IMPROVEMENTS IN INSULATED CONDUCTORS, LEADS AND CABLES FOR TELEPHONIC PURPOSES
Year: 1883

page_text: PROVISIONAL SPECIFICATION left by Alfred Rosling Bennett at the Office
of the Commissioners of Patents on the 19th September 1883.
ALFRED ROSLING BENNETT, of Glasgow, in the County of Lanark, Telegraph
Engineer, "IMPROVEMENTS IN INSULATED CONDUCTORS, LEADS AND CABLES FOR
TELEPHONIC PURPOSES,"
It is the custom to use copper wire insulated with gutta-percha, india-rubber,
paraffined cotton, bitumen, ozokerit, and other non-conducting substances, for the
purpose of leading telephonic wires into telephonic exchange offices and switch-
rooms, where it is necessary to pack a large number of conductora closely together,
and yet to prevent any metallic contact between them, and into the offices or
other buildings occupied by persons using telephonic communication, where it is
necessary to prevent the contact of the copper forming the conductor with any
metallic fittings, or other substances capable of conducting electricity, with damp.
surfaces, or with liquid matter. In such cases, the portion of telephonic line
which lies outside the exchange office, switch-room, or other building which is
usually of naked iron or phosphor-bronze, is brought as close as practicable to the
door, window or sky-light through which it is desired to introduce the telephonic
wire into the building. The covered copper conductor is then attached and
conveyed into the building by a gimlet-hole in the framing of the door, window,
or sky-light, or other convenient means. It is then led to the telephonic
apparatus, usually by being fastened to the walls by means of cleats or staples,
and afterwards from the telephonic apparatus to a gas-pipe or water pipe, or
other metallic substance which is wholly or partially buried in the earth.
Sometimes, after reaching the telephonic apparatus, the covered copper conductor
is led back to its place of entry into the building, and attached to a second portion
of the wire which lies outside of the building. This is done in the cases known
technically as "metallic circuits." and "intermediate stations." It is also the
custom to make up such covered copper conductors into bundles tied or twisted
tightly together so as to bring many of them into a small space, and to form what
is known as a cable, or multiple conductor; which cables or multiple conductora
are sometimes suspended overhead between poles or other supports planted in the
ground or erected on the roofs of buildings; sometimes placed in metal or earthen-
ware pipes and buried in the earth, and sometimes enclosed in a metal sheathing
and submerged in water. Such cables are also used for conveying telephonic
conductors into exchange offices and switch-rooms, and between different parts of
the same, through tunnels and sewers, and under and over bridges.
I have discovered that it is not necessary that the metal composing the
conductor of such covered wires and cables as are enumerated above should be
copper. I find that telephonic impulses, unlike telegraphic impulses, are not

page_text: appreciably affected by the nature or electrical resistance of the conductor which
conveys them, and that, on telephonic lines of such lengths as are commonly
employed in, and in the neighbourhood of, large towns and cities, no difference in
efficiency is perceptible, whatever may be the nature of the metal of which the
wires, cables, or conductors are formed.
Although the electrical properties of copper and iron are practically equal for
conductors for telephonic purposes, the mechanical properties of iron for such
purposes are greatly superior to those of copper, iron being stronger and tougher
and better able to bear without injury the strains to which telephonic conductors,
leads and cables are necessarily exposed in the course of erection and repair.
Iron is also free from the defect inherent in copper of becoming brittle after
some years use. Again, copper is a very costly metal as compared with iron.
It would therefore be a matter of great public benefit and utility if the latter
metal could be substituted for the former.
The first part of my Invention consists of the use of wire composed of iron or
steel, preferably of a soft and ductile quality, in lieu of copper in all such
covered conductors and cables for telephonic purposes as are set forth above, which
iron or steel may be bare, or coated superficially with zinc, tin, lead, copper or
nickel, or with black oxide of iron. Or it may be painted, varnished, or oiled
before being covered with gutta-percha, india-rubber, paraffined cotton, bitumen,
ozokerit or other insulating material.
The iron or steel cores of the insulated conductors may either be of solid
wire, or be composed of two, three, four, five, or any greater number of wires
twisted together.
I am aware that iron wire has previously been covered with a coating of tapo
or cotton saturated with tar, both for telegraphic and telephonic purposes. But
the wire so treated has invariably been intended for outside use in single strands,
that is to say, for suspending in the air to form the outside portion of telegraphic
or telephonic lines in lieu of the naked iron wire usually employed for such
purposes, and bears no analogy to my Invention which treats only of such
conductors, leads, and cables used in telephonic work for the purposes herein set
forth, as have hitherto invariably been composed of copper.
The second part of my Invention is designed to provide a cheap system of
underground telephonic communication for use chiefly in towns and cities, which
shall be free from inductive disturbances between wire and wire; and to provide
means of inter-communication between any telephonic system on the metallic
circuit plan and any telephonic system composed of single wires joined to earth at
their extremities.
The cables hereinafter described may be laid underground in any description of
tube, pipe, box, tunnel, sewer, subway conduit or culvert, or in hollow kerbstones
or kerb boxes, or in aqueducts, as is at present practised and well understood.
My system is on the metallic circuit plan. The conductor I use consists of an
iron wire, either solid or composed of several or many iron wires twisted
together, which is covered with gutta-percha, india-rubber, or any other suitable
insulating material.
Two of the insulated conductors so formed are twisted together throughout their
length, in which form, when the four free ends of the iron wires are connected
together, they form a metallic circuit.
For some purposes, such as fitting up wires in connection with telephonic
apparatus inside offices or other buildings, such a single metallic circuit can be
used without further preparation, but it may also be covered with hemp, cotton,
wool, silk, or other suitable material, or with a sheathing of tin or lead so as to
make the double twisted insulated wires appear as one to the eye.
For use underground, I form a number, which may vary from two upwards, of
these insulated metallic circuits into a bundle or cable by tying or twisting them
together, which bundle or cable may be uncovered, or it may be protected with
any of the coverings in common use for such purposes by telegraph engineers.

