United States Patent
`
`72 Inventors Walter L. Roberts
`Hickory;
`Frederic N. Wilkenloh, Conover, both of
`N.C.,
`(21) Appi, No. 778,073
`22 Filed
`Nov. 22, 1968
`45) Patented Nov. 23, 1971
`73) Assignee Superior Continental Corporation
`Hickory, N.C.
`
`5
`(50
`
`56
`
`54 TELEPHONECABLE WITH IMPROVED
`CROSSTALK PROPERTIES
`37 Claims, 24 Drawing Figs,
`174/36,
`52 U.S. Cl................. . . . . . . . . . . . . . . . . . . . . .
`74/25, 174/27, 174/103, 174/105, 174/07,
`74/1 3, 174/ 15
`lint. Cl................................. . . . . . . . . . . . . . . .
`H01 b 1708
`Field of Search...................................... 74/102-109,
`13, 15, 16, 119, 36,27, 25, 26
`References Clted
`UNITED STATES PATENTS
`l/1885 Clark...........................,
`31, 174
`3,233,036 2/1966 Jachimowicz.
`3,306,971
`2/1967 Olson et al....................
`FOREIGN PATENTS
`105,876 l l 1937 Australia......................
`l, 20,216 7/1956 France.........................
`775,84
`1 / 1935 France .........................
`657,41 1
`3/1938 Germany.......
`34,564 7/1929 Great Britain................
`
`174/105
`174/07
`174/19
`
`174/36
`1741 13
`174/36
`174/36
`174/36
`
`
`
`(113,622,683
`434,855 9/1935 Great Britain................
`174/36
`449,582 6/1936 Great Britain.....
`1747 103
`995,582 6/1965 Great Britain................
`74/23
`367,814 2/1932 Great Britain................
`174/36
`OTHER REFERENCES
`Communications News, Apr., 1969
`M. C. Biskeborn & D. P. Dobbin, Jelly Blend Waterproofs
`Cable, Bell Laboratories Record, March 1969, p. 71, 72, 73,
`74, 75. Copy in 174-23
`Primary Examiner-Lewis H. Myers
`Assistant Examiner-A. T. Grimley
`Attorney-Roy B. Moffitt
`
`ABSTRACT: Disclosed herein is an economical telephone
`cable structure and method of making same, such cable struc
`ture poss.cssing improved crosstalk propertics. A plurality of
`insulated electrical conductors (pairs), of an otherwis: con
`ventional telephone cable design are divided into at least two
`portions by plastic-coated metal foil strip or tape. Measure
`ments between pairs, divided by this plastic-coated metal foil,
`of unwanted energy transferred from one conductor to
`another by means of mutual inductive, capacity, or conductive
`coupling (crosstalk), shows greatly improved properties over
`undivided cable pairs or divided cable pairs of prior art. By
`dividing electrical conductor telephone pairs within a
`telephone cable structure with plastic-coated metal foil, the
`crosstalk properties are so vastly improved that a greater spac
`ing between repeaters can be designed into a telephone cable
`system, as compared to a cable system employing prior art di
`vided or undivided cable pairs.
`
`
`
`SA
`
`w
`
`

`

`PATENTED NOY 23 197
`
`3, S22,683
`
`SHEET 01 OF 15.
`
`
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`F. G.
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`F. G. 2
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`NVENTORS
`WALTER L ROBERTS
`FREDERIC N. WILKENLOH
`
`x4, 4 4-7,
`
`AORNEY
`
`PATENTED ROY 23 1971
`
`3,622,683
`
`SHEET
`
`O1 OF 15°
`
`
`
`FIG. 2
`
`INVENTORS
`WALTER L. ROBERTS
`FREDERIC N. WILKENLOH
`
`Key /S Meiviry :
`ATTORNEY
`
`

