US2999224A - Strain clamp - Google Patents

Description

Sept. 5, 1961 w. w. KRAASE ET AL 2,999,224

STRAIN CLAMP Filed April 8, 1957 2 Sheets-Sheet 1 llllll-llllllll Hg INVENTORS 13 14 WALTER vv, KRAASE RONALD J. BERTLINO BY I ATTORNEY Sept. 5, 1961 w. w. KRAASE ET AL STRAIN CLAMP 2 Sheets-Sheet 2 Filed April 8, 1957 3 L J \AJ INVENTORS WALTER W. KRAASE RONALD J. BERTLING ATTORNEY 2,999,224 ST CLAW Walter W. Kraase, West Allis, and Ronald J. Bertling, South Milwaukee, Wis., assignors to McGraw-Edison Company, Milwaukee, Wis, a corporation of Delaware Filed Apr. 8, 1957, Ser. No. 651,442 7 Claims. (Cl. 339-265) The present invention relates to strain clamps, and particularly to clamps for holding electrical conductors or cables where they are attached to a supporting pole or other member.

Among the objects of the present invention is the provision of a strain clamp for reception and clamping engagement with an electrical conductor or cable by means of spaced U-bolt members, preferably engageable with an intermediate keeper member adapted for direct contact with the conductor, and which U-bolt members are preferably held relatively captive to the clamping body and to the keeper member by the reception of one leg thereof in an extending aperture boss in the body and in the keeper member, and which U-bolt members are respectively slidable in the said apertures with the opposite leg thereof being received in open-ended notches in the body member, thus permitting clamping engagement of the U-bolt with the conductor by means of the keeper member without requiring complete disassembly of any portion of the connector relative to other portions thereof.

Specifically, among the objects of the present invention is the provision of an improved strain clamp comprising a body or saddle portion and a keeper member arranged to clampingly engage a conductor and including means for maintaining said engagement, and which clamp provides greatly increased holding power on both aluminum and copper conductors through the use of specially designed serrations provided in either or both opposed clamping surfaces of the body and keeper member for firmly gripping copper conductors and transmitting additional clamping force to the steel core of conventional ACSR aluminum conductors.

Embodiments of the invention are shown in the accompanying drawings, in which:

FIG. 1 is a top plan view of a strain clamp constructed in accordance with the present invention;

FIG. 2 is a side elevation of the strain clamp of FIG. 1 further illustrating the various parts in clamping engagement relative to a conductor or cable member;

FIG. 3 is a sectional view taken along line 33 of FIG. 4 (rotated 90) illustrating the intermediate position of both of the U-bolts relative to the body member prior to positioning for final clamping engagement;

FIG. 4 is a partial top plan view showing one of the U-bolts of the strain clamp in the clamping position and the other U-bolt in the intermediate position;

FIG. 5 is a top plan view of the body or saddle member with all cooperating elements removed therefrom;

FIG. 6 is a longitudinal sectional view of the keeper member illustrating its preferred construction;

FIG. 7 is a longitudinal sectional view of the body member taken on lines-77 of FIG. 5;

FIG. 8 is a fragmentary sectional view of the body portion of the present clamp taken on lines 88 of FIG. 5;

FIG. 9 is a fragmentary enlarged view of the body member illustrating, in detail, the preferred outline of the serrations applicable to either the keeper member or body member and taken approximately on lines 7-7 of FIG. 5.

Referring now to the drawings, it will be seen that the strain clamp comprises a body member or saddle 1, provided with a cable or conductor seat in the form of a longitudinal undulating channel or groove 2, preferably 7 Patented Sept. 5, 1961 substantially coextensive therewith. Referring to the views of FIGS. 5 and 7-9, it will be apparent that the groove 2 is preferably provided with longitudinally spaced, depressed serrations 3 for a portion of its length, for purposes, and in detail, hereinafter described.

The body portion 1 is preferably provided at one end with an anchoring attachment in the form of bifurcated legs 4, each including registering openings 5 for the reception of 21 thru pin or bolt (not shown) to provide a connection with a support or other anchoring means. The opposite end of the body portion 1 is preferably formed to provide a laterally extending aperture or eye 6 for connection with a hoisting mechanism or come along device (not shown), which temporarily retains the conductor or cable 7 prior to permanent clamping engagement with the strain clamp.

