Improvements in Electric Cables.
Year: 1892

page_text: Date of Application, 15th Jan., 1892-Accepted, 20th Feb., 1892
[Communicated from abroad by EUGENE FRANCIS PHILLIPS, of Providence,
Rhode Island, United States of America, Electrician.]
Improvements in Electric Cables.
I, WALLACE FAIRWEATHER, C.E., of 62 Saint Vincent Street in the City of
Glasgow, Chartered Patent Agent do hereby declare the nature of this invention
and in what manner the same is to be performed, as communicated to me to be
particularly described and ascertained in and by the following statement:-
This invention relates to electric cables and more especially to those which
comprise a number of electrical conductors.
It is well known that to construct multiple conductor electrical cables having
a working efficiency of the highest order certain conditions must be observed.
The insulation covering of each conductor must be high and uniform; and the
electro static capacity or charge holding properties of each insulated conductor
must be as low as possible.
The construction of the cable must moreover be such that there shall be a
minimum of inductive interference between the different conductors; and it is
likewise requisite that these electrical properties must be attained without
depreciating the mechanical strength of the cable.
In cables whose conductors in whole or in part, are to form portions of circuits
with which are connected electrical receiving instruments capable of being affected
by extremely feeble currents, such for example as delicate galvanometer receivers
or telephones, it is especially essential that the resistance and capacity. of the
conductor shall be minimized, and that the practical neutralization of disturbance
producing induction shall be provided for.
The object of this invention is the construction of a cable based upon the above
condition which has a lower electrostatic capacity that has heretofore been
compatible with high insulation and which at the same time is in virtue of its mode
of manufacture of great mechanical strength.
Many of the non conducting media which have been employed to insulate cable
conductors, while possessing high insulation resistance have unfortunately a high
specific inductive capacity, such for instance being the case with gutta percha,
india rubber, paraffine and like substances.
It is also however well known that dry air is a remarkably good non conductor,
and further that its electrostatic capacity is very low; thus if any practical way
can be found to employ it in electrical cables, it is obvious that advantageous
results will accrue.
The invention comprises a cable in which the several conductors to secure
inductive neutrality and the avoidance of interfering disturbance therefrom are
preferably arranged in pairs, the two members of each pair forming a portion of
the direct and return conductors respectively of a given metallic circuit.
It is necessary that the two conductors of each such circuit to secure immunity
from induction shall be equidistant from other conductors, as otherwise there can
be no balance, and heretofore and prior to this invention such equidistant and
consequent balance has been secured by twisting the insulated members of each
pair together; so that a multiple circuit cable has been made up of a number of
such twisted pairs.
But circuits so made up into a cable, have necessarily a high electrostatic
capacity, whether the conductors formning them are connected in metallic or earth
completed circuits, for in the former case, the capacity to be considered is that
between each wire and its mate; and these being very close together, and separated

page_text: only by the thickness of the insulation covering the two, the capacity is
necessarily high; while in the latter case in which the capacity to be considered is
that of each conductor to earth, it is clear that as the several wires are part of
earth completed circuits, a conductor in connection with the earth is thus brought
into close communion with the individual conductor we are considering and the
result is the same as in the first case, the capacity is high, and the result is a
cable conductor which has a considerable tendency to receive a charge and which
therefore distorts and retards the passage of varying currents.
:
The cable described and claimed herein, though having its conductors arranged
in pairs is not laid up in twisted pairs though it is true, that in virtue of its
construction the members of its several pairs if straightened out do exhibit a long
twist. On the other hand its inductive neutrality is achieved first by constructing
its conductors in individual groups of not more than four, that is to say, two
pairs, and by arranging the plane of the said two circuits at a right angle to
cach other, or the four conductors at opposite quadrantal points of a circle.
Second by disposing the several groups of four relatively in such a manner as
to avoid parallelism between the conductors of any group, and an immediately
adjacent group, it being a fact that the induction exerted by one conductor is
cæteris paribus, dependent upon the degree of parallelisin existing between them,
and is zero when the two are extended in directions, which cross each other at a
right angle. This is brought about by giving the first four conductors a helical
twist in a given direction say right handed and then by adding the second four to
the said group giving them however a helical twist in the opposite, that is to say
in a left handed direction. By this means the conductors of the second four cross
those of the first four nearly at a right angle continually. We thus have
eight individual conductors or four pairs which are practically inductively
neutral.
They however do not require any more space than would be required were there
but four.
