US3781765A - Electrical connectors with internal and external strain-relief for conductor wires - Google Patents

Abstract

A dead-front connector has two means to grip the wires within the housing, plus a means to grip the whole cord outside the housing, and a seal to prevent bits of foreign matter from entering the housing. The outside means grips the cord as a whole and is made to conform to the shape of any standard size wire reducing to a minimum the crushing force and danger of short circuit. One internal gripping means is the connection between the conductor and its respective contact member. The other internal gripping means grips the insulation of each individual wire so that it is not possible to apply a force to the terminal connection of any wire and contact by pulling from outside the housing. Pulling the wires out of engagement with their contact members with the attendant danger of causing a short circuit within the housing is thus prevented.

Description

United States'Patent [191 Schleicher Dec. 25, 1973 [54] ELECTRICAL CONNECTORS WITH 251,676 5/1926 Great Britain 339/103 INTERNAL AND EXTERNAL 702,066 1/1954 Great Britain 339/ 105 611959 Switzerland 3 39/103 STRAIN-RELIEF FOR CONDUCTOR WIRES [75] Inventor: Harold E. Schleicher, West Hartford, Conn.

[73] Assignee: Arrow-Hart, 1nc., Hartford, Conn.

[22] Filed: Apr. 3, 1969 [21] Appl. No.: 813,216

[52] US. Cl. 339/103 R, 339/14 P, 339/206 P [51] Int. Cl 1-10lr 13/58 [58] Field of Search 339/103, 206, 105,

[56] References Cited UNITED STATES PATENTS 1,398,228 11/1921 Grigsby 339/103 X 2,276,557 3/1942 Woodhead 339/103 X 2,970,288 1/1961 Hubbell et al. 339/103 X 2,972,492 2/1961 Mintz et a] 285/117 3,181,105 4/1965 Roach et al..... 339/103 X 3,372,361 3/1968 Wengen 339/97 3,390,371 6/1968 Kramer 339/206 X FOREIGN PATENTS OR APPLICATIONS 1,043,916 6/1953 France 339/105 Primary Examiner-Richard E. Moore AttorneyDavis, l-loxie, Faithfull & l-lapgood [57 ABSTRACT A dead-front connector has two means to grip the wires within the housing, plus a means to grip the whole cord outside the housing, and a seal to prevent bits of foreign matter from entering the housing. The outside means grips the cord as a whole and is made to conform to the shape of any standard size wire reducing to a minimum the crushing force and danger of short circuit. One internal gripping means is the connection between the conductor and its respective contact member. The other internal gripping means grips the insulation of each individual wire so that it is not possible to apply a force to the terminal connection of any wire and contact by pulling from outside the housing. Pulling the wires out of engagement with their contact members with the attendant danger of causing a short circuit within the housing is thus prevented.

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Hara/dESch/a'c/rer ELECTRICAL CONNECTORS WITH INTERNAL AND EXTERNAL STRAIN-RELIEF FOR CONDUCTOR WIRES This invention relates to electrical caps and connectors to which are to be connected multi-wire conductor cords of the sort that have a plurality of individual insulated wires within an insulating sheath. More particularly, the invention relates to caps and connectors of insulation material which have, (a) clamping means on the receptacle and plug contacts housed within the insulation material so as to grip the bared ends of the individual insulated wires; (b) wire gripping means for the individual insulated wires inside the cap and connector and (c) external conductor cord gripping or strain relief means.

Not only the wire connections to the receptacle contact members and the plug contact members are enclosed in the insulation material but likewise the receptacle contacts are enclosed. Only the plug'contacts, which are not on the live side of the circuit, are exposed. Hence, the caps and connectors present what is commonly known as a deadfront cap and connector structure.

In such structures as heretofore known metal chips and other small conductive or semi-conductive pieces could enter the connector members around the conductor cord and cause short circuits. To prevent this, an internal seal is provided by this invention. Also in prior structure the conductor wires could slip within the outside cover or sheath of the cable or conductor cord. According to the present invention there is provided an internal gripping of the individual conductor wires in addition to an external strain relief fitting that clamps the cable sheath or cord containing the insulated wires. Thus any slippage of the wires within the sheath of the cord despite the firmest grip and clamping action of the exterior strain relief fitting is not transmitted to the terminal connection of the wires to the connector contacts and the danger of the wires pulling away from the contacts with attendant danger of short circuit is avoided.

The objects and advantages of the invention will become apparent as it is described in connection with the accompanying drawings.

FIG. I is an exploded perspective view of a receptacle-type connector embodying the invention.

FIG. 2 is a bottom end view of the connector of FIG.

