Improvements in or conneeted with Dry Core Electrical Cables.
Year: 1899

page_text: PROVISIONAL SPECIFICATION.
Improvements in or conneeted with Dry Core Electrical Cables.
We. HENRY SAVage, Electrician, of 14, Nadine Street, Old Charlton, London,
and W. T. HENLEY'S TELEGRAPH WORKS COMPANY, LIMITED of 27, Martin's Lane,
in the City of London, do hereby declare the nature of this invention to he as
follows:-
In
The insulating material of what are known as dry core cables, which are usually
made up of a number of separately insulated wires enclosed in a leaden
tube, is such that it depends for its insulating properties on the
total exclusion of moisture from the inside of the tube. Any moisture entering
the tube either from the ends or through a fault in the tube, such as a flaw or
mechanical damage, lowers the electrical resistance of the insulating material at
that point rendering the wires useless for the transmission of electricity. Before
the cable can be repaired and restored to its former electrical condition the posi
tion of this fault must be determined. This it is desirable, and in some cases
absolutely necessary to do by a system of electrical measurement, which may be
best carried out by means of what is known as a "loop test" wherein a faulty
wire is joined in series with a good wire, running between the same points or
terminals, forming a circuit or loop. It is essential that this second wire shall
be a good one, that is to say its insulation resistance must be many times
greater than the resistance of the fault whose position is to be determined.
dry core cables the presence of moisture affects all the wires in the same degree
that is all the wires in the tube are rendered faulty and it is consequently
impossible to use any of these wires to form a circuit suitable for a loop test,
and it is necessary to use a separate wire, such as another dry core cable, an
overhead line, or any separately insulated wire, which is often impracticable.
The present invention is intended to overcome the difficulty of providing a
suitable return wire, and it consists in the combination with the wires constitut-
ing the cable. of a wire or wires covered with vulcanized indiarubber or other
suitable non-hygroscopic material and forming a centre wire or wires with the
ordinary wires laid up around it, or stranded up with the other wires in any posi-
tion in the cable, or placed outside the tape, braid, or whipping containing the
ordinary wires but within the tube. This wire or wires besides providing a
circuit for locating a fault, being readily distinguishable may be used by the
linesman or jointer to communicate with the exchange or office during the joint-
ing or repairing operations and can be used to communicate between two ter-
minals of the cable during the time the remainder of the cable is useless owing
to a fault.

page_text: Improvements in or connected with Dry Core Electrical Cables.
We, HENRY SAVAGE, Electrician, formerly of 14, Nadine Street, Old Charlton,
London, and now of 28, Craigerne Road, Blackheath, in the County of Kent, and
W. T. HENLEY'S TELEGRAPIE WORKS COMPANY LIMITED, of 27, Martin's Lane,
in the City of London, 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 insulating material of what are known as dry core cables, which are usually
made up of a number of separately insulated wires enclosed in a metallic or vul-
canized rubber tube, is such that it depends for its insulating properties on the
total exclusion of moisture from the inside of the tube. Any moisture entering
the tube either from the ends or through a fault in the tube, such as a flaw or
mechanical damage, lowers the electrical resistance of the insulating material at
that point rendering the wires useless for the transmission of electricity. Before
the cable can be repaired and restored to its former electrical condition the posi-
tion of this fault must be determined. This it is desirable, and in some cases
absolutely necessary, to do by a system of electrical measurement, which may be
best carried out by means of what is known as a "loop testi wherein a faulty
wire is joined in series with a good wire running between the same points or
terminals, forming a circuit or loop. It is essential that this second wire
be a good one, that is to say its insulation resistance must be many times
greater than the resistance of the fault whose position is to be determined. In
a dry core cable the presence of moisture affects all the wires, that is to say all
the wires in the tube are rendered faulty and are therefore not available to form
a circuit suitable for a loop test. It is consequently necessary to use a separate
wire, such as another dry core cable, an overhead line, or any separately insulated
wire, which is often impracticable.
The present invention is intended to overcome the difficulty of finding a suitable
return wire, and it consists in the provision within the cable, of a wire or wires
covered with vulcanized indiarubber or other suitable non-hygroscopic insulating
material and about which the ordinary wires may be laid up, or which may be
stranded up with the other wires in any position in the cable, or be placed out-
side the tape, braid, or whipping containing the ordinary wires but within the
tube. This wire or wires besides providing a circuit for locating a fault, being
readily distinguishable may be used by the linesman or jointer to communicate
with the exchange or office during the jointing or repairing operations and can
be used to communicate between two terminals of the cable during the time the
remainder of the cable is useless owing to a fault.
Havng now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed, we declare that what
we claim is;
In a dry core electrical cable the combination with the wires constituting the
cable of a special wire or wires for use in testing to locate a fault and for other
purposes as described, the said wire or wires being covered with rubber or other
non-hygroscopic insulating material and laid up, stranded or otherwise combined
with the cable wires and enclosed within the tube, substantially as specified.
Dated this 9th day of May 1900.
A. M. & WM. CLARK,
Chartered Patent Agents, 53, Chancery Lane, London.