US3344225A

US3344225A - Pole bonding

Info

Publication number: US3344225A
Authority: US
Current assignee: Gang Nail Systems Inc
Priority date: 1966-06-29
Publication date: 1967-09-26
Anticipated expiration: 1984-09-26
Also published as: GB1130697A; DK123328B; SE329423B; DE1615608C3; DE1615608B2; NO123650B; DE1615608A1

Description

Sept. 26, 1967 J. c. JUREIT L POLE BONDING 2 Sheets-Sheet 1 Filed June 29, 1966 FIG. I

FIG. 2

INVEM'ORS y, c. :11 eerr 04mm an INN- BY 3,51,... i ll ATTORNEYS.

Sept. 26, 1967 J, JURElT ETAL POLE BONDING 2 Sheets-Sheet 2 Filed June 29, 1966 I20 I42 I22 INVENTORS I 30/! G. J'uREIT n. LIFFR0 moon-ram ATTORNEYS,

United States Patent 3,344,225 POLE BONDING John C. Jureit, Miami, Fla., and Albert Clifford Middleton, Keswiclk, Ontario, Canada, assignors to Automated Buiiding Components, linc., Miami, Fla., a corporation of Florida Filed June 29, 1966, Ser. No. 561,512 15 Claims. (Cl. 17445) ABSTRACT OF THE DISCLOSURE Disclosed is a pole bonding structure in the form of a wood pole and cross arm to which are attached conductive metal plates having integral punched out teeth. The integral teeth hold the plates to the wood and form a plurality of current collector points for leakage currents from transmission lines supported by the pole and cross arm. Leakage currents are shunted past the gain area of the pole and cross arm junction to avoid pocket burns and fires.

This invention relates to apparatus for bonding wood structures and more particularly to an apparatus for preventing fires in transmission line poles resulting from the flow of large leakage currents through the wooden electrical transmission line support.

It has been known for many years that leakage currents in transmission lines can do substantial fire damage to the wooden poles and cross-arms conventionally used in supporting electrical transmission lines. Because the majority of the medium voltage lines in the United States are supported on wood poles and cross arms this constitutes a considerable problem.

The burn damage and in some cases fire which break out on the wood supporting structure are caused by power frequency leakage currents which flow over the surface of contaminated insulators and through the supporting wooden members. In some localities these fires may occur at infrequent intervals and are only an incidental nuisance. In other areas they occur frequently and may be of such a character as to result in a complete loss of the cross arm and pole so as to cause a prolonged service outage.

In the so-called medium voltage lines operating, for example, at 33 or 37 kilovolts, it is not uncommon for the leakage currents at the alternating power frequency to be as high as ten milliamperes through the supporting wood structure. In general, these large leakage currents produce two types of burns on the wood, one referred to as a tree burn limited primarily to the wood surface and existing for the most part on the wood cross arm and a second and usually more serious type referred to as pocket burns which extend into the body of the wood members and which are usually located at or closely adjacent to the junction point of the pole and the one or more cross arms which it supports. These latter burns are pocket shaped and extend into the body of the wood so that they are not confined primarily to the wood surface as are the tree burns.

In order to avoid wood burn damage caused by leakage currents between transmission lines it has been proposed to provide conductive leads or metallic jumpers between the transmission line insulators which bypass the high resistance of the supporting wood structure and act to short-circuit leakage current flow through the wood. However, this construction has the serious disadvantage that the jumper wire eliminates any insulation provided by the wood support between the transmission lines other than that afforded by the insulators themselves.

More recently it has become common practice to provide electrical bonding around the wood pole and cross arm juncture of a transmission line support through the use of conductive leads. These have taken many forms including bands around the pole and cross-arm, sheet metal plates, rings, simple wires, and even variously shaped terminating elements or so-called leakage current collectors. In each case the various conductive elements are joined to form a complete current flow path around the wood juncture at the pole and the cross arm, usually by suitable jumpers or copper wire conductors. At least one or more of the conductive elements is customarily in contact with the pole through-bolt which secures the cross arm or cross arms to the pole. The conductive leads or hands are often stapled or nailed to the wood support at locations spaced somewhat from the bolt.

