US 2186482 A
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GROUND ROD Filed July 16, 1938 INVENTOR Robef'f J. FranK MMWA Patented Jan. 9, 1940 GROUND ROD Robert J. Frank, Pittsburgh, Pa" allignor to Oopperweld Steel Company, a corporation of Pennsylvania Application July 16, 1938, Serial No. 219,572
This invention relates to ground connections for electrical circuits, in the form of sectional rods adapted to be driven into the earth.
Sectional, driven ground rods have been known heretofore (Hamilton et a1. Patent No. 1,756,641) Their chief advantage is that they can be driven by hand quite conveniently. The use of threaded joints between ground rod sections has recommendeditself because such joints are cheap, easy to assemble, and capable of transmitting tension as well as compression. This last is very important in ground rods inasmuch as it is frequently necessary to withdraw a driven rod upon striking an obstruction, or on moving poles or towers supporting a transmission line. In spite of these characteristics, rods with threaded joints have not been used heretofore, so far as I am aware, because the ends of rod sections, if threaded in the ordinary manner, are easily damaged either 30 by rough handling in shipment or by the impact of the tools used in driving the rod, and the threaded portions of ferrous rods rust very rapidly. To avoid these objections, other types of joints have been used in which the advantage of tension transmission has been largely sacrificed (Newpher Patent No. 2,111,799)
I have invented a novel form of sectional ground rod adapted to be driven in the earth, employing threaded joints of novel form, which 50 overcomes the aforementioned objections to ground rods having threaded joints and, furthermore, provides a ground rod having other advantages over those known heretofore. In a preferred form, the invention comprises a plurality of sections of rod having threads of novel form at each end for cooperation with threaded sleeve couplings. The rod sections are preferably each composed of a steel core which provides sumcient rigidity for driving and a copper sheath to protect 10 the core against corrosion. Further details of the invention will be referred to in the course of the following extended description and the novel features will be particularly pointed out in the appended claims. The accompanying drawi5 ing illustrates a preferred embodiment of the invention.
In the drawing: Fig. 1 is a view partly in side elevation and partly in section showing a ground rod in the process of being driven;
Fig. 2 is an elevation of a rod section; Fig. 3 is an axial section through a joint between sections; and I Fig. 4 is a diagrammatic view partly in section 55 illustrating the operation of driving the rod.
Referring now in detail to the drawing, a ground rod II in accordance with the invention, comprises a plurality of sections ll connected by coupling sleeves l2. The sections ll may be of any convenient length and are threaded at oppo- 5 site ends as shown at l3. The sections Ii are preferably composed of a steel core i4 enclomd within a copper sheath I5 welded thereto. The upper end of each section may be slightly chamfered as at I 8 and the lower end provided with 10 a blunt point il having a flat end I8. The threads ii are formed by cold rolling and, therefore, have a crest diameter greater than the diameter of the unthreaded portion of the rod. The threads are formed only in the copper sheath 15 and do not extend into the steel core, although the rolling of the threads slightly distorts the core. By rolling the threads I avoid materially reducing the sectional area of the rods at the threaded portion which would result if the 20 threads were cut in the usual manner. The cold working efiected in working the threads, furthermore, tends to harden and toughen them, increasing their resistance to injury.
The coupling sleeves I! are preferably of bronze 25 and are threaded throughout their length as shown. The ends of the sleeves are counterbored for a short distance inwardly thereof, as shown at [9, to cut oil the threads to half their initial height. This permits the entire threaded portion 0 of the sections ii to enter the coupling sleeves when screwed home therein, and automatically positions the ends of the sections at the medial transverse plane through the sleeves. The latter results from the fact that the rod sections cannot be threaded into the sleeves beyond the point at which the end of the threaded portion of the rod engages the full thread in the sleeve.
The length of the portions of the sections H covered by the threads i3 bears a relation to the length of the sleeves I2 such that when two sections are screwed home within a coupling as shown in Fig. 3, the flat end ll of the upper section will abut firmly against the chamfered end of the lower section. This causes the driving iorce applied to the upper section in the manner to be explained shortly, to be transmitted directly to the lower section. I thus avoid subjecting the threads to the impact of the hammer blows and protect them from any injury which might result from such impact.
Fig. 4 illustrates the manner of installing a rod according to the invention. A section II is first started into the ground with its blunt point I'I downward or a special starting section having an unthreaded, sharp-pointed lower end may be used if desired. A sleeve I2 is threaded onto the first section H and a cap screw 20 threaded in the upper end thereof. The shank of the cap screw is long enough to permit it to abut against the upper end of the section II before its head seats on the end of the sleeve l2. The section II is then driven in to the ground level by a light sledge or a pneumatic hammer, the driving blows being delivered to the head of the screw 20. The screw is then removed and a second section H as indicated in chaimlines in Fig. 4 is threaded into the sleeve l2 and screwed home tight as shown in Fig. 3. The cap screw 20 isthreaded into the sleeve l2 at the upper end of the next section H and the driving operation continued with the addition of successive rod sections and sleeves until the desired depth has been attained.
The rod may also be installed by methods other than driving with a hammer, e. g., by screwing the rod into the ground after the attachment of a suitable boring tip to the lower end of the first section, connecting couplings and additional sections being added as the rod penetrates the earth. In this method of installation, the abutment of the ends of adjacent sections aids in transmitting the necessary torque from one section to the next section below.
It will be apparent from the foregoing description that the invention is characterized by numerous advantages and novel features compared to driven ground rods as known heretofore. In the first place, a highly durable ground connection is provided by virtue of the exterior sheath of copper which encloses the rod sections through- -out their full length. The steel core, furthermore, permits the rod to be made in small diameters with suflicient rigidity to be driven easily in almost any type of soil. A rod section 8' long and in nominal outside diameter can be driven readily without bending. This reduces to a minimum the loss involved in scrapping bent or deformed rods.
The copper sheath and steel core are permanently united by welding so there can be no corrosion or electrolysis therebetween. The copper sheath also gives the ground connection the desired high conductivity. There is likewise little or no chance of corrosion between the rod sections and the bronze couplings, which would increase the joint resistance. The end-to-end pressure between rod sections also maintains a good contact therebetween.
Because of the resistance of the steel core to deformation under repeated impact, little or no mushrooming of the upper end of a rod section occurs during driving. This makes it pos sible to slip a ground rod clamp over the end of a rod section after it has been driven, which is preferable to placing it thereon before driving.
The method of installing the rods as explained herein does not involve any mutilation of the threads on the rod sections or couplings. The impact necessary for driving the rod is transmitted directly from one rod section to the other so that the threads of previously driven sections are protected from injury. Other advantages of the invention have already been pointed out.
Although I have illustrated and described herein but a preferred form of the invention, it will be recognized that changes in the details of the invention as disclosed may be made without departing from the spirit of the invention or the scope of the appended .claim.
A ground rod including a cuprous sleeve having a cylindrical bore therein threaded internally, and a pair of rod sections each having a. ferrous core and a cuprous sheath with threads at the end formedexclusively in the sheath, said ends being threaded into said sleeve until they abut whereby driving blows are transmitted directly from one rod section to the adjacent section.
ROBERT J. FRANK.