EP1043804A2

EP1043804A2 - Grounding lug clamp

Info

Publication number: EP1043804A2
Application number: EP00302945A
Authority: EP
Inventors: Darrell R. Childers; Jeffrey R. Elledge; Eric W. Kent
Original assignee: Corning Optical Communications LLC
Current assignee: Corning Research and Development Corp
Priority date: 1999-04-09
Filing date: 2000-04-07
Publication date: 2000-10-11
Also published as: CA2302132A1; BR0001196A; EP1043804A3

Abstract

A grounding lug clamp (10) has a top (12) and bottom (14) with a passageway (22) therethrough to withstand extremely high currents for sustained periods of time. The lug clamp (10) is secured to the armor wrap of an armored cable to ground the cable without splitting the armor wrap. The lug clamp (10) has a post or screw (38) for connecting to ground. The top (12) and bottom (14) are secured around the cable with dowel pins (32), a hinge and pins, or a sleeve.

Description

Field of the Invention

This invention relates in general to a grounding lug clamp, and in particular to a lug clamp that clamps a armored cable and is able to withstand high currents for extended periods of time.
Typical grounding clamps usually require that the jacket on the cable (copper and fiber cables or either type alone) be split open to access the armor wrap/jacket under the outer jacket A connector bottom with a post or tab is then slid underneath the armor wrap or core wrap and a connector top is then secured to the connector bottom by a securing nut screwed down on the post The top and bottom may have teeth or tabs to engage the armor wrap. 3M makes such a shield connector, which it calls the Scotchlok™. However, this shield connector does not allow for sufficient contact area between the armor/jacket and the shield connector to withstand large currents for extended time periods. The contact area between the shield connector and core wrap needs to be larger and tighter than achieved by simply sliding a shield connector around a portion of the core wrap. Additionally, this type of shield connector may also cause problems by the connector unnecessarily splitting the outside jacket and the armor wrap and potentially allowing undesirable elements into the length of the cables.
Thus, a clamp is needed that alleviates the problem of tapping into the cable's armor and is able to withstand the higher currents for longer periods of time.
The invention accordingly provides a grounding lug clamp according to Claim 1.
The accompanying drawings which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the principles of the invention.
Figure 1 is an exploded, perspective view of a grounding lug clamp constructed in accordance with the invention;
Figure 2 is a cross-sectional view from the top of the grounding lug clamp of Figure 1 in an assembled state;
Figure 3 is a front elevational view of the lug clamp with a bolt inserted to connect the grounding lug clamp to ground;
Figure 4 is a view of the clamp of Figure 1, opened to show the interior of the lug clamp of Figure 1;
Figure 5 is a front elevational view of the grounding lug clamp shown with a representative armored cable inserted therein;
Figure 6 is an exploded view of the grounding lug clamp and an armored cable, the armor being exposed;
Figure 7 is a cross-sectional view of the grounding lug clamp installed on an armored cable and inserted into a cable fitting; and
Figure 8 is an exploded view of the assembly of Figure 7.