Diificulties have been experienced with these prior bonding methods due not only to the substantial cost and labor involved in applying the bonding materials to the wood pole and cross arm but also because with time the wires, bands, plates, or other bonding elements tend to become loose due to shrinkage of the wood as it is exposed to the elements over a number of years. This loosening of the staples or nails in conjunction with wood shrinkage substantially worsens the already poor electrical contact of the conductive bonding elements with the wood surfaces which it is desired to protect.

The present invention avoids the above mentioned difficulties by providing novel bonding apparatus in the form of a fiat conductive metallic plate having a plurality of integral elongated slender and nail-like teeth punched out therefrom and extending perpendicular to the one surface of the plate. The plate is preferably formed of US. Standard 20 gauge mild steel, either uncoated or galvanized and may be pressed into the wood or readily driven with a standard two-pound ball peen hammer. A plate of this thickness possesses sufiicient flexibility so as to readily adapt itself to the more or less irregular contour of the transmission line support structural surfaces and may be easily pierced at the bolt hole location through the use of a pointed punch and one blow of the hammer.

In the preferred embodiment the bonding plates are preferably provided with a hot dipped galvanized coating in a conventional manner so as to more readily withstand the adverse effects of the elements. In new constructions the bonding plates are preferably applied as elongated strips extending vertically on each of two sides of the pole and preferably along the top surface of each of the pole cross arms. Where more than one cross arm is provided on a pole the cross arm bonding strips may be electrically coupled by means of one or more jumper wires retained by and captured beneath the bonding plates when they are driven into the wooden cross arms. It has also been found advantageous to utilize the bonding plates in existing structures to more securely attach the bonding wires or other conductive elements to the pole and to increase the number of electrical contact or current collecting points so that the bonding makes better contact with the wood to ensure more efficient short-circuiting of the protected wood areas.

It is therefore one object of the present invention to provide novel apparatus for bonding wooden electrical transmission line supporting structures.

Another object of the present invention is to provide novel bonding apparatus for minimizing the occasion of pocket burns on transmission line poles and cross arms.

Another object of the present invention is to provide improved bonding apparatus providing a substantially increased number of contact or current collecting points between the joined wood and conductive metallic bonding structures of a transmission line support.

Another object of the present invention is to provide a bonding apparatus including conductive plates having a large number of integral, elongated and slender nail-like teeth having increased withdrawal resistance so as to insure that the conductive structure will remain in firm engagement with the wood even though the wood is subject to shrinkage over the years.

Another object of the present invention is to provide apparatus for protecting the wood supporting structure of an electrical transmission line from tree and pocket burns occasioned by the flow of leakage currents between the transmission lines and from the transmission lines to a ground. The bonding apparatus takes the form of a p111- rality of bonding plates preferably formed of 20 gauge conductive metal which plates have a large number of integral teeth punched out therefrom to extend perpendicular to one surface of the plate. The teeth are uniformly distributed in a predetermined pattern over the area of the plates. The plates are applied in various widths and lengths to the pole and cross arm surfaces to provide shunt conductive paths for leakage currents to bypass high resistance areas of the wood. The slender, elongated and nail-like bonding plate teeth provide a large number of electrical current collecting points penetrating into the body of the wood and because of their shape and disposition have increased withdrawal resistance so that they do not become readily withdrawn or loosened as the wood shrinks. In the preferred embodiment the plates are provided with a galvanized or other suitable coating so as to better withstand the elements. The plates may be applied in any of a number of sizes and shapes to existing structures so as to better bind the conductors to the wood or may be provided in elongated narrow strips for use in conjunction with new structures.

These and further objects of the invention will be more apparent upon reference to the following specification, claims and appended drawings wherein:

FIGURE 1 is a front view of a conventional transmission line pole having a single cross arm and subject to leakage current burns.

FIGURE 2 is a plan view with parts in cross-section illustrating the type of weathering which may produce burn damage.

FIGURE 3 shows an equivalent resistive circuit for the transmission line supporting structure of FIGURES l and 2.

FIGURE 4 is a perspective view showing the novel bonding apparatus of the present invention.