The body portion 2, as will be particularly apparent from FIG. 5, is provided with means for receiving spaced U-bolt members in the form of elongated apertures 1t and it) and opposed notched openings 11 and 11, both of which preferably lie in a plane obliquely disposed jointly relative to the longitudinal plane of the body portion and of the axis of the conductor or cable 7 to pro vide greater clamping surface and prevent yielding of the cable strands.

It will be apparent that the U-bolts 12 and 12" are slidably received in the elongated openings 10 and it) and are held captive in these apertures when the nut and washer assemblies 13 and 13 are threadingly engaged with the U-bolt legs 14 and 14. The opposite U-bolt legs 15 and 15 are engageable with the notches 11 and H and are assembled and are maintained in clamping position by means of washer and nut assemblies 16 and 16, respectively, as will hereinafter be described.

it is preferred to provide an intermediate member in the form of a keeper 20 having a clamping channeled surface 21 (see FIGS. 3 and 6) directly engageable with the conductor 7. The surface 21 is preferably provided with longitudinally spaced depressed serrations 22 throughout a portion of its length for purposes herein after described. The keeper 20 is preferably provided with longitudinally spaced transverse grooves 23 and 23 for reception of the bail portion of the respective U-bolts l2 and 12. A bail or loop portion 24 is preferably provided to extend laterally of the keeper 2t), and is adapted to slidably receive the leg 14' of the U-bolt 12' as a means of holding the keeper captive during installation and removal of the conductor 7, as will be later described.

in operation, the clamp is anchored to a support means, such as a transmission tower, pole, or the like (not shown) by means of the bifurcated leg portions 4. A come along or other hoisting device is then secured to the conductor 7 in the usual manner and the device is further secured to the eye 6. The conductor 7 is then brought to position at a predetermined sag or stress and placed in the channel or groove 2 of the clamp body 1. It is to be noted that the U-bolt members 12 and 12' are preferably preassembled to the clamp body portion 1 by inserting the respective legs 14 and 14' in the longitudinally spaced apertures 10 and 10'. The washer and nut combinations 13, i3, 16 and 16' are then threaded loosely upon both legs of each U-bolt, preferably leaving as much space as possible above the threaded engagement for later manipulation of the respective bolt.

After the conductor has been seated in the groove 2, the keeper 2t and the bolts 12 and 12' are rotated into clamping position relative to one another and to each other. Inasmuch as the legs of the U-bolt have been provided of sufiicient length, the respective nut members may be threaded towards the free end of each leg to permit clearance of all mating parts during assembly. These members are next tightened in place at a desired torque to retain the conductor 7 between the body member 1 and the keeper 20.

The come along is then next released from the conductor and from the eye 6 to complete the installation.

Referring now, in particular, to the clamping surfaces, or conductor seats, 2 and 21 of the body member 1 and of the keeper 24 respectively, it will be apparent that each of the surfaces preferably define an undulating contour. As shown in FIGS. 6 and 7, the contour of the surface 21 of the keeper is complementary to that of the surface 2 of the body member, each surface being arranged to permit substantially direct entrance of the conductor '7 without axial deviation for a distance spaced in wardly of the conductor entrance. action provided by the mating undulations will not cause the conductor to be materially bent away from direct axial stresses.

Another important feature to the present invention is in the provision of the serrations 3 and 22 of the body member 1 and the keeper 20, respectively, and their arrangement with respect to the conductor seating surfaces. As shown in FIGS. 8 and 9, it is preferred to provide the respective serrations as elongated depressions spaced apart from one another and with the group of depressions being spaced inwardly for a predetermined distance from the conductor entrance.

Heretofore, raised depressions have been provided substantially coextensive with relatively flat surfaces with some degree of success. However, in the cases where ACSR cable is used, the cable conductor comprises a steel supporting core strand surrounded by a series of juxtaposed aluminum strands. It is well known that aluminum is notch sensitive and serrations in clamping membersand especially those near the mouth or entrance of a clamping member-tend to bite into the strand and cause the aluminum to flow to either side and offer relatively less surface to resist stresses exerted thereon. In many cases, the aluminum strands have been completely ruptured and stripped away from the steel core, leaving little or no compressive clamping forces to retain the supporting core from axial tensile stresses.

The present clamp contemplates the above problem and provides serrations removed inwardly from the conductor entrance. At the smooth entrance portion a uniform clamping pressure may be applied to the aluminum strands which are subject to vibration and other factors aiding in deflecting the conductor, and which permitted additional non-uniform forces to bear upon relatively small surfaces exposed by serrations. In addition, by placing the serrations rearwardly, and preferably as depressions, the intermediate clamping surface flats of the mating members provide an intermittent application of compressive loading on the steel core through the aluminum strands to develop high unit pressure on the steel. Further, the aluminum tends to flow into the depressions and offer additional frictional resistance to tensile forces in an axial direction. However, this crimping and subsequent flowingof the aluminum is inwardly of the entrance where the smooth seating surface develops the highest possible compressor loading of the aluminum strand bundle.

