Improvements in Electrical Cables.
Year: 1892

page_text: Date of Application, 11th Mar., 1892-Accepted, 16th Apr., 1892
COMPLETE SPECIFICATION.
[Communicated from abroad by EUGENE FRANCIS PHILLIPS, of 516, Broad Street,
Providence, Rhode Island, United States of America, Electrician.]
Improvements in Electrical Cables.
1, 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 electrical 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
conditions, which has a lower electrostatic capacity that has heretobefore 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, paraffin and like substance.
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 imetallic circuit.
It is necessary that the two conductors of cach 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 equidistance 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 forming them are connected in metallic or carth
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
only by the thickness of the insulation covering the two, the capacity is necessarily.

page_text: 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 parts 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.
In a former application for Letters Patent filed 15th January 1892 No. 825 I
described a novel construction of multiple conductor cable, having its conductors
laid up in braided series of eight conductors, four of which in said braid were
caused to have a left handed helical twist, and the remaining four a right handed
helical twist, the position and stiffness of such an arrangement of conductors being
maintained by interbraiding a suitable number of fibrous threads or strands together
with said conductors; an entire cable being built up of a number of such series,
which may be superimposed concentrically over each other.
My present invention consists in providing a solid and semi rigid central
foundation core which may preferably be made of twisted or braided insulated
conductors, so that the said core also shall be utilizable, to serve as a central base
for the outer cable conductors, although if desired the said foundation core may be.
made of solid insulating material such as jute, rope or paper, and in braiding over
the said foundation core and without any filling of interbraided fibrous cores or
twines, two series of four conductors, the four conductors of each series being at the
four quadrantal points of a circle inscribed round them; the two series having
opposite helical directions of winding; the necessary distance to ensure a low
capacity being maintained, and at the same time the necessary firmness being
ensured by braiding the conductors with wide intermediate spaces, but solidly upon
the core.
It also consists in forming a number of such braided constructions each having a
central foundation core as above, into a cable, and providing them with a common
external protective covering; and also by superposing a second and if desired a
third compound longer pitch braid over the first.
The several conductors are firmly held in the required positions indicated above,
by being braided together in a manner well understood by insulated wire manu-
facturers firmly upon the foundation core. 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 those 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 cach 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.
The inner or central core may be composed first, of insulating fibrous mass as
indicated above, or it may be formed, second, of four conductors loosely insulated
with paper, bunched and twisted together; or it may consist third, of eight
conductors braided together, four conductors or two pairs, having a helical twist
to the right, the other four conductors or two pairs having a helical twist to the
left, being formed the same as its surrounding braid, except that they are braided
closely without a central airspace. In either construction, the electrostatic capacity
of the central core conductors, when such are employed, is slightly in excess of that
of its surrounding conductors forming a sleeve on said core owing to the fact of
their contiguity to each other; and the consequent thinness of the air space
between them.
Eight insulated conductors, in two series of opposite helical direction are
braided over the central core, each being diametrically opposite in position
throughout to some other one of the same helical direction, and when formed into
metallic circuits, the two conductors of each such circuit, (or as it may be stated,)

