Burlington weekly free press. [volume] (Burlington, Vt.) 1866-1928, 1904-09-22
ELECTRIC CAR FUSES.
what II Il Tint Happens when They
"BIo,y out"

what II IL Tint Happens when They
"Biow out"
One often sees bright fash and n
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 il often causes panic among
the passengers, especially on elevated
trains The greatest danger 10 pas
scngcrs 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 Elcc-
trical Review, TO help people to under
stand what happens, makes the follow
ing explanation. which should he plain
to lay minds "lf II 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 tho other
hand, a motor when overloaded tries
It's best TO do the work thrown uron IT,
If it cannot run ut full speed ii will run
ut whatever speed il 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
ciiort is sufficient to cause rotation and
dc 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 viii continue to
flow unless interrupted by Il suitable
mechanism
"The current which will flow through
almost all cases far in excess of that
which the motor is designed to carry.
and. indeed. in Il well designed motor
current dangerous for the motor will
be reached bcfnrp the motor has been
stalled. The effect of this heavy cur
rent on the motor. If allowed 10 con-
tinue, is TO heat the windings TO Il dam
gcrous degree and destroy the insua-
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
are used. \ fuse is simply short
piece of wire Of such size that It will
be melted by Il current which, If allow
ed to flow through The motor for any
time. will damage it. When n 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 Cf the fuse opens the
circuit and cuts off the current from
the motor. To protect the car the fuse
is incloscd in fircproof box.
"Thpre is another device for accom-
plishing this purpose, which is known
ms the circuit breaker. This is Il switch
controlled by an electro magnet. which
opens Whenever the current reaches Il
certain dangerous value This mechAn-
ism is now generally installed upon
electric cars in addition to the fuse. 1t
Is often placed on the roof of the plat
form over the mOtorman's head. where
It is easily reached, and 1t is SGT to
operate at a higher current value than
the fuse. because the circuit breaker
acts almost lnsthntancously while it
takes Il little time for the fuse to be
melted. Now. II motor car can stand
for Il second or two current which
would destroy ii if applied for longer
period. The circuit breaker. then. takes
care of heavy overloads, and the fuse
protects the motor against those small
er currents which are dangerous if APP
Piled for a considerable time.
when fuse blows out, there is gem
orally volatilizaton of the metal of
the fuse and a slight explosion. These
explosions usually cause n report and
some smoke. When the circuit breaker
is opened it draws an electric arc in
breaking the circuit and. rs in this arc
| n considerable amount of energy is dis
! sipHtcd in heating the air. there may be
! here also something of IN explosion.
but in neither case is there any danger
| to the passengers when the apparatus
! is properly installed. Tho fuse and the
circuit breaker are safety devices. the
| operation Of which indicates not that
! there is danger To those on tho car. but
( that danger TO the motors has been
/ nVCrtpd -