The clectrostatic capacity of each circuit is at a minimum because the several
conductors are so laid up in connection with a fibrous and porous filling that they
are a considerable distance from each other, and that the major part of the
intervening insulation between any two conductors is in fact dry air, which fills up
all the interstices between them, and charges every pore of the said fibrous filling
material.
The several conductors are firmly held in the required positions indicated above
by being braided in a manner well understood by insulated wire manufacturers,
together with a suitable number of filling, twines, twisted paper or other fibrous
cord, and the braid thus constructed is preferably produced in the form of a tube.
The size, form, and number of the filling cords can of course be varied at will, but
it may be stated that a satisfactory specimen has been made in which twelve
fibrous cords have been interbraided together with eight wires cach wire being first
lightly covered with cotton. If the paired conductors of such a core are worked
as metallic circuits as they would preferably be, the equidistance of each conductor
of each circuit from these of the other circuits is superadded to the distance apart,
and to the opposite helical direction of adjacent groups as an interference preventing
device, but if the said conductors each form part of a single wire circuit, the
distance and opposite helical direction alone can be depended upon for this
purpose, and the neutralization is by no means so effectual. Even in this event
however the capacity is low, and in this respect alone, the result is a greatly
improved cable.
It should also be stated that the several pairs of lightly insulated conductors,
may be interbraided with the fibrous filling cords preserving their required
relative distance and positions but in form of a ribbon or strip instead of in that
of a tube, in which case the said strip would itself. be. helically twisted into
tubular form to constitute a core or nucleus for outer conductors or layers.

page_text: If desired, the tube formed by either mode may have a twisted pair of insulated
conductors of the ordinary type threaded through them.
An additional double wire conductor is thereby secured, which however has by
no means as low an electrostatic capacity as those which are as hereinbefore
described separated by a relatively wide air space loose filled merely by dry fibre.
Other eight conductors may now be interbraided with a sufficient number of
filling threads or fibrous cords over the original tubular core, four in one helical
direction, and four in the other, and these may in like manner be formed into four
additional double conductor circuits, their reciprocal inductive neutrality being
achieved by the same means as herein before described; the capacity of each
conductor measured to its mate being reduced by the relatively great width of the
air space.
While inductive interference between them and the circuits of the inner
group is substantially prevented by the fact that the conductors of this outer
layer are braided with a longer pitch than that of the inner ones, and also by the
fact that by means of the braiding itself, the conductors are prevented from
paralleling each other. Other layers as many as may be desired, can be added in
like manner and the cable is finished by being externally coated either with a
strong woven or braided fabric, or preferably with a leaden pipe or tube.
Instead of making a large cable of successively larger braided tubes super-
imposed, each over the preceding one, it is often preferable in practice to form a
complete cable of several of the small braided compound tubular conductors
enclosed in a suitable protecting leaden pipe. In a cable which has been
constructed on this plan, seven such tubular cores were employed, six of them
surrounding the other which served as a central core.
In the drawing which illustrates this invention, Figs. 1 and 2 are respectively
a cross section and a longitudinal skeleton view of a cable embodying the principle
of the invention, and for clearness of illustration showing but two pairs of
conductors braided together with their filling cords, and all winding helically in
the same direction.
Figs. 3 and 4 are similar diagrammatic views of a cable in which there are
eight conductors, four running helically each way.
Figure 5 shows a cable composed of an inner and outer tube constructed in
accordance with the invention. Fig. 6 shows a braided tape or strip from which a
helically wound core tube may be formed. Fig. 7 shows a skeleton cable formed
by interbraiding a series of paired conductors and their several filling cords over
a central tubular core made by helically winding the strip shown in Figure 6; and
Figure 8 is a cross sectional view of a finished cable in which seven unit compound
conductors, each embodying the principle of my invention are enclosed together in
a suitable enveloping pipe.
In Figs. 1 and 2, four conductors are shown. These are prearranged to be
operated in pairs, cach member of each pair will then be adapted to form a section
or portion of one side of a metallic circuit of which its mate forms a like
portion of the other side. In the drawings, 1 and 2 are paired conductors,
and 3 and 4 are also members of a similar. They are lightly covered
with cotton or similar material and are interbraided with fibrous fillers a,
consisting of strings or twines, twisted paper, or other fibrous cords.
