Improvements in Safety Fuses for Electrical Conductors.
Year: 1898

page_text: Date of Application, 25th Jan., 1898-Accepted, 19th Mar., 1898
COMPLETE SPECIFICATION.
Improvements in Safety Fuses for Electrical Conductors.
I, LOUIS ALOYSIUS FERGUSON, of No. 139, Adams Street, in the City of Chicago,
County of Cook, State of Illinois, United States of America, Gentleman, 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:-
The present invention has relation to that class of safety fuses or catches that are
now commonly employed for connecting the terminals of electric conductors more
especially in underground systems, the fuses being so constructed as to melt at a
pre-determined amperage and thus protect the systems against dead short circuits and
against overloads. This invention comprises a safety fuse of such character that the
ends or terminals of the fuse shall be connected by an arch, a small portion of the
length of which arch is contracted to constitute the point at which the rupture of
the fuse will occur in case of the passage of excess current between the terminals, the
portions of the arch adjacent the fuse terminals being expanded.
In carrying out the invention the precise details of construction hereinafter set
forth may be varied but I shall describe what I regard as the preferred embodiment
of the invention, the exact scope of the invention being particularly pointed out in
the claim at the end of the specification.
Figure 1 is a plan view of a safety fuse or catch embodying my invention. Fig. 2
is a view in front elevation of such fuse or catch after the contracted portion has been
melted by passage of excess current. Fig. 3 is a view in section on line 3-3 of
Fig. 1. Fig. 4 is a perspective view of the safety fuse or catch.
The improved fuse is shown as formed from a single piece of metal (preferably
copper) with broad ends or terminals a, a, having suitable slots a¹ therein to straddle
the terminals of the conductors with which they will be connected. The ends or
terminals a of the fuse are united by the arch a², the sides of this arch a² being
expanded at its base and a small portion of the length of the arch being contracted
to form the point at which the rupture of the fuse will occur under passage of excess
electric current. The area of the contracted portion of the arch will determine the
amount of current that can pass through the fuse without melting the same and
ordinarily each fuse will be marked with the number of amperes for which it is
adapted. When electric current in excess of that for the transmission of which the
fuse is proportioned passes through the fuse (as will occur in the case of a dead short
circuit or an overload of the conductor) a rupture of the fuse will occur at the
contracted point of the arch thereby breaking the circuit through the fuse. By
forming the arch with a contracted portion of limited length and by forming the
base of the arch with expanded ends it follows that a very small portion of
the arch becomes heated under passage of excess current, the intense heating of the
contracted part of the arch under normal loads being prevented by radiation of the
O heat through the expanded portions of the arch. So also by forming the fuse so
that the melting point shall invariably occur at the limited contracted part of the
arch, the rupture of the fuse will take place with the least possible melting of the
metal thus avoiding all danger of the melted metal flowing on to the terminals as is

page_text: apt to be the case with composition fuses heretofore employed. By uniting the ends
of the fuse by an arch having a short contracted portion and an expanded base
sufficient extent of metal is provided to form not only a limited contracted part at
which the rupture of the fuse shall occur, but also ample metal is provided at each
side of this contracted part of the arch to prevent the excess heating of the contracted
part of the arch except under conditions. With composition fuses such as have been
heretofore employed the melting point of the compositions has necessarily been so
low that the fuses are frequently melted because of the heat generated by reason of
poor contacts between the ends of the fuses and the conductor terminals even under
normal loads; but with my improved fuse no such melting or rupture of the fuse
is possible.
A further important advantage of my improved construction is that the reduced or
contracted portion of the arch renders the same quite flexible so that the ends of the
fuse can be readily contracted, spread apart or otherwise adjusted in order to com-
pensate for any variation between the conductor terminals to which the fuse is to be
attached.
Having now particularly described and ascertained the nature of my said invention
and in what manner the same is to be performed, I declare that what I claim is :-
A safety fuse having broad ends to engage the conductor terminals, said ends being
connected by an arch, a shall portion of the length of which arch being contracted to
constitute the point at which the rupture of the fuse will occur, the portions of said
arch adjacent the fuse terminals being expanded, substantially as described.
Dated at Chicago, Illinois, United States of America, this Eighth day of January
A.D. 1898.
LOUIS ALOYSIUS FERGUSON.
Haseltine Lake & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.