Evening star. [volume] (Washington, D.C.) 1854-1972, 1903-12-14
ELECTRIC FUSES
WHAT HAPPENS WHEN THEY
BLOW OUT"
No Cause for Fear or Panic-Hov II
Prevents Damage to the
Motor.


One often sees q bright nash ana . sud<
der stop OF an electric car, with all the
lights out. This IL frequently described a.
more or less serious accident, and 10
often causes panic among the passengers.
especially on elevated trains. The greatest
danger to passengers. however. u q pos
s1tIe panic, which might be avoided II II
Was generally known how little chance
there Is OF fire or other danger. To help
TecEle to understand what happens We
make the following explanation. which
should be plain, to lay minds: II a steam
engine is overloaded 1t will stop and refuse
to work. although the full pressure of
steam may remain upon the piston. and not
ceIse any damage. On the other hand, q
motor when overloaded, tries it's best to do
the work thrown upon 1t. II it cannot run
at full speed 1t will run at whatever speed
1t can. AS the speed decreases the current
through the motor increases, and the
motor adjusts itself to that speed at which
the turning effort is sufficient to cause ro-
tation and do the work. II the effort de-
manded OF the motor 10 so great that the
current which passes through It when
standing still IL not sufficient to cause 70.
tauon, the motor will, of course, not turn,
but the current will continue to flow unless
interrupted by suitable mechanism.
Use Of the Fuse.
The current which will flow through g
motor when 1t IL standing still In in almost
all cases far in excess OF that which the
rotor Is designed to carry; and, indeed,
IN well-designed motor a current danger
Gus for the motor will be reached before
the motor has been stalled The effect Of
TINS heavy current on the motor. II allowed
70 continue, IL to heat the windings to a
dangerous degree and destroy the insula-
tlon possibly setting 1t on fire; and 1t IL to
preVent TINS occurrence, whether due to
careless handling of the car or to unex-
pected causes, that the fuses are used A
fuse Is simply a short piece of wire of such
81. that 1t will be melted by a current
Wmch, II allowed to flow through the motor
ior any time. Will damage 1t. When a fuse
piows then. 1t simply means that one OF
the safety devices on the car has operated
to prevent damage to the motor The melt
Ing OF the fuse opens the circuit and cuts
on the current from the motor. To protect
the car the fuse is inclosed In a flreproof
box.
The Circuit Breaker.
There Is another device for ACCOMPLISHING
this purpose, which is known as the circuit
breaker. This Is switch controlled by an
electromagnet, which opens whenever the
current reaches a certain dangerous value
Ihls mechanism is now generally installed
upon electric cars in addition to the fuse II
is often placed on the roof of the platform
over the motorman's head where II is easilv
reached, and 1t is set to operate at a higher
current value than the fuse. because the cir.
cult breaker acts almost instantaneously,
while 1t takes little time for the fuse to
be melted. Now a motor car can stand for
second or two current which would de-
stroy 1t If applied for longer period The
circuit breaker then. takes care of heavy
overloads and the fuse protects the motor
against those smaller currents which are
dangerous If applied for a considerable time
A Slight Explosion.
When fuse blows there is generally a
volatilization of the metal Of the fuse and
a slight explosion. These explosions usually
cause report and some smoke. When the
circuit breaker is opened 1t draws an cleo
trio arc in breaking the circuit. and an in
this arc considerable amount OF energy IL
dissipated in heating the air, there may be
here also something Of an explosion: but In
neither case is there any danger to the pas
sengers when the apparatus Is properly in
stalled. The fuse and the circuit breaker
are safety devices. the operation of which
indicates. not that there is danger to those
on the car. but that danger to the motors
has been averted."