`

`PATENTED NOY 23 197
`
`3,622,683
`
`SHEET O2 OF 15.
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`
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`F. G. 3
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`PATENTEDNOY 23 197
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`3,622,683
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`SHEET
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`2 OF 15°
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`PATENTEDXOY 23 i971
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`3,622,683
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`SHEET
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`03 OF 15,
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`INVENTORS
`WALTER L. ROBERTS
`FREDERIC N. WILKENLOH
`Ke, 1. clegsom
`
`
`
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`ATTORNEY
`
`

`

`PATENTED NOY 23 197
`
`3,622,683
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`PATENTED NOY 23 197
`
`3, 622, S83
`
`SHEET OS OF 15
`
`
`
`NVENTORS
`WALTER L. ROBERTS
`FREDERC N, WLKENOH
`
`(76.472
`
`ATTORNEY
`
`PATENTEDNOV 2.3 1871
`
`3,622,683
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`INVENTORS
`WALTER. L. ROBERTS
`FREDERIC N. WILKENLOH
`Ke, 5, Llepis
`ATTORNEY
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`

`

`PATENTED NOY 23 197
`
`3,622,683
`
`SHEET OS OF 15
`
`
`
`TAPE
`
`METAL FO
`PLASTIC COVERN
`POLYETHYLENE GREASE
`
`NVENTORS
`WALTER L. ROBERTS
`FREDERC N. WILKENLOH
`
`ATTORNEY
`
`

`

`PATENTED NOY 23 197
`
`3, 622,683
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`WALTER L ROBERTS
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`PATENTED NOY 23 197
`
`3,622,683
`
`SHEET O8 OF 15
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`2
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`NVENTORS
`WALTER L. ROBERTS
`FREDERC N. WLKENOH
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`AT TORNEY
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`

`

`PATENTED NOY 23 197
`
`3,622,683
`
`SHEET O9 OF 15
`
`PLASTC JACKET
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`9.
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`INVENTORS
`WALTER L. ROBERTS
`FREDERC N, WIKENLOH
`/s, -5 1672, sm
`AT TORNEY
`
`

`

`PATENTED NOY 23 197
`
`3, 622,683
`
`SHEET 10 OF 15
`
`PLASTIC
`COVERING
`
`
`
`POYETHYLENE
`GREASE
`
`NVENTORS
`WALTER L ROBERTS
`FREDERC N. WILKENLOH
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`AORNEY
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`PATENTEDx 23 Sl
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`3, 622,683
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`POLYETHYLENE
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`NVENTORS
`WALTER L. ROBERTS
`FREDERC. N. WKENLOH
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`PATENTED NOY 23 1971
`
`3, 622,683
`
`SEET 12 OF 15
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`PATENTED NOY 23 1971
`
`3, 622,683
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`SHEET 13 OF 15
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`WALTER L ROBERTS
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`— PATENTEDNOY
`23 1971
`
`3,622,683
`
`SHEET 13 OF 15
`
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`INVENTORS
`WALTER L. ROBERTS
`FREDERIC N. WILKENLOH
`
`

`

`PATENTED NOY 23 197
`
`3, S22,683
`
`SHEET 14 OF 15.
`
`
`
`s
`
`NVENTORS
`WALTER L. ROBERTS
`FREDERIC N, WLKENO
`1.ey 45-6-7, -
`Air TORNEY
`
`PATENTEDNOY 23 1971
`
`SHEET
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`14 OF 15°
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`3,622,683
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`23
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`WALTER L. ROBERTS
`FREDERIC N, WILKENLOH
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`ey DS. Maw ln, =
`ATTORNEY
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`

`

`PATENTED NOY 2397
`
`3, 622,683
`
`SHEET 15 OF 15
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`WALTER L ROBERTS
`FREDERC N. WLKENLOH
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`

