rt thereof, be used exclusively as the return,
and when connected to the earth system, the negative wire or bonded
track shall be of ample capacity, exclusive of the pipe line, to
carry the current.

[=Trolley wires; how erected.=] The trolley wire shall be carried
upon hangers or other fixtures which will properly insulate it from
contact with the roof or other substances, and so the trolley wheel
can trail without the necessity of being constantly attended for
that purpose, and no trolley shall be run on any wire not so
carried.

[=Locomotive must not be operated improperly.=] No locomotive shall
be operated by means of a person holding and sliding upon or
frequently making contact with the positive wire with any device
attached to the cable as a substitute for a trolley, but these
provisions shall not prohibit the operation of a locomotive by means
of a cable without the use of the trolley, provided the cable be
connected to and disconnected from the positive wire when the
locomotive is not in motion.

[=Protection to machine cable crossing entry track.=] Means shall be
provided by which machine runners may readily carry the machine
cable from the machine to the feed wires on one side of the entry,
either under or over the track rails, in the entry where such wires
are located, and so the cable will not come in contact with such
track rails, thereby reducing the danger of shock to persons or
animals required to travel such entry, to the minimum. (Sec. 911,
948; Penalty, Sec. 976.)

Sec. 948. [=Voltage at mines hereafter electrically equipped.=] The
owner, lessee or agent of a mine at which electricity with a
pressure or potential of more than three hundred and twenty-five
volts, or alternating current, is used, shall in addition to the
provisions of the preceding section, observe the following:

[=Limit to voltage in or about working places.=] At each mine
equipped with electric power after the passage and approval of this
act, the current used to operate gathering locomotives, mining
machines, shearing machines, drills and other machinery, used in or
about the working places of the mine, shall not exceed in pressure
or potential, three hundred and twenty-five volts, direct current,
as shown at the nearest switchboard, and the wires conducting the
power from the nearest switchboard shall not carry a higher pressure
or potential.

[=Relating to alternating current.=] At each mine equipped with
el