US2554169A

US2554169A - Ground strap

Info

Publication number: US2554169A
Application number: US658490A
Authority: US
Inventors: Martin D Bergan
Original assignee: Thomas and Betts Corp
Current assignee: ABB Installation Products Inc
Priority date: 1946-03-30
Filing date: 1946-03-30
Publication date: 1951-05-22
Anticipated expiration: 1968-05-22

Description

May 22, 1951 M. D. BERGAN 2,554,169

GROUND STRAP JJM.. nu

INVENTOR. /VAPT//v 0. 5f/P @AW Patented May 22, 1951 GROUND STRAP Martin D. Bergan, Westfield, N. J.,4 assignor to The Thomas & Betts Co., Elizabeth, N. J., a corporation of New Jersey Application March 30, 1946, Serial No. 658,490

6 Claims. (Cl. 173-273) The invention relates in general to a ground strap for mechanically and electrically connecting a ground wire with a Water pipe or other form of grounded conductor. Such conductors are of different diameters and it not infrequently happens that an operator does not know what size of pipe or conductor he might encounter on any particular job where'he desires to make a temporary or permanent grounding connection. It has been necessary heretofore to provide the operator With grounding straps of different dimensions and sizes in order to meet the different requirements relative to size which he may encounter in making such connections. Accordingly one of the objects of the invention is to provide a form of ground strap which is of a length to provide a strap of diierent circumferential lengths, which can be readily bent in situ by the operator to accommodate it to the particular size of tubular pipe or other form of grounded conductor to which the ground wire is to be attached.

While the size of the pipe may vary, the Electric Code at present permits the use of only one size of grounding conductor, that is #8 AWG gauge solid Wire of a normal diameter of 0.128 inch for use with a copper strip type of ground strap.

It has been known in the art as shown by the patent to S. N. Buchanan 1,922,077, August 15, 1933, to provide a grounding strap in which the grounding wire is first bent into am, hairpin or loop form and inserted into the holding element of a clamp organized to get sulcient pressure to prevent the conductor from turning or otherwise moving in the clamp. However, in actual practice it has been found that as a rule the installing operator will not go to the trouble of initially bending the grounding wire into a hairpin loop but insists on leaving the end of the wire unbent and more or less straight and hopes that it Will be held even though under these conditions only one side of the conical element of the clamp engages the wire. However, the wire receiving space in the Buchanan and similar forms of clamps has considerable leeway for positioning the loop, and which if the wire is straight would not properly locate the parts to afford a good clamping effect.

Accordingly the primary object of the invention is to provide a form of ground strap which will effectively secure a ground wire thereto under those conditions wherein the clamped end of the wire is straight.

Broadly this objective is attained first by providing a form of ground'strap, an outturned end portion of which forms the relatively fixed element of a clamp and which fixed element is designed to engage one side of the straight end ground wire over a material and extensive length thereof and which fixed element is also backed solidly by the pipe or other rugged support encircled by the strap; and second by providing as the relatively movable clamping element of the clutch a pressure distributing plate or pad for engaging the ground wire on the side thereof opposite the side bearing on the fixed clutch element and engaging the wire over an equally material and extensive length of the straight end of the wire.

Still another feature of the disclosure is that the device in addition to its Wire clamping features is designed in its outturned end portion forming the fixed clutch element to provide a pair of offset loops capable of performing two functions: rst, to act as stops to restrain rotation of the pressure distributing plate after contact with the wire and particularly as the plate approaches its final clamping position, and second, the loops provide a pair of aligned tube-like orifices dimensioned just large enough to receive the straight end of a standard size of grounding wire with a snug but sliding fit and organized to locate and temporarily secure the wire in proper position in the clamp between its broad bearing relatively fixed and movable elements even before the clamping pressure is applied.