FIG. 3 is a perspective view of receptacle contacts embodied in FIG. 1.

FIG. 4 is aside elevation view of the connector of FIG. 1.

FIG. 5 is a side elevation view of a plug-type connector embodying the invention.

FIG. 6 is an exploded view of the plug-connector of FIG. 5.

FIG. 7 is a plan view looking down into the shell of FIG. 6.

FIG. 8 is a bottom plan view of the inner or prongreceiving body of FIG. 6.

FIG. 9 is a longitudinal diametrical section view, partly broken away, of the connector of FIG. 6.

FIG. 10 is an exploded detail view of one exterior cord gripping clamp member and insert.

FIG. 11 is a plan view of members of the exterior clamping means of the type shown in FIG. 6 with inlarge or small diameter.-

Referring to the drawings, the assembled connector has two main parts, a receptacle as seen in FIG. 4 and a plug as seen in FIG. 5. These parts may be pushed together and pulled apart in usual fashion to connect and disconnect them. The invention is illustrated and described as embodied in three-wire form, two wires w, w being conductor wires and the third G, being a ground wire. However, as will clearly appear, the invention is not limited to a particular number of wires.

Referring to FIG. 1 the receptacle is built up from three insulation members 20, 30 and 40 plus a gasket 49, and a strain relief fitting 50, 60 all as more fully described hereinafter. The body part 20 is cylindrical and has three parallel independent and isolated recesses 21, 22, and 23 extending therethrough parallel to the axis of the body. These recesses are adapted to receive stationary stamped sheet metal contact members or receptacle contacts 25, 26 and a ground contact 27 of conventional form having two facing spring fingers 25a, 25b and a third finger 25c at right angles thereto. Bent up from the fingers is a wire terminal tab such as 25! through which freely passes a wire binding screw 29 that threads into a tapped hole in a wire clamping plate 28.

On top of the outer body is mounted an inner body 30 made of insulating material such as nylon and having a generally cylindrical or thick disc shape, but of slightly less diameter than the body'20. Three recesses (not shown) are formed in that face of the inner body 30 which is adapted to lie against and on top of the inner face of the outer body 20. These recesses register in part with the recesses in the outer body and receive the wire terminal gripping elements 25t, 28 and 29 of the fixed contacts. The recesses in the inner body extend radially outward as at 31 and 32 to provide access to the wire binding screws 29, so that the clamping plates 28 can be moved toward and away from the terminal tabs 25! of the contact members.

Within the recesses 21, 22 and 23 of the outer body, V-shaped steel spring (not shown) members stamped from sheet metal with upstanding fingers may be inserted with the fingers to lie in back of and press against the fingers of the receptacle contacts inwardly to provide a firmer grip by the contact fingers against the prongs of a plug member when a plug is connected with the connector member.

The inner body member 30 is adapted to fit or seat within the inner portion 41 of a hollow cylindrical cupshaped shell 40 made from insulating material and having approximately the same outer diameter as the outer body 20. The shell 40 has a central passageway 42 for the passage therethrough of the three wire conductor cord.

Mounted upon the shell at the opposite end from the inner body is a strain relief fitting 50 which is secured to the top wall of the shell by screws or other suitable securing means passing through three holes 54 and which register with three holes 44 in the outer (top) face of the shell 40. The strain relief fitting is preferably made of insulating material such as nylon or other suitable moldable material and comprises a flat annulus 51 from which two parallel arms 52 extend up at diametrically opposite positions around the annulus. The arms extend in the same direction and are parallel to the axis of the shell 40 and the annulus 51. For the purpose of keeping dust, chips, and moisture from the inside of the connector assembly, the strain relief fitting clamps between itself and the shell 40 a thin soft rubber gasket or washer 49 through which the conductor cord passes. The gasket may be made of other flexible moisture proof material. Due to its resilient elastic nature the periphery of its central hole 49a can lightly embrace conductor cords of different diameters.

The receptacle is normally factory assembled, but need not necessarily be so. The outer body and inner body 30 may be secured together by a central bolt 38 or by any other suitable means, with the fixed contacts 25, 26 and 27 in their respective recesses. For passage of the conductor wires w, w" and ground wire G, three wire holes 35, 36 and 37 are bored or molded through the inner body 30 parallel to the body axis adjacent and leading to the wire terminals of the fixed contacts so that the bared ends of the wires can pass through the holes and be clamped to the wire terminals of the fixed contacts.

To secure the strain relief member 50, over the shell 40 (with gasket 49 between them) and all three to the inner and outer bodies 30 and 20, three bolt holes are formed in each of those members, in register such as 24, 34, 44, and 54 for securing bolts.

