An Improved Automatic Electric Control or Cut-out.
Year: 1891

page_text: Date of Application, 6th June, 1891
Complete Specification Left, 7th Mar., 1892-Accepted, 9th Apr., 1892
PROVISIONAL SPECIFICATION.
An Improved Automatic Electric Control or Cut-out.
We, HENRY ALABASTER, and TOM ERNEST GATEHOUSE, both of 22 Pater-
noster Row, in the City of London, Electrical Engineers, do hereby declare the
nature of this invention to be as follows:-
This invention relates to means known as safety fuzes or cut outs now employed
on electric circuits to automatically break the circuit when the current is much in
excess of that which it is normally intended to convey, and this invention consists
of an improved automatic device to be used in substitution of such safety fuzes or
cut-outs and so arranged that at a predetermined rise of temperature due to
increased current flowing through a part of the device, the circuit may be either
temporarily broken and automatically renewed after a short period when normal.
conditions are restored, or which need not break the circuit at all, but by the
introduction of special resistance may bring the heating effect of the current back
to its normal condition.
The objections to the use of such known safety fuzes and cut-outs employed to
prevent over heating of the leads and so causing danger of fire are well known.
Among the more serious is the impossibility of insuring the metal or alloy of
which the the fusible wire is made being of unvarying quality.
There is no certainty to their action at any specific rise of temperature of the
conductor, nor can they be depended upon not to fuze even with a normal current.
Moreover when fusion has taken place the circuit is broken and the lamps are
extinguished until another fusible wire has been re-inserted.
Besides forming a series of weak points in an electric light circuit, their vagaries
are a source of continual vexation and annoyance to users of the electric light and
they are now generally considered as an unreliable means of preventing fire unless
what is technically known as a "short circuit" occurs in the mains.
In the invention hereinafter described the apparatus may be arranged to act at
any desired degree of temperature above that produced by the normal current and
the circuit may be broken or not as desired. If broken, the circuit will
automatically re-establish itself in the course of a brief period of time but the
circuit may remain completed through a resistance automatically called into play
which will sufficiently reduce the current to keep the heating effect within the
margin of safety.
To accomplish this object we make use of the well known thermostatic
arrangement of two metals having unequal co-efficients of expansion and this we
make part of the electric circuit, the sectional area of the thermostat being
proportioned to that of the copper conductors. One end of the thermostat which
may be flat or coiled is fixed to one end of the conductor and the other is free to
dip into and rise out of a metal cup, say of iron containing mercury, from which
the other end of the conductor is led away.
The current passes through the thermostat forming a part of the circuit and on
any excess above the normal the slightly extra heating immediately takes effect on
the thermostatic bar and the contact between the end of the thermostat and the
mercury is broken under water or oil if desirable.
Upon cooling sufficiently the circuit is re-established. To prevent however a
complete severance of the circuit, we insert between that end of the thermostat
which dips into the mercury and the end of the conductor which is led away from
the mercury cup, a resistance equivalent to that of the lamp circuit or of any
desired proportion; the current then flows, when the thermostat is withdrawn from

page_text: the mercury, through this resistance, which reduces the current and therefore the
heating effect again to the normal state.
If the extra resistance is high compared to that of the thermostat it may be
placed in shunt with the latter if desirable.
In some cases we may dispense with the mercury cup and make direct contact
between the end of the thermostatic bar and a contact boss or screw connected to
the end of the conductor, the contact surfaces being preferably tipped with carbon
or platinum or tinned in the well known manner. We may also use the direct
expansion of a simple metal bar or wire heated by the current to effect the breaking
of the contact. Sparking may be entirely prevented by the application of a fine
wire shunt or condenser between the points of contact in the manner well known to
electricians.
27
It is also evident that the apparatus may readily be utilized as an "earthing
device by the arrangement of a suitable contact, or for the purpose of giving
a signal.
Dated this 6th day of June 1801
FELL & WILDING,
1, Queen Victoria Street, London, E.C., Agents for the Applicants.
COMPLETE SPECIFICATION.
An Improved Automatic Electric Control or Cut-out.
We, HENRY ALABASTER and TOM ERNEST GATEHOUSE, both of 22 Pater-
noster Row, in the City 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 :-
This invention relates to means known as safety fuzes or
"
" cut-outs now
employed on electric circuits, to automatically break the circuit when the current
is much in excess of that which it is normally. intended to convey, and this
invention consists of an improved automatic device to be used in substitution of
such safety fuzes or "cut-outs," and so arranged that at a predetermined rise of
temperature due to increased current flowing through a part of the device, the
circuit may be either temporarily broken and automatically renewed after a short
period, when normal conditions are restored, or which need not break the circuit
at all but by the introduction of special resistance may bring the heating effect of
the current back to its normal condition.
The objections to the use of such safety fuzes and cut outs at present employed
to prevent over heating of the leads, and so causing danger of fire, are well known.
Among the more serious is the impossibility of insuring the metal or alloy of which
the fusible wire is made being of unvarying quality.
There is no certainty to their action at any specific rise of temperature of the
conductor, nor can they be depended upon not to fuze even with a normal current.
Moreover, when the fusion has taken place the circuit is broken and the lamps are
extinguished, until another fusible wire has been re-inserted.
Besides forming a series of weak points in an electric light circuit, their vagaries
are a source of continual vexation and annoyance to users of the electric light, and
they are now generally considered as an unreliable means of preventing fire unless
what is technically known as a "short circuit " occurs in the wires.
In the invention hereinafter described the apparatus may be arranged to act at
any desired degree of temperature above that produced by the normal current, and
the circuit may be broken or not as desired. If broken, the circuit will
automatically re-establish itself in the course of a brief period of time, but the
circuit may remain completed through a resistance automatically called into play,
which will sufficiently reduce the current to keep the heating effect within the
margin of safety.

