Safety Cut-outs for Electric Circuits.
Year: 1897

page_text: Date of Application, 9th Feb., 1897--Accepted, 27th Mar., 1897
Safety Cut-outs for Electric Circuits.
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 (as communicated to us from abroad by Siemens.
& Halske of Berlin in the German, Empire, Electrical Engineers) and in what
manner the same is to be performed to be particularly described and ascertained
in and by the following statement :-
This invention relates to an improved construction of safety cut-outs for high
tension electric circuits wherein the continuance of a luminous arc after the melting
of the fusible metal is prevented by forming a channel containing the fuse of such
a length that no arc can pass through the same after the fuse is burnt, while at the
same time the channel is made of such a form that the distance apart of the pole
plates or terminals of the cut-out remains of the same moderate dimensions as in
existing cut-outs.
The construction of the cut-out for the above purpose is shewn on the
accompanying drawing in which
Fig. 1 shews a vertical section, and
Fig. 2 a developed peripheral section.
The body of the cut-out, made of suitable insulating material, is constructed of
cylindrical form and has a number of peripheral passages formed through it,
parallel to its axis. These passages are connected together in sets of three by
means of horizontal passages r that respectively connect the top of the middle
channel with one side channel and the bottom thereof with the other side channel
thus forming together a long channel of zigzag form. Into these channels are
introduced the fuse wires or strips ss of corresponding zigzag form the ends of
which are soldered respectively to the to the upper and lower contact plates or pole
surfaces k, while the horizontal passages rare filled in with insulating material,
whereby the zigzag channel through which the fuse passes is entirely enclosed by
insulating material. Thus it will be seen that the fuses and their channels have a
length nearly equal to three times the length of the body of the cut-out so that an
electric arc which may possibly be momentarily formed in the passage at the
moment of the melting of the fuses, would immediately become extinguished.
In order to provide a free escape for the gases produced on the burning of the
fuses, lateral openings o are provided communicating with each of the channels, such
openings being so arranged as to lead the issuing gases as much as possible away
from the pole surfaces k of the cut-out.
With the object of still farther preventing the possibility of those metallic
vapours coming in contact with the plates k k and thus establishing an external
short circuit between them, these plates are entirely covered in, on the one hand by
an insulating cap with downward projecting flange d, and on the other hand by an
upward projecting flange d' on the insulating base.
The other metallic parts of the cut-out that serve to connect it with the circuit.
such as the screws a, also require to be preserved from contact with the metallic
vapours, in order to prevent their forming a short circuit for the arc; this may be
effected by suitably enclosing such parts by means of insulating material Z.
The insulating material for forming the body of the cut-out requires to be of
such a refractory nature as to withstand effectually the intense heat of the are

page_text: momentarily produced on the burning of the fuse, so that ordinary insulating
material such as porcelain, cannot be used for the purpose, as it would become
melted by the electric arc, and in this condition would constitute a conductor
favouring its continuance.
According to the present invention cement is employed for forming the body, as
it has been found that this material, while it possesses good insulating properties,
effectually withstands the heat of the arc, and at the same time offers the requisite
strength and resistance to atmospheric influences.
In order to prevent the possibility of mistakes being made by the use of a
cut-out on a circuit the fuses of which are not properly adapted to the maximum
strength of current allowable in such circuit, the central bore of the cut-out body
through which passes the stem b connecting the upper pole plate k with the one
terminal of the circuit, is, for a cut-out adapted to a current of a certain strength,
made with an enlargement of a certain size, and the central stem of the base is
formed with a corresponding enlargement in which may conveniently be a screw
nut, so that on fitting a cylindrical cut-out body on to the base, it can be at once
seen by comparing the enlargement of the bore with that of the stem, whether the
cut-out is correctly adapted to the circuit. Figure 3 shews by way of example six
different configurations of the bore adapted to as many different classes of cut-outs
for currents of different strengths the first being adapted for a central stem without
an enlargement, the next four for stems with enlargements of four different heights,
and the last for a stem enlarged, along its entire length.
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 :-
1. A safety cut-out wherein one or more fuses are contained within closed
zig-zag or serpentine channels so arranged as to be of considerably greater length
than the distance between the pole plates or terminals to which the ends of the fuse
are attached such passages being provided with lateral holes for the escape of
the metallic vapours resulting from the burning of the fuse, substantially as
described.
2. In a safety cut-out such as is referred to in the first claim, the combination of
a block of insulating material, having zig-zag channels containing correspondingly
formed fuses having their ends fixed to pole plates k'at the top and bottom of the
block, lateral openings o for the escape of the metallic vapours from the channels,
and flanges d on the cap and base that cover the pole plates, so as to protect these
from contact with the said vapours, substantially as and for the purposes described
with reference to the drawing.
3. The use of cement as refractory insulating material for the construction of
channels containing the fuses of safety cut-outs, substantially as described.
4. In safety cut-outs such as are referred to in the first claim, insuring the use of
a body with fuses properly adapted to the maximum strength of current of the
circuit, by forming the body with a longitudinal perforation which is made with
enlargements of different sizes, for fuses of different degrees of strength which
enlargements fit corresponding enlargements on a stem of the cut-out which passes
into the said perforation substantially as described.
Doted this ash 1... f
1607
ABEL & IMRAY,
Agents for the Applicants.