`

`3,622,683
`2
`TELEPHONECABLE WITH IMPROVEDCROSSTALK
`possible from one material to the other. This is not the case in
`PROPERTIES
`the instant invention where there is used as a shield, an alu
`minum foil either perse or coated with a plastic.
`DETAILED DISCLOSURE
`For the purposes of this disclosure, a foil is defined the same
`This invention relates to multiconductor cables and has par
`as found on page 18 of the METALS HANDBOOK, Eighth
`ticular reference to arrangements for shielding certain of the
`Edition, published by the American Society for Metals, to wit:
`conductors of such a cable from other conductors of the ca
`A foil is a metal in sheet form possessing a thickness of less
`ble. In order to transmit currents of the same frequency in
`than 0.006-inches,
`both directions within the same cable, more particularly when
`The invention will now be more fully understood from the
`10
`the currents to be transmitted are of carrier frequencies, it is
`following descriptions, when read in connection with the ac
`companying drawing,
`desirable that the conductors used for transmitting in one
`direction be shielded (electrically) from those transmitting in
`FIG. 1 of which is a cutaway pictorial view of one embodi
`the opposite direction. Accordingly, it is the purpose of this
`ment of the instant invention, showing two groups of conduc
`disclosure, to show how to arrange the conductors of a cable
`tors separated by a longitudinally disposed circumscribing foil
`into two concentric groups, with a shield between the two
`shield;
`groups of conductors. In such an arrangement of a cable,
`FIG. 2 is a pictorial cutaway view of another embodiment of
`those conductors on one side of the shield may all be used for
`the instant invention, similar to that shown in FIG. 1, wherein
`transmitting carrier frequencies in one direction, while the
`the shield between the two groups of electrical conductors is
`returned channels for transmission in the opposite direction
`not longitudinally but helically disposed;
`20
`will be applied to the conductors on the other side of the
`FIG. 3 is an additional pictorial cutaway view of one of the
`shield. The shield has the effect of reducing so called "near
`embodiments of the instant invention, showing two groups of
`end' crosstalk since the weak attenuated currents coming in
`electrical conductors separated by a shield made from a plu
`at a repeater point are in a compartment of the cable electri
`rality of tapes helically disposed, the lateral edges of which
`cally shielded from a large amplified current entering the con
`overlap adjacently lying tapes;
`25
`ductors in the other compartment of the cable. The instant in
`FIG. 4 is a portion of that cable shown in FIG. 2 in a cu
`vention also envisions and incorporates the concept of two
`taway view, emphasizing the helical seam formed by the over
`distinct bundles of conductors inside a cable structure, one
`lapping terminal edges of a helically wound tape shield;
`such bundle being electrically shielded from the other bundles
`FIG. 5 is a cross-sectional view of a metal foil coated on
`and neither one of the aforesaid bundles necessarily being
`30
`both sides with a plastic, used to shield one group of electrical
`concentric around the other.
`conductors from another;
`In one embodiment, a cable with a shield is formed by ar
`FIG. 6 is a cross-sectional view of an uncoated metal foil
`ranging a group of conductors into a cylindrical bundle,
`shield;
`spirally wrapping or twisting tapes of aluminum foil, either per
`FIG. 7 is a cross-sectional view of an embodiment of a foil
`se or coated with a plastic such as polyethylene terapthalate
`tape shield showing a metal foil coated only on one side by a
`(Mylar), upon the cylindrical bundle of insulated wires, and
`plastic;
`then mounting another group of insulated wires, preferably
`FIG. 8 is a cross-sectional view of a piece of metal foil shield
`equal in number, outside of the shielding tape in the form of a
`having a plastic coating that completely surrounds said foil;
`concentric cylindrical bundle, upon which another sheath of