page_text: the two conductors or each pair are those which are so diametrically opposite to each
other.
Although this braid of eight conductors is an openwork, and has no interposed
filling fibres, cords, or other supports, it having the central core foundation, is
sufficiently stiff and rigid to comply with all necessary mechanical requirements.
Other eight conductors may now he interbraided over and concentric with the
first layer, four in one helical direction, and four in the other, and these in like
manner may be formed into four additional double conductor circuits, their
reciprocal inductive neutrality being achieved by the same means as hereinbefore
described; the capacity of each conductor measured to its nate 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 superimposed,
each over the preceding one, it is often preferable in practice to form a complete
cable of a number of the compound concentric and centrally cored, braided or
woven conductors enclosed in a suitable protecting leaden pipe. In a cable
constructed on this plan, seven such compound braids may be employed, six of them
surrounding the other which is placed at the center.
In the drawing which illustrates this invention, Figs. 1 and 2 are respectively
a side view and a cross section of a central core for a cable in which are eight
insulated conductors, braided together, four winding to the right and four to the
left, forming a close and solid foundation core having no central air tube or space.
Figs. 3 and 4 are respectively a side view and a cross section of a central
foundation core for a cable, in which the four conductors are insulated with paper,
loosely wound around them, the conductors being bunched together and twisted
with a long twist; and Figs. 34 and 4* are a side view and cross section of a
foundation core made wholly of insulating material. Figs. 5 and 6 are respectively
a side view and cross section of a cable, having a solid core of four wires, like that
shown in Figs. 3 and 4, and having braided over it, eight conductors, four winding
to the right and four to the left. I have shown in dotted lines a section of lead or
other covering for the cable. Figs. 7 and 8 are respectively a side view and cross
section of a cable, having a central foundation core, and concentric compound
conductor braids built up or superimposed thereon, the inner concentric braid being
the same as shown in Figs. 5 and 6, the outer tubular compound conductor braid
being the same in all respects as the inner, excepting that the conductors have a
longer pitch. Fig. 9 represents a cross section of a compound cable composed of
seven such cables as are represented in Figs. 5 or 7, enclosed in a suitable enveloping
pipe.
Figs. 1 and 2 represent a braided core of eight conductors four of which 1, 2, 3, 4,
comprising two pairs, are twisted to the right, and the other four 5, 6, 7, 8, com-
prising other two pairs having a twist to the left, they are lightly covered with
cotton or other similar material, and are braided lightly yet firmly together so that
there is no longitudinal or tubular air space through the center thereof; the twist
given the conductors however is of such length that each conductor is separated
from its mate, except at the places they cross each other in the braid.
The conductors of one direction cross those of the other direction at a 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 that of the first the capacity for
the reason already stated being also kept low.
Figs. 2 and 3 represent a form of core employed by me in my improved cable as

page_text: an alternative. It consists of four conductors, in two pairs, each conductor being
covered with paper loosely wound thereon; the four conductors are twisted together
with a long twist as shown, they make a comparatively solid core or filling of low
capacity. Both of the forms of core shown, are excellent for the purpose desired
and.over which to braid the other conductors to form my cable.
It is not necessary that the central or foundation core be formed of conductors.
If desired, it may as shown in Figs. 3 and 4 be formed solid of any suitable
fibrous or nonfusible insulating material such as rope, jute, twines braided or
otherwise, cotton or paper, it being apparent that a foundation core thus formed
while not serviceable in affording additional conductors is equally serviceable for
use as a solid foundation, for a superimposed loose braiding of insulated conductors,
whereby cach conductor of such braid may be enabled to retain its necessary position
without the aid of interposed fibrous filling cords.
In Fig. 5 the next step is indicated. In this fig. four conductors 1, 2, 3 and 4
forming a left handed helix and four others 5, 6, 7 and 8 forming a 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 in the manner indicated above.
But as this compound conductor is braided over the central core (which has an
approximately circular cross section) it is evident that it virtually forms an open-
work tube which by its interior surface closely clasps the said foundation core; and
the two members of each pair of conductors of which such openwork tube is
formed, are universally so arranged, that they are at diametrically opposite points
of the said openwork tube, and as a consequence the plane of each pair is at a right
angle to and bisects that of the other pair in the same group of four having like
helical direction, notwithstanding the said helical lay up.
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. 6 shows the
appearance of such a compound core if cut across.
In Fig. 7 the inner compound braided conductor A, is made exactly as that shown
in Figure 5 and has an outer tubular compound conductor B having four pairs
braided or woven over it as shown, the conductors whereof like those of Fig. 5
being interbraided or interwoven with each other, and clasp the interior braid,
which consequently supports them firmly, and with a sufficient degree of rigidity.
The relation of the two conductors of each pair, with the two of the other pair
of like direction is the same as if found in the inner tubular braid.
Two of the pairs as in Fig. 5 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, thus be braided over the
layer B, and if desired a fourth, thus forming an entire cable built up of such layers
and externally protected by the leaden tube or pipe E or any suitable sheath.
This of course will however be determined by the number of desired circuits and
by mechanical considerations.
One very practical mode of forming a complete cable in accordance with this
invention is shown in Figure 9 where a number (seven) of single tubular cores or
sub-cables A, each made up as in Fig. 5 are enclosed in a suitable external
sheathing E. 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 or sub-
cables 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 E is indicated as being the external
protecting envelope of the section of cable shown in Fig. 5.
It will now be evident that by my invention a multiple conductor cable may be
manufactured in which the several conductors when joined in pairs, form an

