Strain Relief Liquid Tight Electrical Connector

The present invention relates generally to improvements in electrical cord and cable fittings and it relates particularly to an improved device for hermetically sealing and anchoring and grounding an armored cable to a wall or partition through which the cable passes to relieve the strain on the leading end of the cable.

It is a common practice to pass a flexible plastic sheathed metal or armored or jacketed electrical cord or cable through a wall or partition and connect the cable conductors to one or more terminals and ground the metal jacket. The wall or partition may be a metal wall of a junction, switch or terminal box or the like and it is important that any strain on the cable be prevented from being transmitted to the terminals to which the cable conductors are connected to thereby maintain a reliable connection to the terminals and to ground the metal jacket. It is additionally desirable that the cable be hermetically sealed to the wall through which it passes to prevent the exposure of the conductors and terminals to moisture and corrosive ambient atmospheres. Many devices have been available and heretofor proposed for anchoring and sealing a cable to a wall of a junction terminal or switch box or the like but these have possessed numerous drawbacks and disadvantages. They have been complex and often unreliable devices, of little versatility and adaptability, expensive and have otherwise left much to be desired.

A cable fitting of the subject type is disclosed in U.S. Pat. No. 4,835,342, dated May 30, 1989, and, while the disclosed fitting is highly superior for use with electrical cord or cable of the non-armored type, its use with metal armored or jacketed cable, particularly where the jacket is plastic sheathed, possesses an important drawback in that the metal jacket is ungrounded and its hermetic sealing presents many problems.

It is a principal object of the present invention to provide an improved electrical fitting.

Another object of the present invention is to provide an improved electrical fitting for ground and preventing the transmission of stress or strain on armored electrical cable.

Still another object of the present invention is to provide an improved electrical cable strain relief device which grounds and hermetically seals a plastic sheathed armored cable in a selected area.

A further object of the present invention is to provide an improved fluid tight strain relief coupling for grounding and allowing the passage of an armored electrical cable through a wall or partition.

Still a further object of the present invention is to provide a device of the above nature characterized by its high efficiency and reliability, ease of application, ruggedness, simplicity, low cost and great versatility and adaptability.

The above and other objects of the present invention will become apparent from a reading of the following description taken in conjunction with the accompanying drawings, which illustrate preferred embodiments thereof.

An electrical fitting in accordance with the present invention comprises a tubular body member having an inside abutment below its bottom and a centrally apertured gland cap in thread engagement with the body member upper part to delineate with the body member wall and abutment a compression chamber, a preferably elastomeric packing member or grommet located in the compression chamber and including an axially bored cylindrical upper section and longitudinally depending peripherally spaced fingers and a metal grip member including an upper ring encircling the packing member and inwardly swingable grip fingers depending from the ring and interdigitating the packing fingers and having top faces underlying the underface of the packing member upper section, the grip fingers and body member being so related whereby tightening of the gland cap longitudinally contracts the compression chamber to contract the packing member axial bore and depress the grip member to contract the lower portions of the grip fingers.

In the preferred form of the improved fitting the body member includes a lower coaxial section of reduced diameter delineated from the upper section by a peripheral shoulder having a cam defining inwardly downwardly inclined top face defining the chamber bottom abutment, the top and bottom body member sections being externally threaded. The gland cap has a stop wall defining peripheral flange which bears on the packing member top face through a low friction washer. The packing member fingers and grip fingers have inwardly extending side faces, cylindrical outer faces and either coaxial cylindrical inner faces or planar faces delineating a rectangular axial bore, the side faces of adjacent fingers being contiguous and the finger inside face delineating a passageway coaxially extending from the packing member bore. The grip finger inside faces have upwardly facing shoulders proximate their lower free ends.

The fitting may be easily and rapidly applied and effects a tight slip-proof grip and a hermetic seal with the wall of a cable or conduit traversing the fitting which are efficient and reliable and the fitting is highly versatile, adaptable, rugged and inexpensive. The plastic cable sheath is cut back and its leading end abuts the grip finger shoulders and the exposed cable metal jacket is gripped by the grip finger end portions which electrically connects the jacket to the metal tubular body member.