`FIG. 9 is a cross-sectional view of that cable structure as
`plastic, or other material, is applied in the usual manner.
`shown in FIG. 1, employing as a shield a metal foil coated on
`The prior art has recognized the same problem to which the
`both sides with a plastic;
`instant invention only crosstalk and it is interesting to note
`FIG. 10 is a cross-sectional view of that cable structure as
`that Nyquist, U.S. Pat. No. 1,979,402, (179/78), teaches that
`shown in FIG. 3, employing a shield composed of a plurality of
`the shielding material should be thin tape of soft iron, alternat
`tapes made from a metal foil coated on both sides with a
`ing with layers of copper. Nyquist goes on to teach that while
`45
`plastic, the lateral edges of which overlap adjacently disposed
`various materials may be used, iron (in particular soft iron) is
`tapes,
`preferred for one group of the alternating layers. This, accord
`FIG. 11 is a cross-sectional view of the cable structure as
`ing to Nyquist, is so because the product of the permeability
`shown in FIG. 1 wherein the metal foil shield is completely
`by the conductivity of the iron is large, thereby making its at
`surrounded by a plastic coating;
`50
`tenuating effect large. Furthermore, Nyquist teaches that the
`FIG. 12 is a cross-sectional view of that cable structure as
`ratio of permeability of the iron to its conductivity is quite dif
`shown in FIG. 3, wherein a shield composite is shown, made
`ferent from that of the copper or other conductive material,
`up of a plurality of metal foil tapes each of which is completely
`which may be used for the other alternating layers. Such a
`surrounded on both sides by a plastic;
`combination, according to Nyquist, causes electromagnetic
`FIG. 3 is a cross-sectional view of a cable structure show
`55
`wave reflection losses brought about by interfering waves
`ing four groups of insulated conductors, only two of which are
`penetrating through the shield. For a sake of completeness
`longitudinally circumscribed by a shield made of metal foil
`and reference, the entire specification of the aforementioned
`coated on both sides with a plastic and the remaining groups
`United States patent of Nyquist is incorporated specifically
`being longitudinally circumscribed by a plastic tape;
`herein by reference.
`60
`FIG. 14 is a cross-sectional view of a cable structure the
`In passing, it might be well to note that the prior art
`same as that shown in FIG. 13 except that the plastic coating
`teaching, concerned with the transmission of carrier energy
`on the metal foil shield or screen completely surrounds the foil
`along telecommunication cable, addresses its shield design
`screen;
`solution to the use of alternating layers of different metals,
`FIG. 15 is a cross-sectional view of a cable structure the
`e.g., copper and soft iron. At least one of these two metals is
`same as that shown in FIG. 14 except that the shield is com
`magnetic (soft iron). In contradistinction, the instant inven
`posed of a plurality of foil tapes, coated on both sides by a .
`tion addressed its solution to the same problem by using alter
`plastic, the lateral edges of which overlap adjacently disposed
`nating layers of a metal and a nonmetal, neither one of which
`tapes;
`is magnetic. As stated above, the instant invention uses as its
`FIG. 16 is a cross-sectional view of a cable structure the
`shield, an aluminum foil either perse or coated with a plastic,
`70
`same as that shown in FIG. 15 except that the plastic coating
`such as polyethylene terapthalate. Furthermore, the prior art
`of the metal foil completely surrounds the foil;
`teaches that the materials to be used must have electromag
`FIG, 17 is a cross-sectional view of a cable structure show
`netic properties such that the product of permeability and
`ing a screen or shield dividing groups of insulated electrical
`conductivity should be as large as possible and that the ratio of
`conductors that does not longitudinally circumscribe any
`permeability to conductivity should be as much different as
`75
`group of conductors;
`
`35
`
`15
`
`65
`
`