In fact, in the present arrangement, it has been found that the clamp will develop a resistance to axial pull substantially approximating the full rated strength of conventional ACSR cable.

It will be apparent that we have provided a novel strain clamp including a means for loosely holding captive various mating portions for relative ease in assembly and substantially eliminating the possibility of parts becoming separated during field assembly where they may fall to the ground and be lost. In addition, it will be apparent that We have provided a means applicable to the present clamp, as well as any conventional strain clamp, which aids in retaining the supported conductor Thus, the snubbing t 4 and which will substantially develop the rated strength of that conductor.

We claim:

1. A strain clamp for supporting a conductor comprising a body member including an anchoring attachment and a conductor seat in substantial alignment therewith, conductor hold-down means comprising a keeper engageable with said conductor, said body member defining at least one pair of apertures disposed in spaced relationship at opposed sides of said conductor seat, a U-bolt member having threaded legs arranged to be axially slidably received by said apertures and having its bail portion embracingly engageable with said keeper, one of said opposed apertures having an open end for laterally slidably receiving one leg of said U-bolt, and threaded not members engageable with respective U-bolt legs, the other of said pair of apertures being of a size to permit passing the U-bolt legs and bail portion axially therethrough, the legs of said U-bolt being of sul'ficient length to permit said nut members to remain in threaded engagement at the ends thereof and to further permit slidable rotation of said U-bolt within the plane of said U- bolt and relative to the said opposed apertures, whereby said U-bolt may be rotated into and out of clamping position relative to said keeper and to said body member with one leg being held slidably captive in one aperture and the other leg being releasably received by said openended aperture.

2. A strain clamp for supporting a conductor comprising a body member including an anchoring attachment and a grooved conductor seat in substantial alignment therewith, conductor hold-down means comprising a keeper having a grooved conductor seat, said body member defining at least one pair of apertures disposed in spaced relationship at opposed sides of said conductor seat, a U-bolt member having threaded legs arranged to be axially slidably received by said apertures and having its bail portion embracingly engageable with said keeper, one of said opposed apertures having an open end for laterally slidably receiving one leg of said U-bolt, and threaded nut members engageable with respective U- bolt legs, the other of said pair of apertures being of a size to permit passing the U-bolt legs and bail portion axially therethrough, the legs of said U-bolt being of sufficient length to permit said nut members to remain in threaded engagement at the ends thereof and to further permit slidable rotation of said U-bolt within the plane of said U-bolt and relative to the said opposed apertures, whereby said U-bolt may be rotated into and out of clamping position relative to said keeper and to said body member with one leg being held slidably captive in one aperture and the other leg being releasably received by said open-ended aperture.

3. A strain clamp for supporting a conductor comprising a body member including an anchoring attachment and a grooved conductor seat in substantial alignment therewith, conductor hold-down means comprising a keeper having a grooved conductor seat and an integral laterally offset loop portion, said body member defining at least one pair of apertures disposed in spaced relationship at opposed sides of said conductor seat, a U-bolt member having threaded legs arranged to be axially slidably received by said apertures with said loop portion surrounding one of said legs and having its bail portion embracingly engageable with said keeper, one of said opposed apertures having an open end for laterally slidably receiving one leg of said U-bolt, and threaded nut members engageable with respective U-bolt legs, the other of said pair of apertures being of a size to permit passing the U-bolt legs and hail portion axially therethrough, the legs of said U-bolt being of sufiicient length to permit said nut members to remain in threaded engagement at the ends thereof and to further permit slidable rotation of said U-bolt within the plane of said U-bolt and relative to the said opposed apertures and to said keeper loop portion, whereby said U-bolt may be rotated into and out of clamping position relative to said keeper and to said body member with one leg being held slidably captive in one of said apertures and in said keeper loop portion and the other leg being releasably received by said open-ended aperture.

