Strain Relief Clamp For Electrical Wiring Connector

Abstract

A clamping device is designed for use on general purpose multipin connectors by attaching to the connector and extending therefrom to terminate in a wire-bearing surface with means to facilitate retention of a band or tie string to secure all the wires extending from the connector. This bundle of wires is thereby gripped in a firm and immovable position so that all linear and lateral movement thereof which might occur in operation is prevented from being applied to the point of connection of the several wires with the connector. Thus, stressing and eventually breaking of the connection point of any of the several wires is obviated.

Description

This invention relates broadly to fittings of the type employed in electrical installations, and more particularly to a strain relief clamp, as it is commonly called, adapted for attachment to electrical connector elements, both plugs and receptacles, with multiple conductors or wires in order to secure the wires extending from the element or fitting individually and as a bundle in substantially fixed position relative to their respective connections within the fitting.

Since each of the tires or conductors is relatively flexible, it is especially subject to wear and tear adjacent its point of connection to the fitting during installation and normal operation due to both lateral and pulling forces in it and on the bundle of wires of which it is one. This is particularly true of the wires to the plug element since the plug is movable as compared to the receptacle which usually remains in a fixed position when mounted to supporting structure such as a wall, bulkhead, or the like. Under such normal operation and movement, any one or more of the wire terminations may become impaired and/or broken.

In the more dynamic applications onboard vehicles, notably aircraft, the wire bundles are especially subjected to flexing, pulling and movement in general. This is aggravated by the fact that these bundles are lengthy and circuitous as well as oftentimes required to be forced into out-of-the-way places and small areas due to stringent space conditions typical of aircraft.

At the same time since over-stressed and defective electrical wiring connections constitute a fire hazard, regulations concerning all such fittings are very strict. Thus, positive means is required to secure each electrical wire connection against movement that may weaken or break the connection of the wire and cause a short circuit, arcing, etc.

The practice has, therefore, developed of providing a strain relief clamp in the form of a generally tapered fitting which is secured to the projects from the and element, the outer, smaller end of which is adjustable to clampingly engage and secure the wire bundle. Movement and flexing of the several wires along their lengths is thereby prevented from passing this clamp and being transmitted to the point of the connection thereof in the connector element. For aircraft applications, these fittings have been lightened as much as possible by the removal of large portions of the material in the tapered section between fitting ends so that the ultimate part comprises in effect a pair of concentric rings. The larger of these rings is adapted to attach to a standard connector element with the smaller ring in spaced relationship thereto to clampingly engage the wire bundle.

Unfortunately, the number and size of wires that comprise a bundle vary so that the aggregate transverse dimension of each bundle differs in an unpredictable manner. Inasmuch as the clamping ring is rigid, its minimum transverse adjustment is usually greater than that of the wire bundle. In this case, tape of appropriate dielectric material is wrapped around the bundle to enlarge it to the size necessary for snug engagement thereof by the clamping ring.

This practice has proven to be very objectionable for many reasons. It is time-consuming and expensive not only because of the quantities of tape used, but also the quantities wasted. It results in undue weight, and with the ever-increasing size of aircraft and the numbers of such fittings now employed, the aggregate weight becomes appreciable. It is not a satisfactory retainer because during normal operation of the aircraft and flexing of the wire bundle, the several wraps of tape gradually extrude from their installed, overlying position extending along the wire bundle. This results in a loosening of the clamp and possibly a fraying of the wire insulation or breaking of one or more of the wire connections.

The present invention proposes to overcome the foregoing and other objections with prior fittings by the provision of an improved clamp which offers optimum efficiency and reliability in the retention of multiple wires in a bundle connected to a connector element. To this end, the clamp herein proposed is formed by an attaching ring which engages and secures to the electrical connector element and is provided with a single extension arm angularly disposed and projecting therefrom to terminate in a keeper element for coaction with a tying strap, band or tape.

This keeper element is formed or otherwise provided with an inner surface which is arcuate to establish the periphery of the bundle of wires from the connector element. The extending wires are thereby cradled therein and the strap or band encircles the wires and arm to apply the clamping pressure when drawn taut. The dimension of the arm in the area of the strap is sized to the transverse dimension of a single wire so that it is effective in its gripping and securing function not only where a bundle of wires are involved but even where only one or two are required to be clamped. The clamping strap or band is of relatively flexible and preferably a dielectric material to minimize any chance of damaging the insulation of the wires causing a short circuit of arcing thereacross.

With the above and other objects in view as will be apparent, this invention consists in the combination, construction, and arrangement of parts, all hereinafter more fully described, claimed, and illustrated in the accompanying drawings, wherein:

FIG. 1 is a side elevation of a clamp designed and constructed in accordance with the teachings of this invention showing the collar or ring adapted for coaction with a connector element, either plug or receptacle, and the projecting arm with a strap-engaging and retaining means at the end thereof;

FIG. 2 is an end elevation or a view taken from the right side of FIG. 1 to show the configuration of the arm which results in a substantially concentric disposition of the strap-engaging and retaining member relative to the attaching ring;

FIG. 3 is a side elevation looking at FIG. 2 from the bottom;

FIG. 4 is a typical installation showing the clamp of FIGS. 1 through 3 applied to a receptacle and also to a plug whereby the several wires comprising the bundle of each connector element are located and retained in a substantially fixed position with respect to its point of connection within the plug or receptacle;

FIG. 5 is a view similar to FIG. 3 of an alternate form of clamp designed and constructed for application where the wires leaving the connector element are required to turn at a substantially 90.degree. angle to show a modified arm and strap-engaging and retaining means configuration;

FIG. 6 is a plan view of the clamp shown in FIG. 5 and corresponds to the view of FIG. 2;

FIG. 7 is a view taken from the side of FIG. 5; and

FIG. 8 is a view similar to FIGS. 2 and 6 with the arm and strap-engaging and retaining means broken away to show primarily a modified form of connector element-engaging collar or ring that is applicable to either form of the clamp shown in FIGS. 3 or 5.

