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 electric power alternating current may be used to convert alternating current to direct current, and to operate motors permanently installed above ground and in underground substations, or buildings especially prepared for them, in a manner subject to the approval of the chief and district mine inspectors, but no wires carrying alternating current shall be used underground except same be carried in an entry or passageway where persons and animals are not permitted to travel. [=Relating to higher voltage mines hereafter equipped.=] At each mine equipped with electric power after the passage and approval of this act, when the current used to operate haulage locomotives, pumps and other machinery not located in or about the working places of the mine, is of a pressure or potential in excess of three hundred and twenty-five volts, direct current, the entry or passage way where such wires are carried shall not be designated or permitted to be used as the principal traveling way, and when designated or used as the escapement way, the wires shall be protected so that persons required to travel near same in emergencies will not inadvertently come in contact therewith. No pressure in excess of six hundred and fifty volts at the switchboard shall be used underground. [=Relating to higher voltage, mines heretofore equipped.=] At each mine equipped with electric power prior to the passage and approval of this act, where the pressure or potential is in excess of three hundred and twenty-five volts, direct current, or where alternating current is used, and the conditions surrounding the use of same are such, in the opinion of the chief inspector of mines, that the provisions of the preceding section do not provide the required protection from shock to persons employed therein, such additional safeguards shall be employed as may be required by the chief inspector of mines, and the district inspector of mines, jointly. (See. 911, 947; Penalty, Sec. 976.)