FIGURE 5 is a plan view of the apparatus of FIG- URE 4.

FIGURE 6 is an elevational view similar to that of FIGURE 4 but taken from the opposite side of the pole.

FIGURE 7 is an equivalent resistive circuit diagram for the bonded support structure of FIGURES 4 through 6.

FIGURE 8 is a plan view of a portion of one of the bonding plates shown in FIGURES 4 through 6.

FIGURE 9 is an elevational view taken at right angles to that of FIGURE 8.

FIGURE 10 illustrates the novel bonding apparatus of the present invention as applied to existing bonded structures and FIGURE 11 is a plan view of the structure illustrated in FIGURE 10.

Leakage current induced pole fires are usually preceded by three general conditions, namely, (a) a prolonged dry period in which the wood members dry out, (b) during this dry period contamination accumulates on the insulator surfaces. The accumulated contamination layer reduces the surface leakage resistance of the insulator, particularly when it becomes dampened. The contamination may be salt deposits in coastal areas, dust on the plains, or smoke and other air-borne byproducts from industrial establishments. Finally, (0) the dry period is followed by a fog, a misty rain, or even snow.

The magnitude of leakage currents that fiow through a porcelain-wood combination as provided by the support structure and insulators is controlled principally by the total resistance of the wood plus the surface leakage resistance of the insulators. In the dry or the lesser surface contamination conditions the leakage current is controlled mostly by the insulators. Leakage currents have been found by measurements to be in surges. Magnetic oscillogram records of leakage current surges have shown that they vary in magnitude of maximum current, frequency of the occurrence, and time duration of the individual surges.

Under the proper combination of surface contamination and wetting, leakage current flow paths are established both between conductors, i.e., the transmission lines, and between the conductors and ground. However, if the wetting happens to be selective, certain areas of the wood structure are left relatively dry and constitute short high resistance paths for the leakage currents. With leakage currents in the neighborhood of from one to t n milliamperes these high resistance paths generate sufiicient heat to cause burn damage and to even initiate fires on the poles and cross arms. The action of the leakage currents is cumulative in that the high current-high resistance path in generating 1 R heat losses causes the already relatively drier area of the wood to dry out even more thus raising its resistance and increasing the likelihood of a fire.

Referring to the drawings, FIGURE 1 illustrates a supporting structure generally indicated at 10 including a wood pole 12, either treated or untreated, and a similar single wooden cross arm 14 secured to the pole by the conventional electrically conductive through-bolt 16. Cross arm 14 is provided adjacent each end with conventional ceramic or

porcelain insulators

18 and 20 customarily secured to the cross arm by conductive metal pins 22 and 24 and

nuts

26 and 28. A similar insulator 30 is suitably mounted at or adjacent the top of the pole 12. The insulators support the three illustrated

transmission lines

32, 34 and 36 which by way of illustration only may carry alternating electrical energy in the so-called medium voltage range, i.e., approximately 33 kilovolts.

FIGURE 3 illustrates an equivalent resistive circuit for the structure of FIGURE 1 wherein the insulation afforded by

insulators

18', 20 and 30 are illustrated by

variable resistors

38, 40 and 42, respectively. Normally these insulators provide the greater portion of the resistance existing in the circuit between the

transmission lines

32, 34 and 36 and between any one of the transmission lines and ground illustrated at 44. The through-bolt 1 6 is coupled to ground through the resistance of the lower portion of the pole illustrated in FIGURE 3 at 46 and to the top insulator 30 through the pole resistance 48. The cross arm resistances are illustrated at 50 and 52.

Referring now to FIGURE 2, when the insulators become contaminated by foreign matter and subsequently become wet their electrical resistance is substantially reduced, i.e., their surface resistance may fall by several orders of magnitude. If it is further assumed that the support structure is subjected to a selected wetting by means of a wind driven mist, rain, or fog. in the direction of the arrows 54 in FIGURE 2, then much of the wood surface on the windward side of the pole and support arm becomes wet and consequently relatively much more conductive. For example the resistivity of wood having a wet surface may be reduced by a factor of 12,000 or 14,000 to 1, as compared to relatively dry wood (i.e., a moisture content of about 10%). The wetted area of the pole and cross arm is illustrated by the surface hatching in FIGURE 2.