`

`3,622,683
`
`15
`
`20
`
`25
`
`30
`
`35
`
`3
`4
`FIG. 18 through 2 inclusive are cross-sectional views of
`Turning now to FIG. 1, the overall general configuration of
`various metal shields used in that cable structure of FIG. 17;
`the cable structure is exhibited by element (1). Shown at (14)
`FIG. 18 being a metal foil coated on both major surfaces with
`is a first group of insulated conductors, the outer peripheral
`a plastic; FIG. 19 being a metal foil coated only on one side
`surface thereof being longitudinally circumscribed by a
`with a plastic; FIG. 20 being an uncoated metal foil; and FIG.
`plastic-coated foil shield shown at (15), this foil shield being
`21 being a metal foil completely surrounded by a plastic coat
`either uncoated, coated on one or both of its major surfaces as
`well as completely surrounded by a plastic. Indicated by ele
`ling;
`FIG.22 shows in schematic form, a wire twisting apparatus
`ment (16), is a second group of insulated electrical conduc
`used to apply the plastic-coated metal foil shield in between
`tors disposed in an annular fashion on the outermost surface
`O
`first and second groups of electrical conductors;
`of the plastic-coated metal foil shield (15). Disposed in a lon
`FIG. 23 is an enlarged diagrammatic view of a rotating die
`gitudinally and circumscribed fashion around the composite
`member used to apply the plastic-coated metal foil shield
`formed by the first and second group of insulated electrical
`between first and second groups of electrical conductors; and,
`conductors (14) and (16) and the interposed metal foil shield
`FIG. 24 is an exemplary plot of crosstalk values derived
`(15) is a polyethylene terapthalate (Mylar) tape shown at
`from the improved cable structure of the instant invention.
`(17). Longitudinally circumscribing the tape (17) is a corru
`One embodiment of the cable to be considered herein is
`gated metal armor tape shown at (18). This metal armor, hav
`made up of the usual cylindrical plastic or leadsheath with the
`ing a thickness greater than a foil, (18), is a tapelike strip that
`conductors arranged in the usual fashion, except that they are
`has been longitudinally folded or wrapped around the plastic
`separated into two equal or substantially equal but separate
`tape (17). This particular piece of armor is in a sense an elec
`concentric groups by means of an essentially cylindrical con
`trical, as well as a mechanical, shield and it can have a plastic,
`centric shield. When a signal is transmitted over any circuit in
`such as polyethylene, firmly adhered to either one or more
`this cable, it is permissable to consider an electromagnetic
`surfaces thereof. Disposed on the outer most surface of metal
`field as spreading out from this circuit in the form of a wave
`shield (18) is a molded plastic sheath (19). This outer most
`motion. This wave reaches other conductors and may induce
`plastic sheath is the customary extruded polyethylene that can
`currents and electromotive forces in other circuits unless they
`be and usually is filled with carbon black.
`are perfectly balanced. The first of these circuits may be
`Shown in FIG. 2 is essentially the same cable structure as
`called the disturbing and the other the disturbed circuit. If the
`that set forth in FIG. 1. The overall structure (2) differs from
`disturbing and disturbed circuits are on opposite sides of a
`that cable structure (1) only in the respect that the plastic
`shield, it is obvious that the disturbance is reduced due to the
`coated metal foil shield (15) has lateral edges that overlap in a
`attenuation the wave energy undergoes when passing through
`helically rather than a longitudinal fashion. The metal shield
`a shield and such reflections as may occur. This object is
`(15) of FIG. 1, is longitudinally disposed, the lateral edges of
`achieved in the instant invention by using a piece of metal
`the shield overlapping one another. (See 15a))
`(copper, aluminum, silver, steel, and etc.) foil, either per se,
`A further cable structure is shown at (3) in FIG. 3, wherein
`coated on both sides, coated only on one side, or completely
`the difference between structure (3) and (2) being that the
`surrounded by a plastic such as polyethylene, polypropylene,
`shield of element (2) is formed from a plurality of tapes
`or polyethylene terapthalate (Mylar). It is, however, one of
`(15b), (15c), and (15d) rather than a single tape. The lateral
`the many preferred embodiments of the instant invention to