DETAILED DESCRIPTION OF THE INVENTION

Referring to Figure 1, grounding lug clamp 10 has a top 12 and a bottom 14. In the preferred embodiment, the top 12 and bottom 14 each tabs 16 have along surface 18, with holes 20 passing through the tabs 16. Tabs 16 are offset from each other on the top 12 and bottom 14, such that when the top 12 and bottom 14 are mated, the grounding lug clamp 10 completely encloses a passageway 22 (see, e.g., Figure 5). While passageway 22 is generally cylindrical, it could be any shape that is similar to the shape of cable to which it will be attached so that will ensure maximum contact with the armored cable 24. Passageway 22 also has a configuration 26 on the inside to secure the armored cable 24 within the grounding lug clamp 10. The configuration 26 can be undulations, corrugations, or grooves 28. Ground lug clamp 10 is preferably made of brass, but could also be made of zinc.
As seen in Figure 6, armored cable 24 typically has a covering jacket 29, and armor covering 30. Armor covering 30 is a metal sheath that has undulations or corrugations 31 and protects any copper cables and optical fibers in the cable 29 and provides grounding capabilities for the cable. It should be understood that armor covering 30 is intended to include all wraps, coverings, wires, etc., used to ground an armored cable. The ALTOS® Armored Cable sold by Siecor Corp. of Hickory, N.C. is such a cable.
By having the undulations 28 in the lug clamp that correspond to the undulations 33 in the armored cable 24, the contact area between the lug clamp 10 and the cable armor 30 is maximized. Additionally, the passageway 22 of grounding lug clamp 10 has a diameter that is slightly smaller than the diameter of the armored cable 24 so that the grounding lug clamp 10 compresses the armored cable 24. The compression by the clamp 10 functions to not only secure the cable 24 within the passageway 22, but forces the corrugations 31 of the cable 24 into the grooves 28 of the grounding lug clamp 10.
To secure the clamp 10 around an armored cable 24, dowel pins 32 are inserted into holes 20 to hold top 12 and bottom 14 together in tight compression around cable 24. Rather than having two loose dowel pins 32 as shown in Figures 1 and 6, one of the pins 32 could be placed and secured within the holes 20 along one side of the grounding lug clamp 10 to form a hinge. The grounding lug clamp 10 could also be made to have a hinge along one side, rather than having tabs 16 and holes 20 on both sides as shown. Alternatively, a sleeve (not shown) could be slid around the outer surface 34 of the clamp 10 to hold the top 12 and bottom together rather than using the pins 32. In this alternative embodiment, the top 12 and bottom 14 could still have tabs 16, or they could each be true half cylinders and flat along surface 18. The sleeve would be made of brass, stainless steel, aluminum, or zinc, and would preferably by cylindrical in shape to provide space for a grounding bolt or post, discussed below.
The top 12 also has a recess or hole 36 to allow a screw 38 to be mechanically and electrically connected to the grounding lug clamp 10. A grounding wire (not shown) is then connected by the screw 38 to connect the cable 24 and grounding lug clamp 10 to electrical ground. Alternatively, the grounding lug clamp 10 could have an integrally formed post with or without threads (not shown), which is preferably short, rather than the hole 36 to allow for connection of the grounding wire to grounding lug clamp 10. (It should be noted that the top 12 and the bottom 14 could be reversed in that the connection point for the grounding wire could be in the bottom 14 rather than the top 12.)
Figures 3 and 5 show that the grounding lug clamp 10 is substantially circular in cross-section. Figure 5 also illustrates one type of cable that could be used with the grounding lug clamp 10. As shown, cable 24 has an armor covering 30 that is in direct contact with clamp 10, and cable 24 may also have optical fibers 23 and copper wires 25 (such as twisted pairs for telephone applications). Depending on the specific application, the cable may have either only optical fibers, only copper wires, or both. Therefore, the present invention is not limited to any specific type of cable 24.
As can also be seen in Figures 3 and 5, the outer surface 34 of grounding lug clamp 10 is preferably divided into two portions, a first curved portion 40 and a second portion 41 near the hole 36 and screw 38 that is substantially flat. As shown in Figures 7 and 8, this allows the clamp 10 and the screw 38 to fit within a cable fitting 42. If the cable fitting 42 were of a sufficient size, then grounding lug clamp 10 would not need the substantially flat portion 41. In this case, the grounding lug clamp 10 could be entirely circular or oval, or the flat portion 41 may only have a reduced radius (eventually approaching zero and thus a flat portion). However, in order to minimize the space requirements for the clamp 10, it is preferable to have second portion 41. In Figure 8, cable fitting 42 comprises a fitting 44, an O-ring 46, and a fitting nut 48. Fitting 44 is placed over the cable (not shown) and then grounding lug clamp 10 is attached to the cable. O-ring 46 and fitting nut 48 help to prevent adverse effects from exposure to the elements. After assembly, a heat shrink 50 is placed over the fitting 44. (The closure to which the cable fitting is attached is not shown to allow for greater clarity). The grounding lug clamp 10 could also be used in other enclosures, areas, etc., where ever a grounding lug clamp 10 is needed.
The grounding lug clamp 10 passes BellCore Standard GR 950, which requires that the grounding lug clamp 10 be able to withstand 1000 amps for 20 seconds and still be able to conduct current thereafter. Applicants have been unable to find any other clamps that will withstand that amount of current for that time period. Typically, after applying the 1000 amps for 20 seconds, the prior art clamps will no longer conduct current. At the point of contact between the clamps and the armor, especially if they are of the alligator clamp type (with the teeth or points engaging the armor wrap), the armor has disappeared or been burned away, preventing contact between the clamps and the armor (an ohm-meter test reveals that the resistance approaches infinity, indicating that contact has been broken). The clamp according to the present invention, however, is still in contact with armor, having little to no effect on the resistance before and after the testing.
While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.

Claims

A grounding lug clamp for grounding an armored cable, comprising:
a top and a bottom, the bottom being mateable to and/or rotatably coupled to the top and the arrangement being such that the top and bottom, when mated together, define a passageway therethrough for securing the armored cable.
A grounding lug clamp according to Claim 1, wherein the passageway has a configuration to engage the armored cable.
A grounding lug clamp according to Claims 1 or 2 further comprising;
a recess in one of the top and bottom to secure a ground wire therein.
A grounding lug clamp according to Claim 4, wherein the recess is a threaded hole, and the ground wire is secured to the lug clamp with a screw.
A grounding lug clamp according to Claims 1 or 2 further comprising a post extending from one of the top and bottom to secure a ground wire thereto.
A grounding lug clamp according to Claim 2 or any one of Claims 3-5 as appended thereto wherein the configuration in the passageway comprises undulations, corrugations, or grooves.
A grounding lug clamp according to Claim 2 or any one of Claims 3-5 as appended thereto wherein the configuration in the passageway is configured to mate with undulations in the armor cable.
A grounding lug clamp according to any one of Claim 1-7 further comprising pins to mate the top and bottom.
A grounding lug clamp according to any one of Claims 1-8 in combination with an armored cable the passageway has a second diameter, the first diameter being greater than the second diameter.
A grounding lug clamp according to any one of Claims 1-9 wherein the top and bottom have first and second sides, the clamp further comprising a hinge along the first side.