page_text: And in order that our invention may be the better understood, we now proceed
to describe the same in relation to the drawings hereunto annexed, reference being
had to the letters and figures marked thereon. Like letters refer to like parts in
the various figures.
Figure 1 is a diagrammatic view of our invention.
Figures 2 and 3 are modifications of the same..
To accomplish our object we make use of the well known thermostatic
arrangement of two metals having unequal co-efficients of expansion and this
thermostat A we make part of the electric circuit, the sectional area of the
thermostat being proportioned to that of the copper conductors B B. One end
of the thermostat which may be flat or coiled is fixed to one end of the conductor B,
and the other is free to dip into and rise out of a metal cup C say of iron,
containing mercury M from which the other end of the conductor B¹ is led away.
The current passes through the thermostat A, forming a part of the circuit,
and on any excess above the normal, the slightly extra heating almost immediately
takes effect on the thermostatic bar, and the contact between the end of the
thermostat and the mercury is broken, under water D, or oil if desirable.
Upon cooling sufficiently the circuit is re-established. To prevent however a
complete severance of the circuit, we insert between the that end of the thermostat
which dips into the mercury M and the end of the conductor B which is led away
from the mercury cup, a resistance E equivalent to that of the lamp circuit or of
any desired proportion; the current then flows, when the thermostat is withdrawn
from the mercury M through this resistance, which reduces the current, and
therefore the heating effect, again to the normal state.
The resistance need not necessarily be attached to the movable end of the
thermostat but at the fixed end if considered more convenient.
If the extra resistance E is high, compared to that of the thermostat it may be
placed in shunt with the latter if desirable.
In some cases we may dispense with the mercury cup and make direct contact
between the end of the thermostatic bar A. and a contact boss or screw F, Figure 2
connected to the end of the conductor, the contact surfaces being preferably tipped
with carbon or platinum, or tinned in the well known manner. We may also use
the direct expansion of a simple metal bar or wire heated by the current to effect
the breaking of the contact. Sparking may be entirely prevented by the
application of a fine wire shunt, or condenser, between the points of contact, in
the manner well known to electricians.
It is also evident that the apparatus may readily be utilised as an "earthing
device" or for the purpose of giving a signal, by the arrangement of a suitable
alternative contact and earth circuit H, Figure 3, which contact can be made
permanent if wanted by any simple mechanical means.
The thermostat also need not be confined to one bar, but may be made of
multiple strips.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
1st. An automatic electric control or "cut-out," consisting of a thermostatic bar
or bars forming a portion of a direct or main circuit, normally completing or
closing the said circuit on a fixed contact, but automatically breaking the said
circuit for a short period by the action of the said thermostat under the heat
generated therein by the direct passage therethrough of a current in excess of
the normal.
2nd. In an automatic electric control or "cut out," the combination of a
thermostatic bar or bars connected to one part of a main circuit or conductor, with
an insulated fixed mercury or plain metal contact, connected to the other part of
a main circuit or conductor, and a shunt resistance circuit between the said bar and
the said contact, substantially as and for the purposes described.

page_text: 3rd. In an automatic electric control or "cut-out," the combination of a
thermostatic bar or bars connected to one part of a main circuit or conductor with
two alternative fixed contacts one on each side of the said bar or bars, and one
connected to the other part of the main circuit or conductor, and the other to
earth or to any signal apparatus, substantially as described.
Dated this 7th day of March 1892.
FELL & WILDING,
1, Queen Victoria Street, London, E.C., Agents for the Applicants.