page_text: I prefer to sheath the completed cables in tin or leaden piping to protect it from
mechanical injury and the influence of wet.
The underground pipe or other channel in which the cables are led is caused,
according to one modification of the second part of my Invention, to communicate
at intervals along the streets with hollow upright tubes or pillars of a height to be
determined by the nature of the vehicular traffic in the streets, (which upright
pillars may advantageously be also utilised as lamp-posts) to the upper portion of
which are fixed insulators of porcelain or other suitable material. The upright
tubes or pillars are fixed only in the vicinity of buildings occupied by persons
using telephonic communication.
From the telephonic exchange office a cable is led to each upright tube or pillar
containing as many metallic circuits as there are, or are expected to be, users of
telephonic communication in the neighbourhood of the pillar. The metallic
circuits are led up the inside of the pillar and connected to wires which are
attached to the insulators, and which stretch from the insulators on the pillar to
insulators fixed to the walls or roofs of buildings occupied by the users of
telephonic communication. The wires which so form the connections between the
pillar and the users' buildings may be either naked or covered wires, stretched
singly, (in which case two will be required for every user) or they may be two
covered wires bound or twisted together, so as to form a metallic circuit, in which
case they may be covered, so as to present the appeurance of a single wire to
the eye.
Instead of being led to the upright tubes or pillars as described, the cables may be
carried up the walls, and to the roofs of suitable buildings in piping or boxing, and
these attached to wires provided for the purpose of connecting them with the users
of telephonic communication.
Or the metallic circuits may be led in suitable piping underground direct from
the channels conveying the main cables into the buildings occupied by the users of
telephonic communication. When working on this plan, I prefer to convey by
means of an underground pipe, branching from the main channel, a cable containing
as many metallic circuits as are likely to be required within a convenient distance
from a given building, or block of buildings, to a weather-tight box or case fixed to
the wall, or on the roof of the building most favourably situated for distributing
the wires. In some instances the box or case might be advantageously situated
within the building. Within the box or case each metallic circuit in the cable is
connected by means of suitable screws, or by soldered joints to corresponding
single metallic circuits hermetically enclosed in tin or leaden piping, which single
metallic circuits are led along the walls of the buildings, from the box or case to
the offices or premises occupied by the users of telephonic communication, being
attached to the walls along which they are conveyed by staples, hooks, brackets,
cleats, or other suitable fastenings.
At the telephonic exchange office the cables are led to the switch-boards where
if the whole system of the town or district is on the metallic circuit plan, they are
connected together as required by one of the devices now practised for that
purpose. But if one portion of the system is on the metallic circuit plan, and the
other portion consists of single wires joined to earth at their extremities, as in the
case of a town or district in course of conversion from the single-line to the metallic
circuit plan, I make the connections between the metallic circuits and the single
wire lines by means of induction coils, constructed and arranged substantially as
set forth in the specification of Letters Patent N° 4,428 for "Improvements in
telephonic apparatus," granted to me on October, 11, 1881.