30 CFR § 75.524
Electric face equipment; electric equipment used in return air outby the
last open crosscut; maximum level of alternating or direct electric current between
frames of equipment.
The maximum level of alternating or direct electric current that exists
between the frames of any two units of electric face equipment that come in
contact with each other in the working places of a coal mine, or between the
frames of any two units of electric equipment that come in contact with each
other in return air outby the last open crosscut, shall not exceed one ampere
as determined from the voltage measured across a 0.1 ohm resistor connected
between the frames of such equipment.
[38 FR 29998, Oct. 31, 1973]