Assembly for an electrical cable providing strain relief and a water-tight seal

• US 4,789,759 A
• Filed: 11/23/1987
• Issued: 12/06/1988
• Est. Priority Date: 03/25/1986
• Status: Expired due to Fees

• Current Assignee: AMP Incorporated (Johnson Controls International plc)
• Original Assignee: AMP Incorporated (Johnson Controls International plc)
• Inventors: Jones, Marvin H.
• Primary Examiner(s): Grimley, Arthur T.
• Assistant Examiner(s): TONE, DAVID
• Application Number:
  US07/123,680
• Time in Patent Office: 379 Days
• Field of Search: 174/65 R, 174/65 SS, 174/77 R, 439/449, 439/452, 439/461, 439/462, 248/56, 411/1, 411/2, 411/402, 411/410, 403/2, 285/3, 285/39
• US Class Current: 174/655
• CPC Class Codes: F16B 2200/406 Clamping parts being collars, bushings or wedges
• CPC Class Codes: H02G 15/007 Devices for relieving mechanical stress
• CPC Class Codes: H02G 3/065 with means biting into the conductor-insulation, e.g. teeth-like elements or gripping fingers H02G3/0675, H02G3/0683 take precedence
• CPC Class Codes: H02G 3/0675 with bolts operating in a direction parallel to the conductors

Abstract

A fitting for establishing a seal between an insulated electrical cable (70) and an electrical junction box, where the junction box wall has a threaded bore and a profiled through-hole having a camming surface and shoulder. The fitting includes a threaded nut (50) and a ferrule (30) which has tines (34) extending from a ring portion. The ferrule (30) and the nut (50) are slid over the insulated cable (70) and the assembly is brought in registry with the threaded bore (8) of the junction box. Screwing the nut (50) and ferrule (30) forwardly causes the tines (34) on the ferrule (30) to contact the camming surface (12), forcing the tines (34) into the insulation (72) and the insulation (72) into the shoulder (16), thereby establishing a sealed connection. In a further improvement, the nut (50) has first and second wrench-engaging portions (100, 101) formed integrally therewith. The first wrench-engaging portion (100) partially fractures at a predetermined torque level corresponding to more than a desired minimum axial pull-out force on the cable (70). However, the structural integrity of the nut (50) is maintained, such that a wrench (105) may be applied to the second wrench-engaging portion (101) of the nut (50) for removing the nut (50).

Claims

1. An assembly for establishing a sealed interconnection for an insulated electrical cable, the assembly comprising:

a bulkhead, having a through-hole extending from an outside to an inside surface and having three concentric bores, a first bore being internally threaded and extending from the outside surface into the bulkhead, a second bore spaced apart from the first bore by a camming surface, and a third bore in transition with the second bore by means of a shoulder, the third bore extending to the inside surface;

a nut portion having an axial bore extending therethrough, said bore having a diameter greater than the diameter of said insulated cable, and an externally threaded portion matable with said internal threads on said first bore; and

a ferrule of cylindrical shape having a band portion and a plurality of radially disposed tines extending from said band portion in an axial direction, said ferrule being slidably receivable over said insulated cable;

whereby

when said cable is prepared by removing a portion of the insulation therefrom exposing a length of the conductor, the nut portion and the ferrule are slid over the prepared end of the cable, and the cable inserted into the through-hole until the insulation abuts the shoulder and the conductor extends through the third bore, bringing the threads of said nut into registry with the threads of the first bore and screwing the nut forward into the through-hole causes the tines of said ferrule to contact the camming surface and forces the tines radially inward and into the insulation of the cable, and drives the insulation axially forward against the shoulder, thereby establishing a sealed interconnection.

