Milford chronicle., 1904-04-15
ELECTRIC CAR FUSES.
What It Is That Happens When They
"BIOVv Out"


One often sees bright fash and a
sudden stop of an electric car, with all
the lights out. This is frequently de
scribed as a more or less serious acct
dent, and it often causes a panic among
the passengers. especially on elevated
trains. The greatest danger to pas
sengers, however, is Il possible panic,
which might be avoided if it was gen.
orally known how little chance there
is Of fire or other danger. The Elec-
trical Review, TO help people to under
stand what happens, makes the follow
ing explanation, which should be plain
TO lay minds: IF a steam engine is
overloaded it 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, a motor when overloaded tries
its best TO do the work thrown upon it.
If it cannot run at full speed it will run
at whatever speed it 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 TO cause rotation and
do the work. If the effort demanded
of the motor is so great that the cur
rent which passes through it when
standing still is not sufficient to cause
rotation the motor will, Of course, not
turn, but the current will continue to
flow unless interrupted by a suitable
mechanism.
''The current which will flow through
a motor when it is standing still is in
almost all cases far in excess Of that
which the motor is designed to carry,
and, indeed, in well designed motor
a 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 a dan
gerOus degree and destroy the insula-
ton. possibly setting it on fire. and it
is to prevent this occurrence. whether
due TO careless handling of the car or
to unexpected causes, that the fuses
ere used 4 fuse is simply n short
piece of wire Of such size that it will
be melted by current which. if allow
ed to flow through the motor for any
time, will damage it, When a fuse
blows then, it simply means that one
of 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 off the current from
the motor To protect the car the fuse
is inclOsed in a iireprOof box.
"There is another device for accom-
plishing this purpOSe. which is known
as the circuit breaker. This is a switch.
controlled by an electro magnet. which
opens whenever the current reaches u
certain dangerous value. This mechan-
ism is now generally installed upon
electric cars i'm addition 10 the fuse. 1t
is often placed or lie roof Of the plat
form over the motOrman's head. where
it is easily reached. and it is set TO
operate at Il higher current value than
the fuse, because the circuit breaker
acts almost instantuneously. while it
takes little time for the fuse to be
melted Now. Il motor car edn stand
for a second or two a current which
would destroy it if applied for longer
period The circuit breaker. then. takes
care Of heavy overloads, and the fuse
protects thp motor against these small
er currents which are dangerous if APP
Piled for a considerable time.
when a fuse blows out. there is gen.
orally volatilization of the metal Of
the fuse and slight explosion. These
explosions usually cause a report and
some smoke When the circuit breaker
ia opened. it draws an electric arc in
breaking the circuit. and. as in this arc
n considerable amount Of energy IS dis
sipated in heating the air. there may be
here also something Of an explosion,
but I'm neither case is there any danger
to the passengers when the apparatus
is properly installed. 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
nverteG" "