`edges of the helically disposed tapes overlap adjacently lying
`use aluminum foil coated on both sides with a plastic. The
`tapes. A representative cross-sectional view of this particular
`reason for this preference is that the instant invention uses the
`40
`cable structure is shown in FIG. 9.
`plastic coating of the metal (aluminum) foil as a dielectric to
`Element (4) of FIG. 4, is a portion of the helically wound
`keep unwanted currents emitting from pinholes in the insula
`tape, as shown in FIG. 2. Here in this drawing, the low number
`tion of individual electrical conductors), from reaching the
`of turns or helical dispositions per linear length is emphasized.
`metallic shield (aluminum foil). It is quite obvious that when a
`As will be remembered, the tape (15) of FIG. 2 was a single
`45
`metal foil, coated only on one side, is employed, that the bun
`tape, and it was helically disposed around the first group of in
`dle of electrical conductors in nearest proximity therewith is
`sulated electrical conductors (14). The lateral edges of this
`tape (15) overlap, forming the seam (14e).
`not protected by a dielectric from the electrical conductors,
`other than that dielectric used as the insulation on the electri
`Elements (5), (6), (7), and (8) of FIGS. 5, 6, 7, and 8,
`respectively, show a cross-sectional view of the particular
`cal conductors themselves. Thus, there is in this instance a
`preference for the aluminum foil shield, coated on both sides
`metal foil tapes, both plastic coated and otherwise, used by the
`with the polyethylene terapthalate (Mylar) dielectric.
`instant invention. Element (5) shows a metal foil (6), coated
`It is also an embodiment of the instant invention to employ
`on both sides with a plastic, whereas element (6) shows an un
`as a shield, a metal foil which is completely surrounded on all
`coated metal foil shield. Element (7), of FIG. 7, shows a metal
`sides by a plastic coating, e.g., an aluminum foil, completely
`foil (6), coated only on one side, with a plastic coating 5 (a) J.
`surrounded
`by
`polyethylene
`terapthalate
`(Mylar),
`Either one of the embodiments (5), (6), (7), and (8), shown
`polyethylene, polypropolyene, polystyrene or PVC. An alu
`in respective figures, are viable as a shield from both a struc
`minum foil, which is coated only on its two major surfaces
`tural and electrical standpoint. Foil (6) has a thickness
`with a plastic, still has exposed naked aluminum surfaces at
`between l and 5 mils and is generally twice the thickness of
`the edges thereof. When considering a cable of many miles in
`plastic coating (5 (a)). All of elements (5), (6), (7), and (8)
`60
`length, this amount of exposed conductive metal becomes sig
`of FIGS. 5, 6, 7, 8, as well as 18, 19, 20 and 21, can be corru
`gated to increase its mechanical strength. For the purposes of
`nificant. Therefore, the instant invention takes this into ac
`count in one of two ways: the first way is to employ a metal foil
`this disclosure, when reference is made to a shield, other than
`which is completely surrounded by plastic. As an example,
`element (18), an electrical shield is meant. Even though the
`such a foil would be envisioned as being aluminum with the
`word "shield' has an accepted double meaning, i.e. electrical
`plastic covering being polyethylene terapthalate (Mylar).
`as well as mechanical (armor) protection, the metal foil shield
`Another way to mitigate undesirable electrical properties
`of the instant invention connote primarily an electrical shield.
`created by having an exposed surface (edge) of metal to the
`Element (9) of FIG. 9, shows a cross-sectional view of that
`electrical conductors is to fill that portion of the space created
`cable structure as depicted in FIG. 1. Like numbers of FIG. 1
`by the plastic-coated metal foil shield not otherwise occupied
`also represent like elements in FIG. 9. Here it will be noted
`by the electrical conductors therein with a polyethylene
`that the plastic-coated metal foil shield (15) is coated on its
`greaselike material. This greaselike material acts as both a
`two major surfaces with a plastic; however, it can be seen by
`dielectric protection, as well as an inhibitor of any subsequent
`element (20), that thin strips of uninsulated metal are exposed
`incoming moisture. This particular feature will be more fully
`to the first and second group of electrical conductors (14) and
`(16) respectively. It is quite obvious that pinholes in the elec
`discussed later.
`
`70
`
`50
`
`55
`
`65
`
`75
`
`

