An Artificial Ground and Compound Metallic Circuit System for Electric Telephones and the like.
Year: 1890

page_text: Date of Application, 30th Sept.. 1890-Accepted, 11th Apr.,
1891
COMPLETE MEUITIVATION.
An Artificial Ground and Compound Metallic Circuit System for
Electric Telephones and the like.
I, CHARLES EDWARD MCCLUER, of Richmond, County of Henrico, State of
Virginia, United States of America, Gentleman, do hereby declare the nature of
this invention, and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement :-
It being well known that a current of electricity flowing over a conductor will
generate in an adjacent conductor an induced or secondary current, it was very
natural that during the early history of the telephone, the adverse influence of all
extraneous or foreign currents upon that extremely sensitive electrical instrument,
should have been included in the general term "induction." Observation and
experiment have however, demonstrated the fallacy of this theory, and proved
that the chief cause of telephonic disturbances is leakage or conduction, not
induction. Through what distance induction occurs, depends mainly upon the
character of the primary or inducing current, but even when the wires of telephone
and electric lighting and power systems are arranged for considerable distances in
close proximity, the currents induced on the telephone wires by the dynamo
currents are less disastrous to the telephone service than the currents which leak
over, or are conducted from one system to the other.
When it is considered that there is no perfect electrical insulator or conductor
known, and that substances classed as such differ only in degree, a good conductor
merely transmitting electrical impulses readily, while a good insulator propagates
them with difficulty, it can be conceived that an electrical current of high potential
or electro motive force, may spread over or through the very best insulators
and become diffused through any conductor, or system of conductors, that may
conveniently offer, in strict conformity to the laws governing the transmission of
electricity.
Until recently, electricians have concurred in the belief that the earth is an
infinite conductor of electricity, and that it offers no resistance whatever to the
propagation of electrical impulses. In view of recent observations and experiments,
however, the correctness of this theory is questioned, and the earth is held to be
merely an extraordinarily good conductor because of its immense mass, but really
offering an appreciable resistance to the transmission of electrical force.
"
"
Accepting then, these two facts, that the very best "insulators will, under
proper conditions, become "conductors and that the best known conductor, the
"earth," does not offer an appreciable resistance to the transmission of electricity,
it follows that electrical currents of high potential may leak or be conducted over
the best glass, or other insulating substances, and reaching the earth, may there
meet with such resistance as to compel them to traverse any convenient conductors
in exact proportion to their respective conductiveness, in obedience to Ohm's well
known law.
Hence it is that telephone lines and systems dependent upon the earth as a
common return are often adversely affected to a serious extent by a leakage from
electric light and power systems as well as by natural earth currents and atmospheric
electricity. For, although it is customary for all electric lighting systems, both
arc and incandescent, to be operated in conjunction with the ordinary "metallic
circuits," thus dispensing with the use of the earth for the return circuit, the high
potential dynamo currents, in their efforts to follow the shortest paths, or paths of
least resistance from one electrode to the other, will leak through the covering of
the wires, over the insulators and down the poles to the earth, in quantities pro-
portioned to the electro motive force of the current, the electrical potential at

page_text: various parts of the circuit, and the defects in the insulation. These escaping
currents after reaching the earth tend to proceed by the paths of least resistance
to the dynamo electrodes of opposite polarity, diffusing themselves all over
contiguous conductors in exact proportion to the various resistances offered to their
transmission; be those conductors metaliferous veins, subterranean streams of water,
or the metal conductors of other electrical systems. Thus in a town or city,pro-
vided with an extensive system of telephone wires, connected, as is customary, to
the municipal water and gas pipes, these fugitive currents from electric light or
..power metallic circuits find the telephone ground wires and lines a very convenient
and ready means of completing circut, to the serious impairment of the efficiency of
the sensitive telephones.
The "mixed or metal and earth circuits of the modern single trolly electric
railways, now being so largely and rapidly introduced, although the currents used
for the propulsion of the cars are less intense, or of much lower electro motive
force than the electric light currents, are more disastrous to telephone interests by
reason of their entire volume being constantly poured into the earth through the
motors of every moving car, thence being diffused over all contiguous conductors,
the water and gas pipes with their attached electric wires being thus liberally
.utilized. Hence as long as the conducting wires of the sensitive telephones are
connected to the earth, so long will the satisfactory character of the telephone
.service be impaired by extraneous or leakage currents.
