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THE COAL TRADE BULLETIN. 47
SAFEGUARDING THE USE OF ELECTRICITY IN MINES*
By Clyde G Brehm, Chief Electrician Oliver & Snyder Steel Co., Oliver, Pa.
For the government of outside electrical installations
the National Board of Fire Underwriters
have compiled a most complete book of rules consisting
of about 175 pages.
When a piece of electrical work is completed
or repairs or changes made the board is notified
and their inspector calls and goes over the work.
If in accordance with the code a certificate is
granted, if not no certificate is granted until it is
put in strict accordance with the code.
The great risk that the National Board of Fire
Underwriters have to guard against is fire, but in
the mine many things tend to make the use of
electricity dangerous because, as a general thing,
there is little space, little light and much dampness,
so we not only have the fire risk to contend
with, but the more common risk of shock.
At this point I wish to compliment the author
of the Electrical section of the Bituminous Mining*
law of Pennsylvania. It is well gotten up and
most complete, and, if strictly complied with,
practically solves the problem of safeguarding the
use of electricity in mines.
The mine management should use great care in
their selection of a mine electrician, for to quote
Mr. Clark of the Bureau of Mines, "The supervision
of the electrical equipment of a mine is a
task that requires ability, sound judgment, and
experience of a peculiar sort. To select suitable
apparatus, to install it properly and economically,
and to maintain it free from interruption of service
at a minimum cost demands much ability.
When the requirements of safety are added to the
list of duties 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 also to assume
that a man who is competent to maintain a high
factor of safety is no less able to maintain as
low a cost of maintenance as is consistent with
satisfactory operation."
The writer understands that in England and
some other countries the mine electrician is required
to pass an examination before he is permitted
to take charge of the electrical equipment
of a mine. If this were also true in this country
we would have greater assurance of the efficiency
and ability of tbe man in charge.
Another point to consider along this line is the
state's inspection of niining electrical equipment.
If it is important to have competent men in
•Paper read before the Coal Mining Institute of America,
Pittsburgh. Pa, December 4 and 5. 1913.
charge, it is just as important to have competent
inspection. We cannot expect our mine inspectors
to be electrical engineers as well, but if one or
two competent men were appointed to work with
our mine inspectors and make rigid electrical inspections
periodically it would do much toward
safeguarding the use of electricity in mines.
While alternating current is used at mines for
running pumps, fans, etc., direct current is more
commonly used. The voltages usually employed
are 110, 220 and 500, the 110 volts being used
mostly for lighting, and on account of its low
pressure it is not hard to guard against as far as
shock is concerned, accidents resulting from such
voltage being very rare. The 220 volts, however,
has in several instances been known to kill, and
naturally, the higher voltages are all the more
dangerous and every precaution should be taken
to escape shock.
Usually the track or the earth is used for the
return circuit, so a person
STANDING ON THE TRACK
or even the earth is in reality in contact with one
side of the generator, and by touching the trolley
wire, the bare parts of a switch or any other current
carrying conductor, he establishes a circuit
and thus receives a shock.
Reports of the mine inspectors show that the
majority of electrical shocks received in mines
results from contact with the trolley line. The
recommendations of the Mining law of Pennsylvania,
pages 66 and 67, should be strictly observed
in reference to safeguarding the men from the
trolley wire, and exceptional care should be taken
when traveling in the same entry with a trolley
wire. A person cannot usually receive a shock
by standing upon the earth or rails and touching
the electric locomotive, on account of the motor
being of the same potential as the rail and a
shock can only be received when there is a difference
of potential. But the motor may be almost
insulated from the rail by too much sanding or
even coal on the track and in such a case the full
line potential or voltage would exist between the
motor and the rail, and by touching the motor at
such a time a person would receive a severe shock,
and since all the cars of this trip are connected
to the locomotive by their draw bars and hitchings
a person would receive a shock by touching
them as well. This particular danger could be
eliminated by bonding the draw-bars of all cars
to iron axle, and since it is hardly probable that
the entire trip would be insulated from the rail
at the same time, any one car in good contact
with the rail would prevent the entire trip from