Pittsburg dispatch. [volume] (Pittsburg [Pa.]) 1880-1923, 1891-01-04
WHY LIGHTS GO OUT.
The Usual Cause is the Burning Out
Of the Safety Fuses.
ADVANTAGES AND DISADVANTAGES
How Fires Are Often Started From Electric
Light Wires.
A GOOD FIELD FOB THE INVENTORS
DVANTAGES AND DISADVANTAGES
A GOOD FIELD FOB THE INVENTORS
WRITTEN FOR THE DIsPArcH.I )

In every electric circuit there is, or should
be, lead fuse-the object of the fuse being
to interrupt tine circuit whenever the current
becomes abnormal. Any abnormal current
will. through the medium of fuse, cause
interruption of the circuit by the heating
effect of the current and subsequent melting
of the lead fuse, When the lead is melted
air is the only medium left through which
the current can flow in that part OF the
circuit previously occupied by the lead.
But as air is a very poor conductor OF
electricity, the current will be unable to
fow-it will be damned up, so to speak.
1t frequently happens that an electric
generator becomes short circuIted-a short
circuit on dynamo corresponding to the
giving away of the dam of a reservoir Of
water; but if there is fuse in the circuit
the tremendous rush of current, due to the
short circuit, instantly melts the fuse and
danger is thus averted. A lead fuse is then
an automatic safety device or circuit inter-
rupter, and at first sight it would appear
cheap and reliable, and in fact everything
that could be desired for that purpose. But
on closer inspection, it is found to be EUR
of lead fuse is that of a ribbon and about
two inches long. The ends OF these short
ribbons or fuses are punched to admit of
clamping screws, so that the fuse can be
readily connected in the electric circuit.
HARD TO MAKE CONTACT.
The first trouble occurs right here with
these clsmping screws, for lead having little
or no elasticity, the screws soon work loose
and produce poor contact between them
and the lead. Now a poor contact means
greater resistance at that point, and this In
creased resistance causes heat, which will
soon result in melting the fuse, though the
current had not become excessive. Corrosion
is another of the many troubles connected
with lead fuses, more especially with very
thin fuses intended for light currents. If
corrosion gets in under the clamping screws
poor contact Is formed and the fuse destroyed
at q most inopportune moment. Corrosion
will also reduce the carrying capacity of the
fuse, and again the fuse will ''les go" when
least expected to. It is in this way that
fuses have become largely responsible for the
now familiar expression, "the electric hghta
went out"
Further trouble is found in large fuses,
intended to carry verv heavy currents. Such
fuses have to be comparatively thick and
contain quite volume of metal. The con-
sequence is, that, if short circuit on the
line should occur when the fuse is cool, it
would take some time, perhaps half a
minute or more to heat it up to the heating
point, and in the meantime much damage
might be done to the electric apparatus in
the vicinity. Still another danger aud weak
point in lead fuses is their failure to
promptly open a circuit containing high
pressure current. The failure here is due to
the fact, that when the lead melts, heavy
metallic fumes are formed through which
an electric arc is maintained. This vapor
of lead, although poor conductor conI-
pared with copper, is much better than air;
so that currents having low pressure Of
only 200 or 300 volts are unable to force
through il and so maintain the circuit. But
high pressure volts of 800 or /, 900 volts find
the lead vapor a sufficiently good con-
ductor.
HOW FIRES ARE STARTED.
The result is an arc often of great magni-
tude, which, if not promptly extinguished,
will set fire to and otherwise destroy all OBJ
jects within its reach. Even castings and
all copper connections are melted like so
much wax. And yet, in spite of all these
drawbacks and Objectionable features, bad
fuses are in constant use on all electric cir
cults. Here, then, is a rich field tor in
ventors-and one that will pay handsomely
for reasonable success. Many electro-me-
chanical devices have been invented for
automatically partially or wholly checking
the flow of an electric current under ab-
normal conditions, but all have the OBJ
jectionable features of great cost and COM
plication, as compared with the bad fuse.
Some of the weaknesses OF bad fuses are
overcome by using other metals. On many
circuits copper fuses are used, but the OBJ
lection to copper or any other similar metal
is that it has such high melting point. In
order to melt a copper or iron fuse its in
spiration would have to be raised higher
than that of red heat, SO that for hours
such q fuse might be dangerously hot before
it would "let CO." and this, of course, means
danger from fire.
The main features, then, to be avoided in
fuse or circuit "cut out" are high temper
ature, poor contacts, Rrcing, complications
and any considerable expense Arcing 10
ingeniously overcome by placing the fuse ia
a magnetic fluid. It is a very curious and
interesting fact that an arc cannot be MAIN
tanned in strong magnetic fluid. If we
take the two ends Of an electric circuit and
bring them together in between the two
poles of horseshoe magnet and then sep
arate the ends again, tine arc, which tends to
be formed between the two receding ends of
the circuit, is instantly "blown out, 30 to
speak.
SECONDARY WIRE.
Still another ingenious and very simple
device, used, believe, by the Westinghouse
Electric Company, to prevent the formation
OF an arc, when the fuse melts, is the shunt
attachment. This ia simply a short piece of
hne wire shunted around the fuse, that is
the fne wire is attached to the two ends OF
the fuse. Under these conditions no current,
or at least very little current, will flow
through the wire for the reason that it has q
much higher resistance than the lead fuse;
but. when the lead fuse melts the resistance
through the hne wire is much less than that
offered by the lead vapor found by the fuse,
50 that all the current is then instantly
forced through the wire, and this, having
very small volume, Immediately melts with
out forming vapor, and the circuit is thus
Interrupted. The objection, however, to this
Drangement Is that there are two things to
replace every time the fuse is melted
Another device intended to hasten the
rupture of the fuse, and so lend promptness
to its action, is to hang a small weight from =
the lead midway between the binding screwa
Thus, when the lead softens, due to any ex-
cessiye dov of current, the weight pulls the
lead away from its connections and opens
the circuit This however, does uot pre-
vent arcing, and would, therefore, be unre- .
liable on high pressure circ uits. Fusible
metal, made Of equal parts of tin and lead.
Is often used tor light current fuses, but this
gives very Door satisfaction, for the reason
that fusible metal has q too low melting
pOint-abOut the emnerafura oF hoil;u~