In recent times considerable attention has been paid to the subject of
laying telegraph cables underground, and various methods have been
devised. In some cases the cables have been covered with an armor of
iron, and in others they have been inclosed in cast-iron pipes. For
telephonic service they are generally inclosed in leaden tubes. What
this external envelope shall be that is to protect the wires from
injury is a question of the highest importance, since not only the
subject of protection is concerned, but also that of cost. It is
therefore interesting to note the efforts that are being made in this
line of electric industry.
[Illustration: FIG. 1. Section of the Pipe Open.]
[Illustration: FIG. 2. Section of the Pipe Closed.]
Messrs. Delune & Co. have recently taken out a patent for an
arrangement consisting of pipes made of beton. The annexed cuts,
borrowed from _L'Electricite_, represent this new system. The pipes,
which are provided with a longitudinal opening, are placed end to end
and coupled with a cement sleeve. The cables are put in place by
simply unwinding them as the work proceeds, and thus all that traction
is done away with that they are submitted to when cast iron pipes are
used. When once the cables are in place the longitudinal opening is
stopped up with cement mortar, and in this way a very tight conduit is
obtained whose hardness increases with time. The value of the system
therefore depends, as in all cement work, on the care with which the
manufacturing is done.
Experiments have been made with the system at Toulouse, by the
Minister of Post Offices and Telegraphs, and at Lyons, by the General
Society of Telephones. Here, as with all similar questions, no opinion
can be pronounced until after a prolonged experience. But we cannot
help setting forth the advantages that the system offers. These are,
in the first place, a saving of about 50 per cent. over iron pipe, and
in the second, a better insulation, and consequently a better
protection of the currents against all kinds of disturbance, since a
non-conducting mass of cement is here substituted for metal.
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