GB2184298A - Conductive plastics pins for test plug - Google Patents

Abstract

An electric test plug (Figure 1) has three square pins injection moulded from polypropylene copolymer including carbon black to render them conductive. The pins are clipped into spring holders (17) on a board (11) in the body of the plug (14). <IMAGE>

Description

SPECIFICATION Electrically conducting component This invention relates to electrically conducting com- ponentsforexample pins orsockets.

One object of the invention is to provide an alternative to the conventional brass pins and sockets used to make electrical connections.

According to the present invention an electrically conducting component, for example a pin ora socket, is formed from a plastics material. It has been the practice to machine electrically conducting pins for plugs and the like from brass or another metal, and not only is that rather an expensive process but thearrangementforconnecting electrical conductors to the pins tends also to be expensive and tricky to use.

Plastics mouldings are not normally electrically conducting and so have never been considered for use as pins in electrical circuits, although there have been proposals for using plastics materials to enable static charge to leak away from electrical components and also to provide for some shielding against radio frequency interference.

The invention is based on the novel concept that a moulded or other plastics component can act as a connector, conductor or component in an electrical circuit. It is possible to design the constituents ofthe plastics material to ensure that itwill have a certain conductivity or looking at it from another point of view to have a certain electrical resistance.

One satisfactory plastics material is polypropylene copolymerandthat may include a proportion of carbon black to give it its conductivity. The amount of carbon black may determine the resistivity.

The component may constitute a pin of a standard electrical plug and then the pins of a multi-pin plug can be moulded in one operation, each being joined to a connecting piece by a breakable strip. Such pins will not require any further machining and they can be moulded with means enabling them to be easily assembled with a carrier for example a printed circuit board or another board carrying electrical components. Such a board could befitted with spring clips into which the various plugs can be fixed.

Injection or other moulding is preferred for many electrical conductors of plastics material but it may also be possible to extrudethem.

The moulded components could constitute electrical resistors or electrical fuses in addition to acting as current carrying pins or otherconductors.

According to another aspect ofthe invention an el ectrical plug has one or more pins for insertion in a corresponding socket which pins are formed from a plastics material.

The plug may include a printed circuit board or other board carrying electrical connections and means for ready fixing of the pins.

The invention may be carried into practice in various ways and one embodiment as applied to an electric circuittesterwill now be described by way of example with referenceto the accompanying drawings in which Figure 1 is a perspective view of a circuit tester; Figure2 is a circuit diagram ofthe tester of Figure 1; and Figures 3 and 4 are respectively a front elevation and a side elevation of a componentofthe plug of Figures 1 and 2 showing howthe invention is incorporated.

The circuit tester of Figures 1 and 2formsthesub- jectof British Patent Specification No. 1,261,518 and is in theform ofa standard 13 amp square pin plug, although the plug does not have an external lead leading to a load appliance but has three neon tubes A, B, and C apparent in its upper face, and contains electric circuit components constituted by four resistors R within the body of the plug and connected with the three square pins as indicated in Figure 2.

As originally described,and as sold,the resistors were positioned on a circuit board within the body of the plug and the pins were of brass and were connected to components on the board conventionally through grub screws co-operating with conductor holes in the ends ofthe pins.

In accordance with the invention, the pins are moulded from a plastics material which in the example being described in an electrically conducting compound based on carbon black and a polypropylene copolymerwhich is available underthe trade ma rk CABELEC 736.

The three pins L, E and N can be injection moulded in a single moulding operation with the three pins being connected with a carrier barthrough breakable connectors. They can then be assembled on the printed circuit board 11 by being clipped into spring metal channels 12 mounted on one side of the board.

If necessary the pins can be moulded with external projections for making positiveengagementwiththe clips 12. Such a projection is shown at 16.

The three neon tubes A, B, and C and the resistors Rare mounted conventionally on the other side of the board 11 and then the complete sub-assembly shown in Figures 3 and 4 is ready for insertion in the body 1 4 of the plug, following which a cover plate 15 is fitted having windows forthetubes A, B and C and indicating marks enabling the userto interpret the combination oflightswhich are alight to determine the state ofthe circuit being tested and into which the plug has been plugged. That is in the mannerdescribed in the above mentioned patent specification.

The moulded plastics pins L, E and N are cheaper to manufacture and easiertofitthan the con- ventional brass pins, and also they can be designed to have a particular chosen electrical resistance so that in some applications it may be possible to use the resistance ofthe pins as circuit components.

The chosen resistance ofthe pins can restrict the current that can be drawn by a circuit on the board 11 or otherwise connected to the pins.

Moulding is a convenient way of forming the pins from the plastics material but in some applications they could be extruded and possibly cut to length from a uniform section strip.

There will also besomeapplicationswherethe pins are not required to have substantial resistance and the characteristics ofthe particular plastics material will then be designed accordingly.

Carbon resistors may be moulded integ rally with the pins.

In Figure 4 one pin is shown as moulded with indentations 17 for engagement with the spring clip.

Claims (9)

1. An electrically conducting contact pin, for ex- ampleforan electrical plug,which pin isformed from a plastics material.

2. Aconducting pin as claimed in Claim 1 constituted by a plastics moulding.

3. A pin as claimed in either ofthe preceding claims incorporating electrical resistance.

4. A pin as claimed in any ofthe preceding claims in which the platics material is polypropylene copolymerwith orwithouta carbon additive giving it conductivity.

5. A set of pins for an electrical plug which are in a one piece moulding with each pin joined to a connecting piece bya breakable strip.

6. An electrical plug having one or more pins for insertion in a corresponding socket which pins are formed from an electrically conducting plastics material.

7. An electrical plug as claimed in Claim 6 including a board carrying electrical connections or electrical components and also carrying means for ready fixing and connection ofthe pins.

8. An plug as claimed in Claim 7 in which the connecting means comprise spring clips.

9. An electric plug constructed and arranged sub stantially as herein spec.ifically described with refer- pence to the accompanying drawings.