However, with the wind direction as illustrated by the arrows in FIGURE 4 there remains a certain shadow area of the cross arm and pole illustrated at 56 which remains relatively dry. Thus, while the remainder of the pole and cross arm surfaces between the transmission lines are relatively wet and conductive, a small shadow area adjacent the juncture of the pole and cross arm may remain fairly dry so as to possess its original relatively high resistance. The high resistance of this shadow area is illustrated by the larger resistance 58 in FIGURE 3. In addition to this shadow area certain portions of the so-called gain area of the support structure, i.e., the common or notch area illustrated at 60 where the cross arm and pole meet, is sheltered and likewise frequently remains dry. These high resistance or dry areas, i.e., the shadow area 56 and the gain area 60, represent those places where serious wood damaging pocket burns and even actual flame burning may occur.

FIG'URES 4 through 6 illustrate apparatus constructed in accordance with the present invention for eliminating or at least substantially reducing leakage burns, and

especially the pocket burns likely to occur at and closely adjacent to the gain area of the structure, i.e., the area where the cross arm meets or engages the pole. In FIG- URES 4 through 6, a similar treated or untreated wood pole 62 is illustrated as provided with a pair of spaced

cross arms

64 and 66 each engaging one of two opposite sides of the pole 62. These cross arms support the 'usual insulators 68 in all respects similar to those previously described while a similar insulator 70 is suitably attached to the top of the pole so that the assembly may support transmission lines such as

transmission lines

32, 34 and 36 of FIGURES 1 through 3.

Cross arms

64 and 66 are again attached to the pole 62 by the conductive through-bolt 16. In addition the structure is provided with four cross arm braces 72, 74, 76 and 78, two on each side of the pole. These braces are customarily secured at their ends to the pole and to the respective cross arms by suitable lug screws 80.

Connected to each side of the pole is a vertical strip of bonding plate as illustrated at 84 in FIGURE 4 and 86 in FIGURE 6.

Similar strips

88 and 90 are secured to the tops of the

cross arms

64 and 66 as illustrated in FIG- URE 5. Secured beneath these latter two strips are the ends of a pair of

conductive wires

92 and 94, preferably formed of No. 9 braided copper fire. The ends of the wires are placed beneath plates 88 and'90 prior to attachment and when the plates are driven into the wood are tightly clamped beneath the lower surface of the plate and the upper surface of the cross arm so as to form good electrical contact with the conductive plates 88 and '90. Also adjoining the

cross arms

64 and 66 is the conventional cross arm angle brace 96 secured at each end by bolts passing through the cross arms as illustrated at 98 in FIGURE 6. The ends of the angle brace 96 preferably overlie and are in electrical contact with the

plates

88 and 90 so that the angle brace forms an additional electrically conductive element in the bonding system.

FIGURE 7 illustrates the equivalent resistive circuit for the structure of FIGURES 4 through 6 where the insulators 68 are again illustrated as variable resistors, the cross arm resistances by the

reference numerals

64 and 66, and the pole resistances by the reference numeral 62.

Cross arm plates

88 and 90 provide short circuit paths over much but not all the length of the cross arms as illustrated at 8840, whereas the

vertical plates

84 and 86 provide a short circuit conductive path around the wood for substantial distances along the pole above and below the through-bolt 16.

A portion of the bonding strip or plate 84 of FIGURE 4 is illustrated to an enlarged scale in FIGURES 8 and 9. The other strips 86, 88 and 90 are of the same construction. In the preferred embodiment these bonding plates or strips take the form of thin plates of mild steel having struck therefrom a plurality or rows such as rows 100 and 162 of slender elongated nail-like teeth which leave parallel rows of elongated slots. All the teeth are provided with diagonally cut or scarfed points, with the teeth in alternate longitudinal rows being scar-fed in opposite directions such that straight lines extending along the scarfed ends of the teeth would intersect in an apex above the row of teeth intermediate the alternate rows.