It has been found-that when using strain relief arrangements of the form described and illustrated that slippage can occur of the wires w, w" and G within the sheaths of the conductor cord C, if the wires are pulled while the receptacle member is held. This results in unwanted strain being transmitted to the wire terminals directly in prior art constructions.

The present invention provides an important structural difference from the prior art in the formation of the inner body 30 and the adjacent cooperating surface of the shell-40. Referring to the top or innermost face of the inner body 30 there are formed a series of concentric circular steps 39 creating a stepped circular pyramidal formation concentrically located on the inner body. This formation lies directly under the conductor cord passage 42 of the shell and extends radially outward with respect thereto beyond the periphery of that passage. The surface of the shell over the pyramidal formation in assembled condition of the shell 40 and body 30 lies far enough away from the pyramidal formation to permit passage of the wires w, w and G when they are separated and spread and inserted into their separate holes 35, 36 and 37 leading to the wire terminal clamps, e.g. 28, but close enough, nevertheless, so that when the inner body and shell are secured together the wires are clamped between the body and shell and frictionally gripped by the pyramidal formation whose steps bite into the insulation of the wires and firmly hold each one individually.

Preferably, to accomplish this clamping, gripping and holding action, a thin annulus 43 of tough resilient material, such as nylon, is located between the inner body 30 and the shell 40. The annulus rests against a shoulder 45 inside the shell between the shell wall and the center hole 42 through which the cord C passes. The

annulus is held against the shoulder by the bolts or rivets which hold the strain relief member 50, shell 40 and inner body 30 together. The annulus being flexible can move a very slight amount, and being thin can bite into the insulation on the individual wires of the conductor, on the opposite side from the pyramidal steps. This slight flexibility enables resilient gripping of the individual wires which may vary in thickness in wires of different diameters, thus providing self-adjustability. Thus despite any slippage of the wires within the sheath of the conductor cord no strain can be transmitted to the wire terminals.

Referring more to the plug member illustrated in FIGS. 5 and 6, it is formed, generally speaking, similarly to the connector member in that it is built up of three insulation members 120, 130 and 140 plus a strain relief fitting and clamps 50 and 60 gasket 49. Through three independent spaced, axially extending passages 121, 122 and 123 the outer body which again is cylindrical but thinner than body 20 extend the contact fingers 131 and 132 and ground contact prong 133 that are mounted on the inner body 130. The inner body is similar to the inner body of the connector but instead receives the wire terminal ends of the plug contacts and grounding prong. As in the receptacle contacts, the plug fingers 131 and 132 and the ground prong 133 have wire clamping plates and binding screws 129. I

The shell 140, strain reliefmember 50 and the clamping members 60 may be formed similarly to the corresponding members previously described in connection with the receptacle member.

As in the case of the receptacle, the inner body 130 has its inner face (the bottom not-visible face in FIG. 6) formed with a stepped pyramidal formation 139 like 39 in FIG. 1 so that it will, in cooperation with the annulus 43 in the shell 140, grip and bite into the insulation of the individual conductor wires connected to the fingers and prongs 131, 132 and 133.

In order to transmit any strain to the shell 40 and connector body 30 which is imposed upon the conductor by a person inadvertently or purposely pulling upon the conductor cord C, a pair of identical insulating clamps 60 are provided on opposite sides of the conductor cord and on opposite sides of the arms 52 of the strain relief fitting. These clamping members may be made of nylon, delrin, or any other suitable strong insulating material in different forms of which one form is illustrated in FIGS. 1, 10, 11 and 12. Clamping screws 62 pass freely through holes in. one end of each of the clamping members and thread into threaded recesses in the opposite ends of the other clamping member.

In order for the clamping members to be adaptable to the multi-wire cord conductors of different diameters, the clamping members are formed to receive an insertable member which may be used with small diameter cords, or removed and not used when large diameter cords are connected to the connector members.

The two clamp bodies which make up the strain relief fitting may be molded as elongated blocks having in their mid-portions an arcuate indentation 62, within which is another arcuate recess 64 sunk deeper into the body 60. Into the deeper recess an arcuate insert 66 preferably of molded insulation is insertable. The insert and the recess 64 are made in complementary arcuate form so that the insert will fit snugly against the recess walls but extend outwardly sufficiently to present a smaller size opening between the two clamp members when they are placed in confronting position. FIG. 11 shows the inserts in place, for use with a small diameter conductor cord. FIG. 12 shows the clamp bodies used with a large diameter conductor cord, with the inserts removed.