My invention furnishes a system of "compound metallic circuits" which can
readily be adopted as a substitute to the ordinary two wire metallic circuits and
applied to any existing exchange system or switch board without any inconvenient
and objectionable multiplication of wires, and without change whatever in either
. the switch board, or switch board methods or connections beyond the simple
substitution, of the "artificial ground "connections in place of the usual earth
connections, and yet afford all the immunity from interference from extraneous
currents leaking from the earth secured by the adoption of the ordinary "two wire
-metallic circuits," and at but a small fraction of their cost.
It is not of much practical importance what location upon the supports of
aerial systems, or in the conduits of underground systems, shall be allotted to
the "artificial ground" conductors, or what their position shall be relatively to the
direct wires of the system, but I prefer to place them beneath the aerial wires, as
near to the earth, and as far from the direct wires as may be convenient, and in
the centre of the underground cables as far as may be practicable.
flexibility of my invention is being readily adapted to any existing conditions
being one of its chief recommendations and placing it far in advance of any
means heretofore devised for the accomplishment of the same purpose.
.
The
Having thus endeavoured to explain the object and nature of my invention, I
will.now proceed to describe it in connection with the accompanying drawings.
Fig. 1 represents my invention applied to a number of single electric wires
following the same route;
Fig. 2 as applied to an entire exchange system;
Fig. 3, as applied to one section of an exchange only, with the "artificial
ground" connected to the earth at the central office; while
Fig. 4 is intended to illustrate the manner in which circuits are completed
between stations connected to the "artificial ground," and those which are still
connected to the earth.
Recurring to Fig. 1, a copper wire, or other wire of relatively large conductivity,
is represented by the heavy line R connecting the various telephone or telegraph
stations, indicated in order to avoid complication by the single main line connections
of the telephone transmitters T, T2, T3, and T. This wire R, of large con-
ductivity, forming as it does, a common return wire for all the direct wires, is used
in identically the same manner as the earth in mixed circuits, being in reality an
artificial substitute for the earth. Hence the term "artificial ground."
Supposing the direct wires 1, 2, 3, and 4 to be constructed of No. 14 steel wire,

page_text: the resistance of which is 75 ohms per mile, the "artificial ground" wire R, should
be of Nos. 10 or 12 copper wire or other similar conductor, offering between
the two points at which the terminals of any single line are connected to it,
approximately one tenth, or better still, one twentieth, the resistance of the direct
wire between the same points. Thus if the direct wire No. 1, with its normally
included instruments T and T, should measure 100 ohms, or better still only
5 ohms, between the points at which the line 'No. 1 is connected to it. In like
manner did line 2 and its included electrical apparatus, T2, T2, measure 1000 ohms
between the points at which the terminals are connected to the "artificiál
ground" R, then the latter should measure 100 ohms, or still better only 50 ohms,
between the same points. Under these conditions the electrical undulations pro-
duced upon the direct wires by the vibrations of the transmitters diaphragms,
will be almost wholly confined to their own circuit, the high conductivity of the
"artificial ground" R, preventing any appreciable leakage from one circuit to the
other. This would more certainly be the case at the very time when such leakage
would be most objectionable. That is, while two parties are engaged in a
telephonic conversation the resistance of the hand phone and transmitter coils
being then in circuit and offering a largely increased resistance to the passage
of extraneous or leakage currents from the other wires. Thus were two parties
engaged in conversation from stations T & T of line 1, at the same time that
other parties were talking from T2, and T2, over line 2, there would be no serious
or objectionable interference as long as the resistance of the "artificial ground "R,
bears the proportion to the resistance of the direct wires 1 and 2, but the currents
in motion upon each direct wire will be almost wholly confined to their own wire
and that portion of the "artificial ground" wire extending between the two stations.
In like manner all four wires may be in use simultaneously without any serious
mutual interference, or one station may ring up the other station on the same
wire, without interfering with the conversations on the other wires of the system,
the currents from the magneto generator or the galvanic battery, like those set
in motion by the microphone or transmitter batteries, preferring to confine
themselves to their own direct wire and the low resistance'"artificial ground,"
rather than encounter the much larger resistance offered by the other direct wires
and their telephones or other included electrical apparatus. It will thus be
clearly seen that by the substitution of a single return wire in place of the earth,
all connection with the earth is severed, to the perfect exclusion of earth currents,
atmospheric electricity, the leakage between contiguous telegraph or electric light,
and power systems, thereby gaining all the advantages of the ordinary two wire
metallic circuits, by the addition of only a single wire, if that wire is of the proper
conductivity. Hence the term "compound metallic circuits."