In the known art the ground strap had to be made sumcently flexible so that at least one of its clamping portions could be deformed, as by means of the conical wedge in the above identilied patent, into engagement with the U-turn of the grounding Wire, and in turn to force the wire loop into binding engagement With the companion and equally distortable portion of the clamp. There are many situations Where a more rugged and thus less exible type of grounding strap is desired than is necessary to form the relatively light form of clamp disclosed in the Buchanan patent. However, with increase in cross sectional area of the material of which the clamped portion is formed, it becomes more and more impossible in practice to flex or distort the clamping portions of such known forms of fitting so as to clamp the grounding wire, and this becomes more and more diiiicult, and often iinpossible, where a particularly small size of clamping device is used and where it is not always possible to bend the ends of the conductor into the U-loop form heretofore used and which had to be bent in order to provide the necessary holding,

effect.`

Accordingly. another object of the invention is to provide a standard form of ground fitting of a single size which can receive the usual grounding wires, and which can secure the same directly to the strap without necessity of bearing through some portion of the strap and in this way avoid the necessity of involving any element of flexibility or distortability of the strap in the clamping operation.

The invention herein disclosed then particularly features a single clamping means operatively connected to both conductor and wire so that when moved into its tightened position, it will cause the strap first to accommodate itself to the particular grounded conductor which is to support it, then it will firmly clasp itselfv to the supporting conductor and in the nal stages of its clamping movement will secure the ground wire fixed securely to the ground strap and the ground strap to the supportingv conductor all with one tightening operation.

Various other objects and advantages of the invention will be in part obvious from an inspection of the accompanying drawings and in part will be more fully set forth in the following particular description of one form of' device embodying the invention, and the invention also consists in certain new and novel features of construction and combination of parts hereinafter set forth and claimed.

In the accompanyingl drawings:

Fig. 1 is a plan view of a flat punched blank of thiny sheet metal from which the ground strap herein featured is formed;

Fig. 2 is a view in side elevation of the blank of Fig. 1 with one end pre-formed and showing the strap before it is bent into the final position engagingv a water pipe;

Fig. 3 is a slightly enlarged plan view looking down upon the strap formed from the Fig. 2 disclosure bent and locked in operative position connecting a water pipe with a ground wire;

Fig. 4 is a view in side elevation of the structure shown in Fig. 3;

Fig. 5 is a transverse sectional view through the pipe, taken on the line 5-5 of Fig. 3 looking in the direction indicated by the arrow and showing the ground strap in side elevation;

Fig. 6 is a similar view showing the ground strap in section,l taken on the line 6 6 of Fig. 4 f

and looking in the direction indicated by the arrows; and

Fig. '7 is a detailed plan View of the under side of the clamping nut shown in the preceding gures.

In the drawings there is shown two conductors, a relatively large conductor A specifically intended to disclose a grounded water pipe, and a cable B provided with a` conductor C hereinafter referred to as a ground wire.

The strap I particularly forming the subject matter of this disclosure is designed to connect the conductors A and C both mechanically and electrically.

The strap comprises one main and three minor parts; a strip of flexible metal I I, a bolt I2, a nut I3 threaded on the bolt and a clamping broad faced bearing saddle or pressure distributing plate I4 loose on the bolt and forming a washer or pressure pad or plate tted beneath the head ofthe bolt. The strip I I is provided adjacent one. end with a rst bolt hole I and in spaced relation thereto with other bolt holes I6 of which four are shown in the blank of Fig. 1. The strip II is provided on opposite sides of the bolt hole at right angles thereto.

I5 with a pair of short parallel slits I'I and I8. The material between the slits I'I and I8 is bent inwardly out of the plane of the strip to form a relatively long inner loop I9. The material between each of the slits and the adjacent outer edge of the strip are bent. outwardly to form a pair of

outer loops

20 and 2|. It will be noted by reference to Figs. 2 and 5 that the loops 20 and 2l with loop I9 offset therebetween forms an opening tube or long eye 22 designed to receive the straight end portion of a small diametered conductor C snugly fitted therein as particularly shown in Figs. 3-6. The slitted end of the strip is preformed as indicated at the left of Fig. 2 and as hereinafter described and it is this partly formedarticle` which is delivered to the operator when he leaves the shop to make the connections. rIhe mid-portion of the strip as shown in Fig. 2 is bent around the relatively large diametered conductor A to form a clutching band 23 which almost completely encircles the conductor and is provided with an upper outstanding portion 244 and an opposing lower outstanding portion 25. The portion 2,4 is bent into a step 26, the lower free edge 2 of which finally abuts the portion 25' The bolt I2V is passed' through the bolt hole I5 and whichever one of the bolt holes I6 may happen to be more or lessr aligned therewith after the band 23 has been formed.

