Geometrical instruments
Patent
1980-08-20
1983-01-25
McQuade, John
Geometrical instruments
339196M, H01R 1358
Patent
active
043700160
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an electrical coupling device, in particular but not exclusively a 3-pin plug, comprising a cable grip.
It is a requirement in many forms of electrical coupling devices, for example multi-pin plugs and pin and socket connectors, that the electrical cable entering the coupling device shall be gripped, independently of the electrical connection(s) to the conductor(s) of the cable, by means of a cable grip. This is to ensure that when a tensile force is applied to the cable, the force is resisted by the cable grip and not transmitted to the electrical connections within the coupling device.
The commonest cable grip used in electrical coupling devices, particularly in multi-pin plugs, has a strip of electrically insulating material which is caused to clamp the electrical cable against a surface of the coupling device by means of two screws which engage screw-threaded holes in the strip. Although capable of accommodating cables in a wide range of different sizes, this kind of cable grip has the serious disadvantage that the screw threads in the strip are very easily sheared by the metallic screws, and when this happens the cable grip is rendered useless. Furthermore, parts of the cable grip are easily lost.
Another known kind of cable grip in electrical coupling devices provides resilient blades of plastics material which flex apart when an electrical cable is placed between them and bite into the electrical insulation of the cable. It is not unknown for this kind of cable grip to strip the insulation from the electrical cable being clamped when an external tensile force is applied to the cable.
The present invention aims to provide an electrical coupling device having a cable grip which does not have the disadvantages mentioned above.
According to the invention, an electrical coupling device of the kind comprising a housing, meams within the housing for effecting electrical connection to one or more conductors of an electrical cable which enters the housing in use of the device and a cable grip for clamping the cable relative to the housing, is characterised in that the cable grip comprises a pair of cooperating jaws adapted to receive the cable therebetween and camming means formed in the housing into which the pair of jaws with the cable therebetween can be pressed, said camming means being arranged to exert pressure on a pair of opposed surfaces of the pair of jaws to force the jaws towards one another to grip the cable when the jaws are pressed into the camming means in a direction substantially perpendicular to the path of the cable through the jaws, and said housing comprising means to limit movement of the jaws in the direction of said path when a tensile force is applied to the gripped cable in a direction tending to pull the cable out of the coupling device.
Said housing may comprise a base, for example of electrically insulating material, and a cover removably mounted on the base. The camming means may then be in the form of a recess in the base and the jaws may be secured to the cover. Alternatively, the camming means may be in the form of a recess in the cover and the jaws may be secured to the base. In either case, the recess may have inlet and outlet apertures which, in use of the coupling device, accommodate the electrical cable in its passage through the recess. In the particular case of a 3-pin, 13 amp plug of the kind shown and described in FIGS. 1 to 4 of German laid-open patent application No. P. 26 45 143.4, now German published patent application No. 2,645,143 which is incorporated herein by reference, (hereinafter referred to as "the aforesaid Specification"), a fourth pair of jaws similar to the jaws 14a, 14b may be secured to the plug cover 6 in place of the illustrated cable grip 12 and a fourth recess similar to the recess 23 may be provided in the base 2 to receive and press together the jaws of the fourth pair when the cover 6 is assembled on the base 2. In the wiring-up of such a plug, the cable 7 may be placed between the jaws of the fourth pair before t
REFERENCES:
patent: 1601255 (1926-09-01), Marra
patent: 2258712 (1941-10-01), Miller
patent: 2673968 (1954-03-01), Smith
patent: 2690470 (1954-09-01), Moorhead
patent: 3056852 (1962-10-01), Sachs
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