In Fig. 2, I have represented five stations of a telephone or other electrical
exchange system entirely disconnected from the earth, and connected to the
artificial ground instead. By means of the usual switching appliances of the
general office C, any two of the direct wires 1, 2, 3, 4, or 5, can be connected
together in complete metallic circuit, or the central office telephones or other
electrical apparatus, can be connected to either of the five lines, as they are.in
the figure represented as being connected to line five. While the central office is
thus engaged in conversation with the most distant station T, over a circuit con-
sisting of the direct wire 5, on one side and the entire length of the "artificial
ground," on the other, any two of the remaining stations may be placed in
communication with each other by the central office terminals being connected
together in the usual manner. If T and T2, are thus connected, the circuit would
consist of the two direct wires 1 and 2, and included devices, and that portion of
the "artificial ground" between the points at which the ground side of the two
station instruments T and T2 are connected to it. Thus any number of exchange
"wire as a
stations may be connected to and served by an "artificial ground
substitute for the earth, it only being essential that the resistance of that portion
of the "artificial ground" R, included in the circuit should bear relatively to the

page_text: resistance of the two direct wires, approximately the proportions mentioned above.
It is frequently the case that serious interference with a telephone exchange
service by extraneous or leaking currents is experienced in only certain localities
or on certain routes, while the other sections of the exchange or other routes, are
comparatively exempt from such disturbances, these conditions depending largely
upon the extent and character of the electric system from which the disturbance
comes, and the character of the earth to which the telephone lines are immediately
connected. In such cases it is unnecessary to incur the expense of applying the
"artificial ground" to the entire system, its application to the routes and wires
adversely affected serving every purpose. But it is manifestly impracticable
to satisfactorily operate purely "metallic" circuits in direct connection with
"grounded circuits." Hence the modification shewn in Fig. 3, is necessary.
As before R represents the "artificial ground" with the five lines and stations
connected to it precisely as represented in Fig. 2, but with the "artificial ground'
connected to the natural earth at the central office. Any of these stations on the
"artificial ground" system can be connected to the central office or to each other,
and all the talking and calling circuits will traverse the metallic circuits only, as in
Fig. 2, but some slight disturbance from extraneous currents from the earth, will
still be experienced by reason of their following the ground wire to the "artificial
ground" and thence over the subscribers' wires and to the earth again over
insulators and down the poles. But even this arrangement of the artificial ground
connected to the earth at the central office, or any other convenient locality will
eliminate seventy five or eighty per cent. of the trouble arising from the leakage on
the grounded circuits.
"
Fig. 4 is designed to shew the necessity of grounding the "artificial ground" at
the central office or elsewhere, as described above in connection with Fig. 3, as
long as any of the subscribers' wires in the exchange system remain connected to
the natural carth. It will be readily seen that no "circuit" will exist between
grounded stations to, and "compound metallic circuit". T³, were not the "artificial
ground" connected to the earth at some point. But connected to the earth as
represented, the return circuit is completed from T5, through the "artificial ground
to the earth at the central office, and through the earth to the direct wire and
station ; and so with any other stations.
"
By substituting my artificial ground in place of the earth between the central
office and the station to, and disconnecting the "artificial ground" R, from the earth
at the central office, and connecting it to the artificial ground on the other route
extending to the station to, we should have my system applied to two routes, and at
once see the increased necessity for providing for a high conductivity or low
resistance "artificial ground" wire near the central office with a gradual rise in
resistance and fall in conductivity toward the more distant station. Otherwise the
resistance of the "artificial ground" between stations to and T5, the whole of which
has to be traversed by the microphone currents when stations to and T are connected,
would be too great, and serious leakage would occur over lines connecting inter-
mediate stations with each other, or in the case of "magneto or normally
"grounded" switch-boards, with the "artificial ground" at the central office.