It is a feature of this disclosure that the clamping plate I4 is a freely floating member andV is sufficiently rigid to transmit squeeze forces therethrough without deformation. The plate is located beneath the head 29, of the bolt and throughl which plate the bolt extends loosely. It is noted that the clamping plate is non-circular and, specifically, is rectangular in plan and fits between the stops, formed by the outstanding loops 20 and 2I so that this plate does not turn with the bolt. .The plate I4 overlaps and bears directly on the conductor C as best shown in Fig. 6 and the parts are so disposed that when the bolt is drawn tight the under side of the plate is forced into engagement with the portion of the conductor C exposed thereto. Preferably, the, under side 36 of the plate I4 is corrugated or otherwise roughened to enhance the engagement between this plate and the conductor.

In operation and assuming that the parts are in the position approachingl those shown in Figs. 5 and 6, the tightening of the bolt, will first draw the band 23 tightly into engagement with the conductor A, and this, will continue until edge 2l is bearingl rmly on the projection 25. At this time the threaded nut I3 will be bearing on the portion of the strap which contains the bolt hole I5 through which the shank end of the bolt is projecting. At the beginning of the bolt tight.- ening operation itI will be necessary to hold nut I3 from rotating with thebolt.

The continued rotation of the bolt will then cause its head 2S to act through the clamping plate I4 to cause the` conductor C to bind firmly against the lower loop I9, and at the end of the` tightening movementsl the several parts will be in the position shown in Fig. 6. If the connection is to` be permanent the surplus length of metal strip beyond the bolt hole I6, then in use will be cut, olf to provide a neat form of connection.

I claim:

1. A groundstrap comprising a, strip of flexible sheetv metal provided adjacent one end with a. rst bolt hole and with a second bolt hole in spaced relation to the'rst hole, said strip adapted to be'bent circularly into position to encircle a supporting conductor to bring the bolt holes into axial alignment, the portion of the strip on opposite sides of the iirst hole and offset therefrom inwardly frornthe adjacent end of the strip being slitted lengthwise of the strip and with the portion between thevslits ybent inwardly out of the plane of the strip to form an inner loop forming an outwardly exposed relatively fixedelement of a clutch, and the outer portions between each slit and the adjacent edge of the strip being both bent outwardly of the plane of the strip to form a pair of outer loops disposed oiset from the inner loop, said inwardly bent loop and said pair of outwardly bent loops coacting to form in eiect a tube adapted to receive a ground wire intruded therein, a single clamping means for mechanically .and electrically securing the ground wire to the strap and to secure the strap to the support, said means including a headed bolt passed through the aligned bolt holes, a non-circular clamping plate through which the bolt is loosely passed and which constitutes the coacting movable element of the clutch, said clamping plate located between the head of the bolt and the ground wire for directly engaging the ground wire over a material length thereof and to force the same into engagement with the fixed clutch element, said plate being iitted between the outer pair of loops and held thereby from rotating with the bolt, and a nut engaging the opposite end of the bolt and adapted to bear on the portion of the strip provided with the second hole.

2. The ground strap dened in claim 1 and in which the underside of the clamping plate which is designed to engage the ground wire is roughened.

3. The combination with two conductors of materially different diameters and in which a straight end of the smaller conductor extends in close relation to and parallel to the larger conductor, a strap forming device for mechanically and electrically connecting said straight end of the smaller conductor to the larger conductor, said device including a flexible band substantially encircling the larger conductor and whose end portions project from the larger conductor to form parallel outstanding overlapping flanges, one of the flanges provided Vwith three loops integral with their associated flange having a common axis and coacting to encircle closely said straight end, the middle loop disposed in bearing engagement with the larger conductor and the two end loops offset outwardly from the middle loop to leave the portion of the straight end between the end loops outwardly exposed, means for squeezing the flanges towards each other to bind the band on the larger conductor and to bind the straight end on to the middle loop which overlaps the same, said means including a headed bolt and nut assembly passed through the iianges and a pressure plate fitted between the two outer loops and held thereby from rotating and bearing directly on the portion of the straight end so exposed between the end loops.