The purpose of this particular scarfed tooth construction is to cause a clinching action as between adjacent pairs of teeth in a given transverse row. This creates a locking action which provides a greater withdrawal resistance than could be secured by this length of tooth alone. With the lightweight sheet metal utilized there is a definite limit to the length of the tooth which can be used without encountering tooth bending which renders the teeth uninsertable from a practical standpoint. With the particular tooth structure shown in FIGURES 8 and 9 and its concomitant clinching action, an adequate withdrawal resistance can be secured without objection able tooth bending. These bonding plates are similar in all respects to the connector plates described in more detail in co-pending application Ser. No. 293,949, filed July 10, 1963.

The tooth arrangement of FIGURES 8 and 9 makes possible an unusually high ratio of holding power per unit weight of metal obtained through the utilization of a much higher tooth density. Thus, according to the preferred embodiment of the invention the tooth density of the bonding strips is approximately seven teeth per square inch of plate surface and should be no lower than approximately five teeth per square inch of plate surface. According to a specific and preferred embodiment of the invention the bonding plates are formed of 20 US. Standard Gauge mild steel either uncoated or galvanized, having a nominal thickness of .039 inch. The tooth length is inch or .375 inch. The ratio of tooth length to plate thickness is approximately 9.5 and should be no less than 6. Each of the strips, when used in the manner illustrated in FIGURES 4 through 6, is preferably approximately one inch wide and 48 inches in length. These 20 gauge plates are used on both sides of the pole, behind the cross arms, and extending below the cross arm brace lag bolts. Similarly, plates of the same size are secured to the top face of each of the cross arms.

The relatively small thickness of the plate material makes it possible for the plates to readily conform to the surface to which they are attached, and especially to the gain areas of the pole and the cross arms, which very often are cut out or notched slightly to better support the cross arms. The plates may be driven into the wood in any suitable manner and have been found to be easily installed with a standard two pound ball =peen hammer. Holes can be formed in the plates at the bolt hole locations through the use of a pointed punch and one blow of the hammer. The high tooth density provides not only increased withdrawal resistance insuring tight engagement of the bonding plates with the wood accompanying wood shrinkage over a substantial period of time but have the additional advantages of providing a multitude of current collection points deeply penetrating into the wood so as to insure an efiicient operation of the bonding plates in shorting out any dry areas in the wood which may result from the selective wetting conditions described above. The integral plates constitute relatively large low-resistance conductors to leakage currents to effect this shunting or shorting action.

FIGURES 10 and 11 show a modified embodiment of the novel bonding apparatus of the present invention as applied to existing rather than new structures. In those figures there is shown a pole having the

cross arms

112 and 114 in all respects similar to the pole and the cross arms of the embodiment of FIGURES 4 through 6. In FIGURES l0 and 11 like parts bear like reference numerals and the cross arms are again attached to the pole by a through-bolt 16 and are reinforced by a cross arm angle brace 96, as well as the four lower braces, two of which are again illustrated in FIGURE 10 at 76 and 78.

As illustrated in this embodiment the pole 110 and cross

arms

112 and 114 are provided with the usual bonding comprising upper and lower encircling

bands

116 and 118 which pass completely around the pole a short distance above and below the cross arms, respectively.

The cross arms themselves are suitably encircled by conductive bands such as are illustrated in FIGURE 11 at 120 and 122 around cross arm 112 and 124- and 126 around cross arm 114. These encircling bands are conventionally electrically connected together by suitable jumpers such as those illustrated at 128, 130, 132 and 134 in FIGURE 10. An additional jumper 136 electrically connects the bonding structure to the through-bolt 16 and the entire conductive assembly is conventionally connected to the angle brace 96 by means of one of its securing bolts 98. Thus, all six bands, i.e., the four around the

cross arms

112 and 114 and the two around the pole 110 are in direct metallic conductive communication for the flow of leakage currents shunting the wood structure of the support. The specific more or less conventional bonding arrangement thus far described is illustrated by way of example only and the bonding elements may take the form of metallic bands, copper wires, or other similar structures which in conventional assemblies are either nailed at spaced intervals or simply stapled at spaced intervals to the wood supporting structure.