`

`3,622,683
`6
`5
`trical insulation of the insulated electrical conductors (14) or
`ticular plastic-coated metal foil shield is used to separate a
`(16), or the shield (15), would allow unwanted electrical
`first group of insulated electrical conductors (14) from a
`energy to reach exposed portions (edges) of the aluminum foil
`second group of insulated electrical conductors (16). The
`shield, through the edges (20) or pinholes in its plastic coat-
`balance of the cable structure is essentially the same as that
`ing. From an electrical standpoint, it is desirable to avoid this. 5 shown by element (9) of FIG. 9. Here again, that innermost
`It is also electrically desirable to keep moisture away from the
`cavity defined by the overlapping plurality of plastic-coated
`electrical conductors. Thus, the instant invention envisions an
`metal foil shields (15), (15'), and (15'), not otherwise occu
`embodiment in which a polyethylene greaselike material (a
`pied by insulated electrical conductors (14), can be essentially
`flooding compound) is disposed in that cavity created or
`filled with the same polyethylene grease described in associa
`defined by the foil shield (15) not otherwise occupied by insu-
`tion with the description of element (9) of FIG. 9. Also that
`lated electrical conductors (14). Furthermore, it is also envi-
`cavity defined between outer plastic tape (17) and the plastic
`sioned that the same polyethylene greaselike material can be
`coated metal foil shield (15), (15'), and (15'), not otherwise
`disposed in that cavity created by the plastic-coated metal foil
`occupied by insulated electrical conductors (16), can be also
`shield (15) and plastic tape (17) not otherwise occupied by is filled with the polyethylene greaselike material described
`the insulated electrical conductors (16). Such a polyethylene
`above. In element (10) of FIG. 10, as was the case with ele
`greaselike material is described as an amorphous
`ment (9) of FIG. 9, the exposed metal edges (20) present a
`polyethylene, having an average molecular weight below
`problem. Electrical energy escaping through pinholes in the
`about 10,000 and a density of below about 0.9l, namely
`insulation of the electrical conductors into that uninsulated
`0.851 grams per milliliter at 25 C.). This grease is marketed 20 portion of shield (14) and (16) where there is exposed metal
`by Dow Chemical Company of Midland, Michigan, under the
`foil is electrically undesirable. As was the case with element
`designation of QX-4213.3, and has been tested by the same
`(9) of FIG. 9, the polyethylene greaselike material can be used
`equipment used to test well-known polyethylenes as defined
`here to serve two functions: the first to provide a dielectric in
`by ASTM D-1238,65T. Essentially the same method as em-
`terposed between the exposed metal edge (20) and the insu
`ployed by this ASTM designation was used to test this 25 lated electrical conductors (16) or (14); and the second to in
`polyethylene greaselike material, except for slight modifica-
`sure the exclusion of water, either in the liquid or vapor state,
`tions. One such modification was that the extrusion barrel was
`from that portion of the cable structure where the electrical
`heated to 100° C., instead of 125 C., as called for in the afore-
`conductors are disposed.
`mentioned ASTM Specification. This temperature modifica-
`Element (11) of FIG. 11, shows a cross-sectional view of a
`tion was necessary because of the viscosity of the polyethylene 30 further embodiment of the instant invention. The cross-sec
`grease material, i.e., it is characteristic of this grease to
`tional structure of element (11) is essentially the same as ele
`become highly fluid when exposed to any high degree of heat.
`ment (9) of FIG.9, except for one specific deviation. It will be
`The melt index (flow rate) measured using this modified
`noted that in element (9) of FIG.9, there were exposed metal
`ASTM method was 10 to 20. A 2,160 gram load (piston and
`foil edges (20). Shield (15) of FIG. 11, does not have any
