 1 500 C, polyester material, polyvinyl chloride, ethylenevinyl acetate and certain grades of polytetrafluoroethylene and other fluorocarbon polymers and copolymers. The invention also includes an electrically insulated electric plug pin substantially as hereinbefore described. The invention will be further illustrated by a description, by way of example, of a preferred 13 amp three pin plug with reference to the accompanying drawings, in which: Figure 1 is a pictorial view of the electric plug; and Figure 2 is a fragmental perspective view of a hollow line pin of the electric plug shown in Figure 1. Referring to Figure 1, the electric plug comprises an insulating body 1 which houses the plug terminals (not shown) and from one face of which project line pins 2 and an earth pin 3. Each line pin 2 has, over a substantial part of its length adjacent the plug body 1, a sleeve 4 of plastics insulating material that has been heat-shrunk about and grips said part of the pin. As will be seen on referring to Figure 2, each line pin 2 is of hollow form and is made by folding a sheet brass preform 5. The sheet brass preform 5 is of reduced thickness over a part of its length so that, when it is folded to form the hollow pin 2, a part 6 of reduced overall cross-section is formed on which the sleeve 4 of cross-linked polyethylene is heat-shrunk. The sleeve 4 is so shaped and dimensioned externally that its outer surface forms a smooth continuation of the surface of the unreduced part of the length of the pin 2. CLAIMS

2. An electric plug having an insulating plug body from which at least two line pins project, wherein each line pin is a hollow pin which is formed by folding or otherwise shaping a sheet metal preform and which, over a substantial part of its length adjacent the plug body, is of reduced cross-section, and wherein a separate sleeve of plastics insulating material has been heat-shrunk about and grips said reduced part of each hollow pin. The heat-shrunk plastics sleeve being so shaped and dimensioned externally that its outer surface forms a substantially smooth continuation of the surface of the unreduced part of the length of the hollow pin.

3. An electric plug as claimed in Claim 1 or 2, wherein each line pin is of substantially rectangular external transverse cross-section.

4. An electric plug as claimed in any one of the preceeding Claims, wherein the part of the length of each line pin which is of reduced overall cross section extends to the end of the pin within the plug body.

5. An electric plug as claimed in any one of the preceding Claims, wherein the external surface of said part of at least one of the line pins gripped by the heat-shrunk plastics sleeve is serrated, etched ',or otherwise roughened.

6. An electric plug as claimed in any one of the preceding Claims, wherein the heat-shrunk plastics sleeve is bonded to the reduced part of the length of the pin.

7. An electric plug as claimed in any one of the preceding Claims, wherein the transverse configuration of said reduced part of each line pin has a transverse cross-sectional shape differing from that of the pin.

8. For use in an electric plug as claimed in Claim 1, an electric plug pin which, over a substantial part of its length remote from the nose end of the pin, is of reduced overall cross-section and has a separate sleeve of plastics material heat-shrunk about and gripping said reduced part of the length of the pin, the heat-shrunk plastics sleeve being so shaped and dimensioned externally that its outer surface forms a substantially smooth continuation of the surface of the unreduced part of the length of the pin.

9. For use in an electric plug as claimed in Claim 2, a hollow pin which is formed by folding or otherwise shaping a sheet metal preform and, over a substantial part of its length remote from the nose end of the pin, is of reduced overall cross-section and which has a separate sleeve of plastics material heat-shrunk about and gripping said reduced part of the length of the pin, the heat shrunk plastics sleeve being so shaped and dimensioned externally that its outer surface forms a substantially smooth continuation of the surface of the unreduced part of the length of the pin.

10. An electric plug substantially as hereinbefore described with reference to and as shown in Figure 1 of the accompanying drawing.

11. For use in an electric plug as claimed in Claim 1 or 9 an electrically insulated electric plug pin substantially has hereinbefore described with reference to and as shown in Figure 2 of the accompanying drawing.