The Wallace miner. [volume] (Wallace, Idaho) 1907-current, 1914-03-12


gas dust or explosives. Electricity
becomes actively dangerous only when
1t breaks away from its proper chan
nels in stray currents or as sparks and
ares.
AS far as stray currents are con-
cerned the confinement of electricity
in its proper place Is primarily a ques-
ton of insulation, a term that in
cludes the covering of conductors, the
insulators upon which they are sup
ported and the insulating material
used in motors and accessory equip
ment. Against insulating coverings
for conductors is brought the argu-
ment that such coverings deteriorate
rapidly and are an added element of
danger because they give false I'M
pressions of safety. The truth of this
Insulation and the conditions of ser
vice, and can not be regarded as uni
verSally applicable. If bare conduct
ors are used they must be we'll in
l,
guarded. in order to contlne the cur
rent With the possible exception of
high voltage cables all conductors,
bare or insulated. should be support
ed upon insulators that are mechanic
ally strong as Well as electrically ETH
Client. If bare conductors are used.
confinement of the current depends
entirely upon the insulators. More
over, dampncss and dust can come
into direct contact with the wire. a
condition not consistent with tho high
est factor of safety
In order to insure high factor of
safety in the insulation Of motors and
other electrical machines they must
be carefully selected with a view to
the service which they are to perform.
They must then be protected from
moisture and dust unless such pro-
lection is Inherent In their design
Care in this respect will be rewarded
not only by increased safety. but also
by decreased cost Of upkeep. The
maintenance cost Of nclosed motors
operated in damp and dusty places
should be less than for open motors
operated under the same conditions If
both types of machines are properly
designed. constructed and rated.
1t must be admitted that the cleo
trio current can not be kept where It
belongs in the sense of eliminating en-
tirely such sparks and arcs as occur
at fuses, circuit breakers, air break
switches, starting rheostats, and the
commutators of direct current ma
chimes. In this connection the factor
Of safety must be applied by arrang-
ing to confne the outbursts of current
to a limited area unoccupied by any
thing which may be affected by heat
or fire.
j Additional Precautions.
Assuming that in the selection and
installation Of electric equipment care
has been exercised to insure the pro-
per confinement Of the current, the
factor Of safety may be increased by
grounding the dead metallic parts of
apparatus by providing means for in
sulating the bodies of those who work
upon such apparatus, and by barring
from the vicinity of the current such
elements as are explosive or combusti-
/ bic.
Maintenance Of Safety Factor.
It is as important to maintain a
high factor Of safety az to obtain 1t In
the first place. and this requisite calls
for careful and frequent inspection by
the mine electrician, whose RESPONSE
bili'ies can scarcely be overrated The
supervision Of the electrical equip
ment Of a ninc IS task that requires
unusual ability sound judgment and
experience Of peculiar sort. To sell
ect suitable apparatus, to install 1t
properly and economically, and n
maintain 1t free from interruption of
service at a minimum cost demands
much ability When the requirements
of safety are added to the list OF dut-
les the responsibility Is not lessened.
The establishment and maintenance
Of a high factor Of safety rests as
much with the man who has direct
charge of the electrical equipment as
with anyone. It seems reasonable al
so TO assume that man who is com
petent to maintain a high factor Of
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