2. The assembly of claim 1 wherein the shoulder is chamfered, leading from the second bore into the third bore.

3. The assembly of claim 1 wherein the bulkhead is an outer wall of a sealed electrical junction box.

4. The assembly of claim 1 wherein the camming surface is profiled as a concave radius.

5. The assembly of claim 1 wherein the ferrule is stamped and formed from a flat metallic sheet.

6. The assembly of claim 1 further including an electrical cable, wherein the cable is provided with insulation and has a conductor therein;

wherein a portion of the insulation on the cable is removed to expose a length of the conductor adapted to extend forwardly of the bore in the bulkhead; and

wherein the nut exerts an axial compressive force on the member, such that the member engages the insulation on the cable and compresses the cable against the forward portion of the bore in the bulkhead to thereby provide a water-tight seal for the cable.

7. A method for establishing a sealed interconnection for an insulated cable, comprising the steps of:

stripping away a portion of the insulation of the cable exposing a length of the conductor;

placing over the prepared end of the cable a nut portion having an axially extending bore and an externally threaded portion;

placing over the prepared end of the cable a ferrule of cylindrical shape having a band portion and a plurality of radially disposed tines extending from said band portion;

placing the prepared end of the cable, the ferrule and the nut into a bulkhead having a through-hole extending from an outside to an inside surface and having three concentric bores, a first bore being internally threaded and extending from the outside surface into the bulkhead, a second bore which is spaced from said first bore by a camming surface, and a third bore in transition with the second bore by means of a shoulder, the third bore extending to the inside surface;

projecting the cable into the through-hole until the insulation abuts the shoulder and the length of the exposed conductor extends through the third bore; and

threading the nut into the threaded portion of the first bore until the tines of the ferrule are projected into the insulation by the action of the camming surface and the insulation is forced into the shoulder.

8. A method for establishing a sealed interconnection for an insulated cable, comprising the steps of:

placing a ferrule into a through-hole of a bulkhead, the ferrule having a cylindrical shape having a band portion and a plurality of radially disposed tines extending from said band portion, the through-hole extending from an outside to an inside surface and having three concentric bores, a first bore being internally threaded and extending from the outside surface into the bulkhead, a second bore which is spaced from said first bore by a camming surface, and a third bore in transition with the second bore by means of a shoulder, the third bore extending to the inside surface;

placing a nut into said threaded portion of said first bore, said nut having a threaded portion and an axially extending bore therethrough;

preparing an insulated cable by tripping a portion of said insulation away exposing a length of a conductor;

placing the prepared end of the cable through the axial bore of the nut and through the ferrule, until the exposed conductor projects through the third bore and the insulation abuts the shoulder; and

screwing the nut into the threaded portion of the first bore until the tines of the ferrule project into the insulation under the action of the camming surface, and the insulation is forced against the shoulder.

9. A method for establishing a sealed interconnection for a conductor of an insulated cable, comprising the steps of:

providing an insulative body means having an inner sealed portion and an outer unsealed portion;

providing an opening in the insulative body means which communicates between the inner sealed portion and the outer unsealed portion, the opening including a cable receiving portion and a conductor receiving portion where the conductor receiving portion has a smaller profile than the cable receiving portion, thereby defining a shoulder within the opening;

stripping the insulation from the end of the conductor thereby forming an end of the insulation;

inserting the cable into the opening such that the conductor is placed within the conductor receiving portion and the insulation abuts the shoulder; and

forcing the insulated cable inwardly to create a seal between the end of the insulation and the shoulder.

10. The method of claim 9 wherein the step of forcing the insulated cable inwardly includes the steps of:

further providing within the opening a camming surface;

providing a threaded surface on the insulative body;

providing a threaded nut complementary with the threaded surface;

providing a ferrule having a cylindrical shape with a band portion and a plurality of radially disposed tines extending from the band portion;

placing the nut and the ferrule over the stripped cable and threading the nut and threaded surface together until the tines of the ferrule are projected into the insulation by the action of the camming surface, and the insulation is forced into the shoulder.