FIG. 1 is a front elevational view of an electrical fitting embodying the present invention shown in assembled and cable applied position;

FIG. 2 is an exploded perspective view of the core assembly thereof;

FIG. 3 is a front elevational view of the core assembly;

FIG. 4 is a sectional view taken along lines 4--4 in FIGS. 1 and 5;

FIG. 5 is a sectional view taken along line 5--5 in FIG. 4;

FIG. 6 is a sectional view taken along line 6--6 in FIG. 5;

FIG. 7 is a view similar to FIG. 6 of another embodiment of the present invention; and

FIG. 8 is a sectional view taken along line 8--8 in FIG. 7.

Referring now to the drawings, particularly FIGS. 1 to 6 thereof which illustrate a preferred embodiment of the present invention, the reference numeral 10 generally designates the improved strain relief electrical fitting shown applied to a cable 11 of known construction which includes a plurality of insulation covered conductors 12 enclosed in a flexible metal jacket or conduit 15 of rectangular cross-section covered by a waterproof plastic sheath 13, it being understood that the fitting 10 is applicable to various cable constructions, particularly plastic sheathed metal armored cable. The fitting 10 comprises a rigid tubular metal housing 14, a sealing and grip core assembly 16 including a packing member 17 and a metal grip member 18, a gland cap 19 and a low friction washer 20.

The housing 14 is formed of metal or other suitable electrically conducting material and includes an upper large diameter section 21 defined by an externally threaded cylindrical wall 22 and a small diameter lower section 23 defined by an externally threaded cylindrical wall 24 coaxial with wall 22 and joined thereto by an outwardly directed hollow peripheral flange 26. Flange 26 is integrally formed with walls 22 and 24 and has a flat outer underface 27 spaced from wall 24 by a peripheral groove 28 and peripherally spaced outside flats 25 for the reception of a wrench. Wall 24 terminates at its top in an outwardly directed upwardly convex peripheral shoulder 29 and wall 22 has formed at its bottom an inwardly downwardly inclined lip 30 extending to shoulder 29 the inside faces of shoulder 29 and lip 30 defining a cam face 32. The top inner edge of wall 22 is bevelled as at 33.

The gland cap 19 is likewise formed of metal and includes an internally threaded peripheral skirt wall 34 in threaded engagement with threaded wall 22 and an enlarged head 36 having peripherally spaced flats 37. Head 36 terminates at its top in an inwardly projecting peripheral shoulder 38 delineating a large central rectangular opening 39 and having an upwardly inwardly inclined peripheral underface 40.

The washer 20 is a thick annulus formed of nylon or other low friction material and is housed in the upper part of gland cap 19 and has a central rectangular guide opening 41. The upper part of washer 20 is of reduced diameter and projects through cap opening 39 and is delineated from the lower part of washer 20 by a downwardly outwardly inclined shoulder 42 which is in sliding mating engagement with cap underface 40.

The assembly 16 is housed in the compression chamber delineated by the washer 20 and shoulder 29. Packing member 17 is formed of neoprene or other elastomeric material and includes an upper main body section 43 of circular cylindrical outside configuration with a central axial bore 44 of the transverse cross-section and peripheral dimensions of opening 41 and being slightly downwardly tapered. Packing main body 43 is of an outside diameter about that of the inside of cap wall 34 and has a flat or convex top face 46 in mating sliding engagement with the underface of washer 20. The bottom outer peripheral edge of packing main body section 43 is inwardly downwardly tapered as at 45 and bears on the bevelled edge 33 of chamber wall 22.

A plurality, for example four, regularly peripherally spaced fingers 47 are integrally formed with packing body section 43 and depend longitudinally therefrom shortly inwardly from its bottom outer peripheral edge. Each finger 47 includes opposite side faces 48 lying in planes converging inwardly to a vertical axis offset from the central axis of packing body section 43 and an approximately cylindrical outer face 50, the upperpart 51 of outside face 50 being slightly downwardly outwardly inclined and the bottom outer face 52 of each finger 50 being downwardly inwardly inclined. The bottom outer edges of fingers 47 bear on the curved inside face of shoulder 29.