Referring more particularly to the drawings, 10 designates a strain relief clamp as herein proposed in its preferred form. This clamp is formed by an annular collar or ring 11 which is internally threaded as indicated at 12 to correspond to the external threads 13 of a connector element either a receptacle 14 or plug 15 whereby it is secured thereto. The receptacle 14 is mounted in a wall 16 or other relatively stationary structure where it is adapted to receive the plug is which is locked thereto by an appropriate connecting collar 17.

To facilitate threading of the clamp 10 on its receptacle 14 or plug 15, the external surface or periphery of the ring 11 is knurled as at 11' or otherwise provided with projections whereby torque is readily applied thereto either by hand or by a suitable tool. At one side the ring 11 is formed with an integral extension arm 18 which terminates at its outer end on a pair of spaced arcuate lateral projections 19 interconnected by an extension arm portion 18' of substantially smaller transverse dimension approximating the transverse dimension of the smallest wire to be clamped thereby as will become more apparent.

The inner surfaces 19' of the projections 19 are disposed in a common plane which is concentric with respect to the ring 11. The intermediate portion of the arm 18, i.e., that portion between the ring 11 and the projections 19, is bent or offset to locate the arcuate surfaces 19' of the projections 19 radially inward of the corresponding arc of the ring 11.

Referring more particularly to FIG. 4, it is shown that each clamp 10 when attached to one of a pair of connecting elements 14 or 15 so as to extend therefrom in the direction away from the other connecting element 14 or 15, the inner surfaces 19' of the arcuate projections 19 are each adapted to abut and define the periphery of a bundle of wires 20 extending from the associated connecting element 14 or 15. Thus disposed, a band or strap 21 encircling portion 18' of the arm 18 and passing between the pair of projections 19 and around the wire bundle 20 can be tightened so as to firmly secure the several wires constituting the bundle is substantially immovable relative position.

While any band or strap 21 may be employed to apply the clamping pressure to each wire bundle 20 provided it is generally flexible and can be secured against slippage in the fully taut condition, it is preferred that this be fabricated of dielectric material. One such strap 21 ideally suited for this application is disclosed in U.S. Pat. No. 3,186,047issued to D. P. Schwester et al. on June 1, 1965. This strap is fabricated of nylon and contains an internal metal self-clinching means 22 within a keeper element 23 whereby as the strap is retained in a taut position when it passes through the keeper, and is drawn tight and then cut.

Referring now to that form of the clamp 10a shown in FIGS. 5, 6, and 7, the arm 18a is an integral extension on collar 11a and turns angularly outwardly with respect to the center thereof. The are 18a is comparatively wider than the arm 18 to assure containment of all of the wires 20 from the associated connector element and which it is intended to clamp. In this case, a single terminal projection 19a is provided being connected to the arm 18 by an appreciably smaller portion 18'a and with its arcuate surface 19'a disposed at substantial right angles to the inner periphery of the collar 11a.

As shown in FIG. 8, the collar 11 or 11a may, if desired, by interrupted as at 24 to allow connection and/or disconnection of one or more of the wires 20 in the bundle from the associated connector element without the necessity of complete removal and replacement of the clamp 10 or 10a . The dimension of this interruption or space is preferably held to a minimum, i.e., approximately equal to the transverse dimension of the largest wire 20 of the bundle so as not to unduly weaken it structurally when fully assembled and installed for operation.

While shown and described in what is believed to be the most practical or preferred form or embodiment, it is apparent that departures from the specific structure will suggest themselves to those skilled in the art. Such departure and innovations may be made without departing from the spirit and scope of the invention as covered by the appended claims.

Claims

What is claimed is:

1. A strain relief clamp for an electrical connector element having multiple attachment points for the connection of the ends of several wires extending therefrom comprising:

an attaching member including engagement means for the connection thereof to the end of said element; and

an arm carried by and extending in a direction away from said attaching member, said arm having a relatively wide root end and narrowing outwardly to terminate in a keeper element formed by an extension arm portion of smaller transverse dimension than said narrowing arm and of generally uniform transverse dimension sized to accommodate the transverse dimension of a wire of said connector element to be connected to said member as aforesaid, a step between said narrowing arm and said extension arm portion and a lateral projection at the extremity of said extension arm portion on each side thereof, said projection being defined by a surface disposed in a predetermined position relative to an inner periphery of said attaching member adapted to act as a bearing surface for said wires when said member is connected to said element as aforesaid.

2. The clamp of claim 1 adapted to be connected as aforesaid to connector elements having wires of different transverse dimensions wherein said attaching member is a ring interrupted by a space to accommodate the transverse dimension of the largest wire accommodate by said member.

3. The clamp of claim 1 wherein said projection surface is an arc of a circle.

4. The clamp of claim 1 wherein said arm is angularly offset relative to said attaching member, and said projection surface is concentric with respect to said attaching member.

5. The clamp of claim 1 wherein said keeper element includes a second lateral projection on each side of said extension arm portion in spaced relation to and inwardly of the extreme lateral projection aforesaid, said lateral projections having inner surfaces in alignment and concentric with respect to said attaching member.

6. The clamp of claim 5 adapted to be connected as aforesaid to connector elements having wires of different transverse dimensions wherein the transverse dimension of said arm disposed between said extreme and said second lateral projection approximates that of the smallest wire of any said connector element.

7. The clamp of claim 1 wherein said arm is angularly offset relative to said attaching member, and said projection surface faces away from and at substantial right angle to said attaching member.

8. The clamp if claim 7 wherein said keeper element surface is an arc of a circle.