page_text: 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; while strength
is imparted to the elements of the cable by interbraiding them, as described herein.
upon a solid foundation core, which if constructed in the preferred way, affords.
additional conductors thus effecting great economy of space.
Having now particularly described and ascertained the nature of the 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. In an electric cable, a series of insulated conductors interbraided loosely with
respect to each other 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.
low inductive capacity is maintained for the said conductors; and means for centrally
supporting the conductors of said series and for maintaining them in position
substantially as described.
2. The combination in an electric cable substantially as hereinbefore described.
of a central solid foundation core, and a tubular multi-conductor braid formed
thereon, and supported thereby, the said tubular braid being composed of two pairs,
of insulated conductors braided or woven together in a uniform helical direction,.
the plane of each of the said pairs being at a right angle to and bisecting that of
the other.
3. In an electric cable, the combination of a solid central foundation core, and
an openwork tube of independent insulated conductors braided or woven thereover,
resting thereon and supported thereby, the said openwork braid being composed of
two groups of conductors, each group comprising two pairs of braided insulated
conductors of uniform helical direction, the plane of each pair being at a right angle
to and bisecting that of the other and the helical direction of the conductors of
each group being reversed with respect to those of the other, substantially as
described.
4. The combination in an electric cable, of a stiff and solid central foundation
core consisting of twisted or braided insulated conductors, and four insulated
conductors braided thereover into the form of an openwork tube compressing the
said foundation core, and maintained in position thereby, the four said conductors
being arranged in two pairs of uniforin helical direction, the plane of each
pair being vertical to the center of the plane of the other substantially as
described.
5. The combination in an electric multi-conductor cable of a stiff and solid
central foundation core formed of two or more pairs of insulated conductors twisted
or braided together; and two groups of insulated conductors braided thereover into
the form of an openwork tube compressing the said foundation core and held in
place thereby, each of the said groups comprising four conductors arranged in pairs,
having a uniform helical direction, the plane of each pair being vertical to the
center of the plane of the other the helical direction of the conductors of
one of the said groups being opposed to that of the other substantially. as
described.
6. In an electric cable a central foundation core composed of two or more
insulated conductors braided or woven together into a firm and solid strand, a series
or layer of insulated conductors in two groups respectively of opposite helical
direction braided tightly over said core into a tubular openwork, its two groups each
comprising two pairs cf conductors adapted as described herein to form portions of
inductively neutral metallic circuits, and one or more successive similar series of
conductors braided each over the immediately preceding interior series, into
successive concentric tubes, cach compressing its inner neighbour, the conductors of

page_text: each succeeding series being braided with a longer pitch or at an increased angle to
those of each underlying series, substantially as described.
7. An electric cable comprising a tubular openwork, series of insulated conductors
braided over and upon a solid central foundation core formed of a number of pairs
of conductors twisted or braided as indicated, the said series being composed of two
groups, each comprising two pairs, the helical direction of the conductors of one
group being opposed to that of the other, and the two pairs of each group being
each arranged so that at any point of cross section, the plane of each pair is at a
right angle to the center of the plane of the other; other successive similar series
braided over and resting upon the immediately preceding similar series, the conductor
of each being braided with a longer pitch than the immediately underlying series,
and an external protective sheath such as a lead pipe enclosing the whole substan-
tially as and for the purpose described.
8. An electric cable comprising a protecting envelope or sheath, such as a tube
of lead, or lead alloy, and a series of compound cores or sub-cables enclosed
symmetrically therein, each of the said sub-cables, consisting of a solid and seini-
rigid central core, and one or more concentric series braided over and upon said
central core into the form of an openwork tube, each of the said series comprising
two groups of two pairs of conductors each, the pairs of each groups being each
arranged in a plane vertical to the center of the other, and the four conductors of
each group being all braided in a direction similar to those of the same group but
opposed to that of the other group, substantially as specified herein.
Dated this Tenth day of March 1892.
CRUIKSHANK & FAIRWEATHER,
62, St. Vincent Street, Glasgow, Agents.