Improvements in Safety Fuse Devices for Electrical Installations.
Year: 1895

page_text: Date of Application, 14th Dec., 1895
Complete Specification Left, 28th Aug., 1896-Accepted, 17th Oct., 1898
PROVISIONAL SPECIFICATION.
[Communicated from abroad by SIEMENS AND HALSKE, of 94 Markgrafen.
Strasse, Berlin, in the Empire of Germany, Electrical Engineers.]
Improvements in Safety Fuse Devices for Electrical Installations.
We, SIEMENS BROTHERS & Co. LIMITED of 12 Queen Anne's Gate,
Westminster, in the County of London, Electrical Engineers, do hereby declare
the nature of this invention to be as follows:-
This invention has for its object to ensure the rapid extinction of the electric arc
which is generally formed on the melting of a safety fuse device and which if
allowed to continue, acts destructively upon the clamps.
For this purpose, according to one arrangement we provide above the strip of
lead or other metal that constitutes the safety fuse, a vertical plate or shutter, that
is pressed down upon the metal strip by a suitable spring. Immediately below the
said shutter there is provided a groove in the base on which the lead strip rests,
so that, when the strip is melted by the passage of an excessive current and by the
arc which is then formed, the shutter, in losing its support is pressed downwards
by its spring and, in entering the groove forms an effectual barrier against the
continuance of the electric arc that may have been formed between the unfused ends
of the lead strip.
In order not to interfere with the reliable working of the fuse, it is necessary not
to subject that part of it to the pressure of the shutter which is intended to be
fused by the excessive current, for this purpose we make that part of the metal
strip on which the shutter rests thicker than the other part, so that the latter
is fused by the current, while the thicker part on which the shutter rests is only
fused by the arc which is then formed, and which is at once extinguished by the
dropping of the shutter.
By preference we provide two such spring shutters, one on each side of the
thinner middle part of the metal strip that is to be melted by the current. The
arc formed between the remaining thicker parts then rapidly fuses both these
causing both the shutters to fall and to cut off the arc from the clamps.
Dated this 14th day of December 1895.
ABEL & IMRAY,
Agents for the Applicants.
Improvements in Safety Fuse Devices for Electrical Installations.
We, SIEMENS BROTHERS & Co. LIMITED, of 12 Queen Anne's Gate,
Westminster, in the County of London, Electrical Engineers, 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 :-
In safety fuses for electrical installations in particular those for domestic
purposes that are not under continual supervision and are yet required to afford.
perfect security against fire, it is essentially necessary that the electric arc produced
on the melting of the fuse shall be with certainty extinguished.

page_text: may
be
The lengths of the usual fuse strips or wires, that is to say the distance apart of
their clamps are however too small to prevent the electrical
that
energy
present (in particular when short circuiting under high tension occurs) from forming
an arc between the clamps on the melting of the fuse, that will continue to burn
and injure the apparatus.
According to the present invention, the rapid extinction of such electric arc is
effected by an automatically acting shutter device as we will describe with reference
to the accompanying drawing, in which Figs. 1 and 2 shew respectively a front
view and cross section of one arrangement with the fuse intact and the shutter
held thereby in a state of tension, while Fig. 3 shews the same arrangement with
the shutter released on the melting of the fuse.
In the base A of insulating material, is formed a groove B, above which is situated
a shutter T also of insulating material. This shutter is formed with a grooved outer
edge round which is passed a helical spring C, the ends of which are fixed to the.
base, and which consequently tends to press the shutter downwards. The shutter
is however held up against this pressure by its lower edge being made to rest upon
the fuse strip S which passes across the groove B. If now, owing to the passage
of an excessive current, the fuse S is melted or burnt, the shutter T in losing its
support will then be rapidly forced down into the groove by the spring C, as at
Fig. 3 and will thus present a mechanical obstacle to the electric arc, which will be
on the point of being formed between the unburnt ends of the fuse.
The arrangement so far as it has been described, and assuming that the fuse strip
or wire is of uniform section throughout, is open to the objection that by the
mechanical compression of the fuse wire by the shutter this may have its physical.
properties so modified that it will no longer operate with certainty in the desired
manner. While a safety fuse that is only subject to the heating action of the
current in the usual manner, can have its action determined with accuracy within
allowable limits, for a given sectional area and strength of current, it will on the
other hand be exceedingly difficult if not impossible to determine the action of such
fuse if it be subject, at the same time to compression. In order therefore not to
detrimentally affect the action of the fuse it is necessary so to arrange the above
device that at the part where the fusion of the strip or wire is to take place, it shall
not be subject to any other action than that of the current, and to subsequently
effect the melting or burning of the part that is subject to the pressure of the
shutter by the more intensive heat produced by the electric arc which is then
formed.
This is effected in the apparatus above described by making the part of the fuse
strip or wire on which the shutter rests of greater sectional area than the other
part, as shewn in the plan view at Fig. 4. so that the thinner parts on each side of
the middle part will be subject to the fusing action of the excessive current, and
this action will not be affected by the compression to which the middle part is
subjected. When these thinner parts are melted by the current an arc will be
formed, by the intense heat of which the thicker middle part will be melted or
burnt and the shutter T will then descend and extinguish the arc by intersecting
the air space which is necessary for its existence.
The above arrangement may still be open to the objection that the arc might be
formed at the clamps of the fuse, thereby injuring them and it is also undesirable
to have two separate parts subject to melt by the current the fuse being preferably
provided with only a single part of reduced section, as in the ordinary fuses.
These objections are obviated by the modification shewn in longitudinal section,
plan and end view, respectively at Figs. 5, 6 and 7.
In this construction there are provided two shutters T T arranged above two
grooves B B in a similar manner to that previously described but resting respectively
upon thickened parts of the fuse strip S ou each side of the reduced centre part
which will thus alone be subject to fusion by excessive current.
By this arrangement, when the fusion of such centre part occurs, the electric arc
is only formed between the thickened parts on each side thereof, so that when the

page_text: parts or parts supporting the shutters are burnt or melted thereby, one or both of
the shutters will drop and thereby extinguish the arc, so that the clamps are
effectually protected against injury.
For renewing the fused strip or wire, the shutter or shutters are raised and a
fresh strip or wire is secured between the clamps in the known manner. Of course,
when the middle of the safety fuse is melted by a less powerful current, the electric
arc may become extinguished before the thickened parts are melted thereby and
consequently without causing the shutter or shutters to drop.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
In a safety fuse device for electric installations, the combination of a fuse strip
or wire having a thickened part or parts and one or more shutters resting upon such
thickened part or parts the said shutters being so arranged that when after the
melting of the thinner part of the fuse strip or wire by excessive current, the said
thickened part or parts is or are also destroyed by the electric arc formed the
shutter or shutters will drop and interrupt the said arc, substantially as described.
Dated this 28th day of August 1896.
ABEL & IMRAY,
Agents for the Applicants.