11. An assembly for assuring a proper strain relief for interconnection of an insulated electrical cable in a bulkhead such that the cable will withstand a desired minimum axial pull-out force, comprising:

a nut having an externally-threaded portion and further having an axial bore formed therethrough for receiving an electrical cable;

a bore in the bulkhead having a first portion provided with internal threads adapted to receive the externally-threaded portion of the nut, the bulkhead bore further having a forward portion;

a member adapted for receiving the electrical cable therethrough and to be disposed in the bore of the bulkhead between the nut and the forward bore portion, wherein the member has at least a portion thereof adapted to be compressed radially inwardly thereof to engage the cable received therethrough and to prevent the cable from being pulled out of the bulkhead upon the application of a desired minimum axial pull-out force on the cable, thereby providing a proper strain relief for the cable;

the nut having a first wrench-engaging portion formed integrally therewith for facilitating rotation of the nut in a first direction into the threaded portion of the bore in the bulkhead, wherein the first wrench-engaging portion of the nut is adapted to fracture at a predetermined torque level corresponding at least to the desired minimum axial pull-out force on the cable, thereby preventing further rotation of the nut in the first direction while still maintaining the structural integrity of the nut; and

the nut further having a second wrench-engaging portion formed integrally therewith for facilitating rotation of the nut in a second and opposite direction for removing the nut from the bulkhead.

12. The assembly of claim 11, wherein the first wrench-engaging portion of the nut partially fractures at the predetermined torque level, such that the first wrench-engaging portion of the nut does not become totally separated from the nut.

13. The assembly of claim 11, wherein the second wrench-engaging portion of the nut is larger than the first wrench-engaging portion thereof.

14. The assembly of claim 11, wherein the first and second wrench-engaging portions of the nut are hexagonally formed.

15. The assembly of claim 14 wherein the wrench-engaging portions of the nut form an irregular hexagon in that at least one pair of opposite sides of the nut are dimensioned in different units of measurement.

16. The assembly of claim 11, wherein the nut and its integrally-formed first and second wrench-engaging portions comprise a unitary article molded from a glass-filled polyester.

17. The assembly of claim 16, wherein the glass-filled polyester includes 15%-35% glass.

18. The assembly of claim 17, wherein the glass-filled polyester includes 18%-30% glass.

19. An assembly for assuring a proper strain relief for interconnection of an insulated electrical cable in a bulkhead such that the cable will withstand a desired minimum axial pull-out force, the assembly further assuring a water-tight seal for the cable, comprising:

a nut having an externally-threaded portion and further having an axial bore formed therethrough for receiving an electrical cable, the bore in the bulkhead having a first portion provided with internal threads adapted to receive the externally-threaded portion of the nut, the bore in the bulkhead further having a forward portion;

a ferrule adapted for receiving the cable and to be disposed between the nut and the forward portion of the bore in the bulkhead, the ferrule having a plurality of circumferentially-spaced tines, the forward portion of the bore in the bulkhead including a radiussed surface forwardly of the internal threads in the bore;

the cable being provided with insulation and having a conductor therein, a portion of the insulation on the cable being removed to expose a length of the conductor adapted to extend forwardly of the bore in the bulkhead upon inserting the cable through the axial bore of the nut, the ferrule, and the bulkhead bore;

the nut having a first wrench-engaging portion formed integrally therewith for facilitating rotation of the nut in a first direction into the threaded portion of the bore in the bulkhead, whereby the nut drives the ferrule axially and forwardly into the bore, and whereby the tines on the ferrule engage the radiussed surface and are cammed radially inwardly of the bore to engage the insulation on the cable, wherein the first wrench-engaging portion of the nut is adapted to partially fracture at a predetermined torque level corresponding to at least the desired minimum axial pull-out force on the cable, thereby preventing further rotation of the nut in the first direction while still maintaining the structural integrity of the nut;

the nut having a second wrench-engaging portion formed integrally therewith for facilitating rotation of the nut in a second and opposite direction for removing the nut from the bulkhead, the second wrench-engaging portion of the nut being larger than the first wrench-engaging portion thereof, the first and second wrench-engaging portions of the nut being hexagonally formed, and the nut and its integrally-formed first and second wrench-engaging portions comprising a unitary article molded from a glass-filled polyester.

20. The assembly of claim 19, wherein the bulkhead is an outer wall of a sealed electrical junction box.