The insert is provided with a stem 68 extended radially from the convex side thereof. The stem is insertable as a sliding fit into a hole or passage 69 through the clamp body 60 within the deep recess 64. The stem extends entirely through the body 60 so that its end protrudes. This enables pressure to be put against it to fatcilitate removal of the insert when desired.

The insert preferably has ridges in its concave surface to bite into the conductor sheath as the clamping members are clamped together.

While the clamp bodies and inserts are preferably made of insulation, it is possible also to make them of stamped sheet metal, with some danger of short circuiting if the clamping is too tight.

As shown in FIG. 13, the clamping members may have arcuate jaws 60a projecting from their inner surfaces and curved to engage around the surface of the conductor cord C. Ridges (not visible) may be formed on the inner surfaces of the jaws 60a to bite into the insulation of the conductor. The jaws may be connected to the body of the clamp members by a rib 60c which extends axially with respect to the conductor cord which the jaws are to engage. Thus, in both the forms of clamping members in FIGS. 1 and 13, as the clamping screws are tightened the jaws grip the insulation of the conductor and at the same time the passage of these screws through the arms of the strain relief fitting hold the clamp to the fitting and to the connector. ln form of FIG. 13 arcuate jaws 60a are comparatively thin and are flexible enough to adapt to the diameter of the cord and more closely embrace the cord.

From the foregoing, it will be apparent that the invention provides both external and internal strain relief to hold not only the sheath conductor cord but also the conductor wires individually in a firm grip and prevent slippage of the wires within the sheath from transmitting strain of the wires directly to the wire terminals.

Also dirt, dust, and metal chips which might enter the cord hole are prevented from reaching the wire terminals.

Modifications within the scope of the invention will occur to those skilled in the art. Therefore the invention is not limited to the specific forms and configuration illustrated and described.

What is claimed is:

1. An electrical connector having an insulating body, contact and terminal means supported by said body, said body means having a passage for a conductor cord having a plurality of wires, strain relief means mounted on said body comprising a pair of clamping members adapted to be positioned on opposite sides of the cord, means to draw said clamping members toward'each other against the cord, means to secure the clamping members to said body, said clamping members comprising a transverse portion tangential to the cord and a flexible arcuate cord-gripping portion spaced inwardly from said tangential portion, said arcuate portion being connected to said transverse portion by a rib permitting movement of said arcuate portion to adapt to the cord.

2. An electric connector as claimed in claim 1 in which the clamping members are one-piece molded insulation members.

3. An electrical connector comprising first rigid insulating body means, a plurality of contact means, wire terminal means on said contact means, said wire terminal means being mounted within said body means, second rigid insulating body means including a passage for a conductor cord having a plurality of insulated wires, a pyramidal stepped formation comprising a plurality of steps formed integrally on one of said bodies and extending toward the other individually engaging the individual wires on one side between said passage and said wire terminal means, a thin flexible member on one of said bodies engaging the wires individually on the opposite side from said stepped formation when said bodies are secured together, said flexible member being adapted to accommodate different thicknesses of wires and resiliently bite into them, whereby said wires are gripped to prevent strain exerted on said conductor cord and wires from reaching said terminal means, and means to secure said first and second body means together.

Claims (3)

1. An electrical connector having an insulating body, contact and terminal means supported by said body, said body means having a passage for a conductor cord having a plurality of wires, strain relief means mounted on said body comprising a pair of clamping members adapted to be positioned on opposite sides of the cord, means to draw said clamping members toward each other against the cord, means to secure the clamping members to said body, said clamping members comprising a transverse portion tangential to the cord and a flexible arcuate cord-gripping portion spaced inwardly from said tangential portion, said arcuate portion being connected to said transverse portion by a rib permitting movement of said arcuate portion to adapt to the cord.

2. An electric connector as claimed in claim 1 in which the clamping members are one-piece molded insulation members.

3. An electrical connector comprising first rigid insulating body means, a plurality of contact means, wire terminal means on said contact means, said wire terminal means being mounted within said body means, second rigid insulating body means including a passage for a conductor cord having a plurality of insulated wires, a pyramidal stepped formation comprising a plurality of steps formed integrally on one of said bodies and extending toward the other individually engaging the individual wires on one side between said passage and said wire terminal means, a thin flexible member on one of said bodies engaging the wires individually on the opposite side from said stepped formation when said bodies are secured together, said flexible member being adapted to accommodate different thicknesses of wires and resiliently bite into them, whereby said wires are gripped to prevent strain exerted on said conductor cord and wires from reaching said terminal means, and means to secure said first and second body means together.

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