`weight) was used in this modified ASTM test, as well as an ori- 35 metal edges exposed. It will be noted that in FIG. 11, a plastic
`fice of 0.020 inches. Other data supplied by the Dow Chemi-
`coated metal foil shield (15), having a cross-sectional similar
`cal Company on other properties of the polyethylene grease
`to that as shown by shield (8) of FIG. 8, is employed. Thus, by
`are as follows:
`using this particular embodiment, no metal of the plastic foil
`TABLE I-PROPERTIES OF POLYETHYLENE GREASE GREASE
`Condition
`Value
`Property
`Power factor-------------------------------------- 1 to 100 kc.--------------------- Less than 5X10.
`Pour point.-------------------------------------------------
`... Approximately -10° C.
`Coefficient of volumetric expansion
`25°C
`-- 7.3x10-4.
`Density---------------------------
`- 25 C-
`... 0.58 gram per milliliter.
`Water absorption (percent).------
`- 24 hours at 100% RH-
`-- 0.01%.
`Meal specific heat.------------------------------- -40 to 100 C--------...------- Less than 53 call C.igm.
`
`
`
`shield is exposed at any time to any electrical conductor. This
`By placing the above described polyethylene greaselike
`is not to say, however, that the polyethylene grease used in the
`material in the two areas indicated, two functions are served.
`The first function is that of interposing a dielectric between 50 structure of cable (9) or (10) can not also be used here. Either
`the electrical conductors and the exposed metal edge portion
`that innermost cavity, not otherwise occupied by insulating
`(20); the second function is to exclude water, in any form, i.e.,
`conductors (14), defined by plastic-coated metal foil shield
`vapor or liquid, from ingressing into that area where the elec-
`(15), or that cavity defined between the plastic-coated metal
`trical conductors are situated. In essence, the polyethylene
`foil shield (15) and plastic tape (17), not otherwise occupied
`greaselike material is a hydrophobic material, as shown by its 55 by electrical conductor (16), or both, can be essentially filled
`extraordinary low (less than 0.01 percent) water absorption at
`with polyethylene greaselike material as previously discussed.
`24 hours at 100 percent relative humidity. Thus, by using the
`Thus it can be seen that in the case of a cable structure like
`polyethylene grease as discussed, water tight cable can be pro-
`that of element (11), of FIG. 11, the polyethylene greaselike
`vided. That is to say, the cable using the polyethylene grease 60 material serves basically as a water-repellant substance. How
`as disclosed, can be directly buried in the ground without the
`ever, in the case where there are pinholes in both the insula
`benefit of pressurization, and remain in service for an in-
`tion of the electrical conductors (14) and (16) as well as the
`definite length of time without the ingressing of water into the
`plastic-coated metal foil shield (15), the polyethylene
`area where the electrical conductors are situated.
`greaselike material serves as a dielectric and keeps unwanted
`Element (10) of FIG. 10 shows the overall cross-sectional 65 electrical energy from being transferred into the shield (15).
`view of a further embodiment of the instant invention. The
`Element (12) of FIG. 12 shows a cross-sectional view of a
`basic difference between the cable (10) of FIG. 10 and cable
`cable structure essentially the same as element (10) of FIG.
`(9) of FIG. 9, is that the plastic-coated foil shield (15) is not a
`10. The only difference between element (12) and that of ele
`single unitary tape as shown in element (9) of FIG. 9. In this
`ment (10) of FIG. 10 is that in element (12) a plurality of
`particular embodiment, the shield (15) is made up of a plurali- 70 plastic-coated metal foil shields is used, the plastic-coating of
`ty of tapes, the lateral edges of which overlap adjacently
`which completely surrounds the metal foil. Generally speak
`disposed like tapes. Elements (15), (15'), and (15') show this
`ing, a plastic foil completely surrounded by an integral coating
`particular feature with the individual plastic-coated metal foil
`of plastic material would be available to a man