As soon as the "artificial ground" is applied to the entire exchange, and all
stations are disconnected entirely from the earth, there is no longer any necessity
for maintaining the "artificial ground" in connection with the earth at the central
office or elsewhere, and the moment this, the last earth connection is removed, the
entire system is converted into a "compound metallic circuit "system and entirely
relieved from all interference or leakage from the earth.
It is not claimed that the use of an "artificial ground” offering even one-twentieth
of the resistance of the direct wire, will entirely prevent conduction or leakage
.from one circuit to another. That is forbidden by the terms of Ohm's law, which
correctly states that a current of electricity from any source or any electro-motive
force, will divide among any number of paths offered it precisely in proportion to
their legal individual resistances; but I do claim that the currents leaking over

page_text: from one circuit to another in my artificial ground and compound metallic circuit
system, if constructed in accordance with the foregoing Specification will be so
small as not to interfere to any appreciable or serious extent with the satisfactory
working of the telephone. But the more nearly the conductivity of the "artificial
ground" approximates the conductivity of mother earth, the better will be the
result. When it is inconvenient or impracticable to reduce the resistance of the
artificial ground to the requisite degree, increasing the resistance of the direct wire
will accomplish the same result.
While the drawings and foregoing Specification may seem to refer especially to
aerial lines and single wires, my device is equally applicable to cable systems; either
aerial-or underground. The cables containing the conductors for the subscribers"
or direct wires may be constructed each with a central core, composed of a large
copper wire possessing the requisite conductivity to serve the purpose of an "arti-
ficial ground"; or a special wire for aerial cable systems or a special insulated
wire or cable for underground cable systems can be utilised with just as satisfactory
results, provided all the conditions as to conductivity and insulation as described
above are present.
In like manner while I have illustrated and described my invention mainly in
connection with telephone lines and systems, it is equally applicable to any known
telegraph or electrical system which it is found necessary or desirable to disconnect
from the earth and operate on metallic circuits.
It is well known to me that even the ordinary metallic circuit consisting of two
separate and distinct wires is no protection from "induction" proper, and I do not
claim that my device will eliminate the evils of induction, but
do contend that it
does eliminate the evils of conduction or leakage, which are the greatest enemies of
telephones or other sensitive electric systems and allows the electrician a better
opportunity to introduce the well-known anti-induction cables and the "trans-
position of direct wires, in order to still further improve the operation of
the instruments by neutralising or eliminating induction. But my invention is not
to be confounded with any of these "anti-induction" devices, having an entirely
different and much more important mission, in protecting telephones and other
electric systems from the more serious evils of conduction and leakage.
Having now particularly described and ascertained the nature of the said
invention, and in what manner the same is to be performed, I declare that what
I claim is
1. In combination with a system of ordinary electrical conductors, such as
telephone or telegraph wires and including electrical apparatus, of one or more
conductors of comparatively low resistance insulated upon the earth and forming a
substitute for the earth to which the terminals of all the direct wires are connected,
substantially as and for the
purpose described.
2. In combination with a system of line wires including translating devices, of
a common return conductor insulated upon the earth, and connected to the terminals
of the line wires, and of comparatively low resistance, or high conductivity to
which the terminals of all the line wires are connected, substantially as and for the
purpose set forth.
3. In a telephone exchange or other electrical system, consisting of a number of
wires radiating from the central office switch-board to the places of business or
residence of subscribers and equipped at the central station and at the local stations
with the usual appliances in combination with a series of metallic conductors of
comparatively low resistance, radiating likewise from the central station and
following the different wire routes and insulated from the earth, thus forming a
system of "artificial grounds" to which all other conductors of the system are
connected, both at the central office and the local stations, instead of to the earth,
substantially as and for the purpose described.
4. In a telephone or other electrical exchange system, the combination of a
number of subscribers' lines radiating from a central office and including the

page_text: necessary working apparatus with electrical conductors of large conductivity and
low resistance, constituting an "artificial ground or substitute for the earth, to
which subscribers' lines are connected at their distant ends and which are insulated
from the earth at all points save one where they are connected to a ground switch,
whereby the system can be converted into a compound metallic circuit" system
by breaking connection with the earth, or can be worked in connection with the
earth and another of ordinary "mixed" circuits, at will, substantially as and for
the purpose described.
Dated this 30th day of September 1890.
C. E. MCCLUER,
By L. W., Per. F. B.