US 3146053 A
Description (OCR text may contain errors)
Allg- 25 1954 H. E. sTRocK POTENTIAL TAP DEVICE 2 Sheets-Sheet l Filed Feb. 2l. 1961 FEA Aug, 25, 1964 H. E. s'rRocK POTENTIAL TAP DEVICE 2 Sheets-Sheet 2 Filed Feb. 2l. 1961 INVENTOR. HOW/i190 f. 577905K B Y Har/fm avg, 51654. 62:75 f'fff United States Patent O 3,146,053 POTENTIAL TAP DEVICE Howard E. Struck, Charlotte, N.C., assgnor to Associated Engineering Company, Matthews, N.C., a corporation of North Carolina Filed Feb. l21, 1961, Ser. No. 90,808 2 Claims. (Cl. 339-97) This invention relates to potential tap devices and more particularly to means for making an electrical connection to an insulation covered cable in a more efficient and less costly manner than has been possible with prior art dev1ces.
After an electrical installation has been made it is often found necessary to make additional electrical connections at points in the installation not having means provided for this purpose. This invention provides a novel means for making these electrical connections.
Briefly, the device of the instant invention comprises an adjustable band in combination with a self-threading pointed screw. The band is positioned with the insulated cable passing therethrough and the screw threaded to the band which serves as an anchoring device which enables the screw to be threaded through the cable insulation and into the conductor. External electrical connections are made either directly to the tapping screw or to an electrical titting mounted to the band.
The device of the instant invention as hereinbefore described is more economical than somewhat similar prior art devices and the instant invention does not require the provision of a separate female threaded device so that bolts and nuts are eliminated on the puncturing or contact making part. This is achieved by utilizing a screw which is self-threading at the anchoring band and into the cable insulation and conductor.
The device of the instant invention provides a more reliable electrical connection than somewhat similar devices of the prior art in that the device of this invention includes a self tapping feature by which the connecting screw taps into the conductor itself to provide a holding j action. This is especially true in the case of a stranded conductor with the screw penetrating between the strands to be held there by a binding action.
Self-threading minimizes the possibility of loosening the screw thereby reducing the possibility of high resistance at the point of contact if the potential tap device should be subjected to mechanical vibration. The tapping of the anchoring band and the cable insulation provides additional positive holding means for the screw.
vAccordingly, a primary object of this invention is to provide a novel construction for a potential tap device which is more economical and more reliable than prior art devices.
Another object is to provide a potential tap device which utilizes a self tapping screw which taps into an anchoring band as well as into the insulation and conductor of the cable.
Still another object is to provide a potential tap device which may readily be utilized in conjunction with an instrument transformer.
A further object is to provide a potential tap device including an anchoring band which, when used in conjunction with a plastic molded instrument transformer, will put the plastic housing of the transformer in compression and will spread the mechanical stresses of tapping around the periphery of the housing.
A still further object of this invention is to provide a potential tap device which does not require a separate female threaded member for tapping purposes.
Yet another object is to provide a potential tap device in which most of the anchoring band is covered with an 3,146,053 Patented Aug. 25, 1964 ice insulating coating which is penetrated by the self tapping screw which penetrates the cable conductor.
FIGURE 1 is a perspective illustrating the potential tap device of this invention mounted to a stranded cable.
FIGURE 2 is a cross section taken through line 2-2 of FIGURE 1.
FIGURE 3 is a plan view of the member from which the band is formed.
FIGURE 4 is a side elevation of the band of FIGURE 3 looking in the direction of arrows 4-4 of FIGURE 3.
FIGURE 5 is an end view of an instrument transformer having the potential tap device of this invention mounted thereto.
FIGURE 6 is a plan view of the combination illustrated in FIGURE 5.
FIGURE 7 is a side elevation of the combination illustrated in FIGURE 5.
FIGURE 8 is a plan view of a band forming membe having an insulating covering.
FIGURE 8A is a side elevation of the band of FIG. 8.
FIGURE `9 is an end view of the instrument transformer of FIGURES 5-7 with a power tapping device including the anchoring band of FIGURES 8 and 8A.
Now referring to the figures and more particularly to FIGURES 1-4, potential tap device 10 comprises band 11 which surrounds insulated cable 12, tapping means comprising screw 13 mounted to band 11, and take-ott means comprising terminal connector 14 also mounted to band 11.
Band 11 is constructed of an elongated strip 25 (FIGS. 3 and 4) preferably comprised of a non-magnetic metal such as stainless steel. Strip 25 is provided with a plurality of apertures 15 spaced along the longitudinal axis. The left end of strip 25 is provided with an overlying portion 16 to which connector 14 is mounted. Apertures 15 are provided so that the size of band 11 can be readily adjusted so as to be compatible with the size of the cable to which potential tap device 10 is mounted.
Tapping means 13 is comprised of a self-tapping pointed screw, preferably a sheet metal screw.
Potential tap device 10 is installed by placing strip 25 over cable 12 and drawing it into the form of band 11 with portions of strip 2S overlapping so that two of the apertures 15 are in alignment. Screw 13 is then entered into the aligned apertures and rotated. Screw 13 is closely iitted to apertures 15 so that the rotation of screw 13 will cause it to be tightly gripped by band 11. This rotation also causes the tip of screw 13 to iirst penetrate the insulation covering 17 of cable 12 and thereafter enter between the strands 18 which comprise the cable conductor.