In the embodiment of FIGURES 10 and '11 the existing bonding apparatus so far described is reinforced by the application of a plurality of bonding plates constructed in accordance with the present invention and having the same structure as shown and described in detail in conjunction with FIGURES 8 and 9. Two plates such as

plates

138 and 140 are hammered, pressed or otherwise suitably driven into each side of the pole, one over the upper bonding band 16 and the other over the lower bonding band 118. These plates are driven completely in so that they tightly contact the existing bonded structure, and so that their teeth penetrate the wood to insure against a later withdrawal and to form the desirable large number of current collecting contacts or points embedded in the wood. The upper of the two plates on the other side of the pole is illustrated at 142 in FIGURE 11.

With respect to the cross arm bands, a plate is driven into each of the four surfaces of the cross arms approximately midway of their edges to overlie and tightly engage each of the

respective bonding bands

120, 122, 124 and 126. Thus, a total of some 20 bonding plates is preferably applied to the existing bonding structure of the pole 110. Where lesser assurance against loosening of the bonding is required a lesser number of plates may be used. Similarly, it will be understood that with different existing bonding arrangements more or less plates may be required to provide adequate retention against loosening and to provide the current collection wood penetrating teeth or points.

As previously described, each of the same 20 plates utilized in the embodiment is in all respects identical to the plate 84 of FIGURES 8 and 9 with the exception that the plates of FIGURES 10 and 11 are of substantially shorter length but of somewhat greater width. By way of example only, 20 gauge connector plates having an overall length of approximately six inches and a width of approximately three inches have been found quite satisfactory for insertion over copper wire bonding of the type illustrated in FIGURES l and 11.

It is apparent from the above that the present invention provides a novel arrangement for bonding wood poles and cross arms to prevent destruction of the wood supporting structures from burns occasioned by leakage currents from transmission lines. The length of the bonding strips illustrated in FIGURES 4 through 6 provides good protection not only for the more serious pocket burns occuring in the gain and shadow areas adjacent the Wood junctures but also provides increased protection against other types of leakage induced wood burning including the tree burns often found on other portions of the support structure. The bonding plates of this invention are relatively inexpensive to manufacture and are very easy to apply to the poles and to cross arms since they may be readily driven in by hand as well as pressed in by means of suitable presses if so desired. The plates not only have increased withdrawal resistance to insure good contact with the wood even after many years of service, but have a relatively high density, i.e., a large number of nail-like teeth distributed uniformly over their entire surface so as to insure maximum efficiency in terms of wood penetration and leakage current collection points to insure optimum shunting of any relatively dry areas of Wood. The bonding plates described may be used in conjunction with other bonding elements such as wires, bands, rings or the like or may be used as the sole bonding elements for the transmission line support. For example, in the embodiments of FIGURES 4 through 6 it is possible to utilize additional bonding plates in place of the captured

copper wires

92 and 94.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

1. Bonding apparatus comprising a support structure for electrical transmission lines including a wood pole and cross arm, and at least one electrically conductive bonding plate driven into said structure adjacent the juncture of said pole and cross arm, said plate having a plurality of elongated, slender, nail-like teeth punched therefrom and extending perpendicular from one side of said plate, said teeth being embedded in said structure to form a plurality of integral current collector points for leakage current passing through said structure.

2. Apparatus according to claim 1 including a throughbolt joining said pole and cross arm, said bonding plate being in conductive metallic contact with said throughbolt.

3. Bonding apparatus comprising a support structure including a wood pole and cross arm, insulators on said cross arm for supporting transmission lines, a gain area in said pole forming a juncture for said pole and cross arm, and conductive metallic means spanning said area of said pole, said conductive means comprising flat metallic plate means having plurality of slender, elongted naillike teeth punched therefrom and extending perpendicular from one surface of said plate means, said teeth being embedded in said pole to form a plurality of conductivity coupled current collecting points for leakage currents on opposite sides of said gain area of said pole.

4. Apparatus according to claim 3 wherein said plate means comprises a single elongated strip of plate material having teeth embedded in said gain area of said pole behind said cross arm.

