30 CFR § 18.91
Electric equipment for which field approvals will be issued.
(a) Individual field approvals will be issued by MSHA under the
provisions of this Subpart E for electrically operated machines commercially
built, or constructed, by the owner-coal mine operator of such machines
including any associated electrical equipment, electrical components, and
electrical accessories.
(b) Approvals will not be issued under the provisions of this Subpart
E for electrically operated mining equipment manufactured or rebuilt
primarily for sale or resale to any operator of a coal mine, or for small
electrically operated equipment which consumes less than 2,250 watts of
electricity, or for instruments and other small devices which employ
electric power.