Virginia citizen. (Irvington, Va.) 1891-1921, 1904-01-29
ELECTRIC CAR FUSES.
what It IL That Happens when They
sBiow ouf.v

One often sees bright fash and q
sudden stop or an electric car. with oil
the lights out. This is frequently de-
scribed as a more or less serious acct
dent. and &c often causes a panic among
the passengers. especially on elevated
trains. The greatest danger to pas
sengers. however. is possible panic,
which might be avoided il il was gen.
orally known how little chance there
Is or IRE or other danger. The Elec-
tricai Review. TO help people to under.
stand what happens. makes the follow
ing explanation. which should be plain
10 lay minds: "lf steam engine is
overloaded II will stop and refuse to
work. although the full pressure OF
steam may remain upon the piston and
not cause any damage. On the other
hand. motor when overloaded tries
Its best TO do the work thrown upon IL.
II IL cannot run az full speed it will run
at whatever speed ii can. AS the speed
decreases the current through the mo-
tor increases. and the motor adjusts it
self TO that speed at which the turning
effort Is sufficient 10 cause rotation and
w NLN WI n Al tAlt Ctt
OF the motor is so great that the cur
rent which passes through IL when
standing still is not Sufficient to cause
rotation the meteor will, of course. not
turn. but the current will continue to
how unless interrupted by q suitable
mechanism.
THE current which will dow through
motor when il is standing still is in
almost all cases far i'm excess of that
which the motor Is designed TO carry,
ana. indeed. in well designed motor
current dangerous for the motor will
be reached before the motor has been
stalled. The effect of this heavy cur
rent OH the motor, If allowed to con-
tinue, is to heat the windings to q dan
gerous degree and destroy the lnsula-
ton. possibly setting it on fire. and 1t
rs to prevent this occurrence, whether
due to careless handling OF the car or
TO unexpected causes, that the fuses
are used. A fuse is simply n short
piece OF wire of such size that il will
be melted BY n current which, IL allow
ed to dow through the motor for any
time. Will damage IL. When fuse
blows, then, ii simply means that one
or the safety devices on the car has
operated to prevent damage TO the mo-
tor. The melting Of the fuse opens the
circuit and cuts of the current from
the motor. To protect the car the fuse
is inclosed I'm a freproof box.
There is another device for accom-
plishing this purpose. which Is known
as the circuit breaker. This Is switch.
controlled by an electro magnet. which
opens whenever the current reaches q
certain dangerous value. This mechnn-
ism is now generally installed upon
electric cars In addition 90 the fuse. II
Is often placed on the roof of the plat
form over the motorman's head, where
IL Is easily reached. and 1t Is set to
operate ut higher current value than
the fuse, because the circuit breaker
acts almost instantaneously, while II
takes little time for the fuse to be
melted. Now. a motor car can stand
for n second or two current which
would destroy 1t IL applied for longer
period. The circuit breaker, then, takes
care OF heavy Qverloats. and the fuse
protects the motor against those small.
er currents which are dangerous II ap.
piled for n considerable time.
when fuse blows out. there Is gen.
orally volatiliZation Of the metal Of
the fuse and slight explosion. These
explosions usually cause report md
some smoke. When she circuit breaker
Is opened. IL draws an electric arc in
breaking the circuit. and, as In this arc.
a considerable amount of energy is dis,
sipated I'm heating the air. there mny be
here also something OF All explosion.
but in neither case is there any danger
to the passengers when the apparatus
Ia properly installed. The fuse and the
circuit breaker are safety devices. the
operation OF which indicates not that
there Is danger 10 those on the car. but
that danger TO the motors has been