4. A strain clamp for supporting a conductor comprising a body member including an anchoring attachment and a grooved conductor seat in substantial alignment therewith, conductor hold-down means comprising a keeper having a grooved conductor seat, said body member defining two longitudinally separated pairs of apertures disposed in spaced relationship at opposed sides of said conductor seat, two U-bolt members each having threaded legs arranged to be axially slidably received by respective aperture pairs and having its bail portion embracingly engageable with said keeper, one of said opposed apertures of each pair having an open end for laterally slidably receiving one leg of a respective U-bolt, and threaded nut members engageable with respective U- bolt legs, the other of said pair of apertures being of a size to permit passing the U-bolt legs and hail portion axially therethrough, the legs of each of said U-bolts being of suflicient length to permit said nut members to remain in threaded engagement at the ends thereof and to further permit slidable rotation of said U-bolt within the plane of said U-bolt and relative to the said respective opposed apertures, whereby a respective U-bolt may be rotated into and out of clamping position relative to said keeper and to said body member with one leg being held slidably captive in one aperture and the other leg being releasably received by said open-ended aperture.

5. A strain clamp for supporting a conductor comprising a body member including an anchoring attachment and a conductor seat in substantial alignment therewith, conductor hold-down means comprising a keeper having a conductor seat, said body member defining at least one pair of apertures disposed in spaced relationship at opposed sides of said conductor seat, a U-bolt member having threaded legs arranged to be axially slidably received by said apertures and having its bail portion embracingly engageable with said keeper, one of said opposed apertures having an open end for laterally slidably receiving one leg of said U-bolt, and threaded nut members engageable with respective U-bolt legs, the other of said pair of apertures being of a size to permit passing the U- bolt legs and bail portion axially therethrough, the legs of said U-bolt being of suflicient length to permit said nut members to remain in threaded engagement at the ends thereof and to further permit slidable rotation of said U-bolt within the plane of said U-bolt and relative to the said opposed apertures, the respective conductor seats of said body member and of said keeper each defining complementary relative longitudinally undulating contoured surfaces.

6. A strain clamp for supporting a conductor comprising a body member including an anchoring attachment and a conductor seat in substantial alignment therewith, conductor hold-down means comprising a keeper having a conductor seat, said body member defining at least one pair of apertures disposed in spaced relationship at opposed sides of said conductor seat, a U-bolt member having threaded legs arranged to be axially slidably received by said apertures and having its bail portion embracingly engageable with said keeper, one of said opposed apertures having an open end for laterally slidably receiving one leg of said U-bolt, and threaded nut members engageable with respective U-boat legs, the other of said pair of apertures being of a size to permit passing the U-bolt legs and bail portion axially therethrough, the legs of said U-bolt being of sufiicient length to permit said nut members to remain in threaded engagement at the ends thereof and to further permit slidable rotation of said U-bolt within the plane of said U-bolt and relative to the said opposed apertures, said respective conductor seats each further defining a plurality of Iongitudinally spaced depressed elongate serrations disposed transversely relative to said respective conductor seats and being further spaced a selected distance from the entrance end of said conductor seats.

7. A strain clamp for supporting a conductor comprising a body member including an anchoring attachment and a grooved conductor seat in substantial alignment therewith, conductor hold-down means comprising a keeper having a grooved conductor seat, said body member defining at least one pair of apertures disposed in spaced relationship at opposed sides of said conductor seat, a U-bolt member having threaded legs arranged to be axially slidably received by said apertures and having its bail portion embracingly engageable with said keeper, one of said opposed apertures having an open end for laterally slidably receiving one leg of said U- bolt, and threaded nut members engageable with respective U-bolt legs, the other of said pair of apertures being of a size to permit passing the U-bolt legs and hail portion axially therethrough, the legs of said U-bolt being of suflicient length to permit said nut members to remain in threaded engagement at the ends thereof and to further permit slidable rotation of said U-bolt within the plane of said U-bolt and relative to the said opposed apertures, the respective conductor seats of said body member and of said keeper each defining complementary relative longitudinally undulating contoured surfaces, said respective conductor seats each further defining a plurality of longitudinally spaced depressed elongate serrations disposed transversely relative to said respective conductor seats and being further spaced a selected distance from the entrance end of said conductor seats.

References Cited in the file of this patent UNITED STATES PATENTS 706,393 Darling Aug. 5, 1902 1,370,544 Leeper Mar. 8, 1921 1,940,704 Sumpter et al Dec. 26, 1933 2,009,318 Highfield Jan. 23, 1935 2,177,364 Fotsch Oct. 24, 1939 2,915,733 Toedtman et al. Dec. 1, 1959 FOREIGN PATENTS 1,025,428 France Jan. 21, 1953

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