AN IMPROVED METHOD OF AND MEANS FOR PROVIDING GROUND OR EARTH CONNECTIONS FOR ELECTRICAL CIRCUITS."
Year: 1882

page_text: LETTERS PATENT to Amos Emerson Dolbear of Somerville Massachusetts
United States of America now of Queen Victoria Street, in the City of
London for an invention of "AN IMPROVED METHOD OF AND MEANS FOR
PROVIDING GROUND OR EARTH CONNECTIONS FOR ELECTRICAL CIRCUITS."
PROVISIONAL SPECIFICATION left by the said Amos Emerson Dolbear at
the Office of the Commissioners of Patents on the 21st March 1882.
AMOS EMERSON DOLBEAR of Somerville Massachusetts, United States of America,
now of Queen Victoria Street in the City of London "AN IMPROVED METHOD OF
AND MEANS FOR, PROVIDING GROUND OR EARTH CONNECTIONS FOR ELECTRICAL
CIRCUITS
"
What is technically called a good."ground" in telegraph systems consists of an
earth-connection of such a character that the electrical resistance is reduced to the
lowest practicable extent, and this result is generally obtainable in cities or towns
by connecting the wires to the gas and water mains which have an extensive
surface-connection with the ground.
•
Since the invention, and during the use of the telephone great inconvenience has
been occasioned by the difference of electrical potential between points at a distance
of say more than about a mile from each other, this difference of potential being in
some instances so great as to maintain a very considerable current of electricity in
any closed circuit between the said points or places and thereby cause great incon-
venience in the working. Sometimes the current is strong enough to work the
well known "Morse" instruments without any other source of electricity. The
reason is that the various batteries having terminals in the same place or neighbour-
bood charge the ground in the vicinity thereof and in distributing the electricity
any closed circuit extending to a place of lower potential will furnish a better
conductor than the earth itself. It therefore becomes necessary to provide a
ground" possessing the additional quality of an unvarying zero potential or as
nearly so as possible.

page_text: To accomplish this object I propose to extend the lines requiring such a
"ground" to any convenient body of water of sufficient magnitude and then
connect the same with a suitable conducting body say a metal plate of sufficient
area and arrange the same in contact with the water. When two or more circuits
are to find their "ground" in the same body of water they should be insulated
from each other and each should have a separate"ground" as far removed from the
other circuit or circuits as practicable.
"
The same arrangement should be provided at both ends of the line. Inasmuch
as the ocean or large rivers and other bodies of water have a degree of conductivity
much higher than that of the material of the land, it follows that their differences
of electric potential will be less local in their action and hence such bodies placed
in water as above described are less likely to have a notable difference of potential
than any substance or body on land and are therefore better suited to be the
"ground" for such circuits as need to be free from the disturbances known as earth
currents.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Amos Emerson Dolbear in the Great Seal Patent Office on the
21st September 1882.
AMOS EMERSON DOLBEAR, of Somerville, Massachusetts, United States of
America, now of Queen Victoria Street, in the City of London. "AN IMPROVED
METHOD OF, AND MEANS FOR PROVIDING GROUND OR EARTH CONNECTIONS FOR
ELECTRICAL CIRCUITS
1
"3
The said Invention relates to an improved method of and means for providing
ground or earth connections for electrical circuits and is illustrated in the
accompanying drawing or diagram in which B represents any place, (say Boston,)
Pa second place many miles away, (say Providence) and D the coast line between
them.
What is technically called a good "ground" in telegraph systems, consists of an
earth connection of such a character that the electrical resistance is reduced to the
lowest practicable amount and this result is generally obtainable in cities or towns
by connecting the wires to the gas and water mains which have an extensive
surface connection with the ground.
Such "grounds" have long been regarded as practically perfect, and this would
be the fact but for disturbing conditions which have been hitherto overlooked.
These disturbing conditions are due to the facts that there is a great difference of
electric potential, between two places several miles apart, due to natural causes,
and that the electric potential of gas or water pipes is affected not only by the
natural potential of the places where they are buried but also by the number, and
electric character of the circuits grounded upon them.
Referring to the drawing. Suppose for example;-there is but one line grounded
in Boston and but one in Providence and that this line is between Boston and
Providence and is grounded on the gas or water pipes at those places; then the
"grounds" would be regarded as practically perfect at both of these places; and
would be in fact practically perfect, but for one circumstance viz-the natural
variation or difference of potential between the two places, which would cause
what are properly called earth currents over the line; which earth currents exist
whenever there is a difference between the potentials at the two places, and vary
in strength in direct proportion to the difference between the two potentials. But
in fact there are usually such numbers of lines grounded at cities or towns of any
importance as to very greatly affect the potential thereat; consequently the actual
condition of lines grounded as described, at both ends is that one end of these lines
is nearly always at a potential considerably different from that of the other end,
so that varying currents pass whenever the circuit is closed. This result has
frequently been observed when the strength of these currents has been sufficient to
work the ordinary telegraph instruments; and when it has been attempted to use
magnéto telephones in such lines, the disturbance of the currents is very serious
and rarely intermitted. This result is commonly attributed to induced currents
and earth-currents without suspicion bitherto, so far as I am aware of the main
cause, viz, the difference between the potential of the "ground" of the line caused
by the difference between the number and electric character of other lines grounded
at the two places.
My invention is carried into practice by providing a grounding conductor at
each end of the line, and placing these grounding conductors in the same body of
water so that each grounding conductor will always remain at substantially the
same potential as all of the others; I thereby provide “grounds” having not only

page_text: the well-known requisite of low resistance, but having the additional feature
(hitherto wholly disregarded, so far as I know) of always remaining at substantially
the same potential. That is to say the distinguishing characteristic of my invention
is the use of grounding conductors each carried into the same body of water, one
end of the line being grounded upon one of these grounding conductors and the
other end of the line upon a like grounding conductor.
In the said diagram a, a, a, a³, represent a number of lines between B and P;
t and t represent telephones or other instruments at B and P; C represents a
number of grounding conductors at B and C¹ represents grounding conductors at P.
Either of the lines, a, a', a², or a³, may be connected with either of the instru-
ments t, t, and with either of the grounding conductors C, C, and when thus
connected, the line will be substantially free from earth currents (so called)
including all currents due to difference between the potentials of the "grounds
at B and P, and almost wholly free from interfering currents of any kind, and will
therefore be well adapted for the use of magneto-telephones and other instruments
affected by weak currents.
In order to prevent any difference of potential each grounding conductor should
be carried far enough into the water to ensure its being always at the potential of
the water, that is to say substantially at zero,-and the surface contact between
the metal of the grounding conductor and the water should be made ample for the
same reason. The best method of accomplishing these objects is that indicated in
the diagram where the grounding conductors are copper wires brought together
into a cable, for convenience, at the proper point but insulated from one another
and diverging as they enter the water so as to ensure that the potential of each of
them will remain always near zero.
>
In practising my invention in grounding electric lines it is necessary to bear in
mind the familiar requirement of a ground of low resistance, and the novel require.
ment of the connection of the grounding conductors with the same body of water
in such a manner that the potential of any one current materially differs from the
potential of the water, which is substantially zero.
Having thus fully described my said Invention and the manner of performing
the same I wish it understood that I claim;—
The improvements above described consisting in grounding each end of an
electric line-wire by connecting it with a grounding conductor, and placing the
conductors in the same body of water, as, and for the purpose specified.
In witness whereof I the said Amos Emerson Dolbear have hereunto set my
hand and seal this first day of September in the year of our Lord. One
thousand eight hundred and eighty two.