Improvements in Fusible Cut-outs.
Year: 1898

page_text: Date of Application, 14th Dec., 1898-Accepted, 18th Feb., 1899
COMPLETE SPECIFICATION.
Improvements in Fusible Cut-outs.
We, CHARLES MARK DORMAN and REGINALD ARTHUR SMITH, both of Ordsal
Electrical Works, Salford, in the County of Lancaster, 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:
Our improvements relate to that class of fusible cut-outs generally known as
replacement fuse bridges in which the fuse wire is connected to two metallic
contact pieces attached to an insulating bridge or handle, the whole being so
arranged that it can be quickly and easily attached to the fixed terminals of the
conductors by means of spring clips or other contact making arrangement. It is
a common practice to make the insulating bridge or handle of replacement fuse
bridges in the form of a tube of glass or other insulator through which the fusible
wire is threaded. The rush of gas from the tube when the fuse wire melts or
volatilizes then has a tendency to prevent the formation of an electric are or to
blow it out if formed. When the voltage is high it is found that a permanent
arc is sometimes maintained between the terminals through the tube, even if
pierced diaphragms or other partial obstructions are placed in the tube. Our first
improvement consists in using a tube the bore of which is not continuous but is
entirely stopped up for a portion of its length the fuse wire being carried past the
obstruction by being threaded through holes to the outside of the tube thus
forming a loop round the obstruction. This arrangement generally prevents the
formation of an are between the terminals even at high voltages.
Our second improvement consists in fixing a pad or damper of some incom-
bustible non-conductor of electricity such as asbestos or slag wool firmly over that
portion of the fusible wire which is exposed on the outside of the tube. The
effect of this pad is to arrest or damp out any arc or series of ares which might
otherwise be formed between the terminals through the holes originally occupied
by the fuse wire. Another useful purpose served by the pad or damper is to
prevent the hand of the operator from being burnt in case the fuse wire should melt
or volatilize at the moment when the fuse bridge is being attached to the fixed
terminals.
Referring to the drawings, Figs. 1, 2, & 3, show the side elevation, plan, and
end elevation respectively of a simple form of our improved fuse bridge. Figs. 4,
5 & 6, show the same views of a form of our improved fuse bridge
with our pad or damper attached, and Figs. 7, 8, & 9, show the same
views of another form. The same letters are used to indicate the same parts
on all the figures. A is the fuse wire shown on the drawings by a thick line
which is connected to the metallic contact pieces B₁, B, by means of the screws
or nuts C, C D is the tubular insulating bridge or handle to which the contact
pieces B, B., are attached by means of the screws or bolts E₁, E. F is the bore
of the tube. G is the stoppage or obstruction in the bore. It will be seen that
in all the fuse bridges shown the fuse wire is carried past the obstruction in the
bore of the tube by being brought to the outside of the insulating bridge or

page_text: handle through two small holes H₁, H. The bore of the tube in our improved
fuse bridges may be either cylindrical as shown in the illustrations or may be
of square, oval, oblong or polygonal section. The walls of the tube may be
made of considerable thickness and may be extended and shaped so as to form
convenient handles or insulating barriers between the contact pieces B₁, B₂, as
clearly shown in the drawings. Our improved tubular insulating bridge or
handle may be made of any ordinary insulating substance but it is preferable
that it should be of an incombustible nature such as slate, glass, or porcelain.
In some cases it is preferable that the two portions of the bore of the tube which
are on opposite sides of the obstruction should not be in a straight line, thus in the
fuse bridge shown in Figs. 4, 5, & G the two parts of the bore of the tube which
are on opposite sides of the obstruction are inclined at an angle with one another in
order that the fuse bridge may be handled without danger of placing the fingers
over the openings of the tube. The fuse bridge shown in Figs. 7, 8, & 9 varies
from the other bridges illustrated in having the barrier or obstruction placed
close to one end of the fuse tube and not near the centre. K is a pad of some
soft incombustible substance such as asbestos or slag wool which is held down
firmly by means of the plate L and the screw or screws M over that portion of the
fuse wire which is exposed outside the fuse tube. It is convenient but not
essential that the pad or damper K should be sunk into a recess formed on the
outside of the fuse tube as shown in order to prevent its being easily displaced.
In some cases we prefer to use the form of fuse bridge shown in Fig. 1 with the
addition of the pad or damper and the forms of fuse bridges shown in Figs. 4
and 7 without the pad or damper.
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:
(1) A tubular replacement fuse bridge in which the bore of the tube is not
continuous but is entirely stopped up for a portion of its length the fuse wire
being carried past the obstruction by being threaded through holes to the outside
of the tube thus forming a loop round the obstruction.
(2) The addition to the fuse bridge as specified in Claim 1 of a pad or damper
fixed over that portion of the fuse wire which lies on the outside of the tube
substantially as and for the purposes described.
(3) The improved fuse bridges each as a whole substantially as described and
shown.
Dated this 13th day of December 1898