In this way
a strong tube is formed consisting of two pairs of covered wires, each pair of
wires having one of the members of the other pair equidistant from and between
them, so that the induction exercised between it and them shall be equal but
opposite. The two members of each pair are mechanically by this means held
parallel to one another throughout, yet at some distance (in practice they may be
half an inch) apart; and the air space between them being but partially occupied
by fibrous material and the intermediate wire, the electrostatic capacity between
the said two conductors is very low, while as long as dryness is maintained in the
interior of the cable, for the same reason the insulation is very high. If a core so
formed be cut across at any point the cross section will present the present

page_text: appearance of Figure 1 in which the members of each pair are diametrically
opposite each other.
In Figure 4 the next step is indicated. In this figure four conductors 1, 23
and 4 forming a left handed helix, and four others 5, 6, 7 and 8 forming 21. right
handed helix are shown, these being arranged as before for connection in pairs,
1 with 2 3 with 4; 5 with 6 and 7 with 8 and interbraided with fibrous filling
strands or cords a in the manner indicated above. The conductors of one direction
cross those of the other direction at a very considerable angle, thus keeping the
reciprocal induction between the members of the two sets at a minimum, while that
tending to be exercised between the several members of the second group is
minimized in the same manner as is that of the first; the capacity for the reason
already stated, being also kept low. Fig. 3 shows the appearance of such a
compound core if cut across.
In Fig. 5, the inner compound tubular conductor A, is made exactly as that
shown in Figure 4, and has an outer tubular compound conductor B having four
pairs braided or woven over it as shown; these like those of Figure 4, being inter-
braided or interwoven with the fibrous fillers a. Two of the pairs as in Fig. 4 are
braided with a right handed, and two with a left handed helix. The pitch given to
the helices or spiral curves is greater than is given to the conductors of the inner
tube.
A third tubular conductor formation may in turn be braided over the layer B, and
if desired a fourth. This of course will however be determined by the number of
desired circuits and by mechanical considerations.
Figure 6 shows that two or more lightly covered conductors 1 and 2 may be
interbraided or interwoven with fibrous filling a in the form of a tape or flat strip D,
which then may be helically twisted into tubular form as shown in Figure 7, while
over it, any desired additional layers of pairs of wires, interbraided with fibrous
cords a, as in B may be braided.
The central space extending from one end to the other of these several forms,
may if desired, be utilized as a receptacle for one or more ordinary twisted pairs of
insulated wires y as shown in Fig. 4.
One very practical mode of forming a complete cable in accordance with this
invention is shown in Figure 8, where a number (seven) of single tubular cores A,
each made up of four papers as in Fig. 4 are enclosed in a suitable external
sheathing C. This if desired may be of braided or woven coarse fibrous material,
but a leaden or leaden alloy tube is preferred into which the several cores may
together be drawn. Thus the requisite mechanical strength is imparted to the cable
as a whole, its component parts being already strong in virtue of their mode of
manufacture.
Such a leaden tube C is indicated as being the external protecting envelope of
the section of cable shown in Fig. 5.
Having now fully described the invention it will now clearly be seen that by it, a
multiple conductor cable may be manufactured in which the several conductors
when joined in pairs, form an inductively neutral system which does not require
the members of each pair to be twisted together, which has high insulation and low
capacity, in virtue of the mode in which the insulating and low capacity
characteristics of dry air are utilized, and in which the said properties are
maintained constant and unchanged, and strength imparted to the elements of
the cable by interbraiding them, together with the necessary fibrous fillers as
described herein.
Finally it should be stated that in some cases it may be preferred to leave the
foundation tube as in Fig. 2 with but four conductors adapted to form but two
circuits; and to braid thereover immediately a second and succeeding series of four.
It is evident that in this case the four conductors of the first series must all be
wound in the same direction, while those of the succeeding series are braided on the
opposite direction.

page_text: Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed as communicated to me
I declare that what I claim is-
1. An electric cable core comprising a group of insulated conductors inter-
braided with fibrous cords into a tubular form, each conductor being thereby held
apart from its adjacent conductor and practically surrounded by the air occupying
the pores and interstices of said fibrous filling, whereby a high insulation resistance
and a low inductive capacity is maintained for the said conductors.
2. An electric cable core composed of four insulated conductors adapted to be
arranged in pairs to form parts of electric circuits, braided or woven together with
fibrous filling cords into a tubular form, each conductor of each circuit section being
disposed parallel to and between the two conductors of the other circuit and all of
the said conductors being braided with a helical twist in the same direction, and
held at a uniform distance from each other by the interposed fibrous filling, so that
at a cross section taken at any point, the plane of the two conductors of one circuit,
will be perpendicular to that of the other whereby inductive neutrality and low
inductive capacity is secured.