The grip member 18 is integrally formed of metal, for example, die cast aluminium, or other suitable electrically conducting material and includes an upper ring 53 and a plurality, equal in number to fingers 47 of grip fingers 54 longitudinally depending from and integrally formed with ring 53. In the assembled condition of the packing and grip members the ring 53 encircles the upper parts of fingers 47 with the top flat face 56 thereof abutting the underface of packing section 43, the peripheral face of ring 53 being radially inwardly of the bottom outer edge of the packing section underface.

Grip fingers 54 interdigitate with packing fingers 47 and their inside faces are rectangular and delineate an axial bore of rectangular transverse cross-section. Grip fingers 54 include inwardly extending planar side faces 58 confronting proximate side faces 48 of adjacent fingers 47, outside cylindrical faces 59 having tapered bottom outer borders 60, the faces 59 being substantially coaxial and coplanar with the corresponding outer faces of packing fingers 47. The top faces 61 of fingers 54 are flat and coplanar with ring top face 56 and abut the underface of packing member section 43. The bottom faces of fingers 54 are flat and coplanar with the flat underfaces of fingers 47. The bottom outer edges 63 of grip fingers 54 define followers which bear on the cam defining top inner faces of shoulder 29.

The inside faces of grip fingers 54 include rectangular vertical planar upper parts 65 which delineate a vertical bore of rectangular cross section and vertical rectangular lower parts 66 inwardly offset from upper parts 65 and delineated therefrom by upwardly facing horizontal shoulders 67. Grip fingers 54 are swingable inwardly about ring 53.

In the application of the improved fitting 10 to a cable 11, the plastic sheath 13 at the leading end portion of cable 11 is stripped to expose a portion of metal jacket 15 and the cable is inserted through the fitting by way of the longitudinal passageway defined by the openings and bores in washer 20 and assembly 16 with gland cap 19 in loose condition on body member 14 until the leading end of sheath 13 abuts grip finger shoulders 67. The gland cap 19 is then tightened to advance washer 20 and assembly 16 downwardly, rotation of the cap being facilitated by the slipping along the washer faces. With the advance of assembly 16 the packing finger and grip finger bottom cam follower defining edges follow the cam defining face of shoulder 29 to urge the bottom inside faces of grip fingers 54 inwardly to press the inside bottom faces of grip fingers 54 into tight direct clamping engagement with the cable metal jacket preventing axial movement, or stress and strain transmission by the cable and preventing further advance of the assembly 16 and to ground metal jacket 15 to housing 14 which in turn is grounded to the fitting support wall. With further tightening of gland cap 19 elastomeric packing section 43 is longitudinally compressed to contract the bore 44 into tight hermetically sealing engagement with cable 11 and to tightly press together packing section tapered face 45 and body member wall bevelled edge 33 to contract the lower part of packing section 43 and effect a seal between face 45 and edge 33. The threaded lower section 23 permits the coupling and liquid tight sealing of fitting 10 to an apertured wall or panel, not shown, by means of a suitable rubber washer or O-ring which engages groove 28 and a lock nut 75 which grounds housing 14 and hence jacket 15 to the wall or panel.

The embodiment of the present invention illustrated in FIGS. 7 and 8 of the drawings differs from that above described only in the configuration and dimensions of the packing member washer and the grip member in that the axial bore is circular instead of rectangular to accommodate a round cable and in all other respects is similar to the first described embodiment. Specifically the modified fitting 70 includes a body member 71, a gland cap and a larger opening washer similar to those earlier described except that the washer bore is circular, and a core assembly comprising a packing member including a main section 75 and depending spaced fingers 72 having cylindrical vertical inside faces and a metal grip member including depending grip fingers 73 joined at their top by a connecting ring and interdigitating fingers 72. The fingers 72 and 73 differ from fingers 47 and 54 primarily in that their inside faces are cylindrical and delineate a circular cylindrical bore and in that the packing section bore is of circular cylindrical configuration. The fingers 73 terminate at their bottoms in inwardly projecting flanges 76 having upwardly facing shoulders 77.

The last described embodiment is employed with plastic sheathed circular metal armored cable 78 of conventional construction and has the fitting 70 applied thereto in the matter of the application of the first described embodiment in the manner earlier explained.

While these have been described and illustrated preferred embodiments of the present invention it is apparent that numerous alterations, omissions and additions may be made without departing from the spirit thereof.