Improvements in Laying and Insulating Underground Electric Conductors.
Year: 1887

page_text: Date of Application, 1st Feb., 1887.
Specification Accepted, 1st Mar., 1887.
Improvements in Laying and Insulating Underground Electric
Conductors.
I, DAVID BROOKS, of East Washington Lane, Germantown, Philadelphia, State of
Pennsylvania, United States of America, Electrician, do hereby declare the nature of
the said Invention, and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement:-
The object of this Invention is to provide a practicable plan of using, for the purpose
of insulating electrical conductors laid in under-ground tubes or conduits, insulating
material which is normally of a solid or semi-solid character, and must be heated to
render it liquid.
In Patents heretofore granted to me, as for instance, British Patent No. 4824 of 1877,
I have described the use, as a means of insulating electrical conductors laid in under-
ground tubes or conduits, of oil or other liquid insulating material, maintained under
pressure in said tubes or conduits.
My present Invention is intended for adoption in cases where the use of oil or other
liquid insulating material under pressure in the pipes or conduits is not available, the
insulating material used by me in the present case being paraffine, ozokerite, asphaltum,
rosin or other equivalent insulating material, which is normally of a solid or semi-solid
character and must be heated in order to render it liquid.
Underground pipes for containing electrical conductors are usually provided with
splice boxes at intervals of several hundred feet; a length of cable or other conductors
being drawn through the pipe or conduit from one splice box to another and the ends
of adjoining lengths of cable being properly connected before closing the splice box.
When an attempt is made to use, for the purpose of insulating the conductors, a
material other than that which is normally of liquid character, it is a matter of difficulty,
if not impossibility, to properly fill with the insulating material the length of pipe or
conduit between two splice boxes, the insulating material becoming solid and refusing
to flow before it has traversed the length of pipe.
I overcome this objection in the manner which I will now proceed to describe,
reference being had to the accompanying drawing, in which
Fig. 1, is a diagram illustrating a portion of an underground telegraph line
constructed for carrying out my invention.

page_text: Fig. 2, a longitudinal section on an enlarged scale, of part of the line; and
Fig. 3, a transverse section on the line 1-2, Fig. 2.
Each section of the line between the splice boxes, a, is composed of a number of
pipes, a, in lengths of say twenty or twenty-five feet, and these pipes are connected by
means of T-couplings, b, one joint of the T-coupling being placed vertically and being
provided with a suitable closing plug, d.
After a cable of conductors has been drawn through a section of the line from one
splice box to another, I remove the plugs from the T-couplings connecting the different
lengths of pipe, and into that coupling which occupies the lowest position on the
section of the line I pour the insulating material, which has been previously heated to
reduce it to a liquid condition. For instance, in the line shown in the diagram, Fig. 1,
I should commence to fill the pipe at the coupling, 1, the air escaping from one or more
of the other couplings on the line as the filling is proceeded with. As soon as the
lowest portion of the line has been filled with insulating material, I proceed to a higher
coupling and pour insulating material into the same, this operation being repeated in
succession at higher and higher points until all portions of the section of conduit
between the splice boxes have been filled with insulating material, the plugs being
applied to the T-couplings after the pouring of the insulating material into the same
has been completed.
By thus introducing the insulating material at a number of points on the line, each
section to be filled is so short that the material will not harden and obstruct the flow
before it reaches the end of said section. The conductors are thus thoroughly
insulated from one splice box to another.
If desired, the pipe at and near the coupling through which the insulating material is
being poured may be heated in order to ensure a freer flow of said insulating material
through the pipe, and in order to facilitate the escape of air from the pipe, the
coupling in advance of that through which the insulating material is being poured may
be propped up so as to occupy a higher level, as will be readily understood.
Having now particularly described and ascertained the nature of my said Invention,
and in what manner the same is to be performed, I declare that what I claim is :—
1. The improved mode hereinbefore described of applying to electrical conductors
contained in a pipe or conduit, insulating material which is normally of a solid or
semi-solid character, said mode consisting in first drawing the conductors through a
continuous length of the pipe, and then pouring the melted insulating material into the
pipe at a number of points successively along said length, whereby the conduit is filled
by sections with insulating material throughout its length, all substantially as herein-
before specified.
2. The improved mode hereinbefore described of applying to electrical conductors
contained in a conduit, insulating material which is normally of a solid or semi-solid
character, said mode consisting in first drawing the conductors into a length of the
line, and then introducing the melted insulating material into said length of line at a
number of points successively, commencing at the lowest level, the air escaping from
the conduit at the higher levels as successive sections of the conduit are filled with
insulating material, all substantially as hereinbefore specified.
DAY, DAVIES & HUNT,
321, High Holborn, London, W.C.,
Agents for the Applicant.