5. Apparatus according to claim 3 wherein said plate means is provided with a galvanized coating.

6. Apparatus according to claim 3 wherein said plate means is formed of US. Standard 20 gauge sheet metal.

7. Bonding apparatus comprising a support structure for electrical transmission lines including a wood pole and cross arm, a gain area in said pole, an electrically conductive through-bolt coupling said cross arm to said gain area of said pole, and conductive means on both said pole and cross arm providing a shunt path for leakage currents around said gain area, said conductive means comprising a plurality of conductive metal plates each having a plurality of elongated, slender nail-like teeth struck out therefrom uniformly over the entire surface of each plate, the teeth of respective plates being embedded in said pole and cross arm to form a plurality of conductively coupled current collecting points for said leakage currents.

8. Apparatus according to claim 7 wherein said teeth are provided with an :average of at least approximately five teeth per square inch of plate.

9. Apparatus according to claim 8 wherein said average is approximately seven teeth per square inch of plate.

10. Apparatus according to claim 7 wherein said plates comprise elongated strips approximately one inch wide and four feet long.

11. Apparatus according to claim 7 wherein said plates are approximately six inches long and three inches wide.

12. Bonding apparatus comprising a support structure for electrical transmission lines including a Wood pole and a pair of wooden cross arms joined to opposite sides of said pole, electrical insulators adjacent the ends of said cross arms and the top of said pole for supporting electrical conductors, a pair of vertical conductive metal strips joined to said opposite sides of said pole and spanning the junctures of said cross arms with said pole, a conductive metal strip on the top of each cross arm and extending on opposite sides of said pole, and a conductive metal lead having its ends captured beneath said cross arm strips, each of said strips having .a plurality of slender, elongated nail-like teeth struck therefrom and imbedded in said structure, said teeth being spaced uniformly over the surfaces of said strips.

13. Apparatus according to claim 12 wherein said cross arms are joined to said pole by a conductive metal through-bolt passing through said vertical strips, and said metal lead comprises a length of braided copper Wire.

14. .Bonding apparatus comprising a support structure for electrical transmission lines including a wood pole and a pair of wooden cross arms joined to opposite sides of said pole, conductive metal bands around said pole above and below said cross arms, and around each of said cross arms on each side of said pole, conductive metallic means electrically coupling all of said bands, and conductive metallic plates overlying portions of at least some of said bands, each of said plates having a plurality of slender, elongated nail-like teeth struck therefrom and embedded in said structure, said teeth being spaced over the surfaces of said plates to form a plurality of collection points for leakage currents in said structure.

15. Apparatus according to claim 14 including four plates overlying each of said cross arm bands and two plates overlying each of said pole bands, a conductive metal through-bolt joining said cross arms to said pole and conductive metallic means coupling said bands to said through-bolt.

References Cited UNITED STATES PATENTS 2,844,852 7/1958 West 287--20.92 2,877,520 3/1959 Jureit 287--20.92 3,011,226 12/1961 Menge 287--20.92 3,016,586 l/ 1962 Atkins 287-20.92

OTHER REFERENCES Electrical World, vol. 141, No. 22, May 31, 1954,

pages

92 and 98.

LARMIE E. ASKIN, Primary Examiner.

Claims

1. BONDING APPARATUS COMPRISING A SUPPORT STRUCTURE FOR ELECTRICAL TRANSMISSION LINES INCLUDING A WOOD POLE AND CROSS ARM, AND AT LEAST ONE ELECTRICALLY CONDUCTIVE BONDING PLATE DRIVEN INTO SAID STRUCTURE ADJACENT THE JUNCTURE OF SAID POLE AND CROSS ARM, SAID PLATE HAVING A PLURLAITY OF ELONGATED, SLENDER, NAIL-LIKE TEETH PUNCHED THEREFROM AND EXTENDING PERPENDICULAR FROM ONE SIDE OF SAID PLATE, SAID TEETH BEING EMBEDDED IN SAID STRUCTURE TO FORM A PLURALITY OF INTEGRAL CURRENT COLLECTOR POINTS FOR LEAKING CURRENT PASSING THROUGH SAID STRUCTURE.