A New Construction of Underground Conduits for Electric Conductors.
Year: 1892

page_text: Date of Application, 17th Oct., 1892-Accepted, 10th Dec., 1892
COMPLETE SPECIFICATION.
A New Construction of Underground Conduits for Electric
Conductors.
I, THOMAS WALLACE of 3 Montpelier Terrace, Knightsbridge, London W.,
Engineer, 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:-
The object of this invention is to provide a new and useful conduit to be used
under the footways and carriage ways of cities, towns, and other places, for the
accommodation and protection of electric wires or cables; also to provide a con-
venient method of constructing the same. The conduits constructed according to
this invention will mainly consist of continuous passages, preferably of rectangular
section, having their sides, bottom, and top formed, in position, of asphalte, concrete,
or other suitable material but preferably of a concrete composition of Portland
cement. The top of the conduit may be formed partially of wood or iron as will be
hereinafter described. The conduit may have branches in any desired direction, and
the whole conduit with its branches is preferably constructed so that there are no
joints either in the top, bottom, or sides. If necessary, the conduit may be drained
of any water accidentally introduced, by connecting the lowest points of it, through
a trapped drain pipe, to the common sewer. The conduit may be ventilated if
necessary, either by connecting it with special vertical ventilating tubes, or by
other means, one convenient method of ventilation being to connect the conduit by
pipes with street lamp-posts specially constructed in such a manner that the heat
of the lamp is utilised to promote a draught through the ventilating pipes.
An important feature of my invention consists in providing suitable rollers,
preferably of insulating material, on which the cables will rest, such rollers being
free to turn on the spindles which support them for the purpose of facilitating
the introduction or renewal of cables by reducing frictional resistance to the
longitudinal movement of said cables.
In describing the manner in which this invention is to be performed, I refer to
the accompanying drawing in which,
Fig. 1 is a longitudinal section, and
Fig. 2 is a plan, of a portion of a conduit having a branch at right angles.
Fig. 3 is a cross section through a conduit.
Figs. 4 and 5 are cross sections through conduits in course of construction.
Similar letters refer to similar parts throughout the various figures of the
drawing.
The sides a, a, and the top and bottom b, b, are of concrete or other suitable
material capable of being formed or moulded in position.
c, c, are stout pieces of kiln dried wood, preferably creosoted or dipped in
asphalte. They are placed across the conduit as shown for the purpose of
strengthening the top thereof, and also to facilitate the construction and opening
up of the conduit for making connections.
e, e, are rollers of insulating or other material, carried on the spindles f, f, for
the purpose of supporting, guiding, and insulating the cables which the conduit is
to accommodate. For the purpose of supporting the spindles f,f, their ends may
be embedded into the sides or bottom of the conduit as shown at k, or they may
be rivetted into conveniently supported metal strips or plates as shown at i and j.
The rollers, with their supporting spindles and frames, are placed at such
intervening distances as may be convenient for supporting the cables, or wherever
their presence would be useful in reducing friction when cables are drawn through
the conduit. The rollers are preferably made up of short lengths of, say, half an

page_text: inch each in order that any part may revolve independently. In the conduit
illustrated in Figs. 1, 2, and 3, some of the rollers are arranged horizontally at
suitable intervals along the conduit in such a way as to conveniently support three
rows or tiers of cables at k, l, m, others being placed vertically at the corners to
act as guides to those cables which are to be carried at right angles up the
branch conduit.
n, & o, are portions of cable in position.
The most convenient and economical method known to me for constructing
these continuous conduits is as follows:-A trench is dug in the ground of sufficient
depth and width to allow space for the conduit with its sides bottom and top. The
bottom, (assuming the conduit to be rectangular), is then laid over the whole width
of the trench. I then take three pieces of timber of convenient length, and having
such transverse sections that when placed together they form a mould for the interior
of the conduit as shewn in Fig. 4, which is a section of a conduit in course of con-
struction. Having placed this mould in the proper position I proceed to form the
walls of the conduit by filling in concrete material at the sides of the mould,
which not only forms a core but also a guide as to the proper height of the sides.
The middle piece of timber forming the mould, is tapered to permit of its being
withdrawn for the purpose of loosening the mould in the conduit when the concrete
The middle or wedge piece may be tapered either transversely as shown
in Fig. 4, or longitudinally as must necessarily be the case in constructing a conduit
of the section shewn in Fig. 5. The mould having been loosened in the conduit
by withdrawing the wedge piece, it can be moved forward in readiness for con-
structing another length of conduit. To complete the conduit as shewn in
Figs. 1, 2, 3 and 4, I place the pieces of timber c across the top and completely
fill the remainder of the trench with the concrete material, having first placed in
position the brackets or supports i and j carrying the spindles and rollers.
has set.
In places where extra strength is necessary or where access to the conduits is not
likely to be required, I may construct conduits having other than rectangular
sections, such, for instance, as oval sections. In such cases the wedge piece of the
interior mould may be tapered longitudinally, so that the sides, bottom, and top
may be formed at one operation, and the mould withdrawn or otherwise operated
from the open end of the conduit; and to further facilitate the operation of the
mould, the wedge piece itself may be made in two parts as shown at p in Fig. 5,
the two parts being each longitudinally tapered in opposite directions at the joint p.
I may use metal moulds and wedges for the interior of the conduits, and I do not
confine myself to the use of one continuous wedge piece, but where it may be con-
venient or desirable, I may employ any number of separate wedges for the purpose
of maintaining the mould in its proper form and position, and facilitating its
removal. By this part of my invention I provide, generally, a collapsible..mould
for facilitating the construction of my continuous conduits. The various parts. of
the moulds will be held together by suitable removable bands or straps while the
concrete is being placed round them.
I may gain access to the conduit by providing manholes of ordinary construc-
tion at suitable points, but for the purpose of gaining access thereto at any
particular spot with the object of making connections, with, any of the cables or
wires therein, I remove a portion of the concrete top of the-conduit, and raise one
or more of the wooden slabs c.
It is evident that iron or steel plates might take the place of the wooden slabs
or pieces c.
By this invention I provide a conduit which is impervious to moisture, and which
has all its parts accessible without incurring great expense.
My conduit will
accommodate a very large number of cables in proportion to its dimensions and
cost, and said cables being kept drier than heretofore, their insulation will the
longer retain perfect. The cables will be better insulated from the fact that they
are suspended or supported on the above described rollers instead of lying on the
bottom of a conduit as is commonly the case, and being suspended in a conduit of

page_text: non conducting material there can be no loss or retardation of the electric currents
due to their inductive action, as would be and is the case where the conductors or
cables are placed in conduits composed of metal.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is:
1. An underground conduit for electric conductors, constructed mainly of
concrete or equivalent material, having its sides, bottom, and top continuous and
without joints, and having the covering plates or slabs e, or equivalents thereof, all
substantially as and for the purposes described.
2. An underground conduit for electric conductors, which is fitted with rollers
for supporting and guiding the said conductors, substantially as described.
3. An underground conduit for electric conductors, having its sides, bottom, and
top continuous and without joints, said conduit being constructed mainly of concrete
or other equivalent material and having the covering plates or slabs c, and fitted
with rollers of insulating material or otherwise, all substantially as and for the
purposes stated.
4. The above described method or process of constructing continuous conduits of
concrete or similar material with the aid of collapsable moulds having wedge
pieces or wedges for facilitating their withdrawal from the conduit, substantially as
described.
1000
For the Applicant,
FRANK WM. DODD,
Engineer.