Code of Federal Regulations Title 30. Mineral Resources § 30.75.524 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.