Thus, it is seen that band 11 acts as an anchoring means while screw 13 is rotated to pierce insulation 17 and the conductor comprised of strands 18. The passage of Screw 13 between strands 18 results in a binding action which produces good electrical contact. In addition, the fact that screw 13 is self tapping into band 11 and insulation 17 as well as into the cable comprised of strands 18 results in a mechanical securement which resists loosening which would otherwise result from vibrations.
The output of the potential tap device 10 may readily be taken directly from tapping screw 13. However, terminal means 14, in the form of screw 21, cupl washer 22 and nut 23 are provided. The threaded portion of screw 21 is entered into aligned apertures in the overlying portion 16 and the main portion 25 of the strip comprising band 11. The resilient nature of the material comprising band 11 causes the overlying portion 16 to normally be positioned in somewhat spaced relationship from main portion 25 as best seen in FIG- URE 4. Because of this, even if nut 23 were to be removed from screw 21, screw 21 would be retained in a mounted position upon band 11.
Now referring more particularly to FIGURES 5 7 which illustrate the potential tapping device utilized in conjunction with a current transformer 50, current transformer 50 is of conventional design and includes molded insulating housing S1 wherein a multi-turn coil (not shown) is disposed. The coil terminals (not shown) are engageable by terminal screws 52, 53 whose heads are disposed externally of housing 51 and are positioned at the top thereof. Housing 51 is formed with passage 54 extending longitudinally therethrough with current carrying cable 55 disposed within passage 54.
Cable 55 comprises conductor 56 surrounded by insulating cover 57. As is well known to the art, conductor 56 forms a single turn primary while the coil within instrument housing 51 comprises a multiturn secondary whereby the current flowing in conductor 56 induces current in the coil of instrument 50.
Passage 54 is partially defined by axially extending circular lip 59 at one end of housing 51. The band of the potential tap device surrounds lip 59 with screw 13 passing through closely tted aligned apertures in band 11, through clearance aperture 61 of lip 59, through the space between cable 55 and the wall defining passage 54, through cable insulation 57, and into cable conductor 56.
It is to be noted that during the installation of the potential tap device housing 51 is placed in compression rather than in tension. This is most advantageous in that molded rigid plastic materials are usually much better able to resist compression forces rather than tension forces. In addition, anchoring band 11 serves to spread the stresses over the entire periphery of lip 59.
FIGURES 8 through 9 illustrate an embodiment of my invention in which a sleeve 99 of tiexible electrical insulation covers most of the anchoring band 11. That is, sleeve 99 covers band 11 except for portion 16 and the part of main portion 25 which portion 16 overlies.'
When the potential tap is being installed as in FIGURE 9, self-tapping screw 13 penetrates sleeve 99 with the tight fit between screw 13 and aligned aperture 15 insuring a low resistance electrical path through band 11 to terminal means 14. This construction eliminates an extensive exposed energized area around the periphery of transformer lip 59.
Thus, it is seen that this invention provides a novel construction for a potential tap device whereby no separate threaded female component is required in connection with the tapping screw so that all bolts and lock washers required of prior art devices are eliminated in connection with the power tapping screw. In addition, the utilization of a self-tapping screw results in a superior electrical connection to the current carrying cable and also results in superior mechanical securement of the tapping device.
Although I have here described preferred embodiments of my novel invention, many variations and modications will now be apparent to those skilled in the art,
and I therefore prefer to be limited, not by the specific disclosure herein, but only by the appending claims.
1. In combination, a current carrying cable including an insulated covered conductor and a potential tap device operatively mounted thereto; said device compris ing a single anchor band surrounding said cable to dene an enclosed volume for the reception of said cable; a self-threading screw means extending through and threadedly engaging tightly tting aligned aperture means in overlapping portion of said band with the tip of the screw means entered into the conductor for electrical and mechanical connection thereto; said band being constructed of an elongated strip whose length exceeds the circumference of the band, with said band tightly engaging substantially the entire periphery of said cable, whereby the drive force of said screw means is transferred about the periphery of said cable; said overlapping portions closely abutting said conductor at the point of entry of said screw.
2. In combination, an insulation covered conductor, a measuring means instrument operatively associated with said conductor, and a potential tap device mounted to said instrument and including a part in operative engagement with said conductor; said instrument including an insulating housing having a passage through which said conductor extends; said passage being partially defined by a circular lip of said housing formed of a material more resistive to compressive forces than tension forces; said device comprising an anchor band surrounding said lip and a self-threading screw extending through and threadedly receiving tightly tting aligned aperture means in overlapping portions of said band, through a p hole in said lip, and through a tight ting threaded aperture of said insulation with the tip of the screw entered into the conductor for electrical and mechanical connection thereto; said band tightly engaging substantially the entire periphery of said lip, whereby the drive force of said screw means is transferred as compressive forces about the periphery of said lip, said overlapping portions closely abutting said lip at the point of entry of said screw.
References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Mulder, German application 1,090,286, printed Oct. 6, 1960 (Kl. 21c 21/01).