An Improvement in Safety Fuses for Electrical Circuits.
Year: 1899

page_text: Date of Application, 16th Dec., 1899-Accepted, 27th Jan., 1900
COMPLETE SPECIFICATION.
An Improvement in Safety Fuses for Electrical Circuits.
We, SIEMENS BROTHERS & Co., LIMITED, of 12, Queen Anne's Gate, West-
minster, S.W., Electrical Engineers, do hereby declare the nature of this inven-
tion (as communicated to us from abroad by Siemens & Halke Aktien Gesells-
chaft, of Markgrafen Strasse, 94, Berlin, S.W., Germany, Electrical Engineers),
and in what manner the same is to be performed, to be particularly described
and ascertained in and by the following statement;-
;-
In
With that description of safety fuse apparatus for electrical circuits in which
the fusible strips are entirely enclosed in insulating material, it is often difficult
to ascertain, whether such strip has been burnt through or is still in order.
particular when the burning through is not effected by a short cireuiting of the
current, but by a current of excessive strength no alterations are externally
perceptible in many cases, when such fuse apparatus are of good construction.
The present invention has for its object to provide a reliable external indication
of the condition of the fuse strip, by employing in combination therewith an
auxiliary or indicator fuse strip or wire, which is connected to the same contacts
as those to which the main fuse strip is connected, but which is so arranged
that it is externally visible, or can be made visible on opening an enclosure con-
taining it.
This indicator fusible strip or wire is made of considerably smaller section
than the main fusible strip and it may be made of a metal that requires a some-
what higher temperature to melt or burn than the main fuse strip, so that on
the passage of an excessive current through the fuse apparatus the main strip
will be certain to be burnt through before the indicator strip or wire is burnt.
Thus the burning through of the latter will afford a reliable indication that the
main strip has been burnt through.
Fig. 1 of the accompanying drawing shews by way of example a longitudinal
section of one arrangement for carrying out the said invention; Fig. 2 shews a
cross section. a is a tubular chamber of insulating material, which is divided
by a partition 6 into a large and a small compartment.
In the outer wall of the smaller compartment is formed an opening c. In the
larger compartment which is completely closed is placed the main fusible strip d,
which is secured at each end by soldering to metal contact plates e e connected
to e circuit leads.
To these contact plates are also fixed the ends of the indicator fuse strip or
wire f of considerably smaller section which passes through the smaller compart-
ment. If now, owing to short circuiting or to the passage of excessive current,
the main fuse strip d be burnt through, the indicator strip or wire f will also be
certain to be burnt, but as the latter has relatively a much greater exposed sur-
face than the main strip d it will not become so highly heated as the latter, and
will consequently not be burnt through until, after the burning of d, the whole
of the current passes through it. As before stated this retardation of the burning
rn

page_text: off can be further insured by making it of a metal of a slightly higher fusing
point or of a greater specific resistance than d.
As the indicator wire f is thus made with certainty to burn through only
after d is burnt, it will be seen that on observing through the opening that the
wire is still intact, it may be concluded that the strip d is also in working
order, while if it be found that the wire f is burnt through, it may be concluded
with equal certainty that the strip d is also burnt through.
Indicator devices such as that above described may be employed with advantage
in combination with safety fuse apparatus of any description in which the main
fuse strip is enclosed so as not to be visible.
We are aware that safety fuse apparatus with enclosed fusible strip have been
proposed in which the fusible strip on burning is made to release and actuate a
mechanical indicating device, and we do not claim such an arrangement.
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
The combination with electrical safety fuse apparatus in which the fusible strip
is entirely enclosed of a visibly arranged auxiliary or indicator fuse strip or wire
which is connected in parallel with the main fuse strip to the same circuit leads,
so that on observing the condition of the said indicator strip or wire a reliable
indication of the condition of the enclosed main fuse strip will be thereby afforded
substantially as described.
132
י.
1
101 .
1000
ABEL & IMRAY,
Agents for the Applicants.