3. The combination substantially as hereinbefore described in an electric cable,
of a central tubular core formed by braiding or weaving four pairs of insulated
conductors with a series of fibrous threads, cords, twines or equivalent fibrous
material, whereby a considerable air space is left in and between the said fibrous
cords two of the said pairs being so disposed in the braid as to form in the tubular
core a right handed helix, and the remaining two being braided in the opposite
direction so as to constitute a left handed helix.
4. An electric cable comprising a central tubular core formed by braiding two or
more pairs of insulated conductors together with a series of fibrous cords, twines or
threads, combined with one or more unbraided but twisted pairs of insulated
conductors extended longitudinally through the said tubular core to serve as
supplementary metallic circuit conductor, substantially as specified.
5. The hereinbefore method of manufacturing electric cables which consists in
laying the insulated conductors in groups of four (that is to say two pairs) and in
braiding them together with a fibrous and porous filling in such a manner that the
planes of the two circuits are at a right angle to each other, or the four conductors
at opposite quadrantal points of a circular cross section taken at any point of such
cable.
6. As an improvement in the art of manufacturing electric cables, the herein
described method which consists in disposing the insulated conductors in group of
four pairs, and in interbraiding them loosely with fibrous cords or fillers, giving to
two of the said pairs a right handed helical twist and to the remaining two a left
handed helical twist, substantially as set forth.
7. In an electric cable a series of conductors interbraided or woven with fibrous
twine, twisted paper or like material, into tubular form, to constitute a foundation
or core, and one or more successive similar series of braided conductors and fibrous
cords braided thereover, the conductors of each succeeding series being braided
with a longer pitch or at an increased angle to those of each underlying series,
substantially as described.
8. In an electric cable the combination of four pairs of conductors interbraided
or woven with a series of fibrous cords into tubular form to constitute a base or
core, the conductors of two of the pairs being braided in a direction opposite to
those of the remaining two, and one or more successive similar series of conductors
and fibrous filling cords braided thereof and superposed on each other, each series
having a like number of pairs of conductors, each having the conductors of one
half its pairs braided in a direction opposite to that of the other half, and each
succeeding series having its conductors braided at a longer pitch than those of the
preceding or underlying series substantially as described.
9. In an electric cable a central core having two or more pairs of insulated

page_text: conductors braided together with a series of fibrous filling cords into a tubular form
whereby each pair are maintained in parallelism with each other but at a suitable
distance apart, so that both are equidistant from any other conductor, and so that
the electrostatic or inductive capacity measured between them be at a minimum.
10. An electric cable having a compound conducting core or nucleus composed of
a series of conductors, adapted to be arranged in pairs, braided with fibrous cords
or twines into tubular form, and one or more successive series of conductors
likewise braided with fibrous cords into tubular form, each successive series being
braided over the other, and each pair of braided conductors having its two
members approximately equidistant from the other cable conductors substantially
as described.
11. An electric cable consisting of a central tubular core having two or more
pairs of insulated conductors interbraided as described with a series of fibrous cords,
one or more like series of pairs of insulated conductors braided or woven thereover
together with similar fibrons material in successive concentric tubes, the pitch of
the conductors of each successive series in ontward progression being greater than
that of those of the preceding series and a leaden sheath or pipe, or other suitable
protective covering substantially as specified.
12. An electric cable formed of a series of insulated conductors interbraided
with fibrous material into a continuous flat strip or ribbon, which is wound or
twisted into a helical tube having a central chamel core or air space, and a
succession of similarly constructed tubes, or of braided tubes formed as described
herein wound upon or braided over the central tubular core to build up a cable of
the desired size, the conductors of each successive tube in outward progression
being arranged in a helical direction opposite to that taken by those of the
preceding series, and a leaden or other protective sheath, substantially as specified
herein.
13. An electric cable formed of a series of separate groups of conductors, each
group being made by braiding or weaving into a tubular form a series of pairs of
insulated conductors, electrically separated but mechanically united by fibrous
threads or cords forming a part of said braided tube, the said groups being
symmetrically disposed and drawn into an external protecting envelope of lead or
lead alloy, substantially as described.
14. A cable core formed of two or more pairs of insulated conductors so inter-
woven or interbraided with filaments or cords of fibrous material as to form
interstices or spaces between the said conductors which together with the substance
of said fibrous material are adapted to receive and retain an insulating medium of
dry air or gas, substantially as described.
Dated this 14th day of January 1892.
CRUIKSHANK & FAIRWEATHER,
62, Saint Vincent Street, Glasgow, Agents.