IMPROVEMENTS IN ELECTRIC FUSES
Year: 1881

page_text: LETTERS PATENT to David Johnson, Barrel Well House, Chester, and Ernest
Spon, 121, Bishopsgate St. Within, London, for an Invention of "IMPROVEMENTS
IN ELECTRIC FUSES."
PROVISIONAL SPECIFICATION left by tho said David Johnson and Ernest
Spon at the Office of the Commissioners of Patents on the 28th June
1881.
DAVID JOHNSON, Barrel Well House, Chester, and ERNEST SPON, 121, Bishopsgate
Street Within, London. "IMPROVEMENTS IN ELECTRIC FUSES."
.
This Invention has for its object the improvement of tension or spark fuses, so
that they may be rendered more certain in their action and less liable to be affected
by moisture or other causes, which occasion the priming or fuse composition to be
rendered inoperative. In tension or spark fuses as heretofore made, the priming
composition is fired by the passage of electricity or of a spark through it. Tho
circuit is interrupted within the casing of the fuse, and the priming is interposed
in the break. This break is usually formed by stripping the ends of insulated
wire, and dividing the wire so as to cause an interruption across which the spark
is caused to leap. In fuses heretofore made there are but two points, from one of
which the spark is caused to leap to the other, but by our Invention we introduce
additional points so that the spark is divided into two or more parts, and thus has
better means of access to the fuse composition, and secures with more certainty the
firing of the fuse, so that a cheaper and less sensitive fuse composition can if
necessary be used.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said David Johnson and Ernest Spon in the Great Seal Patent Office
on the 27th December 1881.
DAVID JOHNSON, Barrel Well House, Chester, and ERNEST SPON, 121, Bishopsgate
Street Within, London. IMPROVEMENTS IN ELECTRIC FUSES."
EE
This Invention has for its object the improvement of tension or spark fuses, so
that they may be rendered more certain in their action and less liable to be affected
by moisture or other causes which occasion the priming or fuse composition to be
rendered inoperative.
In tensions or spark fuses as heretofore made the priming composition is fired by
a current of electricity, or by a spark passing through it. The circuit is inter-
rupted within the casing of the fuse, and the priming is interposed in the break.
This break is usually formed by stripping a portion of insulated wire and dividing
the stripped portion of wire so as to cause an interruption across which the spark
is caused to leap. In such fuses as heretofore made there are but two points from
one to the other of which the spark is caused to leap.
According to our Invention however we introduce additional points, so that the
spark is divided into two or more parts, and thus has better means of access to the
fuse composition, and secures with the more certainty the firing of the fuse, so that
a cheaper and less sensitive fuse composition can be used.
Our Invention is illustrated on the accompanying Drawings, Figs. 1 to 5 of
which are illustrative of an advantageous method of carrying our Invention into
practical effect.
According to this modification two wires are twisted together, as shown in
Fig. 1, an untwisted portion (say of about half an inch in length) being left in the
centre of their length; the wires are then doubled over at the untwisted portion
and inserted in a small tube of paper, metal, or other suitable material, as shown
in Figs. 2, the tube being then filled in with a' composition of vulcanized india
rubber, celluloid, sulphur, cement, or other suitable insulating material to form the
body. When this is thoroughly hardened the end nearest the loop of wire is filed
smooth, and it will then present the appearance shown in Fig. 3, where a repre-
sents the main wires, and b, the subsidiary wires for subdividing the sparks; tho
wires are then connected by means of a plumbago line, and the fuse as thus made
is placed in circuit with a galvanometer, and the resistance caused by the plumbago
line is then reduced to within any required limit by removing a sufficient portion
thereof, and when the required resistance is reached the fuse is removed from the
circuit. The plumbago lines are divided by drawing across them a sharp point so
as to have a break at c and d, as shown in the plan of Figs. 4, and we thus cause
the fuse to be mechanically sensitive and very effective, especially for use with
magneto or dynamo electric machines.
Fig. 5 represents an outside elevation of the fuse inserted into a case containing
fuse composition.
Another modification of our Invention is illustrated in Figs. 6 to 9.
According to this modification, which is especially suitable for use with frictional
electric machines, we place within the loop of two twisted insulated wires, as
shown in Fig. 6, a small piece of wire or other substance which will serve to keep
them a little distance apart, and on each side of this we place a small piece of
insulated or other wire and tie the whole together, as represented in Fig. 7, the
tied end is then transversely cut so as to leave the ends or points of the wires
separated, as shown in Figs. 8; this then forms the fuse head, and may be inserted
into a cap of paper, wood, metal, or other suitable material containing priming
composition, as hereinbfore described, the whole being shown complete in Fig. 9.

page_text: Having now described the nature and object of our said Invention, together
with the manner in which the same is to be or may be performed or carried into
practical effect, we would remark in conclusion that we wish it to be distinctly
understood that we do not claim as our Invention the method of connecting the wire
points by means of plumbago, but what we do claim as the improvements con-
stituting the Invention secured to us under our horeinbefore in part recited Letters
Patent are,-
-
First. The improved method of subdividing the electric spark by causing it to
jump from and to more than one point in the fuse head, substantially as and for
the purposes hereinbefore described.
Second. The improved method of arranging the fuse head with three or more
wires, substantially as and for the purposes hereinbefore described.
Third. The general method of constructing electric fuses, substantially as
herein before described, with reference to Figs. 1 to 5 of the accompanying
Drawings.
Fourth. The general method of constructing electric fuses, substantially as
hereinbefore described with reference to Figs. 6 to 9 of the accompanying
Drawings.
In witness whereof, I, the said Ernest Spon, on behalf of the said David
Johnson and myself, have hereunto set my hand and seal, this Twenty-
third day of December, in the year of our Lord One thousand eight hundred
and eighty-one.
ERNEST SPON. (L.S.)