4. In a ground strap connector, the combination of a flexible strip of metal adapted to be wrapped about a first conductor to form a cylindrical portion and provided with overlapping end portions outstanding radially from the cylindrical portion, said end portions provided with a pair of aligned bolt holes, the upper of the out- 6 standing end portions provided with a pair of parallel slits on opposite sides of the bolt hole therein, the portion of metal between each slit and the adjacent edge of the strap being bent upwardly to form a pair of upper loops and the portion of metal between the slits being bent downwardly to form a lower loop, said loops being coaxially aligned and forming in effect an incomplete tube fashioned to receive therein and to hold in place a second conductor, a clutch for clamping the second conductor directly to the lower loop of the strap, the lower loop being offset from its associated bolt hole towards the cylindrical portion and forming the relatively fixed jaw element of the clutch, a freely floating plate rectangular in plan iitted in the space between the upper loops, otherwise independent thereof and forming the coacting, relatively shiftable jaw element of the clutch, said plate provided with a bolt hole substantially aligned with the said pair of bolt holes, the part of the plate which lies between its bolt hole and the cylindrical portion of the strap overlapping the iixed jaw element of the clutch for direct bearing engagement with the second conductor, and pressure creating means passed through the bolt holes and reacting between the iixed and movable clutch elements to draw them together and thus secure the second conductor to the strip.

5. In a ground strap connector, the combination of a iiexible strip of metal adapted to be wrapped about a rst conductor to form a cylindrical portion and provided with overlapping end portions outstanding radially from the cylindrical portion, said end portions provided with a pair of aligned bolt holes, the upper of the outstanding end portions provided with a pair of integral loops upstanding from the portion between the loops, said loops being coaxially aligned to form in effect an incomplete tube fashioned to receive therein a second conductor and said loops being axially spaced apart to expose therebetween a portion of the second conductor, a clutch for clamping the second conductor to the strip, the part of the upper end portion between the loops forming the relatively iixed jaw element of the clutch and adapted to form a seat for receiving the portion of the second conductor exposed between loops, a freely floating pressure distributing plate fitted between the loops and restrained thereby from rotary movement, said plate provided with a bolt hole substantially aligned with the said pair of bolt holes, and the part of the plate which lies between its bolt hole andthe cylindrical part of the strap overlapping the ixed jaw element of the clutch, and a headed bolt passed through the pair of aligned bolt holes and through the bolt hole in the floating plate, the head of the bolt bearing downwardly on the shiftable clutch element, and a nut on the bolt bearing upwardly on the lower outstanding end portion of the strap.

6. A ground strap sufficiently flexible to be wrapped about a cylindrical form of support to form an incomplete circle and with the ends of the strap outstanding from said circle and disposed in overlapping parallel relation to form a pair of overlapping flanges, threaded fastening means including a headed bolt passed through the anges and provided at the end opposite its head with a nut for engaging the adjacent ange, the portion of the strap between the bolt and the circle and at the headed end of the bolt provided with a pair of parallel slots with the ma 57, terial between the slots pressed towards the circle to form a concaved L-shaped shoulder forming a relatively xed element of a clutch and the portions of the material outwardly of each of the slits pressed outwardly away from the circle to form a pair of outstanding loops, said loops and shoulder coacting to receive a conductor therebetween with the outer side of the conductor opposite the shoulder outwardly and upwardly exposed between the loops, and a pressure pad rectangular in plan loose on the shank of the bolt, underlapping the head of the bolt, tted between the loops and held from rotation thereby, said pad forming a Shiftable clutch element with the portion on one side of the bolt and located between the loops, disposed to bear on the exposed outer side of the conductor with a squeeze force directed diametrcally through the conductor leaving the opposte portion of the pad .free to assume'what` ever position it may, and said pressure pad being otherwise free of the strap.

MARTIN D. BER'GAN.

REFERENCES -CITED The following references are of record in the file 4of this patent:

UNITED STATES PATENTS Number Name Date 931,706 Stevens Aug. 17, 1909 1,163,372 Schade Dec. 7, 1915 1,495,493 Lipschutz May 27, 1924 1,542,074 Mayer June 16, 1925 1,725,120 Williams Aug. 20, 1929 1,809,009 Andre June 9, 1931 1,922,077 Buchanan Aug. 15, 1933 2,062,690 Weynand Dec. l, 1936