An Electrical Safety Cut Out.
Year: 1891

page_text: Date of Application, 13th June, 1891
Complete Specification Left, 12th Apr., 1892-Accepted, 14th May. 1892
PROVISIONAL SPECIFICATION.
An Electrical Safety Cut Out.
I, HENRY SHEEHY KEATING, of No. 11 Prince's Gardens, Kensington in the
County of London, Barrister at Law, do hereby declare the nature of this invention
to be as follows:-
My invention relates to apparatus introduced in an electric circuit which operates
as a safety cut out, that is to say, it automatically opens the circuit when the
electricity conveyed by it becomes excessive.
For this purpose, I divide the conducting wire and introduce the end of the one
into one limb of a U bent glass tube containing mercury in which the end of the
wire is immersed. The other limb of the tube terminates in a bulb into which the
end of the other wire is sealed and in which it may be bent into a coil, its end
dipping into the mercury in the tube. When the electrical current conveyed by
the one wire through the mercury to the other becomes excessive, the wire in the
bulb becomes heated and the air is expanded so that the mercury in the one limb of
the tube is depressed breaking contact with the wire.
Dated this 13th day of June 1891.
ABEL & IMRAY,
Agents for the Applicant.
COMPLETE SPECIFICATION.
An Electrical Safety Cut Out.
I, HENRY SHEEHY KEATING, of No. 11 Prince's Gardens, Kensington in the
County of London, Barrister-at-Law, do hereby declare the nature of this inven-
tion and in what manner the same is to be performed to be particularly described
and ascertained in and by the following statement :-
My invention relates to apparatus introduced in an electric circuit, which operates
as a safety cut out, that is to say, it automatically opens the circuit when the
electricity conveyed by the circuit becomes excessive. The accompanying drawing
is a front view of a cut out according to my invention. A is one limb of a glass
tube bent to U form and made with a bulb B and a space C closed at the end
through which is sealed a wire D. The wire within the space C is preferably bent
to helical or zig-zag form so as to present a considerable surface. The tube is
partly charged with mercury in which are immersed the ends of the circuit
wires D and E, so that, under ordinary conditions, the mercury forms part of the
circuit. The space C is charged with nitrogen or other gas that does not combine
with the mercury, and I prefer that the gas in C should have a pressure a little
above that of the atmosphere causing the mercury to stand at a higher level in the
other limb A and thus, should there be accidental fracture of the limb C, the
mercury will descend in A leaving the wire E and thus opening the circuit.
A similar result might be attained by making the pressure in C less than that of
the atmosphere, the mercury in that case standing higher in C than in A, but, in
The
case of accidental fracture, descending from the end of the wire D.
wires D and E being connected to the circuit, when the current exceeds a certain
amount, the wire D becomes heated and the gas in C is thus so far heated and
expanded as to force the mercury down from the end of the wire D, thus opening
the circuit, and acting as a safety cut out.
In order to prevent oxidation of the mercury in the limb A, when that limb is
open, the surface of the mercury may be covered by glycerine. In some cases,

page_text: however, instead of leaving the limb A open at the top, it may be sealed leaving
sufficient space above the mercury.
Having now particularly described and ascertained the nature of this inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is :-
:-
An electrical safety cut out consisting of a bent tube containing mercury which,
having circuit wires dipping into it, usually formis part of the circuit, but which,
by expansion of gas heated in one limb of the tube by excess current in the
wire, is forced away from the wire thus opening the circuit, substantially as
herein described.
Dated this 10th 1.
_ 1000
ABEL & IMRAY,
Agents for the Applicant.